Master's Thesis Peer Permien


Implementing and generation of a comparative study of two hybrid heat pumps

For the reduction of greenhouse gas emissions of the building sector, heat pump technology has the potential to be a key technology. It is estimated that three-quarters of the energy used in the heating sector can be attributed to the existing building stock. Especially air heat pumps are suitable to be integrated subsequently into existing buildings. However, in the course of a building renovations, the heat transferral system is barely changed. A comparatively low efficiency at low outside temperatures, as well as at high flow temperatures require an over-dimensioning of the air heat pump in monovalent operation mode. One possible solution is a combination of an air-heatpump and a conventional generator, e.g. a gas condensing boiler. These so-called hybrid heat pumps consist of already commercially available components and are also offered as complete systems by various manufacturers. However, large differences between the individual concepts still exist due to the low degree of technological maturity, as well as hardly any long-term experience during actual operation. The objective of this study is to compare two different hybrid heat pump systems, the TzerraHP 690-5 by Remeha and a Vitocaldens 222-F (A26) by Viessmann. It is to be determined which annual workloads are achieved by these systems in real operation and what differences exist between the systems. For this purpose, experiments are carried out with both hybrid heat pumps on a hardware-in-the-loop test bench using the typical-day method. The HiL test bench, wich is designed for heat pump experiments, is therefore retrofitted for the hybrid systems. Both hybrid systems are successively testet with an economic and an ecological control strategy. For the evaluation of the results the energy efficiency, the heat retention costs and the primary energy consumption of the hybrid systems are compared. Here the Vitocaldens achieves the lowest primary energy consumption with 0.92 kWh of useful heat generated per kWh of PE. The influence of the control strategy is 40% higher in the Vitocaldens than in the TzerraHP with 20%. By contrast, the annual operating costs of the systems hardly differ. The heat production costs for both systems are 8.4ecents per generated kWh of useful heat. The shared load of the heat pump in the total heat generation in both systems is at about 0.2 with the economic control strategy and can be increased to more than 0.7 with the ecological control strategy. For the TzerraHP, the heat pump has practically no share in the hot water preparation. The cause of this can be identified in the plant concept. In addition, both systems do not achieve the expected energy efficiency values, which points to an optimization potential of the hybrid systems.​