[Equest-users] PVVT vs PVAVS

[Bishop, Bill]

Jeremy,

First thing I would do is look at the BEPU reports and compare space heating, space cooling, vent fans and unmet hours. If there is a difference in unmet hours, investigate in the SS-R reports. Then compare the monthly energy breakdown for the above categories as shown in the PS-E reports. Also look at SV-A to see differences in default system sizing if you didn't enter the same values manually.

These are the differences I notice in the default settings:
PVAVS has slightly higher fan power. However, I suspect differences in fan energy will probably be more of a function of cooling control differences between PVAVS and PVVT.
Fan control is "Inlet" for PVAVS and "Variable Speed" for PVVT.
Different performance curves.

I'm not sure if PVAVS assigns zone reheat automatically, but that is a big difference between the system types.
PVVT is going to be in heating/cooling mode based on the control zone, so you should expect unmet hours in multiple zones assigned to the system.
It is not surprising that PVVT is giving you less energy than PVAVS for these reasons.

Regards,
Bill

[Senior Energy Engineer 28Jun2012]<mailto:wbishop at pathfinder-ea.com>

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Jeremy Poling
Sent: Wednesday, February 27, 2013 11:25 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] PVVT vs PVAVS

I'm having a hard time understanding how the PVVT and PVAVS systems would end up with dramatic differences in heating energy consumption and wanted to know if anyone had ever compared the two before?

I'm calibrating a model for an existing building.  The installed system is one of the common Trane SWUD units with single-stage electric heat and three-stage cooling.  If I model the system as a PVVT system to capture the staging, the energy use in June/July/August is within 5% of actual consumption but is understated by ~25% in the shoulder months and almost 50% in Dec/Jan.  If I model the system as a PVAVS system, heating months are within 5% but cooling months are overstated by ~15%.

The only keywords I adjust between the two are the ones that eQuest automatically adjusts when the system type changes.  One possible cause of the problem from what I can see is that the PVVT system requires a control zone and that control zone defines temperature for all of the other zones (resulting in a lot of unmet load hours - up to 88% depending on the control zone selected).  Any thoughts?
Jeremy R. Poling, PE, LEED AP+BDC


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20130228/dbddf459/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 20869 bytes
Desc: image001.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20130228/dbddf459/attachment-0002.jpg>