Influence of occupants' behavior on the performance of net-zero emission buildings
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This thesis investigates how the occupant behavior influences the performance of residential net zero emission buildings (Net-ZEB) in cold climates such as in Norway, and proposes guidelines for better design, operation and control strategies. The thesis focuses on the occupant related variations in the internal gains and the domestic hot water use, and studies their influence on the building’s heating needs, its heating system performance and finally, its interaction with the onsite renewable generation and the grid. The application of the tightly insulated envelope in Net-ZEB significantly reduces the space heating needs. This increases the share of the occupant-related heat gains in the total space heating needs, and the related DHW heating in the total heating needs of the building. These changes can eventually influence the heating system and its interaction with the grid. This research analyzes a typical single-family detached house. Such houses are the most common type of residences in Norway. There is a large variation in the occupancy, household appliances, and work-schedules in these houses. This research models these occupant variations, and classifies them using three parameters; the occupancy patterns, the appliance use behavior and the family size. This study compares a ‘low-energy house class 2’ building with a moderate insulation, and a ‘passive house’ with a very tight insulation. The comparison confirms an increase in the significance of the occupant behavior with increasing insulation. Extensive investigation of each parameter on the building gives an interesting insight into the relation of these occupant parameters with the building and the response of its heating system. The building’s net energy needs and the performance of the heating system are directly dependent on the internal gains and the domestic hot water use of the households, and are influenced by the three defined parameters. The study observes that in well-insulated houses, the utilization of both the internal gains and the system losses is largely limited due to the extremely reduced heating periods and the significantly reduced space heating needs. The increasing internal gains often lead to a reduced recovery of the system losses, and reduce the performance of the heating system. Moreover, the distribution losses due to the DHW use increases outside the heating period and also negatively influences the system performance. The research shows that the short-term random temporal variation in the household’s loads, and in the internal gains and DHW use, have no noticeable impact on the heating system performance, but does influence the building’s interaction with the onsite renewable generation, as well as with the grid. This thesis emphasis that neglecting the occupant-related diversity often leads to an unpredicted operation of the energy supply system that is not well-understood and undesirable. A good estimation of the occupants’ diversity is an important factor to correctly design and size the overall heating system. The thesis further emphasizes that the performance of a heating system in well-insulated buildings is strongly dependent on the sub-systems’ design strategies. The study shows the influence of losses from the heat distribution system on the total system performance. These losses can be reduced through proper planning, sizing and placement strategy for the heat distribution systems during early design stage. The research demonstrates that a net zero emission building can offer a large flexibility to the grid, using proper control strategies for the heating system. However, such strategies often reduce the energy performance of the heating system, and considering their application in the overall context is important.