Humidity Control

HVAC tab in model data - Simple HVAC

When using the Ideal loads Mechanical ventilation method you have the option to control humidity by checking the Humidification and/or Dehumidification checkboxes on the HVAC tab.

Note: In real HVAC systems humidity control can require considerable energy consumption to achieve. If you require an accurate assessment of this energy then you should consider using Detailed HVAC humidity control which allows you to track energy flows in more detail.

Humidification

Humidification control type

When humidification is selected there are 2 further options:

• 1-Constant supply humidity ratio means that during heating the supply air will always be at the Maximum heating supply humidity ratio.
• 2-Humidistat means that the humidity in the zone is controlled using the Humidification setpoint defined on the Activity tab. The ideal loads system will attempt to meet the humidistat request, i.e. it will humidify according to the setpoint.

Dehumidification

Dehumidification control type

When dehumidification is selected there are 3 further options:

• 1-Constant supply humidity ratio means that during cooling the supply air will always be at the Minimum cooling supply humidity ratio.
• 2-Humidistat means that the humidity in the zone is controlled using the Dehumidification setpoint defined on the Activity tab. The ideal loads system will attempt to meet the humidistat request, i.e. it will dehumidify according to the setpoint.
• 3-Constant sensible heat ratio. means that the ideal loads system will be controlled to meet the sensible cooling load, and the latent cooling rate will be computed using the constant sensible heat ratio (SHR) defined below.

For 3-Constant sensible heat ratio and 2-Humidistat options, if the mixed air humidity ratio is less than the target humidity ratio, then the mixed air humidity ratio will be used. For all options, the supply air humidity ratio will never be allowed to exceed saturation at the supply dry bulb temperature. The selected dehumidification control type is always applied when the unit is in cooling mode. If the unit is in deadband mode (not actively heating the supply air) control type Humidistat will be active. If the unit is in heating mode, control type Humidistat will be active if the Humidification Control Type field below is set to Humidistat or None. This allows the ideal loads system to heat and dehumidify at the same time.

Cooling sensible heat ratio

When the Dehumidification control type above is set to 3-Constant sensible heat ratio the ideal loads system will be controlled to meet the sensible cooling load, and the latent cooling rate will be computed using the value of Cooling Sensible Heat Ratio (SHR), where SHR = Sensible Cooling divided by Total Cooling (sensible plus latent). The default is 0.7.

Humidity Control Linkage with Heating and Cooling Schedules

In Simple HVAC, the timing of humidification control is the same as that for heating. So at times when heating is available (in setpoint or setback mode) humidification control is also available. Likewise the timing of dehumidification control is the same as that for cooling. So at times when cooling is available (in setpoint or setback mode) dehumidification control is also available.