Stencil: Zone HVAC Stencil: Grp-VAV Vrble Spd Fan w/reheat
Type: Air Terminal
Sub Type: VAV_Reheat_VariableSpeedFan
Note: Requires a connection to a hot water loop
EnergyPlus Object - AirTerminal:SingleDuct:VAV:Reheat:VariableSpeedFan
The VAV terminal unit with variable-speed fan and reheat coil is an air system terminal unit consisting of a variable speed fan in series with a heating coil. These units are usually employed in under floor air distribution (UFAD) systems where the air is supplied at low static pressure through an under floor plenum. The fan is used to control the flow of conditioned air that enters the space. When the fan is off the plenum pressure drives the minimum air flow through the terminal unit. At maximum cooling the fan runs at its maximum speed. At full heating the fan runs at its heating maximum – usually less than the cooling maximum flow rate. Thus this unit has two separate maximum flow rates – one for heating and one for cooling.
For cooling, control is maintained simply by varying the fan speed. For heating, the unit first tries to meet the heating load by varying the heating coil output while keeping the air flow at minimum (fan off). If this is not adequate the fan turns on and operates in variable flow mode up to the heating maximum flow rate.
This unit is modeled in EnergyPlus as a compound component – a variable speed fan and a heating coil in series in the air stream. The unit is blow through – the fan is upstream of the heating coil.
The table shows the properties that are displayed when the component is selected while in diagram mode. The second column shows the selection options available that are dictated by EnergyPlus or it shows the source for the library entries that are displayed in the drop down list.
| Property Name | Value Sources/Options |
|
Name |
Simergy provides unique name (editable) |
|
Availability Schedule Name |
|
|
Maximum Cooling Air Flow Rate |
0-Min, Autosize |
|
Maximum Heating Air Flow Rate |
0-Min, Autosize |
|
Zone Minimum Air Flow Fraction |
0-1 |
|
Fan Name |
Libraries/Plant and Equip/Fans & Pumps/Supply Fan |
|
Heating Coil Name |
|
|
Maximum Hot Water or Steam Flow Rate |
0, Autosize |
|
Minimum Hot Water or Steam Flow Rate |
0-Min; 0 default |
|
Heating Convergence Tolerance |
0-Min; 0.001 Default |
Simergy automatically defines a unique name for each component. This can be changed by the user if desired.
The name of the schedule (ref: Schedule) that denotes whether the unit can run during a given hour. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during the hour. A value less than or equal to 0 (usually 0 is used) denotes that the unit must be off for the hour.
The maximum volumetric air flow rate through the unit in cubic meters per second when the thermostat is calling for cooling. Normally this is the same as the unit’s fan maximum volumetric flow rate.
The maximum volumetric air flow rate through the unit in cubic meters per second when the thermostat is calling for heating.
The minimum flow rate to the zone while the system is operating, specified as a fraction of the maximum air flow rate. For this unit this is the flow rate when the fan is off.
The type of fan in the terminal unit. At this time the only type of fan allowed is Fan:VariableVolume.
The name of the heating coil object contained in this terminal unit.
The maximum hot water volumetric flow rate in m3/sec through the unit’s heating coil. If the heating coil is gas or electric this field should be blank.
The minimum hot water volumetric flow rate in m3/sec through the unit’s heating coil. If the heating coil is gas or electric this field should be blank.
The name of the HVAC system node which regulates the flow of hot water through the unit. This should be the same node as the water inlet node of the unit’s hot water coil. For gas or electric heating coils, this input should be blank.
The control tolerance for the unit heating output. The unit is controlled by matching the unit output to the zone demand. For units with water coils, the model must be numerically inverted to obtain a specified output. The convergence tolerance is the error tolerance used to terminate the numerical inversion procedure. Basically this is the fraction:
For gas or electric heating coils, this input should be left blank. The default is 0.001.
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