Improving cooling energy efficiency in Hong Kong offices using Demand-Controlled Ventilation (DCV) and Adaptive Comfort Temperature (ACT) systems to provide Indoor Environmental Quality (IEQ) acceptance

Abstract

Space cooling is a significant energy consumer in office buildings in the subtropical climate zone. An adequate energy policy for indoor spaces should accordingly incorporate both energy conservation and an acceptable level of indoor environmental quality (IEQ). This study investigates the cooling energy consumption for IEQ acceptance in Hong Kong offices adopted for four space-cooling strategies: the ventilation strategies of conventional constant air volume (CAV) systems with a fixed fresh air flow rate; demand-controlled ventilation (DCV) by indoor CO2 concentration; adaptive comfort temperature (ACT) set-point adjustment; and a combination of DCV and ACT operations. Numerical equations and multiple regression formulae were used to evaluate the cooling energy consumption and IEQ acceptance in the target offices, respectively. The results show that systems equipped with DCV are more energy efficient than conventional CAV systems, while a temperature set-point adjusted between 22°C and 23°C should satisfy the occupants’ thermal requirements at a reasonable rate of energy expenditure. Meanwhile, the DCV + ACT method was found to be an effective ventilation strategy in terms of its energy saving potential (21.4%-24.3%) and an “average” IEQ acceptance, as presented in the sample office. The results of this study could be useful for the promotion of energy saving measures with IEQ consideration in air-conditioned office buildings in Hong Kong.