Economizer Cooling Solutions

The data center cooling system is a primary target for energy efficiency improvements. Emerson Network Power analyzed data center energy usage and found that cooling systems — comprised of cooling and air movement equipment — account for 38 percent of energy consumption within this mission critical facility. Fortunately, cooling system technologies, such as Economizers, exist that can substantially slash costs from the data center electricity bill.

Economizer systems can have a significant impact on energy usage. In many locations, economizers can be used to allow outside cool air to complement data center cooling systems and provide “free cooling” during colder months. A study on building control systems conducted by Battelle Laboratories and reported by the National Building Controls Information Program, found that on average the normalized heating and cooling Energy Use Intensity (EUI) of buildings with economizers was approximately 13 percent lower than those without economizers¹.

When an economizer system is operating, the use of an air conditioning system’s compressor(s) and related electro-mechanical components is reduced or eliminated. This reduces energy consumption.

Types of Economizers and How They Work (PDF Download)

The two basic types of economizer systems are air economizers and fluid economizers. While both have the ultimate goal of free cooling, they possess fundamental differences that impact the environments in which each is most appropriately used. The air economizer serves as a control mechanism to regulate the use of outside air for cooling in a room or building. It admits into the room the appropriate volume of outside air to satisfy cooling demands. Sensors on the air economizer measure the outside and inside air conditions. If outside conditions are suitable for the use of outside air for cooling, the economizer introduces the outside air for complete or partial cooling of the space. During the time these conditions exist, the need for the air conditioning system’s chiller(s)/compressor(s) is reduced or eliminated, which results in significant energy savings.

Air economizers are available in two types: a “dry air” system and an “evaporatively conditioned” air system. The former is the most common, but its use is restricted to a few geographic locations because of contamination issues and the high cost of energy required to add moisture to the room when the outside humidity is too low or too high. The evaporatively conditioned system is an economical method for conditioning the air before it comes into the data center, but reliability issues (mildew concerns and high maintenance requirements) have generally made this approach unattractive to most data center operators.

As its name would suggest, a fluid economizer system is typically incorporated into a chilled water or glycol-based cooling system. This type of economizer works in conjunction with a heat rejection loop consisting of a cooling tower or drycooler to satisfy cooling requirements. With the economizer operating, the fluid used in the cooling system passes through an additional heat exchanger/coil, minimizing the need for chiller/compressor operation.

During colder months, the glycol solution returning from the outdoor drycoolers or cooling tower feeding the CRAC units is routed to the second coil, which becomes the primary source of cooling for the room. As long as the “free cooling” fluid is 8 degrees Fahrenheit below the air temperature returning to the CRAC unit, there is some benefit for having the free cooling running, because it minimizes the load on the primary cooling method. Similarly in CRAH units, a secondary heat exchanger between the cooling tower fluid and the chilled water loop takes away part of the heat from the return water loop and reduces the load on the chiller.