Climate and environmental issues is now high on the agenda. We live in a generation that must try to solve some major environmental problems. Buildings and habitations account for approximately 40 % of Sweden's total energy today. To reduce this figure, as needed, more research in the field of energy efficiency is required.

This thesis concerns the heating of buildings. The load on district heating is heavy during certain times of the day. This is partly because we are in need of a high power output of the heat in our homes in the winter. The power demand is also increased in response to the patterns in our daily lives.

To avoid these heating peaks that occur, one could use the building's thermal inertia. This work examines the relationship between a building's energy consumption and the thermal inertia of a concrete building. Can the space heating be turned off at certain times of the day without having the residents being adversely affected as a result of poor thermal comfort?

In order to draw conclusions, energy simulations of a multi-family building were implemented. Simulations were made in the program IDA Indoor, Climate and Energy 4.0. Crucial to the result, is the material and the layer thicknesses, the apartment's location in the house, etc.

To assess whether it is feasible to turn off the heat for a few hours then examined the definition of thermal comfort based on the operating temperature drop that occurs during heating off.  The results of the three simulations showed that rapid temperature drops occurs during the first hour, and then a slower decline in temperature over time. The operative temperature drops to its lowest values ​​above requirement of the operating temperature of the Social Board.

The results of the PPD- index by Fanger's comfort equation shows that the number of dissatisfied with the operative temperature ranges between 5- 8 %. After completing simulations it turned out that with the help of stored heat, temporary heating peaks can be avoid. The assessment of this is that it is possible to maintain a thermal comfort in view of the operative temperature, which occurs during the suspension of heating.

This can contribute to sustainable development in terms of reduction of energy use in the buildings sector.