Discussion of 1.08 CFM Delta T

[john1]

All,

I was hoping to have a discussion / direction on applying q=1.08 CFM delta T. I have a pump room that is 10' high, 13.3' wide and 14.8' long. Equipment is providing heat gain to the space of 52,480 Btu/hr and I am using a wall exhaust fan and intake louver. I have traditional designed around a 15 to 18 degree rise (use 18 for here). This calculates out to be about 2,700 CFM (81 ACH). This is about 20ft/s and the outside air is 99 deg. The equation tells me that I will be exhausting 117 degree air which I am having trouble (today) believing that air will actually heat up that much moving it through such a small space and that quickly. An air turn over rate of 15 seems more reasonable, but equation wise that is 500 CFM and a 97 degree wise.

The goal is to limit the temperature rise in the room. Is "q=1.08CFM delta T" being applied/interpreted correctly in this situation? Am I outside the limits of what that equation is meant to provide?

thanks

j

 

[AbbyNormal]

Bernoulli equation is all in head, meters or feet of whatever is flowing.

You can use a constant like 4005 for example to allow for 2 times gravity, a denisty conversion between water and air, a time conversion from seconds to minutes, and a conversion from feet to inches

Pretty much any type of pressure regulating valve by danfoss sold on the west side of the Atlantic is in Bars with bar being another soft conversion of atmospheric pressure in SI.

Inch of water makes sense as that was the technology of the day on how to measure. Pascals are a good unit for air pressure in HVAC systems the base unit is puny enough, it is sort of like how grains are easier to work with then lb of water per pound of dry air, as it gets rid of the zeroes.

In the IP system for HVAC, pretty much everything to do with heat transfer is based on water.

Heat up one pound 100 degrees with 100 Btu.

little easier to work with than four thousand and something joules per kilogram. Can use calories and grams then I suppose.





The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install