VAV & CAV Humidity Control

HVAC tab in model data - Compact HVAC

With VAV and CAV Compact HVAC systems, 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.

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 each zone.

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.

Humidification control zone

The control zone to be used to control humidification.

De-Humidification

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

You must also define the de-humidification control zone.

Control type

For VAV and CAV only one option is available:

• 1-Cool Reheat 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 terminal unit reheat coils if available.

Dehumidification control zone

The control zone to be used to control dehumidification.

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.