Improving the performance of hot water storage tanks using chimney type heaters

Abstract

Hot water storage tanks (HWST) are high energy consumption devices. One way of reducing energy consumption is improving thermal stratification of the HWST. Improving thermal stratification will supply hot water faster for users, reduce the energy they consumed, increase efficiency in solar collectors or heat exchanger. In this work, the electrically heated HWST is led under investigation to improve the thermal stratification by imposing a chimney over the heating element to accelerate the top layer temperature by natural convection. Various tank sizes (38, 50, 62, and 75 litres) were investigated. The chimney height (HC), chimney diameter (DC) and chimney natural flow area (Df= 9.5, 2.5 and 1.5 cm) were also analysed to find the optimal chimney. The experiments revealed that using chimney in the HWST will accelerate the natural circulation to the upper layer in the storage tank. This will reduce the amount of energy required to perform the same operation without a chimney. Using chimney type heaters (CTH) in the HWST is favorable especially when tanks volume to heating element power increases. The entropy generation and distorted exergy of the system were improved by using CTH, thus the available reversable work increases. High hot water temperatures were attained in a shorter time which favorite such HWST. Higher efficiencies in case of solar heat collectors (due to lower cold-water temperatures in the bottom layers). Dynamic mode of CTHHWST represents a significant issue which needs detailed investigation which is currently under investigation.

Keywords

• Hot storage tank
• Chimney type heater
• Natural heat transfer
• Thermal performance
• Thermal stratification