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Low temperature hot water boilers Introducing energy saving opportunities for business

Technology Overview

2Low temperature hot water boilers

Preface

Reducing energy use makes perfect business sense; it saves money, enhances corporate reputation and helps everyone in the fight against climate change.

The Carbon Trust provides simple, effective advice to help businesses take action to reduce carbon emissions, and the simplest way to do this is to use energy more efficiently.

This technical overview of low temperature hot water boilers introduces the main energy saving opportunities for businesses and demonstrates how simple actions save energy, cut costs and increase profit margins.

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Contents


energy consumptionAbout a third of the UK’s energy consumption is used for heating or producing hot water.

A significant proportion of this is provided by commercial boiler plant, so it should be included in any energy reduction strategy.

Typically, energy improvements of 10% or more can be made relatively easily through maintenance and low cost, straightforward improvements. The financial rewards of these are often immediate or have a very short payback.

Longer-term measures are also well worth considering. Many buildings may still be using very old hot water boilers that had an operating efficiency of only about 70% when first installed and which will now be worse due to poor maintenance. New condensing boilers can achieve efficiencies of over 90% and consequently it can be worth considering replacement.

This overview covers some of the simple steps to saving on boilers, as well as the best approach to choosing a new boiler.

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Summary of key areasBoilers offer many energy saving opportunities, ranging from replacement of the boiler itself to retrofitting of controls and other equipment.

The most appropriate solution will depend on what type of boiler and heating system you have, your business needs and your budget.

Savings in existing systems

These can range from the addition of boiler and pipework insulation to retrofitting of new controls or flue gas heat recovery systems. See page 12.

Maintenance and monitoring

Both new and existing boilers require an effective maintenance programme to ensure that they operate to peak efficiency. See page 19.

Selecting a new boiler

Not just as simple as replacing like for like, going through a careful analysis of what you really need can save a fortune. See page 22.

There are also significant opportunities to save by considering improved boiler controls (see page 14) and by monitoring your energy use (see page 28).

Case studyEffective boiler replacement

A knitwear manufacturer in Hawick, Scotland, replaced their old, inefficient oil-fired boiler with two new high-efficiency gas-fired boilers that were sized to match more accurately the actual heating demand of the site. In addition, the new boilers had improved burner controls linked to a Building Management System. The resulting savings were £13,200 and 276 tonnes CO2 per year, with an overall payback time of under five years. The company also reported improved productivity and staff working conditions following the retrofit.

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Technology overviewLow temperature hot water boilers produce hot water for space heating, general hot water demand or, occasionally, industrial processes.

Low temperature hot water (LTHW) boilers produce hot water at around 90ºC and are the type most commonly found in houses and commercial premises. The hot water produced is distributed via pipework to ‘wet’ heating systems and hot water storage tanks.

Most LTHW boilers are designed to use natural gas, but there are also designs that use mineral or bio-oils or LPG. These are used particularly in areas with no natural gas supply. Dual fuel designs that can use oil or biomass and gas are also available. Oil and LPG are more expensive

than gas and emit more carbon dioxide to the atmosphere. Biomass boilers which use wood, specially grown ‘fuel crops’ or organic waste as the fuel, are becoming more popular. These create very little net carbon dioxide, but are more expensive to buy. The availability and storage of fuel can be more difficult although the supply chain has developed significantly. Gas-fired boilers are the main focus of discussion in this publication; however, much of the energy saving advice is applicable to boilers using other fuels.

There are numerous types of biomass boiler, many of which are based on concepts used in the past for coal fired boilers. For more information about the types of biomass boilers available, order or download the Carbon Trust’s in depth guide, A practical guide for potential users: Part 2 – Technical manual (CTG014).

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How does a low temperature hot water boiler work?

The diagram in Figure 1 shows the major components of a gas-fired LTHW boiler.

The controls on the boiler set the required temperature and pressure of the water. If the water in the feed (the return water) is at a lower temperature than required, the boiler must ‘fire’ to produce heat, i.e. it must burn fuel. The gas burners ignite a mixture of gas (from the gas inlet ) and air (from the boiler surroundings) to produce hot combustion gases. The precise mixture of gas and air is controlled by the gas valve and burner controls (this is covered in further detail later). The hot combustion gases pass over the heat exchanger (a network of pipes) to heat the circulating water within. This water is circulated by a pump . The resultant hot water is distributed to the heating system via the hot water outlet and the exhaust gases escape to the atmosphere via a flue or chimney . Any condensate leaves the boiler via a drain . To prevent heat loss from the boiler, the whole mechanism is contained within an insulated metal enclosure .

Figure 1 Major components in a typical gas hot water boiler

Exhaust gases

Heat exchanger

Flue

Gas valve andburner controls

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Draft hood

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Hot water outlet

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Drain

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Gas burners

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Identifying your heating system

There are a variety of heating systems that can be used with LTHW boilers, offering different opportunities for savings. Understanding your type of heating system will help in identifying what kind of boiler you have, and where the best chances of saving are.

Radiators are metal units which emit the heat from the system’s hot water pipes. Effective temperature control and low maintenance make radiator systems a popular choice, and they are the most common type of system found in the UK.

Convectors draw room air through a casing across a hot water to air heat exchanger and direct hot air back into the room. They have a low surface temperature making them popular in schools and hospitals, where a high temperature radiator-based system could present a burning risk to occupants. Compared with radiators, they have a greater heat output per unit size and a faster heat-up time; however, their maintenance costs are greater. The running costs are further increased when the convector has a fan within the casing.

Under floor heating consists of a network of hot water pipes that is embedded between the floor finish and the main concrete floor slab.

These pipes heat the whole floor surface and cause heat to rise throughout the space. The main advantage of under floor heating over radiators and convectors is that it provides much more even heat distribution and operates at lower temperatures. Both of these can contribute to a more efficient system with lower energy use. It is also ‘invisible’ and can give greater flexibility in the use of a space (for example, positioning of furniture). However, these will not be found in buildings which require under floor electrical services or in older buildings with wooden floors.

While all systems can work with any type of LTHW boiler, some applications are more efficient with certain types of boiler. The next section covers these in more detail.

Identifying your boiler

Since the end of 1997, legislation has imposed minimum efficiency requirements for boilers with outputs of up to 400kW. Current UK boiler efficiency regulations recognise three types of boiler “standard”, “low temperature” and “condensing”.

The UK Building Regulations recognise only two types “standard” and “condensing”. These can be used alone or combined together within systems.

Conventional boilers

If your boiler is more than 15 years old, it is likely to be a conventional type of standard boiler, designed to operate with an average water temperature of 60 to 70°C. They often have a cast iron heat exchanger and use atmospheric burners, which draw the air required for combustion from around the boiler by natural convection. They tend to be larger than boilers of more modern design.

Medium/high temperature hot water boilers and steam boilers tend to be found on large multi-building sites or industrial premises. They produce water or steam at high temperature and are not suitable for smaller commercial premises (for example, in offices) due to safety risks. For information about boilers which operate at higher temperatures , order or download the Carbon Trust’s technology overview, Steam and high temperature hot water boilers (CTV008).

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Some standard boilers and most other boiler types have forced draught burners. These use a fan to force air into the boiler and up the flue. These burners enable the amount of combustion air to be controlled more closely, producing lower flue gas volumes than for atmospheric burners and allowing narrower flues to be used. The operation of the fan may give rise to additional noise. Boilers which use separate forced draught burners are usually easy to identify by the fan and controls fitted outside the boiler case.

Standard boilers which do not meet the minimum efficiency requirements are no longer available to buy new. Businesses using such boilers should consider replacing them with models that comply with current regulations.

High-efficiency boilers

Standard and low temperature boilers that meet the minimum efficiency requirements of the current regulations are generally marketed as high-efficiency boilers. So if you have a standard boiler which was installed from 1997 onwards, it is likely to be this type. These boilers have; a lower water contents, larger heat exchanger surface areas and greater insulation of the boiler shell compared to conventional designs.

High-efficiency boilers can work with all types of heating system. They are particularly suited to applications where a higher water temperature is required, such as space heating systems using radiators designed to operate at typical flow temperatures of 80°C or, some process heating applications. However, they are not well suited to low temperature applications, such as, under floor heating, where a condensing boiler is a better option.

Condensing boilers

Even in modern high-efficiency boilers, waste heat in the exhaust gases is lost to the atmosphere via the boiler flue. Water vapour makes up some of these exhaust gases. Condensing boilers have extra heat exchanger surfaces to extract much of the waste heat and return it to the system. The temperature of the exhaust gases is reduced causing the water vapour to condense, and this is drained away. Condensing boilers are the most efficient on the market and since April 2005, regulations require that they must be considered as the first choice for all new or replacement space heating installations. However they may not be the appropriate choice for businesses with applications with continuous full load demands for water at higher temperature (up to 90°C).

Condensing boilers work best with low-temperature applications, such as under floor heating. However, efficiencies will still be increased when used with radiator or convector circuits.

Combination boilers

In a combination (or ‘combi’) boiler, there is a secondary heat exchanger integrated within the boiler housing that is used to provide hot water instantaneously. There is no need for a hot water storage cylinder and associated cold water feed tank and pipework. They can be particularly attractive options in properties where space is limited and are used mainly in domestic buildings.

Combination boilers are limited to smaller applications so will not be appropriate for most businesses. However, if your business is run from a very small building and hot water demand is limited to taps, they may be an option.

Quick tip

You can find out things like your boiler’s rating, age and settings from the manufacturer’s plate. This is usually found on the side of the boiler casing.

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Modular boiler systems

A modular boiler system is where a series of boilers are linked together to meet a variety of heating demands. Modular boiler systems are best suited to buildings or processes with a significant, variable heat demand.

LTHW boilers give optimum efficiency at a particular load point (standard boilers at full load, condensing boilers at part load) so, it makes sense to have a series of boilers operating at around their peak efficiency loads and together matching the range of heating demands that may be experienced in one of the UK’s commercial buildings. For example, consider a building with a peak winter heating demand of 100kW. If a single standard boiler were to be used, it would operate at full capacity, and peak efficiency, for only a few weeks of the year. If five modular boilers of 20kW each were used instead, lower heating demands experienced at other times of the year could be met by a

reduced number of boilers operating at full capacity. Modular systems are generally composed of several identical boiler units although a mix of condensing and conventional boilers could be used. The condensing boilers should in general be the ‘lead’ to maximise system efficiency. To gain the maximum benefit from arrangements of this type appropriate sequence control needs to be implemented – see section ‘Boiler Controls’.

Boiler efficiency

No boiler is 100% efficient. Energy (heat) is lost via the flue gases and through the main body of the boiler itself. Poor maintenance will exacerbate these losses.

Take care when considering boiler efficiencies. Manufacturers often quote instantaneous efficiencies which provides a means of comparing the relative performance of different

boiler models. However, it does not take into account the actual operation of the boiler or its practical use. For a more meaningful indication of performance in space heating applications a ‘seasonal efficiency’ can be calculated and is often quoted by manufacturers targetting this market. This takes into account the efficiencies of a boiler meausured at full and part load. It is a weighted average of a defined number of hours of full and part load operation which represents a full year of operation.

The table on page 11, shows the seasonal efficiencies for the different boiler types discussed above and how this would affect the energy input required to meet a heating demand of 100kW. Note that the boiler efficiency is also affected by the heating system type.

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Table 1 Typical seasonal efficiency

Boiler type Typical seasonal efficiency Energy input rate required to meet 100kW* heating demand

Standard, old, poor condition 45% 222kW

Standard, good condition 70% 143kW

High-efficiency 82% 122kW

Condensing (used with fixed temperature radiators) 85% 118kW

Condensing (used with variable temperature radiators) 87% 115kW

Condensing (used with under floor heating) 90% or more 111kW or less

* As a general rule of thumb, most commercial buildings will require a heating demand of around 70-90W/m2. So, a 100kW boiler would be sufficient to heat a building of 1,100-1,400m2. Retail and educational buildings will have a bigger heat demand (100-110W/m2) and so a 100kW boiler would be sufficient to heat a space of 900-1000m2.

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Improvements to existing boiler plantIt may not be cost-effective to replace boilers that are relatively new. However, there are still opportunities to make substantial savings through improvements to other items of the boiler plant.

Many of these measures will need specialist help. If in doubt, always consult a qualified technician.

Insulate boilers, pipework and valves

Heat loss through the boiler, pipework and valves leads to poor efficiency. All businesses should check their systems’ insulation.

Most modern boilers are well insulated to reduce heat losses from the body of the boiler and these can account for less than 1% of the total energy input. However, on older boilers, the insulation may be in poorer condition and can account for heat losses of as much as 10% of the energy input. The boiler insulation should be assessed and replaced where it is insufficient or showing signs of degradation. Similarly, the insulation on the associated boiler pipework and

valves should be assessed and replaced if necessary. This can result in additional savings of up to 10% of the boiler energy input.

Particular attention should be paid to valves as these are often left uninsulated because of access concerns. Modern valve-wraps solve this problem by providing suitable levels of insulation but allow easy access to the valve through quick-release fastenings.

Fit flue dampers

On larger boilers, the flue can cause a flow of air through the boiler, even when it is not firing. This cools the boiler and valuable heat is lost to the atmosphere – known as ‘standing losses’. A flue damper can be used to close off the flue automatically when the boiler is not firing, thus preventing this energy loss.

Since 1998, regulations have required boilers to have improved efficiencies at both full and part-loads, and this has led to lower standing losses in modern boilers. Retrofitting flue dampers is therefore applicable to older, conventional boilers with a large load (typically >100kW). The advice of a qualified technician is essential.

Install variable speed drives and pumps

On forced/induced-draught boilers, a variable speed drive can be installed on the fan. The enables the fan to operate at lower speeds when less air flow is required. A reduction in fan speed of just 10% can result in fan energy consumption savings of around 20%, and a reduction in fan speed of 20% will save up to 40%. This is particularly relevant for big boiler systems.

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Variable flow control works on a similar principle. Most heating systems use the same amount of energy for pumping, regardless of the load on the system, but they normally require maximum flow for only a limited time. This is usually during the ‘boost’ period when trying to raise the temperature of the building to a comfortable level. Variable speed pumps can be fitted which decrease the flow in the system to match demand. This can save 25-50% of the annual pumping energy consumption.

Retrofitting of variable speed drives and pumps is best suited to larger systems with variable loads. If the load on the fan/pump is constant, energy consumption may actually increase through the installation of a VSD. The advice of a qualified technician is essential to assess the economic feasibility of this option.

For further information about Variable speed drives, please download the Variable speed drives technology overview (CTG070).

Recover heat from exhaust gases

In conventional boilers, the heat contained within the exhaust gases is lost to the atmosphere. If replacement with a condensing boiler is not possible, this heat can be recovered through the use of a heat exchanger. The heat can be used to pre-heat the return water or the combustion air. Increasing the temperature of the combustion air by 20ºC can improve the overall efficiency of the boiler by 1%.

This technology is best suited to conventional and highefficiency boilers with flue gases of a sufficient temperature. It is important that the economics of retrofitting such a system are assessed as the potential savings are relatively small. They will be most economical when applied to a larger system. Always consult a qualified technician.

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Boiler controlsThe most effective way to improve boiler performance is through controls.

The first step is to assess what controls already exist, find out if they are calibrated accurately, and check that their settings match the business’s requirements. If they do not, adjust them either by asking for help from a qualified professional, or referring to the operating manual (usually downloadable from manufacturers’ websites if they have been lost).

The next step is to decide whether additional controls would be beneficial. Again, installation of new controls should be carried out by a professional.

A brief description of a number of different control options is given below, with details on the optimum settings for these controls. Manufacturers will be able to give more advice on the best control options for particular boilers.

Please refer to the Carbon Trust‘s technology guide Heating control (CTG065) for more in-depth information.

Burner controls

Burner controls manage the fuel-to-air ratio which is critical to the efficient operation of the boiler: too little air and there will not be enough oxygen for complete combustion to occur resulting in a build-up of potentially dangerous carbon monoxide in the flue; too much air and energy will be wasted in trying to heat the excess. The fuel-to-air ratio is normally set on the burner controls and will be based on the boiler manufacturer’s recommendations. Proper control of this ratio will ensure that the boiler is as efficient as possible.

As part of routine servicing, a qualified technician will measure the fuel-to-air ratio of a boiler. This can then be compared with the manufacturer’s recommendations and, where necessary, the appropriate remedial actions

taken. In some cases, the boiler technician will simply adjust the burner as part of the service but for more complex systems, particularly those operating at part load for much of the year, it may well be cost-effective to consider a replacement burner control that will improve efficiency and result in energy savings.

Types of burner control

The simplest form of burner control is single-stage or ‘on-off’ control and is the type of control found on most older, standard boilers. With this type of control, the burner fires at full capacity when heat is required and is off otherwise. Air purges immediately before the burner is switched on and after the burner is switched off to ensure that no residual fuel or combustion vapour remains in the boiler, but this also causes heat to escape via the flue.

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An improvement to the above is two-stage or ‘high-low’ control. With this type of control, rather than being completely switched off, the burner has the option of going to a low firing rate, typically 40% of full capacity. This reduces the number of times the burner switches off and the number of air purges, and improves boiler efficiency under part-load conditions.

A further improvement is modulating control. With this type of control, the fuel and air supplies are regulated to exactly match the required heat demand. This ensures good efficiency across the whole heat output range of boilers. Modern burners typically use micro-processors based controls. These adjust air and fuel flows continuously, compensating for changing conditions to ensure that the correct fuel-to-air ratios are maintained accurately.

Retrofitting of burner controls is best suited for older, conventional boilers with large, variable heat loads.

For information about boiler controls in the context of heating systems download the Carbon Trust’s technology overview, Heating, ventilation and air conditioning (CTV046).

Boiler interlock

Boilers can continue to fire even when there is no demand for heat (called dry-cycling) and so all the heat energy is lost to the flue. Find out whether this is happening by turning off the heat distribution system and then observing the boilers themselves. If they continue to fire when no load is required, dry-cycling is occurring. Clearly this should be avoided.

Linking the boiler controls with the heating system controls (such as room thermostats) via a boiler interlock will ensure that the boiler does not operate when there is no heat demand and will prevent dry-cycling. This can be done using standard wiring between the boiler control and the main heating control, or can be achieved through the installation of a specialised integrated controller. The best option will be determined by the size of the system and location of the boiler and controls. A qualified technician should be consulted for advice.

Interlock control is appropriate for all types of boiler.

Sequence control

If there are two or more boilers, it is a good idea to consider sequence control if it is not already installed. Find out whether or not sequence control is operating by observing the boilers during part-load conditions, such as in spring or autumn. If all boilers are firing and shutting down simultaneously, it is likely that they are operating only at part-load and do not have sequence control.

Good sequence control ensures that only the minimum number of boilers required to meet the heat demand fire and that these boilers are used at their optimum efficiency load. Also, sequence controllers ensure that the order in which the boilers fire can be rotated to minimise maintenance costs. Note that where there are both condensing and standard boilers installed, the condensing boiler should always take the lead. Good sequence control could save 5-10% of the overall energy consumption of the boiler plant.

Where not already installed, sequence control should be retrofitted to multiple boiler applications with a variable load pattern.

Did you know?

A poorly maintained boiler can use 10% more energy than one that is well-maintained.

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Optimised start/stop control

Most heating systems will be controlled via a timeswitch. This will be set to switch the heating system (and hence the boiler) on and off at pre-set times in the morning and evening, corresponding to building occupancy patterns. An optimiser is a sophisticated timeswitch linked to the internal and external thermostats that switches the boiler on at exactly the right time to ensure that the building reaches the required internal temperature in time for occupation. Similarly, the boiler is switched off early so that the internal temperature is maintained only when required. Savings of 5-10% of the overall energy consumption of the boiler plant could be achieved.

Most buildings with standard operating hours would benefit from installing optimised start/stop control.

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Figure 2 Sequence control

Figure 3 Optimised start/stop control

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Building Energy Management Systems

Controls work best when their operation is integrated and linked to the actual requirements of the building. A Building Energy Management System (BEMS) is a computer-based control system which automatically monitors and controls a range of building services. Installing a BEMS means that control options such as sequencing, optimisation and compensation can be carried out by one system. It allows various environmental parameters to be taken into account and provides logs of useful data that can be used in maintenance, energy monitoring and assessing further improvements to the system. 10-20% of heating energy can be saved by installing a BEMS in place of several independent control options. However, they are expensive and may only be cost-effective for larger boiler plant. They will also be effective only if operated by trained staff and maintained and calibrated regularly. Manufacturers can advise on the most suitable BEMS for their boiler plant.

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Figure 4 Direct weather compensation control

Direct weather compensation control

To achieve more savings, the temperature of the water can be regulated according to outside temperature. In milder weather, the flow temperature is reduced, thus saving energy. This is done through the use of a compensator linked to internal and external thermostats.

This form of control is particularly useful in condensing boilers as lower return water temperatures can be achieved, thus ensuring that maximum condensation occurs within the boiler and increasing efficiency.

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Check controls

The benefits of improved controls will be realised only if frequent checks are carried out on control settings and their operation. This is particularly important if business needs have affected the controls. For example, controls are set to cover a period when staff work out of hours, but are not returned to their original settings. A regular check will spot where energy is being wasted in this way.

Simple control settings (such as timeclocks) can be adjusted by non-professional building staff as circumstances require, provided they have had appropriate training and take care. More sophisticated controls should be adjusted by a qualified technician. Similarly, control operation and calibration should be checked annually by a qualified technician.

A simple way of assessing the effectiveness of boiler controls is to plot heating energy consumption on a graph and compare with periods of building operation and outside weather conditions. Does the building show a high energy use out-of-hours? Is there a high heating load when the weather is mild? These are indications that control settings are inaccurate or that additional controls are required.

Table 2 Summary of control options

Boiler size What are the minimum controls you should have?

Minimum standard

Want to save even more energy?

Good standard

For boilers up to 50kW Boiler interlock Minimum standard

PLUS

Optimisation

Direct weather compensation

For boilers over 50kW Boiler interlock

Sequence control

Minimum standard

PLUS

Optimisation


Building Energy Management System (BEMS)

Sequence controls, optimised start/stop controls and direct weather compensation controls can be purchased as a unit or can be programmed as part of a Building Energy Management System (BEMS).

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MaintenanceEffective maintenance is essential in getting the best performance from your LTHW boilers. Without it, boiler efficiency can drop significantly and equipment life expectancy is reduced.

Effective maintenance can also highlight potential problems quickly and enable remedial action to be taken before there is a major impact on performance.

Perform regular servicing

A full boiler service should be carried out by a qualified technician on an annual basis, ideally before the start of the heating season. This service should include a flue gas analysis (to check fuel-to-air ratio), an operational check, controls calibration, burner cleaning and limescale treatment.

Boiler maintenance should be carried out by GAS Safe or OFTEC registered contractors ONLY.

Analyse flue gas

As mentioned in the previous section, the fuel-to-air ratio is critical in ensuring efficient boiler operation. Analysis of the boiler’s flue gases for levels of carbon dioxide (CO2), oxygen (O2) and carbon monoxide (CO) will determine whether this ratio is correct and what adjustments need to be made. Different ratios will be required for different boilers and your boiler manufacturer or maintenance technician can give the appropriate advice.

Flue gas analysis should be carried out every three months by a suitably qualified technician. Ask for a report on the combustion efficiency which includes measures for improving it.

Remove soot

If combustion conditions are not correct, particularly if too little air is used, fuel combustion will not be complete. So excessive amounts of CO and particles of carbon (soot) will form. If these particles build up on the fire side of the boiler’s heat exchanger they will form an insulating layer, inhibiting heat transfer to the water. More heat input is required to meet the heat demand and more heat energy will be lost to the flue.

All hydrocarbon fuels – gas, oil, coal – may create soot. Properly controlled gas boilers create insignificant amounts of soot and will rarely require cleaning, although the manufacturer’s guidance should always be followed. However, if combustion checks show poor combustion then the heat exchanger should be check and cleaned if necessary. Oil, coal and biomass are more likely to form soot and should be carefully monitored. Cleaning should be carried out by a qualified technician.

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For very large boilers, typically used in industrial application, integrated soot-blowers are often installed in boilers to provide continual cleaning; however, these will need to be checked regularly to ensure good working.

Minimise limescale build-up

In hard water areas, limescale can build up on the water side of the boiler’s heat exchanger. This creates an insulating layer, inhibiting heat transfer to the water in the same way as the soot deposits above.

The most effective method of limescale removal is through chemical treatment of the water. This should be done annually by a qualified technician to minimise limescale build-up and keep your boiler running at its most efficient.

Produce a maintenance plan, manual and logbook

To ensure effective maintenance is carried out, a maintenance plan should be put in place. This will detail what maintenance tasks are to be carried out, the frequency of these tasks and who is responsible.

A maintenance manual should be produced that is updated regularly. This manual should include:

• The maintenance plan.

• Block diagram of the boiler plant showing the of key components and controls.

• Schematic diagrams of the heating system and the controls.

• Operating instructions and control settings Emergency shutdown procedures.

• Contact details of installation/maintenance technicians and boiler manufacturers.

Particular attention should be paid to specific instructions from manufacturers as these will ensure the optimum performance of the boiler plant. Also, failure to follow them may invalidate warranties.

A maintenance logbook should be kept giving detailed records of maintenance tasks, including which actions were taken, the person responsible, and when they were completed. This logbook will ensure that tasks are carried out at the correct frequency and will highlight ongoing problems.

Did you know?

A 1mm layer of soot will cause a 10% increase in energy input to the boiler to meet the same heat demand.

A 1mm layer of limescale will cause a 7% increase in energy input to the boiler to meet the same heat demand.

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Table 3 Summary of maintenance requirements

Maintenance task Frequency Responsibility

Review boiler maintenance policy Yearly Energy/facilities manager with the advice of qualified technician

Full service Yearly Qualified technician

Flue gas analysis (combustion check) Quarterly Qualified technician

Remove soot deposits Six-monthly (more frequent for oil/coal boilers) Qualified technician

Limescale treatment Yearly Qualified technician

Check/adjust simple control settings Quarterly, or as changes to building operation demand

Building staff

Adjust/re-programme complex controls Yearly, or as changes to building operation demand Qualified technician

Check control operation Yearly Qualified technician

Calibration of controls Yearly Qualified technician

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Replacing boilersIf a boiler is more than 15 years old, or if it is showing signs of inefficient operation, it should be replaced.

This is not as simple as noting the old boiler’s rating and purchasing a new, condensing model. To find the best solution, thoroughly review the building’s heating demand and your business needs, and check these against your technical, financial and policy requirements.

When considering a boiler replacement, advice should be sought from a qualified building services engineer or boiler technician. To help them, consider the following information.

The building’s heating requirements

The most important aspect in selecting a new boiler is getting the size right. It was once common practice to oversize boiler plant with the mistaken notion that this would provide greater flexibility in the future. However, it is now realised that this is unnecessary as the heating demand for many commercial buildings has fallen. This is due to improvements in building fabric and an increase in internal heat gains, such as from IT equipment, lighting and occupants. If a boiler has not been replaced for many years, the heating load of the building may have changed significantly.

Start by reviewing the building’s internal environment and general operation. What is the current internal temperature of the building? Are employees happy with the internal environment? Are there any hot or cold spots within the

building? Are there any areas of the building where temperature is critical? When is the building occupied?

Next, review your annual energy bills. What fuel do you currently use for heating? How much energy has the building used over the last year and how much did it cost? How does this compare with other similar building types? To do this, divide the annual heating energy used by the area of the building to gain a ‘benchmark’ in kWh/m2.

Smaller boilers cost less, so look for ways of reducing the heating demand. Can the insulation of the building be improved? Could draught-proofing be improved?

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Technical considerations

The choice of boiler will be dependent on a number of technical issues. A building services engineer or boiler technician can give advice, but you can provide some basic information to help.

Fuels

Ultimately, the choice of fuel will be based on cost and availability of supply. Ask which fuels are available on-site. Boilers are designed to operate with particular fuels and are rarely interchangeable so it is important to make an appropriate selection.

Of the fossil fuels natural gas is the best choice where a supply is available, as it is the most versatile and has the lowest carbon emissions. Is there a natural gas supply? Remember that the situation may have changed since the current equipment was installed. If not, then consideration must be given to which alternative fuels are available such as LPG, mineral oils or biomass. These fuels are delivered in batches and careful consideration must be given to issues relating to their long term availability, supply routes and storage.

Table 4 Find out the building’s heating requirements

Information Source How is this information used?

Floor area of building Property documents

Direct measurement

Energy benchmarks

Occupied hours Staff records Calculating heating demand

Selecting boiler controls

Internal environmental data, such as temperature

Direct measurement

Control settings

Staff comments

Calculating heating demand

Assessing effectiveness of existing heating system

Annual energy use/cost for heating

Utility bills

Energy monitoring and targeting system

Energy benchmarks

Details of planned energy saving measures

Company energy policy Calculating heating demand

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If you think that biomass boilers may suitable for your requirements and you need some more information order or download the Carbon Trust’s introductory guide, Biomass heating – An introduction for potential users (CTG016).

Location

Where you have more than one boiler, find out if the existing boiler plant is centralised or de-centralised.

Centralised plant (where all boilers are in one plantroom) may be easier to maintain and control, but heat losses through long pipework runs will be higher. Combine the replacement of boilers with upgrades to the pipework insulation. Also take advantage of the central location to install upgraded controls or re-programme existing ones.

De-centralised plant (where a number of smaller boilers are located around the building) will reduce pipework losses, but you will not have the option of integrating control operation and maintenance may be more problematic and expensive. This is because it costs more to carry out maintenance checks on several smaller boilers than one large boiler.

If you are considering changing to biomass boilers the available space for the boiler and the associated fuel store must be adequate and their relative positions such that any automated fuel transfer systems (from storage bunker to feed hopper) can function effectively.

Flue outlet

Where is the boiler flue outlet? Condensing boilers generate lower temperature flue gases and visible plumes of steam. This may cause problems if the flue outlet is close to other building surfaces.

Heating system

What type of heating system is currently used in the building? Unless a major refurbishment is planned, it may not be cost-effective to replace the whole heating system so the new boiler must be compatible with what is there already. Condensing boilers work best with low temperature. applications such as under floor heating, but will still provide a higher level of efficiency when applied to a radiator circuit. It may be necessary to upgrade the heating controls of the system to get the best from the

new boiler. Do not forget to account for these costs when considering the purchase price.

Biomass boilers are best suited to steady heating loads between 30% and 100%. They may need to be partnered with a heat store of a gas or oil fired boiler to match overall output and to meet peaking demands. They might also be a suitable component for a decentralised system.

For information about biomass boilers in the context of heating systems, order or download the Carbon Trust’s in-depth guide, Biomass heating – A practical guide for potential users (CTG012).

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Condensing boilers are more expensive than high-efficiency standard boilers, but they are more efficient and cost less to run. So the extra cost is often paid back in two years or less.

The business may be able to take advantage of Energy Efficiency Financing or the Enhanced Capital Allowance Scheme (see next page for information on the Carbon Trust’s financial products). The Enhanced Capital Allowance Scheme covers the most efficient gas and oil fired hot water boilers and biomass boilers.

Fuel

Fuels vary in price. Consider your current and projected energy use and calculate the cost of running the boiler.

Maintenance

As stated previously, maintenance of boilers is important. Will the maintenance costs of the new boiler be higher? Will extra staff training be required to ensure efficient operation? Can maintenance be done in-house or will it be contracted out? Make sure that all staff involved in the operation and maintenance of the boiler plant have a say in the choice of the new boiler.

Table 5 Find out the technical requirements


Fuel supply available Utility companies

Local authority

Specification of boiler type

Centralised or de-centralised plant

Observation Specification of boiler type


Pipework insulation required

Location of flue outlet Observation Specification of boiler type


Type of heating system Observation Specification of boiler type

Heating controls

Financial considerations

Consider the costs of the new boiler, including capital expense, fuel and maintenance. This is called life costing, that is, how much will the boiler cost over its actual lifespan. It is important to capture all the activities associated with the ownership of a boiler if it is to last its normal life expectancy. The introduction of the Renewable Heat Incentive near the end of 2011 provides a mechanism to

encourage the installation of renewable heat equipment including biomass boilers.

Capital expense

How quickly will the investment pay for itself through reduced running costs? Will this influence the purchasing budget?

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Table 6 Find out financial considerations


Purchase budget Finance/Company director Specification of boiler

Availability of loans/ tax incentives

Carbon Trust

HM Revenue and Customs

Changes to purchase budget

Running costs of new boiler

Building services engineer

Boiler technician

Manufacturers

Utility bills

Calculating payback periods

Predicting future energy expenditure

Life costing

Maintenance costs of new boiler


Boiler technician

Manufacturers

Finance department



Assessing staff training needs

Developing a maintenance plan

Life costing

Did you know?

Replacing a conventional boiler with a condensing model can save 10-20% of annual energy costs – more if the original boiler is in a particularly poor condition.

Example: A building with a heating demand of 100kW has an annual gas bill of £8,930.1 A new condensing boiler is installed at a cost of £3,000 with a seasonal efficiency of 90%. The new annual gas bill is £6,940 – a saving of 22% or £1,980/year. Maintenance costs are decreased by £200 per year. Therefore, the cost of the new boiler is paid back within 20 months.

1 Based on a 70% efficient boiler, 2,500 operating hours/year and 2.5p/kWh gas price.

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Tax incentives

Enhanced Capital Allowances (ECAs) are a straightforward way for a business to improve its cash flow through accelerated tax relief. The ECA scheme for energy-saving technologies encourages businesses to invest in energy saving plant or machinery specified on the Energy Technology List (ETL) which is managed by the Carbon Trust on behalf of Government.

The ECA scheme provides businesses with 100% first year tax relief on their qualifying capital expenditure. The ETL specifies the energy-saving technologies that are included in the ECA scheme. The scheme allows businesses to write off the whole cost of the equipment against taxable profits in the year of purchase.For further information please visit www.carbontrust.co.uk/eca or call the Carbon Trust on 0800 085 2005.


Environmental considerations

As well as reducing running costs, condensing and high-efficiency boilers will have reduced emissions of carbon dioxide (CO2) and harmful pollutants such as sulphur dioxide (SO2) and nitrogen dioxide (NO2). Does your company have an environmental policy? Will this influence the choice of a new boiler?

Preparing a detailed brief

Once this information has been gathered, use it to prepare a detailed brief for a building services engineer or boiler technician. They will use this information to select the best boiler to achieve your needs within the proposed budget. A detailed brief will save time and money and ensure that your new boiler is both efficient and effective.

Table 7 Find out environmental considerations


Environmental policy Company director Specification of boiler to ensure reduced emissions

Energy Efficiency Loans

Investing in energy efficient equipment makes sound business and environmental sense, especially with the easy, affordable and flexible Energy Efficiency Financing scheme brought to you by Carbon Trust Implementation and Siemens Financial Services. To find out more visit www.energyefficiencyfinancing.co.uk

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www.carbontrust.co.uk/eca

www.energyefficiencyfinancing.co.uk


energy monitoring and targetingIf energy use is not monitored, it cannot be controlled. An energy efficiency strategy will be most effective when accompanied by appropriate energy monitoring and targeting.

By monitoring the energy used by the boiler plant, the effect of improvements can be assessed in both financial and environmental terms. In addition, unusually high energy consumption can be spotted quickly, problems identified and remedial action taken.

The first step is to take regular meter readings – at least monthly, although weekly would be better for larger buildings. If a BEMS is installed, it may be possible to automate this process. This will be dependent on the type of meter installed and advice should be sought from the BEMS manufacturer and/or the utility company. Depending on the size of the building, utility companies may be able to provide half-hourly energy data.

The meter readings should be recorded on a table and the energy consumption for the period calculated. Graphs can then be produced to show the energy consumption over time and comparisons can be made to assess performance.

If the individual performance of a boiler is required, spot meters should be installed on the individual fuel intakes. This may not be cost-effective for smaller boilers so should be considered carefully.

It is important to assess heating energy use in the context of weather conditions and building operation. For example, heating energy will increase when the weather is colder and heating energy should be minimal when the building is unoccupied.

If your heating energy use profile does not match weather conditions or building operation, it may be an indication of poor control.

Set targets and monitor progress

Simply monitoring energy use will not result in savings. Targets for reduction should be set and measures put in place to achieve those targets. A 10% reduction in heating energy can often be achieved through simple adjustments to existing boiler plant. Greater reductions can be achieved through the replacement of equipment, components or controls.

Keep a check on progress towards meeting targets. If progress is slow, carry out another review of the heating system and look for additional measures that can be taken. Report progress to all building occupants – this will increase energy awareness and get everyone involved in reducing the building’s energy use.Effective energy monitoring

and targeting can highlight potential problem areas and lead to swift, remedial actions.

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Next stepsThe checklist below will help you to carry out an initial review of the boiler plant and assess what actions can be taken. Many such actions can be taken in-house; however, you may need specialist support from your contractor or consultant for others.

Review Questions Actions to be considered Comments

Make, model, size, type and age of boiler

Is the boiler more than 15 years old?

Is the boiler oversized?

Replacement

Replacement

Different improvement options will apply depending on boiler type

Fuel consumption of boiler plant

How efficient is the plant? Assess through meter readings. Estimate efficiency based on consumption and rated output

Check physical condition

Is there any corrosion?

Is insulation adequate/ in good condition?

Get service done

Replace/upgrade insulation

Replacement

Poor physical condition will cause poor performance; consider replacement

Assess controls What type?

Are sequencers, optimisers or compensators used?

Install additional controls Improved control will reduce energy consumption

Check control settings Are they appropriate?

Do they match building operation patterns?

Adjust settings Improved control will reduce energy consumption

Review maintenance history

When was the last maintenance carried out?

Is a proper maintenance plan in place?

Establish a proper maintenance plan

Order service/maintenance check

Poor maintenance can reduce boiler performance by up to 10%

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Atmospheric burner A burner where the air required for combustion is drawn in via natural convection.

Boiler A vessel for converting heat produced by combustion of fuel into hot water or steam.

Boiler efficiency A comparison of the energy output versus the energy input of the boiler.

Boiler interlock Where the boiler and system controls are linked to ensure the boiler does not fire when there is no heating demand.


A computer-based system that operates all building controls and enables automatic adjustment and monitoring of settings.

Burner The device producing the flame for combustion in the boiler.

Combustion The process of turning fuel into useful heat.

Compensator A device, or feature within a device, that adjusts the temperature of the water circulating through the heating system according to the temperature measured outside the building.

Condensing boiler A boiler that reclaims heat from the exhaust gases to improve overall efficiency.

Convector A heat emitter that heats a room through either natural or forced convection.

Energy benchmark A measure of a building’s energy use that can be compared to other buildings of a similar type. Expressed in kWh/m2.

Flue The boiler’s chimney – used to transport exhaust gases to the atmosphere.

Flue damper A device that shuts off the flue, avoiding cold air penetrating the boiler when it is not firing.


Glossary

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Forced/induced draught burner

A burner where the air required for combustion is drawn in via a mechanical fan.

Heat exchanger A network of pipes within a boiler whereby the heat from the burner is transferred to the circulating water.

Modulating burner control Where the fuel and air intake are controlled over the whole range of boiler output.

Optimiser A sophisticated timeswitch linked to the internal and external thermostats that switches the boiler on at exactly the right time to ensure that the building reaches the required internal temperature in time for occupation.

Radiator A heat emitter, made of metal, that heats a room through a combination of radiation and convection.

Sequencer A controller for multiple boiler systems that ensures the minimum number of boilers is used to meet the required heating demand.

Single-stage burner control Where the burner is either ‘on’ or ‘off’ and fuel/air intakes are the same regardless of heating demand.

Two-stage burner control Where the burner can revert to a low-firing range under part-load conditions.

Under floor heating A network of low temperature hot water pipes installed under the floor finish which heat a room from beneath.

Variable flow control Where the pump flow is regulated to match demand and flowrate.

Variable speed drive A device fitted to electric motors that regulates speed to match demand.

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Go online to get moreThe Carbon Trust provides a range of tools, services and informationto help you implement energy and carbon saving measures.

Website – Visit us at www.carbontrust.co.uk for our full range of advice and services. www.carbontrust.co.uk

Publications – We have a library of publications detailing energy saving techniques for a range of sectors and technologies.

www.carbontrust.co.uk/publications

Case Studies – Our case studies show that it’s often easier and less expensive than you might think to bring about real change.

www.carbontrust.co.uk/casestudies

Energy Efficiency Financing – Investing in energy efficient equipment makes sound business and environmental sense, especially with the easy, affordable and flexible Energy Efficiency Financing scheme brought to you by Carbon Trust Implementation and Siemens Financial Services. www.energyefficiencyfinancing.co.uk

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www.energyefficiencyfinancing.co.uk

CTV051

The Carbon Trust receives funding from Government, including the Department of Energy and Climate Change, the Scottish Government, the Welsh Government and Invest Northern Ireland.

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Published in the UK: March 2012.

© The Carbon Trust 2012. All rights reserved.

The Carbon Trust is a not-for-profit company with the mission to accelerate the move to a low carbon economy. We provide specialist support to business and the public sector to help cut carbon emissions, save energy and commercialise low carbon technologies. By stimulating low carbon action we contribute to key UK goals of lower carbon emissions, the development of low carbon businesses, increased energy security and associated jobs.

We help to cut carbon emissions now by:

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www.carbontrust.co.uk 0800 085 2005

Low temperature hot water boilers Introducing energy saving opportunities for business

Technology Overview


Preface

Reducing energy use makes perfect business sense; it saves money, enhances corporate reputation and helps everyone in the fight against climate change.

The Carbon Trust provides simple, effective advice to help businesses take action to reduce carbon emissions, and the simplest way to do this is to use energy more efficiently.

This technical overview of low temperature hot water boilers introduces the main energy saving opportunities for businesses and demonstrates how simple actions save energy, cut costs and increase profit margins.

Contents


Energy consumptionAbout a third of the UK’s energy consumption is used for heating or producing hot water.

A significant proportion of this is provided by commercial boiler plant, so it should be included in any energy reduction strategy.

Typically, energy improvements of 10% or more can be made relatively easily through maintenance and low cost, straightforward improvements. The financial rewards of these are often immediate or have a very short payback.

Longer-term measures are also well worth considering. Many buildings may still be using very old hot water boilers that had an operating efficiency of only about 70% when first installed and which will now be worse due to poor maintenance. New condensing boilers can achieve efficiencies of over 90% and consequently it can be worth considering replacement.

This overview covers some of the simple steps to saving on boilers, as well as the best approach to choosing a new boiler.


Summary of key areasBoilers offer many energy saving opportunities, ranging from replacement of the boiler itself to retrofitting of controls and other equipment.

The most appropriate solution will depend on what type of boiler and heating system you have, your business needs and your budget.

Savings in existing systems

These can range from the addition of boiler and pipework insulation to retrofitting of new controls or flue gas heat recovery systems. See page 12.

Maintenance and monitoring

Both new and existing boilers require an effective maintenance programme to ensure that they operate to peak efficiency. See page 19.

Selecting a new boiler

Not just as simple as replacing like for like, going through a careful analysis of what you really need can save a fortune. See page 22.

There are also significant opportunities to save by considering improved boiler controls (see page 14) and by monitoring your energy use (see page 28).

Case studyEffective boiler replacement

A knitwear manufacturer in Hawick, Scotland, replaced their old, inefficient oil-fired boiler with two new high-efficiency gas-fired boilers that were sized to match more accurately the actual heating demand of the site. In addition, the new boilers had improved burner controls linked to a Building Management System. The resulting savings were £13,200 and 276 tonnes CO2 per year, with an overall payback time of under five years. The company also reported improved productivity and staff working conditions following the retrofit.


Technology overviewLow temperature hot water boilers produce hot water for space heating, general hot water demand or, occasionally, industrial processes.

Low temperature hot water (LTHW) boilers produce hot water at around 90ºC and are the type most commonly found in houses and commercial premises. The hot water produced is distributed via pipework to ‘wet’ heating systems and hot water storage tanks.

Most LTHW boilers are designed to use natural gas, but there are also designs that use mineral or bio-oils or LPG. These are used particularly in areas with no natural gas supply. Dual fuel designs that can use oil or biomass and gas are also available. Oil and LPG are more expensive

than gas and emit more carbon dioxide to the atmosphere. Biomass boilers which use wood, specially grown ‘fuel crops’ or organic waste as the fuel, are becoming more popular. These create very little net carbon dioxide, but are more expensive to buy. The availability and storage of fuel can be more difficult although the supply chain has developed significantly. Gas-fired boilers are the main focus of discussion in this publication; however, much of the energy saving advice is applicable to boilers using other fuels.

There are numerous types of biomass boiler, many of which are based on concepts used in the past for coal fired boilers. For more information about the types of biomass boilers available, order or download the Carbon Trust’s in depth guide, A practical guide for potential users: Part 2 – Technical manual (CTG014).


How does a low temperature hot water boiler work?

The diagram in Figure 1 shows the major components of a gas-fired LTHW boiler.

The controls on the boiler set the required temperature and pressure of the water. If the water in the feed (the return water) is at a lower temperature than required, the boiler must ‘fire’ to produce heat, i.e. it must burn fuel. The gas burners ignite a mixture of gas (from the gas inlet ) and air (from the boiler surroundings) to produce hot combustion gases. The precise mixture of gas and air is controlled by the gas valve and burner controls (this is covered in further detail later). The hot combustion gases pass over the heat exchanger (a network of pipes) to heat the circulating water within. This water is circulated by a pump . The resultant hot water is distributed to the heating system via the hot water outlet and the exhaust gases escape to the atmosphere via a flue or chimney . Any condensate leaves the boiler via a drain . To prevent heat loss from the boiler, the whole mechanism is contained within an insulated metal enclosure .

Figure 1 Major components in a typical gas hot water boiler

Exhaust gases

Heat exchanger

Flue

Gas valve andburner controls

Gas inlet

Draft hood

Water feed

Hot water outlet

Temperature andpressure controls

Circulating pump

Drain

Insulated metal enclosure

Gas burners

1

10

11

2

3

4

5

6

7

8

9


Identifying your heating system

There are a variety of heating systems that can be used with LTHW boilers, offering different opportunities for savings. Understanding your type of heating system will help in identifying what kind of boiler you have, and where the best chances of saving are.

Radiators are metal units which emit the heat from the system’s hot water pipes. Effective temperature control and low maintenance make radiator systems a popular choice, and they are the most common type of system found in the UK.

Convectors draw room air through a casing across a hot water to air heat exchanger and direct hot air back into the room. They have a low surface temperature making them popular in schools and hospitals, where a high temperature radiator-based system could present a burning risk to occupants. Compared with radiators, they have a greater heat output per unit size and a faster heat-up time; however, their maintenance costs are greater. The running costs are further increased when the convector has a fan within the casing.

Under floor heating consists of a network of hot water pipes that is embedded between the floor finish and the main concrete floor slab.

These pipes heat the whole floor surface and cause heat to rise throughout the space. The main advantage of under floor heating over radiators and convectors is that it provides much more even heat distribution and operates at lower temperatures. Both of these can contribute to a more efficient system with lower energy use. It is also ‘invisible’ and can give greater flexibility in the use of a space (for example, positioning of furniture). However, these will not be found in buildings which require under floor electrical services or in older buildings with wooden floors.

While all systems can work with any type of LTHW boiler, some applications are more efficient with certain types of boiler. The next section covers these in more detail.

Identifying your boiler

Since the end of 1997, legislation has imposed minimum efficiency requirements for boilers with outputs of up to 400kW. Current UK boiler efficiency regulations recognise three types of boiler “standard”, “low temperature” and “condensing”.

The UK Building Regulations recognise only two types “standard” and “condensing”. These can be used alone or combined together within systems.

Conventional boilers

If your boiler is more than 15 years old, it is likely to be a conventional type of standard boiler, designed to operate with an average water temperature of 60 to 70°C. They often have a cast iron heat exchanger and use atmospheric burners, which draw the air required for combustion from around the boiler by natural convection. They tend to be larger than boilers of more modern design.

Medium/high temperature hot water boilers and steam boilers tend to be found on large multi-building sites or industrial premises. They produce water or steam at high temperature and are not suitable for smaller commercial premises (for example, in offices) due to safety risks. For information about boilers which operate at higher temperatures , order or download the Carbon Trust’s technology overview, Steam and high temperature hot water boilers (CTV008).


Some standard boilers and most other boiler types have forced draught burners. These use a fan to force air into the boiler and up the flue. These burners enable the amount of combustion air to be controlled more closely, producing lower flue gas volumes than for atmospheric burners and allowing narrower flues to be used. The operation of the fan may give rise to additional noise. Boilers which use separate forced draught burners are usually easy to identify by the fan and controls fitted outside the boiler case.

Standard boilers which do not meet the minimum efficiency requirements are no longer available to buy new. Businesses using such boilers should consider replacing them with models that comply with current regulations.

High-efficiency boilers

Standard and low temperature boilers that meet the minimum efficiency requirements of the current regulations are generally marketed as high-efficiency boilers. So if you have a standard boiler which was installed from 1997 onwards, it is likely to be this type. These boilers have; a lower water contents, larger heat exchanger surface areas and greater insulation of the boiler shell compared to conventional designs.

High-efficiency boilers can work with all types of heating system. They are particularly suited to applications where a higher water temperature is required, such as space heating systems using radiators designed to operate at typical flow temperatures of 80°C or, some process heating applications. However, they are not well suited to low temperature applications, such as, under floor heating, where a condensing boiler is a better option.

Condensing boilers

Even in modern high-efficiency boilers, waste heat in the exhaust gases is lost to the atmosphere via the boiler flue. Water vapour makes up some of these exhaust gases. Condensing boilers have extra heat exchanger surfaces to extract much of the waste heat and return it to the system. The temperature of the exhaust gases is reduced causing the water vapour to condense, and this is drained away. Condensing boilers are the most efficient on the market and since April 2005, regulations require that they must be considered as the first choice for all new or replacement space heating installations. However they may not be the appropriate choice for businesses with applications with continuous full load demands for water at higher temperature (up to 90°C).

Condensing boilers work best with low-temperature applications, such as under floor heating. However, efficiencies will still be increased when used with radiator or convector circuits.

Combination boilers

In a combination (or ‘combi’) boiler, there is a secondary heat exchanger integrated within the boiler housing that is used to provide hot water instantaneously. There is no need for a hot water storage cylinder and associated cold water feed tank and pipework. They can be particularly attractive options in properties where space is limited and are used mainly in domestic buildings.

Combination boilers are limited to smaller applications so will not be appropriate for most businesses. However, if your business is run from a very small building and hot water demand is limited to taps, they may be an option.

Quick tip

You can find out things like your boiler’s rating, age and settings from the manufacturer’s plate. This is usually found on the side of the boiler casing.


Modular boiler systems

A modular boiler system is where a series of boilers are linked together to meet a variety of heating demands. Modular boiler systems are best suited to buildings or processes with a significant, variable heat demand.

LTHW boilers give optimum efficiency at a particular load point (standard boilers at full load, condensing boilers at part load) so, it makes sense to have a series of boilers operating at around their peak efficiency loads and together matching the range of heating demands that may be experienced in one of the UK’s commercial buildings. For example, consider a building with a peak winter heating demand of 100kW. If a single standard boiler were to be used, it would operate at full capacity, and peak efficiency, for only a few weeks of the year. If five modular boilers of 20kW each were used instead, lower heating demands experienced at other times of the year could be met by a

reduced number of boilers operating at full capacity. Modular systems are generally composed of several identical boiler units although a mix of condensing and conventional boilers could be used. The condensing boilers should in general be the ‘lead’ to maximise system efficiency. To gain the maximum benefit from arrangements of this type appropriate sequence control needs to be implemented – see section ‘Boiler Controls’.

Boiler efficiency

No boiler is 100% efficient. Energy (heat) is lost via the flue gases and through the main body of the boiler itself. Poor maintenance will exacerbate these losses.

Take care when considering boiler efficiencies. Manufacturers often quote instantaneous efficiencies which provides a means of comparing the relative performance of different

boiler models. However, it does not take into account the actual operation of the boiler or its practical use. For a more meaningful indication of performance in space heating applications a ‘seasonal efficiency’ can be calculated and is often quoted by manufacturers targetting this market. This takes into account the efficiencies of a boiler meausured at full and part load. It is a weighted average of a defined number of hours of full and part load operation which represents a full year of operation.

The table on page 11, shows the seasonal efficiencies for the different boiler types discussed above and how this would affect the energy input required to meet a heating demand of 100kW. Note that the boiler efficiency is also affected by the heating system type.


Table 1 Typical seasonal efficiency

Boiler type Typical seasonal efficiency Energy input rate required to meet 100kW* heating demand

Standard, old, poor condition 45% 222kW

Standard, good condition 70% 143kW

High-efficiency 82% 122kW

Condensing (used with fixed temperature radiators) 85% 118kW

Condensing (used with variable temperature radiators) 87% 115kW

Condensing (used with under floor heating) 90% or more 111kW or less

* As a general rule of thumb, most commercial buildings will require a heating demand of around 70-90W/m2. So, a 100kW boiler would be sufficient to heat a building of 1,100-1,400m2. Retail and educational buildings will have a bigger heat demand (100-110W/m2) and so a 100kW boiler would be sufficient to heat a space of 900-1000m2.


Improvements to existing boiler plantIt may not be cost-effective to replace boilers that are relatively new. However, there are still opportunities to make substantial savings through improvements to other items of the boiler plant.

Many of these measures will need specialist help. If in doubt, always consult a qualified technician.

Insulate boilers, pipework and valves

Heat loss through the boiler, pipework and valves leads to poor efficiency. All businesses should check their systems’ insulation.

Most modern boilers are well insulated to reduce heat losses from the body of the boiler and these can account for less than 1% of the total energy input. However, on older boilers, the insulation may be in poorer condition and can account for heat losses of as much as 10% of the energy input. The boiler insulation should be assessed and replaced where it is insufficient or showing signs of degradation. Similarly, the insulation on the associated boiler pipework and

valves should be assessed and replaced if necessary. This can result in additional savings of up to 10% of the boiler energy input.

Particular attention should be paid to valves as these are often left uninsulated because of access concerns. Modern valve-wraps solve this problem by providing suitable levels of insulation but allow easy access to the valve through quick-release fastenings.

Fit flue dampers

On larger boilers, the flue can cause a flow of air through the boiler, even when it is not firing. This cools the boiler and valuable heat is lost to the atmosphere – known as ‘standing losses’. A flue damper can be used to close off the flue automatically when the boiler is not firing, thus preventing this energy loss.

Since 1998, regulations have required boilers to have improved efficiencies at both full and part-loads, and this has led to lower standing losses in modern boilers. Retrofitting flue dampers is therefore applicable to older, conventional boilers with a large load (typically >100kW). The advice of a qualified technician is essential.

Install variable speed drives and pumps

On forced/induced-draught boilers, a variable speed drive can be installed on the fan. The enables the fan to operate at lower speeds when less air flow is required. A reduction in fan speed of just 10% can result in fan energy consumption savings of around 20%, and a reduction in fan speed of 20% will save up to 40%. This is particularly relevant for big boiler systems.


Variable flow control works on a similar principle. Most heating systems use the same amount of energy for pumping, regardless of the load on the system, but they normally require maximum flow for only a limited time. This is usually during the ‘boost’ period when trying to raise the temperature of the building to a comfortable level. Variable speed pumps can be fitted which decrease the flow in the system to match demand. This can save 25-50% of the annual pumping energy consumption.

Retrofitting of variable speed drives and pumps is best suited to larger systems with variable loads. If the load on the fan/pump is constant, energy consumption may actually increase through the installation of a VSD. The advice of a qualified technician is essential to assess the economic feasibility of this option.

For further information about Variable speed drives, please download the Variable speed drives technology overview (CTG070).

Recover heat from exhaust gases

In conventional boilers, the heat contained within the exhaust gases is lost to the atmosphere. If replacement with a condensing boiler is not possible, this heat can be recovered through the use of a heat exchanger. The heat can be used to pre-heat the return water or the combustion air. Increasing the temperature of the combustion air by 20ºC can improve the overall efficiency of the boiler by 1%.

This technology is best suited to conventional and highefficiency boilers with flue gases of a sufficient temperature. It is important that the economics of retrofitting such a system are assessed as the potential savings are relatively small. They will be most economical when applied to a larger system. Always consult a qualified technician.


Boiler controlsThe most effective way to improve boiler performance is through controls.

The first step is to assess what controls already exist, find out if they are calibrated accurately, and check that their settings match the business’s requirements. If they do not, adjust them either by asking for help from a qualified professional, or referring to the operating manual (usually downloadable from manufacturers’ websites if they have been lost).

The next step is to decide whether additional controls would be beneficial. Again, installation of new controls should be carried out by a professional.

A brief description of a number of different control options is given below, with details on the optimum settings for these controls. Manufacturers will be able to give more advice on the best control options for particular boilers.

Please refer to the Carbon Trust‘s technology guide Heating control (CTG065) for more in-depth information.

Burner controls

Burner controls manage the fuel-to-air ratio which is critical to the efficient operation of the boiler: too little air and there will not be enough oxygen for complete combustion to occur resulting in a build-up of potentially dangerous carbon monoxide in the flue; too much air and energy will be wasted in trying to heat the excess. The fuel-to-air ratio is normally set on the burner controls and will be based on the boiler manufacturer’s recommendations. Proper control of this ratio will ensure that the boiler is as efficient as possible.

As part of routine servicing, a qualified technician will measure the fuel-to-air ratio of a boiler. This can then be compared with the manufacturer’s recommendations and, where necessary, the appropriate remedial actions

taken. In some cases, the boiler technician will simply adjust the burner as part of the service but for more complex systems, particularly those operating at part load for much of the year, it may well be cost-effective to consider a replacement burner control that will improve efficiency and result in energy savings.

Types of burner control

The simplest form of burner control is single-stage or ‘on-off’ control and is the type of control found on most older, standard boilers. With this type of control, the burner fires at full capacity when heat is required and is off otherwise. Air purges immediately before the burner is switched on and after the burner is switched off to ensure that no residual fuel or combustion vapour remains in the boiler, but this also causes heat to escape via the flue.


An improvement to the above is two-stage or ‘high-low’ control. With this type of control, rather than being completely switched off, the burner has the option of going to a low firing rate, typically 40% of full capacity. This reduces the number of times the burner switches off and the number of air purges, and improves boiler efficiency under part-load conditions.

A further improvement is modulating control. With this type of control, the fuel and air supplies are regulated to exactly match the required heat demand. This ensures good efficiency across the whole heat output range of boilers. Modern burners typically use micro-processors based controls. These adjust air and fuel flows continuously, compensating for changing conditions to ensure that the correct fuel-to-air ratios are maintained accurately.

Retrofitting of burner controls is best suited for older, conventional boilers with large, variable heat loads.

For information about boiler controls in the context of heating systems download the Carbon Trust’s technology overview, Heating, ventilation and air conditioning (CTV046).

Boiler interlock

Boilers can continue to fire even when there is no demand for heat (called dry-cycling) and so all the heat energy is lost to the flue. Find out whether this is happening by turning off the heat distribution system and then observing the boilers themselves. If they continue to fire when no load is required, dry-cycling is occurring. Clearly this should be avoided.

Linking the boiler controls with the heating system controls (such as room thermostats) via a boiler interlock will ensure that the boiler does not operate when there is no heat demand and will prevent dry-cycling. This can be done using standard wiring between the boiler control and the main heating control, or can be achieved through the installation of a specialised integrated controller. The best option will be determined by the size of the system and location of the boiler and controls. A qualified technician should be consulted for advice.

Interlock control is appropriate for all types of boiler.

Sequence control

If there are two or more boilers, it is a good idea to consider sequence control if it is not already installed. Find out whether or not sequence control is operating by observing the boilers during part-load conditions, such as in spring or autumn. If all boilers are firing and shutting down simultaneously, it is likely that they are operating only at part-load and do not have sequence control.

Good sequence control ensures that only the minimum number of boilers required to meet the heat demand fire and that these boilers are used at their optimum efficiency load. Also, sequence controllers ensure that the order in which the boilers fire can be rotated to minimise maintenance costs. Note that where there are both condensing and standard boilers installed, the condensing boiler should always take the lead. Good sequence control could save 5-10% of the overall energy consumption of the boiler plant.

Where not already installed, sequence control should be retrofitted to multiple boiler applications with a variable load pattern.

Did you know?

A poorly maintained boiler can use 10% more energy than one that is well-maintained.


Optimised start/stop control

Most heating systems will be controlled via a timeswitch. This will be set to switch the heating system (and hence the boiler) on and off at pre-set times in the morning and evening, corresponding to building occupancy patterns. An optimiser is a sophisticated timeswitch linked to the internal and external thermostats that switches the boiler on at exactly the right time to ensure that the building reaches the required internal temperature in time for occupation. Similarly, the boiler is switched off early so that the internal temperature is maintained only when required. Savings of 5-10% of the overall energy consumption of the boiler plant could be achieved.

Most buildings with standard operating hours would benefit from installing optimised start/stop control.

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Timeswitchset for 6am

Optimisedstart

Typical settingsMaximum heat-up periode.g. 6am to 9amNormaloccupancy periode.g. 9am to 5pm

Figure 2 Sequence control

Figure 3 Optimised start/stop control


Building Energy Management Systems

Controls work best when their operation is integrated and linked to the actual requirements of the building. A Building Energy Management System (BEMS) is a computer-based control system which automatically monitors and controls a range of building services. Installing a BEMS means that control options such as sequencing, optimisation and compensation can be carried out by one system. It allows various environmental parameters to be taken into account and provides logs of useful data that can be used in maintenance, energy monitoring and assessing further improvements to the system. 10-20% of heating energy can be saved by installing a BEMS in place of several independent control options. However, they are expensive and may only be cost-effective for larger boiler plant. They will also be effective only if operated by trained staff and maintained and calibrated regularly. Manufacturers can advise on the most suitable BEMS for their boiler plant.

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Flow temp ºC

Normally two settingsMinimum flow temperatureRatio or slope of graph

Figure 4 Direct weather compensation control

Direct weather compensation control

To achieve more savings, the temperature of the water can be regulated according to outside temperature. In milder weather, the flow temperature is reduced, thus saving energy. This is done through the use of a compensator linked to internal and external thermostats.

This form of control is particularly useful in condensing boilers as lower return water temperatures can be achieved, thus ensuring that maximum condensation occurs within the boiler and increasing efficiency.


Check controls

The benefits of improved controls will be realised only if frequent checks are carried out on control settings and their operation. This is particularly important if business needs have affected the controls. For example, controls are set to cover a period when staff work out of hours, but are not returned to their original settings. A regular check will spot where energy is being wasted in this way.

Simple control settings (such as timeclocks) can be adjusted by non-professional building staff as circumstances require, provided they have had appropriate training and take care. More sophisticated controls should be adjusted by a qualified technician. Similarly, control operation and calibration should be checked annually by a qualified technician.

A simple way of assessing the effectiveness of boiler controls is to plot heating energy consumption on a graph and compare with periods of building operation and outside weather conditions. Does the building show a high energy use out-of-hours? Is there a high heating load when the weather is mild? These are indications that control settings are inaccurate or that additional controls are required.

Table 2 Summary of control options

Boiler size What are the minimum controls you should have?

Minimum standard

Want to save even more energy?

Good standard

For boilers up to 50kW Boiler interlock Minimum standard

PLUS

Optimisation


For boilers over 50kW Boiler interlock

Sequence control

Minimum standard

PLUS

Optimisation



Sequence controls, optimised start/stop controls and direct weather compensation controls can be purchased as a unit or can be programmed as part of a Building Energy Management System (BEMS).


MaintenanceEffective maintenance is essential in getting the best performance from your LTHW boilers. Without it, boiler efficiency can drop significantly and equipment life expectancy is reduced.

Effective maintenance can also highlight potential problems quickly and enable remedial action to be taken before there is a major impact on performance.

Perform regular servicing

A full boiler service should be carried out by a qualified technician on an annual basis, ideally before the start of the heating season. This service should include a flue gas analysis (to check fuel-to-air ratio), an operational check, controls calibration, burner cleaning and limescale treatment.

Boiler maintenance should be carried out by GAS Safe or OFTEC registered contractors ONLY.

Analyse flue gas

As mentioned in the previous section, the fuel-to-air ratio is critical in ensuring efficient boiler operation. Analysis of the boiler’s flue gases for levels of carbon dioxide (CO2), oxygen (O2) and carbon monoxide (CO) will determine whether this ratio is correct and what adjustments need to be made. Different ratios will be required for different boilers and your boiler manufacturer or maintenance technician can give the appropriate advice.

Flue gas analysis should be carried out every three months by a suitably qualified technician. Ask for a report on the combustion efficiency which includes measures for improving it.

Remove soot

If combustion conditions are not correct, particularly if too little air is used, fuel combustion will not be complete. So excessive amounts of CO and particles of carbon (soot) will form. If these particles build up on the fire side of the boiler’s heat exchanger they will form an insulating layer, inhibiting heat transfer to the water. More heat input is required to meet the heat demand and more heat energy will be lost to the flue.

All hydrocarbon fuels – gas, oil, coal – may create soot. Properly controlled gas boilers create insignificant amounts of soot and will rarely require cleaning, although the manufacturer’s guidance should always be followed. However, if combustion checks show poor combustion then the heat exchanger should be check and cleaned if necessary. Oil, coal and biomass are more likely to form soot and should be carefully monitored. Cleaning should be carried out by a qualified technician.


For very large boilers, typically used in industrial application, integrated soot-blowers are often installed in boilers to provide continual cleaning; however, these will need to be checked regularly to ensure good working.

Minimise limescale build-up

In hard water areas, limescale can build up on the water side of the boiler’s heat exchanger. This creates an insulating layer, inhibiting heat transfer to the water in the same way as the soot deposits above.

The most effective method of limescale removal is through chemical treatment of the water. This should be done annually by a qualified technician to minimise limescale build-up and keep your boiler running at its most efficient.

Produce a maintenance plan, manual and logbook

To ensure effective maintenance is carried out, a maintenance plan should be put in place. This will detail what maintenance tasks are to be carried out, the frequency of these tasks and who is responsible.

A maintenance manual should be produced that is updated regularly. This manual should include:

• The maintenance plan.

• Block diagram of the boiler plant showing the of key components and controls.

• Schematic diagrams of the heating system and the controls.

• Operating instructions and control settings Emergency shutdown procedures.

• Contact details of installation/maintenance technicians and boiler manufacturers.

Particular attention should be paid to specific instructions from manufacturers as these will ensure the optimum performance of the boiler plant. Also, failure to follow them may invalidate warranties.

A maintenance logbook should be kept giving detailed records of maintenance tasks, including which actions were taken, the person responsible, and when they were completed. This logbook will ensure that tasks are carried out at the correct frequency and will highlight ongoing problems.

Did you know?

A 1mm layer of soot will cause a 10% increase in energy input to the boiler to meet the same heat demand.

A 1mm layer of limescale will cause a 7% increase in energy input to the boiler to meet the same heat demand.


Table 3 Summary of maintenance requirements

Maintenance task Frequency Responsibility

Review boiler maintenance policy Yearly Energy/facilities manager with the advice of qualified technician

Full service Yearly Qualified technician

Flue gas analysis (combustion check) Quarterly Qualified technician

Remove soot deposits Six-monthly (more frequent for oil/coal boilers) Qualified technician

Limescale treatment Yearly Qualified technician

Check/adjust simple control settings Quarterly, or as changes to building operation demand

Building staff

Adjust/re-programme complex controls Yearly, or as changes to building operation demand Qualified technician

Check control operation Yearly Qualified technician

Calibration of controls Yearly Qualified technician


Replacing boilersIf a boiler is more than 15 years old, or if it is showing signs of inefficient operation, it should be replaced.

This is not as simple as noting the old boiler’s rating and purchasing a new, condensing model. To find the best solution, thoroughly review the building’s heating demand and your business needs, and check these against your technical, financial and policy requirements.

When considering a boiler replacement, advice should be sought from a qualified building services engineer or boiler technician. To help them, consider the following information.

The building’s heating requirements

The most important aspect in selecting a new boiler is getting the size right. It was once common practice to oversize boiler plant with the mistaken notion that this would provide greater flexibility in the future. However, it is now realised that this is unnecessary as the heating demand for many commercial buildings has fallen. This is due to improvements in building fabric and an increase in internal heat gains, such as from IT equipment, lighting and occupants. If a boiler has not been replaced for many years, the heating load of the building may have changed significantly.

Start by reviewing the building’s internal environment and general operation. What is the current internal temperature of the building? Are employees happy with the internal environment? Are there any hot or cold spots within the

building? Are there any areas of the building where temperature is critical? When is the building occupied?

Next, review your annual energy bills. What fuel do you currently use for heating? How much energy has the building used over the last year and how much did it cost? How does this compare with other similar building types? To do this, divide the annual heating energy used by the area of the building to gain a ‘benchmark’ in kWh/m2.

Smaller boilers cost less, so look for ways of reducing the heating demand. Can the insulation of the building be improved? Could draught-proofing be improved?


Technical considerations

The choice of boiler will be dependent on a number of technical issues. A building services engineer or boiler technician can give advice, but you can provide some basic information to help.

Fuels

Ultimately, the choice of fuel will be based on cost and availability of supply. Ask which fuels are available on-site. Boilers are designed to operate with particular fuels and are rarely interchangeable so it is important to make an appropriate selection.

Of the fossil fuels natural gas is the best choice where a supply is available, as it is the most versatile and has the lowest carbon emissions. Is there a natural gas supply? Remember that the situation may have changed since the current equipment was installed. If not, then consideration must be given to which alternative fuels are available such as LPG, mineral oils or biomass. These fuels are delivered in batches and careful consideration must be given to issues relating to their long term availability, supply routes and storage.

Table 4 Find out the building’s heating requirements


Floor area of building Property documents

Direct measurement

Energy benchmarks

Occupied hours Staff records Calculating heating demand


Internal environmental data, such as temperature

Direct measurement

Control settings

Staff comments

Calculating heating demand


Annual energy use/cost for heating

Utility bills

Energy monitoring and targeting system

Energy benchmarks

Details of planned energy saving measures

Company energy policy Calculating heating demand


If you think that biomass boilers may suitable for your requirements and you need some more information order or download the Carbon Trust’s introductory guide, Biomass heating – An introduction for potential users (CTG016).

Location

Where you have more than one boiler, find out if the existing boiler plant is centralised or de-centralised.

Centralised plant (where all boilers are in one plantroom) may be easier to maintain and control, but heat losses through long pipework runs will be higher. Combine the replacement of boilers with upgrades to the pipework insulation. Also take advantage of the central location to install upgraded controls or re-programme existing ones.

De-centralised plant (where a number of smaller boilers are located around the building) will reduce pipework losses, but you will not have the option of integrating control operation and maintenance may be more problematic and expensive. This is because it costs more to carry out maintenance checks on several smaller boilers than one large boiler.

If you are considering changing to biomass boilers the available space for the boiler and the associated fuel store must be adequate and their relative positions such that any automated fuel transfer systems (from storage bunker to feed hopper) can function effectively.

Flue outlet

Where is the boiler flue outlet? Condensing boilers generate lower temperature flue gases and visible plumes of steam. This may cause problems if the flue outlet is close to other building surfaces.

Heating system

What type of heating system is currently used in the building? Unless a major refurbishment is planned, it may not be cost-effective to replace the whole heating system so the new boiler must be compatible with what is there already. Condensing boilers work best with low temperature. applications such as under floor heating, but will still provide a higher level of efficiency when applied to a radiator circuit. It may be necessary to upgrade the heating controls of the system to get the best from the

new boiler. Do not forget to account for these costs when considering the purchase price.

Biomass boilers are best suited to steady heating loads between 30% and 100%. They may need to be partnered with a heat store of a gas or oil fired boiler to match overall output and to meet peaking demands. They might also be a suitable component for a decentralised system.

For information about biomass boilers in the context of heating systems, order or download the Carbon Trust’s in-depth guide, Biomass heating – A practical guide for potential users (CTG012).


Condensing boilers are more expensive than high-efficiency standard boilers, but they are more efficient and cost less to run. So the extra cost is often paid back in two years or less.

The business may be able to take advantage of Energy Efficiency Financing or the Enhanced Capital Allowance Scheme (see next page for information on the Carbon Trust’s financial products). The Enhanced Capital Allowance Scheme covers the most efficient gas and oil fired hot water boilers and biomass boilers.

Fuel

Fuels vary in price. Consider your current and projected energy use and calculate the cost of running the boiler.

Maintenance

As stated previously, maintenance of boilers is important. Will the maintenance costs of the new boiler be higher? Will extra staff training be required to ensure efficient operation? Can maintenance be done in-house or will it be contracted out? Make sure that all staff involved in the operation and maintenance of the boiler plant have a say in the choice of the new boiler.

Table 5 Find out the technical requirements


Fuel supply available Utility companies

Local authority

Specification of boiler type

Centralised or de-centralised plant

Observation Specification of boiler type


Pipework insulation required

Location of flue outlet Observation Specification of boiler type


Type of heating system Observation Specification of boiler type

Heating controls

Financial considerations

Consider the costs of the new boiler, including capital expense, fuel and maintenance. This is called life costing, that is, how much will the boiler cost over its actual lifespan. It is important to capture all the activities associated with the ownership of a boiler if it is to last its normal life expectancy. The introduction of the Renewable Heat Incentive near the end of 2011 provides a mechanism to

encourage the installation of renewable heat equipment including biomass boilers.

Capital expense

How quickly will the investment pay for itself through reduced running costs? Will this influence the purchasing budget?


Table 6 Find out financial considerations


Purchase budget Finance/Company director Specification of boiler

Availability of loans/ tax incentives

Carbon Trust

HM Revenue and Customs

Changes to purchase budget

Running costs of new boiler


Boiler technician

Manufacturers

Utility bills



Life costing

Maintenance costs of new boiler


Boiler technician

Manufacturers

Finance department



Assessing staff training needs

Developing a maintenance plan

Life costing

Did you know?

Replacing a conventional boiler with a condensing model can save 10-20% of annual energy costs – more if the original boiler is in a particularly poor condition.

Example: A building with a heating demand of 100kW has an annual gas bill of £8,930.1 A new condensing boiler is installed at a cost of £3,000 with a seasonal efficiency of 90%. The new annual gas bill is £6,940 – a saving of 22% or £1,980/year. Maintenance costs are decreased by £200 per year. Therefore, the cost of the new boiler is paid back within 20 months.

1 Based on a 70% efficient boiler, 2,500 operating hours/year and 2.5p/kWh gas price.

Tax incentives

Enhanced Capital Allowances (ECAs) are a straightforward way for a business to improve its cash flow through accelerated tax relief. The ECA scheme for energy-saving technologies encourages businesses to invest in energy saving plant or machinery specified on the Energy Technology List (ETL) which is managed by the Carbon Trust on behalf of Government.

The ECA scheme provides businesses with 100% first year tax relief on their qualifying capital expenditure. The ETL specifies the energy-saving technologies that are included in the ECA scheme. The scheme allows businesses to write off the whole cost of the equipment against taxable profits in the year of purchase.For further information please visit www.carbontrust.co.uk/eca or call the Carbon Trust on 0800 085 2005.


Environmental considerations

As well as reducing running costs, condensing and high-efficiency boilers will have reduced emissions of carbon dioxide (CO2) and harmful pollutants such as sulphur dioxide (SO2) and nitrogen dioxide (NO2). Does your company have an environmental policy? Will this influence the choice of a new boiler?

Preparing a detailed brief

Once this information has been gathered, use it to prepare a detailed brief for a building services engineer or boiler technician. They will use this information to select the best boiler to achieve your needs within the proposed budget. A detailed brief will save time and money and ensure that your new boiler is both efficient and effective.

Table 7 Find out environmental considerations


Environmental policy Company director Specification of boiler to ensure reduced emissions

Energy Efficiency Loans

Investing in energy efficient equipment makes sound business and environmental sense, especially with the easy, affordable and flexible Energy Efficiency Financing scheme brought to you by Carbon Trust Implementation and Siemens Financial Services. To find out more visit www.energyefficiencyfinancing.co.uk


Energy monitoring and targetingIf energy use is not monitored, it cannot be controlled. An energy efficiency strategy will be most effective when accompanied by appropriate energy monitoring and targeting.

By monitoring the energy used by the boiler plant, the effect of improvements can be assessed in both financial and environmental terms. In addition, unusually high energy consumption can be spotted quickly, problems identified and remedial action taken.

The first step is to take regular meter readings – at least monthly, although weekly would be better for larger buildings. If a BEMS is installed, it may be possible to automate this process. This will be dependent on the type of meter installed and advice should be sought from the BEMS manufacturer and/or the utility company. Depending on the size of the building, utility companies may be able to provide half-hourly energy data.

The meter readings should be recorded on a table and the energy consumption for the period calculated. Graphs can then be produced to show the energy consumption over time and comparisons can be made to assess performance.

If the individual performance of a boiler is required, spot meters should be installed on the individual fuel intakes. This may not be cost-effective for smaller boilers so should be considered carefully.

It is important to assess heating energy use in the context of weather conditions and building operation. For example, heating energy will increase when the weather is colder and heating energy should be minimal when the building is unoccupied.

If your heating energy use profile does not match weather conditions or building operation, it may be an indication of poor control.

Set targets and monitor progress

Simply monitoring energy use will not result in savings. Targets for reduction should be set and measures put in place to achieve those targets. A 10% reduction in heating energy can often be achieved through simple adjustments to existing boiler plant. Greater reductions can be achieved through the replacement of equipment, components or controls.

Keep a check on progress towards meeting targets. If progress is slow, carry out another review of the heating system and look for additional measures that can be taken. Report progress to all building occupants – this will increase energy awareness and get everyone involved in reducing the building’s energy use.Effective energy monitoring

and targeting can highlight potential problem areas and lead to swift, remedial actions.


Next stepsThe checklist below will help you to carry out an initial review of the boiler plant and assess what actions can be taken. Many such actions can be taken in-house; however, you may need specialist support from your contractor or consultant for others.

Review Questions Actions to be considered Comments

Make, model, size, type and age of boiler

Is the boiler more than 15 years old?

Is the boiler oversized?

Replacement

Replacement

Different improvement options will apply depending on boiler type

Fuel consumption of boiler plant

How efficient is the plant? Assess through meter readings. Estimate efficiency based on consumption and rated output

Check physical condition

Is there any corrosion?

Is insulation adequate/ in good condition?

Get service done

Replace/upgrade insulation

Replacement

Poor physical condition will cause poor performance; consider replacement

Assess controls What type?

Are sequencers, optimisers or compensators used?

Install additional controls Improved control will reduce energy consumption

Check control settings Are they appropriate?

Do they match building operation patterns?

Adjust settings Improved control will reduce energy consumption

Review maintenance history

When was the last maintenance carried out?

Is a proper maintenance plan in place?

Establish a proper maintenance plan

Order service/maintenance check

Poor maintenance can reduce boiler performance by up to 10%

Atmospheric burner A burner where the air required for combustion is drawn in via natural convection.

Boiler A vessel for converting heat produced by combustion of fuel into hot water or steam.

Boiler efficiency A comparison of the energy output versus the energy input of the boiler.

Boiler interlock Where the boiler and system controls are linked to ensure the boiler does not fire when there is no heating demand.


A computer-based system that operates all building controls and enables automatic adjustment and monitoring of settings.

Burner The device producing the flame for combustion in the boiler.

Combustion The process of turning fuel into useful heat.

Compensator A device, or feature within a device, that adjusts the temperature of the water circulating through the heating system according to the temperature measured outside the building.

Condensing boiler A boiler that reclaims heat from the exhaust gases to improve overall efficiency.

Convector A heat emitter that heats a room through either natural or forced convection.

Energy benchmark A measure of a building’s energy use that can be compared to other buildings of a similar type. Expressed in kWh/m2.

Flue The boiler’s chimney – used to transport exhaust gases to the atmosphere.

Flue damper A device that shuts off the flue, avoiding cold air penetrating the boiler when it is not firing.


Glossary


Forced/induced draught burner

A burner where the air required for combustion is drawn in via a mechanical fan.

Heat exchanger A network of pipes within a boiler whereby the heat from the burner is transferred to the circulating water.

Modulating burner control Where the fuel and air intake are controlled over the whole range of boiler output.

Optimiser A sophisticated timeswitch linked to the internal and external thermostats that switches the boiler on at exactly the right time to ensure that the building reaches the required internal temperature in time for occupation.

Radiator A heat emitter, made of metal, that heats a room through a combination of radiation and convection.

Sequencer A controller for multiple boiler systems that ensures the minimum number of boilers is used to meet the required heating demand.

Single-stage burner control Where the burner is either ‘on’ or ‘off’ and fuel/air intakes are the same regardless of heating demand.

Two-stage burner control Where the burner can revert to a low-firing range under part-load conditions.

Under floor heating A network of low temperature hot water pipes installed under the floor finish which heat a room from beneath.

Variable flow control Where the pump flow is regulated to match demand and flowrate.

Variable speed drive A device fitted to electric motors that regulates speed to match demand.


Go online to get moreThe Carbon Trust provides a range of tools, services and informationto help you implement energy and carbon saving measures.

Website – Visit us at www.carbontrust.co.uk for our full range of advice and services. www.carbontrust.co.uk

Publications – We have a library of publications detailing energy saving techniques for a range of sectors and technologies.


Case Studies – Our case studies show that it’s often easier and less expensive than you might think to bring about real change.


Energy Efficiency Financing – Investing in energy efficient equipment makes sound business and environmental sense, especially with the easy, affordable and flexible Energy Efficiency Financing scheme brought to you by Carbon Trust Implementation and Siemens Financial Services. www.energyefficiencyfinancing.co.uk

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The Carbon Trust receives funding from Government, including the Department of Energy and Climate Change, the Scottish Government, the Welsh Government and Invest Northern Ireland.

Whilst reasonable steps have been taken to ensure that the information contained within this publication is correct, the authors, the Carbon Trust, its agents, contractors and sub-contractors give no warranty and make no representation as to its accuracy and accept no liability for any errors or omissions. All trademarks, service marks and logos in this publication, and copyright in it, are the property of the Carbon Trust (or its licensors). Nothing in this publication shall be construed as granting any licence or right to use or reproduce any of the trademarks, services marks, logos, copyright or any proprietary information in any way without the Carbon Trust’s prior written permission. The Carbon Trust enforces infringements of its intellectual property rights to the full extent permitted by law.

The Carbon Trust is a company limited by guarantee and registered in England and Wales under company number 4190230 with its registered office at 4th Floor Dorset House, Stamford Street, London SE1 9PY.

Published in the UK: March 2012.

© The Carbon Trust 2012. All rights reserved.

The Carbon Trust is a not-for-profit company with the mission to accelerate the move to a low carbon economy. We provide specialist support to business and the public sector to help cut carbon emissions, save energy and commercialise low carbon technologies. By stimulating low carbon action we contribute to key UK goals of lower carbon emissions, the development of low carbon businesses, increased energy security and associated jobs.

We help to cut carbon emissions now by:

• providing specialist advice and finance to help organisations cut carbon

• setting standards for carbon reduction.

We reduce potential future carbon emissions by:

• opening markets for low carbon technologies

• leading industry collaborations to commercialise technologies

• investing in early-stage low carbon companies.

www.carbontrust.co.uk 0800 085 2005

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