Research PaperA frost-free dedicated outdoor air system with exhaust air heat recovery

- An efficient DOAS with exhaust air heat recovery is proposed.
- System cooling COP reaches 3.3 and heating COP achieves 4.8 at design conditions.
- In winter, evaporating temperature of exhaust air coil is regulated for frost-free operation.

DOAS (dedicated outdoor air system) has drawn much attention recently. However, it is quite energy-intensive resulted from the big temperature and/or humidity difference between outdoor air and supply air. This paper proposed a new DOAS with exhaust air heat recovery. In cooling mode, there are one evaporator and three condensers in parallel. The outdoor air is cooled and dehumidified by the evaporator. Besides the outdoor condenser, another two are used for supply air reheat and exhaust air heat recovery. In heating mode, the reheat coil is off and two evaporators work for exhaust air heat recovery and ambient heat absorption, respectively. A pressure regulating valve equipped on the indoor evaporator keeps proper evaporating temperature for a frost-free operation. A validated model is applied to fulfill the system design and performance prediction. The results showed that the system cooling COP reaches 3.3 at ambient temperature 35°C/28°C and the heating COP achieves 4.8 at ambient temperature 7°C/6°C, respectively. In winter the proposed system can maintain the desired supply temperature and keep both evaporators frost-free (ambient temperature −20°C to 10°C). The proposed system can efficiently recover waste energy from exhaust air in the whole year and has the extensive applicability, especially in the cold climate where considerable energy savings can be found.