| A typical Canadian solar domestic hot water (SDHW) system comprises mainly a flat plate solar collector, a storage tank, and a collector-side heat exchanger. The collector-side heat exchanger is used for transferring heat from an anti-freeze collector fluid to the water in the storage tank. Heat exchangers of the side-arm type have been widely used over the past years. Despite the improvements obtained through constant research and development, side-arm heat exchangers continue to present several inconveniences related mainly to the high heat losses they impose on the system, and manufacturing/maintenance costs.This thesis examines the performance of SDHW systems with immersion heat exchangers. Immersion heat exchangers are located near or at the bottom of the storage tank, and thus require less piping. Less piping translates into lower system costs and heat losses.In the experimental part of this work, five different configurations of immersion heat exchangers were built and tested. A full-scale model was used, and each heat exchanger was tested for several weeks. Additionally, a commercially available side-arm heat exchanger, the Shell-and-Coil(TM), was also tested. The heat exchanger UA value was used to characterize and compare the performance of the heat exchangers. Three different system configurations were analyzed, i.e. SDHW system with immersion heat exchanger only, SDHW system with side-arm heat exchanger only, and SDHW system with immersion/side-arm heat exchanger combination. The performance of each system configuration was analyzed in terms of heat losses, system efficiency, and tank thermal stratification. Additional experiments studied the effect of water draws on tank stratification and heat exchanger UA value.Finally, five semi-empirical models were created to first, predict the UA values, and second, obtain information on the magnitude of the natural convection heat transfer coefficients for each of the immersion heat exchangers tested. |
