Energy efficiency improvement and fuel savings in water heaters using baffles

Abstract

Thermal efficiency improvement of a water heater was investigated numerically and experimentally in response to presence of a baffle, particularly designed for modifying the flow field within the water reservoir and enhancing heat transfer extracted into the water tank. A residential natural gas-fired water heater was selected for modifying its water tank through introducing a baffle for lowering natural gas consumption by 5% as a target. Based on the geometric features of the selected water heater, three-dimensional models of the water heater subsections were developed. Upon detailed studies of flow and heat transfer in each subsection, various sub-models were integrated to a complete model of the water heater. Thermal performance of the selected water heater was investigated numerically using computational fluid dynamics analysis. Prior to baffle design process and in order to verify the developed model of the water heater, time-dependent numerically-predicted temperatures were compared to the experimentally-measured temperatures under the same conditions at six (6) different locations inside the water tank and good agreement was observed. Upon verifying the numerical model, the fluid flow and heat transfer patterns were characterized for the selected water heater. The overall design of the baffle and its location and orientation were finalized based on the numerical results and a set of parametric studies. Finally, two baffle designs were proposed, with the second design being an optimized version of the first design. The verified three-dimensional model of the water heater was modified to include the baffle designs and same thermal performance analysis was simulated confirming potential improvements in thermal efficiency. Thereafter, designed baffles were prototyped and assembled in identical water heater units and experiments were conducted according to standard water heater test procedures. Finally, numerical and experimental results verified thermal efficiency improvement in the water heater after introducing the baffles. As a result, baffle’s second design is capable of lowering the natural gas consumption of the water heater by 4.95% under steady-state thermal efficiency test condition which meets the target of this research. However, the gas savings under actual usage patterns might be less than this value.