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:
1-None - no economizer operation will be simulated.
2-Return air temperature - whenever the outside air temperature is greater than the Economiser upper temperature limit or less than the Economiser lower temperature limit the outside air flow rate is set to the minimum.
3-Return air enthalpy - when the outside air enthalpy is greater than the Economiser upper enthalpy limit or less than the Economiser lower enthalpy limit the outside air flow rate is set to the minimum.
4-Return air temperature and enthalpy - either temperature or enthalpy limit is used.
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).
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.
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.
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.
Unitary systems can also have lockout control:
1-No lockout - default option.
2-Lockout with heating - when the packaged unit is in heating mode, the economiser is locked out – i.e., the economiser dampers are closed and there is minimum outside air flow.
3-Lockout with compressor - in addition to locking out the economizer when the unit is in heating mode the economizer is locked out when the DX unit compressor is on. In other words, when the DX coil is off, the economizer must meet the entire cooling load – it isn’t allowed to operate in conjunction with the DX cooling coil. Similarly, when the DX coil is operating, the economizer is not allowed to operate. The Lockout with compressor option is sometimes called a 'non-integrated economizer'.