On the Role of External Walls in the Reduction of Energy Demand and the Mitigation of Human Thermal Discomfort

The structure and thermal properties of external walls affect both the thermal conditions inside the building and the energy demand. This applies to the energy requirement for heating as well as cooling. While the relationship between thermal insulation and heating is well-known, the effect of thermal insulation on overheating is not evident. One can find opinions that thick thermal insulation creates a “thermos effect” and significantly deteriorates the comfort conditions during the summer. In order to prove these statements, an office room with south-oriented glazing and a high thermal load from equipment was simulated by means of the Energy Plus program. The reference variant was a two-layer wall made from ceramic blocks and a 10 cm layer of thermal insulation. The duration of overheating in the investigated intensively used office space without window shading was approximately 26 to 29 days per year, depending on the expected comfort acceptance range, while in the case of the not insulated wall, it would be shorter by over 3 days. Increasing the thickness of the thermal insulation layer by up to 30 cm extended the overheating period by 4% to 9%. In relation to the whole simulation period, covering four summer months, this means approximately two extra days of discomfort. The effects of various passive methods of protecting buildings against overheating were also investigated. The use of night ventilation in this facility enables reducing the unfavorable conditions by as much as 31%, or up to 46% of the initial period of overheating. The change of the thermal inertia of a building by replacing the ceramic layer with heavy structural concrete allows a further reduction of the overheating duration by 8% to 9%. When the most effective ways of overheating protection are applied, such as night cooling, even a significant thickening of insulation no longer has any impact on its duration. The results shown above are obviously related to the adopted assumptions. However, on the basis of the conducted analyses, it is possible to reduce concerns relating to excessive insulating the building with respect to overheating. Having an optimal window area with nighttime cooling of buildings, window shading, and the inertial benefits associated with a massive construction are the most important and effective measures of protection against overheating. Efficient thermal insulation of the walls does not conflict with the thermal comfort conditions.