AHU Air Handling Unit Fundamentals - · PDF fileObjectives • Review primary components of...
Transcript of AHU Air Handling Unit Fundamentals - · PDF fileObjectives • Review primary components of...
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AHUAir Handling Unit
Fundamentals
j.ilangumaran
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Objectives
• Review primary components of an AHU
• Understand the basic progression and advantages of advanced AHU control
• Understand the basic control sequences
• Review key operating concepts• Review key operating concepts
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HVAC System in a Building
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HVAC Air Systems
• HVAC air systems are made up of:– AHU - Air handling units
– Dampers
– Coils and Valves
– Fans
– Distribution ducts and terminal boxes
– Pumps and Plumbing– Pumps and Plumbing
– Control devices and control loops
– Unitary equipment: fan coils, perimeter radiation, unit ventilators, unit heaters, etc.
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AHU - Components & Terminology
RAEA Return From Space
OA
FilterCooling Coil
Heating
DA
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AHU componentsHeating coil
& valveCooling coil
& valve
Mixed airdampers section
Mixed Airsensor
Discharge airsensor
Discharge airDuct
Supply fan
Return air DuctReturn Air
sensor
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AHU components
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Types of Air HandlersAir Handling Units – Mixed Air
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Types of Air HandlersAir Handling Units – Mixed Air
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A “Single Duct” AHU variation• The exhaust air damper is not in this air
handler; the building air is exhausted elsewhere, but the basic mixed air and other functions are unchanged.
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Air Handler Components
The fan section with access door open.
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Air Handler Components
The filter section.Notice the cross stacking of
the filters to increase surface area.
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Air Handler Components
Temperature Sensor:
• Temperature sensors are used for measurement of temperatur of a Room, Air Duct, Hot /Cold Water, Outside Air etc.
• Models are available with PT1000, NTC20K, BALCO500 sensing elements.
LF20 : AIR DUCT TEMP. SENSOR (NTC 20k)
elements.T7412 : ROOM TEMP. SENSOR (PT1000/NTC 20k)
T7413A : IMMERSION TEMP. SENSOR (PT1000)
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Air Handler Components
Relative Humidity Sensor:
• Relative Humidity sensors are used for measurement of Relative humidity of a Room, Air Duct, Outside Air etc.
• Sensor Type : Capacitance
• Combined Relative Humidity and Temperature Sensors are available H7015 : DUCT RELATIVE HUMIDITY SENSORTemperature Sensors are available with PT1000, NTC20K, BALCO500 sensing elements.
H7015 : DUCT RELATIVE HUMIDITY SENSOR
H7012 : ROOM RELATIVE HUMIDITY SENSOR
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Air Handler Components
Differential Pressure Switch:
• Differential Pressure switches are used for monitoring of Filter, Fan, Pump, Fire Damper, Water Flow, Air Flow Status of air handling systems.
DPS1000 : AIR DIFFERENTIAL PRESSURE SWITCHDPS1000 : AIR DIFFERENTIAL PRESSURE SWITCH
TDIAP SERIS : AIR FLOW SWITCH
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Air Handler Components
Differential Pressure Sensors/Transmitter:
• Used for measuring diff. Pressure, positive pressure and vacuum.
DPT1000 : AIR DIFF. PRESSURE TRANSMITTERDPT1000 : AIR DIFF. PRESSURE TRANSMITTER
ST 3000 Pressure Transmitter
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Air Handler Components
Coils :Heating CoilsCooling Coils
Coil Construction
• Copper with Aluminium fins,
• 13 Fins /inch
• Number of Rows, I.e 4/6/8 depending on the latent heat load & Bypass Factor.
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Air Handler Components
The coil section of a AHU.
Note:There may be a widevariety of actual configurations
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Air Handler ComponentsValves & Actuators
Valve Types
� 2 Way or 3 Way
Actuator Types
� Motorised
� Magnetic
� Pneumatic
Operation
� On - Off,Floating, Modulating
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Air Handler ComponentsHeat Recovery :
A heat-recovery system is often used in buildings where a significant quantity of outdoor air is used. Several types of heat-recovery systems are available Runaround systems
� Heat pumps
� Runaround systems
� Rotary heat exchangers
� Heat pipes.
Heat Wheel
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Air Handler ComponentsHeat Recovery : Heat Wheel
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Typical AHU Damper Sequences
• Manually adjustable quantity of outdoor air:
• Similar to “Fixed”, but with a user adjustment device for adjusting damper setting from 0% to damper setting from 0% to 100% outdoor air.
• No automatic control.
• W/WO exhaust or return air ducts.
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Typical AHU Damper Sequences• Mixed Air Dampers:
• Mixes OA and RA to maintain a mixed air setpoint via direct acting controller.
• Modulates 0% to 100%.
• Provides ventilation for IAQ.
• Provides free cooling.
• Provides proper temperature for • Provides proper temperature for H/C coil operation.
• OA and EA dampers close via relay with fan off.
• RA damper opens via relay with fan off.
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Typical AHU Damper Sequences
• Example of operation:– Setpoint = 55 deg.
– MAT = 55 deg.
• Proportional Controller output = 50%50%
• Fan = On
• Dampers:– OA = 50%
– RA = 50%
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Typical AHU Damper Sequences
• Example of operation on temperature rise:– Setpoint = 55 deg.
– MAT = 57.5 deg.
• Controller output = 75%
• Fan = On
• Dampers:• Dampers:– OA = 75%
– RA = 25%
• More outdoor air!
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Typical AHU Damper Sequences
• Example of operation on temperature fall:– Setpoint = 55 deg.
– MAT = 50 deg.
– Controller output = 0%
– Fan = On
• Dampers:• Dampers:– OA = 0%
– RA = 100%
• No outdoor air; no fresh air in the building!
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Mixed Air Dampers with a Minimum Position Setting
• Maintains a “minimum” outdoor damper position via a minimum adjustment device when building is occupied. (fan on)
• Meets IAQ code requirements.requirements.
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Typical AHU Damper Sequences - Mixed Air
75%75%75%75%
• Example of operation on temperature fall:
– Setpoint = 55 deg.
– MAT = 50 deg.
– Controller output = 0%
• Min. Position Setpoint = 25%
• Fan = On
• Dampers:
25%25%25%25%
25%25%25%25%
– OA = 25%– RA = 75%
Even though the Mixed Air controller is sendinga control signal to completely close OA dampers,the minimum position controller or logic is maintaining setpoint. Fresh air is maintained in the building!
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50%50%50%50%
Typical AHU Damper Sequences
.
• Economizer Overrideof Outdoor Air:
• Requires an additional reverse acting controller in the outdoor air.
• Brings OA damper to minimum when outdoor air temperature is high.
50%50%50%50%
temperature is high.
• Provides for economical operation of the cooling coil.
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Typical AHU Damper Sequences
50%50%50%50%
• Example of economizer operation withlowoutdoor temp.– MA StPt = 55 deg
– MA temp = 55 deg
– MA controller out = 50%
– OA StPt = 70 deg
– OA temp = 67 deg50%50%50%50%
– OA temp = 67 deg
– OA controller out = 100%
• Min. Pos. StPt = 25%• OA damper = 50%:
• MA controller is in control of
• the OA damper due to OAT acceptable for efficient use of mechanical cooling.
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Typical AHU Damper Sequences
75%75%75%75%
• Economizer Override with outdoor temperature high:– MA StPt = 55 deg
– MA temp = 55 deg
– MA controller out = 50%
– OA StPt = 70 deg
– OA temp = 74 deg
– OA controller out = 0%
– Min. Pos. StPt = 25%25%25%25%25%
– Min. Pos. StPt = 25%
• OA damper = 25%:
OA controller is in control of the OA damper due to OAT unacceptable for efficient mechanical cooling.
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Typical AHU Damper Sequences
• Enthalpy controlled override of Mixed Air control:
• Total heat (enthalpy) of outdoor airis compared to total heat of return airto total heat of return airto decide which is more economical for efficient cooling coil operation.
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Typical AHU Damper Sequences
• Example of operation with OA enthalpy lower:
• MA StPt = 55 deg– MA temp = 55 deg
– MA controller out = 50%
• OA humidity = 35%
• OA temp = 60 deg
• RA humidity = 39%
• RA temp = 71 deg
• Outdoor air enthalpy is lowerthan return air enthalpy, so relay passes MA controller signal.
• Min. Pos. StPt = 25%
• OA damper = 50%
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100%Outside Air AHU :
Practical Example
OA AHU Seq
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Mixed Air AHU :
Practical Example
Seq of Oper AHU
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Chiller Plant
Plant
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Chiller Plant systems are made up of:– Chiller/Condenser Unit– Chilled Water Pumps– Condenser Water Pumps– Cooling Towers – Makeup Water Tank– A/C Expansion Water Tank
Chiller Plant
– A/C Expansion Water Tank
TRANE Chiller
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Chiller Plant
Chiller Plant Concept :
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Typical Cooling Tower
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Typical Chiller Plant
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Example Chiller Plant
Seq of Oper CHILLER
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Example Chiller Plant (THL New Building)
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Example Chiller Plant
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Boiler Plant systems are made up of:– Boiler Units– Primary Pumps– Secondary Pumps
Boiler Plant
Typical Firetube Boiler
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Boiler Plant
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Boiler Plant Example
Seq of Oper BOILER
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Boiler Plant Example
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Boiler Plant Example
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