I am having a problem modeling a building which has a PVAV with a
pre-heat furnace and VAV electric reheat boxes. The pre-heat furnace is
intended to raise the temperature up to 55F while the heating is done
locally at the VAV electric reheat box. (This is where I have the
problem) At night (and weekend) the electric re-heat on the boxes are
shutoff and outside air is shut off. The building is set back in
temperature and heated via the preheat furnace. This is what I am
trying to find out:
1. Is there a way to schedule the electric reheat coils on the VAV
boxes?
2. Is there a way to shut off the outside air damper at
night/weekend?
Any help will be appreciated.
Thank you in advance,
ARTURO HERNANDEZ
1) Air-side HVAC Zone Parameters > Heating > Heating T-stat schedule
the schedule setting is temperature type, you could manipulate the
set-point such that it acts according to your design.
2) Air-side HVAC System Parameters > Outdoor Air > Minimum Air Schedule
the schedule setting is Frac/Design type, you could set it to "0" if
you want to shut off OA.
Schedule can be defined by right clicking on the schedule folder, then
"create schedule". Create Daily first, then Weekly, then Annual.
The system is supposed to run as an integrated unit, by changing
schedule of any individual component may result in too many unmatched
hours, you should check the SS-F report to see if that is the case. If
so, you might also want to check hourly result to see in details the
reason behind, and modify your schedule accordingly.
I hope I haven't misinterpreted your questions.
Bruno Lee
Thank you for your input. However I have these coments.
1) I need the zones to maintain at least 65F but only via the preheat
furnace. No electric re-heat via VAV boxes... I am not following how
setting the t-stat in the zone will help out.
2) The min outside air ratio is set to 0% but shouldn't at night but
that is just the Minimum.... wouldn't I want the maximum ratio (if it
exist)?
ARTURO HERNANDEZ
1) T-stat could be set to undefined, if you want to turn re-heat OFF
all the time. If you want to schedule the re-heat coil OFF at the same
schedule as min outside air ratio (such that, say at night, when min
OA = 0, re-heat is OFF), set it inside "user input expression".
2) When min outside air ratio set to "0", the system intakes
absolutely no OA (not just minimum ratio, although the variable name
implies so). I am not sure if that's what you want since you mentioned
you want to "shut off the outside air damper".
However, as mentioned, some zones may experience too many unmatched
hours if zone re-heat is OFF.
There may be other better ways to achieve your goals, please let me
know. Thanks.
Bruno