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Riksbanken, Stockholm. (The Swedish Government Bank in Stockholm)
Reduction of peak demands on electricity grid through utilisation of the buildings dynamic in the operating policy.
The building of Riksbanken is one of many examples on how a lack of knowledge about the laws of nature led to insufficient operating policies for over-dimensioned HVAC. Cooling and heating often worked at the same time and resulted in large peak demands and waste of energy.
We have done this brief of the case to exemplify our experiences. The original investigation is in Swedish and includes a more detailed technical description and the result of the simulations. It is available for publishing in Swedish and further translations, if it is a high demand for it. It is also a very representative case for a majority of office buildings.
BACKGROUND
To "save energy" the HVAC system was normally shut down at the end of the working day. At this point of time, large surplus energy is stored in the building construction. This originate from internal activity sources and the solar radiation. The room temperature is going up fast and high, when the HVAC system shuts down. During the summer, the heat losses are small and the temperature is still high when the HVAC system is started the next morning. The HVAC system then have to lower the temperature (remove stored energy from the day before) and cope with the loads from people, lighting, office equipment, sun radiation, etc., when the office activities starts. Because the low angle of the sun, the solar radiation through windows and the facade, is also highest at dawn and dusk.
If some "individual temperature adjustments" are possible and somebody want to use it by changing thermostat settings, the heating system must be active. This add to energy demand, not only for the heating but also for cooling.
The result of all of the above leads to a large peak demand on the electricity feed. The introduction of more office machines add to the situation. The HVAC system is largely over-dimensioned and can cope with the peak demand, but the local electricity grid have problems in answering to the high peak demand.
Suggestions was made to change to "high voltage feed", to cover the peak demand. Our investigation, with simulations, points to the possibility to avoid this large investment and the rise in consumption. It is a large saving potential, in the construction's capacity to even out variations in temperature. This capacity is normally not used in "modern" office buildings. The normal operating policies starts from a static philosophy and compensate immediately any movement with adding or removing heat.
SUGGESTIONS
We know by experience that temperature changes are slow in a traditional building. We can use this (in the same way as it has been done for hundreds of years) and add energy for heating or cooling when the loads are low. The nature will take care of the temperatures in between. We suggested a comfort definition of temperatures between 21 to 23 degree Celsius, instead of the 21.7 to 22.3 degree Celsius. We also suggested some changes in the construction, to enhance the storage capability.
Summer case:
We suggested to cool down the building during the night, to get rid of the stored energy from the day before. This is also done more effectively, since the lower night temperatures assist in the task. The goal was to have the building at the low 21 degree Celsius in the morning. Prepared to pick up large energy amounts without any temperature rise during the morning hours. The extended comfort definition also added to the time before energy was needed to cool the building and when it was needed, it was at lower levels.
Winter case:
Even during the winter it was a surplus from internal heat sources. The extended comfort definitions allowed storage of this heat and use it to maintain temperatures during nights and weekends. At the close of the working day, the ventilation to the outside was reduced and the temperature was moving slowly to the lower level of the comfort definition for the morning. During a large part of autumn, winter and spring, the need for nights and weekends is covered by the stored heat.
RESULT
The Bank did not need to invest in "high voltage feed" and did not have to implement our suggestions for changes in construction. The only changes needed, was the changes in operating policies. Changes in temperature range and a couple of timers was enough. The simulations was confirmed by measurements with a high correlation. Large savings in consumption was experienced, but not quantified.
The reactions on the new comfort definitions was very positive. Research has shown that the body reacts negatively on fixed temperatures and prefer gliding temperatures.
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