Re: [TRNSYS-users] Help with two parallel ground loop heat exchangers simulation (Borehole and Horizontal Loop)

Dear Dr C.K.Lee and Jeff,

The external water circuit system is the same to supply the inlet and outlet water conditions of both vertical heat exchangers and horizontal loop heat exchangers.

Attached is the result I did for two cases.

Case 1: borehole heat exchanger and horizontal loop heat exchanger connected in parallel

Case 2: Simply just horizontal loop heat exchanger

In case 1: almost 3^oC temperature difference between the inlet and outlet temperature from the horizontal loop heat exchanger when there was no flow.

In case 2: there was no temperature difference.

I assume that there is something to do with the added borehole heat exchanger. But still struggling finding out the reason.

Many thanks!

Regards,

Su Huang

Ph.D Candidate in Sustainable Buildings Research Centre

University of Wollongong

Email: sh377@uowmail.edu.au

From: a8304506@graduate.hku.hk <a8304506@graduate.hku.hk>
Sent: Friday, 16 August 2013 10:28 AM
To: thornton@tess-inc.com; TRNSYS users mailing list at the Solar Energy Lab, UW-Madison
Subject: Re: [TRNSYS-users] Help with two parallel ground loop heat exchangers simulation (Borehole and Horizontal Loop)

Hello.

I think the problem can be interpreted in this way. As mentioned by Jeff, the
outlet temperature is calculated in a specific way according to the ground heat
exchanger model. However, the water circuit outside the ground heat exchanger
tends to bring the outlet temperature back to the inlet temperature,
particularly if you do not add any thermal mass in the external water circuit.
In this sense, both the inlet and outlet temperatures decay at no flow amd they
appear to be the same. Hence, I think the problem is in the horizontal loop
system. Su, is the same external system used when employing the vertical and
horizontal ground heat exchangers?

Best Regards
Chun Kwong LEE
City University of Hong Kong

Quoting Jeff Thornton <thornton@tess-inc.com>:

>
>
> <I got a problem during the simulation. When the heat pump is not in
> operation (also the fluid flow rate in both ground loop heat exchangers
> are 0), the outlet temperature of the borehole is same as the inlet
> temperature of the borehole. But the outlet temperature of the
> horizontal loop is lower than the inlet temperature when the fluid flow
> rate in the pipe is 0. I cannot understand why there exists a
> temperature difference of the horizontal loop when the system is not in
> operation.>
>
> I'm not sure what you're doing wrong without taking a
> closer look, but neither the vertical nor horizontal ground heat
> exchanger models set the outlet temperature to the inlet temperature
> when there is no flow. Both models calculate the fluid temperature in
> the pipes and report the temperature as it decays with time towards the
> local soil temperature. To check this, run both models with a high inlet
> temperature (100 C) and vary the flow on and off each for 24 hours using
> a forcing function. You'll notice neither model sets the flow to the
> inlet temperature and both models show a decay when the flow is off.
>
>
> Jeff
>
> ---
>
> Jeff Thornton
>
> _President - TESS LLC_
>
> _22 N. Carroll
> Street, Madison WI USA 53703_
>
> _Office: (608) 274-2577 Fax: (608)
> 278-1475_
>
> _www.tess-inc.com_
>
> _E-Mail: thornton@tess-inc.com_
>
> On
> 08/15/2013 4:35 am, Su Huang wrote:
>
> > Dear All,
> >
> > Results.jpg
> >
>
> > I did one test with a simple GSHP system, in which one horizontal
> loop heat exchanger and vertical borehole heat exchanger connect in
> parallel with one water source heat pump.
> > I got a problem during the
> simulation. When the heat pump is not in operation (also the fluid flow
> rate in both ground loop heat exchangers are 0), the outlet temperature
> of the borehole is same as the inlet temperature of the borehole. But
> the outlet temperature of the horizontal loop is lower than the inlet
> temperature when the fluid flow rate in the pipe is 0. I cannot
> understand why there exists a temperature difference of the horizontal
> loop when the system is not in operation.
> > Much appreciated if anyone
> can help!
> > Many thanks! (Attached is the file).
> > Regards,
> > Su
> >
>
> > -------------------------
> > Su Huang
> >
> > Ph.D Candidate in
> Sustainable Buildings Research Centre
> >
> > University of Wollongong
> >
>
> > Email: sh377@uowmail.edu.au [1]
>
>
> Links:
> ------
> [1]
> mailto:sh377@uowmail.edu.au
>