A simplified double grade meteorological data model for the simulation of the annual performance of a domestic-size renewable energy system is proposed. With the model, only two representative days (clearest and cloudiest) during each season of the year are necessary to estimate annual energy balances, carbon emissions and the running costs. The model was chosen in preference to other simplified models based on the error distributions from the results of the continuous simulations in a test period. Detailed numerical simulation studies show that the carbon emissions from the renewable energy system are about 16% of a comparable conventional system. The thermal energy produced by a solar collector during the winter season, however, is insufficient to meet all the loads so that frequent heat pump operations and the auxiliary boiler are necessary in cold climate regions.

Five different kinds of domestic-size renewable energy system configurations for very cold climate regions were investigated. From detailed numerical modeling and system simulations, it was found that the consumption of fuel oil for the auxiliary boiler in residentialtype households can almost be eliminated with a renewable energy system that incorporates photovoltaic panel arrays for electricity generation and two storage tanks: a well-insulated electric water storage tank that services the hot water loads, and a compact boiler/geothermal heat pump tank for room heating during very cold seasons. A reduction of Greenhouse Gas Emissions (GHG) of about 28% was achieved for this system compared to an equivalent conventional system. The near elimination of the use of fuel oil in this system makes it very promising for very cold climate regions in terms of energy savings because the running cost is not so dependent on the unstable nature of global oil prices.

An actual renewable energy house, equipped with a geothermal heat pump (GHP)-powered floor heating system was investigated and analyzed. Daily annual monitoring between February 2005 ~ February 2006 and real-time continuous system monitoring within selected periods during the winter season between November 2006 ~ January 2007, were carried out in order to establish the actual performance of the system. It emerged that the GHP-powered floor heating system is sufficient for space heating, with the maintenance of near-uniform room temperatures even during the coldest days in a very cold region like Hokkaido, Japan. About 37% average of the floor heat losses are recoverable and more than 50% of the ventilation heat losses are recovered due to various innovative energy-saving techniques built into the system. Annual heat loss from the house estimated by the numerical simulation showed good agreement with the measured annual thermal demand for room heating. The simulation also estimated that annual running costs and Green House Gas (GHG) emissions reductions of 47% and 49% respectively, can be realized with this system compared to an equivalent conventional system. A detailed cost analysis for the GHP-only system revealed that if the cost of fuel oil increases by about 50% from the current value of ¥80/L, then the payback period for a GHP-powered renewable energy system is about 14 years. This payback period reduces to about 10 years if 30% of the initial cost of the GHP-powered system is externally funded.

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