Water Source Heat Pumps
The water-to-air heat pump is a compound component consisting of a fan, water-to-air cooling and heating coils, and a supplemental heating coil. The heat pump switches between cooling and heating depending on the zone’s demand. The load side of the water-to-air heat pump is on the airside of the equipment. The source side (water) of the heat pump is connected to a condenser loop with a heat exchanger (ground heat exchanger or other type) or a plant loop with a heating source such as a boiler and a cooling source such as a chiller or cooling tower. The load side and control options for the Water Source Heat Pumps are configured in this section of the library. The associated coils and condenser options are defined in separate sections of the equipment library.
Note: Standard TRACE library members cannot be modified or deleted but they can be copied and edited.
Nominal Cooling Capacity
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Default: Auto Size box checked
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Typical Range: 6 to 25 Tons
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Min Max: 0 to 1,000,000,000,000,000
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Units: % Clg Capacity; W; kW; W/m2; W/ft2; tons; Btuh; MBh; tons/ft2; Btuh/ft2
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This checkbox indicates whether or not the capacity used for the selected cooling coil will be auto sized by the program or referenced from the user defined input.
Nominal Heating Capacity
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Default: Auto Size box checked
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Typical Range: 7 to 19 Mbh
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Min Max: 0 to 1,000,000,000,000,000
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Units: % Htg Capacity; W; kW; W/m2; W/ft2; tons; Btuh; MBh; tons/ft2; Btuh/ft2
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This checkbox indicates whether or not the capacity used for the selected heating coil will be auto sized by the program or referenced from the user defined input.
Supply Fan
Fan Placement
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Default: Blow Through
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Typical Range: N/A
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Min Max: N/A
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Units: N/A
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This input indicates whether or not the supply fan is placed upstream or downstream of the heat pump coil. Two options are available: Blow Through or Draw Through.
Cycling Mode
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Default: Cycling Fan
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Typical Range: N/A
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Min Max: N/A
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Units: N/A
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This input indicates whether or not the supply fan for the water source heat pump is continually operating or if it is allowed to cycle. Two options are available: Cycling Fan or Continuous Fan.
If the Cycling Fan option is selected, then the supply fan for the water source heat pump will cycle on and off in operation in step with the compressor operation. If the Continuous Fan option is selected, the supply fan for the water source heat pump will continue to operate whether or not there is a cooling or heating load that needs to be met.
Supply Fan Type
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Default: Constant Volume
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Typical Range: N/A
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Min Max: N/A
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Units: N/A
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This is the type of supply fan that is associated with the library member. Two options are available: Constant or Variable Volume.
Supply Air Fan
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Default: Direct Drive Plenum Fan
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Typical Range: N/A
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Min Max: N/A
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Units: N/A
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This input selection refers to the name of the fan library member that is used as a sub-component of this equipment.
Fan Full Load Energy Rate
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Default: 0.0002 kW/(cfm); Auto Size box is unchecked
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Typical Range: 37 W – 5.5 kW
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Min Max: 0 – 1,000,000,000,000,000 (this field cannot be left blank)
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Units: W; kW; W/(m3/sec); W/(m3/sec)-Pa; W/(cfm); W/(L/sec); W/(L/sec)-Pa; kW/(cfm); kW/(L/sec); kW/(cfm)-in H2O; kW/(L/sec)-Pa; W/(cfm)-in H2O; bhp
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This checkbox indicates whether or not the full load energy rate used for the selected fan will be auto sized by the program or referenced from the user defined input.
Pressure Rise
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Default: 4 inches H2O
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Typical Range: 0.25 to 3 inches H2O
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Min Max: 0 – 1,000,000,000,000,000 (this field cannot be left blank)
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Units: in H2O; lb/ft2; psig; Pa; kPa; mm Hg; mm H2O; bar; in Hg; atm; mm CE; m CE; m H2O; mbar
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The value will be populated by default based on the fan library member selected. You can override this value and the units of measure.
Dead Band Airflow
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Default: Auto Size box checked
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Typical Range: N/A
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Min Max: 0 – 1,000,000,000,000,000 (this field cannot be left blank)
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Units: m3/sec; cfm; cfm/ft2; (m3/s)/m2; % Clg Airflow; % Htg Airflow; L/s; m3/hr; (m3/hr)/m2
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This numeric field defines the supply air flow rate leaving the Water Source Heat Pump when neither cooling nor heating is required (i.e. the cooling and heating coils are not operating). This field is only used when the Water Source Heat Pump supply air fan operating mode schedule specifies continuous fan operation.
If the heat pump’s supply air fan operating mode schedule specifies continuous fan operation and this value is set to zero, then the model assumes that the supply air flow rate when no cooling/heating is needed is equal to the supply air flow rate when the cooling or heating coil was last operating (for cooling operation or heating operation).
Supply Fan Delay Time
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Default: 60 s
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Typical Range: N/A
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Min Max: 0 – 999,999,999,999,999 (this field cannot be left blank)
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Units: s (seconds)
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This numeric field contains the time delay in seconds for the heat pump supply fan to shut off after the compressor cycles off. This value can be obtained from the manufacturer or the equipment specific catalog data. Suggested value is 60 seconds. This value is ignored when the selected fan cycling mode is continuous fan.
Heat Pump
Heat Pump
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Default: 10.5 to 17.5 kW WSHP Comp, Evap, Cond
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Typical Range: N/A
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Min Max: N/A
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Units: N/A
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This field allows you to select the Self Contained and WSHP - WSHP Components library member that will be used as a subcomponent of this Zone Forced Air - Water Source Heat Pump equipment.
Cooling Design Airflow
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Default: Auto Size box checked
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Typical Range: 300 to 9000 cfm
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Min Max: 0 – 1,000,000,000,000,000 (this field cannot be left blank)
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Units: m3/s; cfm; cfm/ft2 (Floor); (m3/s)/m2 (Floor); % Clg Airflow; cfm/ton; (m3/s)/(kW of Cooling Capacity); (m3/hr)/(kW of Cooling Capacity); (m3/s)/(W of Cooling Capacity); m3/hr ; m3/hr/m2 (Floor); L/s; (L/s)/(kW of Cooling Capacity)
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This input refers to the design cooling airflow value associated with the Water Source Heat Pumps library member.
Heating Design Airflow
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Default: Auto Size box checked
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Typical Range: 300 to 9000 cfm
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Min Max: 0 – 1,000,000,000,000,000 (this field cannot be left blank)
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Units: cm3/s; m3/s; cfm; cfm/ft2 (Floor); (m3/s)/m2 (Floor); % Htg Airflow; cfm/ton; (m3/s)/(kW); (m3/hr)/(kW); (m3/s)/(W); m3/hr ; m3/hr/m2 (Floor)
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This input refers to the design heating airflow value associated with the Water Source Heat Pumps library member. This input can be used to scale the size of the coil as well.
Time Constant
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Default: 60 s
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Typical Range: N/A
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Min Max: N/A
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Units: s (seconds)
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This numeric field contains the time constant for the cooling coil’s capacity to reach steady state after start up. Suggested values are shown below (Henderson et al. 1999):
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Heat Pump Condition
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Recommended Values
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Typical
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60
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Good
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60
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Poor
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60
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Cycle Rate
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Default: 2.5 cycles/hr
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Typical Range: N/A
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Min Max: 0 – 999,999,999,999,999 (this field cannot be left blank)
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Units: cycles/hr; cycles/s
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This numeric field contains the maximum on/off cycling rate for the compressor, which occurs at 50% run time fractions. Suggested values are shown below (Henderson et al. 1999):
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Heat Pump Condition
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Recommended Values
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Typical
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2.5
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Good
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2.5
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Poor
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3.0
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Supplemental Heating Coil
Supplemental Heating Coil Type
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Default: none
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Typical Range: N/A
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Min Max: N/A
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Units: N/A
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This selection specifies the type of supplemental heating coil associated with this Water Source Heat Pump equipment. There are four coil types to choose from: Electric, Gas, Water, and Steam.
The hot water and steam heating coil options will require you to specify the plant loop that supports it. This assignment is handled by the user in the Assign Systems section of the program. This coil resides on the demand side of the plant loop. The hot water flow modulation through the supplemental heating coil does not require additional controller specification or user input. The parent object itself provides the “controller” function of modulating water flow.