Utilization of waste heat from commercial kitchen exhaust for water heating and dish drying

In the cooking process, abundant waste heat is generated and usually discharged out of a room along with the exhaust air directly. Obviously, recovering heat from the exhaust air by a heat pump is a promising technology in net-zero energy buildings, which can improve energy utilization efficiency and reduce exhaust emissions. A water-heating and dish-drying system based on a heat recovery unit was proposed in the current work to recover heat from the exhaust air of a commercial kitchen. The influences of key factors, including terminal functions, cooking methods, exhaust air modes and drying items, on the operating performance of this system were investigated. Results indicate that the heat transfer rates of water-heating and dish-drying are 7.17 kW and 0.40 kW respectively, accounting for 95% and 5% of the total heat transfer of the system. For these two functions, the total heat transfer rate and COP of this system are almost the same, leading to no influence on the system's performance, except for the changes in the heat distribution. Furthermore, due to differences in the temperature, moisture content, and stability of the smoke produced by different cooking methods, the proportions of the sensible heat and latent heat are different when the smoke exchanges heat on the evaporator. However, the total heat of the evaporate side has little change by different cooking methods.