Can Transfer Air Effectively Cool a Small Server Room?

[Samj008]

Hi there,

I need to prove to an architect that the most economical and efficient way to cool our server room will be with an Airconditioner.

At present we have a system which is supposed to recycle the warm air downstairs suring winter and Outside during summer, only it doesn't draw nearly enough air to keep the server room cool.

The room is 1.1M x 1.8M x 2.5M and the machinery inside is producing roughly 5,000 BTU P/hr. The room temperature at the moment is getting up to 30 plus degrees C on mild days with the door wide open (I Dare not close the door to test)

The architecht wants to drill a whole in the floor and allow the marginally cooler air in from below, possibly putting another fan in the floor to provide more flow.

My argument is that the amount of flow required to cool that room to what is necissary using fans and electricity is going to outway any supposed environmental benifit from not using Air Conditioning, however I need to prove that.

Is there a calculation for the amount of air needed to cool a room that size where that much heat is being produced??

Cheers for your help in advance.
Sam

 

[Topher925]

It's a simple first law of thermodynamics problem. You basically have an open system where 5,000 BTU/hr of heat is being added and needs to be removed my a mass flow of air in order to reach a steady state temperature.

The first step is to determine the mass flow rates of air required to remove the heat from the server from both the hole in the floor and the air conditioner. The mass flow rate of the air from the AC will obviously be less than that coming from the hole in floor because its probably going to be at a lower temperature (peak efficiency).

Then its basically just comparing the electrical and capital costs of the fan and AC unit to see which one is cheaper. For this you will need to find the power consumption of the fan and the AC unit and probably include maintenance costs as well.

BTW, AC units are expensive and suck up a lot of juice, so don't be surprised if a hole in the floor with a fan is considerably cheaper.

 

[mgb_phys]

Whats the outside temperature where you are?
It's a lot cheaper (economically and environmentally) to just move a lot of outside air than to cool it.
Then take a look at the layout of your systems and the airflow.
Do you have racks full of servers with fans blowing out of the back straight into a wall?
Adding ducting and fans to get the best airflow around the machines is better than just overcooling everything.

 

[russ_watters]

It is almost always cheaper to use transfer air than to cool air, if the required delta-T isn't too low. What you need to do is use the temperature requirements of the equipment to dictate the answer to the problem. If, for example, the air downstairs is at 75F and your maximum allowable temperature is 78F, then you need 5000/1.1/(78-75)= 1500 CFM.

That said, it is typical for network closets to require the air be cooler than occupied spaces, so using transfer air would be out of the question in that case.