Performance of solar water heaters with narrow mantle heat exchangers

This paper evaluates the performance of narrow-gap vertical mantle heat exchangers with a two-pass arrangement for use in pumpedcirculation solar water heaters. Both measured mantle side and tank side heat transfer correlations have been developed and implemented in a TRNSYS model of a complete solar water heater incorporating this type of heat exchanger. Predictions of the annual solar contribution for mantle–tank systems are compared to direct-coupled systems. The direct-coupled systems are found to provide slightly higher annual energy saving than mantle–tank systems for standard domestic hot water demand in Australia. However, the reduction in performance is outweighed by the benefit of freeze protection provided by incorporating a collector loop heat exchanger in the system. 2008 Elsevier Ltd. All rights reserved.