Technico-economic modelling of ground and air source heat pumps in a hot and dry climate

Abstract

In a hot and dry country such as Saudi Arabia, air-conditioning systems consume seventy per cent of the electrical energy. In order to reduce this demand, conventional air -conditioning technology should be replaced by more efficient renewable energy systems. These should be compared to the current standard systems which use air source heat pumps (ASHPs). These have a poor performance when the air temperature is high. In Saudi Arabia, this can be as much as 50 °C. The purpose of this work, therefore, is to simulate and evaluate the performance of ground source heat pumps (GSHPs) compared with systems employing (ASHPs). For the first time, both systems were comprehensively modelled and simulated using the Transient System Simulation (TRNSYS). In addition, the Ground Loop Design (GLD) software was used to design the length of the ground loop heat exchanger. In order to assess this configuration, an evaluation of a model of a single story office building, based on the climatic conditions and geological characteristics that occur in the city of Riyadh in Saudi Arabia was investigated. The period of evaluation was twenty years in order to determine the Coefficient of Performance (COP), Energy Efficiency Ratio (EER) and power consumption. The simulation results show that the GSHP system has a high performance when compared to ASHP. The average annual COP and EER were 4.1 and 15.5 for the GSHP compared to 3.8 and 11 for the ASHP respectively, and the GSHP is a feasible alternative to ASHP with an 11 years payback period with an 18% total cost saving over the simulation period and 36% lower annual energy consumption. The TRNSYS model shows that despite the positive results of the modeling, the high rate of the underground thermal imbalance (88%) could lead to a system failure in the long term