Using the AHU Room as a Mixing Chamber

[WRNR]

When we test the units capacity (Grand Total Heat delivered by the unit), we are getting a low capacity. Is it possible that another AHU can affect the performance of its adjacent unit if both return air of the units are being mixed in a common chamber or the room it self is used as a plenum box?

We have the following data for the two units:
AHU No.1 = 60 Tons of Ref.
Supply Air Temp.=23ºC DB/18.5ºC WB
Return Air Temp.=24ºC DB/21ºC WB
Fresh Air Temp.=32ºC DB/24ºC WB

AHU No.2 = 60 Tons of Ref.
Supply Air Temp.=23ºC DB/19ºC WB
Return Air Temp.=24.5ºC DB/21ºC WB
Fresh Air Temp.=30ºC DB/23ºC WB

AHU Room Temp.=25ºC DB/20ºC WB

Im using the formulas,
Grand Total Heat, Q = m (h2-h1) and
Grand Sensible Heat, Q = 0.24 m Delta T

 

[walkes]

Why do two AHU's sharing the same fan room have different Fresh Air temperatures?

 

[HVAC68]

What are the air quantities ? Fresh air as well as the supply air.

You have mentioned that the supply air temperature is 23 deg C. I suppose this is the room temperature. To find out the coil capacity, apply the following formula

Q = 4.5 x cfm x (Delta h)

HVAC68

 

[WRNR]

To Walkes, that was the design/intent of the consultant and the fresh air measured is from the two (2) fresh air openings. The fresh air opening is not connected to the units, since the fan room is being used as planum box.

To HVAC68, i'll try that formula. Thanks.

 

[ND2005ME]

WRNR,

Watch your units! That "4.5" factor is for the ft.lb.s system, not the m.kg.s system. Unless you convert your volumetric flow to cubic feet (per minute not per second) and your enthalpy from SI to American units, you will get incorrect results.