Utilization of Domestic Gas Heater Exhaust Energy for Heating Water

Abstract

The worldwide energy demands and its increasing cost in addition to the environmental problems of using the fossil fuels, has made the efficient use of energy inclouding heat recovery strategy in thermal systems. Although many equipments have been developed to re-use some of waste heat in large scales but there is few works on small scale and low grade sourses such as domestic gas heaters. This paper describes a water heating apparatus based on utilization of exhaust energy of domestic gas heater. The device is mounted on the roof, connected to the stack and the hot exhaust flows through its inner gear-shaped tube. The potential of heat recovery of this parallel-flow heat exchanger has been tested for 5.2 and 7.2kW heater powers and different exhaust temperatures in the range of 100-185 ⁰C. The results indicate; at the desired water temperature 45 ⁰C, the effective heating power enhances in the range of 290-940W proportional to the exhaust temperature and or gas heater power. The appliance could utilize up to 13% of total heat which is wasted, and it is fit to low grade, domestic gas heaters which are widely used and can supply hot water from low temperature exhaust gas even at 100 ⁰C. Economical considerationns reveals that the payback time of installation this appliance is 4 years.