Dear All,
The following is the procedure i use to calculate unmet hours:
1)??? Percentage of Plant and system unmet is got from BEPU report.?
2)??? The number of hours fan is on is got from SS-E report.?
3)??? Percentage of system unmet(BEPU) multiplied by number of fan on hours(SS-E) gives the Unmet hours.
4)??? Plant and system unmet together should not exceed 300 hours.
But as per ASHRAE 90.1, the 300hours of unmet is w.r.t. a simulation for 8760 hours. If the building is only 8 hours working 5 days a week, then the fan on hours vary. Will the same 300 hours hold good for 3500 hours of operation also.
The maximum percentage of Unmet for 8760 hours of operation is 3.4% amounting to 300 hours. Do we have to take 3.4% of the total fan on hours to calculate maximum unmet hours if the fan on hours is anything other than 8760?
Please help.
Regards,
Rathnashree
Hi Ratnashree,
You can directly see no of unmet hours for each system from SS-R report and
total number of hours (all systems) should not be exceed 300 hours.
Thanks!
Ashu
Rathna,
The simulation covers 8760 hours, but this does not imply 8760 hours of
fan operation. I don't see anything in Appendix G that requires you to
prorate the 300 unmet load hours based on the schedules of building
operation. So, just stick with the 300 hour threshold.
I suggest you follow your four-step procedure (in eQUEST or other
DOE-2), except that I've never had unmet plant loads so I'm not sure how
I would take that into account. I disagree with Ashu - adding up all the
unmet hours in all SS-R reports can double-count (or more) coincident
unmet hours.
Regards,
Bill
Unmet hours for occupied hours only has been discussed but there was no good consensus on exactly how to do this. So, yes, unmet hours are of the entire (8,760) simulation and are building level, meaning one zone or all zones unmet that hour is still just one unmet hour.
Trane CDS has a good document for combating unmet hours in TRACE 700. I think it's probably generic enough to be used for any tool.
Scott Hintz
CEM, LEED-AP BD+C, BEMP
Rathnashree and others,
I can further nail down the eQuest-specific procedural queries.
Summing the zone-level unmet hour reports (SS-R) can result in
"double-counting." I personally started out doing exactly that, but
eventually learned better =).
For the record, SS-R reports remain very useful for identifying &
isolating the spaces/systems involved in a high-unmet hour situation.
It's also worth noting the same totals for each zone & system are much
more easily reviewed under the 'Summary' tab under 'Air-side HVAC'
following a simulation.
Some discussion on the topic in the archives may be misleading for those
using eQuest version 3.64 and onwards. We used to follow a specific
"hunt and peck" procedure to correctly determine the number of unmet
hours using the "hours fans on" output in report SS-E. Users of 3.64
onwards can enjoy a much more simplified approach: Look to the summary
BEPS report!
Here is an excerpt from the BEPS report of a dummy file I have handy:
TOTAL SITE ENERGY 988.49 MBTU 39.5 KBTU/SQFT-YR GROSS-AREA
39.5 KBTU/SQFT-YR NET-AREA
TOTAL SOURCE ENERGY 2860.57 MBTU 114.4 KBTU/SQFT-YR GROSS-AREA
114.4 KBTU/SQFT-YR NET-AREA
PERCENT OF HOURS ANY SYSTEM ZONE OUTSIDE OF THROTTLING RANGE = 15.68
PERCENT OF HOURS ANY PLANT LOAD NOT SATISFIED = 0.00
HOURS ANY ZONE ABOVE COOLING THROTTLING RANGE = 6
HOURS ANY ZONE BELOW HEATING THROTTLING RANGE = 427
Here, you can clearly see the model has a total of 6 unmet cooling hours
and 427 unmet heating hours. Those are what some of us on the list have
coined "coincidental unmet hours," so that's to say there is no
double-counting involved. If this were the results of a model following
90.1 appendix G, one would need to identify and correct problems in the
model and/or system design to reduce that 427 figure to an acceptable
level.
Hope that helps clarify!
NICK CATON, P.E.
Thanks everyone for the inputs.
Currently i am working on the visual Doe software and this does not generate SS-R report. Therefore, i will have to rely on my 4 step procedure.
With regards to plant unmet hours, the total number of unmet hours is got in PS-D (Plant load satisfied) report. I can add this with system unmet to arrive at the total unmet hours.
Regards,
Rathnashree