30 May 2005

STATUS OF DESIGN TOOLS FOR GROUND-SOURCE HEAT-PUMP SYSTEMS

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Design tools for ground-source heat pumps (GSHP) trace their history back to the period
after the first horizontal loop installation in 1945. Simple engineering formulas have evolved to
user-friendly design software and detailed simulation models for the dynamic interaction between
complete energy systems, internal heat sources, and weather conditions.
The quest for reliable and sustainable long-term operation, improved efficiency, and reduced
costs has led to a development of more elaborate descriptions of system components: ground
properties, borehole heat exchanger, ground loop layout, hydraulic coupling of loop field,
circulation pumps, and heat pumps. Heat conduction is usually the main heat transport mode in
the ground, but the influence of regional ground water and natural convection has also been
assessed. Analytical methods and advanced numerical methods for the thermal performance of
GSHP have been compared and validated with numerous field tests. The use of in-situ thermal
response tests has been important in determining the critical design parameters for the ground and
to assess the borehole thermal resistance, which has also been studied theoretically and in the
laboratory.
The paper treats the current status of GSHP design tools. The knowledge of system
components and in-situ techniques to obtain necessary ground properties makes it possible to do
reliable simulations of GSHP system performance for both domestic and commercial
applications. The future challenge for GSHP designers is to use these tools to find the optimum
system configuration and control in different situations.