why is there higher humidity in the SA than the RA my AHU
why is there higher humidity in the SA than the RA my AHU
(OP)
we have a building with a bad humidity problem.
the building is in a neg. pres. in baton rouge, LA
the RH is near 80% through out the building
when I place the probe of the RH meter in the SA duct when the AC is off it reads the same as the conditioned space
when I turn on the AC the RH rises to 90% in the SA duct
why does the SA duct read higher RH than the RA
if in fact the chiller water coil is removing moisture
the building is in a neg. pres. in baton rouge, LA
the RH is near 80% through out the building
when I place the probe of the RH meter in the SA duct when the AC is off it reads the same as the conditioned space
when I turn on the AC the RH rises to 90% in the SA duct
why does the SA duct read higher RH than the RA
if in fact the chiller water coil is removing moisture





RE: why is there higher humidity in the SA than the RA my AHU
Do you have reheating arrangement after the cooling coil? If not the RH should be high because you are narrowing the difference between DBT and WBT. Once the air comes into the room it picks heat from the surroundings and DBT increases. Check along the length of the ducting and you will find decreasing RH.
The less the difference between DBT and WBT the more is RH and vice versa.
Regards,
Repetition is the foundation of technology
RE: why is there higher humidity in the SA than the RA my AHU
RE: why is there higher humidity in the SA than the RA my AHU
RE: why is there higher humidity in the SA than the RA my AHU
RE: why is there higher humidity in the SA than the RA my AHU
IE..you know that the unit is cooling..thus removing moisture from the air..
Verify that you have an 18-20 degree drop across the coil.
Verify you are'nt pulling in an excessive amount of outside air at the ahu.
Verify the ahu is not outputting very far above the design requirements(cfm).
and most of all...find out why the building has a negative.
IE...90+ degree outside air being sucked into the building is a major problem....have a big kitchen hood or other exhaust in there? Outside air cfm's are all set?
Test and balance the job...remove the negative..have the other items i mentioned checked...should be a problem solved.