<div dir="ltr"><div><div>I can't aggree more. If your flowrate falls below the turbulant thresholds, then you may as well switch the equipment off completely. Usually the manufacturer's information will contain schemes on how to divide up and connenct up the active areas so hit the right balance between retaining minimum pressure loss whilst maintaining turbulant flow. Also make sure that your poor pump is not opperating at an inefficient turndown point for 90% of the time.<br><br></div>Lastly, and very importantly, if you are using the active surface to cool, keep a very tight eye on the surface temperatures. If they fall closely within the range of the air dewpoint, you may get condensation problems. Real systems ramp the fluid temperature in combination with sensors to avoid this, but for you it is another very good reason to split the active surface out exactly in the model otherwise this effect won't be captured. You will find also that a lot less surface is active (and often at less extreme temperatures) thereby reducing the ability to transfer heat with the zone air. This is often forgotten in enery models.<br><br></div><div>Kind regards,<br></div><div><br></div>Jean Marais<br></div><div class="gmail_extra"><br><div class="gmail_quote">2015-10-05 18:32 GMT+02:00 David BRADLEY <span dir="ltr"><<a href="mailto:d.bradley@tess-inc.com" target="_blank">d.bradley@tess-inc.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
Brad,<br>
There is an example of using a PID to control flow through a
radiant floor (SunSpace - Floor heating PID controller.tpf). You'll
probably need to put a lower limit on the flow rate that your
controls decide should go through the radiant floor. However, far
from that being a workaound, it is a physical reality that pumps
have minimum turndown ratios and the flow through the pipes in the
floor must stay turbulent in order for there to be heat transfer.
The requirement of maintaining turbulent flow is what causes the
minimum flow rate in the first place. Lastly if you need to use a
lower flow rate then you need to go into TRNBuild and autosegment
the floor. What this does is to break the floor into smaller pieces
that are in series with one another instead of being in parallel
from a liquid flow point of view.<br>
regards,<br>
David<br>
<br>
<br>
<div>On 10/04/2015 21:52, Bradley Painting
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">I received a suggestion to use a Type 1669
controller for a radiant slab, and it seems to work well (thanks
Ben Heymer). However, right now I am using it to modulate
temperature, but what I would really like to do is modulate the
flow rate through the slab because I have a variable
(uncontrolled) input temperature. The problem is that TRNSYS
will not allow me to decrease the flow rate much below 2,000
kg/hr based on the size of my radiant floor.
<div><br>
</div>
<div>(Error Message: "Specific fluid mass flow of active layer
in surface 9 below minimum value of 6.74 kg/m2h Please,
increase the minimum mass flow rate or use the
autosegmentation feature of TRNBuild for subdividing the
surface"). </div>
<div><br>
</div>
<div>The proportional controller will inevitably fall below this
rate because it will ramp down to zero when no heating (or
cooling) is needed. Is there a workaround for this? I looked
into the autosegmentation feature and it doesn't seem to
subdivide the surface at all, and I'm not sure how this would
help. Thanks again.<br>
</div>
<div>
<div><br>
</div>
-- <br>
<div>
<div dir="ltr">
<p style="color:rgb(136,136,136);font-size:13px;margin:0px"><font color="#073763" face="arial, helvetica, sans-serif">Brad
Painting<br>
</font></p>
<p style="color:rgb(136,136,136);font-size:13px;margin:0px"><font color="#073763" face="arial, helvetica, sans-serif">Master
of Science Candidate, Renewable Energy Engineering<br>
</font></p>
<p style="color:rgb(136,136,136);font-size:13px;margin:0px"><font color="#073763" face="arial, helvetica, sans-serif">Department
of Technology & Environmental Design</font></p>
<p style="color:rgb(136,136,136);font-size:13px;margin:0px"><font color="#073763" face="arial, helvetica, sans-serif">Appalachian
State University</font></p>
<p style="color:rgb(136,136,136);font-size:13px;margin:0px"><font color="#073763" face="arial, helvetica, sans-serif">Boone,
NC 28608</font></p>
</div>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
<br>
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<pre cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
P:<a href="tel:%2B1.608.274.2577" value="+16082742577" target="_blank">+1.608.274.2577</a>
F:<a href="tel:%2B1.608.278.1475" value="+16082781475" target="_blank">+1.608.278.1475</a>
<a href="mailto:d.bradley@tess-inc.com" target="_blank">d.bradley@tess-inc.com</a>
<a href="http://www.tess-inc.com" target="_blank">http://www.tess-inc.com</a>
<a href="http://www.trnsys.com" target="_blank">http://www.trnsys.com</a></pre>
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