Low Energy House, Biomass Boiler, Building Simulation, Control Strategy, Comfort
The aim of this work is to analyze the energetic performance of a low energy house, situated in the region of Lower Austria (48° 11’ N, 15° 5’ E), by means of dynamic building simulation and on-site monitoring. According to the Austrian regulations, the annual heat demand of a low energy house is below 50 kWh•m2•yr-1. The building under study is a pre-fabricated house manufactured by an Austrian company. It has highly insulated walls made of lightweight materials and triple glazed windows. Indoor air quality is ensured by a ventilation system equipped with a heat recovery unit. The living space is heated by a 6 kW pellet boiler supplying hot water to a floor heating system. The house, inhabited by two people, is currently monitored in the frame of the BioMaxEff project, a European project aiming at the demonstration of biomass boilers in real life conditions. Parameters describing the boiler operation (water flow rate, inlet and outlet water temperature, pellet consumption etc.) as well as outdoor and indoor temperatures are registered continuously during the whole heating season. A coupled simulation of the building and its energy systems has been performed in a dynamic simulation environment (TRNSYS). First, the building envelope and the internal heat gains have been analyzed to calculate the annual heat demand, the annual peak load and the duration of the heating season. Second, the heating system has been added to simulation, including all its components and its control unit. The boiler has been simulated with the “Type 869” boiler model, which describes accurately the performance of pellet boilers. The model has been calibrated and validated with reference to laboratory data and successively integrated in the TRNSYS simulation. A new TRNSYS component has been programmed to simulate the heating system control unit, according to the specifications of the manufacturing company. Interviews with the house owner informed about the settings of the control strategy. Simulation results reveal that the boiler is slightly undersized and cannot completely fulfil the heat demand of the house. Moreover, the settings imposed in the heating system control unit are not adequate to maintain a comfortable indoor temperature during the whole day. These results have been confirmed by the data registered during on-site monitoring. To conclude the study, some improvements of the system control strategy have been proposed. In particular we suggest to adjust the system’s heating curve and the night setback temperature. By taking advantage of the thermal inertia of the floor heating system, the new control strategy improves the indoor comfort.