Improving the Traditional Heat Pump System Control through Prediction of Daily Solar Radiation

Heat pump systems represent a well-established technology that has been growing in the last decades, reaching a mature technical development. In parallel, a new perspective for improving the efficiency and flexibility of heating and cooling systems has been rising thanks to the availability of cost-effective and powerful controller units. The computational power of electronic devices has been increasing in the last decades, together with storage and connection capability, and there has been a growing interest in the possibility of introducing advanced features in heat pump system controllers. The Swedish EffSys Expand project P18, “Smart Control Strategies for Heat Pump systems”, evaluated several methods that can be potentially implemented in the controller of heat pump systems in order to increase the overall energy efficiency while guaranteeing indoor comfort conditions.

This article presents a short description of one of the solutions proposed, considering the improvement of the traditional control approach for heat pump systems through the prediction of the daily solar radiation. The traditional and basic control approach for heat pump systems in residential buildings is based on the calculation of the supply temperature to the heating distribution system based on the outdoor temperature. The approach is based on the idea that, for a given outdoor temperature, a supply temperature can be defined to balance the building heating demand in order to guarantee an indoor temperature that corresponds to the thermal comfort conditions. In Sweden, a large portion of the heat pump installations for residential buildings consider the heating curve as the only input for the system controller. Solar radiation and occupant activities, for example, represent energy gains that can affect indoor temperature stability and thermal comfort. The adjustment of the heating curve based on additional inputs has been considered in project P18, and the results of an improvement potential study have been presented.

In principle, the prediction of the daily solar radiation would allow the heating curve to be adjusted to avoid, for example, the overheating of the indoor environment and, at the same time, reduce the energy consumption of the heating system. The clear sky radiation represents the maximum radiation that can be available at a given time and can be calculated considering the relative position of the sun to a given location. In project P18, a method to predict the daily solar radiation based on the prediction of the attenuation of the clear sky radiation was developed and implemented in simulation models of single-family house heat pump systems. The results show that the modulation of the heating curve through predicting the daily solar radiation allows monthly energy saving higher than 10% in some cases. It is very important to mention that no additional sensors are required for the implementation of this control strategy. In particular, no direct measurement of solar radiation is required, and no hardware modifications of the system are needed.

Davide Rolando and Hatef Madani, KTH Royal Institute of Technology, Sweden.
The text has been shortened by the HPC team

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