In this first phase of the study, the heat losses of an earth-sheltered dwelling through transmission have been studied by means of a mathematical model. These results have been supplemented by approximate values for passive solar heating and other energy sources. The calculated energy demand of the studied house is 90 kWh/m2/year. A similar house, though not earth-sheltered, would demand some 110 kWh/m2/year. A number of other test projects on energy conservation also indicate energy demand in the region of 110 kWh/m2/year. The average Swedish detached house consumes 28 000 kWh/year, corresponding to 250 kWh/m2/year. It seems that improvements to the house studied are possible and that these would result in a further significant reduction in energy demand.
The idea of earth-sheltered housing has met with considerable interest in the U.S. The Underground Space Center at the University of Minnesota has given itself the task ot studying the concept and of disseminating information about it. The Swedish Council for Building Research, in cooperation with the Underground Space Center, has awarded a research grant to VBB AB and Hagconsult AB, for a study project on the characteristics of earth-sheltered housing in Scandinavian climate and geology.
Earth-sheltering can vary between conventional houses with grass on their roofs to fully recessed houses which receive their daylight via an atrium. The Swedish study concerns a house on a sloping site, the roof and three walls of which are covered with at least So cm of earth. The exposed fourth wall faces south in order to receive maximum passive solar heating. This basic model is applied rather strictly - the effects of alterations may be studied in projects to come. The house, see Fig. 1, is a concrete structure with sufficient styro insulation to meet the requirements demanded by the Building Code. Where the earth shelter is greater than 3 metres, no insulation is necessary. CLIMATIC DATA In the Stockholm area, the monthly mean temperature varies between -3.2 and +17.5°C. Most of the earth around the house is only subject to minor variations in temperature, from +70C which is the average temperature over the year. The latitude of Stockholm is S90N, where the solar angle varies between 7 and 550.
Heat losses due to transmission through the earth have been calculated by means of a finite element model, as shown in Fig. 2. The two-dimensional heat flow is calculated for a section of the house. The effects at the two ends of the house are not included, but they will not, however, significantly affect the results obtained. The model must be extended 20 m outside the structure of the house itself. The heat losses depend on the geological conditions. For calculation purposes, they have been assumed to be as is shown in Fig. 3. At an indoor temperature of 200C and an outdoor temperature of 7°C (mean yearly temperature) transmission losses will be 70 W/m house.