Air Conditioning for a Data Center

Praveen-- I think it's to tighten the temperature control loop. HVAC engineers out there......Did I guess right on this one?

Ed Weldon

Dear Praveen.

In air conditioning air is cooled and humidity level is normally about 50-55%. To reduce humidity is to heat air to certain temperature. Normally you can bring down humidity to 40-45%.

If humidity level requirement is lower than you have to use other process.

Regards

Panthaki

cynny@rediffmail.com

Baroda.

Dear Panthaki ,

I thank you very much for your comment . Now iam clear with the addition of heaters

in data centre .

Regards,

Praveen

praveen.hc@rediffmail.com

Data center air conditioning have to be sensitive to humidity beacuse condensation and electronic equipment do not mix. Heat is used to keep discharge air above the dew point.

We cool the air to get the humidity to the desired level - then "reheat" the air for the comfort of the occupants.

Reheating is necessary not for comfort, it's part of temperature control. In data centers temperature have to be between well-defined values. In addition, the speed of temperature change is also critical.

Praveen,

I'm limiting my answer to Data Centre spaces as this is my field, Labs etc have different requirements and I can not answer for those environments.

In Data Centres, the Computer Room Air Conditioning (CRAC) units have No heaters in them at all. The heat source is the servers, disk arrays and other IT equipment installed in the room. These are specially build for this environment.

The recommended conditions for a Data Centre or Computer Room are 21.5C (+\-1.5C) with a humidity of 40-80%. Too Dry and Static becomes a problem, Too humid and condensation may become a problem.

Air Conditioning by its nature de-humidifies (dries) the air flowing through the A\C unit, to correct this effect CRAC units will have a "Jug" or Humidifier in them, this is basically a Plastic Kettle with a Heating element in it to boil water and inject the steam (Very low pressure) into the Supply Side (Output) of the unit to keep the humidity in the correct range in the environment it is supporting.

For a Lab or the like in a cold environment I could see a need for heating to maintain temperature, but as I said I'm a beginner in that space and working on an educated guess.

Hope this Helps,
Regards,
Sapper

Hai Sapper ,

Thanks for the comments . It helped me a lot .

Can you please send me your mail id , it will help in future correspondence.

Regards,

Praveen

praveen.hc@rediffmail.com

The key is the humidity control. When you have to humidify the air, it's not a problem, you only have to inject some steam into the outlet of the A/C. When you have to decrease the humidity you have to cool the airflow down below the actual dew point in order to have the excess water condensed. Sometimes this cooling is too much for maintaining the expected temperature and would cool down the whole machine room below the optimal value so you have to reheat the air to the expected outlet temperature.

The interesting part is that you most often need the heater in summer, after a heavy rain...

THE KEY WORD IS DEWPOINT. PASSING THRU THE EVAPORATOR YOU LOWER THE TEMP AS WELL AS THE HUMIDITY BUT YOU ARE CLOSE TO THE DP SO YOU REHEAT TO RAISE THE DP. THIS AVOIDS THE RISK OF CONDENSATION ON AND IN YOUR EQUIPMENT.

I like GUEST #9's comment best. I would add that the refrigeration cycle ( aka air conditioning in this case) is also used to overcome the heat load, as well as humidity control. The electric heat compensates for this heat load reduction if only dehumidification is needed, as lowering the temperature below set point is usually undesirable.

There Have been lots of very informative answers.

Heat in a Data Center.

In the old days Data centers had tape drives. The humidity needed to stay at a pretty tight 50%, so the emulsion on the tapes did not dry out. It also kept the static at an appropriate level so that people or equipment did not receive any static discharges. So not only were humidifiers used but heaters as well.

The most important factor to remember is the dew point.

Most evaporator coils in a data rooms run about a 35 degree coil temperature. This is perfect for removing the moisture in the room. Some rooms we used to lower the fan speed so that we could get more water out of the air if it was running to high a humidity. The lower the fan speed, the slower the air moves over the coils so the evaporator can collect more moisture and send it down the drain. The heaters were driven by the Humidistats in the room to come on, warm the air and put a false load on the A/C systems to get it to run and collect more moisture on the coil.

Todays equipment uses heaters to put the false load in the room and ultra Violet lighting to steam the water troughs for humidity addition.

Hope this helps a bit