Advanced pressure drop calculations with GHEtool

We’ve expanded the pressure drop calculation features in GHEtool Cloud to include manifolds, main headers, and Tichelmann connections — allowing you to model 99% of your borefield designs with ease. Read the article below to find out how it works!

What is the pressure drop

The pressure drop is a fluid dynamic concept defined as the difference in pressure between point A and point B, caused by friction — and this friction is key. It can occur between the fluid and the pipe walls, at valves, pumps, etc., but also within the fluid itself, between different fluid ‘droplets’. The pressure drop can therefore be seen as the effort required to move the fluid through the system.

!Note
For more background on the theoretical foundations of pressure drop, the reader is referred to this article.

Typically, there are two contributors to pressure drop: the flow losses in the pipes themselves, which occur throughout the system and are referred to as major losses, and the losses caused by bends, contractions, and other fittings, which are localised and hence called minor losses. Both types of loss are proportional to the flow velocity and thus to the flow rate. A typical pressure drop curve is shown below.

!Note
There is quite a lot of discussion around which local loss factors should be used. Within GHEtool Cloud, the bends connecting the lateral, horizontal pipes to the boreholes are modelled using a local loss factor of k = 0.3 (applied to both inlet and outlet), while the connections between the lateral pipes and the manifold are modelled with k = 0.5 (again, for both inlet and outlet). Other local losses — such as those caused by additional bends or fittings in the circuit — are not yet accounted for.

Pressure drop and GHEtool Cloud

GHEtool Cloud has always included a module for calculating the pressure drop in the borefield (for more details, you can refer to our previous article on this topic). This module comprised two main components:

• A simulation of the pressure drop across a single borehole, calculated by default
• A simulation of the pressure drop in the horizontal piping, assuming all boreholes were individually connected to the manifold

While this provided a solid first estimate of the system’s hydraulic performance, its simplicity meant it could not accommodate more complex configurations, such as Tichelmann connections and main headers. These features have now been incorporated in the latest update of GHEtool and are briefly discussed below.

Tichelmann connections

For both small and large borefields, individually connecting each borehole to the manifold—where the flow can be calibrated to achieve hydraulic balance—can be very costly. An alternative solution is to use a Tichelmann connection (also known as reverse return), where two or more boreholes are linked via the same horizontal pipe that connects to the manifold. This reverse return configuration approximates an equal pressure drop across the different boreholes, allowing you to minimise the number of horizontal connections, reduce the size of the manifold, and limit the number of flow rates that need adjustment to achieve a hydraulically balanced system.

!Caution
There are various ways to connect boreholes in parallel, but only the Tichelmann (reverse return) configuration results in a hydraulically balanced system.

Main pipe

Another important aspect in the hydraulic design of larger borefields is the main pipe connecting the manifold to the plant room. For smaller borefields, the manifold is typically located within the building itself, making this effect negligible. However, for larger borefields, it is not uncommon for the manifold to be situated tens of metres away from the plant room. In such cases, since the main pipe carries 100% of the borefield’s flow rate, the pressure drop between the manifold and the plant room can become quite significant.

Example 1: Small building

As a first example, let’s consider a small building with two double DN32 boreholes, each 150 metres deep. The furthest borehole is located 10 metres from the building, and DN40 pipes are used for the horizontal connections. We will examine three different ways of connecting the boreholes to the plant room: direct connection, Tichelmann connection, and series connection.

Direct connection

The most straightforward way to connect boreholes to the plant room is by using a manifold, with both boreholes connected directly. To determine the pressure drop in this configuration, both the series and Tichelmann factors should be set to 1, and the length of the horizontal pipe to the manifold is entered. (As the manifold is located inside the building, the pressure losses in the main pipe are negligible.)

The total pressure drop in this system is 22.74 kPa, of which 20.74 kPa is due to the boreholes themselves. This is an ideal scenario in terms of hydraulic performance, but it is often too costly in practice. Let us therefore consider the Tichelmann configuration, which can be simulated by setting the Tichelmann factor in GHEtool Cloud to 1.

Tichelmann connection

In this configuration, the boreholes are connected using a Tichelmann setup. Only two pipes enter the building, eliminating the need for a manifold (although it is still shown for clarity). As the Tichelmann setup balances the fluid flow equally between both boreholes, the pressure drop across each borehole remains 20.74 kPa. However, because 100% of the flow now passes through a single horizontal pipe (instead of being split across two), the losses in the horizontal piping increase from 1.98 kPa to 6.48 kPa, bringing the total system pressure drop to 27.22 kPa.

Series connection

In a series configuration (modelled by setting the series factor in GHEtool Cloud to 1), one borehole is connected directly after the other. This is often less expensive to install than a Tichelmann layout, as it involves fewer welds.

In this case, the horizontal pressure losses remain the same since they still carry the full flow rate. However, the pressure drop across the boreholes increases significantly. Each borehole now handles 100% of the flow, resulting in a pressure drop of 81.70 kPa across each borehole. As components in series have cumulative losses, the total borehole-related pressure drop becomes 163.40 kPa, and the total system pressure drop rises to 169.78 kPa—far higher than the 27.22 kPa seen in the Tichelmann configuration.

!Note
The pressure drop in the horizontal system may differ slightly between the Tichelmann and series configurations. This is because both hydraulic arrangements influence the effective borehole thermal resistance, which in turn affects the fluid properties. Minor changes in viscosity can therefore lead to small differences in pressure drop. For more information on temperature-dependent fluid properties, you can refer to this article.

!Note
It is also possible to combine both Tichelmann and series connections by setting both the Tichelmann factor and the series factor to values greater than 1. For instance, if there are three groups of two boreholes connected in series, and these groups are then arranged in a Tichelmann configuration, the Tichelmann and series factors should be set to 3 and 2 respectively.

Example 2: Auditorium

Let us now examine a more detailed example involving 20 boreholes (again, double DN32 and 150 m deep), connected to a manifold located 20 m away from the plant room. The lateral pipes connecting the boreholes to the manifold are DN40, with the longest distance 36m. We will first explore two cases where the boreholes are directly connected to the manifold, varying only the main pipe diameter—from DN63 to DN90. Finally, we will analyse a case in which the boreholes are grouped in Tichelmann configuration before connecting to the manifold.

!Note
A Design licence of GHEtool Cloud is required to simulate the pressure drop in the main pipe.

Direct with a DN63 main pipe

In the first case, the total pressure drop amounts to 104.63 kPa, distributed as follows: 21.87 kPa in the boreholes, 4.31 kPa in the lateral connections, and a substantial 78.45 kPa in the main pipe. Even though the main pipe is only 20 m long—relatively short compared to the 150 m boreholes—the pressure loss is significant due to the high flow rate in this section.

Direct with a DN90 main pipe

Keeping the lateral connections unchanged and increasing the main pipe diameter to DN90 reduces the pressure drop in the main pipe from 78.45 kPa to just 14.46 kPa. As a result, the total pressure drop drops to 40.64 kPa—less than half of the previous case. This clearly highlights the importance of correctly sizing the main pipe in borefield design.

Tichelmann with a DN90 main pipe

Since connecting 20 boreholes directly to a manifold can become costly, an alternative approach is to group the boreholes in pairs using a Tichelmann (reverse return) configuration, as shown below.

In comparison to the previous scenario, the pressure drop in the main pipe remains unchanged because the total flow rate is the same. However, the pressure drop in the lateral system increases from 4.31 kPa to 23 kPa due to the higher flow rate in each lateral pipe.

!Note
For larger borefields, where the lateral distance between boreholes and the manifold can also be considerable, the choice of pipe diameter for the lateral connections becomes a key factor in the system’s hydraulic performance.

Conclusion

This article outlined the new and more advanced methods for simulating the hydraulics of a geothermal borefield. From now on, it is possible to account for Tichelmann connections and main pipes linking the manifold to the plant room. These additions extend the applicability of GHEtool Cloud’s pressure drop calculations to 99% of typical projects, significantly enhancing the accuracy and efficiency of your system designs.

References

• Watch our video explanation over on our YouTube page by clicking here.