Thermodynamic analysis of an innovative heat pump using indoor and outdoor air as heat source

roposes a novel heat pump system to efficiently utilize the exhaust air. The system has two heat sources: exhaust air and ambient air. It consists of a condenser, two parallel evaporators and compressors, and two throttle valves. The exhausted indoor air is first used to heat the refrigerant in the medium-pressure evaporator. The exhaust air at a reduced temperature is then mixed with the ambient air to heat the low-pressure evaporator. The advantages of the mixed air source heat pump (MASHP) with two-stage evaporation over a conventional exhaust air heat pump (EAHP) include a larger heating capacity, higher waste heat recovery and lower carbon emission. Besides, the exhaust air can be employed for defrosting without additional power consumption. Thermodynamic performance of the system is investigated. Comparison is made with a conventional EAHP and a directly mixed air source heat pump with single-stage evaporation. The results indicate that under the conditions of exhaust air temperature of 20 oC, mass flow rate of 1.0 kg/s and ambient temperature of 0 oC, the profits for the proposed MASHP, conventional EAHP and MASHP with single-stage evaporation are about 11.5, 5.1 and 3.7 pound/day, respectively