Reference Temperature (To)

Hello,

I'm working on a heat transport problem. Am I on the right track that you can define the Reference Temperature exclusively for the complete model? Is there no option for defining a slice specific value?

Anybody knows good the problem?

Thank You.

The reference temperature is indeed a reference value for the entire model. It is used to reference the density ratio parameter and the conductivities input. Instead of putting different values on different slices, you should reference the input conductivity values to the same reference temperature.

In BHE utility, what is reference temperature meant for?
Should I put the undisturbed mean temperature value (i.e. the ground temperature at half depth of my BHEs)?
Thank you

Hello,
you have two options in the BHE dialog: either define an Input Heat Rate for which an equivalent Inlet Temperature (see bottom of the dialog) is computed; or you can insert an Inlet Temperature and calculate an equivalent Heat Input Rate.
In both cases the respective value is calculated using the reference Temperature, i.e.:

T_inlet = [Heat Input Rate] / ([Volumetric Heat Capacity] * [Flow Discharge]) + [Reference Temperature]

In case you use an Inlet Temperature equal to the Reference Temperature the Heat Input Rate is zero.

The Heat Input Rate of an BHE is different to the Heat Input Rate of a regular 4th kind heat boundary condition (BC). The real heat input (balance) of an BHE is the result of the subsequent computation while for a regular 4th  kind BC it is exactly this value.

In most cases it is a good idea to use a reference temperature which is smaller than any temperature occurring in your model. Zero can be a good choice or maybe 273.15 (absolute zero).

Actually you could use also very large numbers. However due to this (some) signs while change (i.e. for the Budget calculations) which can make understanding the results hard.

Kind regards
Wolfram

So using a BHE 4th kind heat transport boundary condition, I can't decide the heat input/withdrawal, but only the inlet temperature...is it true?

How can I impose a heating/cooling load to a BHE and then evaluate the inlet/outlet temperatures?

After all it is the inlet temperature which is specified. If you need a specific heat extraction rate, there is a free IFM module (BHE-Loop) available. Please contact support@dhi-wasy.de, they can send it to you.
Kind regards
Wolfram

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

Dear  Alessandro, did you assign the time varying power function to the BHE itself? This is not the correct procedure for the BHE_Loop module. Please assign the number solely to the nodal reference value at this node. Please see the html documentation of the module for details. If the problem persists please sent an e-mail to support@dhi-wasy.de. Kind regards Wolfram

Dear all.

I'm a new user of FEFLOW-5.4 for BHE modeling.
Basically I want to reconstruct a Thermal Response Test data set (evolution of temperature along time, for more or less 3 days), but I haven't managed yet to reconstruct the curve. The principle problem is related to reference temperature as far as it is controlling the inlet temperature. If I use a constant reference temperature I will never be able to have the profile of inlet temperature that I have in the real case.
(Ah, I've worked with a variable power, inserted in the "time varying functions" in BHE boundary condition and settled as the power rate for my BHE).
Then reading this forum I got to know about the BHE loop module, I'd installed it and had tried, without success, to put a temperature differential to the top node of the BHE following the tutorial (thinking that maybe the variable power was not working properly). No way, I couldn't make it. Probably I'm not doing the right procedure.
Anyone can help me?  Anyone ever tried to reconstruct a real TRT curve?
Thanks a lot.
Sara

Dear sara,
I have the same problem with you and I do not know how to do it, I just want to say if you understand or solved this problem, could you please teach me ?
Thank you very much .
Lemon

Dear Lemonok

I still have no solution for the problem..I saw your posts and I think that we are facing the same problem.
My email is sara.focaccia2@unibo.it, if you wanna contact me about the topic in a more direct way.
For the rest, I'm hoping someone will answer to our questions/solve our doubts!

Sara

There's a number of FEFLOW users who have simulated and are simulating their TRT results on a regular basis, some of them even trying automatic parameter estimation on the heat transport properties of different layers. The first question you will have to clarify is about the availabe data: You might know the thermal power applied between inlet and outlet, or you might know the inlet temperature by measurement. In the first case, you will have to use the BHE Loop plug-in, providing the power as a curve. In the latter case, you have to calculate the curve of the heat input rate from the equation Wolfram has cited in this thread before:
T_inlet = [Heat Input Rate] / ([Volumetric Heat Capacity] * [Flow Discharge]) + [Reference Temperature].

The curve ID then has to be selected in the light-blue box between Time-varying function ID's and the Mesh Inspector BEFORE you click on the BHE button to set the BHE. You will then see the ID, e.g., "ID = 1", in the Heat input rate box.

Thanks a lot Peter!!
Sara

Thank you very much Peter
Lemon

Hi, Peter,
Thank you for all your answer, and may I ask what is BHE loop plug-in ? and how can I use it ?
Thank you a lot.
Lemon

Hi Lemon,

Please see the attached description for the BHELoop plug-in. The plug-in can be obtained for free from FEFLOW Support (support@dhi-wasy.de).

Peter

Thank you so much  Peter.  :D

Dear FEFLOW users,

I have read the posts on this forum trying to get some ideas with respect to the reference temperature. I am comparing the FEFLOW results for a pure conductive scenario with the SBM model which originally uses Eskilson and Claesson analytical solution. So for such scenario the results should be the same or at least pretty similar, but this is not the case.

Basically the problem is that I do not know how to assign the same energy extraction rates or equivalent ones in both models.  In order to assign the same load patterns I just followed Dr. Rühaak suggestion (previous post) using zero as a reference temperature. By doing this, I get the same input rate as in SBM, however, FEFLOW results are much more lower, around 2 K, than those form SBM. In addition, the input and output temp are pretty differents. (I am modelling a field with 25 BHE equally distributed)

Until now, it is not clear to me what exactly the reference temperature is. I have read Eskilson and Claesson paper and the FEFLOW white paper 5 and I can not find the physical interpretation of this parameter. In the SBM code the initial inlet pipe temperature is calculated by the code itself using kind of an optimization approach and not by a prescribed BC. Have somebody else already compared the FEFLOW BHE tool with the SBM code? What is the subsequent calculation for the heat extraction rates mentioned previously in this post? Is there a reference of this calculation on the corresponding white paper?

I have not tried the IFM plug in, I just sent an email some minutes ago to WASY, maybe with this I could get rid of this problem or understand how the BHE tool really works.

Thanks in advance

Jozsef