Welcome to the sixth part of the course ‘Design borefields with confidence’.
Summary of part 5
In the last part of the course, the focus was on using all the knowledge we had gained so far to carry out some sensitivity analyses and see for ourselves how even small design changes can have a significant impact on the final result.
In Part 5.1, the seemingly simple question, ‘Which is better: the single or double U tube?’, was discussed from a thermal perspective. By investigating the effective borehole thermal resistance for different situations, the conclusion was that there is no definitive answer to this question. It turns out that, depending on the choice of grout, antifreeze, flow rate and even whether you are designing for peak heating or cooling, one can perform better than the other.
In Part 5.2, the same question was investigated, but this time from a hydraulic perspective, looking at the pressure drop. Here, it was clear that, for the same pipe diameter, the double U tube always performs better and that a larger pipe diameter also always results in a lower pressure drop for the same number of pipes. However, when comparing single and double U tubes with different diameters, there was again no definitive answer to this question.
In Part 5.3, the importance of working with the actual borehole coordinates was discussed. Typically, borefields are designed using standard configurations, such as a rectangle, but in reality they can differ significantly. Therefore, it was shown that designing with the actual borehole coordinates can significantly change your design. Since it is relatively easy to draw coordinates on a map in GHEtool or import them from an AutoCAD drawing, it is highly recommended to design in this way to obtain the most accurate result.
In Part 5.4, the focus was on imbalance, the yearly heating up or cooling down of the ground. Given a certain load profile, imbalance is a fact of life and we have to cope with it. In this chapter, mitigation strategies such as increasing the borehole spacing or decreasing the effective borehole thermal resistance were discussed. It was also shown that adding extra boreholes is not always a good strategy for dealing with imbalance.
Content of part 6
Up until now, all the probes used throughout this course have been traditional, brand neutral products such as single and double U tubes. However, more and more manufacturers have developed innovative heat exchangers that can be beneficial under certain conditions from both a thermal and hydraulic perspective. In this part, we shed some light on a selection of these products, for which rigorous mathematical models have been developed and implemented in GHEtool Cloud.
In the first chapter, the TurboCollector from MuoviTech is introduced. This is a circular probe with internal fins that enhance turbulence at lower flow rates. In the second chapter, its younger cousin, the MuoviELLIPSE, is explained. It has the same internal fins but an elliptical cross section.
In the third chapter, the GEROtherm VARIO and FLUX probes from HakaGerodur are discussed. These are circular probes with a varying wall thickness in order to minimise pressure losses whilst maintaining the same pressure rating as a regular probe.