Mapping the performance of reversible air-to-water heat pump for improving energy savings estimation in energy flexibility scenarios

Reversible heat pumps are key technologies for the decarbonization of space heating and cooling in buildings. Considering the ongoing research on these technologies, it is important to build models that better describe heat pump operation when installed in the field, allowing for a more precise estimation of energy savings. Most studies are usually based on models that reproduce heat pump operation at part load by correcting factors taken from Standards or catalogs. The risk of incorrectly estimating the achievable energy savings is therefore real, as is the adoption of physically unfeasible operating strategies. The present study compares an approach based on correcting factors, with a more complete one in which both the thermodynamic model and control are considered. For an office building in the Mediterranean region, the performance of an air-to-water heat pump is evaluated using both approaches during the entire heating and cooling seasons and in the case of a demand response event. The results show that the typical approach leads to a large variation in estimated performance in the case of low demand with a percentage variation of more than 50%. In addition, about 15.3% overestimation in carbon dioxide emissions is found. In the case of a demand response event that involves reducing the temperature setpoint of the heat pump, disregarding the controller's action could lead to a significant underestimation (from 65% up to 118%) of the achievable energy savings. Additionally, the integrated approach revealed a compressor overcycling in the case of controller dead-band variation (more than 12 compressor cyclings in one hour), which could not be detected by a simplified approach. This study confirms the importance of including a more comprehensive modeling of heat pumps in energy flexibility studies to obtain more accurate estimate of the achievable energy and environmental impacts.