Dear eQuest community,
I am working on a LEED project and have an issue where my higher efficiency
proposed system is using significantly more gas than the baseline system.
The proposed system is central AHU with zone VAV terminals fed by 96% AFUE
boilers. The Baseline system is Appendix G system type 3 PSZ with 80%
efficient gas furnace. I know there are tons of factors that go into this.
I noticed that the higher baseline fan energy and higher lighting load are
doing some of the work that the furnaces would do, but this doesn't account
for the whole difference. Anything that jumps out comparing these two
systems would be much appreciated.
since I have no one with greater eQuest knowledge in house, I am open to a
few hours consulting with someone at a reasonable hourly rate if you think
this could be resolved.
Thanks,
Jacob
Anytime that you compare to different system types you're opening yourself
up to a ton of potential issues just from the differences in how eQUEST
models each system.
For a VAV system that is using more energy than a packaged single zone type
system I'd recommend you look into a few things:
? Night fan cycling - if you've got single duct VAV terminals with reheat,
your entire AHU system will have to come on to address night heating hours.
Verify that you have a minimum OA schedule so that you're not ventilating
the whole building during these hours as well.
? Minimum airflow setpoints - Verify your minimum airflow setpoints at the
zone level are correct. This is where most of your reheat energy will come
from.
Those are the two that come to mind immediately, but there may be other
potential sources of error. Feel free to attach your building model (.pd2
& .inp files) to the list and maybe someone can look into it for you in
more depth.
Hope that helps,
-Robby
Jacob,
I looked at your file. If you look at the cfm's for each zone, the proposed
zones have more cfm than baseline. If the cfm is more than required, it
leads to more reheat energy also - since you have min flows in the 30-40%
range. You might want to check that or see why the baseline cfm numbers are
lower than proposed (since lighting is reduced to almost half in proposed).
Hope this helps.
-Rohini