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Thread: Fan Sizing and V.A.V.'s
05-13-2012, 10:29 PM #1Regular Guest
- Join Date
- Feb 2010
- New York City
Fan Sizing and V.A.V.'s
A supply air fan , controlled by a Variable Frequency Drive, supplying multiple V.A.V.'s
If all the V.A.V.'s are 100% open Is the Fan generally Sized so that it will
operate at Less than 100% Speed,And still maintain the desired staic setpoint
05-14-2012, 04:03 PM #2Professional Member*
- Join Date
- Jun 2010
- Philadelphia PA
The reason you have a VAV system is YOU ARE NOT GOING TO HAVE ALL THE BOXES CALLING AT THE SAME TIME
It is called diversity, that means the East boxes call in the morning with the west not needing the max until PM then the sun is no longer on the east. 80% of the max peak loads is the rule of thumb for the max demand with the partial load needs less than thatYou have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!
06-06-2012, 10:22 AM #3
the only time the VAV boxes are at 100% are during morning warm up and or night setback for full fan and to make a preset setpoint...basically a constant volume system.typical VAV systems run 1.5" of static at 55F and when the space is satisfied the VFD is running a 30Hz signal to the fan.as the VAVs move around from minimums to maximums the VFD will react to that duct static build up maint.that 1.5""when in doubt...jump it out" http://www.youtube.com/watch?v=aMy-sAHwS4E
06-06-2012, 11:07 PM #4
They ramp down to maintain static and its how the old pnuematic systems with variable inlet guide vanes and pnuematic reciever controlers worked.
Lowered amp draw too as the load in the building decreased.
I still have a couple of small office buildings that are from the ground up pnuematic. Once they're calibrated correctly and as long as the air drier and air compressor dump works they're practically bullet proof.
Only time I get zone issues us when some engineer monkees with the T stats.
06-07-2012, 06:29 AM #5
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