BTU calculations question

[Boogity]

I'm presently in the field under poor working conditions. I do not have any of my reference materials. All "heck" is breaking loose and people are starting panic. I'm using someone's PC to get this request out to this forum.

What amount of BTUs will it take to lower 26,000 CFM air by 10 degrees F?

I know this is a lot to ask but would you please provide your calcualtions in your response. I'm under a lot of pressure here. Thanks.

 

[25362]

At what pressure and from what temperature ? Are these standard CFM or actual ?

 

[MintJulep]

Assuming you are talking sensible heat only:

BTU = 1.07 x cfm x delta T

However, cooling of real air almost invariably involves latent heat as well, in which case you need to know the starting and ending temperature and humidity.

One of many psychrometric calculators here:

http://www.engineeringtoolbox.com/psycrometric-air-calculator-8_240qframed.html

 

[Boogity]

Thank you very much folks. Isn't it strange how ones thinking ability diminishes in direct proportion to the stress applied?

We are trying to get a ballpark idea of the size of A/C unit required to lower 26,000 scfm by 10 deg. F. Latent heat ignored.

Actually the guys over in the mfg. area need to do some backwards engineering . . . they have an existing electrical equipment room with a panel fan blowing into the room from ourdoors. This air is passed over the equipment and out of the room via louvers into the mfg. area. The panel fan is rated at 26,000 scfm @ 0.1"wg. Due to the physical arrangement of the fan installation I cannot get a good airflow reading to determine the actual fan performance. So we decided to use the 26,000 cfm published by the fan manufacturer. We no longer want the equipment room air to enter the mfg. area because this part of the mfg. area is goint to be a clean room.

Assumptions:
1. A typical delta T for cooling of an equipment room of this type is 10 deg. F.
2. Someone (years ago) sized this fan at 26,000 cfm and it has been adequately cooling the equipment. We do not know the cooling load of the existing electrical equipment. I think the 0.1"wg is very light but I'll have to live with it.

Our goal:
1. Remove the panel fan and the transfer louvers.
2. Seal the room.
3. Install a package (thru-the-wall) DX air handling fan/coil unit.

Based upon the calculation you provided above I could size this unit for 300,000 BTU cooling and do the job that the existing OA fan is doing now. We could recirculate 95% of this cooling air with only 5% outside air. I'm considering a VFD drive on the supply fan to reduce the airflow during cold outdoor temperatures. This would eliminate the need for any type of heating in this A/C unit as the elect. equipment never requires heat.

Any comments or suggestions?

 

[MintJulep]

Boogity,

Too many assumptions!

Currently you have some flow of air through the room. You should measure the actual temperature rise of the flow.

Can you measure the flow at the exit louvers? If you could get the louvers cfm vs pressure curve you could simply measure the pressure drop across the louvers.