This paper analyzes the performance of a heat exchanger type, low-pressure household water heater that is commonly used in the northern part of Australia. The water in the tank is stored at atmospheric pressure and is heated with an electric resistance heater to about 75?C. The cold water at low pressure flows through a heat exchanger, which is immersed inside the water tank. Australian test standard AS1361 (1995) is used to compare the performance of six different designs that use different heat exchangers for improving the energy efficiency of the water heater. It explores the heat transfer characteristics of one of the heat exchanger designs (HX2) and presents the relative performance of the others. It presents actual designs tested under standard conditions. The test conditions were set to draw off hot water at a constant flow rate of 9 liters per minute until the outlet water temperature (from the heat exchanger) was at least 30°C warmer than the entering cold water or continuous “draw off” of warm water up to 7 minutes, whichever is less. The duration for this temperature drop illustrates the delivery capacity of a heat exchanger: the longer the time taken for the temperature drop, the more usable the hot water is delivered. The results could help the manufacturer develop a base for design of a cost-effective water heater with higher efficiency.

Units: SI