• ### Multiple BHE simulations

I am modelling a Borehole Heat Exchanger field with 168 exchangers, all of them with the same features, the same thermal load and the same depths.
I would like to know if it is possibile to insert them in the mesh with a special procedure (e.g. using a .trp file with assign_>database, or something similar), or if I have to put them one by one.

Thanks,
Alessandro
• ### Re: About the time step in borehole simulation

which timestep scheme you adopted?
I experienced some troubles with the Adams-Bashfort scheme, you could try with Forward Euler/Backward Euler...
• ### GSHP - Heat pump variation with COP

I'm researching about Ground Source Heat Pumps and I would like to get a graph, a table or a formula of a typical source temperature-COP relation for a heat pump.
The hot source would be a radiant panel (35°C) or fan coils (45°C).
Usualy, HP manufacturers give only a W0/B35 (that is: water temperature of the cold source = 0°C, brine temperature of the hot source = 35°C) COP value (i.e. 4.2-4.5), or a W0/B45.

Can somebody help me?
• ### borehole heat exchanger: numerical settings

I am carrying out a sensitivity analysis on which settings work better with a flow and heat transport modeling of a Borehole Heat Exchanger, vaying:
- automatic timestep control (FE/BE, Adams-Bashforth, fully implicit and semi-implicit);
- error tolerance (10, 5, 1 x 10^-3) applied to RMS norm;
- upwinding scheme.

Which is your advice for BHE modeling?

Kind regards,
Alessandro Casasso
• ### Re: Heat conductivity constitutive law

I found that the IFM module "lambdat.dll" is able at varying the thermal conductivity according to the node temperature, using the Zoth and Hänel (1988) formula...
• ### Heat conductivity constitutive law

I was looking on the white papers and I saw that constitutive laws can be implemented in FEFLOW for viscosity, density etc. and also for parameters like heat conductivity.
I am very interested in this possibility, because it can be useful for modelling, i.e., groundwater filled borehole heat exchangers in which water can become ice and hence heat conductivity can be greatly enhanced (from 0.59 to 2.2 W/(mK)!!!).
Is it possibile, and if, how?
Thank you for your attention.

• ### Re: problem running batch mode

About PEST, I am trying to run a model with the IFM module of PEST loaded, but it doesn't work...is there any restrictions in launching models with IFM modules in batch mode?

I can explain better.
I am using a transient 3d flow model with the IFM module PEST 2.0.
I would like to run it in a batch mode for a faster run, writing a .dac file and a .log file (is it possible to write also the record file? .rec).

My batch code is:
"C:\Programmi\WASY\FEFLOW 6.0\bin32\feflow60c.exe" -module "C:\Programmi\WASY\FEFLOW 6.0\modules32\pest20.dll" -run -demo -work C:\ -steps steps.pow -dac PEST.dac 10_10_01_PEST.fem

(I own a license, but I'm working in demo mode because another PEST model is already running...).

As I try to run this .bat file, this screen appears:

[img width=200 height=160]http://areeweb.polito.it/ricerca/groundwater/troubles/batch_mode_PEST_error.png[/img]

What do these messages mean?

Thanks a lot,
Alessandro Casasso
• ### Re: Reference Temperature (To)

I tried the IFM module bhe_loop we saw at the course in Offenburg, but this strange error occurs:

[img width=200 height=160]http://areeweb.polito.it/ricerca/groundwater/troubles/bhe_loop_troubles.JPG[/img]

[url=http://areeweb.polito.it/ricerca/groundwater/troubles/bhe_loop_troubles.JPG] http://areeweb.polito.it/ricerca/groundwater/troubles/bhe_loop_troubles.JPG [/url]

A message "A transient BC cannot be modified" appears.

I made the nodal reference distribution BHE-dT, putting a value of 1 in the BHE node, and -9999 elsewhere.
I put the BHE boundary condition with ID=1. As I started, this message box appeared.

Can you please help me? Thank you.

Kind regards,
Alessandro Casasso

• ### Re: BHE: average heat vs T pipe out at top

Dear Wolfram,
thank you for your help!

Here you can see an example:
[img width=200 height=160]http://areeweb.polito.it/ricerca/groundwater/troubles/slight_differences.GIF[/img]

[url=http://areeweb.polito.it/ricerca/groundwater/troubles/slight_differences.GIF] http://areeweb.polito.it/ricerca/groundwater/troubles/slight_differences.GIF [/url]

I am simulating a 100m deep 2U borehole heat exchanger.
The reference temperature is 10°C, and the prescribed inlet temperature is of about 14.7 °C.
For every other parameter, I kept the default value.
No hydraulic gradient is present, as I put a uniform fixed hydraulic head value on the boundary.
The aquifer is unconfined with "phreatic" option.

A slight difference of about 0.3 °C occurs.

This bug occurs only with Feflow 5.4; in the 6.0 version (with the "old fashion" Motif GUI), everything is ok with outlet temperatures...

Kind regards,
Alessandro
• ### Re: BHE: average heat vs T pipe out at top

It's the 5.4.5412-x86 version, I think it's the most recent one.