AHU approach

[hvacers]

almost all of the approach of my AHUs in my building are very high eventhough it has already under gone its cleaning by pressure washer. the range of approach is 5F to 10F.

as what i know, the approach of the AHU should be normally ranging from 0 to 3F.

what could be the cause of this high AHU approach??

 

[MintJulep]

Did you fold all the coil fins over when you pressure washed them?

 

[hvacers]

yup, we straightened the fins using a small comb... but still the approach is high..

 

[ChasBean1]

Is the 0-3°F per mfr. for this particular coil? Is it chilled water? How many fins per inch and # of rows?

 

[SAK9]

Another thing to consider is the coil face velocity.Too low values(say less than 2m/s) can make the flow laminar and reduce approach

 

[hvacers]

the 0 to 3F is the standards as per AHSRAE... i havent seen the manufacturers specs because the building wasnt able to provide it to us.


it is chilled water, fin spacing is 2.12mm... the coil face velocity is 2m/s for air... right???

 

[SAK9]

Coil face velocity is for air side.Tube velocity(water side) should not be less than 1.2m/s.Also check if coil piping connection is done in a counterflow pattern ie warm air first to make contact with warmer coil tubes