Study on the intermittent operation mode characteristic of a convection-radiation combined cooling system in office buildings

Abstract

Convection-radiation combined cooling systems are commonly used in residential buildings in hot summer and cold winter areas because of their high thermal comfort. When this system is used in office buildings, combined with the characteristics of office building’s working time occupancy patterns and building typologies, the operation strategy can lead to different energy consumption under the same thermal comfort. In this study, three operation strategies are compared to a system that combines two different terminal units in the same thermal zone: a radiant floor and fan coil. The performance of the combined system is assessed in terms of the thermal comfort level, hourly refrigeration performance coefficient, and energy consumption. The results indicate that the system with an intermittent operation strategy reduces energy consumption by approximately 39% compared with a continuous operation strategy, with little impact on thermal comfort. The room temperature under the three control strategies meets the temperature requirements of the office building during working hours. The fluctuation in room temperature is smaller under the continuous operation strategy than under the intermittent operation strategy, which indicates that the thermal environment of the room has better stability during continuous operation. The maximum indoor vertical gradient is always less than 3 °C, which meets the ASHRAE55-2017 standard. The room-temperature fluctuations are strongly affected by solar radiation. Therefore, building shading measures should be considered in building designs to avoid local discomfort or energy waste. When the system operates stably, the Predicted Mean Vote (PMV) value is low. The reason for this is that the radiant cooling system reduces the average radiant temperature of the building to adjust the room temperature. Therefore, it is recommended that the indoor design temperature of the radiant cooling system be increased by 2–3 °C to ensure better indoor comfort.