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<p>Grégoire,</p>
<p> A 30% oversize on necessary heating capacity is not unusual in
US HVAC design practice. I will refrain from adding personal
opinions about whether this is a good practice or not. ASHRAE 90.1
suggests a 25% oversize in their Appendix G. <br>
</p>
<p><br>
</p>
<p> You mention that you have sized the heating based on envelope
losses and infiltration. Don't forget that there is also usually
some fresh air that must be supplied to a space and that air must
also be conditioned (ie be part of your heating capacity).</p>
<p> </p>
<p> The recovery time also has a good bit to do with the thermal
capacity of a zone and of the delivery systems. In some work that
we have done on radiant floor systems we have seen that aggressive
night time setbacks are a bad idea because the thermal flywheel of
the radiant floor becomes very hard to control.</p>
<p><br>
</p>
<p>kind regards,</p>
<p> David</p>
<p><br>
</p>
<br>
<div class="moz-cite-prefix">On 04/26/2017 06:48, Greg B via
TRNSYS-users wrote:<br>
</div>
<blockquote
cite="mid:AM5PR0901MB0852D9E1DDEF61FF6F0E99D3F4110@AM5PR0901MB0852.eurprd09.prod.outlook.com"
type="cite">
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<p>Hello,</p>
<p><br>
</p>
<p>I'm currently modeling an old terraced building (construction
type bricks / 8 zones / North Europa - Belgium) with a certain
level of refurbishement (let's say an overall of 8cm
insulation). I designed the heating power of the different
zones, in the heating manger of type 56 in limited power,
based on the heating losses by transmission and infiltration
(design temperatures : internal temp 20°C / external -10°C).
But when I launch the simulation in winter in a intermittent
set point scenario (0h-6h : 16°C 6-8h: 20°C 8h-15h :16°C
15h-22h:20°C 22h-0h :16°C) the recovery time is very high and
in some cases it is not even possible to reach the high set
point even after more than 8 hours.</p>
<p><br>
</p>
<p>I don't know if some of you experienced this same problem
(such long recovery times)? I read in most of documentations
that I have to oversize the heating power in order to have a
reasonnable recovery time (let's say between 1 or 2 hours to
reach the high set temperature). When I do this I have to
oversize at least 30% of the original power and this seems
quiet high, isn't it? Any idea or doucmentation about a such
issue?</p>
<p><br>
</p>
<p>Thank you in adavance.</p>
<p><br>
</p>
<p>Best regards,</p>
<p><br>
</p>
<p>Grégoire</p>
<p><br>
</p>
<p> </p>
</div>
<br>
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<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>
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