Economizer Enthalpy Changeover
Differential-enthalpy: enable free cooling when outdoor enthalpy < return (accounts for humidity); fixed-dry-bulb.
Example
You enter
- Changeover type differential_enthalpy
- Outdoor-air enthalpy (Btu/lb) 24
- Return-air enthalpy (Btu/lb) 28
- Outdoor dry-bulb (°F) 70
- Fixed high-limit setpoint (°F) 65
You get
- Margin to changeover 4
Details, formula, and sources
Enable below a setpoint. OA 24 vs RA 28 Btu/lb -> enable (4 margin); a humid OA 32 vs 28 locks out even if cool; fixed 70 F vs 65 F setpoint locks out. The ASHRAE 90.1 high-limit governs.
differential enthalpy: enable if h_outdoor < h_return; fixed dry-bulb: enable if t_outdoor < setpoint; margin = the difference to the limit.
The air-side economizer high-limit (changeover) control, differential enthalpy and fixed dry-bulb, from ASHRAE 90.1 6.5.1.1.3, by name.
The differential-enthalpy and fixed-dry-bulb high-limit logic is the published ASHRAE 90.1 economizer control requirement.
Estimate. AHJ and licensed professional govern.
Field names used by the API: mode, h_outdoor, h_return, t_outdoor_f, setpoint_f, margin
- Differential enthalpy enable when h_outdoor < h_return (accounts for latent load)ASHRAE 90.1 6.5.1.1.3
- Fixed dry-bulb enable below a dry-bulb setpoint (climate-zone dependent)ASHRAE 90.1 6.5.1.1.3
- Decision only does not model reset, minimum position, or free-cooling energyscope of this tile