The building sector makes up 40% of the total energy use in Norway. That is why policy makers aim to encourage the construction of buildings and neighbourhoods that are significantly more energy efficient. However, in the operational phase of those energy efficient buildings, the consumed energy appears to be higher than the design paperwork anticipated. Why is that?
When we stay home, we tend to open windows, switch the lights on and off, run electric appliances and use hot water as we like or prefer. This is normal human behaviour, and it can result in a real energy performance being different than the planned energy performance. In our study, a high performance dwelling (an energy efficient demo house in Larvik with energy efficient appliances and local renewable energy production) is analysed by using simulation tool IDA-ICE. The aim of the analysis is to compare the proposed standard values for light use, temperature levels, domestic hot water use, and ventilation air volume rates with real values. In our study, we compared the standard requirements and input data recommended by Norwegian building regulations to people’s actual energy behaviour. The real occupant behaviour parameters are obtained from the literature review and studies explaining occupant behaviour. For the analysis of the building’s electricity grid interaction, two parameters are used: electricity grid stress and the annual energy balance reliability.
What is electricity grid stress?
The grid stress is used to describe stress put on the electricity grid by the power mismatch. This means to describe the grid stress caused by the bigger electricity generation from the PV than the building demand. The power mismatch is measured as the difference between the PV generation and the total building electricity use. A larger grid stress value presents heavier stress on the electricity grid caused by the building. For example, in summer months, the PV generation from a zero emission building (ZEB) will be much higher than the electricity demand. In the case that all this electricity is exported to the grid, it will cause a high grid stress and it is not desirable.
The grid stress describes stress put on the electricity grid by the bigger electricity generation from the PV than the building demand.
What is the annual energy balance reliability?
The annual energy balance reliability is calculated as the ratio between the total generated electricity from the photovoltaic panels (PV) and the total electricity use of the building. If the building is designed to be a zero energy building, this ratio would be 1 on an annual basis. However, in the operation phase, due to different building use and occupant behavior, this parameter may be different than 1. In the case when this is lower than 1, it means than a building is using more electricity than it is producing.
How occupants influence the building performance and the electricity grid interaction?
The deviation between standard and actual energy use is particularly problematic when dealing with energy efficient buildings, and e.g. zero emission buildings (ZEBs), as the relative deviation (in %) between predicted energy demand from standard values and real values will most likely be higher than for a low performing building.
The results of our study show that the change in occupant behavior resulted in electricity grid stress variance from −5% to +13% compared to the reference case based on the standard values. The results showed that the occupant behavior might change the annual energy balance reliability by 20%. Therefore, it is highly important to have detailed occupancy models for precise energy use prediction in high performance buildings.
The change in occupant behavior resulted in electricity grid stress variance from −5% to +13%
The energy balance reliability may be calculated on monthly and annual basis. For an overall estimation, it may be enough to consider the annual value of the energy balance reliability. However, observing the monthly values of the energy balance reliability may give a better picture on the buildings energy performance. For example, in winter months, this parameter is very low, around 0.2, while in the summer months, it is higher than 1 and almost approaching 2. A low value of this factor means that a building is using electricity from the grid. A high value of this parameter means that a building is exporting electricity.
A detailed analysis of the introduced factors with considering occupant behavior may help better sizing of the high performance building energy supply systems and electricity batteries.
Contact ZEN Centre