VRF Indoor Unit Heat Pumps
VRF systems are air-conditioning systems that vary their refrigerant flow rate using variable speed compressor(s) in the outdoor unit, and the electronic expansion valves (EEVs) located in each indoor unit. The system meets the space cooling load requirements by maintaining the zone air temperature at the thermostat cooling set point. The ability to control the refrigerant mass flow rate according to the cooling load enables the use of as many as 60 or more indoor units with differing capacities in conjunction with one single outdoor unit. The system curve based model is used to describe the VRF system performance in this program.
These VRF Indoor Unit Heat Pump library members represent the indoor “cassettes” serving the zone they are applied to. They are capable of both cooling and heating operation. To properly complete the overall system configuration, they will need to be paired with an outdoor VRF condensing unit library member that is capable of either heat pump operation or heat recovery operation.
Note: The inputs for this library member describe a single cassette. Each zone assigned to the configured VRF system will be supplied with one of these cassettes.
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: 7 to 95Mbh
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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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 cassette coil in cooling operation 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 95 Mbh
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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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 cassette coil in heating operation will be auto sized by the program or referenced from the user defined input.
Misc. Power during Off Cycle
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Default: 0 W
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Typical Range: N/A
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: hp; W; kW
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This field defines the parasitic electrical energy use of the zone cassette when the coil is not operating.
Misc. Power during On Cycle
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Default: 0 W
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Typical Range: N/A
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: hp; W; kW
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This field defines the parasitic electrical energy use of the zone cassette when the coil is operating.
Supply Fan
Supply 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 selectable input field defines how the supply fan is arranged. There are two choices, Blow Through or Draw Through. The Blow Through choice indicates that the fan is located upstream of the coils. The Draw Through choice indicates that the fan is located downstream of the coils
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 field is used to determine how the unit fan is to be controlled. There are two possible choices:
1. Cycling Fan: The fan cycles on and off with the coil for either cooling or heating operation.
2. Continuous Fan: The fan speed is held constant to produce a fixed air flow rate whenever the unit is scheduled on.
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 in this object.
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 to 1 kW
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Min Max: 0 to 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 1 inches H2O
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: inches 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 to 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 VRF Indoor Heat Pump cassette when neither cooling nor heating is required (i.e. the cooling and heating coils are not operating). This field is only used when the cassette supply air fan operating mode schedule specifies continuous fan operation. If the cassette’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).
Unitary Cooling
Rated Sensible Heat Ratio
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Default: 0.7 (Auto Size box unchecked)
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Typical Range: 0 to 1
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: N/A
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This field is used to capture manufacturer specific data for the equipment regarding the rated sensible heat ratio that the unit has been designed for.
Unitary Cooling Design Airflow
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Default: Auto Size box checked
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Typical Range: 100 to 200 cfm
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Min Max: 0 to 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 VRF Indoor Unit Heat Pumps library member.
Unitary Heating
Unitary Heating Design Airflow
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Default: Auto Size box checked
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Typical Range: 100 to 2000 cfm
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Min Max: 0 to 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 VRF Indoor Unit Heat Pumps library member.