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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 class="moz-cite-prefix">On 10/04/2015 21:52, Bradley Painting
wrote:<br>
</div>
<blockquote
cite="mid:CAOLtPNBHY+FjGzrHHH7Gc2jgOLc53+c-u-rCi+-pgBBYqzms2A@mail.gmail.com"
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 class="gmail_signature">
<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>
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<br>
<pre class="moz-signature" cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
P:+1.608.274.2577
F:+1.608.278.1475
<a class="moz-txt-link-abbreviated" href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.tess-inc.com">http://www.tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.trnsys.com">http://www.trnsys.com</a></pre>
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