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Proposed ASHRAE 90.1 – 2007 Addenda for Data Centers

Introduction: In working on the up-coming LEED Data Centers standard, I needed to take a deep dive into the proposed changes to the ASHRAE 90.1 energy standard. The good news here is that the revised 90.1 standard, to be released this year (2010), will contain very specific language on minimum energy efficiency requirements for data centers. Prior to this, there was really nothing in the standard that discussed how to apply the requirements to data centers, which often caused difficulties in showing conformance with the energy standard.

However, there is still no mention of electrical system efficiency requirements in the proposed addenda from ASHRAE. This is necessitating writing a new procedure to determine minimum electrical system efficiency based on UPS technology, reliability level of the facility, PDU efficiency, etc. More to come on that later.

 Part 1: Overview definitions and system fan power calculations

Items from Addendum cj and bu:

Overarching rules

  • A data center (ASHRAE uses the term computer room throughout the 90.1 document) is defined as room with a load of 20 watts/SF across the conditioned floor area

  • Air conditioning units serving a data center are covered by ASHRAE Standard 127, specifically table 6.8.1H

  • Air or water economizer is required except:

  • o tier IV facilities (as defined by TIA 942 standard)

  • o data centers with a cooling load less than 880 kW and which are not served by a central chilled water plant

  • o data centers with a load less than 175 kW and are served by a central chilled water plant

  • o local authority does not allow a cooling tower

  • o data centers with a load less than 175 kW being added on to a larger facility

  • o greater than (or equal to) 75% of the total load is for an essential facility (defined in the Addendum) such as fire and police facilities, emergency communications centers, critical national defense facilities, data centers in the financial sector providing core clearance and settlement services

  • Water economizer for data centers must cover 100% of the load starting at outdoor conditions of 40F dry bulb and 35F wet bulb temperatures

  • Normative references:

  • o ANSI/ASHRAE Standard 127-2007 Method of Testing for Rating Computer and Data Processing Room Unitary Air Conditioners

  • o ANSI/TIA-942- 2005 Telecommunication Infrastructure Standard for Data Centers

  • o The Interagency Paper on Sound Practices to Strengthen the Resilience of the US Financial System, April 7, 2003

  • o NFPA 70 Article 708 -2008 - Critical Operations Power Systems(COPS)

Definitions of baseline

  • Small data centers - baseline is air-cooled DX systems - use system 3 or 4 for baseline system as defined in table G3.1.1B

  • Large data centers - baseline is central plant, chilled water with CRAHs and VAV controls - use system 9 for baseline system as defined in table G3.1.1B

  • Large data centers have loads greater than 166 tons or 50 tons if the data center is located in a larger building with a central chilled water system

Fan Power Calculations - the following are functions written in VBA for Microsoft Excel. They are based on the formulae in the ASHRAE documents. With these functions a user will be able to determine the maximum allowable fan brake horsepower of the fans based on the total supply air volumetric rate. Also, based on the brake horsepower, the minimum motor efficiency can be determined. Finally, based on part load, the user will be able to determine the system fan power at part load.

For systems 3 and 4


  • This function calculates the minimum fan efficiency for systems 3 and 4 based on ASHRAE 90.1-2007 table 10.8. Systems 3 and 4 are baseline systems based on DX rooftop units

  • Fan_Motor_Efficiency_System_3_4 = (0.0242 * (Log(System_3_4_BHP) / Log(2.718282))) + 0.834


  • This function calculates the maximum allowable brake horsepower for systems 3 and 4

  • Fan_BHP_per_CFM_System_3_4 = (0.00094 * System_3_4_CFM)


  • This function calculates the maximum allowable system fan power in kW

  • System_Fan_Power_System_3_4 = (System_3_4_BHP * 746/ Fan_Motor_Efficiency_System_3_4) / 1000

For system 9


  • This function calculates the minimum fan efficiency for system 9 based on ASHRAE 90.1-2007 table 10.8. System 9 is a baseline system based on a chilled water plant

  • Fan_Motor_Efficiency_System_9 = (0.0242 * (Log(System_9_BHP) / Log(2.718282))) + 0.834


  • This function calculates the maximum allowable brake horsepower for system 9

  • Fan_BHP_per_CFM_System_9 = (0.00062 * System_9_CFM)

System_Fan_Power_System_9(System_9_BHP, Fan_Motor_Efficiency_System_9)

  • This function calculates the maximum allowable system fan power in kW

  • System_Fan_Power_System_9 = (System_9_BHP * 746 / Fan_Motor_Efficiency_System_9) / 1000

For all systems


  • This function calculates fan power at part load based on ASHRAE 90.1-2007 Table G3.1.3.15

  • System_Fan_Power_Fraction_at_PLR = (0.0013 + (0.147 * Fan_System_Part_Load_Ratio) + (0.9506 * Fan_System_Part_Load_Ratio ^ 2) - (0.0998 * Fan_System_Part_Load_Ratio ^ 3))

Proposed ASHRAE 90.1 - 2007 Addenda for Data Centers - Part  2: Additional Information and Energy Modeling Parameters

This is a high-level summary of the major items contained in the current addenda cj and bu: (Please note that the items listed are the changes proposed in the addenda that apply to data centers only. Additionally, they do not contain all of the language necessary to verify compliance with the ASHRAE 90.1-2007 standard).

Items from Addendum cj and bu:

Exception G3.1.1

  • This was the exception that data centers would fall under prior to these addenda. This no longer applies.


  • Outdoor air economizers shall be included in baseline HVAC Systems 3, 4 and 9 (the systems used for data centers) based on climate as specified in Table G3.1.2.6A.

  • Exceptions to G3.1.2.6: Economizers shall not be included for systems that include gas-phase air cleaning to meet the requirements of Section 6.1.2 of ANSI/ASHRAE Standard 62.1. This exception shall be used only if the
    system in the proposed design does not match the building design.

  • Systems that serve computer rooms that are HVAC System 3 or 4 shall not have an economizer.

  • Systems that serve computer rooms that are HVAC System 9 shall include an integrated water-side economizer meeting the requirements of Section in the baseline building design.

  • If the simulation software cannot model an integrated water-side economizer, then an air-side shall be modeled.


  • If the proposed building has humidification, the set points and schedules shall be the same in both the baseline and proposed buildings

(Note: this provision will only allow for savings if the proposed building uses a more energy efficient humidification process, such as adiabatic as compared to isothermal).

Energy Modeling Parameters

Type and Number of Chillers

  • Electric chillers shall be used in the baseline building design regardless of the cooling energy source, e.g., direct-fired absorption, absorption from purchased steam, or purchased chilled water.

  • The baseline building design's chiller plant shall be modeled with chillers having the number and type as indicated in Table G3.1.3.7 as a function of building peak cooling load.

Piping Losses

  • Piping losses shall not be modeled in either the proposed or baseline building designs for hot water, chilled water, or steam piping.

(Note: need to consider this as analogous to electrical system losses . The concept being that both piping losses and electrical distribution losses are small and difficult to standardize across the multitude of projects).

Chilled-Water Supply Temperature

  • Chilled-water design supply temperature shall be modeled at44°F and return water temperature at 56°F.

  • Chilled water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule:

  • 44°F (6.7°C) at 80°F (27°C) and above

  • 54°F at 60°F (12°C at 16°C) and below

  • ramped linearly between 44°F and 54°F (6.7°C and 12°C)at temperatures between 80°F and 60°F (27°C and 16°C).

Chilled-Water Pumps

  • The baseline building design pump power shall be 22 W/gpm (349 kW/1000 L/s).

  • Chilled-water systems with a cooling capacity of 300 tons (1055 kW) or more shall be modeled as primary/secondary systems with variable-speed drives on the secondary pumping loop.

  • Chilled-water pumps in systems serving less than 300 tons (1055 kW) cooling capacity shall be modeled as a primary/secondary systems with secondary pump riding the pump curve.

Heat Rejection

  • The heat rejection device shall be an axial fan cooling tower with two-speed fans.

  • Condenser water design supply temperature shall be 85°F or 10°F (29°C or 5.6°C) approach to design wet-bulb temperature, whichever is lower, with a design temperature rise of 10°F(5.6°C).

  • The tower shall be controlled to maintain a 70°F (21°C) leaving water temperature where weather permits, floating up to leaving water temperature at design conditions.

  • The baseline building design condenser water pump power shall be 19 W/gpm(310 kW/1000 L/s). Each chiller shall be modeled with separate condenser water and chilled water pumps interlocked to operate with the associated chiller.

Computer Room Equipment Schedules

  • Computer room equipment schedules shall be modeled as a constant fraction of the peak design load per the following monthly schedule:

  • Month 1, 5, 9 - 25%

  • Month 2, 6, 10 - 50%

  • Month 3, 7, 11 - 75%

  • Month 4, 8, 12 - 100%

Supply Air Temperature and Fan Control

  • Minimum volume setpoint shall be 50% of the maximum design airflow rate, the minimum ventilation outdoor air flow rate, or the air flow rate required to comply with applicable codes or accreditation standards, whichever is larger.

  • Fan volume shall be reset from 100% air flow at 100% cooling load to minimum air flow at 50% cooling load.

  • Supply air temperature setpoint shall be reset from minimum supply air temperature at 50% cooling load and above to space temperature at 0% cooling load.

  • In heating mode supply air temperature shall be modulated to maintain space temperature and fan volume shall be fixed at the minimum air flow.

LEED for Data Centers: Finally a Reality?


Many people have been inquiring on the status of the LEED for data centers standard that began as a project funded by the California Energy Commission and managed by Lawrence Berkeley National Labs. See for additional information on that effort.


Well the good news is that the US Green Building Council ( has embarked on a process that they call adaptation of the LEED standard 3.0. Simply put, under this process, credits are modified for a particular type of building that does not work well under the LEED standards due to the special nature of the occupancy, equipment, size, etc. This is a summary of the rules:


Credit Modification

  • Changes are proposed based on the current balloted credit language

  • The overall intent of credit cannot be altered

  • Only 6 modifications can be made (regardless of the number of rating systems being addressed)

  • 1 of the 6 modifications can be adoption of a “new” credit from another rating system

  • Entirely new concepts/credits to LEED are not permitted

  • No modifications are allowed to the minimum project and minimum eligibility requirements (though we will note issues for future deliberation/working groups)

  • Proposed modifications must be approved by LEED Steering Committee

  • Changing point values and weightings is not part of this effort

So we are working within the boundaries of the LEED standard for new construction, but are also looking to LEED for Commercial Interiors and LEED for Existing Buildings: Operations and Maintenance to determine the impacts and/or use credits from these standards that make sense for the New Construction standard.


We had our first meeting at the USGBC offices in Washington, DC last month. The team that is working on this effort is as follows:

  • USGBC: four representatives

  • Industry subject matter expert (liaison between working group and USGBC): Bill Kosik – HP

  • Working group: eleven representatives from consulting engineering firms, data center owners, builders, equipment vendors and researchers

The preliminary timeline is to have draft language to the USGBC’s technical and steering committees by late spring 2010. It is not clear yet when a final standard would be made available and/or when pilot projects will be requested.




Using outside air in data centers (AKA "free cooling")

Here are some more analytics and data visualizations, this time on using outside air to cool a data center. When using this type of strategy, the hourly outside temperature and humidity conditions will drive the overall strategy and control of the HVAC systems. This is why it is critical to develop a very granular analysis of the climate for the particular site for the data center.


This is the base case (no economizer).



This is the case using economizer.


No we need to analyze the hourly kW demand of each case, by each sub-system. The following charts were generated from detailed, hourly energy use simulation algorithms developed by HP CFS engineers.


This is the base case. Notice that the blue line which represents the chiller power, is active all year.


This is the economizer case. Here you can see that the chiller power fluctuates much more, reducing the overall power consumption significantly. Notice also that the power for humidification (represented by the purple line) now becomes a larger contributor to the overall energy use. This is where the computer-based simulations become absolutely necessary so we can understand the entire picture before recommending a particular solution.

Will the new presidential order will speed up green IT?

The FEDERAL LEADERSHIP IN ENVIRONMENTAL, ENERGY,AND ECONOMIC PERFORMANCE presidential order went into effect on October 5, 2009. The main goal of the order is to "to establish an integrated strategy towards sustainability in the Federal Government and to make reduction of greenhouse gas emissions a priority for Federal agencies". It requires that "the agency head shall consider reductions associated with: (i) reducing energy intensity in agency buildings; (ii) increasing agency use of renewable energy and implementing renewable energy generation projects on agency property".

There are 3-month and 8-month deadlines for the agencies to put targets and plans in place for reducing their carbon footprint. Could this finally be the push we need?

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  • I’m a Global Strategist, a certified (PMI) Project Manager, specializing in business to IT alignment, agility consulting, Infrastructure Transformation and Strategic Architecture for Big Data, Mobility, Private Cloud, Unified Communications and Collaboration. I drive the strategy, vision and content of strategic consulting services in the Big Data IT Infrastructure services area at HP. As part of this, I meet with senior level customers to understand their challenges, conduct workshops to determine future vision and roadmaps as well as presenting at industry and analyst events.
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  • Having joined HP in 2003 Ian Jagger is the world-wide marketing and program manager for HP Technology Consulting's Strategic Consulting Services, Critical Facilities Services and Energy and Sustainability Management Services, as well as emerging IT services Prior to his current role, he served as the HP Services Marketing Manager for Central and Eastern Europe, Middle East and Africa, having joined HP in a similar role in the Middle East. Prior to HP Jagger had a 15 year international sales career, culminating in being Sales and Marketing Director for Steelcase Inc addressing Northern Europe before focusing more specifically on marketing. His initial focus was consultancy and interim marketing management, primarily for small to mid-sized customers based or looking to expand in the Middle Eastern region. Immediately prior to joining HP he was a strategic marketing consultant addressing investment targets for a technology fund. Born in Rochdale, United Kingdom, Jagger holds an honors bachelor of science degree in economics and a degree in social psychology from Loughborough University, England. He also holds a Masters Diploma in Marketing from the Chartered Institute of Marketing, is a Member of the Chartered Institute of Marketing and a Chartered Marketer. He has one daughter and lives in Cary, North Carolina.
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  • Tim Swiader has twenty plus years in the Information Technology industry. He has worked primarily with the fortune 100 and legacy carriers transforming their applications, networks and data center facilities.
  • Tari is a Distinguished Technologist with 30 years of IT and cyber security experience. He is dual board certified in information security/business continuity and is responsible for a wide range of management and technology consulting services encompassing information security, disaster recovery, privacy, and risk management. His problem-solving skills, knowledge of various technology platforms, compliance statutes, industries, as well as his experience in deploying defense-in-depth and InfoSec Program solution architectures is commonly applied when advising CIOs/CISOs as well as leveraged in numerous HP client engagements throughout the world. Tari has designed, built, and managed some of the world’s largest InfoSec programs allowing them to defend against even the most aggressive attackers.
  • I provide technical consulting services at all phases including analysis, planning, design and implementation. I have a wide range of experience in WAN and LAN technologies, as well as providing security solutions and deploying operating system infrastructure. Besides working directly with clients to deploy technology in their data centers, I also find myself architecting or discussing solutions with a business’s chief information officer, helping to lay out a roadmap for the coming years.
  • Bill Kosik, PE, CEM, BEMP, LEED AP BD+C, is a Distinguished Technologist at HP Data Center Facilities Consulting (DCFC). He is responsible for execution of project work, training and mentoring of internal engineering and consulting teams, research and analysis of topics related to data center energy use, and industry presentations and writing assignments. He is one of the main technical contributors who have shaped the DCFC technical expertise in energy use optimization and sustainable design practices in data centers. He is a member of the Consulting-Specifying Engineer Editorial Advisory Board.
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