Design, Fabrication and Testing of Vapour Compression Refrigeration Cycle Based Domestic Water Heater

Abstract

All are aware of the energy crisis and importance of the ecient utilization of theenergy for everyday purposes. The adverse eect of release of refrigerant like globalwarming and ozone depletion in the atmosphere is known to all. Hot water for do-mestic purpose is used for bathing, washing clothes, cooking cleaning utensils etc.Generally hot water for domestic use is obtained from LPG stove and electric resis-tance heaters. Electric heaters use electricity which is obtained from thermal powerplants which in turn use coal and other fuels.It is well known fact that mechanical heat pump has thermodynamic advantage overelectric heating since useful heat available for heating is always greater than workconsumed for heat pump. While for the electric heaters, the heat available is al-ways less than or equal to work consumed.The aim of the project is to demonstratethe economic benet of using heat rejected in the condenser of Vapour CompressionRefrigeration (VCR) system and to check the feasibility of the apparatus for massproduction. The main aim of the project is to develop economically viable VCR cyclebased domestic water heater (Heat pump) which has a good payback period and lowenergy consumption compare to electric-resistance heater.Various options of evaporator and condenser has been reviewed. Dierent correla-tions for ow boiling, condensation and natural convection for air and water has beenreviewed during project work.A domestic water heater (DWH) of 1 kW heating capacity is designed, fabricatedand tested during the project work. For the said heating capacity, evaporator dutyand hence compressor capacity has been evaluated from VCR cycle calculations. Var-ious designs of evaporator and condenser have been reviewed. Helical coil shapedevaporator directly exchanging heat with atmospheric air has been designed. Sinceviiiit was intended to develop storage type water heater, helical coil shaped condenserbrazed outside the water storage tank has been designed. Since the capacity of theVCR system is less, capillary tube has been used as an expansion device which hasbeen sized for the chosen operating parameters. The VCR cycle based DWH hasbeen tested extensively and heating capacity of about 700 W has been obtained. Thelower capacity may be due to under sizing of evaporator or condenser or may be dueto larger capillary length. This may also due to poor insulation on top of the waterstorage tank. The VCR cycle based DWH can result in to annual saving up to Rs4800 compared to electric resistance water heater. The simple payback period for thedeveloped water heater is calculated to be 2 year and 10 months. The water heatercan reduced CO2 emissions by 775 kg per year.