In English

Response testing and evaluation of groundwater-filled boreholes. Development and validation of a new caculation tool.

Helena Nakos
Göteborg : Chalmers tekniska högskola, 2011. Examensarbete - Institutionen för energi och miljö, Avdelningen för installationsteknik, Chalmers tekniska högskola; 2011:18, 2011.
[Examensarbete på avancerad nivå]

Ground source heat pump, GSHP, systems are an interesting alternative in the energy sector compared to other heating and cooling systems due to the fact they are considered to be energy efficient technologies. The use of GSHP systems, in comparison to the use of more conventional cooling and heating systems, could result in a decrease of emissions according to the U.S. Environmental Protection Agency, EPA. The design of a ground source heat pump system will depend on the ground thermal properties. These properties include ground thermal conductivity, borehole thermal resistance and the undisturbed temperature of the ground. These properties are commonly estimated from in-situ thermal response tests, TRTs. Numerous methods have been developed to evaluate the experimental data obtained from thermal response tests. This Master's Thesis presents a comparison of some of the commonly used methods for the evaluation of ground thermal properties. A new method has also been presented to evaluate experimental data obtained from TRTs. The method is based on mathematical models developed by Javed and Claesson and considers the thermal capacities, resistances and properties of all the borehole elements. The new method has been programmed in the software MATLAB and has been compared to the existing methods. The evaluation of these methods have been performed using experimental data obtained from dierent in-situ TRTs. The TRTs have been performed both for single and multiple injection rates, in increasing and decreasing injection modes. The estimated ground thermal properties have then been used to model a GSHP system where the size of the system obtained from the dierent methods have been compared to each other. The GSHP systems have been modeled in the software, Earth Energy Designer, EED. The results show that the existing methods give similar results when the evaluation is performed for single injection rates. This is also true for the new method. The multiple injection rates in increasing mode gave similar results as the values estimated from the single injection rates. The multiple injection rate performed in decreasing mode showed that the existing methods give inconsistent results of the ground thermal properties. The new method however, gave more consistent results. The EED calculations showed that the borehole lengths obtained from the new method can be compared to the existing methods already used today and that the borehole length variations between the methods do not vary more than 10 % from each other. Javed et al. observed that uncertainties of this magnitude can be expected in this type of comparisons. The analysis in this Master's Thesis have showed that the new TRT evaluation approach can be compared to the existing methods already used today. The new method show good evaluation properties for multiple injection rates compared to the existing methods since they can have problems with the evaluation of groundwater-lled boreholes. Besides the results of the comparison a software tutorial is presented of the new evaluation method.

Nyckelord: Borehole heat exchanger, Borehole thermal resistance, Ground source heat



Publikationen registrerades 2011-10-28. Den ändrades senast 2013-04-04

CPL ID: 147851

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