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Nonresidential Computer Room Efficiency

Measure Description

The proposed code changes apply to computer rooms that have a design information technology equipment (ITE)4 load over 20 Watts per square foot (W/ft2) as defined by Title 24, Part 65 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. 

Increased Temperature Threshold for Economizers

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 to Section 141.1(b) prescriptive requirements for computer rooms.

  • 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 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.

Computer Room Heat Recovery

This submeasure proposal includes adding prescriptive requirements for computer rooms to Section 140.9 to require new buildings with both a computer room and sizable heating loads to recover heat from the computer room to serve other spaces. Computer room heat recovery is being defined as a mechanical system that transfers heat from computer rooms to provide heating to other zones in the building that require heating. This submeasure only applies to computer rooms in new buildings. There are two scenarios when computer room heat recovery would apply. If a building met the triggers for both scenarios, it would only be required to comply with one scenario. 

  1. For new buildings with a total ITE design load exceeding 50 kW ITE and a design heating load exceeding 200,000 Btu/hr in all climate zones, heat recovery would be required for all computer rooms with an ITE load greater than 50 kW and located within 50 feet of zones exceeding 5,000 Btu/hr design heating load. This scenario is intended to apply to computer rooms that are located near heating zones such that centralized heat recovery systems are not needed to implement heat recovery. The cooling load, heating load, and distance thresholds were selected based on the costeffectiveness analysis results. Smaller loads or greater distance between computer rooms and heating loads was determined to not be cost effective. See Section 5 for more details on the cost-effectiveness analysis. 
  2. For new buildings meeting the thresholds described below, a heat recovery system capable of providing at least 50 percent of the total computer room design cooling load or 50 percent of the total building design heating load would be required. These combinations of heating and cooling loads were determined to be cost effective for each climate zone. See Section 5 for more details on the cost-effectiveness analysis. This requirement would apply to: 
  • Climate zones 15, 1114, or 16: new buildings with a total ITE design load exceeding 200 kW and with a design heating load greater than 4,000,000 Btu/hr. 
  • Climate zones 1–5, 11–14, or 16: new buildings with a total ITE design load exceeding 500 kW and with a design heating load greater than 2,500,000 Btu/hr. 
  • Climate zones 6–10, or 15: new buildings with a total ITE design load exceeding 300 kW and with a design heating load greater than 5,000,000 Btu/hr 

This proposal includes recommendations to update the compliance software to allow designers who use the performance approach to model the impacts of computer room heat recovery. Commonly used heat recovery systems such as water-cooled chillers or transfer air are not able to be modeled, which limits the ability to properly capture the energy use of a computer room heat recovery system. The Statewide CASE Team recommends that CBECC-Com be updated to include commonly used heat recovery systems such as heat recovery chillers and transfer air systems. See Appendix D for additional information about proposed changes to the compliance software. 

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 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%, 50%, 75%, and 100% 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%), 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. 

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 

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.

Round Two Utility-Sponsored Stakeholder Meeting Materials

Round One Utility-Sponsored Stakeholder Meeting Materials

Provide Feedback

Draft CASE Report Now Available (Comments accepted until July 17, 2020)

This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email info@title24stakeholders.com. Include the measure name in the subject line.

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The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

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