Optimisation Of Inter-Seasonal Ground Source Heat Pumps With Predictive Behavioural Control

In practice, heat pumps (HP) often do not perform as expected. This is due to many factors such as how well the system and the ground loop are designed, installed and subsequently maintained and how well they are operated and controlled in the field. Improving overall system design and demonstrating increased HP performance and higher reliability are core objectives for this research. Performance instability and variations in ground source heat pump (GSHP) system output has been observed previously and this indicates that detailed research is required for example (i) to identify the relationship between dynamic performance and seasonal ground temperature patterns, (ii) to address the operation, installation and control opportunities that arise from (i). This project investigates all of these issues. This thesis focuses on the monitoring of the long-term operation of a 500 kW installed GSHP system with the aim of understanding and establishing the current trend performance characteristics of the installation. The research involved combination of experimental measurements and analysis, mathematical simulation and the development of an empirical transient model that could be generally applied. Despite the importance of the effect of ground temperatures on performance, relatively little data has been published on the effect of disturbed underground temperature distributions. The author has therefore developed a novel mathematical model for the analysis of disturbed ground temperatures over time. The novel mathematical model developed has been used to predict the disturbed seasonal underground temperatures based on daily fluid and air temperature data and has been validated against real historical data. It was concluded from the critical literature review that the dynamic long term performance investigation of GSHP systems using transient models is not well understood. Therefore the work described in this thesis has focused on the development of a generic empirical transient system model of a GSHP system. This model has been developed using TRNSYS 17 software. This has permitted investigation of the effects of different control strategies using a dry air cooler (DAC) for heat rejection, energy consumption of the HP, the overall performance of the system and ground temperature variations. The main novelty and contributions to science from this work is:  The better understanding of the effect of ground temperature variation over time and its effect on the system’s performance.  The development of new measurement methods for assessing system performance.  The use of ground temperature in the prediction and control of system performance, together with an analysis of the effects of specific interventions or control methodologies.  The development of a novel mathematical model for predicting disturbed ground temperature.  The development of a novel GSHP model using TRNSYS.  The development and investigation of novel control strategies using DAC.