Validation of a method to select the optimal nominal power of a wood stove in residential buildings
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Wood stoves are prominent space heating strategies for detached residential buildings in European countries. However, there are no guidelines for selecting the correct wood-stove nominal power, based on building performance. This should be studied with regards to thermal comfort, because the alternating power output from wood-log stoves can cause overheating. Previous studies show that the risk of overheating is increasing with higher insulation levels, and decreasing with heavier construction modes. Insulation levels ranging from passive house standard (NS3700) to old buildings (TEK87), and construction modes with heavy concrete to light wood, were selected for the construction of the building model used in this Master thesis. Other building performance strategies including living room size and different stove nominal powers, were also considered. Each of these selections were considered for several occupancy behaviours, including opening and closing of internal doors, different set-point temperature for bedrooms and different wood fuel batch sizes (length of combustion cycles). A model of a detached residential building with heated floor area of 173.5 m2 were established and used as a base in IDA ICE with the cli- mate of Oslo, Norway. The newly implemented Zonal Model in IDA ICE 5.0 (initially named IDA ICE 6.0) were utilised to perform annual simulations for this building model for the selected control strategies. The stove was physically integrated into the building model, according to the strongly-coupled approach. It was controlled with a control strategy that was set to lit the wood stove for living room air temperature below 20 ◦C, and only during morning and afternoon hours. This method was more comprehensive with regard to the number of simulations and simulation time, hence there was not enough time for completing the full scope of the Master thesis. In consideration with my supervisors, parts of the problem description were excluded, including building models for row houses and apartment buildings, and climates for Bergen and Karasjok. Results were analysed with regards to the thermal comfort and energy balance, with the goal to produce guidelines for selecting appropriate wood stove based on building performance. Thermal comfort was used as the main criteria for selecting appropriate control strategies for the development of guidelines. An assessment of the energy balance of these control strategies were assessed for a comparison with literature. This study is consistent with most literature findings, on the fact that wood stoves in the current market is oversized compared with the building performance. The most appropriate control strategies were open doors, 16 ◦C set-point temperatures for bedrooms, and long combustion cycles. Guidelines were developed for large, medium and small living room sizes, with recommendations for the maximum nominal power of the wood-log stove to be integrated. The developed guidelines did not match the trends of the simplified method. The stove nominal power suggestions were roughly the same for small living room, however the simplified method calculated too high stove nominal powers for medium and large living room selections. The problem is believed to be the use of different thermal comfort assessments. The method for modelling the wood stove did not perform as predicted, either. The wood stove showed to be too dependent on the indoor air temperature, which caused it to be lit at abnormal time periods and more frequent than what is believed to be normal occupancy behaviour. Improvements on the wood stove control should therefor include more advanced models for occupancy behaviour. There is also a demand for new and more specific standards for assessing thermal comfort for wood stove users, which is recommended for further studies on this topic.