[TRNSYS-users] TRNSYS-users Digest, Vol 49, Issue 40
David Bradley
bradley at tess-inc.com
Mon Jan 26 10:11:10 PST 2009
Mariana,
You might open up the *.inf file with a text editor and search on the
string "32" to see if you can find the surface that way. Otherwise, I
would recommend that you send the *.bui file to your TRNSYS distributor
and see if they can help you find the problematic surface.
Kind regards,
David
ghetu mariana wrote:
> Trnsys users,
>
> I have problems with type56. I’m simulating a heating installation
> with different time-base and time-step. For a time-base of 20 min, 40
> min, 50 min, 100 min (time-step: 2min, 5min, 10min,etc.), I get an
> error message saying that the temperature for zone 3 surface 32 does
> not converge. I looked up zone 3 surface 32 in the “.bui” file but I
> can’t find it, it doesn’t exist!
>
> If I start the debugger on the “.dck” file I get nothing, it’s like I
> have no errors.
>
> Have any of you had this problem before?
>
>
> Thanks,
>
> Mariana Ghetu
>
> --- On *Sat, 24/1/09, trnsys-users-request at cae.wisc.edu
> /<trnsys-users-request at cae.wisc.edu>/* wrote:
>
> From: trnsys-users-request at cae.wisc.edu
> <trnsys-users-request at cae.wisc.edu>
> Subject: TRNSYS-users Digest, Vol 49, Issue 40
> To: trnsys-users at cae.wisc.edu
> Date: Saturday, 24 January, 2009, 8:03 PM
>
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> Today's Topics:
>
> 1. Re: Heat exchanger temperature control (Mario Leroy Ortiz)
>
>
> TRNSYS users,
>
> I found what was wrong. My cold side HX pump was working well while my solar
> loop temperature was close to its controllers set value. However, during the
> shoulder season, when the heating load is well below the heat collected by the
> solar collectors, the solar loop temperature rises above the set point. The
> solar array exit temperature varies widely during the shoulder season when heat
> collected is much less than heat used for heating/cooling load. This is due to
> the solar loop pump running at maximum flow rate to try to reestablish the solar
> array exit temperature to the lower set temperature. Thus, the solar array
> outlet temperature varys with the load and insolation. I had allowed the heat
> exchanger set point to vary at 5 oC below the solar
> array exit temperature.
> Thus, my controller for the cold side heat exchanger pump was confused by the
> ever changing set temperature.
>
> The moral of the story is that a constantly changing set point may cause
> controller issues that are unbearable.
>
> Thank you,
>
> Mario Ortiz
>
> On Wed, 14 Jan 2009 10:01:59 -0600
> David Bradley <bradley at tess-inc.com> wrote:
> > Mario,
> > I have not gotten a chance to look at the attached files but chances are
> that there are some convergence problems associated with the iterative feedback
> controller. As I mentioned in an email yesterday, the simplifying assumptions
> that often get made in building models of hydronic loop components (pumps, heat
> exchangers, etc.) neglect the thermal capacitance of the fluid in the devices,
> which in turn leads to very fast reactions to control decisions. In some cases,
> putting time delays on controllers helps solve the
> convergence problems but
> often, it just masks an underlying issue. My recommendation would be to make
> sure that you have at least one timestep of storage in your loop (in other
> words, model the pipes with some realistic thermal losses), reduce the time step
> and tighten the tolerances to at least 0.0001 (the default is 0.001 I think).
> >
> > Alternatively, there is a model of a heat exchanger that controls the
> outlet temperature using an internal bypass available in the TESS Hydronics
> Library.
> > Kind regards,
> > David
> >
> >
> > Mario Leroy Ortiz wrote:
> >> TESS and TRNSYS users,
> >>
> >> Please help me with the attached files...
> >>
> >> I am having some problems controlling the outlet temperature of the
> cold side of a type 5b counter flow heat exchanger.
> >>
> >> I am modeling a plate and frame heat exchanger where the heat source
> is a
> solar thermal array and the cold side charges a storage tank. Heat is used
> for a building load.
> >>
> >> My example project file is simple.
> >>
> >> Water at a constant temperature (65C) is supplied to a heat exchanger
> with a varying flow rate (low in morning and afternoon, high at midday) to mimic
> what might be supplied by a solar array.
> >>
> >> I am trying to maintain the heat exchanger cold side temperature (tank
> heat supply) at 60C using a variable speed pump and an iterative feedback
> controller.
> >>
> >> Heat is drawn from the tank to the building load.
> >>
> >> There are 7 days in the simulation. Day 4 and day 7 seem to work
> right.
> >>
> >> On the other days, during the last hour of time when solar thermally
> heated water is supplied to the heat exchanger, the cold heat exchanger outlet
> temperature seems to drop prematurely due
> to the cold side pump speeding up.
> Under certain unknown circumstances (days 4 and 7), the cold side pump flow
> mirrors the hot side pump flow and the cold side temperature is maintained for
> most of the time that solar thermal heat is available. For unknown (to me)
> reasons, at other times the cold side pump flow is sporadic (speeds up rapidly,
> decreasing the cold side outlet temperature), especially late in the afternoon.
> >>
> >> Attached are the project file and input file for my tank.
> >>
> >> This is an example of the problems I am seeing in a larger project
> file. This project does not show it, but what I see in the larger project is
> the cold side pump turning off on me when the hot pump is running at full
> capacity, causing my solar loop to get very hot.
> >>
> >> Any assistance with this problem is appreciated.
> >>
> >> Thank you,
> >>
> >> Mario
> Ortiz
> >>
> ------------------------------------------------------------------------
> >>
> >> _______________________________________________
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> >> TRNSYS-users at cae.wisc.edu
> >> https://www-old.cae.wisc.edu/mailman/listinfo/trnsys-users
> >>
> >
> > -- ***********************************************************************
> > Thermal Energy System Specialists (TESS), LLC David BRADLEY
> 22 N. Carroll Street - Suite 370 Partner
> Madison, WI 53703 USA
> > P: +1.608.274.2577 F: +1.608.278.1475
> > E-mail: bradley at tess-inc.com Web Pages: http://www.tess-inc.com and
> http://www.trnsys.com
> >
> > ***********************************************************************
> >
>
>
>
>
>
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--
***********************************************************************
Thermal Energy System Specialists (TESS), LLC
David BRADLEY 22 N. Carroll Street - Suite 370
Partner Madison, WI 53703
USA
P: +1.608.274.2577
F: +1.608.278.1475
E-mail: bradley at tess-inc.com
Web Pages: http://www.tess-inc.com and http://www.trnsys.com
***********************************************************************
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