Two previous studies have been undertaken investigating ISAHP systems. The first study involved developing a model in TRNSYS [12], a transient simulation program, to investigate the feasibility of the system, performing both a performance and cost analysis. The second study involved building a prototype of the system, and performing a range of constant temperature input tests, comparing the results with the simulated results. A brief description of each previous study is provided below.

1.1. Numerical Analysis

The first study was conducted in the Solar Calorimetry Lab by Freeman [3] and simulated the performance of indirect solar assisted heat pump using TRNSYS. The program used mostly component models developed with the TRNSYS software, but models were created for the heat pump, the natural convection heat exchanger, and the heat pump controller. A detailed description of the TRNSYS model, and a theoretical analysis and derivation of the steady-state vapour compression heat pump model is given by Freeman [3], and is briefly summarized in a previous paper by the authors [13].

Results of these previous studies predicted higher seasonal solar fractions than conventional Solar Domestic Hot Water (SDHW) systems. It was concluded that the ISAHP gathered more energy from the environment during marginal weather conditions, as well as during the winter when compared to either an SDHW or air-to-water heat pump systems. The study also found that the life cycle cost of the ISAHP system showed up to 29% savings over the SDHW system for major cities across Canada.