ENERGY CONSUMPTION OF HOUSES UTILIZING NATURAL ENERGY AND THE ISSUES INVOLVED IN REALIZING ZEH

Abstract

 In recent years, Japan and the rest of the world have been aspiring for the development of net zero energy housing (ZEH) to reduce greenhouse gas emissions. Toward that end, it is required that the conditions necessary to achieve ZEH are clarified with regard to electricity generation using a 3-kW photovoltaic (PV) system; because the implementation of PV systems is feasible on popular house types in the crowded Japanese cities. In this study, we examined the actual energy consumption, carbon dioxide emissions, and thermal environment of high thermal performance houses with solar and natural energy utilization systems. Additionally, we compared actual measurement values to the design values of primary energy consumption that is used for the ZEH assessment criterion in Japan. The issues involved in achieving ZEH are also discussed.
 The major findings of this study are as follows:

 ·The examined houses exhibit “nearly ZEH” performance according to Japan's ZEH assessment criterion.
 ·The total energy consumption of the examined houses amounts to approximately 60% of an ordinary house's total energy consumption; purchased energy amounts to approximately 50% of an ordinary house's purchased energy.
 ·The examined houses' reduction rate of CO2 emissions amounts to over 75% reduction. Thus, it was observed that greenhouse gas emissions are greatly reduced.
 ·The energy costs of examined houses are lesser by approximately \223,000 per year (\18,000 per month) compared to the energy costs of ordinary houses. Demonstrating the cost efficiency of energy-efficient housing contributes to the spread of ZEH.
 ·After accounting for domestic use including home appliances, the energy produced from solar power using a PV system with a capacity of approximately 3 kW, results to approximately 63% of energy self-sufficiency. To achieve ZEH (including their home appliances), additional energy-saving measures are required, such as improving thermal insulation, switching to high-efficiency appliances, and residents choosing more energy-efficient life-styles. Additionally, energy producing measures such as solar heating and hot-water systems should also be considered.
 ·Energy self-sufficiency with regard to total energy consumption excluding home appliances was calculated at 94% (or 106%), assuming that the home appliance use accounts for 33% of total energy consumption (or 20.5 GJ per year), which is similar to the design value of primary energy consumption. This means that the examined houses are almost achieved ZEH (excluding their home appliances).
 ·The actual measurement value of total energy consumption for the examined houses is approximately 83% of the primary energy consumption design value. This difference results from the non-consideration of the contribution of solar heating and hot-water system toward the design value. If the calculation method of primary energy consumption considers various additional energy-saving measures, the popularity of energy-saving measures as well as the popularity of ZEH can increase.