A major financial institution operates two mirrored data centers to service its New York City operations. One of these occupies the second floor in a 14-story brick building, originally built in 1912 to house a department store, which is now a multi-tenant structure hosting computing and telecom equipment. The 87,000 square foot data center contains about 30,000 square feet of white space for the computing and storage equipment and a small amount of office space. The rest of the space is used for battery rooms and other ancillary equipment.
The Physical Site
Unlike data centers located in rural areas, which can pull in enough outside air to keep the data center cool, in this case the building is in the middle of a dense urban area where the streets and brick absorb the heat day after day and don’t fully cool down at night, which gradually raises the the temperatures inside the building. To make matters worse, while the urban ambient temperatures themselves are higher than the surrounding countryside, the rooftop temperatures can exceed the ambient temperatures by another ten degrees.
The data center uses an indirect cooling system with CRAC units in the white space. Glycol runs through heat exchangers in the CRAC inits and is then pumped to rooftop units where the glycol is re-condensed and the heat dissipated into the outside air. When the data center went through a major upgrade which added to the heat load, there was enough room on the roof to install five additional condensers to supplement the eight already in use. This arrangement works for most of the year, but for a week or two each summer it does not. The cooling system operates properly as long as the glycol temperature can stay below 100 ˚F. When it exceeds that temperature, the cooling system can trip offline.
“We Have dry coolers on the roof, so we don’t have the benefits of evaporation,” says the data center’s assistant chief engineer. “If we have 1000 tons of refrigeration at 100 ˚F, when it goes to 110 ˚F capacity drops and we are just shy of what we need. On very hot days when it gets above 110 ˚F on the roof the units would have tripped offline on high pressure.”
To keep the data center operating, since there was no room for additional rooftop condensers, the financial institution needed to find a way to get more cooling out of the condensers it did have by bringing down the inlet air temperature. After experimenting with lawn water sprinklers to spray water into the inlet air on the bottom of the condensers, IT decided to put in a more efficient and controllable MeeFog system to keep the glycol temperature and pressure within limits.
“They found that using a Rain bird sprinkler underneath the units gave them a bit more capacity out of the dry coolers, but it wasted a lot of water.” says Gennaro Lombardi, president of Metro Air Products in Hillsborough, NJ. “That’s where we came in, designing a fogging system for them with a series of manifolds and valves that perform quite well.”
The MeeFog system for this application consisted of a single 10 HP, 480V Grundfos CRI-5 pump with Allen Bradley controllers to pressurize the water for use by the eight original condensers. 3/4″ stainless steel feedlines bring the water from the pump to the 90-nozzle fogging arrays placed in the bottom inlet of the condensers. A Marlo, Inc. water softening system keeps minerals from clogging the nozzles or building up on the condensers fins.
“The MeeFog system pressurizes the water to just under 300 psi and it comes out of an orifice in such a fine fog that it cools the outside are and drops the temperature of our glycol by about six to eight degrees,” says the engineer.
Putting it to the Test
Once it was installed, the MeeFog system was quickly put to the test in a heat wave last summer. By the third day of the heat wave, the rooftop temperature was hitting 115 ˚F, even though the air temperature was just 103 ˚F.
“Since we were above our 100 ˚F max, our cooling capacity was below what we needed,” says the engineer. “We didn’t wait until we had units failing, but fired up the MeeFog unit as soon as the temperature hit 100 and the glycol temperature dropped about six degrees. Then, as the day progressed and the outside temperatures climbed, our glycol temperatures didn’t get any higher, so the MeeFog cooling effect was pretty substantial.”
Currently the MeeFog system is only cooling the bottom inlet air, which is enough to meet the original intention of keeping the data center on line during heat waves, but an engineering firm has been to the site and is looking at fogging the condensers on three sides in order to provide additional cooling and reduce the amount of energy required to cool the data center.