[Equest-users] DCV Demand Controlled Ventilation

Karen Walkerman kwalkerman at gmail.com
Thu Dec 4 15:59:07 PST 2008

one trick with eQuest, is that if you specify fan controls as "variable" or
"cycling", is that the fans don't supply the required ventilation air, if,
for example the space requires only 15% to condition it (and 30% ventilation
air).  If I have cycling or variable control fans, I set my fan controls to
"variable" and set the minimum supply ratio equal to my outdoor air ratio.
This then gives a pretty accurate representation of a system that cycles
fans on and off (use the right fan curve to approx cycling), or of a
variable speed system (again, appropriate fan curve), but has constant
ventilation air.

If you don't do this, what happens when you turn on the DCV, is that the
system is now required to provide ventilation air, so your building may now
be getting MORE than it was before, although this obviously won't happen in
real life.

The other (less likely) thing that could be happening, is that if you have
not updated your occupancy schedules from the wizard, is that your occupancy
schedule for this space is not appropriate for a dining room, but is
averaged with all other occupancy types.

Good luck,


On Thu, Dec 4, 2008 at 3:43 PM, larry.howlett <
larry.howlett at htmdengineering.com> wrote:

>  I am trying to model Demand Controlled Ventilation.     Although I know
> that reducing the ventilation when a dining room is empty will save utility
> costs,   My results keep showing that this addition will cause higher
> utility costs.    Am I missing something when setting up the HVAC  system?
> Larry Howlett, P.E.
> *HTMD Engineering*
> 815-751-3741
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
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