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:
- 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)
- 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 G126.96.36.199
- 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:
- 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 G188.8.131.52A.
- Exceptions to G184.108.40.206: 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 220.127.116.11 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 G18.104.22.168 as a function of building peak cooling load.
- 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).
- 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.
- 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.
ATLANTA – A new program to inform building owners and operators, tenants and prospective buyers on the energy use of buildings, similar to a nutrition label on food or miles per gallon ratings on cars, was launched today to encourage the building industry to find ways to cut energy use and costs.
The Building Energy Quotient program, which will be known as Building EQ, will include both As Designed (asset) and In Operation (as operated) ratings for all building types, except residential. It also will provide a detailed certificate with data on actual energy use, energy demand profiles, indoor air quality and other information that will enable building owners to evaluate and reduce their building’s energy use. The program is administered by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
“Information on a building's energy use is the critical first step in making the necessary changes and choices to reduce energy use and costs,” Gordon Holness, ASHRAE president, said. “The Building EQ program provides an easily understood scale to convey a building’s energy use in comparison to similar buildings, occupancy types and climate zone, while also providing building owners with building-specific information that can be used to improve building energy performance.”
Holness noted that building energy use disclosure is already mandatory in California; Washington, D.C.; Austin, Texas; Washington State; the European Union; and Australia.
Those participating in the pilot program are leading building owners and designers, real estate developers and government agencies, including:
· The Durst Organization, the owner, manager and builder of 9 million square feet of mid-town Manhattan office and residential properties, will include 4 Times Square, 1155 Avenue of the Americas and One Bryant Park in New York City in the pilot
· The U.S. General Services Administration, the primary agency responsible for the acquisition and management of federal buildings owns or leases 8,600 properties and maintains an inventory of more than 354 million square feet of workspace for 1.1 million federal employees
· Hines, a privately owned real estate firm involved in real estate investment, development and property management worldwide headquartered in London and Houston, Texas, will place high-profile properties from five major U.S. market in the pilot
· The Detroit-Wayne Joint Building Authority will include the Coleman A. Young Municipal Center, which is home of six branches of city and county government including Circuit and Probate Courts, City and County Clerks and the Executive and Legislative branches of the City of Detroit, in the pilot
· The Michigan Department of Management and Budget, which acquires and manages properties for many of the state’s agencies
Through the pilot program, the Building EQ program will allow fine-tuning and final development of the program. In parallel with this effort, ASHRAE has developed a certification program for building energy modelers. Following completion of the pilot program in mid-June, the program is expected to be fully functional by the end of 2010. Under the program, new buildings will be eligible to receive an As Designed, or asset, rating, which provides an assessment of the building based on the components specified in the design and is based on the results of building energy modeling and simulation. An In Operation rating will be available once the building has at least one year of data on the actual ener gy use and is based on a combination of the structure of the building and how it is operated. Existing buildings would be eligible to receive both an As Designed and In Operation rating. “With procedures for both an As Designed and In Operation rating, building owners can make side-by-side comparisons that could further reconcile differences between designed and measured energy use on an ongoing basis,” Holness said.
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.
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?
On September 22, 2009, the EPA Administrator Lisa Jackson signed the rule on a new greenhouse gas emission reporting program which is a pre-cursor to potential carbon taxing policy. The reporting is for the top carbon emitters in the U.S, primarily from the manufacturing sector where carbon emissions are from the site (as opposed to indirect emissions from electrical generation). In this first round of reporting, automobile manufacturers and other large industrial facilities are not included.
If you read the documentation from the EPA you will see that the threshold for report is emissions of 25,000 metrics tons of CO2e (carbon dioxide equivalent) annually. Furthermore, the EPA documents indicate that facilities with a minimum of 25,000 metric tons of CO2e annual emissions account for 85% of the total GHG emissions in the U.S annually. Keep in mind that these are facilities that manufacture items that involve the use of CO2 in the process and often times have on-site power generation facilities using solid or gaseous fuel located on site. These are considered direct emissions since they are from the actual site.
Since most data centers and other large commercial buildings do not typically have on-site electric generation facilities, the CO2e emission from these facilities s are considered indirect emissions since they are attributable to electric generation at an off-site facility owned by another entity. The EPA has issued Technical Support Document on the Proposed Rule for Mandatory Greenhouse Gas Reporting which discusses the benefit of reporting indirect emissions attributable to a facility as a means to encourage awareness of energy use and as a way to understand the impact that the facilities have on the efficiency of the electric power generators. While this is not part of the new reporting program, it gives insight into the longer-term plans of the U.S. EPA.
The indirect CO2e emissions from the generation of electricity for a data center is derived from the amount of electricity used expressed in kWH, the fuel source and efficiency of the generation. The eGrid documentation makes this calculation easy. If you know the annual electricity usage of the facility in kWH, just multiply this by the factors in the eGrid tables. These are expressed in pounds of CO2 per megawatt-hour, so you will need to convert from pounds to metric tons and from kilowatt-hours (kWH) to megawatt-hours (MWH). The average for the United States is approximately 1300 pounds of CO2 per megawatt-hour of electricity generation.
Why is the relevant to data centers? How many metric tons of CO2e does a data center emit anyway? I did some cursory energy analysis to answer this question. Using the range of emission rates for U.S. electric generators, I modeled a data center located in Chicago, IL. I considered different size facilities : 2, 5, 10 and 20 MW. The data in visualized in this graph:
The way this chart is read is the following:
1. On the X-axis, locate the data center capacity.
2. Draw a line straight up to the curve that best represents the CO2 emission output (in pounds per kWH) of the electrical generator, state or NERC region based on where the data center facility is located.
3. Draw a horizontal line to the Y-axis from where the vertical line intersects the appropriate curve.
4. Read the value on the Y-axis where the line intersects.
Table listing the different eGrid regions and the average GHG emissions from both base loaded and non-base loaded electrical power generation
Maps of the United States showing the different eGrid regions (left) and the average CO2 output per state in lbs per megawatt-hour (right)
So what does it all mean? Based on the analysis, data centers over 10 MW in capacity will likely face scrutiny in the future based on the indirect CO2 emissions. However, as the generation type gets more CO2 intensive, it becomes very difficult for facilities to achieve an upper limit threshold of 25,000 metric tons annually. Remember - I am making assumptions on the capping threshold and that corporations will need to report indirect emissions. But it is important to be prepared if this becomes the case.
CO2e is a metric that includes the other primary contributors to green house gas emissions. The formula that is used to determine CO2e is:
CO2e = (EF1* CO2) + (EF2 * NH4)+ (EF2 * N2O)
where EFi is the emission factor attributable to the particular gas. The US EPA publishes this information in their eGrid documents for all electrical power providers in the United States.