Improved operating strategy for air-conditioning systems based on the indoor occupancy rate

The energy efficiency of an air-conditioning system is reduced when operating under low cooling load, e.g., when few occupants remain in the building, leading to extra energy consumption. This paper proposes an operating strategy for air-conditioning systems based on the indoor occupancy rate (R), where the start-stop is adjusted according to R while still satisfying indoor environment quality (IEQ) requirements. The dedicated outdoor air system (DOAS) is simultaneously used to feed in fresh air and combined with indoor fan coil units to independently control humidity and temperature. An office building air-conditioning system was tested with the improved operating strategy applied. The test results show that the energy efficiency ratio (EER) of the cooling plant reached 4.2, a 7.2% improvement over the same system operating under previous conditions. The IEQ in the test building was also significantly improved. Because the air-conditioning system did not operate at low energy efficiency, 15% of the total energy consumption of the system was saved. •Improved operating strategy based on indoor occupancy rate is proposed.•Independent control of temperature and humidity is suitable for varied cooling load.•Energy efficiency ratio of cooling plant is improved due to its increased load rate.