Welcome to the fifth part of the course ‘Design borefields with confidence’.
Summary of part 4
In the first three parts, the focus of the course was on the thermal design of borefields, with important concepts such as g-functions and the effective borehole thermal resistance. In the previous part, the focus shifted towards the hydraulic design of these systems.
In Part 4.1, the theoretical foundation of pressure drop was introduced. It was explained that the pressure drop consists of both local (i.e. minor) losses and major (i.e. friction) losses. The first contribution to the pressure drop is caused by all bends, junctions and individual components that increase the pressure drop. Friction losses, on the other hand, are distributed throughout the hydraulic circuit. It was explained that these losses are cubically proportional to the flow rate and inversely proportional to the fifth power of the pipe diameter.
In Part 4.2, the concept of pressure drop was applied to geothermal borefields. It was shown that the pressure drop is not constant over time because of varying fluid properties and flow rates, as discussed in Part 3. This meant that both the heating and cooling regimes should be considered when determining the maximum and critical pressure drop. Besides pressure losses, the concepts of pump power and pump energy were also introduced. It became clear that the electricity consumption when working with a variable flow rate is significantly lower than with a constant flow rate.
In Part 4.3, the hydraulic impact of the horizontal configuration was discussed. With the help of the concept of hydraulic balancing, the pressure drop calculation for the entire borefield was reduced to the pressure drop across a single borehole. The differences between Tichelmann, direct and series connected boreholes were discussed, and an example in GHEtool Cloud was presented.
Content of part 5
Given the theoretical foundation of the previous parts, this part will focus on the insights that can be gained from it.
In the first two chapters, we will deepen our understanding of geothermal design by discussing the question “single or double U-tube?” from both from a thermal perspective, focusing on the borehole thermal resistance, and a hydraulic perspective, focusing on the pressure drop. Although these are not the only two probe types that can be selected when designing geothermal systems, focusing on these two can provide valuable insights that are also applicable in a broader context.
Chapter 3 will focus on the importance of the borefield configuration itself, showcasing the difference in results when working with regular versus irregular configurations. It will also be shown how coordinates drawn onto a map in AutoCAD can be imported into GHEtool.
As a final chapter, different ways to cope with a certain imbalance from a geothermal perspective will be discussed.