Monitoring and energy simulation of a dual source heat pump

This Master's Thesis describes and investigates the behaviour of a building-plant system, both with the use of a dynamic energy simulation and experimentally, through the data collected from the Building Management System. In detail, the main objective is to analyse, after several years of operation, whether the replacement of the ground source heat pump with a dual source heat pump actually generated the desired benefits. The intervention, which took place in 2017, was forced by a serious problem of the ground thermal drift and the consequent deterioration of the ground source heat pump's performance. The solution implemented in 2017 to mitigate thermal drift involves a dual source heat pump. This heat pump consists of a boreholes field, which exploits the ground as a source, and an external air condenser, which exploits outside air as a source. The dynamic energy simulation is performed using the EnergyPlus software based on the two previous Thesis projects. Some EnergyPlus sections are updated since the initial model results aren’t coherent with the data collected. The new adjustments provide a simulation that better reflects the real behaviour of the building-plant system. The simulation results, in agreement with the collected data, demonstrate that, replacing the heat pump and introducing a new heat source, allows the electrical energy savings of approximately 26% for the heat pump. Additionally, these changes completely resolve the thermal drift of the ground. Four parametric analyses are also carried out, as part of the project, to examine the potential impacts and benefits of specific changes on the system's operation. The first parametric simulation demonstrates that the mitigation of the thermal drift is achieved, due to the installation of the external air condenser. However, the reduction in electricity consumption cannot be attributed to the external condenser, but is rather the result of the installation of a high-performance heat pump, which is particularly efficient at partial loads. The second parametric simulation compares the system in its current configuration with a configuration, involving an outdoor air condenser of double size. The results highlight that the current size of the external condenser is optimal for the operation of the system, while an increase in size would result in minimal energy recovery that is not justified by the doubled initial cost. The third simulation analyses three possible switching temperatures. The results indicate that this parameter has a little impact on energy consumption, but has a significant effect on the ground temperature. A lower switching temperature allows greater heat injection, while a higher switching temperature limits heat injection. The fourth and final parametric simulation examines the effect of doubling the airflow of the AHU and increasing the efficiency of the recovery unit. The results point out that this configuration would lead to a more significant thermal drift, which couldn’t be completely corrected even with the introduction of the external condenser. In conclusion, the dual source heat pump is an innovative solution in case of severe thermal drift, since the DSHP mitigates it and allows to enhance the performances.