Solar-Assisted Heat Pump and Swimming Pool Synergy for Domestic Heating

In this study for a 150-m² home, performance and economic advantages are shown for a solar-assisted heat pump providing domestic hot water and space heating and cooling when the pump uses a year-round solar-heated swimming pool (capitalized as a luxury) for a large, thermal energy reservoir. The pool can seasonally cycle between 18 and 31°C (64 and 88°F), allowing year-round swimming and providing an excellent water source for the heat pump and the low cost, low temperature, plastic solar collector panels operating at near-optimum efficiency. To optimize the system, we examined the performance and cost characteristics of different glazed and unglazed solar panels (28 to 150 m² and horizontal to 60 deg tilt) at sites in the San Francisco Bay area and San Joaquin Valley. Actual experimental data on the pool and panels have been used together with numerical simulations for performance. The optimum system was found to use 75 m² of a $44 m⁻² unglazed panel at a 48 deg tilt, a 300-GJ yr⁻¹ (30,000-BTU h⁻¹) capacity heat pump, and a standard 50-m² swimming pool with a solar blanket cover. Solar energy supplied about 85 percent of the energy requirements at $6.62 GJ⁻¹ ($6.62/10⁶ BTU) as of July 1979. With 20-yr life financing (15 percent interest), the break-even point was projected at 7 yr with a net savings of 42,701 dollars by the year 2000 (using the 55 percent California State Solar Tax Credit), compared with a conventional, all natural-gas system where the gas cost increases at 14 percent yr⁻¹ from $3 GJ⁻¹. Discounting these savings of 42,701 dollars back to July 1979, its present value of the savings of 6350 dollars would be equivalent to a 9.5 percent return on investment.