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AHU Sizing

AHU Sizing

AHU Sizing

(OP)
Using basic heat transfer rules I have determined how much heat will enter a room on the "design day".  I have also added the amount of heat rejected from equipment in the room to determine the cooling load on the air handling unit responsible for cooling the room to a predetermined temperature.  Now let's say that my total heat dissipation is 100kW, why has the vendor come back to me with a unit that has a potential cooling load of 150kW?  Is this because I have only analyzed the one system (the room) and they have taken the unit as a second system and determined how much cooling is required to cool the outside air?  Can anyone explain this?  Thank you for your help, it is always appreciated.

RE: AHU Sizing

Did you include the following:
-Latent load from people
-Outdoor air sensible & latent load
-Heat gain from the supply air fan
-Heat gain from the return air fan
-Heat gain from supply air ductwork portion in unconditioned soace
- Heat gain from return air ductwork in unconditioned space
- Infiltration (sensible & latent) if any
- Heat gain from lights

The latent capacity of package units may be more than you require but you have to accept it to meet the sensible load.

RE: AHU Sizing

Also, at what conditions is the unit rated for 150KW? It might be nominally rated for 150KW, but de-rated to 100KW for the actual space conditons and outside air temperature for your application.

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