Simulation of borehole configurations
Deciding a borehole configuration (numbers, depth, spacing, geometric form), given demands on heating and cooling, has to be done with computer software simulating the behavior and response of the borehole field, or BTES (Borehole Thermal Energy Storage)..
The most used and most advanced software for this is currently Earth Energy Designer (EED), developed by the same people that established the science around BTES (GSHP, geoenergy etc), mostly, at the University of Lund in Sweden in the late 80-ties and 90-ties.
Earth Energy Designer
EED is built on entering a large number of relevant parameters; properties of the rock, undisturbed ground temperature, type and size of heat exchanger, type of fluid used in the heat exchanger, load of heating and cooling, maximum power of heating and cooling, duration of maximums and a number of other parameters.
Some of the parameters is only possible to know with accuracy after a Thermal Response Test (described here) is performed, but an EED-simulation can be performed anyway by giving this parameters some arbitrary values, typical for the type of rock expected to be found in the area. Of course this means that the level of precision of the simulated model is much lower.
An important parameter is the COP (Coefficient Of Performance), the efficiency of the Heat Pump (or reversed Heat Pump). E.g. a COP of 4 means that one unit of electricity will give four units of heat (or cold). In EED the term SPF (Seasonal Performance Factor) is used instead which simply is the average COP over a year.
When all relevant parameters are entered in EED simulation two constraining factors must be known.
The first constraining factor is in what temperature range the fluid in the heat exchanger must be. E.g. the working temperature interval of the Heat Pumps or, as sometimes is the case, the maximum fluid temperature for free cooling. Going outside of this boundaries means the Heat Pump will not reach the COP aimed for or, in extreme cases, even cease to work.
The second constraining factor is, possibly, the surface space available. The size of the available surface area for placing the BTES can constrain the spacing between the bore holes and the geometric shape of available area can decide the geometrical shape of the BTES at the surface (square, L-shaped, U-shaped, rectangular etc). Even without physical constraining a certain spacing and geometric shape can be decided upon for e.g. facilitating drilling and implementation of the BTES.
Given the parameters and the constraining factor the EED can be run until a reasonable result is produced.
EED can simulate the situation up to a hundred years forward but normally 20 to 30 years is simulated.
Among other things the output can be used for Creating a drilling plan.