Impact of design and thermal inertia on the energy saving potential of capacity controlled heat pump heating systems

The objective of this study was to develop a dynamic model of hydronic heating systems in order to get a more fair comparison of energy efficiency between continuously capacity controlled heat pumps and intermittently controlled heat pumps than what is achieved with steady-state models. Factors such as thermal inertia, different connection principles, temperature levels and lag times are also considered to see how they affect the comparison and the efficiency. The results show that performance of an intermittently controlled heat pump is reduced when using this dynamic model compared to the static models, whereas the results for a variable-speed controlled heat pump stay the same. Introducing different controller dead bands, thermal inertias, etc. change the result only to a small extent.