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.

A residential building which had been subjected to an energy efficiency measures study had its indoor thermal climate investigated using two software approaches to understand how each approach would predict the outcome, using the predicted percentage of dissatisfied (PPD). The computational fluid dynamics software (ANSYS CFX) and the building performance simulation (BPS) software (IDA ICE) were used to simulate the indoor thermal climate before and after the measures. The measures included additional insulation and changing the ventilation system. The results showed a difference in how the software packages handled the thermal radiation. The difference was also because CFX could calculate the indoor thermal climate of the whole interior. While the PPD values could remain similar between the CFX solutions, the area with dissatisfaction in the apartment was decreased when the building envelope was improved. These changes gave an improvement for the CFX solutions, which was not possible to predict with IDA ICE because only the central node was visible. The user should be aware of the shortcomings of BPS and building energy simulation software when evaluating the indoor thermal climate to predict changes. A coupling between BPS and CFX software should be considered when new measures or significant changes are planned.

There is a need to improve the understanding and the knowledge of energy efficiency measures for residential buildings in sub-Arctic climate regions. This paper presents an investigation of two identical multi-family residential buildings in the sub-Arctic climate of northern Sweden, before and after renovation. During the renovation, additional insulation of the external walls and new windows were installed in one building, while the other building retained its original envelope.

The energy usage data for the past four heating seasons were collected, including data from before and after the renovation. Detailed thermal indoor climate data were gathered for specific months. The data from the two separate buildings showed that the renovation did not result in a significant improvement in energy usage. Prior to the renovation, the energy usage data showed a difference of 2-3% in the heat supply between the two buildings, and this difference persisted after the renovation. On the other hand, the indoor air temperature was raised. The renovated building had an indoor air temperature which was 2°C higher than the not yet renovated building.

IDA ICE models were constructed and validated with the measured data to investigate how a lower indoor air temperature would affect the energy usage and indoor thermal climate. The models showed that with a reduction in the indoor air temperature by 2°C after the renovation, the thermal climate would maintain an acceptable level according to PMV/PPD standards, and would result in a 13-14% reduction of the heat supply during the cold months. With an annual reduction of 15%, the heat supply could be reduced by 270 MWh per year for the whole area where the buildings are located. This clearly demonstrates the importance of adjusting the heating system after an energy efficiency measure has been performed.

There is ongoing work related to the energy efficiency of residential buildings in the subarctic regions in northern Sweden. The focus is often on the reduction of energy usage and the economic aspects for the property owners. With the introduction of new technology and changes to the existing building, the indoor thermal climate is affected. While these measures not necessarily create a negative impact on the occupants’ experience, it is essential to understand the outcome of various energy efficiency measures on an indoor thermal climate point of view. It is also crucial to explore used software, methods and how to interpret the outcome of projected simulations.

The present thesis investigates residential buildings subjected to energy efficiency measures in the subarctic region of Sweden, primarily from an indoor thermal climate point of view. Both typical residential buildings in the region and a new pilot building with unconventional approaches were included. The goal of the present thesis was to establish important aspects of energy efficiency measures to improve the knowledge for the region.

Along with measurements in the buildings, the building energy simulation software IDA Indoor Climate and Energy (IDA ICE) and the computational fluid dynamic (CFD) software ANSYS CFX were used in the present thesis. A comparison showed that the IDA ICE software and the CFX software gave different results when predicting the indoor thermal climate, mainly attributed to the thermal radiation. Due to the nature of CFD, the CFX was able to identify the variation of velocities, temperatures and thermal radiation in the whole volume, which also affected the results. Further, CFX could detect potential problems of the interior that could be crucial, that building energy simulation software such as IDA ICE could not.

The results also demonstrate how CFD is an essential tool when evaluating the indoor thermal climate. When it comes to making a fair assessment of changes, it is important to consider the thermal parameters, the occupied zone and the time spent in that zone. Without considering the occupants’ experience or adequately pay attention to heating and ventilation systems, energy efficiency measures could lead to the rebound effect. It is, therefore, important to consider and evaluate the thermal climate and properly adjust heating and ventilation systems after energy efficiency measures.

The thermal comfort in a residential building equipped with an air heating system and located in a sub-Arctic region was investigated with computational fluid dynamics (CFD) software. The predicted percentage of dissatisfied (PPD) was used to identify flaws with the heating system during winter conditions. New scenarios were simulated and compared to each other to see potential improvements of the thermal indoor climate. Comparison was done by combining the discomfort spaces inside rooms, the level of the discomfort and the time spent in these spaces. The discomfort covered 8–38% of the interior volume depending on the test case. The results provide the necessary means to create a satisfactory thermal indoor climate if an air heating system is to be utilized in sub-Arctic regions during the winter. The correct heat demand for each floor and appropriate placement of the supply devices are required. Adding air transfer units or grilles in rooms from which exhaust air is removed further improves the comfort. The results also show the strength of using CFD technique when investigating the indoor discomfort with PPD, and how a fair assessment can be done by combining the PPD with time.

This study investigates the effects of reaction temperature and catalyst loading on product yields and fuel properties of produced slurry during the alkali catalyzed hydrothermal treatment (HTT) of pine sawdust. The yield of the liquid fraction, or the aqueous product (AP), at process temperatures of 180–260 °C obtained after solid/liquid separation of the slurry ranged from 11.1 to 34.3 wt% on a dry, ash free basis. The fuel quality of the produced slurry, such as the elemental composition and the higher heating value (HHV), was mainly affected by the catalyst loading. An increase in the catalyst loading caused the ash content to increase. Although the increase in temperature leads to a higher liquid fraction in the slurry making it more homogeneous, its contribution to the elemental composition of the whole slurry was limited. HHV of the produced slurry ranged from 12.0 to 16.4 MJ/kg. These values are comparable to that of black liquor (BL), which has previously been shown to be a promising feedstock for gasification in a pilot scale entrained flow gasifier. These results imply the possibility of a fuel switch from BL to the HTT slurry for entrained flow gasification though its gasification reactivity and conversion characteristics must be investigated further.