Sensitivity analysis of a vertical geothermal heat pump system in a hot dry climate

Ground source heat pumps (GSHPs) are considered to provide very efficient air conditioning systems, and this assists in achieving sustainability goals as well as reducing electricity consumption and carbon emissions. The design of such systems, however, depends on the climatic conditions and the geological characteristics of the site; in practice, the optimum design of the system also depends on the characteristics of the surrounding soil. The majority of the research into GSHPs has been focused on cold regions, thus this work is a very useful reference and important in GSHPs’ design in Saudi Arabia and therefore in other hot and arid regions.

For the first time in such a hot/dry climate, a rigorous sensitivity analysis method applying the Ground Loop Design software has been employed to analyse 12 parameters that most affect the behaviour of the system. It is concluded that the most important four design parameters are the: thermal conductivity, soil temperature, building load, and fluid flowrate. On increasing these values they have opposing effects on arid environmental conditions, such as those found in the city of Riyadh in Saudi Arabia.

In addition, the near-optimum design of a GSHP system in the city of Riyadh in Saudi Arabia has been investigated. The temperature of the water entering the heat pump is an adjustable factor that determines the performance of a GSHP unit. Because of the coefficient of performance of the heat pump, it can also be measured by the value of the entering water temperature. Thus, the entering water temperature (EWT) was selected to be the performance measure of the system, as all the heat transfer processed between the ground heat exchanger components and the surrounding soil is manifested in the entering water temperature. The value of the EWT was fixed both at the baseline and in the proposed design systems, and these were tested over the lifespan of 20 years. The results showed that the length of the ground heat exchanger and power consumption in the proposed design could be reduced by 15% and 1.12% respectively, compared to the baseline system. These results can be used to simplify the design of buildings in similar arid regions worldwide.