Influence of thermal mass on the heating and cooling demands of a building unit

Sammanfattning: The purpose of this work is to find to what extent the thermal properties of the building materials, the allowed indoor temperature swing, determined by the comfort interval, and, to some extent, the ventilation strategy can affect the heating and cooling demand of a building. It is well known that a thermally heavy building, that is a building with a high heat capacity, often demands less energy for heating and cooling and have a more stabile indoor temperature due to heat storage in the building structure. A great number of studies have been done in this area and it is often debated to what extent the heat capacity of the building structure can be used as heat or cool storage. The heat storage potential of a building structure has been analysed using analytical solutions for both sinusoidal variation and a unit step of the indoor temperature. In three case studies, numerical calculation programs have been used to analyse the thermal behaviour of a building unit. The first case study focuses upon the influence of the building’s thermal mass and of the comfort intervals upon the heating and cooling demand during a 24-hour period. The second case study focuses on how different ventilations strategies can influence the heating and cooling demands of a building during a 24-hour period. The third case study compares the heating and cooling demand during one year for four buildings, each with a heavy and a light construction, respectively. Apart from the main task, two complementary projects are presented. In the first project, heat and moisture conditions are simulated in an earth-tube system designed to pre-heat the inlet air to a terrace building using the thermal mass of the ground surrounding the building. In the second complementary project, the energy use during the life cycle of four buildings is assessed. By choosing the right material in the building structure and adjust the comfort interval and ventilation to the current internal heat gain it is possible to decrease the heating and / or cooling demand of the building when part of the surplus heat is stored in the building structure. However, the amount of heat stored is small compared to the total energy use of a regular building. According to this study, the most important material parameter regarding heat storage is the thermal effusivity.