Grégoire,
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.
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).
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.
kind regards,
David
On 04/26/2017 06:48, Greg B via
TRNSYS-users wrote:
Hello,
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.
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?
Thank you in adavance.
Best regards,
Grégoire
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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
d.bradley@tess-inc.com
http://www.tess-inc.com
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