DUCTINGS LOSSES
DUCTINGS LOSSES
(OP)
HI,
Im an energy engineer of an HVAC company, i have a problem with one of my AHUs. I conducted Duct traverse to one of my ahus and measured the air flow of the diffusers to each area served. i measured 13000 cfm at the main supply ducting which just branched out of the AHU. While i just got a total 5000 cfm for measuring all of the air flow of each diffuser supplied by this ahu. the discrepancy is really large, can this be all accounted to loss??? or do i have i problem somewhere to my ductings?
JLV
Im an energy engineer of an HVAC company, i have a problem with one of my AHUs. I conducted Duct traverse to one of my ahus and measured the air flow of the diffusers to each area served. i measured 13000 cfm at the main supply ducting which just branched out of the AHU. While i just got a total 5000 cfm for measuring all of the air flow of each diffuser supplied by this ahu. the discrepancy is really large, can this be all accounted to loss??? or do i have i problem somewhere to my ductings?
JLV





RE: DUCTINGS LOSSES
What is the duct configuration here? How far from the blower discharge? Transitions? Turns? How was your traverse done?
It's possible that there could be a very large measurement error here.
Or you might have one really big leak in the duct system, or a lot of small leaks.
RE: DUCTINGS LOSSES
RE: DUCTINGS LOSSES
There's this little thing called conservation of mass.
RE: DUCTINGS LOSSES
the duct traverse was conducted at the main ducting from the air suppy of the AHU, where we took about 40 points spreaded all over the rectangular area of the ducting and took the average of all the 40 readings...
is there any rule of thumb about the conservation of the airflow?? example only 90% of the supply air will be delivered to the diffusers???
thanks for sharing ideas
RE: DUCTINGS LOSSES
RE: DUCTINGS LOSSES
RE: DUCTINGS LOSSES
I would suggest a physical inspection of the ducting and re sealing where needed.
B.E.
RE: DUCTINGS LOSSES
RE: DUCTINGS LOSSES
With the losses you are talking about, I would consider it a serious energy issue. Either traverse data was bad or instrument out of calibration, or you have a gaping hole. Spot manometer/dP readings should help localize, but at that flow you should be able to hear it. I would recommend physically observing every section of duct if the readings are correct.
RE: DUCTINGS LOSSES
RE: DUCTINGS LOSSES
but the problem is i dont know which traverse reading is correct. what my technician did is, he did not plug the static pressure(-) to the device. he only connected the total pressure(+) to the device.
while
I connected both the total(+) and Static(-) pressure to the device.
which setup is correct?
RE: DUCTINGS LOSSES
RE: DUCTINGS LOSSES
Maurice is correct you need both total( pitot ) and static at the duct. If your tech simply measured pitot pressure in the duct and room static, your reading is going to be way too high.
B.E.
RE: DUCTINGS LOSSES
RE: DUCTINGS LOSSES
Brian
RE: DUCTINGS LOSSES