Dear Jeannie,
This criteria comes from ASHRAE 90.1 ,as you probably know. ASHRAE
90.1 does not define this value, although I think perhaps they should. Since
they do not, I suspect that it’s up to some interpretation.
Normally, my “unmet loads” are at startup periods
and do not last for more than an hour or so. In my opinion, this is not too
important, since you can always start the system a bit earlier on the coldest
or hottest days. I suspect that ASHRAE’s underlying rationale for not
having too many unmet load hours was that they did not want the system
deliberately undersized. If you can justify that it’s not (deliberately undersized),
you may be OK.
p.s., This is my opinion only. I have not debated the issue on
a LEED certification!
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of jeannieboef
Sent: Wednesday, September 29, 2010 2:25 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Time Set Point Not Met - Radiant Floor
Heating System
Time Set Point Not Met Tolerance is 0.2°C ( ... DOE had
specified a tolerance of +-0.5F for this...energyplus has a default of 0.2
degC). Am I justified in relaxing this tolerance on a system that obviously
cannot respond to fast and so accurately to flux in room temperature?
Increasing the "Capacity" of the system will not fix this.
Should I then relax the tolerance on the baseline heating system also?
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