Nonresidential Computer Room Efficiency

Measure Description

The proposed code changes apply to computer rooms that have a design information technology equipment (ITE)3 load over 20 Watts per square foot (W/ft2) as defined by Title 24, Part 64 and impacts both new construction, additions, and alterations unless otherwise noted below. The proposed prescriptive submeasures would appear in Section 140.9(a) and new subsection 141.1(b), and the proposed mandatory PUE monitoring requirement would appear in a new subsection in Section 120.6. All of the prescriptive requirements would have associated updates to the compliance software. No update to the compliance software is required for the proposed new mandatory requirement. 

These proposed code changes include adding definitions to Section 100.1(b) to include UPS, computer room heat recovery, and computer room equipment load term definitions. A new section would be added as Nonresidential Appendix NA7.19 for Computer Room Acceptance Tests and would include an acceptance test for PUE monitoring.  

Increased Temperature Threshold

This submeasure proposal includes the following modifications to Section 140.9(a) prescriptive requirements for computer rooms.

• Establish a single set of outdoor temperatures for all economizer types, instead of having separate requirements for air and water economizers.
• Increase minimum outdoor temperatures for full economizing to 65°F dry-bulb or 50°F wet-bulb for any type of economizer. Currently the thresholds are 55°F dry-bulb and 50°F wet-bulb for air economizers, and 40°F dry-bulb and 35°F wet-bulb for water economizers. An exception is included to allow projects to meet the 2019 Section 140.9(a)1 economizer temperature requirements as long as they also implement higher efficiency fan systems, air containment, and cooling equipment.
• Decrease the computer room minimum size threshold for requiring air containment from 175 kW per room to 10 kW per room ITE design load.
• Modify 140.09(a)1 Exception 4 to allow for the computer room to be served by the maximum spare cooling capacity from the economizing fan system rather than requiring the economizing fan system to serve the full design cooling load of the computer room, as long as at least five tons of economizer cooling is provided. This exception would apply to all computer rooms.

This submeasure proposal includes the following modifications in Section 141.1(b) prescriptive requirements for computer rooms in existing buildings.

• Addition of economizer requirements for computer rooms in existing buildings. This involves moving 2019 Title 24, Part 6, 140.9(a)1 requirements to this new subsection. This would not introduce new requirements for computer rooms in additions/ alterations but would clarify which requirements apply to computer rooms in new buildings and which requirements apply to computer rooms in additions/alterations.

Finally, this submeasure proposal includes recommendations to update the compliance software to allow designers who use the performance approach to model the impacts of computer room economizers. California Building Energy Code Compliance software for commercial buildings (CBECC-Com) is not currently capable of modeling dry cooler or refrigerant economizers. Both of these economizer types are commonly used in California and offered by a number of major manufacturers. The Statewide CASE Team recommends that CBECC-Com be updated so dry cooler and refrigerant economizers can be modeled and projects using these technologies may pursue the performance compliance path.

CBECC-Com currently has limitations on the air temperatures that can be modeled for computer rooms. Based on reviews of dozens of computer room designs, stakeholder consultations, and best practice guideline references such as ASHRAE (ASHRAE, Thermal Guidelines for Data Processing Environments, Fourth Edition 2015), it is evident that a variety of supply and return air temperatures are commonly used in computer room designs, which have a large impact on compressor energy based on economizing hours and on fan energy. The Statewide CASE Team recommends that CBECC-Com be updated so exact design supply and return air temperatures can be modeled and the economizing system incorporates these temperatures.

Uninterruptible Power Supply (UPS) Efficiency

This submeasure proposal includes adding a prescriptive requirement for all alternating current (AC)-output UPSs serving computer rooms, except for UPSs that use NEMA 1-15P or 5-15P input plugs, to match ENERGY STAR® Version 2.0 minimum efficiency and testing requirements. UPS unit efficiency is not currently regulated by Title 24, Part 6.

This submeasure proposal includes recommendations to update the compliance software to allow designers who use the performance approach to model the impacts of UPS efficiency. Because UPSs are currently an unregulated load, they are not included in CBECC-Com. Almost every computer room uses a UPS. The Statewide CASE Team recommends that CBECC-Com be updated to include UPS efficiency. UPS efficiency should be modeled with at least a four-point part-load efficiency curve for 25 percent, 50 percent 75 percent and 100 percent load factors. Users should then have the option to determine the percentage of computer room IT load is served by the UPS (typically this will be 100 percent), which will be used to calculate the operating UPS load factor and UPS efficiency for each hour of the year. The UPS waste heat and IT load are cooling loads on the cooling system. See Appendix D for additional information about proposed changes to the compliance software.

Power Usage Effectiveness (PUE) Monitoring

This submeasure proposal includes adding a mandatory requirement to install PUE monitoring in buildings whose primary function is to house computer rooms (defined as “data centers” in Title 24, Part 6). The major criteria triggering this requirement are a total computer room ITE design load over 2,000 kW and where at least 80 percent of the total cooling capacity serves computer rooms or associated electrical rooms.

Since this submeasure is being proposed as a mandatory requirement, it has no proposed software changes.

Submeasures Moved to Future Code Cycles

The Statewide CASE Team is no longer pursuing the proposed changes listed below as it was determined that they did not meet the Energy Commission’s requirements for market readiness, technical feasibility, cost-effectiveness, or enforceability at the time they were considered.

Server Utilization Monitoring

Server utilization monitoring lets computer room operators know which servers are not being utilized and are therefore candidates for energy savings measures such as server virtualization or decommissioning. After initial research, including interviews with stakeholders, the Statewide CASE Team decided to stop pursuing server utilization monitoring for the 2022 code cycle for two reasons:

1. Server utilization monitoring software and the servers on which it is installed are typically installed in the building after a certificate of occupancy permit is issued. This poses a significant regulatory hurdle for which the Statewide CASE Team does not have a viable solution at this time.
2. Most server utilization monitoring software requires a monthly service subscription. Analysis is not currently showing this measure to be cost effective based on energy savings over the life of the measure.

Generator Crankcase Heating

Generator crankcases must be kept warm at all times, typically around 110°F, which is commonly done with a generator-mounted electric resistance heater. There are several options for reducing crankcase heater energy. After initial research the Statewide CASE Team decided to discontinue pursuit of this submeasure for the 2022 code cycle in an effort to focus on more cost effective measures.

Liquid Cooling Credit in Compliance Software

Using liquid cooling instead of air-cooled server cooling saves energy by eliminating mechanical supply fan energy and server fan energy. While this is a technology that is decades old, it is not common practice for most computer rooms.

The Statewide CASE Team investigated adding a compliance software credit for installing liquid cooling in computer rooms for the 2022 code cycle. Since this would not involve a code change requirement, the Statewide CASE Team decided to consider pursuing this submeasure outside of the CASE Report process.

Materials that the Statewide CASE Team developed when investigating this code change for the 2022 code cycle will be moved to the Future Code Cycles section of this website. Follow this link to find materials on computer room efficiency.

Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.

• CASE Study Results Report – Nonresidential Computer Room Efficiency
• Final CASE Report – Nonresidential Computer Room Efficiency (Updated March, 2021)
• Draft CASE Report – Nonresidential Computer Room Efficiency

Round Two Utility-Sponsored Stakeholder Meeting Materials

• Agenda – March 12 – Nonresidential and Single Family HVAC Part 1
• Presentation – March 12 – Nonresidential and Single Family HVAC Part 1
• Computer Room Efficiency Submeasure Summary
• Notes – March 12 – Nonresidential and Single Family HVAC Part 1

Round One Utility-Sponsored Stakeholder Meeting Materials

• Data Center Efficiency Submeasure Summary
• Presentation – Oct. 15 – Nonresidential HVAC Part 1 Utility-Sponsored Stakeholder Meeting
• Notes – Oct. 15 – Nonresidential HVAC Part 1 Utility-Sponsored Stakeholder Meeting