Unitary Humidity Control

HVAC tab in model data - Compact HVAC

When using Unitary Compact HVAC you can control humidity in zones by including separate humidification and/or dehumidification equipment and controls. Both humidification and dehumidification require settings at building level for Unitary multizone systems or at zone level for Single zone unitary systems (of course in the latter case defaults can be set at building level).

Humidification

To include humidification check the Humidification checkbox and make further settings. The humidifier is electric powered and the data required is: availability schedule, rated capacity and water supply rate. The humidification setpoint is defined on the Activity tab.

For Unitary multizone systems you must also define the humidification control zone.

Humidification availability schedule

Select the schedule that defines the availability of humidification. The schedule values denote whether the humidifier can run during a given time period. A schedule value of 1.0 indicates that the humidifier can be on during a given time period. A value of zero denotes that the humidifier cannot be used during that time period.

Humidifier Rated Capacity

Enter the rated moisture output rate in m3/s or CFM. The humidifier does not currently autosize, so the default is very large to allow for adequate capacity. The default is 0.000001 m3/s.

De-Humidification

To include dehumidification check the Dehumidification checkbox and make further settings. The dehumidification setpoint is defined on the Activity tab.

For Unitary multizone systems you must also define the humidification control zone.

Control type

For unitary systems, there are two dehumidification control type options available:

• 1-Cool-Reheat Heating Coil cools beyond the dry-bulb setpoint as required to meet the humidity setpoint if the system is capable of doing so. Reheat is provided as required by the heating coil. In the simulation, two instances of the heating coil are modelled, one for heating, and one for reheat. The two coil objects represent the same physical coil and never operate simultaneously.
  
  
• 2-Cool-Reheat Desuperheater cools beyond the dry-bulb setpoint as required to meet the humidity setpoint if the system is capable of doing so. Reheat is provided by a desuperheater coil.

For Unitary multizone systems you must also define the dehumidification control zone.

Note that dehumidification will result in simultaneous heating and cooling to achieve reduced humidity of the zone air.

Note: EnergyPlus autosizing does not yet account for dehumidification so in many cases you will have to increase the Compact HVAC sizing factor above the default of 1.2 to a value up to 10 to obtain adequate cooling coil sizes, depending on latent loads and the dehumidification setpoint.

Note: If you use one of the reheat dehumidifiers you must have reheat available to heat during times when dehumidification is required. In practice this normally means having reheat available all year.

Note: You may need to use shorter timesteps for accurate humidity control. We recommend 10 per hour.