All,
What are some common sources/inputs that could cause unmet load hours,
especially for cooling hours?
Almost all of my systems are creating unmet load hours and I'm not sure
what inputs could be the cause.
Any suggestions would be greatly appreciated.
Thanks,
Lauren Rosenthal
There are so many things that can contribute to this issue or it could be a
lack of inputs that may be causing some issues. It depends, on underheating
or undercooling, it depends if all of the hours are happening in one zone
only or spread across all the zones?
You'll need to start by reviewing the SS-F and SS-R reports to get more
insight, then you might want to look at the SS-O reports for the specific
zones that are troubled. Sometimes it can be affected by schedules, or by
lack of inputs, or equipment sizing ratios, or by specifying CFM's or
equipment capacities, or , or, or....there are so many things that could
affect this.
Suggestions are to do a little engineering analysis on what could be causing
the types of under-conditioning you are getting, (i.e. is it because there
is not enough CFM being supplied to handle the loads?), next you could do
experiements by "turning off" some of the inputs that you have used and see
if one of those is the culprit, or you can ask someone else to look at your
file. You are welcome to send your .pd2 & .inp files to us and maybe
someone will have some time to take a look at it and help find your issue.
pasha
Lauren,
I can't offer any "typical" reasons that would sound like specific solutions based on my memory... but as you asked a general question here's my general thought-process...
Unmet load hours generally mean one of 3 basic things, and each of those have things to explore:
o Your heating and/or cooling loads are too high
? Check internal loads (i.e. people/equipment)
? Check envelope constructions and elements (i.e. walls/windows/shades)
? Check schedules
o Your systems are undersized
? Check airflow CFM's for expected/entered values
? Check hydronic GPM's for expected/entered values
? Check any entered capacities for all components - autosizing something previously specified and re-simulating sometimes gives you a clue or eliminates a possibility...
? Check any water and air temperature setpoints and coil delta-T's
o Your systems are not operating correctly in the model.
? Check operation/schedules of systems to be sure they can run when they need to
? Heed any cautions/warnings/errors presented in your SIM ATTN and try to resolve
? Check thermostat setpoints/throttling ranges and such
Much more similar advice can be found searching the mailing list archives - others have put together more specific lists you may want to peruse =)!
NICK CATON, E.I.T.
Lauren,
What is the system type?
Carol