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

Sun Aug 18 17:54:11 PDT 2013

Hello, Su.

The problem you encounter arises from the mixing valve (Type649).  According to
the model code, when both streams have no flow, the temperature of the outlet
is taken as the inlet temperature of the first stream (i.e. the one connected
to the vertical ground heat exchanger).  Hence, you get a temperature
difference between the inlet and outlet of the horizontal ground heat exchanger
at no flow.  However, as a gentle reminder, I recommend you not to put two
pieces of Type997 in one project file, as they may not work properly.

Best Regards
Chun Kwong LEE

Quoting Su Huang <sh377 at uowmail.edu.au>:

> Dear Dr C.K.LEE.
> 
> Many thanks for your help! 
> 
> I attached the files, I built the two separate system in one file. 
> 
> Many thanks!
> 
> Regards,
> Su 
> 
> ________________________________
> Su Huang
> 
> P.h.D Candidate in Sustainable Buildings Research Center
> 
> University of Wollongong
> 
> Email: sh377 at uowmail.edu.au
> 
> 
> 
> 
> 
> 
> 
> ________________________________________
> From: a8304506 at graduate.hku.hk <a8304506 at graduate.hku.hk>
> Sent: Sunday, 18 August 2013 4:35 PM
> To: Su Huang
> Subject: Fwd: RE: [TRNSYS-users] Help with two parallel ground loop heat
> exchangers simulation (Borehole and Horizontal Loop)
> 
> Sorry, Su.
> 
> I need case 1 with both types of ground heat exchangers connected.
> 
> Best Regards
> Chun Kwong LEE
> 
> ----- Forwarded message from a8304506 at graduate.hku.hk -----
>     Date: Sun, 18 Aug 2013 14:25:58 +0800
>     From: a8304506 at graduate.hku.hk
> Reply-To: a8304506 at graduate.hku.hk
>  Subject: RE: [TRNSYS-users] Help with two parallel ground loop heat
> exchangers
> simulation (Borehole and Horizontal Loop)
>       To: Su Huang <sh377 at uowmail.edu.au>
> 
> Hello, Su.
> 
> Can you send me the related files for case 2 only?
> 
> Best Regards
> Chun Kwong LEE
> 
> 
> Quoting Su Huang <sh377 at uowmail.edu.au>:
> 
> > 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 3oC 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
> >
> >
> >
> >
> > ________________________________
> > Su Huang
> >
> > Ph.D Candidate in Sustainable Buildings Research Centre
> >
> > University of Wollongong
> >
> > Email: sh377 at uowmail.edu.au<mailto:sh377 at uowmail.edu.au>
> >
> >
> >
> >
> >
> >
> >
> > ________________________________
> > From: a8304506 at graduate.hku.hk <a8304506 at graduate.hku.hk>
> > Sent: Friday, 16 August 2013 10:28 AM
> > To: thornton at 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 at 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 at 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 at uowmail.edu.au [1]
> > >
> > >
> > > Links:
> > > ------
> > > [1]
> > > mailto:sh377 at uowmail.edu.au
> > >
> >
> >
> >
> >
> >
> >
> 
> 
> 
> 
> ----- End forwarded message -----
> 
> 
> 
> 
> 
> 