Energy Flexibility Characterization of Norwegian Residential Buildings Heated by Direct Electricity
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The objective of this thesis is to evaluate the energy flexibility that Norwegian residential buildings can provide to the electricity grid, by applying rule-based control (RBC) strategies. Aspects that are assumed to influence the energy flexibility, such as the impact of internal heat gains and occupants preferences concerning thermal zoning of bedrooms are to be evaluated. The literature study showed that the energy flexibility is an ongoing area of investigation and there is currently no standard metrics to identify a buildings potential to offer flexibility. However, many studies have investigated the topic by applying RBC strategies, and some general properties to describe the buildings ability to offer flexibility exist. Besides, as the building stock gradually moves towards a more energy efficient standard, the impact of internal heat gains (IHG) is becoming increasingly important. However, realistic IHG profiles are difficult to model and several modelling approaches exist. In addition, the relevant literature demonstrates that there is a high level of dissatisfaction with too high bedroom temperatures in passive houses and that it is difficult to achieve this, due to a desire for higher temperatures in the rest of the building. Two different RBC strategies have been applied to evaluate the flexibility potential using the detailed dynamic simulation tool IDA ICE. Both control strategies adjust the set-point temperature (SPT) on the direct electric space heating system. One control strategy is based on a schedule for pre-defined peak hours (OPCS) and the other is based on the spot price (SPCS). Four different building types with different levels of insulation and construction modes are investigated. Overall, both RBC strategies showed potential for shifting the power and consumption use to off-peak hours for all the evaluated building types. The potential for shifting the power and energy consumption is higher for the highly insulated buildings, but the magnitude is much more significant for the less insulated buildings. Different IHG profiles have been evaluated in the context of energy flexibility. The results show that the timing of IHGs is important, especially for the highly insulated buildings. The results with a stochastic IHG profile distributed in both time and space achieved the largest potential for energy and power shifting, and this indicates that the flexibility potential might be under-estimated when modelling the IHGs according to the current practice. This is also supported by the aggregated result of 20 buildings with different stochastic IHG profiles. The type of radiator control is found to have an impact on the flexibility potential at a building level. However, when investigating several buildings together, the results indicate that the more predictable behaviour with proportional control can be used to describe the behavoiur of several buildings with thermostatic control. The increase of bedroom temperatures due to the implemented RBC strategies and IHGs is most significant for the highly insulated buildings. The influence of the RBC strategies on the bedroom temperatures is found to be largest in the colder months, as the impact of the IHGs becomes more dominant with lower heat loss from the building envelope. By decoupling the bedrooms from the RBC strategies, the temperatures are improved, but the improvement is dependent on the internal constructions of the building. Moreover, the flexibility potential is reduced by decoupling the bedrooms.