UPS Room Cooling with a rooftop unit

[BronYrAur]

I have been asked to provide a redundant cooling system for a UPS room. Actually, this new system would be the primary with the existing being a backup. Right now they have a Carrier split system with a 40RM012H air handler and a 38ARD014 condensing unit. The room has some envelop load so 12 tons is the design capacity, but 2nd stage cycles. This gives them some redundancy with the dual circuiting, but basically they are in trouble if this system fails.

I have always seen Liebert or other precise cooling units on these types of rooms, but in this case I don't see how to make it work. We have absolutely no floor, wall, or ceiling space to put another split system. The roof is my only option, and I will have to duct down outside the room and punch through in the only free wall space available.

Any recommendations on manufacturers or at least what to look out for? I don't want to put a standard HVAC unit for such a critical application. I would like something with more precise control. Also, what about outside air? There are no people in the room, so I am guessing I can get away with no OA, but an economizer sounds appealing for energy use. I don't know the humidity parameters, but will an economizer cause me any problems if I use enthalpy?

Any ideas are appreciated.

 

[willard3]

Tell your client that he is going to have to provide some space for a redundant Liebert unit or other data cooling equipment.

Standard roof-top HVAC stuff is not designed for computers and will not provide right dry bulb and wet bulb control.

 

[NCDesign]

If this room only holds UPSes(s?), I would suggest double checking the environmental requirements of the UPSes in the room. UPSes are generally rated to operate in a much larger temperature and humidity range than the servers they protect. Such that a standard HVAC unit and its range of control may be more than adequate. Obviously this hinges on the UPSes environmental requirements.

For some idea of what I am talking about, take a look at these APC tech specs, APC UPS and check out the environmental requirements at the bottom. I just finished a job with several of these APC UPSes and we stuck them in the main building electrical room along with several transformers. The only reason we cooled the space was because with the transformers located in the space, we would easily exceed the 104F max operating temperature. The additional cooling was with a standard split system. As a side note, the concern above the 104F temp wasn't for unit operation, but performance degradation of the batteries in the UPS.

 

[marcoh]

Take care with UPS though, typically the battery warranty is void if room temperatures exceeds 25C (or similar).

Some UPS have and in-built logging and I have seen warranty claims being rejected due to short periods of excessive temperature!

With some careful selection a rooftop unit could be used, but may need a non-standard unit, just need to talk to the supplier about coils selections.

 

[mike7941]

I would caution against using commercial equipment for UPS cooling. The standard commercial cycle is 3000 hours per year of operation and this equipment lasts 15 or 20 years. A UPS room will require 8760 hours of mechanical cooling per year. This is partly why the computer room units are so expensive. If the owner is aware of the difference going in, he may choose the commercial system, but it would not be my first recommendation.

 

[RossABQ]

I am currently doing a UPS/electrical room for 2.5 MW of units, we are going with an OSA economizer system. There is nothing about UPS's that requires the kind of temp stability of a Liebert unit. As long as you have 85% filters, OSA presents no issues. Why pay the electric company when free cooling is available?

This goes double when you lose normal power; your split system needs to be on its own UPS or you have no cooling just when it is needed the most! Without knowing your climate, most of the year (statistically) OSA is in the range to keep a room like this cool enough without a mechanical refrigeration unit (certain batteries de-rate at 77 degF, the electronics are good above that). With an OSA econ unit, you can likely get by with just the fan running on a UPS, unless you are in Phoenix or Las Vegas...

 

[RossABQ]

PS -- by all means buy an industrial-quality unit, and make sure the controls are on UPS too!

 

[mike7941]

If you are going to use outside air to cool in the winter, fine. But keep an eye on your humidity levels, the electrical guys get a little nervous as they drop below 20%. Not an unsolvable problem, but it should be addressed. Ultrasonic or high pressure water humidifiers can address the issue without using a lot of power.

Mike