Impacts on Building Return Water Temperature in District Cooling Systems

A high temperature differential between supply and return water is most cost effective in district cooling systems. The chilled water supply temperature relies on central plant operation while the chilled water return temperature mainly depends on cooling coil performance of air handling units (AHU) at consumers. Many factors affect the AHU cooling coil performance at the consumers, such as cooling coil size, chilled water supply temperature, AHU supply air temperature, space cooling load, outside airflow and conditions, cooling coil fouling condition and cooling coil control valves types. The AHU chilled water return temperature may deviate from its design valve under off-design conditions. The common method to maintain the required consumer chilled water return temperature is to install a bypass bridge between the chilled water supply and return at consumer connections. This paper studies the impact of these factors on the AHU chilled return water temperature and finally develops the improved chilled water return temperature control method.