Humidity-Constrained Night Ventilation for Cooling-Energy Reduction in a Humid Caspian Climate

Abstract

Abstract—Night ventilation is a low-cost passive cooling strategy, but in humid-temperate climates the cooler night air is often close to saturation, so controls that ignore humidity may trade modest sensible savings for indoor humidity problems. This study asks (i) whether the choice of control logic changes which strategy is best once humidity is considered, and (ii) whether climate-based “ventilation potential hours” predict real cooling-electricity savings. A transparent hourly single-zone model (two thermal nodes, a moisture balance and ideal mixed-mode air conditioning with window lock-out) was driven by the Babolsar TMYx weather file (Caspian coast, Iran) for June–September. Three controls (temperature, temperature plus dew point, enthalpy) were compared with no night ventilation over 300 Latin-hypercube samples of seven uncertain parameters (1,200 simulations). Mean seasonal cooling electricity fell by only 4.2%, 2.0% and 2.3%, respectively, from 1,218 kWh, and the temperature control used the least electricity in 88% of samples. However, it tripled occupied hours above 70% relative humidity (124 → 382 h), whereas the enthalpy control added 47 h. With a humidity constraint (≤100 additional humid hours), the enthalpy control was best in 77% of samples, but this ranking depends strongly on the tolerance chosen. Potential hours correlated strongly with savings (Spearman ρ = 0.84–0.92) yet identified the best control in only 83% of sample–months. Cooling set-point and thermal mass dominated the sensitivity. Energy-only evaluation can therefore mislead in humid climates, and humidity-aware reporting is recommended.

Keywords— night ventilation; humid-temperate climate; enthalpy control; ventilation potential; uncertainty analysis; Latin hypercube sampling; Caspian coast