The Renewable Energy House obtains its complete heating and cooling requirements entirely from renewable energy sources. Using a combination of biomass (wood pellets), solar thermal and geothermal energy, the heating, cooling and ventilation system generates high standards of comfort in the whole building throughout the year. The Renewable Energy House thereby demonstrates that 100% renewable heating and cooling is feasible in a large proportion of Europe’s buildings.
The Renewable Energy House is a 120-year old building, located close to several tall buildings. Therefore, it is a less-than-ideal starting point for the integration of renewable energy and solar technology in particular. If 100% renewable heating and cooling can be comfortably achieved in these conditions, state-of-the-art technologies, when applied to new buildings, can achieve “energy positive houses” that produce more energy than they consume.
Key elements of the renewable heating and cooling system in the Renewable Energy House:
80 kW biomass wood pellet boiler
42 kW (60 m2) solar thermal collectors
4 geothermal energy loops (115 m deep) exploited by a 25 kW ground source heat pump in winter and in summer, used as a “cooling tower” by the Thermally Driven Cooling Machine
A 37.5 kW Thermally Driven Cooling Machine (TDCM)
Heating - Winter operation
In winter, the heating system mainly relies on the biomass (wood pellet) boiler and the geothermal system. The biomass boiler heats the radiators of the main building. The radiators in the back building are heated with energy extracted by the heat pump from the four geothermal energy loops located under the main courtyard. The solar thermal system and biomass boiler heat the same storage tank. Due to shading from neighbouring buildings, the “sunlight” solar thermal contribution is low in winter. However, all the “daylight” solar gains in winter will minimise the consumption of wood pellets. During this season, the geothermal system operates on a separate circuit from the biomass and solar circuits.
Cooling - Summer operation
The core of the cooling system is the Thermally Driven Cooling Machine. While conventional cooling machines consume high amounts of electricity at peak demand times, this thermally driven cooling machine is powered from relatively low temperature heat (80° C) and a small amount of electrical power for the control and pumping circuits. The thermally driven cooling machine used in the Renewable Energy House obtains its heat energy from the solar system which is backed up on cloudy days by the biomass boiler. Since solar radiation levels and cooling demands coincide, the solar thermal system is able to provide much of the heat required by the cooling machine. Solar cooling is an ideal application for a solar thermal system. The solar heat coming from the collectors is released by the thermally driven cooling machine as low-grade excess heat. In most conventional cooling systems of this type, the excess heat is dispersed into the environment through a cooling tower. Such cooling towers have a visual impact and can also add to the ambient temperature in densely populated urban environments. In the Renewable Energy House, the geothermal borehole loops function as a seasonal energy source, absorbing the excess low-grade heat during the summer months so that there is no need for a cooling tower. Through the winter operation of the geothermal system, year-on-year overheating of the boreholes is avoided.
