[EnergyPlus_Support] VAV vs Fancoil Analysis

["ntraughpee" <matthew.sverre.anderson@xxxxxxxxx>]

Hey Everybody,

So our "standard HVAC design" setup where I work at the University of Nebraska (Go Big Red!) is basically a VAV with reheat. One of the big reasons we haven't used any sort of chilled beam design or that we shy away from using higher end unit conditioners is due to the high humidity during the summer and our need to dehumidify. However, as the new convective chilled beam designs have come out and studies in similar climates have shown that with proper humidity control thru a central air conditioning we have become more open to the idea. 

My boss had me model two separate systems to heat/cool the same building (in two separate runs) with demand controls similar to what we would write to model the buildings. The building description is as follows: 4 floors (with 1 being a basement), 12 zones, with schedules similar to what a school would look like (heavy fall/winter/spring use and not very heavy heavy in the summer). I settled on using a fancoil with variable flow/variable speed fans for the unit conditioners, combined with a DOAS, since I felt it was thermodynamically similar to what we were looking for and would answer our questions and models gave out some interesting results.

Obviously the electric use for the VAV system is higher since more energy is used in pumping air but our peak demand is for electric/chw/heating is all higher in the fancoil than the VAV. That being said the CHW and HHW consumed by the fancoil is much higher than the VAV. I understand the CHW consumption being higher (it is about 13% higher) because we lack an economizer but the HHW increases by 10% from VAV to fancoil.  That being said, realistically the total energy consumed by both models is withing 2% of one another which means they are basically equivalent. Does anybody have a good idea why this would be?

I am also looking to see if there is a way to view what the surface temperatures of the zones would be? Does the fancoil heat the surfaces and the air whereas the VAV is just heating the air and the surfaces stay cooler? That is about the only thing I can think of where the VAV is able to use less heating because it loses less energy by convecting heat into the perimeter walls than the fancoil.

Does this make sense? 



------------------------------------

Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx

The primary EnergyPlus web site is found at:
http://www.energyplus.gov

The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/

Attachments are currently allowed but be mindful that not everyone has a high speed connection.  Limit attachments to small files.

EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/

<*> Your email settings:
    Individual Email | Traditional

<*> To change settings online go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/join
    (Yahoo! ID required)

<*> To change settings via email:
    EnergyPlus_Support-digest@xxxxxxxxxxxxxxx 
    EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx

<*> To unsubscribe from this group, send an email to:
    EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/