I recently noticed this as well and decided to revive this thread to see if
anyone has insight. How do the roof conduction loads translate to HVAC
loads?
Based on the models I've run it's obvious that roof conduction is being
accounted for on the HVAC side and it appears to be about the right
magnitude. However, added roof conduction loads to the plenum do not
translate to any added space loads or building loads in the LS-x reports.
Does anyone have insight on how eQuest is handling them and why they do not
show up in space or building loads reports?
Thank you in advance.
Craig Simmons, LEED AP
Aren't they in the return air load? Or if ducted returned, simply translated over time into the space below?
I've definitely noticed the anomaly, and I have definitely had a
difficult time running loads because of it.
The way I have compensated for this is by assigning a temperature set
point to the plenum. eQuest seems to not consider any load going across
the roof and into space because it seems that the entire roof load is
assigned to the return air stream for the "Loads" portion of DOE2. If
the plenum is the same temperature as the space, no heat transfer can
occur, obviously.
By assigning the plenum a temperature, however, eQuest does calculate
heat gain/loss and such gain/loss is shown on the loads report as an
adjacent surface but NOT roof load. I've actually setup parametric runs
where a different plenum temperature is used each month based upon a
calculation that I run outside of eQuest calculating my plenum temp
considering the roofing materials and amount of return air passing
through the plenum. I've also included in my estimate how much heat
comes off the lights. It seems to me to be the only work-around to this
rather mysterious problem, and makes running loads in eQuest very
convoluted, IMHO.
In short, with roof load being assigned to the return air, the only way
you can account for a roof load in a space load calc is to tell eQuest
what temperature the plenum is. You have to do that outside of eQuest,
unless somebody has figured out a way to do it another way.
Thanks,
Gary Schrader
I took a look at the DOE2.2 Vol.4 Manual and I think my confusion is due to the information that is reported in the LS-x reports. The load reports are based on the design insidoor temperatures (e.g., 70F). Therefore, the loads reports do not show any interior surface conduction unless you have different design temperatures in adjacent spaces.
During the simulation, unconditioned spaces (e.g., the plenum) will not have constant temperatures, so hourly reports should show the roof heat being transferred to the space via interior surfaces. I haven?t actually gone fishing for the correct hourly reports yet, but I?m guessing they?re there.
Thanks.
Craig Simmons, LEED AP