Hi All~
I've been posting about loop overload problem and still haven't got any
responses.
In the archive, some equesters had cast questions regarding overload
problems, but they don't seem to get answers either.
It it really that, no one knows how to fix it, or no one had experienced
overload problems but us who question about it.
I just want to know why the over load is being shown in the loop
report(PS-D),
and any possible approach to fix the overload.
Any advice or a mere comment will be a great help!
Thank you!
Kim
All,
I've seen this topic come and go many times as well and have hesitated in the past to share my thoughts, but having spent enough time pondering this I figure I may as well share my opinions to further the discussion:
My understanding is that loop capacity warnings often fall in the category of attention messages that can easily be checked and dismissed as erroneous.
It's my understanding one of two things is the usually case when you get one of these warnings:
1. Your primary hydronic heating/cooling equipment is actually of insufficient capacity to keep up with the highest demand incident on the loop, in which case you have a real problem that will likely manifest as significant block of unmet heating/cooling hours, assuming typical thermostat inputs. One way to check appropriate equipment sizing is to check the PEAK load for the loop/equipment of concern in the PS-C/PS-D reports against a tallied sum of the CAPACITY for all associated equipment, as reported in the PV-A report. Be mindful units are typically of different magnitude between these reports.
2. More commonly, the program has calculated a secondary capacity which exceeds the primary equipment capacities *in sum*. This secondary capacity is a "sum of maximum capacities" (i.e. the most each heating/cooling coil can do, as autosized/specified, in sum), and can easily be well in excess of the maximum hourly load incident on the primary equipment during the simulation. Another way to put it is there's no "whole-building" diversity worked into the secondary capacity figure that shows up in the ATTN report. In such cases, the primary capacity as autosized/specified can in fact be just fine.
The designer sizing the primary equipment should be able to speak to what degree of diversity (if any) is intended for the whole building heating and cooling loads for determining equipment capacities. Different systems will have different ranges of "normal" for whole-building diversity, and it isn't uncommon for hydronic cooling vs. heating systems to be designed with different capacity diversities for the same project.
I'd be interested to hear if others have a similar perspective or further insight as to when such cautions can be disregarded and when they're cause for real concern.
Hope this helps you in the meantime Kim!
~Nick
[cid:489575314 at 22072009-0ABB]
NICK CATON, P.E.
Hi Kim,
This warning on the PS-D means that the equipment on the loop is undersized to meet the demand. You should check to make sure that the peak load reported on the PS-D report for each loop can be met by the capacity of the attached boilers or chillers. If you're allowing the boiler and chiller to size themselves, you can sometimes get this error message if you put a process load directly onto the loop; the equipment won't do a good job of sizing itself properly.
Rosie
Roselin E. Osser, PE, BEMP, LEED AP BD+C
PS: Looks like you may have accidentally replied only to me and not the group - feel free to forward this continuing conversation on to the group if you are comfortable doing so. I will be unavailable for some time personally!
Regards,
~Nick
[cid:489575314 at 22072009-0ABB]
NICK CATON, P.E.
Thank you Nick for your insights.
Please anyone feel free to add comments, further questions regarding this
subject!
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