Measures used to lower building energy consumption and their cost effectiveness

Abstract

This study uses the TRNSYS computer program, for the modelling and simulation of the energy flows of modern houses, to examine measures to reduce the thermal load. For the calculations, a typical meteorological year (TMY) and a typical model house are used. The measures examined are natural and controlled ventilation, solar shading, various types of glazing, orientation, shape of buildings, and thermal mass. In summer, ventilation leads to a maximum reduction of annual cooling load of 7.7% for maintaining the house at 25 °C. The effect depends on the construction type, with the better-insulated house saving a higher percentage. Window gains are an important factor and significant savings can result when extra measures are taken. The saving in annual cooling load, for a well-insulated house, may be as much as 24% when low-emissivity double glazing windows are used, which are recommended since the payback period is short (3.8 years). Overhangs may have a length over windows of 1.5 m. In this way, about 7% of the annual cooling load can be saved for a house constructed from single walls with no roof insulation. These savings are about 19% for a house constructed from walls and roof with 50 mm insulation. The shape of the building affects the thermal load. The results show that the elongated shape shows an increase in the annual heating load, which is between 8.2 and 26.7% depending on the construction type, compared with a square-shaped house. Referring to orientation, the best position for a symmetrical house is to face the four cardinal points and for an elongated house to have its long side facing south. In respect to thermal mass, the analysis shows that increasing the wall and roof masses and utilizing night ventilation is not enough to lower the house temperature to acceptable limits during summer. Also, the analysis shows that the roof is the most important structural element of the buildings in a hot environment. The roof must offer a discharge time of 6 h or more and have a thermal conductivity of less than 0.48 W/mK. The life-cycle cost analysis has shown that measures that increase the roof insulation, pay back in a short period of time, between 3.5 and 5 years. However, measures taken to increase wall insulation pay back in a long period of time, of about 10 years.