Economisers

HVAC tab in model data under Mechanical Ventilation header

 

HVAC Economisers are useful for facilities which require some cooling even when the outdoor temperature is lower than the indoor temperature. An economizer is a damper opening that draws up to 100% outside air when the outside air is cooler than the temperature inside the building, thereby providing free cooling. Economisers can reduce energy use by 15 percent or more, and are often required by energy codes for larger air conditioning units.

 

Economisers can be modelled when using Compact HVAC but not Simple HVAC.

 

See under Heat recovery for information about how economisers interact with heat recovery.

 

Note: economiser operation applies to the overall HVAC system and so for Unitary multizone and VAV systems its' data is set at building level. For Unitary single zone systems the data is used at zone level.

 

There are four options:

 

 

The economiser setpoints below are limits on temperature and enthalpy of the outside air. When the outside air conditions go beyond these limits the EnergyPlus economiser switches to 'minimum outside air mode' (i.e. the outside air damper is closed to its minimum position).

Economiser upper temperature limit

Enter the outside air temperature high limit for economizer operation. If the outside air temperature is above this limit, the outside air flow rate will be set to the minimum and heat recovery will be enabled if available. Zero in this field means that there is no outside air temperature high limit control.

Economiser lower temperature limit

Enter the outside air temperature low limit for economizer operation. If the outside air temperature is below this limit, the outside air flow rate will be set to the minimum and heat recovery will be enabled if available. Zero in this field means that there is no outside air temperature low limit control.

Economiser upper enthalpy limit

Enter the outside air upper enthalpy limit for economizer operation. If the outside air enthalpy is above this value, the outside air flow rate will be set to the minimum and heat recovery will be enabled if available. Zero in this field means that there is no outside air enthalpy limit control.

Lockout

Unitary systems can also have lockout control: