leaving dry and wet bulb difference of Evaporator coil

One of the enquiries from the consultant came 2 me for DX coil

Conditions were

Air IN 87.7F/59.2F (DB/WB)
Leaving 59.3F/47.5F (DB/WB)
CFM 5000
Capacity 153000BTU/hr

I am confused over the difference in DB and WB of leaving temperature Is it POSSIBLE? :confused:

for the figures you gave you would get:
Sensible heat load = 153,610.1 BTU
Latent Heat Load = -6255.5 BTU
Total Heat Load = 147,354.7 BTU
I would suspect the readings as you have negative latent heat..in other words the evap is giving up latent heat......

For your air in/out you have:
air in air out
Dew point = 34.8F 35F
RH = 15.2% 40%
H/Ratio w .00422lb water/lb dry air .00427
H/R g 29.6 grains 29.9g
SV 13.833 cu ft/lb 13.174
Enthalpy 25.69BTU/lb 18.87

Hope these mean something to you.....

tell u what guys i think it is dry surface cooling.

My question was how does this happen.


I know how 2 select the coil. you may see the attachment.

Seems pretty straightforward to me. The entering dewpoint is about 35F. Dew (moisture) is only going to condense on a surface that is colder than dewpoint. The coil surface was not cold enough to extract moisture, therefore you have a dry coil.

The leaving air, not having lost any moisture, still has a dewpoint of about 35F.

34.8 vs 35 is instrument error.