Renewable energy for passive house heating: II. Model

The evaluation of renewable energy used to increase the environmental friendliness of passive houses (PH) is the topic of this paper. A time-dependent model of passive house thermal behavior is developed. The heat-transfer through the high thermal inertia elements is analyzed by using a 1D time-dependent conduction heat-transfer equation that is solved numerically by using a standard Netlib solver (PDECHEB). Appropriate models for the conduction through the low thermal inertia elements are used, as well as a simple approach of the solar radiation transmission through the windows. The model takes into account in a detailed fashion the internal heat sources. Also, the operation of ventilation/heating system is described and common practice control strategies are implemented. Three renewable energy sources are considered. First, there is the passive solar heating due to the large window on the façade oriented south. Second, the active solar collectors system provides thermal energy for space heating or hot domestic water preparation. Third, a ground heat exchanger (GHE) increases the fresh air temperature during the cold season. The model was applied to the Pirmasens Passive House (Rhineland Palatinate, Germany). The passive solar heating system provides most part of the heating energy during November, December, February and March while in January the ground heat exchanger is the most important renewable energy source. January and February require use of additional conventional energy sources. A clever use of the active solar heating system could avoid consuming classical fuels during November, December and March. The ground heat exchanger is a reliable renewable source of energy. It provides heat during all the day and its (rather small) heat flux is increasing when the weather becomes colder. The air temperature at heater exit is normally lower than 46 °C. This is a good reason for the use of renewable energy to replace the classical fuel or the wood to be burn in the heater.