Fan Sizing 1

[Bluzman]

I have a room I need to cool 5-10°F, using outside air only. The volume of the room is 20,000 cuft. The heat load is 200KW. What is the CFM of my fan?

 

[cdxx139]

Q = U A deltaT

Is your outdoor temp 10-15 degF cooler than what you want your indoor conditions to be? Plug in to the formula and what do you get?

knowledge is power

 

[MintJulep]

Good formula, but wrong application.

 

[cdxx139]

Derrrr, Q = 1.08 CFM delta T

Thank you Sir, sorry for the brain fart....

knowledge is power

 

[willard3]

You need some Engineering guidance if you don't already know this formula. Hire one or ask someone in your office.

 

[317069]

How did you calculate 200KW heat load

 

[Bluzman]

200kw is my heat loss

 

[cdxx139]

Yes, and how did you calculate it?

knowledge is power

 

[Bluzman]

This is from the manufacturer of the vfd plus the other equipment. I have my answer it is about 40000 cfm

 

[ChasBean1]

Bluz, please re-think this. A Standard exhaust is 1 cfm/ft2 which is around 2,000 cfm for your space and not 40,000 cfm. A bit of a difference. If you are trying to achieve 80°F in the space and it’s 85°F outside, you can exhaust infinity cfm and not quite reach your goal. Better get a 500 HP fan… Re-consider your requirements.

 

[Waramanga]

+1 Willard, OP needs professional assistance.

 

[Bluzman]

OK.......
It is an electrical room with 3 1900kw VFDs and several MCCs. I have not done this type of calculations in 25 years rusty and not trusty.
the VFDs are ~96.5 eff.=66.5kw x 3 = 199500w + other equipment; roughly total 250kw.
250,000 watts is my heat loss from the equipment = 853,035 btu/hr
I want the temperature in the room no greater than 85°F therefore max delta T=19
Q = 1.08 CFM delta T
do the math and ........41571 cfm

my room is 20,000cuft about 2 min to exchange the air.

Does the room melt?

Thanks for all of your inputs even the ones that provided no help
and your right I need help but that is what this site is all about, have a great day!

 

[317069]

What is the outside temperature, and what is the problem if your exhaust fan was 40000 cfm

 

[Bluzman]

summer day at 100°F. I HAVE TWO FANS AT 20K CFM

 

[317069]

in such a summer day you can not keep 85F inside by using 100F supply air, no matter how much is your cfm unless if you use cooling unit, are you able to use evaporating cooling that is used in hot dray areas.

 

[Bluzman]

I cannot use anything but ventilation outside air. So what is the solution?[pre][/pre]

 

[317069]

No solution, in summer where you have to reject heat from a space, if you supply 100F air to a space, you can not keep this space at 85F without a cooling process.
but in winter where you have to provide heat to a space, you can keep 85F in a space by using supply air of 100F or more depend on the situation.

 

[ProcessHVAC]

If you condition your space to 85 F with 100% OA with ventilation only and no mechanical cooling, you will win an award for defying second law of thermodynamics ..and/or first depending

 

[willard3]

At the risk of repeating myself: you need some Engineering guidance. Hire one or ask someone in your office.

 

[Bluzman]

Willard3 I respect your opinion but....

I may have stated the problem incorrectly lead you down the wrong path, I apologize. I want to limit the rise to 15 degrees. So, for a typical summer looking at 95F, you need about 210 CFM for every KW, therefore, revised heat loss of 220KW gives me about 46,200 CFM.

working out q=1.08cfm delta you get approx. the same thing. using 220kw~751,000btu/hr

thanks