energy savings in utility systems - university college cork · potential solutions to said faults....
TRANSCRIPT
ENERGY SAVINGS IN UTILITY SYSTEMS
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Energy savings in utility systems
2016
ENERGY SAVINGS IN UTILITY SYSTEMS
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Table of Contents Executive summary ................................................................................................................................. 3
Compressed Air Systems ......................................................................................................................... 4
Running costs and energy losses ........................................................................................................ 5
Compressed Air Leakage ..................................................................................................................... 6
Low Dew point .................................................................................................................................... 6
Refrigeration Systems ............................................................................................................................. 8
Running costs and Energy losses ........................................................................................................ 8
Poor Control ........................................................................................................................................ 9
Refrigerant Leakage .......................................................................................................................... 10
HVAC (Heating, ventilation and Air conditioning) ................................................................................ 12
Running costs and Energy losses ...................................................................................................... 12
Poor Maintenance regimes ............................................................................................................... 14
Poor Control ...................................................................................................................................... 14
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Executive summary
This purpose of this white paper is to summarise where energy savings can be made in the utility
systems employed in the industrial sector and to describe some of the faults that cause these
inefficiencies.
This white paper aims to answer the following questions:
What are the main energy performance issues and inefficiencies in industrial utility systems?
What are the costs relating to these issues?
How can these issues or faults in system performance be identified?
Is it cost effective to remedy them?
How long (if possible to calculate) will it take for these changes take to return on the
investment it takes to remedy them?
This paper introduces industrial utilities and highlights two of the most common faults or bad
practises for HVAC (Heating, ventilation and air conditioning), Air-compression and Refrigeration
systems. It then goes on to explain how to determine if energy savings are possible and to describe
potential solutions to said faults.
This paper demonstrates that small but targeted changes to HVAC, air-compression and refrigeration
utilities can result in major energy and cost savings with the more serious issues delivering a payback
on investment of less than one year
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Compressed Air Systems Compressed air generation systems (Figure 1) form an integral part of any factory where
pneumatically actuation takes place, with upwards of 10% of a pharmaceutical plants electricity
being used on air compression. Use of compressed air varies with the type of factory however some
common examples would be; air brakes, air jet, air motor, valve actuation, boiler tube cleaning,
cleaning, buffing and work positioning. With such a large percentage of all electricity in a plant being
used for air compression, implementing some simple changes could result in large reductions in
running costs.
Figure 1. General Arrangement of an industrial Air Compressor System
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Running costs and energy losses As detailed in Figure 2, the majority of cost associated with air compression is electrical. Though end
use is key, the most cost effective place to identify energy savings on air compression systems would
be with the general running and efficiency of the air compressor itself.
Figure 2. Running costs over a 5-year period
Figure 3 details the losses associated with compressed air generation. These would typically be
motor losses, compression and idle losses, cooling and drying losses, pressure losses in filters, dryer
and pipework and leakage and expansion losses. However, for the purpose of this paper, high
leakage rates, which are a major component of idling losses, and low dew point temperatures are
discussed as these are two of the most prevalent issues in industrial compressed air systems.
Figure 3. Energy losses in compression
Electrical, 71%
Servicing, 15%
Purchase cost, 14%
Running costs of an air compressor over a 5 year period
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Compressed Air Leakage Many factories can operate compressed air systems with leakage rates of approximately 20 – 30.
Leakage is commonly found at, but not limited to, joints, drains, valves, flexible hose pipes, filter and
lubricator units, pressure regulators, condenser traps and thread sealants. A 2007 report published
by the Sustainable Energy Ireland (SEI) found that a 4mm hole in a system, operating at 8 Bar, or
800000 PA (pascal) could result in losses of over €2000 per annum. Adjusting for inflation and energy
price increases, this would equal almost €3000. On a factory wide scale this can result in large losses
in energy and an inefficient compressed air system. It is therefore essential to monitor the leakage
rate from industrial compressed air systems to ensure the generation system is not operating at
unnecessary high levels servicing high leakage rates. Figure 4 details losses due to air leakage for a
variety of hole sizes and typical plant compressed air operating pressures.
Figure 4. Costs of leaks in compressed air system for a range of pressures
Low Dew point In an air compressor air can become saturated due to isentropic compression and expansion. This
moisture in the air can become problematic to end users who require a certain dryness of air. Driers,
which are usually mounted in the compression air generation station, are employed to remove this
moisture from the air. A dew point is defined as the atmospheric temperature (varying according to
pressure and humidity) below which water droplets begin to condense and dew can form. Choosing
a dew point which is suitable for a factory/ plant is very important. Choosing a dew point which is
too low will result in over drying the air and hence will result in unnecessarily high energy costs to
operate the system. Choosing a dew point which is too high may result in poor air quality for the end
users.
Table 1 can be utilised to determine a suitable dew point for a specific plant. It is therefore critical to
monitor the dew point set points in use in industrial compressed air installations to ensure they are
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as economically advantageous as possible while not impacting on end use requirements. Too often
multiple systems on the same industrial site will operate with differing dew point settings with no
quality requirement to do so. Therefore, it is essential to monitor the dew point on each system in
isolation and in parallel for maximum energy performance.
Table 1: ISO 8573.1 Quality classes of compressed air
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Refrigeration Systems Refrigeration systems (Figure 5) are core to the operation of any factory which requires cooling of a
process medium or has extensive HVAC equipment and a significant cooling load. Some examples of
where refrigeration may be required in industry are; chilled water, data storage cold rooms, product
storage, air conditioning and mixed use heat exchangers. Refrigeration is expensive and savings of 25
– 30% are easily attainable in most plants by implementing more efficient control and maintenance
practices. These savings can be achieved with little initial cost and can pay off within two years.
Ensuring that a refrigeration system is more efficient ensures better reliability, which in turn results
in fewer breakdowns and less maintenance costs and down-time losses.
Figure 5. A common industrial refrigeration system
Running costs and Energy losses Table 2 shows some examples of typical refrigeration system energy usage in a number of sectors.
As seen in the table, refrigeration costs vary considerably depending on sector. Costs may also be
greatly influenced by ambient temperature. Refrigeration generally amounts to 20 – 70% of overall
energy costs in most facilities requiring cooling. Therefore, if refrigeration efficiency is increased, this
will amount to large energy savings overall.
Energy losses in a refrigeration system are typically as a result of one or more of the following issues;
blocked condensers, Recycling of warm air, oil level too high or too low, inadequate maintenance,
leakage, poor control, distribution head too low, poor choice of refrigerant and obstacles in air flow.
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Table 2: Refrigeration energy usage by sector
Poor Control Often in industrial utility systems, control set points are not optimal for the service that they need to
deliver. While these set points may be safe they do not ensure maximum efficiency. Customizing
these set points to a particular plant can have a large effect on the efficiency of the system.
Commonly plants use traditional control methods resulting in systems potentially running when not
required or sub optimally when they are. Plants with multiple condensers or cooling towers, still
relying on traditional pressure switches would see a large rise in efficiency due to installation of
control microprocessors. Poor sequencing control of processors will cause several processors to
operate at part load simultaneously.
A condenser receives hot refrigerant gas from a compressor and condenses it into a liquid. At lower
temperatures the pressure produced by the compressor may be lower, this reduces the amount of
work required by the compressor. Installing floating pressure head control allows the compressor to
float between high and low pressures according to ambient conditions. This will allow the
compressor to operate most efficiently and cost-effectively. It is therefore essential to monitor the
evaporator and condenser temperature values in comparison to the outside temperature and
humidly levels to ensure optimum energy performance of equipment.
Figure 6 details is a schematic of a typical industrial control system.
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Figure 6. Control schematic
Refrigerant Leakage Refrigerant leakage is a major issue in industry for a number of reasons. Leaking refrigerant greatly
lowers the efficiency of the refrigeration process, increasing operation costs and energy usage.
Refrigerants such as R171, R404A, are also very expensive to replace, often upwards of €45 a kg.
Some of the chemicals contained in a refrigerant can be hazardous and therefore would pose a
considerable risk to staff and end users of the system. Due to the hazardous nature of refrigeration
chemicals, they pose a large risk to the environment, it is illegal to knowingly allow them to leak,
therefore it is a crucial responsibility of a company to ensure that these leaks are repaired.
If leaks are not repaired they will greatly affect the efficiency and day to day running of the plant,
driving up energy usage and costs, as illustrated in Figure 7 below. The effects of leakage will grow in
severity over time as materials and equipment degrade. It is therefore essential to monitor
refrigerant charge levels to ensure optimum refrigeration system operation in terms of energy
performance
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Figure 7. Breakdown of costs associated with neglect of leaks
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HVAC (Heating, ventilation and Air conditioning) HVAC systems (Figure 8) are made up of air handling units services by chilled water and hot water
systems in order to maintain thermal and air quality conditions within an industrial environment.
This system can include ducts, vents, water-coolers, air-coolers, heat exchangers, heat pumps,
boilers and fans each with a packaged AHU or as separate components of a larger system. These
systems maintain conditions in general work areas and also in more extreme environments such as
clean rooms with the latter being especially energy intensive.
Figure 8. A typical AHU
Running costs and Energy losses According to a study conducted by the SEAI in 2007, HVAC can account for up to 80% of a sites total
energy usage. In a study of 14 major manufacturers, it was found that HVAC accounted for 356 of
1000 GWh of total electrical energy and 322 of a total of 726 GWh thermal energy as detailed in
Figure 9.
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Figure 9. HVAC % Energy usage
Possible sources of energy loss/ fault in a HVAC system may be; poor control, design issues, poor
maintenance or calibration, an excessive number of air changes, wasted heat, poor insulation, a
passive control valve, stuck damper, poor control logic, supply set points conflicting with room set
points, poor management and erroneously selected set points.
In a 2007 report, SEI identified 137 opportunities for energy savings in HVAC, having carried out a
case study on a number of factories. Figure 10 identifies the opportunity frequency distribution of
potential energy savings as observed by SEI.
This report will focus on the two largest opportunities, poor maintenance regimes and inefficient
control.
Figure 10. Categories of opportunities, based on frequency of occurrence
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Poor Maintenance regimes Effective HVAC maintenance is key to its efficient operation. Poor maintenance in a system, can
result in large losses in energy. A lack of emphasis on utility systems maintenance with specific
attention to HVAC systems can lead to the number of AHUs in a plant outnumbering those
maintaining them by a factor of 20 to 1. Deficiencies in system operation can hence go undetected
and unrepaired for long periods of time. Maintenance in HVAC systems is generally only carried out
following complaints of end users or from breached limit alarms. Preventative measures are not in
place and parts are not replaced before they fail. For example, filters may be changed on a time
basis, rather than when the maximum differential pressure is exceeded. Policies such as this can
result in parts remaining in place long after fail, seriously effecting the efficiency of the system.
AHUs (Air handling units) are self-correcting and therefore will consistently supply air at the required
standard. Should a fault such as a passing heating coil occur in the AHU, it will over-compensate with
an overly open cooling coil. Therefore, faults that go undetected and unrepaired can have a knock
on effect, over-working other components and causing further failures. It is therefore essential to
monitor key operational parameters within an AHU and HVAC system in general, to ensure it is
operating as efficiently as possible.
Often faults in HVAC systems require down-time for repair, which may affect the overall plant.
Therefore, components should be tested to ensure they will perform until the next annual or
quarterly shut-down. It is therefore essential that HVAC systems are properly maintained, with
proper maintenance policies in place, to prevent energy wastage, failures and to ensure maximum
efficiency.
Poor Control Similar to refrigeration systems, HVAC control set points often are not optimised according to
specific service requirements. This may result in a system operating above the required standard, at
a cost to the factory. Customizing these set points increases efficiency and limits energy losses. It is
common for a plant to rely on the traditional control systems installed with the machines, replacing
entire systems after a period of time. However, minor alterations undertaken to modernise these
control systems can dramatically increase the efficiency of a machine or system, allowing it to
function at a higher standard for longer. This will result in energy savings, while also prolonging the
life of the machine, limiting replacement costs.
Hunting which occurs in most plants, as a direct consequence of poor control, results in the over-
working of HVAC systems, prematurely degrading components and wasting energy. Typically plants
do not have an enthalpy control for its mixing box which would enable free heating and cooling.
Variable load fans running at flat rate, not adjusting output according to demand with use of a VSD
(variable speed drive), run at a constant cost. These systems which are not reconfigured at times of
low occupancy or demand, when temperature, heating and airflow need not run at a continuous
standard, are expensive. Similarly, HVAC systems which use radiators and split air-conditioning units
often run simultaneously, without control in place to prevent this from occurring. Introducing
control measures can result in large energy savings.
Where possible, systems should be automated to optimise control and not left to run in manual sub
optimal operation to overcome some short term issue. For example, often in plants, exhaust fans
have no temperature control, which could automate control of the fan, limiting energy use and
extending life-time of the fan.
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References
Air compression
A guide to ISO 8573.1 – High quality compressed air from generation to application-Domnick Hunter.
Compressed air technical guide – SEI
GPG216-Energy saving in the filtration and drying of compressed air
Refrigeration
Running refrigeration plant efficiently- a cost saving guide for owners (Guide 279)
Good Practice Guide 280 Energy efficient refrigeration technology – the fundamentals
Good Practice Guide 283 Designing energy efficient refrigeration plant
HVAC
SEI, special working group- HVAC spin 1- 2007
HVAC optimisation in pharmaceutical facilities- Biopharma