Welcome to the fourth part of the course ‘Design borefields with confidence’.
Summary of part 3
Building further on the elementary building blocks of the g-functions and the effective borehole resistance, both introduced in the second part of this course, Part 3 focused on the latest state-of-the-art models that can help you design better and more accurate borefields.
In Part 3.1, we revisited monthly and hourly load profiles and discussed the additional insights that can be gained when working with hourly instead of monthly data.
In Part 3.2, the importance of using variable fluid properties was explained. Since the temperatures in a borefield can easily fluctuate by more than 20 degrees over the different seasons, the Reynolds number and the effective borehole thermal resistance will vary accordingly. Working with variable fluid properties is especially important when dealing with projects that have a high cooling demand.
In Part 3.3, the importance of working with variable flow rates was discussed. Nowadays, most circulation pumps are frequency-driven and do not always operate at the maximum rated flow rate. This means that, over the course of the year, the Reynolds number will vary, and so will the borehole resistance. It was shown that, when working with a variable flow rate, a much more accurate picture of the off-peak temperatures can be obtained. In addition, heating and cooling can be modelled more accurately, since both can have different flow rates.
In Part 3.4, we concluded the third part with a discussion on the use of variable efficiencies in borefield design. Historically, almost all geothermal borefields were designed using a constant seasonal efficiency to convert the building load into a ground load. However, this poses several problems, since both the yearly energy demand and the peak demand are converted using the same factor, whereas in reality they should differ. It was shown that, when working directly with a heat pump in GHEtool, a much clearer view of the expected efficiency of the system can be obtained for different designs.
Content of part 4
In this part, another aspect of borefield design will be discussed: the hydraulic aspects. In het eerste hoofdstuk, he concept of pressure drop and its importance for geothermal design will be discussed. In the second chapter, our understanding of hydraulic design will be deepened by examining how the pressure drop evolves over time due to variable fluid properties and flow rate. The concepts of pump power and pump energy will also be defined. In Hoofdstuk 3, the focus will be on the horizontal connections and the actual hydraulic design using GHEtool Cloud.