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Nonresidential Data Center Efficiency

Measure Description

The data center efficiency CASE Report will improve energy performance of data center mechanical and electrical systems by including the following submeasures 

Uninterruptible Power Supply (UPS) Efficiency 

This submeasure proposes adding minimum UPS prescriptive efficiency requirements for Ac-output UPS units used in computer rooms to match EnergyStar minimum efficiency requirements. The minimum average UPS efficiency takes into account UPS efficiency at 100%, 75%, 50%, and 25% load factor. 

Computer Room Heat Recovery 

Computer rooms with airflow containment that are controlled to ASHRAE’s allowable upper limit for server inlet temperature (80.6°F)1 can see high return air temperatures, in many cases in excess of 95°F to 100°F. This high air temperature can be used for direct heating in forced air systems, ventilation preheating, or process load heating. This submeasure proposes a prescriptive requirement to recover computer room return air heat for heating other building heating loads. Analysis will determine the building system constraints and computer room cooling loads for which this measure is cost effective. 

Monitoring 

This submeasure proposes a prescriptive requirement for computer rooms of a minimum size to have metering installed to calculate Power Usage Effectiveness (PUE) and server utilization rates and provide this data to the building operator in an accessible manner. This measure will be evaluated to determine metering, network, and data dashboard display requirements.  

Increased Temperatures 
  • Title 24-2019 prescriptively requires computer rooms to economize 100% of the cooling load with an air economizer at outside air temperatures of 55°F drybulb/50°F wetbulb and below, or to economize 100% of the cooling load with a water economizer at outside air temperatures of 40°F drybulb/35°F wetbulb and below. This submeasure proposes increasing the minimum drybulb temperature for 100% economizing and simplifying the economizer requirement to a single outside air temperature condition of 65°F drybulb/50°F wetbulb for any economizer type. 
  • Title 24-2019 prescriptively requires airflow containment for air-cooled computer racks for rooms exceeding 175 kW/room. Airflow containment is widely implemented in data centers, and there are many containment products on the market that make containment viable and cost-effective even for small computer rooms. This submeasure proposes reducing the IT load threshold where containment is required to 35 kW/room.  
  • This submeasure proposes raising the supply air temperature (SAT)/ return air temperature (RAT) from 60°F/80°F to 70°F/90°F in the baseline compliance modeling software model to better match industry standard practice. Many data centers are designing for a server inlet temperature of nearly 80°F per ASHRAE Thermal Guidelines for Data Processing Environments, Fourth Edition, 2015.

Generator Crankcase Heating 

This submeasure prescriptively requires generators serving computer rooms to be located in an indirectly conditioned space. Generators must have dampers on both intake and exhaust. The goal of this measure is to reduce generator crankcase heating energy through reduced heat loss to the outdoors and more efficient heating sources. There are many options for reducing crankcase heater energy including transferring data center relief air into the generator room before exhausting it to the outdoors or using heat pumps for heating. The ACM will include a baseline heater heating load (Btu/hr) and heater efficiency based on this prescriptive requirement and multiple design options ranging from heating via computer room heat recovery to a worst-case heater efficiency for generators located outdoors without an enclosure using electric resistance heating. Heater runtime will vary depending on the generator location (outdoors vs. enclosed) and climate. 

Liquid Cooling Credit in Compliance Software

This submeasure proposes adding a compliance credit in the compliance modeling software for data centers that use liquid cooling at the server chip level. Using liquid cooling instead of the air-cooled server cooling reduces energy use by eliminating server fan energy and computer room air handler fan energy.  

Mandatory Measures 

The following Prescriptive Requirements in Title 24-2019 will become Mandatory Requirements:  

  • 140.9(a)2: Reheat 
  • 140.9(a)3: Humidification 
  • 140.9(a)5: Fan Control

Relevant Documents

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

Provide Feedback

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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