Henk Witte

Hello,
We are currently investigating the effects of ground water flow on borehole heat exchangers. As a first step we want to validate the Feflow borehole model with standard BHE models, mainly Earth Energy Designer and Finite Line SOurce. In the forum there are some questions concerning this, but I did not find answers.

For the comparsion we compare fluid temperature of the feflow model with the fluid temperatures of EED and the temperature in the borehole / ground (using the EED relation between borehole thermal resistance, borehole wall temperature and energy rate to calculate ground temperatures).

We can set up and run the feflow model using the guidance on borehole configuration (mesh points) etc. However, comparison with Earth Energy Designer for balanced or unbalanced monthly energy loads shows that the higher the energy rate, the higher the difference between the Feflow solution and EED.

Also, when running a constant energy extraction / injection we find the Feflow solution to go to a steady-state very rapidely. This is for instance the case when comparing with an FLS or EED constant energy simulation (several years) but also for a thermal response test data set (about 100 hours).

As it is important that we understand the behaviour of Feflow without natural ground water advection, we hope the forum can give us some suggestions / references how to set up and run the model.

As an example the following graphs shows the feflow and EED solution for contant heat injection:



Thank you !

Henk Witte

Thanks for the fast reply!

Henk Witte

Thank you!

Two further questions:

1) with the "gap"method I assume you introduce one multilayer well BC with flow rate (inject/extract) and one temperature BC with the "gapped" temperature BC. Do you then apply that temperature BC only to the node in the top slice of the multilayer well?

2) with the openloop I can open the help but not edit or assign anything. What I did not see in the help file is how to select the nodes/edges (?) where to apply the plugin to, but perhaps I miss something in how to apply plugins (sorry - steep learning curve and little time due to project deadlines).

Henk Witte

Hello,

Not linked to feflow as such, but in an EU research project some of my colleauges have been working on modelling this type of system, perhaps the papers they published may be of interest and help getting you to run your model:

Shafagh I, Rees SJ. 2019. Analytical Investigations into Thermal Resistance of Diaphragm Wall Heat Exchangers. European Geothermal Congress 2019

Shafagh I, Rees S. 2018. A Foundation Wall Heat Exchanger Model and Validation Study. IGSHPA Research Track

Best wishes,

Henk Witte

hello,

I need to model a system with several wells, each well has an water extraction / injection regime and will have a temperature bc associated with the injection period (6 months). I need to find the resulting extraction temperature.

The final goal is to obtain extraction temperatures affected by other wells and borehole heat exchangers in the vicinity. The borehole model runs OK.

I have tried a multi-layer well with a temperature BC, but I cannot set the BC only during injection period (is that possible)?

I have also looked at the "open loop" plugin but it is not clear how to use that plugin extactly. I cannot "edit" the plugin (error message No nodal reference distribution).

Note I can only model one well of each pair as the data available from the national database only has the "warm" wells.

Thanks!