A mathematical model study was made to compare simulated soil temperature variations with a field situation. The study involved the use of two plots, one of which was cleared of all vegetation and the other left in its natural vegetative state. Each plot was watered at the beginning of three different trial periods and as drying occurred, the following atmospheric parameters were measured on an hourly basis: incoming solar radiation, air temperature, relative humidity, cloud cover, and wind speed. The above parameters provided input for solution of the energy budget equation to determine soil surface temperature variation. Using the soil surface temperature variation as an upper boundary condition, and assuming heat movement by conduction, the temperature at 5 cm increments down to 70 cm in the soil was calculated. The two plots provided model testing for a bare soil surface and also for a soil surface beneath a 30 percent and a 40 percent plant cover. Actual and calculated temperature difference was in most cases less than 2°F. The mathematical model is applicable to any area where the above parameters may be monitored.

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No / There is an increasing interest in the use of Ground Source Heat Pumps (GSHPs) as a source of renewable energy in temperate countries. GSHPs coupled with buried heat collectors can harness the thermal energy from near-surface soils to provide the heating required for domestic properties. The performance of a GSHP system depends greatly on the thermal conductivity of the surrounding soils. Near-surface soils undergo cycles of drying and wetting due to, for example, the infiltration of rain water and/or fluctuations of the ground water table. Several parameters - including the properties of soil, suction head and saturation history - affect the thermal properties as well as the retention and flow of water. This paper presents results from a comprehensive laboratory investigation on sand samples with markedly different grain size distribution. Simultaneous measurements of thermal and hydraulic properties of the sands were taken under incremental increase/decrease in the suction head values to simulate cycles of drying and wetting. The results clearly suggest that the thermal conductivity is better expressed as a function of the matric suction head so as to reflect the saturation history. There has been almost five-fold increase in the measured value of thermal conductivity when the soil was wetted to a residual degree of saturation from being dry.

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published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering

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