Grouping together HVAC RTUs in a Distribution Center eQuest model - Problem with Space Heating Usage (therms)

2 posts / 0 new
Last post

Dear eQuest users,

eQuest novice here. I am attempting to model a large distribution center (650,000 sq ft) located in the North East U.S. with 68 Packaged Rooftop Units (some with gas furnace some without) and 8 rooftop gas Heaters eQuest by grouping together the RTUs and heaters across 8 different HVAC systems that aggregate the zones they serve. I modeled it this way because the distribution center has such a large volume due to its open floor plan and high ceilings that modeling each individual RTU to an individual zone would've been nearly impossible.

My model is currently acting up when it comes to the space heating usage. I have my 8 systems set up to be a "Packaged Single Zone" in eQuest, and when I run the simulation, the results show a large gas usage for Space Heating in Jan, some gas usage in February and Dec, and almost no space heating gas usage in the remaining months. The gas usage profile is attached (Reference Usage Profile Packaged Single Zone.png). The site normally has 400 therms of gas usage in the summer months. I don't understand why the space heating doesn't show a normal profile?

I thought this strange gas usage profile was because the systems were set to Packaged Single Zones. I programmed one system as a Packaged Multizone to test if this was the case, and the new gas profile can be seen in the attachment as well (Reference Usage Profile Packaged Multizone).

Did I miss something in the programming of the Packaged Multizone? Why would it be doing space heating in the summer months? How should I approach modeling this type of scenario?

I appreciate any help anybody can lend me. Much thanks in advance.

Justin Yoo

Justin Yoo's picture
Joined: 2013-09-26
Reputation: 0


It looks to me like the building is being heated by the miscellaneous loads and the lights, so the heat only turns on during extremely cold times.

The old-fashioned multizone system depends on simultaneous heating and cooling for temperature control. I suspect that the system is mixing really cold air with really hot air to get the supply air temperature just right. For much of the year the cold air is coming from the economizer, so the cooling isn't affected as much as the heating. I suggest checking the temperature setpoints of the hot deck and the cold deck.

Keith Swartz, PE, BEMP, LEED AP

Keith Swartz's picture
Joined: 2011-09-30
Reputation: 0