Learn about the Department of Energy's (DOE) current standards for the efficiency ratings of a CRAC

DATACOM’S NEED FOR SCOP RATINGS

Many engineers, representatives and owners are misinformed on what current standards require for the efficiency rating of a Computer Room Air Conditioner (CRAC). In my day to day conversations, our customers wonder which efficiency rating to utilize: EER, SEER, IPLV, IEER, or SCOP. Each of these is incorrect for our industry but one (SCOP). My involvement in AHRI 1360 and ASHRAE 127 committees has given me an understanding into why SCOP is such a valid efficiency requirement for CRAC units as well as insight into potential changes the Department of Energy (DOE) may be implementing for the Datacom industry.

Since the 1990’s, comfort cooling equipment has been regulated by the Department of Energy (DOE) to meet minimum efficiency ratings based on an EER or SEER metric. CRAC’s differ from comfort cooling equipment due to the high sensible heat ratios – as their main purpose is sensible cooling in computer rooms and data centers. Because of this design intent difference, CRAC units rate poorly on the existing efficiency metrics which take both latent and sensible capacities into account and therefore a need arose to have a new metric which fairly and accurately rated CRAC equipment.

STANDARDS ADOPTED Sensible Coefficient of Performance (SCOP) RATINGS

In 2010, ASHRAE 90.1 identified a specific efficiency table for Air Conditioning Units Serving Computer Rooms (CRACs) under Section 6.8.1, which utilizes Sensible Coefficient of Performance (SCOP) as the standard. There was no change to the SCOP values in this table (Figure 1) in the 2013 edition. SCOP is the ratio of net sensible cooling capacity (Watts) divided by the total power input (Watts, excludes reheat and humidifier), at conditions defined in ASHRAE Standard 127. This has become the backbone and common reference for state and federal regulation codes on CRAC equipment, and the reason as to why Data Aire is attempting to provide SCOP ratings of our equipment in lieu of obsolete rating methods.

As of February 2018, Data Aire holds the top three SCOP ratings in the industry. See the information in the DOE’s Compliance Certification Database. Note: click the arrows twice near the SCOP ratings to rank all regulated units in the industry by highest SCOP.

DOE AND STATE ENERGY CODE ADOPTION

These standards are written with the intent for use as code to be adopted into law (by the DOE). The Code of Federal Regulations (CFR) is where these energy codes reside at the federal level, although the U.S. does not have a national energy code or standard, so energy codes are adopted at the state and local levels of government. In Figure 2, you can see that there are varying levels of adoption across the nation.

LOOKING AHEAD

SCOP is the appropriate and preferred method to identify a CRAC unit’s efficiency as federal and local legislations base their energy rating standards on ASHRAE 90.1-2013, but what comes next? It is apparent that the DOE is intending for future energy requirements to cover ceiling mounted units and horizontal units. And AHRI 1360 and ASHRAE 127 committees are already preparing for these new requirements.

Another big topic of discussion is the possibility of a part load efficiency metric as other industries have adopted metrics such as IEER and IPLV. DOE estimated in its May 2012 final rule analysis that CRAC units operate on average at a sensible load of 65 percent of the full load sensible capacity, which means a part load rating may have some merit; although any new ratings will likely take a few years for the standard committees to develop and then for the DOE to adopt.

If you are interested in learning more about this topic, download our whitepaper Breaking the Code: Understanding the Current Standards For Rating Efficiency Of Computer Room Air Conditioning Equipment.