The aim of this work was to investigate the effect on horizontal ground heat exchanger performance of changing soil and load parameters, and pipe horizontal separation distance for ground-coupled heat pumps under Egyptian conditions.Egypt possesses a variety of energy resources; namely fossil and renewable. The amount of renewable energy available is significant and must be utilized perfectly for the sake of achieving sustainable use of energy resources. Soils in Egypt vary widely from being clay with its thermal conductivity of 1.11 (for clay particles) to sand with its thermal conductivity of 5.77 (for sand particles). Two soil samples were chosen from the literature to be used in the investigation held in this work with boundary conditions that match the weather and ground temperature distribution conditions in Egypt.Conduction heat transfer in soils is a very complicated process especially when it is combined with time dependant boundary conditions and temperature dependent thermophysical properties of the medium. A MATLAB code was used to estimate thermophysical properties of the soil samples with three different moisture contents (0, 0.2, and saturation %) and the upper boundary condition bases on two surface dryness conditions (dry and wet). The results of the code were fed to Abqaus/CAE to analysis and predict the temperature distribution in these soils with implementing the time dependant boundary conditions to investigate the ground thermal behaviour of these soils. Also the temperature distribution around two pipes per trench of horizontal ground heat exchanger with applying synthetic load based on estimated cooling and heating degree days for one set of weather conditions. The horizontal separation distance between pipes was investigated by changing it to be 0.2, 0.3, 0.4, and 0.5 metres.Both the MATLAB code and Abaqus environment were validated against measured data published in the literature and their results agreed well with this data.The results of the simulation showed that the ground thermal behaviour depends mainly on the boundary conditions applied on the model. Dry soils are the worst being affected by the variation of the boundaries, because of its low volumetric heat capacities. The moisture content in the soil should be kept around 0.2 or above to get the most benefits from the presence of moisture in the vicinity of ground heat exchangers. The effect of the soil surface dryness is less significant than that of the moisture content of the entire system but it is more controllable than the moisture content. Also it was found that the horizontal separation distance (HSD) between pipes must be selected on the bases of prior knowledge of the site parameters soil type and moisture level. The results showed that the 0.4m HSD is the optimum HSD for the conditions and load profile included in this study.
|Date of Award||1 Aug 2013|
- The University of Manchester
|Supervisor||Rodger Edwards (Supervisor) & Jonathan Dewsbury (Supervisor)|
- horizontal ground coupled heat pumps
- Egyptian weather condition
- soil thermophysical properties