I am modeling a building which uses exhaust fans in the electrical rooms. These fans are designed to be on when the room temperature is above 85?F and off when it is below. How would I set a schedule up in equest to run the fans in this manner?
Thank you,
David Cantrill
My initial thoughts is to model the exhaust fan as a supply fan. then set
up your fan schedule to turn on only to meet space loads and create a 85
deg thermostat schedule. Then set up your system to get its outside air
from another system to simulate the fact that the exhaust fan will be
drawing air in from adjacent spaces. hopefully someone out there might
agree or add to my initial thoughts.... (please)
hope this helps
Rob
How I handle exhaust like this varies from project to project..
As a preface, the easiest/simplest way to handle any exhaust that draws air from another conditioned space is to define an exhaust CFM and schedule on the system from which the conditioned air is being drawn, or at the space the air is being drawn from (I don't believe the exact location where you define the exhaust is critical, but it helps you/others understand what you were doing after the fact) - as a corollary I usually call such spaces without conditioned supply air 'unconditioned' spaces in modeling terms. This approach however funnels you into using a fractional or on/off schedule. This may be perfect if your exhaust is 24/7, running on a fixed schedule via BAS or timeclock, or tied to the restroom lights (just use the light schedule).
If/when you want the exhaust to run off a space thermostat temperature, I don't think you have any alternative but to define a system for the space(s) involved, as Rob is getting at. I'd suggest the simpler approach above unless you have time to spare or want to know a "righter" way to approach the issue ;). There's multiple ways to skin this cat in eQuest...
I'd suggest starting with a PTAC:
? make it CV,
? zero out its cooling EIR (the cooling is "free" being drawn from elsewhere),
? remove any heating element that may be there by default (not sure without looking)
? set its min supply temp to match the conditioned space temp being drawn in,
? input fan energy (kW/CFM) to match the exhaust fan(s) - zero out the temperature rise to the airstream while you're at it
? modify the space/cooling schedule thermostat setpoints to the temperature being maintained
? oh yeah - make sure the control zone matches where the thermostat resides.
That should get you in the ballpark... on further thought you might set the cooling EIR to match that of the system actually conditioning the air being drawn in - invest as much time in this as you deem necessary ;).
~Nick
NICK CATON, E.I.T.
Classification: UNCLASSIFIED
Caveats: NONE
I use Trace, so I don't know if my answer can help.
In Trace I set up a schedule of 100% on, and there is an option to for
conditions and I had the condition as OFF if the room is below 85degrees.
Here is the important thing, I had to model the incoming air as infiltration,
I set up an infiltration schedule and set the infiltration to model the fan.
If I didn't do thing, the wanted to run the air though some piece of
equipment with a coil.
Bottom line, I did this, but I had to set up the fan as infiltration.