Enthalpy control is an economizer strategy that compares the total heat content of outdoor and return air to minimize HVAC energy consumption. Unlike temperature-only economizers, enthalpy controls evaluate both sensible heat (temperature) and latent heat (moisture content) to determine when outdoor air is more efficient than recirculated air. This approach is particularly effective in humid climates where moisture significantly impacts total energy requirements.
Operating Principles
Enthalpy controllers use indoor and outdoor humidity sensors combined with temperature sensors to calculate air enthalpy values in BTU/lb. When outdoor air enthalpy is lower than return air enthalpy, the system increases outdoor air damper opening. Setpoints typically range from 25-35 BTU/lb, with adjustments based on climate zone and building occupancy patterns.
Climate and Efficiency Advantages
Enthalpy control delivers 15-25% greater energy savings than temperature-only economizers in coastal and humid regions. It prevents overventilation during high-humidity periods that would increase cooling loads. Applications include office buildings, retail facilities, and manufacturing plants in climates with outdoor summer humidity exceeding 65% relative humidity.