<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Trnsys users,<br><br>
<p class="MsoNormal"><span style="" lang="EN-US">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 <st1:metricconverter productid="32 in" w:st="on">32 in</st1:metricconverter> the “.bui” file but I
can’t find it, it doesn’t exist!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="" lang="EN-US">If I start
the debugger on the “.dck” file I get nothing, it’s like I have no errors.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="" lang="EN-US">Have any of
you had this problem before?<o:p></o:p></span></p>
<br>Thanks,<br> <br>Mariana Ghetu<br><br>--- On <b>Sat, 24/1/09, trnsys-users-request@cae.wisc.edu <i><trnsys-users-request@cae.wisc.edu></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;">From: trnsys-users-request@cae.wisc.edu <trnsys-users-request@cae.wisc.edu><br>Subject: TRNSYS-users Digest, Vol 49, Issue 40<br>To: trnsys-users@cae.wisc.edu<br>Date: Saturday, 24 January, 2009, 8:03 PM<br><br><pre>Send TRNSYS-users mailing list submissions to<br> trnsys-users@cae.wisc.edu<br><br>To subscribe or unsubscribe via the World Wide Web, visit<br> https://www-old.cae.wisc.edu/mailman/listinfo/trnsys-users<br>or, via email, send a message with subject or body 'help' to<br> trnsys-users-request@cae.wisc.edu<br><br>You can reach the person managing the list at<br> trnsys-users-owner@cae.wisc.edu<br><br>When replying, please edit your Subject line so it is more specific<br>than
"Re: Contents of TRNSYS-users digest..."<br></pre><pre>Today's Topics:<br><br> 1. Re: Heat exchanger temperature control (Mario Leroy Ortiz)<br></pre><pre>TRNSYS users,<br><br>I found what was wrong. My cold side HX pump was working well while my solar<br>loop temperature was close to its controllers set value. However, during the<br>shoulder season, when the heating load is well below the heat collected by the<br>solar collectors, the solar loop temperature rises above the set point. The<br>solar array exit temperature varies widely during the shoulder season when heat<br>collected is much less than heat used for heating/cooling load. This is due to<br>the solar loop pump running at maximum flow rate to try to reestablish the solar<br>array exit temperature to the lower set temperature. Thus, the solar array<br>outlet temperature varys with the load and insolation. I had allowed the heat<br>exchanger set point to vary at 5 oC below the solar
array exit temperature. <br>Thus, my controller for the cold side heat exchanger pump was confused by the<br>ever changing set temperature.<br><br>The moral of the story is that a constantly changing set point may cause<br>controller issues that are unbearable.<br><br>Thank you,<br><br>Mario Ortiz<br><br>On Wed, 14 Jan 2009 10:01:59 -0600<br> David Bradley <bradley@tess-inc.com> wrote:<br>> Mario,<br>> I have not gotten a chance to look at the attached files but chances are<br>that there are some convergence problems associated with the iterative feedback<br>controller. As I mentioned in an email yesterday, the simplifying assumptions<br>that often get made in building models of hydronic loop components (pumps, heat<br>exchangers, etc.) neglect the thermal capacitance of the fluid in the devices,<br>which in turn leads to very fast reactions to control decisions. In some cases,<br>putting time delays on controllers helps solve the
convergence problems but<br>often, it just masks an underlying issue. My recommendation would be to make<br>sure that you have at least one timestep of storage in your loop (in other<br>words, model the pipes with some realistic thermal losses), reduce the time step<br>and tighten the tolerances to at least 0.0001 (the default is 0.001 I think).<br>> <br>> Alternatively, there is a model of a heat exchanger that controls the<br>outlet temperature using an internal bypass available in the TESS Hydronics<br>Library.<br>> Kind regards,<br>> David<br>> <br>> <br>> Mario Leroy Ortiz wrote:<br>>> TESS and TRNSYS users,<br>>> <br>>> Please help me with the attached files...<br>>> <br>>> I am having some problems controlling the outlet temperature of the<br>cold side of a type 5b counter flow heat exchanger.<br>>> <br>>> I am modeling a plate and frame heat exchanger where the heat source<br>is a
solar thermal array and the cold side charges a storage tank. Heat is used<br>for a building load.<br>>> <br>>> My example project file is simple.<br>>> <br>>> Water at a constant temperature (65C) is supplied to a heat exchanger<br>with a varying flow rate (low in morning and afternoon, high at midday) to mimic<br>what might be supplied by a solar array.<br>>> <br>>> I am trying to maintain the heat exchanger cold side temperature (tank<br>heat supply) at 60C using a variable speed pump and an iterative feedback<br>controller.<br>>> <br>>> Heat is drawn from the tank to the building load.<br>>> <br>>> There are 7 days in the simulation. Day 4 and day 7 seem to work<br>right.<br>>> <br>>> On the other days, during the last hour of time when solar thermally<br>heated water is supplied to the heat exchanger, the cold heat exchanger outlet<br>temperature seems to drop prematurely due
to the cold side pump speeding up. <br>Under certain unknown circumstances (days 4 and 7), the cold side pump flow<br>mirrors the hot side pump flow and the cold side temperature is maintained for<br>most of the time that solar thermal heat is available. For unknown (to me)<br>reasons, at other times the cold side pump flow is sporadic (speeds up rapidly,<br>decreasing the cold side outlet temperature), especially late in the afternoon.<br>>> <br>>> Attached are the project file and input file for my tank.<br>>> <br>>> This is an example of the problems I am seeing in a larger project<br>file. This project does not show it, but what I see in the larger project is<br>the cold side pump turning off on me when the hot pump is running at full<br>capacity, causing my solar loop to get very hot.<br>>> <br>>> Any assistance with this problem is appreciated.<br>>> <br>>> Thank you,<br>>> <br>>> Mario
Ortiz<br>>> <br>------------------------------------------------------------------------<br>>> <br>>> _______________________________________________<br>>> TRNSYS-users mailing list<br>>> TRNSYS-users@cae.wisc.edu<br>>> https://www-old.cae.wisc.edu/mailman/listinfo/trnsys-users<br>>> <br>> <br>> -- ***********************************************************************<br>> Thermal Energy System Specialists (TESS), LLC David BRADLEY <br> 22 N. Carroll Street - Suite 370 Partner <br>Madison, WI 53703 USA<br>> P: +1.608.274.2577 F: +1.608.278.1475<br>> E-mail: bradley@tess-inc.com Web Pages: http://www.tess-inc.com and <br>http://www.trnsys.com<br>> <br>> ***********************************************************************<br>>
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