Heat Removal by Ventillation 3

[Golestan]

Dear Fellow ME's
We need to remove heat generated by computers from a very large room by ventillation only. I am looking for equations (method of calculations) or advise on how to calculate how much heat is removed. I can use fans to blow outside air into the space and exhaust air to outside. Heat generation is about 60,000 BTUH.
Regards

 

[willard3]

CFM x 1.085 X delta T = btu/hr

If you know the temperature of the outside air, you know the delta T and can solve for 1 unknown (CFM)

 

[ChrisConley]

You also have to know what the max allowable temperature of the room is. Max room temperature - max outdoor temperature = delta T. If your max room temp is close to the max outdoor temp you may end up moving a _whole_ lot of air.

Computer's generate only sensible load. If you're using a pile of outdoor air to remove load you'll be adding a latent load (humidity problem).

It is probably (definetly) easier to add a 5-6 ton fan-coil into the space.

 

[Golestan]

Thanks Guys,
We will use lots of outside air (20,000 CFM) of OA in Dallas, TX. How would the humidity effect this process if any.

 

[SAK9]

The point raised by Chris is very valid for computer rooms which normally require the relative humidity to be around 55%.With mechanical ventilation you have no control on the humidity.

 

[AbbyNormal]

This must be a winter scheme. Still could be kind of dirty and dusty in Dallas in the winter, not like there is snow all over the place keeping the dust down, so you would have a bit of filters involved.

Summer time the best you could do would be to keep the space a little warmer than it is outside.



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[STYMIEDPIPER]

Is this a personnel occupied space??
Regardless, I agree with Abby and Chris that you should use a cooling unit with filters.
Ventilation only in Dallas??
As Abby indicated, you cannot have the space temp lower than outside temp without some type of mechanical cooling.
ASHRAE DB summer temp 100 deg F
Most computerized electrical mfg max temp is 104 deg F

 

[Golestan]

Thank you all. You are right, Ventillation alone, will not be practical. Room max temp is about 105-F, and outside air in Dallas in summer is about the same. I am thinking about adding some cooling (extracted from the central airhandler) by means of VAV boxes. And mix with outside air-or should we try to bring in any OA at all?

 

[STYMIEDPIPER]

Before you go in circles here--
You must first decide what is your design space temperature before you arbitrarily tie into an existing system which may adversely impact the existing system.
Apparently the existing system was not designed to accommodate your space as a computer room.
Not knowing your existing room physical layout ---bite the bullet and install dedicated system---in the end you will be better off.

 

[redgdon]

If your computer room is within 30m of an outside wall I would suggest using a multi-slpit DX systems to cool the room

 

[AbbyNormal]

The space load will be mainly sensible so you will need a high air flow per ton.

You need to figure out what temperature and humidity you want to maintain in the space. If the equipment gain is 60,000 there may be some gain through the envelope was well.

As a minimum I would guess you would be needing about a 7.5 ton system, and an air handler nominally rated for about 10 tons.

How critical is it if the cooling fails? You may want to consider redundant systems. You could design in a free cooling scheme as well, but as others have told you the first step is to determine what your exact load is and what conditions you want to maintain.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[atlas06]

Don't try to save your client pennies, he will kill you if his server goes down, and you know that the repair tech will blame the lack of AC for any failure.
When it comes to sensitive spaces, do not try to be a nice guy, spend your client's money, or he will be spending yours.
Use two AC units, one as stand-by, use the main VAV system for ventilation only.
The other thing is, you need to get air to the racks. A raised floor will do best if you can afford it.