Welcome to the second part of the course ‘Design borefields with confidence’.
Summary of part 1
In Part 1.1, we discussed the advantages of ground-source heat pumps over air-source ones, considering individual factors such as efficiency and lifetime, as well as collective issues like the urban heat island effect and congestion on the electricity grid.
In Part 1.2, we focused on the importance of borefield design. We compared a traditional rule of thumb design (30 W/m) with a design created using GHEtool. We found that these rules of thumb can significantly oversize or undersize your system in quite unpredictable ways. Therefore, we advise using a real design tool for your borefields, even in the early stages.
The following parts discussed the different pieces of required information, such as ground properties, building demand and heat pump efficiency. In relation to ground properties, conductivity and volumetric heat capacity are important, as are the initial and undisturbed ground temperatures.
Building demand consists of heating, cooling and domestic hot water requirements, and can be calculated or estimated in many ways, from complicated dynamic simulations providing hourly load profiles, to full load hours and static heat losses. We also discussed the method in GHEtool for generating an hourly load profile based on yearly estimates.
Finally, we discussed the heat pump efficiency and the problems associated with using seasonal efficiencies, such as the SCOP, for geothermal simulations.
Content of part 2
In Part 2 of the course, we will create our first geothermal design in GHEtool Cloud based on traditional, simple assumptions. This will enable us to develop our understanding from the ground up. We will discuss the temperature profiles in detail (both hourly and monthly) and what we can learn from them. Building on this knowledge, we will then explore the physical principles underlying geothermal systems in more depth. Here, we will examine the concepts of effective borehole thermal resistance and g-functions, which govern the long-term behaviour of borefields.