Air conditioning services for our San Diego data center locations are provided by a series of three fully redundant chiller systems.
The Lightwave San Diego Data Center has three 500 ton water-cooled chillers, with a computerized chilled water control system that automatically monitors critical mechanical systems. Should the chilled water flow be interrupted and/or the water temperature deviate from the critical operating parameters, the computer will send a series of pages to the San Diego data center personnel to signal the need for manual intervention. The chilled water plant is operated by (3) 500 Ton water-cooled Centrifugal Trane Chillers with (3) 40-HP chilled water pumps. Both the chillers and chilled water pumps are piped in a parallel arrangement. In this parallel piping arrangement, any of the three chillers or pumps can be interchanged to support flow and capacity needs in the chilled water system.
Heat rejection for the Lightwave San Diego Data Center chillers is provided by three (3) newly installed Marley induced draft open cooling towers, located in the cooling tower yard. Three 30-HP pumps help circulate condenser water for each cooling tower, going from the cooling towers to the chillers located in the chiller room.
The San Diego Colocation - Tech Center has three 180 ton air-cooled chillers. These systems provide a minimum of N+1 redundancy for both San Diego colocation facilities.
The San Diego data center floors are fed by a combination of 20 and 30-ton individual, redundant Computer Room Air Conditioning (CRAC) units.
The colocation area at both San Diego data center locations is kept at a low temperature and 45% humidity at all times. Critical airflows at each San Diego data center are monitored for hydrogen, and temperature. In addition, humidity sensors are placed throughout our San Diego data center to provide early warning in the event of a system failure. We adhere to the latest hot row/cold row configurations to ensure maximum cooling for all of our customers equipment.
Two Major Mistakes When Evaluating a Colocation Facility's HVAC Systems
An important, but often overlooked part of any data center, is it's cooling systems. Thermal overloading of a San Diego data center can result in customer equipment failure or shut-down if overheating safety devices are present. There is some argument about the optimum temperature at which a facility should be kept. However, most equipment manufactured today is designed to run at room temperature. Therefore, ambient temperature between 72 and 76 degrees should be considered normal. Humidity should be maintained between 45% and 60%. Make sure your San Diego data center has systems in place to keep the facility in those ranges. Most Computer Room Air Conditioning (CRAC) units have both cooling and humidity controls built in.
Raised Floors vs. Concrete Floors
There is much discussion in data center design on this subject. I will outline a few facts here to help you make an informed decision about which design is best for your situation.
Way back when, data centers were built with raised floors to accommodate the special air conditioning needs of mini and mainframe computers, these computers were designed to have cool air blown into the bottom of them. Today almost all computers are designed to be mounted horizontally in 19" relay racks or cabinets. They are designed to have cold air drawn in at the front, and have hot air exit the rear. Even the large Storage Area Networks (SANS) are designed in this manner with cold air coming in the front and exiting the rear.
Many older MIS professionals are accustomed to a raised floor environment and believe it to be superior to a solid floor with overhead cooling. Many white-papers have been written to show the disadvantages of raised floor cooling in an environment in which servers are designed to take in cold air at the front and exit hot air at the rear. Thus proving that colocation raised floors have some disadvantages. The studies include the fact that, by the time the cold air gets to the top of a cabinet, it is too warm to sufficiently cool the servers in that area. Also, the hot air blowing out the top rear of a cabinet is re-circulated back to the top front, further overheating the servers near the top of a cabinet. That being said, both systems can work well for colocation provided that the facilities and the cabinets are designed specifically for the type of cooling provided. Data center managers with both raised floors and solid floors have to make sure that they pay careful attention to methods discussed below to insure maximum cooling for their customers.
Things to watch out for in a raised floor environment are as follows: If the cold air outlets are in the floor under the cabinets, the cabinets must be designed to get cold air from the floor to the top of the cabinet. Typically these cabinets will have a front with little or no venting and/or special ducting to ensure that cold air does reach the servers at the top. If the cold air vents are in the floor in front of the cabinets, the floor must have sufficient air pressure to blow the cold air up to the top of the cabinets to help offset the natural tendency for the hot air to rise and to be re-circulated from the top rear of the cabinet to the top front of the cabinet.
In both raised floor and solid floor environments, a well-designed colocation facility will have hot rows and cold rows. The cold rows in a solid floor facility will have cold air vents blowing into them from the ceiling and warm air returns at the end of the rows, as opposed to cold air coming up from the floor. In a solid floor overhead air vent environment standard cabinets with mesh front and rear doors are a requirement. Fans can be added to the rear mesh area if necessary to remove heat and keep the cabinets cooler.
An effective but very uncommon method for both raised floor and solid floor data centers to overcome heat issues is to cap the cold rows. Capping the cold rows consists of installing a lid or roof of Plexiglas or other material to the seal the top of the cold rows. This prevents the warmer ambient data center air from mixing with the cold air before it is delivered to the servers. Capping the cold rows effectively extends the cold air vents directly to the cabinets. Providing cold air directly to the servers not only makes the data center air conditioning systems work more efficiently but it means that customer's servers will run cooler.
In both situations make sure that your equipment's air intake is facing the cold row and blowing it's hot air into the hot rows. If you are unsure which is a cold row or a hot row, ask the data center manager. Another trick to keep your cabinet cool is to block all unused rack units with block off plates. The will keep the cold air on the intake side from mixing with the hot air on exhaust side.
Mistake #1 - No redundant Chiller Systems
Chiller systems are the equipment that produces the cold water or water/Glycol combination that is delivered to the CRAC units. Confirm that your colocation facility has redundancy built into the chiller system. Typically, in large facilities, there will be a system of chilled water pipes running from the CRAC units back to the Chillers. Make sure that there is at least one redundant chiller system in case of a chiller failure, and at least one redundant pump that circulates the chiller water though the systems. These redundant systems should all be automatic and have unmanned fail-over to their back up systems. A full data center can overheat in a matter of minutes in the event of a chiller failure. Ask simple questions such as "Do you have redundant chillers?", or "Please show me your redundant chillers". If they are on the roof and it is difficult to access them for a visual inspection, ask them to show you pictures. Have them explain how the redundancy operates. Ask them how many tons of capacity are in each chiller. Chillers are typically from 20 tons and up, to hundreds of tons. Write down this data for later reference to verify that they have sufficient cooling capacity and redundancy.
Air cooled chillers vs. water cooled chillers.
Water cooling is typically more efficient that air cooling however both will work. If the data center has water cooling it will have water cooling towers. Make sure that there are redundant towers plus automatic fail over and that there is enough on site water storage in the event of a water outage to run the facility for several days.
Note - If the data center is using standard HVAC units that are normally used to heat and cool an office space - end your data center tour immediately and locate a real facility. These units are not designed to run 7/24 and will not provide reliable cooling no matter how many of them they have.
Mistake #2 - CRAC unit failure (Computer Room Air Conditioning) units
CRAC units are the noisy mechanical beasts on the data center floor that take in warm air and blow out cold air. They consist of many moving parts and failure of these units will occur even with the best maintained equipment. Make sure your data center has multiple units feeding each area of the data center. In a raised floor environment all units typically blow cold air into an open plenum below the floor therefore the goal here would be to make sure that the data center can operate efficiently in the event of a CRAC unit failure. Many small colocation facilities have a couple thousand square feet fed by two 20-ton Liebert units. This is not a redundant arrangement. If the facility is full and one unit goes down, the data center will over-heat quickly. In a solid floor situation make sure that multiple CRAC units are feeding the overhead plenums creating redundancy with the CRAC unit systems. A good rule of thumb to determine redundancy of both Chillers and CRAC units is to ask the question - How many tons are provided by each unit? CRAC units are typically 20 to 30 tons. Add up all the tonnage in a particular area and divide by the square feet. For example, four 30-ton CRAC units equal 120 tons, divided by 4000 square feet or .030 tons per square feet. .030 should be considered minimum. Anything below .025 would be considered less than adequate. Anything below .020 does not provide sufficient cooling and definitely has no redundancy. The best facilities will have .035 or more tons per square foot. This same formula applies to Chillers.
open & close article 
