COMBINED HEATING AND VENTILATION SYSTEMS FOR LOW-ENERGY RESIDENTIAL BUILDINGS; OPTIMIZATION OF ENERGY EFFICIENCY AND USER COMFORT

Combined heating and ventilation systems are applied here in highly energy-efficient residential buildings to save construction cost. Combining a Heat Pump with a Heat Recovery Ventilation system to heat and cool the building offers faster response times, a smaller footprint and an increased cooling capacity, compared to floor heating systems. As a result, such systems are expected to have a larger market share in the future. The available research on Ventilation Based Heating systems focuses mostly on comparing Exhaust Air Heat Pumps with conventional systems in energy-efficient buildings. The majority of published research neglects the usual existence of electrical backup heaters as well as the need to develop and use an adapted and optimized control strategy for such systems. This work compares the energy efficiency of the common-standard ventilation-based heating concepts including Exhaust Air Heat Pumps with the conventional floor heating systems using single room control strategy to achieve similar user comfort. The comparison is carried out in a simulation environment in order to optimize the systems under exactly reproducible boundary conditions. Additionally, two field tests were performed to achieve a better understanding and validation of the simulation models. The measured data was used to model the dynamic behavior of the Exhaust Air Heat Pump and the air distribution system. These field tests revealed that the overall run time and heating output of the heat pump were much lower than expected. This was the motivation to investigate and optimize the heat pump and electric heater control strategy. It could be demonstrated that the applied control strategy has a significant impact on the overall performance of the system. The suggested control strategy was tested and validated in a third field measurement. Based on the gained knowledge using the system simulation tool and the conducted field tests, an improved second concept for Ventilation Based Heating systems was defined with three optimization steps. It could be demonstrated that using the suggested methodologies in the hard- and software of such a system, can significantly improve its overall efficiency. However, Ventilation Based Heating systems cannot compete with floor heating systems in terms of total system energy efficiency, due to the necessity of electrical backup heaters and due to the higher supply temperatures.