A multi-mode packaged dedicated outdoor air system embedded with a four-coil heat pump

Abstract

Dedicated outdoor air system (DOAS) plays a critical role in building ventilation. In recent years, much attention has been paid to the DOAS with heat-pump heat recovery. It is expected to have better dehumidifying performance and more operating modes to efficiently cooperate with the parallel cooling system. This work proposes a novel packaged DOAS embedded with a four-coil heat pump. Of the four coils, supply air coil and exhaust air coil are basic components of vapor compression heat pump that facilitates heat recovery from exhaust air. Return air coil is added to reduce heat loss in the mixing of return air and additional outdoor air. Supply air coil is introduced to reheat fresh air and avoid moisture condensation on air ducts. Meanwhile, refrigerant subcooling is increased in heat pump cycle for better efficiency. With simple switch the DOAS can also operate in four modes, i.e., outdoor air dehumidification, outdoor air low-load dehumidification, outdoor air heating and return air dehumidification. A functional prototype of 300 m3/h supply air is made and tested. Dehumidification capacity of 101.4 L/day and specific moisture extraction rate (SMER) of 3.22 kg/kWh are reached under the design condition of 30 °C/27 °C. Compared to the system without supply air coil, the new DOAS can see an improvement of 46.3% in SMER at the same supply air humidity ratio of 8.5 g/kga. It also keeps the supply air temperature above indoor air dew point. At last, the system's multi-mode operation for varying outdoor conditions is discussed.