Advice for minimizing chilled water use in server room cooling

[ChrisTwa]

I have a small office space in a research park which I'm using to house a 42U rack of servers. Specs by equipment manufacturers put my cooling demands around a ton.

The building has a chilled water system and bringing it to my space shouldn't be too big a deal. The park would bill me solely on chilled water volume, not temperature rise.

So... what kind of equipment should I use to provide my cooling and use the least amount of chilled water possible. I've googled fan coils and found most of them in my range use at least a gallon per minute with cold water return only 10F higher.

Any advice appreciated,

Thanks

 

[Waramanga]

the 10F higher is pretty well as good as you are going to get for a realistic amount of airflow. You could double the airflow and get an extra 2F or something but the extra fan power will cost you too in terms of heat gain and energy. if you are trying to save chilled water you could look at finding more efficient gear or using an outside air cycle depending on where you are.

 

[sridhar1312]

For high sensible load like servers it is better you have the cfm criteria for the lowside equipment. If it is 1 TR it should be around 2.7 USGPM however what is your cfm it may be high say 500 to 600 cfm.

 

[mauricestoker]

I think the biggest savings would be by selection of supply temp and how hunidity will be controlled.

 

[ChrisConley]

Radiant cooling would allow you to use a much greater deltaT, the downside would be capital cost.

 

[tys90]

You probably aren't going to want to economize on the air side since it's a data room and the load is too small to economize on the water side. Allowing your space set point to be high (80 or 85F) is probably the best way in my opinion. Is the room going to be occupied or is it solely a data storage room?

 

[chicopee]

Is this one ton (12,000 btu/hr) requirement for sensible and latent heat removal? Also what is the temperature of the chilled water inlet, room temperature and relative humidity requirements. Without knowing these parameters, one can only speculate on the equipment that you need.

 

[ChrisTwa]

My knowlege on this is pushing a ten year old course on atmospheric systems -- I'm thinking only sensible heat is an issue as there isn't any change in states of matter. The air here is very dry, heated by servers and exhausted.

Chilled water supply should be between 4-7C. The office is pretty near the start of their loop. The room temperature is currently too hot at 25C. Relative humidity should be around 50% +- 10% for server rooms. I'm not looking for an ice-locker, just for bringing the room down to 19C

The room is currently cooled by a passive radiator panel and two dx portable air conditioners. The air conditioners aren't that effective because they're only exhausting to the plenum which isn't circulated sufficiently to handle the heat load.

 

[CountOlaf]

Like someone said, check the loads. The cooling requirements of the servers (if provided by the server or computer manufacturers in btuh or kW) are typically sensible cooling only. Therefore, if you have 1-ton or 12,000 btuh requirement (once you've added up the numbers), you may need a 1-1/2-ton (nominal) air-conditioner since it will have a gross cooling capacity of 1-1/2 tons, but perhaps 70 or 80% of that in terms of sensible cooling capacity.

1 gpm doesn't seem like a whole lot to be fretting about. You will probably need more like 2.4 gpm for a 1-ton unit(with the 10 deg delta T). Either way, run 3/4" chilled water pipes to the unit and neck down to the connection sizes (probably 1/2"). It doens't get much smaller than this in terms of chilled water based air-conditioning. The actual usage (gpm) will vary if you have say a 2-way modualting control valve. Is someone going to meter the usage and bill accordingly?

If the server stuff is critical, you might want to check out fancier stuff than standard fan-coil units. Liebert, Mitsubishi, etc. Then you could perhaps have something with a dx primary system with chilled water as a secondary stystem. Computer room air conditioing equipment will also have reheaters, humidifiers and other things to maintain more precise temperature/environment control in the space (at a cost of course).

 

[ChasBean1]

Agree, esp. with the term "2-way modualting control valve." Regardless of what exact system you use, don't use a three-way control valve, and you should probably stay away from a two position (open/close only) valve.

 

[marcoh]

Talk to your local CRAC supplier (say Liebert assuming you want a proper CRAC unit, which I would recommend) and get a few selections at different water temperatures.

When you jump up a case size as the temperature difference increase you will probably have the best selection, though might be worthwhile to see the payback would be with the larger unit?

Also get a CRAC unit with EC fans to reduce fan power consumption.

 

[Compositepro]

One is not a lot to worry about but to maximize efficiency it would be best to use a coil with multiple rows of tubes so you get some counter-current flow between hot air and cold water. It would also be most efficient to put the coil into the hottest part of the air flow where the air comes out of the servers.