A Study of the Design and Analysis of Two Exhaust Heat Recovery Systems for Public Shower Facilities

For large-scale public shower facilities which open up at a specified time, (such as those in schools, barracks, and natatoriums), a great deal of heat is wasted. If this exhaust heat can be recovered and recycled, it will have significant impact in saving energy and environmental protection, with significant economic benefits. In this paper, two different kinds of heat pumps, an electric and an absorption heat pump, used in heat recovery systems are proposed. Specifically, the used shower water is drained through a pipe and first collected in a gray water pool. After a period of time, as the wastewater accumulates volume, the heat pump system can begin heat recovery and recycling. The wastewater is filtered through a filter and piped to a heat exchanger to heat the tap water. Therefore, the tap water temperature can be heated from 12°C to 25°C, and the wastewater temperature will drop from 30°C to 17 °C. Afterwards, the wastewater is piped to the heat pump evaporator and the tap water piped to the condenser for additional heating. At the same time, according to the different characteristics of the electric heat pump and absorption heat pump, different heat recovery system processes and control are detailed. On this basis, the paper analyses the economic and environmental benefit of three schemes for retrofitting based on a practical example: “exhaust heat recovery using electric heat pump”, “exhaust heat recovery using electric heat pump + gas boiler” and “exhaust heat recovery using direct-fired heat pump”, then finds that direct-fired absorption heat pump heat recovery have lower energy consumption, less pollution, lower operating costs, payback period is shorter and has a promising practical application.