In Situ Measurement of Ground Thermal Properties

Sponsor:  National Rural Electric Cooperative Association
                  U.S. Department of Energy

Investigators:  J.D. Spitler, S.J. Rees

Students:  W. Austin, C. Yavuzturk, N. Jain

Description:  Determination of the ground's thermal conductivity is a significant challenge facing designers of Ground Source Heat Pump (GSHP) systems applied in commercial buildings. The number of boreholes and the depth and cost of each borehole are highly dependent on the ground thermal properties. Hence, depending on the geographic location and the local drilling costs, the ground thermal properties strongly influence the initial cost to install a GSHP system. In order to be able to predict ground  thermal properties, an experimental apparatus has been built capable of imposing a heat flux on a test borehole, and measuring its temperature response. Parameter estimation techniques in conjunction with a two-dimensional numerical model are used to determine the thermal conductivity of the surrounding ground.

The initial development of the apparatus and analysis techniques are described in an M.S. thesis written by Trey Austin. A more refined version of the analysis procedures and some validation efforts are described in a paper published in the ASHRAE Transactions (Austin, et al. 2000)  and in Cenk Yavuzturk's Ph.D. thesis.  Further work aimed at speeding up the analysis procedure is described in Nagendra Jain's M.S. thesis.  Ongoing research is aimed at reducing the amount of time required to make an in situ measurement, reducing the amount of time required to analyze the results, and further validating the methodology. The initial work was funded by the National Rural Electric Cooperative Association. Additional work was funded by the U.S. Department of Energy. Six page summaries of work done in 1998 and 1999 are available here.

Publications:

Trey Austin M.S. thesis

Cenk Yavuzturk Ph.D. thesis

Nagendra Jain's M.S. thesis

Gehlin, S. and J.D. Spitler. 2003. Thermal Response Test for BTES Applications - State of the Art 2001.  9th International Conference on Thermal Energy Storage Warsaw, Poland, September 1-4, 2003,  pp. 381-387.

Beier, R.A., M. Smith.  2003.  "Removing Variable Heat Rate Effects from Borehole Tests". ASHRAE Transactions. 109(2):463-474.

Beier, R.A., M. Smith.  2003. "Minimum Duration of In-Situ Tests on Vertical Boreholes". ASHRAE Transactions. 109(2):475-486.

Witte, H.J.L., G.J. van Gelder, J.D. Spitler.  2002. In Situ Measurement of Ground Thermal Conductivity: The Dutch Perspective.  ASHRAE Transactions. 108(1):263-272.

Spitler J.D., C. Yavuzturk and S.J Rees.  2000. In-Situ Measurement of Ground Thermal Properties. Proc. of TERRASTOCK 2000, Stuttgart, August 2000. Vol. 1, pp. 165-170.

Austin, W., C. Yavuzturk, J.D. Spitler. 2000. Development Of An In-Situ System For Measuring Ground Thermal Properties. ASHRAE Transactions. 106(1):365-379.

Spitler, J.D., S.J. Rees, C. Yavuzturk. 1999. More Comments on In-situ Borehole Thermal Conductivity Testing.  The Source. Vol. 12, No. 2, March/April 1999. pp. 4-6.