Building

Operator

Certification –

Level I

A Partnership of the

CUNY Institute for Urban Systems

Building Performance Lab, the

CUNY School of Professional

Studies, and the New York State

Energy Research & Development

Authority

Building Operator Certification Level I (BOCI)

Building Systems: Electrical

CUNY School of Professional Studies

CUNY Building Performance Lab

The BOC

Air Conditioning & Chilled Water

Systems: Lesson 8

Lesson 8 Objectives

• Understand the Vapor Compression Cycle

• Learn about the different systems and the

equipment used to provide cooling in

buildings

– DX

– Heat Pumps

– Chillers

Air Conditioning & Energy Efficiency

• To operate your Air Conditioning at peak efficiency:

-Understand the system

-Understand system components

-Prepare for and provide proper maintenance.

How does an air conditioner cool the air?

• The cooling effect of evaporation is the main process: We often experience

evaporative cooling: for example, water from a spray bottle or perfume sprayed on wrist. As water

is sprayed through the nozzle, the trigger inside pushes the water against the (small) opening,

building up pressure. After the water is squeezed through, it atomizes into a mist/vapor of

thousands of tiny droplets of water. The water has gone from a high pressure (inside the nozzle)

to a relatively low pressure (outside the nozzle). In its newly atomized state, the greater surface

area of the water has an enhanced ability to absorb heat: absorbing heat, it feels cool as it

absorbs heat from whatever it touches.

• Change of State: A refrigerant is gas/vapor at atmospheric pressure. Under high pressure it

will liquify. A refrigerant changes state as it turns from a liquid to vapor. Ice turns to water then to

steam - each is a change of state. Water is 32 dF and ice 32 dF, it takes a lot of energy change

ice into water. When something changes state there is a lot of energy embodied in that process.

To enhance this process refrigerants are said to “boil” at very low temperatures approximately -60

dF, which enhances its ability to remove heat at wide range of temperature.

Notes for Vapor Compression Cycle • Component #1 Compressor. The compressor is the heart of the system and does most of the

mechanical work. The compressors raises the pressure of the refrigerant vapor/gas and moves it

through the system. Now at higher pressure, refrigerant molecules are closer together and they

do not have the same ability to hold heat.

• Component #2 Condenser. The refrigerant enters the condenser as a vapor; as it passes

through heat is removed from it, the molecules slow down and the refrigerant condenses and

turns into a liquid. The condenser acts like a radiator, removing heat from the refrigerant and

transferring it to the atmosphere. In the image, the red dots inside the piping represent vapor; the

solid red represents the liquid refrigerant.

• Component #3 Metering Device or Expansion Valve The dividing point between the high

pressure and low pressure sides of the system. The refrigerant enters at high pressure and

leaves at low pressure in a similar fashion to the spray bottle. The metering device is designed to

maintain a specific rate of flow of refrigerant into the low pressure side of the system.

• Component #4 Evaporator The refrigerant enters the evaporator as an atomized liquid as it

passes through the coil because of the lower pressure it continues to expand and turns into a

vapor which enhances its ability to absorb heat. Because the refrigerant is absorbing heat the coil

becomes cold. This process will cool the air, water, or for that matter, ice cream mix if that's what

is flowing over the evaporator.

Activity: Liquid or Vapor? High or Low Pressure

Is the refrigerant a liquid or vapor here? Is the pressure high or low here?

At the outlet of the compressor: vapor and high pressure

At the outlet of the condenser: liquid and high pressure

At the outlet of the Metering Device: low pressure and an atomized liquid and vapor mixture.

At the outlet of the evaporator: vapor and low pressure

The Vapor-Compression cycle is used in many different configurations and equipment packages, based on direct refrigerant expansion (DX units):

Room unit air conditioners

Split Systems

Packaged Rooftop units

Heat Pumps

V-C Direct Expansion Configurations

DX System Schematic

Heat Pump

Packaged Rooftop Unit & Window Unit

Outside air intake (fixed louver, operable damper)

Return fan

Filter section

Supply fan

Cooling coil

Compressor

Condenser unit

Outside

air

Return

air

Supply

airThis is also a DX Air Conditioning System

Point to Each Part and Ask: What is this?Last Question: Where is the gas-fired heating section? Not Labeled: just to the left of the Cooling Coil

Heat Pump

• Vapor-compression cycle can be reversed

• Used for Heating & Cooling

• A heat pump can work both as an air conditioner (in summer) reversing the cycle (in winter) to heat the building. The reversing valve reverses the direction of refrigerant flow, altering the function of the inside and outside coils.

• Air Source Heat pumps are very popular because of their high efficiency during mild outside air temperatures. They are not as efficient when outdoor temper-atures are extreme: they switch-over to electric resistance heating when the air is just above 32 dF.

AC mode

Heating

Compressor Types: Workhorse of the V-C Cycle

• Positive Displacement Compressors– Reciprocating

– Rotary

– Scroll

– Screw

• Centrifugal Compressor

The Workhorse of the V-C Cycle

Compressor-drives

• Usually electric motor

• Alternative drives

– Steam Turbine

– Gas Turbine

Compressor Drives & Maintenance

Compressor life is dependent on adequate lubrication and maintaining operating pressures within the acceptable range, as recommended by the manufacturer.

Electric Motor

Steam Turbine

Gas Turbine

Refrigerants: Lifeblood of the V-C Cycle

•The properties of a refrigerant is essential to the performance of the V-C cycle, but its composition can have real environmental impacts

•Refrigerants are regulated substances: Chlorine impacts the upper atmosphere and depletes the Ozone layer.

•Building operators should have training and certification in refrigerants.

•Individuals handling refrigerants must be certified through a qualified program to ensure that venting to the atmosphere during service is prevented.

•The Montreal Protocol (1989) is an international Treaty eliminating the production of CFC’s

------------------------------------------------

Freon: A general term used to identify any of a group of partially or completely halogenated

simple hydrocarbons containing fluorine, chlorine or bromine used as refrigerants. R-22 is the most

well-known and used of these refrigerants, currently being phased out.

R-22 Refrigerant: An ozone-depleting, hydro-chloro-fluoro-carbon (HCFC) refrigerant - the

refrigerant of choice for residential heat pump and AC systems for decades. Due to its harmful

environmental effects, production of R-22 and systems that use it are being phased out and will

cease in 2015.

Puron R-410a: An environmentally sound refrigerant not harmful to the earth’s ozone layer

but still a greenhouse has (GHG). Boils at -48dC. Puron refrigerant has been approved by

Environmental Protection Agency as replacement for Freon R-22 and other ozone depleting

refrigerants. Used in both residential and commercial applications.

HFC (R134a) Tetrafluoroethane the new refrigerant, an inert gas. Boils at -15 dF. Used as a

“high-temperature” refrigerant for domestic AC, car AC and for the delivery of pharmaceuticals like

bronchodilators.

Ammonia (NH3) has been used in air conditioning systems before 1930, before Willis Carrier invented his air conditioning system. Anhydrous ammonia boils at -28 dF. Household ammonia is diluted with water and only about a 5 – 10% concentration.

Common Refrigerants

The Absorption Cycle

Cooling generated from a different process; used the same

as the V-C core.

• AC driven by heat, not a motor’s mechanical energy.

• Water and lithium bromide solution refrigerant

• Evaporation, Condensation and re-constitution of lithium

bromide solution driven by heat

• Single-stage and two-stage cycles

– Two stage higher efficiency but needs higher quality

input (e.g. – high pressure steam)

Intro to Larger Cooling Systems

Compressor

Evaporator

Heat

Exchanger

Condenser

Heat

Exchanger

Intro to Larger Cooling Systems• Same V-C core…

• New pieces of Equipment

– The Chiller

– The Heat Exchanger

• Condenser - Heat Rejection

– Cooling tower

– Other Methods

• Evaporator - Chilled Water

Delivery

Same

V-C

Core

Heat

Exchanger

Heat

Exchanger

Cooling

Tower Chilled

Water

Schematic of Typical Chilled Water Systems

• Chillers are designed for large cooling loads

• The Chiller has the 4 Core V-C cycle components, as well the Heat Exchangers in one location

• Shell-and-tube Heat Exchangers HX reject heat & transfer cooling

• Water is pumped from the HXs to cooling towers to reject heat and chilled water for space cooling

• Chillers use centrifugal, reciprocal or rotary screw compressors

• Controls are usually integrated into a building automation system BAS

Chillers and Heat Exchangers HX

V-C Cycle Performance & Diagnostics

• Diagnose using temperature and pressures across the cycle

• Some of the most common defects can be addressed by maintenance:

• Dirty coils

• Blocked air flow

• Low refrigerant charge

Air-Conditioning Performance: There is an expected temperature and pressure at each point in the system for a given refrigerant. Using a table with these specifications, a technician can give the system a check-up and run diagnostics when there is an problem (on next slide)

Refrigerant Pressure-Temperature Table

• Tables and tools read temp and pressure

• Table lists temperature and pressure for each refrigerant

• Used to check refrigerant charge and for diagnostics

• Hand-held instrument reads pressure & temperature with tables built-in

This is the table used for V-C

diagnostics. Each column of

the table is for one

refrigerant. Each

temperature has an

expected corresponding

pressure. This will tell the

technician if you have the

correct refrigerant charge.

Automated diagnostics: Honeywell Service Assistant

Definition: The amount of refrigerant

in a system is measured in pounds of

freon.

This diagnostics tool is attached to

the points of the system and it takes

temperature and pressure readings.

It has the table built in. This makes it

faster and easier to diagnosis

problems with the equipment and

determine if it is operating efficiently.

Refrigerant Charge Effect on the System

This chart shows the effect on efficiency from

under or over charging the equipment.

You can see that an over-charge is as bad for

efficiency as an under-charge.

Each bar shows a

percentage of

systems that have the

wrong charge.

Only 17% have the

correct charge.

If you add up all the

bars = 80% of all AC

systems are under-

charged

Survey by Proctor Engineering

What are some of the common causes of inefficiency when the

system is not properly charged?

Rating Terms for AC Performance

• Coefficient of Performance (COP)

= Refrigeration effect / input - in btu(British Thermal Unit)

1 ton = 12,000 btu 1 kW (1000 Watts) = 3,410 btu 1# LP steam = 1,000 btu

• If it takes one kW produce one ton of cooling; output/input; 1 ton/1kW

• 12,000/3,410 = COP of 3.5

• Energy Efficiency Ratio (EER)

= Btu cooling / input - in watts• If it takes one kW (1000W) produce one ton of cooling,

• 12,000 / 1,000 = EER of 12

• If it takes .5 kW (500W) to produce one ton of cooling

• 12,000 / 500 = EER of 24• If you have an EER of 6 it would take 2kW to produce 1 ton of cooling

• EER of 6 = 12,000/ 2,000W, ie – 2 kW per ton

Notes for Rating Terms for AC Performance

•kW/ton

•1 ton= the amount of power it takes to freeze one ton of ice in 24 hours (or 12,000 Btu/hr or 3517 Watts).

•COP = Q out / Work in. The input is in Btu.

•EER = The Energy Efficiency Ratio (EER) of a particular cooling device is the ratio of output cooling (in Btu/hr) to

input electrical power (in Watts).

•SEER = The Seasonal Energy Efficiency Ratio has the same units of Btu/W·hr, but instead of taken at a single

operating condition, it represents expected overall performance for a typical year's weather in a given location.

•The EER is related to the coefficient of performance (COP) commonly used in thermodynamics: the COP of a

cooling device is unit-less: both the cooling load and the electrical power needed to run the device are measured

using the same units, e.g. watts- a COP is universal and can be used in any system of units. The COP is an

instantaneous measure (a measure of power divided by power), whereas both EER and SEER are averaged over

a duration of time (measures of energy divided by energy). The time duration considered is several hours of

constant conditions for EER, and a full year of typical meteorological and indoor conditions for SEER.

•IPLV is an abbreviation for Integrated Part Load Value. Unlike the EER, however, the IPLV measures the

efficiency of air conditioners under a variety of conditions -- that is, when the unit is operating at part load 25%,

50%, 75% and 100% of capacity and at different temperatures.

_________________________________________________________________________________________

•Formulas for determining energy used by chillers and DX systems

Chillers – The formula for output for chillers (500 is a constant, represents the ability of water to carry heat)

Q = 500 * GPM * ΔT

–DX – The formula for output of DX AC units (1.08 is a constant, represents the ability of air to carry heat)

•Qs=1.08 * CFM * ΔT

Compressor Capacity Control Individual feedback controllers adjust the cooling capacity of each chiller to

maintain a specific chilled water supply temperature.

When cooling load is light, we can reduce compressor work by raising the evaporator temperature (chilled water temperature reset). But what happens at the compressor?

The compressor has to work at part load. What is the best way for it to work at part load? Some ways are more efficient than others.

• Hot Gas By-pass (this is the easiest to do, but the least efficient)

• Unloaders

• Multiple compressor staging

• Inlet Vanes (centrifugal compressors)

• Variable Speed drive control, including variable refrigerant flow

______________________________________

All of the listed items are done to make sure that enough heat gets dumped so that

the chiller can work efficiently. Chillers work best when they have about a 12 d ΔT,

change of temperature or the chilled water between when it enters and leaves the

chiller. All of these help to optimize the system

Condenser - Heat Rejection

Mechanisms

• Air-cooled condenser

– DX Type

• Water-cooled condenser

– Cooling tower

• Evaporative condenser

• Direct-Contact Tower

• Indirect-Contact Tower

– Ground and Water loops

• Used with Heat Pumps

Water cooled condenser

and cooling towerWater cooled condenser

Air cooled condenser Water-cooled Evaporative

condenser cooling tower

Condensers remove the heat from the V-C

cycle. These heat rejection components

augment the condenser and help it dump

the heat more efficiently. Cooling towers

are most commonly used with large

systems

Cooling Towers Reject Condenser Heat

drift

eliminators

condenser water in

cooled water out

wet deck

(fill)

air inlet

heated air out

wet deck

air inlet

closed circuit

to condenser

external water recirc

heated air out

Direct-Contact Tower Indirect-Contact Tower

spray pump

warm

cool

Cooling Tower Operations & Maintenance

Cooling tower maintenance considerations

• Fan speed control and multi-cell sequencing– May be staged, usually two-stage

– Cells may be sequenced

• Blockages – air intakes, drift eliminators, nozzles

• Biological growth, including Legionella

Operating Considerations- Efficiency

Cooling tower temperature reliefIf the required temperature of the cooling tower is difficult to achieve because

of exterior conditions, the tower will use a lot of fan energy. If the chiller is only

at part load and the tower temperature can be raised, this can save energy.

Condenser Heat Recovery

If waste heat from condenser can be diverted from the cooling tower and used

to heat domestic hot water or some other use, this can save energy.

Water-side Economizer (see next slide)

If outside conditions are cool enough the chiller can be

bypassed and the tower can indirectly supply the chilled water.

Legionnaires Disease • Legionnaires disease is an infection of the lungs caused by the Legionella

bacteria, which can be found anywhere untreated water is in contact with air

or soil, such as standing water on rooftops near the fresh air intakes of Air

Handling Units. Legionella bacteria has been found in cooling towers,

humidifiers, and warm water spray or mist, shower heads, fountains and a

variety of other sources.

• Legionnaires disease begins like a cold or the flu and gets worse, damaging

the kidney and lungs.

• Thousands of people are hospitalized in the U.S. each year with

Legionnaires disease: most cases occur in the summer and early fall, but

the disease can occur any time or year.

• People most susceptible to the disease are individuals over 50, especially

those who smoke, abuse alcohol, or have immune system deficiencies.

• Approximately 15% of those who contract Legionnaires disease die.

Water-side Economizer Operation

• Water-side economizer: use the cooling tower alone, bypass the chiller, indirectly supply chilled water

Bypass

chiller

Heat

exchanger

Cool air

Free chilled

water

Chiller Plants and the Chilled Water System

Chilled Water System Configurations

Part load operations – Low delta T

– The amount of cooling required is the load. Systems are designed to handle the maximum

anticipated load. On a mild day, the system will only have part of the load to deal with or “part

load. You might think the system works more efficiently on a mild day, that is not the case.

– Systems are designed to remove a certain amount of heat from the fluid it is circulating. The

amount of heat removed drops the temperature of the fluid. The chiller system we are

looking at is designed for a rise in temperature of 12 dF or a delta T of 12 dF. Different

system configurations are designed to efficiently handle a part load condition or low delta T.

– If the system has a secondary loop, the flow can remain constant in the primary/chiller loop

and the flow in the secondary/building load can be slowed to help more heat dissipate.

These are different ways to design systems and deliver

cooling

The operator must know the Design Intent, the Standard Operating Procedures SOP’s and the reasoning behind them

– Common System Designs – {these are the different system configurations designed to deliver cooling in different ways and to efficiently deal with part load conditions.}

– Constant Volume• the amount of fluid being delivered is always the same, control of cooling to the load

required by the zones is by changing the temperature of the fluid or other controls

– Constant Primary / Variable Secondary & Tertiary• same as above, but the control is done at the secondary systems/loops. The

temperature is varied/reset to meet the load by changing the volume of the flow.

– Variable Primary / Variable Secondary• the volume can be changed at the primary, by taking chillers off line, and by changing

the pump speed at the secondary systems

– Modern Systems• All of the systems above use a constant volume at the chillers.

• Today the volume can be varied by varying the refrigerant flow or varying the speed of the compressor.

• The secondary loop is no longer required regulate the CW temperatures

– Variable Prime Only• the volume can be changed at the primary pumps

Chilled Water Distribution

Chiller Plant Piping Configurations

There are many different

ways to set-up

pumping. Each set of

pumps gives better

control.

– Here are three different

pumping

configurations: the 1st

has one set of pumps -

for a small building.

The 2nd- for a larger

building -has one set of

pumps for the chiller

loop and one set to

circulate the chilled

water to the coils. The

3rd -for multiple

buildings -is similar to

the 2nd but also has a

set of pumps for each

building or wing.

1,000 Ton Plant

2,000 gpm, 12OF dT

Ideal Conditions

Chiller System - Full Load – Ideal ConditionsExiting

temp. 45d

Entering

temp. 57d

No

bypass

2000

GPM

supplied2000

GPM

delivered

1000 Ton

Load

Running

at 500

Tons

Running

at 500

Tons

36

Chiller Performance - Issues

Actual performance is often far from nameplate ratings

Why?

– Low refrigerant charge

– Excess refrigerant charge

– Air entrainment

• air trapped in the water reduces its efficiency

– Oil contamination

– Fouled watersides

• build-up on the heat exchanger from minerals and other impurities in the

water reduces conductivity

– Mechanical or Control Issues

Refrigerant level control

VFD & vortex damper control

– Steam Machines

Turbine Issues, Surface Condenser Vacuum, Wet Steam

1OF change in condenser water CW temp =

1% - 1.5% chiller performance

1OF change in chilled water CHW temp =

.75% - 1% chiller performance

Maintenance and Optimizing

General & Preventive maintenance can significantly improve efficiency!

Clean filters and coils (for good air flow)

Maintain correct refrigerant charge

Thermostat – Check for correct temperatureControls are calibrated

Use time-clocks for end-of-day shut-down

Make sure outside air economizer cycle works properly -have a Functional Test procedure

•Air Distribution System

•Contains: terminal units, air handling units, ducts, dampers, fan, cooling coils.

•Cooling Coil: cools and dehumidifies air.

•The flow of water is controlled to maintain a set-point temperature for air leaving the cooling coil.

After chilled water is produced it needs the distribution system to deliver cooling to the

different zones.

Now the chilled water

can get to work

Chilled Water – Air Distribution System

Review & Reading for Lesson 9

Today’s Class:

• Vapor Compression Cycle & Applications

– Dx, Heat Pumps, Chillers

• Chiller & Chilled Water System Components

– Compressors, Evap/Conds, Cooling Towers

• Chilled Water System Configurations & Issues

– Constant Volume , Constant Primary / Variable Secondary & Tertiary,

Variable Primary

Readings for next class:

• FEMP Section 9.7 (AIR HANDLING SYSTEMS)

• Herzog Chap. 8, pp. 119-136