Building design typically has a focus on energy use and economy. The indoor environment is often overlooked or simplified to such an extent that essential aspects are neglected. Additionally, introducing technologies for improving energy efficiency can also affect the indoor thermal climate and, in turn, the perceived indoor comfort. Furthermore, an energy efficiency measure which creates discomfort could end up ineffective due to occupant behaviour.

The main objective of this thesis is to demonstrate why indoor thermal comfort is vital to consider during building design or renovation procedures. It also explores some methods for improving the sub-Arctic region related to this matter.

In this thesis, six different residential buildings have been studied within the northernmost region of Sweden—Norrbotten. This region is sub-Arctic, with long, cold and dark winters. The summers are brief but bright and relatively warm. In this thesis, the winter cases are in focus, but summer cases are also assessed to a minor degree.

Both energy usage and indoor thermal climate parameters were measured throughout the buildings. The results indicate a need to assess implemented energy efficiency measures. The results also show the importance of considering the indoor thermal climate during energy efficiency measures.

The thesis also discusses the use of the popular building performance simulation (BPS) software package IDA ICE. The software package performed well when calculating and predicting energy use and balance. However, IDA ICE could not detect certain indoor thermal climate problems. In these cases, some surface temperatures were incorrect in IDA ICE models, where warm radiator surfaces were the most evident. The error led to the radiation temperatures being too low, affecting thermal comfort parameters such as the predicted percentage of dissatisfied (PPD). The error could give a false impression of thermal comfort.

Computational fluid dynamics (CFD) simulations can acquire more accurate radiation temperatures. With a CFD software package, it is possible to better understand the indoor environment due to higher accuracy than IDA ICE.

This thesis also provides a comparison method for improving the CFD methodology when comparing several scenarios. The PPD can be evaluated by including both space and time. The space evaluation is done by focusing on the problematic areas in the occupied zones. The time evaluation is done by accounting for the time spent in zones.

Using the comparison method in the software package ANSYS CFX, the thesis provides guidance on how to use air heating in the sub-Arctic. A traditional ventilation system setup cannot be used for certain building layouts. Some rooms would have no heat source, which can create an imbalance of heat supply, which leads to thermal discomfort.

The thesis also shows that additional insulation improves thermal comfort more during winter than installing a mechanical ventilation system with heat recovery (MVHR). Since heat can be recovered, an MVHR system can decrease overall energy use. In summer, energy use is increased due to fan operations. However, during summer, it is possible to improve thermal comfort with an MVHR system. Additionally, exhaust air from a basement can cool the supply air in the heat exchanger of the MVHR system.

The results in this thesis also indicate a knowledge gap related to the glazing of buildings in the sub-Arctic region. If glazed balconies are considered an extension of the building envelope during heat demand calculations, the heat demand will decrease. One of the studied buildings did not include glazing of balconies during the design phase. While the building’s heat supply should decrease, it actually increased during operation. Using the software package ANSYS Fluent, missing passive solar gains are identified. The missing passive solar gains are caused by the glazed balconies. This means that the heat supply must be increased.

The CFD methodology in the thesis shows the strengths of using CFD in building design by being able to detect problems with thermal comfort to a higher degree than BPS software. Although time-consuming, the CFD methodology can find potential problems related to ventilation systems, such as draught, which is only visible using finite elements or finite volume methods. The results in the thesis suggest that BPS software should be coupled with CFD when energy efficiency measures could affect the indoor thermal climate.