plant hvac systems

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PLANT HVAC SYSTEMS

DU-109-PP

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PLANT HVAC SYSTEMS

PURPOSE The purpose of the Operations and Maintenance Training Program

is to train Operations and Maintenance Technicians in the operation of the Duke University Plant Heating, Ventilation, and Air Conditioning (HVAC) Systems.

OBJECTIVES Trainees will demonstrate knowledge of

– HVAC System Components– HVAC System Components Operation– HVAC System Configuration– HVAC System Controls and Instrumentation

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PLANT HVAC SYSTEMS

PURPOSE The purpose of the Heating, Ventilation, and Air Conditioning

(HVAC) System is to:– Provide heat and cooling climate control for plant, office/control

room, and electrical room areas of the steam and chiller plants– Maintain Interior Air Quality (IAQ)– Maintain air pressure– Provide emergency exhaust

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PLANT HVAC SYSTEMS

HVAC AIR FUNCTIONS To understand how HVAC works, you need to be familiar with the

six functions of HVAC air.Return Air

– Air inside the building drawn back into the air handlersOutside Air

– Fresh air drawn into the air handlers from outsideSupply Air

– Air blown into the building from the air handlers

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HVAC AIR FUNCTIONSMakeup Air

– Air blown into the building by Makeup Air Unites (MAUs) to maintain air pressure balance when pressure is low

Relief Air– Air exhausted from the building to maintain air pressure balance

when air pressure is highExhaust Air

– Air expelled to remove contaminants from areas where chemicals, hazardous materials, and toxic gases are present

– Air exhausted from the building in case of emergency

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PLANT HVAC SYSTEMS

WHY AIR BALANCE IS IMPORTANTOver Pressure and Under Pressure conditions negatively affect

building efficiency. Over Pressure

– When air pressure inside a building is higher than pressure outside, the conditioned air inside the building is pushed outside.

– High air pressure can require excess energy to condition the air in the building and compensate for energy lost.

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WHY IS AIR BALANCE IMPORTANT?Under Pressure

– When building pressure is lower than pressure outside, the air outside is drawn inside.

– Outside air may come from undesirable sources (trash bins, open doors, cracks, construction, and so forth).

– Unfiltered or unconditioned air can affect the HVAC system’s ability to maintain the desired environment.

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PLANT HVAC SYSTEMS

QUESTIONWhat does IAQ stand for?

– International Air Quality– Industrial Air Quality– Interior Air Quality– In-duct Air Quality

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ANSWER IAQ stands for Interior Air Quality.

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QUESTIONWhat kind of air is blown into building from air handlers?

– Return Air– Outside Air– Makeup Air– Supply Air

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ANSWERSupply Air is recirculated through the air handlers.

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QUESTIONWhat kind of air is added when air pressure is low?

– Return Air– Outside Air– Makeup Air– Supply Air

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ANSWERMakeup Air is blown into a building when air pressure is

low.

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QUESTIONWhat causes Over Pressure?

– Pressure is higher on the lower level than on the mezzanine– Pressure is lower in the building than outside– Pressure is higher in the building than outside– Pressure is lower on the lower level than on the mezzanine

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ANSWEROver Pressure is the condition when pressure inside the

building is higher than outside.

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QUESTIONWhat causes Under Pressure?

– Pressure is higher on the lower level than on the mezzanine– Pressure is lower in the building than outside– Pressure is higher in the building than outside– Pressure is lower on the lower level than on the mezzanine

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ANSWERUnder Pressure is the condition when pressure inside

the building is lower than outside.

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PLANT HVAC SYSTEMS

PLANT HVAC COMPONENTS Air Handler Units (AHUs) Makeup Air Units (MAUs) Fan Coil Units (FCUs) Exhaust fans Supply fans Emergency exhaust fans

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AHU COMPONENTSThe Mixing Box section contains:

– Return Air Damper which connects to the Return Air Duct• The Relief Air Damper also connects to the Return Air Duct

– Outside Air Damper which connects to the duct to the building exterior

RETURN AIRDAMPER

OUTSIDE AIRDAMPER

RELIEF AIRDAMPER

MIXING BOX

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PLANT HVAC SYSTEMS

AHU COMPONENTSThe Filter section contains:

– Access door for filter element replacement– W.C. Meter mounted in door

• Filter is replaced when air pressure reaches maximum resistance

FILTER MIXING BOX

RETURN AIR

RELIEF AIR

OUTSIDE AIR

W.C. METER

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PLANT HVAC SYSTEMS

AHU COMPONENTSThe Cooling Coil section contains:

– In and Out connections for chilled water– Cooling coil heat exchanger

MIXING BOXFILTERCOOLINGCOIL

RETURN AIR

RELIEF AIR

OUTSIDE AIR

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AHU COMPONENTSThe Heating Coil section contains:

– In and Out connections for steam– Heating coil heat exchanger

FILTER

COOLINGCOIL

HEATINGCOIL

MIXING BOX

RETURN AIR

RELIEF AIR

OUTSIDE AIR

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PLANT HVAC SYSTEMS

AHU COMPONENTSThe Fan section contains:

– Fan and motor– Starter Box mounted on

exterior or nearby

FILTERCOOLINGCOIL

HEATINGCOIL

MIXING BOX

RETURN AIR

OUTSIDE AIR

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QUESTIONWhat is accomplished in the AHU mixing box?

– Return air is mixed with relief air– Supply air is mixed with return air– Supply air is mixed with outside air– Return air is mixed with outside air

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ANSWERReturn air is mixed with outside air in the AHU mixing box.

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QUESTIONWhat kind of meter is mounted in the filter section door of an

AHU?– Temperature sensor– Pressure gauge– W.C. meter– Anemometer

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ANSWERA W.C. meter is mounted in the door of the filter section. The

W.C. (Water Column) meter measures resistance through the filter in inches to indicate when the filter needs to be changed.

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QUESTIONWhere is the starter box located for an AHU?

– Exterior of the fan section or nearby– Mixing box– Control Room– AHUs do not need starters

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ANSWERThe starter box is mounted on the fan section of the AHU or

nearby.

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MAU COMPONENTSThe Fan section contains:

– Fan and motor– Outside Air Damper which connects to the duct to the building

exterior

OUTSIDE AIRDAMPER

FAN

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MAU COMPONENTSThe Coil section contains:

– In and Out connections for steam and chilled water

– Heating and cooling coil heat exchangers

COOLINGCOIL

HEATINGCOIL

OUTSIDE AIRDAMPER

FAN

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MAU COMPONENTSThe Filter section contains:

– Filters– Supply Air Damper

COOLINGCOIL

HEATINGCOIL

OUTSIDE AIRDAMPER

FAN

FILTER

SUPPLY AIRDAMPER

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MAU COMPONENTSThe Starter box is located next to the MAU.

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QUESTIONWhat is one way an MAU differs from an AHU?

– The MAU takes in return air and outside air– The MAU takes in relief air only– The MAU takes in outside air only– The MAU takes in return air only

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ANSWERThe MAU takes in outside air only.

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QUESTIONWhat does MAU stand for?

– Main Air Unit– Maximum Air Unit– Mini Air Unit– Makeup Air Unit

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ANSWERMAU stands for Makeup Air Unit.

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QUESTIONWhat is another way an MAU differs from an AHU?

– The MAU has a mixing box– The MAU does not have a mixing box– The MAU has a cooling coil– The AHU has a cooling coil

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ANSWERThe MAU does not have a mixing box.

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FCU COMPONENTSOutside Air DamperElectric Duct Heater

SUPPLY AIR

OUTSIDE AIR DAMPER

RETURN AIR

ELECTRIC DUCT HEATER

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FCU COMPONENTSFilterCooling CoilFan and Motor

COOLING COIL

FAN

FILTER

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QUESTIONWhat does the FCU use to heat supply air?

– Steam – Hot water– Electricity– Friction

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ANSWERThe FCU uses an Electric Duct Heater to heat air in the supply

air duct.

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QUESTIONWhat does FCU stand for?

– Forced Cooling Unit– Facilities Control Unit– Furnace Coil Unit– Fan Coil Unit

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ANSWERFCU stands for Fan Coil Unit.

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PLANT HVAC SYSTEMS CONFIGURATION AND PROCESS FLOWThe flow for Chiller Plant #2 is used as an example.

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CHILLER PLANT #2 AHU-21 SYSTEM Temperature Transmitters on the Return Air Duct, Supply Air Duct,

and Mixing Box of AHU-21 send readings to the Local Controller Digital Control System (DCS).

LOCAL CONTROLLER DCS

RETURN AIR DUCT

SUPPLY AIR DUCTMIXING BOX

AHU-21

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CHILLER PLANT #2 AHU-21 SYSTEM The local DCS controls heating and cooling by modulating the

Cooling Coil chilled water control valve and the steam valve supplying the Heating Coil.

LOCAL CONTROLLER DCS

MIXING BOX

CHILLED WATER CONTROL VALVESTEAM VALVE

COOLING COIL

HEATING COIL

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CHILLER PLANT #2 AHU-21 SYSTEM The Outside Air Damper is set at 2,000 CFM. The Return Air Damper is set at 30,000 CFM.

MIXING BOX OUTSIDE AIR DAMPERD-21F

SUPPLY AIR DAMPERD-21E

AHU-21

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CHILLER PLANT #2 AHU-21 SYSTEM 1,000 CFM exhausted continuously from Chemical Treatment area

by Exhaust Fan EF-23. 350 CFM exhausted continuously from the Break Room, Men’s and

Women’s Restrooms, Shower, and Janitor’s Closet by Exhaust Fan EF-24.

BREAK ROOM

WOMEN’S RESTROOM

MEN’S RESTROOM

JANITOR’S CLOSET

SHOWER

EXHAUST FANEF-24

EXHAUST TO OUTSIDE

LOUVER L-28

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CHILLER PLANT #2 AHU-21 SYSTEM Supply Fans SF-21 and SF-22 run continuously to recirculate air

within the plant.

SUPPLY FAN SF-21

SUPPLY FAN SF-22

EF-24

AHU-21

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CHILLER PLANT #2 AHU-21 SYSTEM Economizer Operation

Based on outside air enthalpy and outside air temperature, when less than 60°F AHU-21 operates in economizer cycle modulating the outside and return air dampers to maintain 60°F supply air temperature.

LOCAL CONTROLLER DCS

RETURN AIR DAMPER

OUTSIDE AIR DAMPER

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CHILLER PLANT #2 AHU-21 SYSTEM Economizer Operation

The chilled water valve to AHU-21 is closed during economizer cycle. In the event of damper failure or mixed air temperature below 35°F, a

freezestat shuts down AHU-21 and sends an alarm.

LOCAL CONTROLLER DCS

FREEZESTAT

CHILLED WATER VALVE

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RELIEF DAMPER RD-21

PRESSURE SENSOR A7AT 0.05” W.C.

AHU-21

PLANT HVAC SYSTEMS

CHILLER PLANT #2 AHU-21 SYSTEM Economizer Operation

Relief Air Damper RD-21 is controlled by differential pressure to maintain a 0.05 inch W.C. positive pressure in the building by modulating the damper.

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CHILLER PLANT #2 AHU-21 SYSTEM Emergency Exhaust

During emergency when refrigerant accumulates above 100 PPM due to leak or rupture, air recirculation dampers to Exhaust Fans EF-21 and EF-22 close and exhaust dampers open forcing the refrigerant from the building.

NORTH EMERGENCY

EXHAUST EF-21

SOUTH EMERGENCY

EXHAUST EF-22

EMERGENCY EXHAUST DAMPER

L-26

EMERGENCY EXHAUST DAMPER

L-25

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CHILLER PLANT #2 AHU-21 SYSTEM Emergency Exhaust

Supply Fans SF-21 and SF-22 shut down.The outside air damper to AHU-21 opens fully and the return air

damper closes.Additional outside air (30,000 CFM) brought into the building from

AHU-21 is exhausted through Positive Relief Damper RD-1.When the refrigerant detectors no longer sense a low refrigeration

concentration of 100 PPM, exhaust air dampers to EF-21 and 22 close and the air recirculation dampers open. SF-21 and 22 then energize and AHU-21 returns to a modulating damper cycle.

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CHILLER PLANT #2 AHU-21 SYSTEM Emergency Exhaust

If an emergency occurs when the supply air temperature is less than 60°F, a temperature sensor opens steam valve TCV-AHU-21B to maintain a supply air temperature of 60°F.

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QUESTIONBased on outside air enthalpy and outside air temperature,

what is the lowest temperature at which AHU-21 will operate before entering the economizer cycle?– 80°F– 40°F

– 60°F

– 72°F

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ANSWERBased on outside air enthalpy and outside air temperature,

when less than 60°F AHU-21 operates in economizer cycle.

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QUESTIONWhen do Supply Fans SF-21 and SF-22 run?

– Only when building pressure is low– Continuously– Only when building pressure is high– Only at night

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ANSWERSupply Fans SF-21 and SF-22 run continuously to recirculate

air within the plant.

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QUESTIONWhere do the temperature transmitters on the ducts and

mixing box on AHU-21 send readings?– Local Controller DCS– AHU-22– Directly to the Control Room– Chiller Plant #1

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ANSWERTemperature Transmitters on the Return Air Duct, Supply Air

Duct, and Mixing Box of AHU-21 send readings to the Local Controller Digital Control System (DCS).

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CHILLER PLANT #2 AHU-22 SYSTEM AHU-22 supplies 10,000 CFM of cooling to the Electric Room. The local DCS modulates the cooling coil chilled water valve in response to

temperature sensors in the supply and return air ducts and mixing box.

LOCAL CONTROLLER DCS

COOLING COIL

COOLING COIL CHILLED WATER VALVE TCV-AHU-

22A

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CHILLER PLANT #2 AHU-22 SYSTEM The Outside Air Damper is set at 9,940 CFM. 60 CFM is exhausted continuously through the Gravity Relief Damper in

the mezzanine floor.

GRAVITY RELIEF DAMPER

RD-22

AHU-22

OUTSIDE AIR DAMPER

L-23

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CHILLER PLANT #2 AHU-22 SYSTEM Economizer Operation

Based on outside air enthalpy and outside air temperature, when less than 60°F AHU-22 operates in economizer cycle modulating the outside and return air dampers to maintain 60°F supply air temperature.

LOCAL CONTROLLER DCS

RETURN AIR DAMPER

OUTSIDE AIR DAMPER

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CHILLER PLANT #2 AHU-22 SYSTEM Economizer Operation

Relief Air Damper RD-21 is controlled by differential pressure to maintain a 0.05 inch W.C. positive pressure in the building by modulating the damper.

RELIEF DAMPER RD-21

PRESSURE SENSOR A7AT 0.05” W.C.

AHU-22

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PLANT HVAC SYSTEMS

CHILLER PLANT #2 AHU-22 SYSTEM Economizer Operation

The chilled water valve to AHU-22 is closed during economizer cycle. In the event of damper failure or mixed air temperature below 35°F, a

freezestat shuts down AHU-22 and sends an alarm.

LOCAL CONTROLLER DCS

FREEZESTAT

CHILLED WATER VALVE

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QUESTIONWhat area is cooled by AHU-22?

– Control Room– Janitor’s closet– Chemical Treatment Area– Electric Room

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ANSWERAHU-22 cools the Electric Room.

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QUESTIONWhere Is the Gravity Relief Damper located?

– Control Room– Mezzanine floor– Electric Room– Operating floor

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ANSWERThe Gravity Relief Damper is in the mezzanine floor.

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QUESTIONWhat volume of cooling air is supplied to the Electric Room by

AHU-22?– 1,250 CFM– 2,000 CFM– 10,000 CFM– 30,000 CFM

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ANSWERAHU-22 supplies 10,000 CFM of cooling to the Electric Room.

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CHILLER PLANT #2 FCU-21 SYSTEM FCU-21 supplies 1,285 CFM of cooling to the Control Room, break

room, office, and vestibule. Cooling is controlled by modulating the cooling coil chilled water

valve in response to a temperature sensor in the Control Room.

LOCAL CONTROLLER DCS

COOLING COIL

COOLING COIL CHILLED WATER VALVE

FCU-21ACONTROL ROOM

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CHILLER PLANT #2 FCU-21 SYSTEM Outside air is set at 175 CFM during cooling with 1,110 CFM of return air. Heating is provided by a 6 KW Electric Duct Heater located in the supply

air duct.

FCU-21

ELECTRIC DUCT HEATER DH-21

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QUESTIONWhere is the Electric Duct Heater located?

– In the return air duct– In the supply air duct– In the relief air duct– In the makeup air duct

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ANSWERThe Electric Duct Heater is located in the supply air duct.

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QUESTIONWhich of the following areas is cooled by FCU-21?

– Operating floor– Chemical treatment area– Electric Room– Control Room

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ANSWERFCU-21 supplies cooling to the Control Room, break room,

office, and vestibule.

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OPERATIONS MONITORING– Operation of the Plant HVAC Systems is monitored through the Control

Room on the top floor of Chilled Water Plant #2.

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PLANT ROUNDS– During an Operator’s routine shift, Rounds are accomplished to

record key information and visually assess HVAC Water System operation.

– Each Plant has a Rounds Sheet to be filled out by the Operator.– Each plant has different requirements for plant rounds.– The information is recorded, not only for the current status, but

also to record system trends.

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EXAMPLE ROUNDS SHEET (front and back)

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HVAC DAILY ROUNDS– Chiller Plants #1 and #2

• Outside temperature• Outside humidity• Outside enthalpy• AHU (On/Off)• Supply Fans (On/Off)• Exhaust Fans (On/Off)

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HVAC DAILY ROUNDS– West and East Campus Steam Plants

• Outside temperature• AHU

• Online/Offline• Space temperature• Supply air temperature

• Supply Fan• Online/Offline

• Space temperature

• Supply air temperature

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PLANT HVAC SYSTEMS

HVAC DAILY ROUNDS– West and East Campus Steam Plants

• Exhaust Fan (not all exhaust fans are checked for all conditions)• Online/Offline

• Space temperature

• Supply air temperature

• Firm alarm OK• Gas alarm OK• E-Stop alarm OK

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TYPICAL PROBLEMS ASSOCIATED WITH PLANT HVAC SYSTEMS– Stuck dampers

• Most likely cause is corrosion or debris– Blocked coils

• Most likely cause is corrosion, faulty filters– Malfunctioning control components

• Components damaged or out of calibration– Clogged condensate drains

• Most likely cause is debris or damage to pipes

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QUESTIONWhere does Operations Monitoring take place?

– Control Room in each steam plant– Control Room in West Campus Steam Plant– Control Room in Chilled Water Plant #2– Control Room in Chilled Water Plant #1

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ANSWEROperations Monitoring takes place In the Control Room in

Chilled Water Plant #2.

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QUESTIONWhich air pressure condition in a building is preferable?

– Under Pressure– Over Pressure– Balanced– Air pressure is not a concern of HVAC

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ANSWEROperations Monitoring takes place In the Control Room in

Chilled Water Plant #2.