# IT Employment

## General discussion

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### How to right size the cooling system in the data center.

By ·
I'm trying to determine what the right size would be for an air conditioning unit to cool my data center. Can anyone tell me the "formula" to determine what it needed?

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### Calculation of Air Flow for a Given Heatload

by In reply to How to right size the coo ...

In a data center, heat loads are known for different computers or server racks. From this
information, we need to obtain the cooling airflow rate in CFM required for satisfactory cooling of the electronics equipment. The objective of the data center airflow design would then be tosupply this flow rate through the perforated tiles located in the immediate vicinity of the server.

The cooling air will normally be supplied at 55?F. An acceptable temperature rise through the
server is about 20?F. Thus, the air will exit from the server at 75?F. The controls on the airconditioning units are normally set to maintain the return air at 75?F.

Therefore, for a given heat load dissipated by the server, the correct airflow rate should lead to a 20?F temperature rise as the cooling air travels through the server. This requirement can be expressed by the following formula:

Cooling airflow rate in CFM = 154 ? Heat load in kW ? (Reference Pressure/Local Pressure)

(In this expression, the reference pressure is 1 atmosphere and the local pressure depends on the
local altitude. Local pressures at selected altitudes are given in the list below. )

When the arrangement of perforated tiles and air-conditioning units in a data center delivers this airflow rate at the foot of each server, proper cooling of the electronics equipment is assured.

If this cannot be done, the equipment will overheat.

Altitude (ft) Pressure (atm)

2000 .93

4000 .86

6000 .80

8000 .74

10000 .69

Enjoy!

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### Maybe I should explain more

by In reply to Calculation of Air Flow f ...

Thanks for the info. The "data center" I'm referring to is actually a regular room without raised floors. The company I work for has been in the dark ages for quite some time. I'm trying to pull them into this century. I've finally gotten them to agree to air condition and control the humidity in this room. (The current temp is 80 degrees F and the humidity is 32%). The contractor we have giving us a quote, arrived at the size unit he's recommending by adding up the wattage of all of the units, then divided that number in half and converted it to BTU's. I'm just wanting to check to make sure what he's quoting will be adequate. Thanks!

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### Here's how we do it.

by In reply to How to right size the coo ...

Get the KVA or Amp load off your UPS (from a guage if possible) if it's just lights then its worthless and you're going to need an amclamp on the load wire of the circuit. take the amp reading and multiply it by the voltage and divide by 1000 gives you KVA reading. If the reading is already in KVA then just convert to KW

A*V/1000=KVA KVA*.85(efficiency number I use 85% pretty accurate for computer equipment)=KW

KW*3413 = BTU

BTU/12000=Tonage for AC

I would do some serious thinking about an AC system before you have it installed.

2 units are better then one. if one breaks the other will at least get some of the job done. Minimal expense. consider the cost if all your servers overheat and **** their lids. plus lost time while they are down.

are you going to expand the number of servers y ou have? if you think you will get 2 more figure out the load per server and add 10 better to build big then small.

Always add a fudge factor for outside air temperature 20-25% the air outside coming through the door in the building WILL influence the size of the AC system you need.

Hope that helps

SA-

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### Thanks

by In reply to Here's how we do it.

I'll check into two versus one A/C unit.

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