Air-Side Economizer for Data Centers

Summary

Air-Side Economizer for Data Centers

Data Center Cooling: Air-side Economizer vs. Conventional

Using up to 100% outside air cooling capability in a data center to provide "free" cooling in an application where outside air would otherwise be provided only to satisfy minimum ventilation requirements.

Synopsis:

Air-side economizers for data centers can provide up to 100% outside air (OSA) cooling in a data center to provide “free” cooling where OSA would otherwise provide only enough air to satisfy the minimum ventilation requirements. Because data centers require air conditioning year-round, significant energy savings can be realized by using OSA for free cooling. The standard practice is to use all mechanical cooling with no economizer, which is inefficient and leads to high energy bills.

This is becoming standard practice and is now required by the energy code in many jurisdictions. In retrofit, it can be cost-prohibitive, depending mostly on the location of the data center. If the data center is near an outside wall, this option should be considered. A well-designed economizer system can save 25% or more of the HVAC energy used in the data center.

Contractors and utilities in the Seattle, WA area, as well as the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and Lawrence Berkeley National Laboratory have had success using this strategy.

Energy Savings: 25%

Energy Savings Rating: Comprehensive Analysis What's this?

Level	Status	Description
1	Concept not validated	Claims of energy savings may not be credible due to lack of documentation or validation by unbiased experts.
2	Concept validated:	An unbiased expert has validated efficiency concepts through technical review and calculations based on engineering principles.
3	Limited assessment	An unbiased expert has measured technology characteristics and factors of energy use through one or more tests in typical applications with a clear baseline.
4	Extensive assessment	Additional testing in relevant applications and environments has increased knowledge of performance across a broad range of products, applications, and system conditions.
5	Comprehensive analysis	Results of lab and field tests have been used to develop methods for reliable prediction of performance across the range of intended applications.
6	Approved measure	Protocols for technology application are established and approved.

Simple Payback, New Construction (years): 13.7 What's this?

Simple Payback, Retrofit (years): 137.2 What's this?

Simple Payback is one tool used to estimate the cost-effectiveness of a proposed investment, such as the investment in an energy efficient technology. Simple payback indicates how many years it will take for the initial investment to "pay itself back." The basic formula for calculating a simple payback is:

Simple Payback = Incremental First Cost / Annual Savings

The Incremental Cost is determined by subtracting the Baseline First Cost from the Measure First Cost.

For New Construction, the Baseline First Cost is the cost to purchase the standard practice technology. The Measure First Cost is the cost of the alternative, more energy efficienct technology. Installation costs are not included, as it is assumed that installation costs are approximately the same for the Baseline and the Emerging Technology.

For Retrofit scenarios, the Baseline First Cost is $0, since the baseline scenario is to leave the existing equipment in place. The Emerging Technology First Cost is the Measure First Cost plus Installation Cost (the cost of the replacement technology, plus the labor cost to install it). Retrofit scenarios generally have a higher First Cost and longer Simple Paybacks than New Construction scenarios.

Simple Paybacks are called "simple" because they do not include details such as the time value of money or inflation, and often do not include operations and maintenance (O&M) costs or end-of-life disposal costs. However, they can still provide a powerful tool for a quick assessment of a proposed measure. These paybacks are rough estimates based upon best available data, and should be treated with caution. For major financial decisions, it is suggested that a full Lifecycle Cost Analysis be performed which includes the unique details of your situation.

The energy savings estimates are based upon an electric rate of $.09/kWh, and are calculated by comparing the range of estimated energy savings to the baseline energy use. For most technologies, this results in "Typical," "Fast" and "Slow" payback estimates, corresponding with the "Typical," "High" and "Low" estimates of energy savings, respectively.

Details

Air-Side Economizer for Data Centers

Data Center Cooling: Air-side Economizer vs. Conventional

Item ID: 119

Sector: Commercial, Industrial

Energy System: HVAC--Rooftop Units & Air Handling Units

Technical Advisory Group: 2010 HVAC TAG (#3)
Average TAG Rating: 3.6 out of 5
TAG Ranking Date: 06/29/2010
TAG Rating Commentary:

May require humidity control.
This is actually pretty well established technology - the big issue is getting through data center managers bias against the new less stringent [data center] environmental recommendations. A demonstration project, and publication of results PG&E has put together, would be appropriate.
"Required by code for new construction.” This appears to be a retrofit technology. May not be practical depending on server location in building; but would be good to get experience, or get case studies of those who have already done it; i.e., to determine what works, what doesn't, and to quantify cost effectiveness. Make sure to include adiabatic humidifier.
This technology is particularly beneficial in a climate where the outside air temperature is rarely high. Huge energy savings can be realized over the classic data system HVAC system. The technology is currently required by code in some areas, and if we are lucky will become standard practice before long. Support from BPA may speed its introduction in smaller data centers, improve the quality of the economizer controls through technical support, and encourage use of the economizers that are installed (there's usually an option of using mechanical cooling instead). I have heard some major data centers are being installed without vapor compression cycle equipment, using merely outside air and direct evaporative cooling. Adiabatic humidification is essential for optimizing use of air-side economizers for data centers. Otherwise the humidification needs in the winter may create a serious energy requirement. Computers are being manufactured now to meet a specification that requires tolerance of a wider range of humidity and temperatures, so the savings from air-side economizers are greater for these new computers. In existing databases (retrofit of air-side economizers), savings depend heavily on ability of mechanical cooling equipment to unload efficiently so that an integrated economizer strategy can be used effectively when the outside air temperature lies somewhere between the supply air temperature required and the return air temperature. The effectiveness of an air-side economizer is enhanced by separation of hot and cold aisles because that separation allows use of a higher supply air temperature set point.
Impact on humidity control is always a concern.
High efficiency filters will be required to minimize dust accumulation. This technology should also consider indirect evaporative cooling.
This is standard practice and required by code in Washington State. I don't think it can be considered emerging technology.

Technical Advisory Group: 2009 HVAC TAG (#2)

Technical Advisory Group: 2013 Information Technology TAG (#8)
Average TAG Rating: 4 out of 5
TAG Ranking Date: 10/25/2013
TAG Rating Commentary:

I support this technology, but have reservations about the tendency to promote direct outside air use for cooling over indirect air side economizing, fluid economizing. There are a number of methods for data center to avoid use of mechanical cooling. Air side economizing is not always the best choice, or most reliable means for a given facility to minimize use of mechanical cooling.
Implications for code (new construction); challenge for retrofit.
With higher air temperatures possible, economizer cooling seems highly attractive for this market.
But difficult to justify as a retrofit measure.
Not an ET. We consider each project as custom with guarantee that we can offer incentives.
In the Northwest this should be the default method of cooling, except near pulp and paper plants. Same as #258, I suggest eliminating #258

Synopsis:

Baseline Example:

Baseline Description: Mechanical cooling all year instead of free cooling
Baseline Energy Use: 810 kWh per year per square foot

Comments:

Baseline and energy savings based on energy use of a "typical" data center as decided as standard by E3T IT TAG team. The energy use of a full data center is 1500kWh/sf/yr. The baseline for this technology is the HVAC portion of that, which is 54%, or 810 kWh/sf/yr. (WSU EEP, 2013)

Manufacturer's Energy Savings Claims:

Comments:

This is a strategy so no manufacturer's statements apply. Energy savings will be based on weather conditions for the site. This is viable, with reasonable payback periods, in most Climate zones. Areas where this may not be a viable strategy include dry climates where humidification may be needed if the air is too dry, and climates that rarely get below 60 degrees.

Best Estimate of Energy Savings:

"Typical" Savings: 25%
Low and High Energy Savings: 15% to 40%
Energy Savings Reliability: 5 - Comprehensive Analysis

Comments:

Success depends on operator confidence in actual use of the economizer (when mechanical cooling also available). Savings are increased by: locations with cool, low humidity summers; separation of hot and cold aisles (because this offers potential for higher supply air temperatures; servers able to withstand high temperatures (increases range of outside air temperatures useful for cooling in product specifications used by those who purchase the IT equipment); adiabatic humidifiers (to avoid losing winter savings due to low relative humidity of outside air); mechanical cooling equipment capable of unloading (effective turn-down) efficiently to allow integrated economizer controls (use of both outside air for cooling and mechanical cooling when outside air temperature between return air temperature and supply air temperature setpoint). Goes well with evaporative cooling because economizer air is once-through. Goes well with direct heat recovery by passing air into adjacent spaces, for the same reason. ** For a quantitative analysis of savings variation with climate, evaporative cooling, and allowable supply air temperature range, see the ASHRAE article about it referenced below. (ASHRAE, 2009 Pg 69-70)

Energy Use of Emerging Technology:

607.5 kWh per square foot per year What's this?

Energy Use of an Emerging Technology is based upon the following algorithm.

Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))

Comments:

Although there are many factors that affect the savings associated with air side economizer, a conservative energy savings based on the baseline condition, assumes 25% reduction. Therefore, operating 1-ton cooling unit (1.2 kW) for 3,750 hours per year results in 4,500 kWh/yr/ton.

Technical Potential:
Units: square foot
Potential number of units replaced by this technology: 4,362,704
Comments:

We have not been able to find accurate data for square footage of data centers in the Northwest. The best, most up-to-date estimate of space in the US we could find is from DataCenterDynamics (DCD, 2014, Pg. 4). According to this report, the total "white space" in the US is 109,067,617 sf. To convert to the Northwest, we use a standard of 4% of national data, based on relative population. In this case, the Northwest probably has more than its share of data centers, so we could probably justify a higher number. However, we are not likely to be serving the mega data centers over 100,000 sf., so we should reduce the number. As a close approximation, we will stick with 4%, which gives a total floor space of non-mega data centers in the Northwest of 4,362,704 sf.

Regional Technical Potential:
0.88 TWh per year
101 aMW
What's this?

Regional Technical Potential of an Emerging Technology is calculated as follows:

Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)

First Cost:

Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $1250.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $1250.00
Baseline Technology Unit Cost (Equipment Only): $1000.00

Comments:

Incremental cost includes larger OSA and relief air ductwork and associated dampers, and is estimated at $500 per ton. As the size of the system increases, the cost decreases. This energy-saving strategy can be augmented with the addition of direct or direct-indirect evaporative cooling for adiabatic humidification and additional free cooling for a slightly higher cost.

Cost Effectiveness:

Simple payback, new construction (years): 13.7

Simple payback, retrofit (years): 137.2

What's this?

Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.

Comments:

Cost effectiveness is not easy to estimate. It depends on the size of the data center, new or retrofit, building construction and other variables.

Detailed Description:

Install an air-side economizer with 100% outside-air-cooling capability in a data center to provide “free” cooling where outside air would otherwise provide only enough air to satisfy the minimum ventilation requirements. Because data centers require air conditioning year-round, significant energy savings can be realized by using outside air (OSA) for free cooling in much of the USA.

Compared to the standard raised-floor computer room air conditioning (CRAC) unit system, this strategy requires additional ductwork, dampers, additional filtration, and increased levels of humidification to handle the low absolute humidity levels in cold OSA. In order to avoid the possible energy penalty from increased winter humidification requirements, only adiabatic (or swamp cooler) humidification is used. Humidification and direct evaporative cooling is typically provided by a wet porous medium in the supply air, or an atomizing humidifier (where droplets of water are introduced to the air, where they evaporate). If the OSA, after adiabatic humidification and/or direct evaporative cooling, is above the allowable supply temperature, mechanical cooling is initiated. If the discharge from the humidifier/evaporator is lower than the hot aisle temperature, OSA for cooling may be used with the mechanical cooling if the mechanical cooling is able to operate at part load. If OSA temperatures fall below acceptable supply air temperatures, the OSA is mixed with air out of the hot aisle. If unloading is a problem, a system with multiple CRAC units may stage the number of CRAC units on to allow part-load operation with integrated economizer controls. As with mechanical cooling, space temperature and humidity ranges are established by the customer and the computer equipment manufacturer. Acceptable temperature and humidity ranges stated in standard guidelines have become broader in recent years, making it easier to meet the required set points with less mechanical cooling.

Standard Practice:

There is not yet a widespread standard for economizers in data centers. The standard practice is to use mechanical cooling only without economizers providing the minimum OSA required for ventilation.

Development Status:

In existing buildings, many large and small data centers use OSA only for ventilation.

Servers used to have very tight humidity and temperature control requirements such that the humidity or temperature could not change unless the rate of change was very small. Economizers do not maintain the humidity and temperature at a small enough rate of change for the older servers. In the last decade however, servers have proven to be more tolerant of changes in temperature and humidity, so allowing economizers to provide “free” cooling is now an option.
In new construction, air-side economizers are now required by the Energy Code for data centers with certain exceptions, including higher mechanical cooling efficiency and/or water side economizers.

The air-side economizer design strategy is reasonably familiar, but there are reliability concerns. It has not yet become standard practice although some large installations are helping to promote this technology as a viable option. Is likely to become common in the next few years, unless the industry switches to direct water cooling.

This technology has already been demonstrated successfully by the owners of the largest data centers, who worked in tandem with computer manufacturers. Computer manufacturers are responding to market requests for computers capable of withstanding wide temperature and humidity ranges.

Non-Energy Benefits:

None

End User Drawbacks:

Risk: The increased complexity of controls where operation depends on integrated economizer operation. Risk and perceived risk will drop as technical support increases and standard practice shifts.

Barrier for retrofit: Difficulty and, in many cases, very high cost of moving OSA into and out of the data center because data centers are often buried in the basement or deep in the interior of the building.

Barrier for new and existing spaces: Architects disapprove of having louvers on exterior walls. Consider placing the data center on the top floor so air can come through the roof without a lot of ductwork.

Potential increased operations and maintenance time for use of adiabatic humidifier and a more complex control strategy.

Operations and Maintenance Costs:

Baseline Cost: $0.00 per: square foot per year
Emerging Technology Cost: $10.00 per: square foot per year

Comments:

There are additional fans and damper actuators that need attention at least once a year. The estimate is at $0.025/cfm. For a 60-ton capacity economizer, the estimated cost is about $600 per year in O&M for calibration, lubrication and belts.

Effective Life:

Anticipated Lifespan of Emerging Technology: 20 years

Comments:

Ductwork and dampers will last many years, at least 20. A direct-evaporative cooler would last 15 years. Controls last 20 years with routine calibration.

Competing Technologies:

Direct water-cooled servers that receive water that has been through a cooling tower but not a chiller (evaporative cooling only).

Use of air-to-water heat pumps to recover heat from the data center return-air before it is re-delivered to the spaces needing cooling in other parts of the building. This is not generally practical because the building may lack year-round heating loads large enough to use the recovered heat. Heat recovery for space heat can be done in combination with an air-side economizer (or without an economizer) by directing data center exhaust air into offices when offices need heating.

For small data centers (closets) in office buildings, the designer may be able to treat the data center as a zone on a central variable air volume (VAV) or variable refrigerant flow (VRF) system if the facility operates 24/7, recovering the heat that way.

Reference and Citations:

Rich Miller, 09/18/2008. Intel: Servers Do Fine with Outside Air
Data Center Knowledge

Don Atwood, 08/01/2008. Reducing Data Center Costs with an Air Economizer
intel

Srirupa Ganguly, 02/26/2009. Impact of Air Filtration on the Energy and Indoor Air Quality of Economizer-based Data Centers in the PG&E Territory
Emerging Technologoes Coordinating Council

ASHRAE, 01/01/2009. Best Practices for Datacom Facility Energy Efficiency
American Society of Heating, Refrigerating and Air-Conditioning Engineers
Special Notes: “Economizer Cycles” (Chapter 4) and “Energy Efficiency Measures” (part of Chapter 6)

ASHRAE, 12/01/2007. Outside Air Economizers For Data Centers
ASHRAE Journal , 49

LBL, 09/16/2013. Data Center Energy Management Best Practices Checklist: Mechanical: Air Handler Systems
Lawrence Berkeley Laboratory

Mark Hydeman, 08/30/2010. Implications of Current Thermal Guidelines For Data Center Energy Use
ASHRAE Journal

ASHRAE, 01/01/2009. 2008 ASHRAE Environmental Guidelines for Datacom Equipment
American Society of Heating, Refrigerating and Air-Conditioning Engineers

ASHRAE, 01/01/2009. Thermal Guidelines for Data Processing Environments, Third Edition
American Society of Heating, Refrigerating and Air-Conditioning Engineers

PG&E, 01/01/2006. High Performance Data Centers: A Design Guidelines Sourcebook
Pacific Gas and Electric Company

Steve Greenberg, 07/12/2006. Best Practices for Data Centers: Lessons Learned from Benchmarking 22 Data Centers
ACEEE

WSU EEP, 12/06/2013. Standard Energy Usage Numbers for E3TNW
Washington State University Energy Program

DCD, 01/22/2014. Global Data Center Space 2013
DatacenterDynamics

ASHRAE, 05/04/2011. 2011 Thermal Guidelines for Data Processing Environments - Expanded Data Center Classes and Usage Guidelines
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

E-Source, 06/01/2010. How Weather Affects Energy-Efficient Technologies
E-Source
Special Notes: There is also a link to the E Source Resource Guide, “Economizers Still Failing – Even in High-Tech Data Centers Air-Side Economizers”.

Tom Harvey, 09/11/2014. Updated Air-Side Free Cooling Maps: The Impact of ASHRAE 2011 Allowable Ranges
Green Grid

Rank & Scores

Air-Side Economizer for Data Centers

2013 Information Technology TAG (#8)

Technical Advisory Group: 2013 Information Technology TAG (#8)
TAG Ranking: 1 out of 57
Average TAG Rating: 4 out of 5
TAG Ranking Date: 10/25/2013
TAG Rating Commentary:

I support this technology, but have reservations about the tendency to promote direct outside air use for cooling over indirect air side economizing, fluid economizing. There are a number of methods for data center to avoid use of mechanical cooling. Air side economizing is not always the best choice, or most reliable means for a given facility to minimize use of mechanical cooling.
Implications for code (new construction); challenge for retrofit.
With higher air temperatures possible, economizer cooling seems highly attractive for this market.
But difficult to justify as a retrofit measure.
Not an ET. We consider each project as custom with guarantee that we can offer incentives.
In the Northwest this should be the default method of cooling, except near pulp and paper plants. Same as #258, I suggest eliminating #258

2010 HVAC TAG (#3)

Technical Advisory Group: 2010 HVAC TAG (#3)
TAG Ranking: 3 out of 36
Average TAG Rating: 3.6 out of 5
TAG Ranking Date: 06/29/2010
TAG Rating Commentary:

May require humidity control.
This is actually pretty well established technology - the big issue is getting through data center managers bias against the new less stringent [data center] environmental recommendations. A demonstration project, and publication of results PG&E has put together, would be appropriate.
"Required by code for new construction.” This appears to be a retrofit technology. May not be practical depending on server location in building; but would be good to get experience, or get case studies of those who have already done it; i.e., to determine what works, what doesn't, and to quantify cost effectiveness. Make sure to include adiabatic humidifier.
This technology is particularly beneficial in a climate where the outside air temperature is rarely high. Huge energy savings can be realized over the classic data system HVAC system. The technology is currently required by code in some areas, and if we are lucky will become standard practice before long. Support from BPA may speed its introduction in smaller data centers, improve the quality of the economizer controls through technical support, and encourage use of the economizers that are installed (there's usually an option of using mechanical cooling instead). I have heard some major data centers are being installed without vapor compression cycle equipment, using merely outside air and direct evaporative cooling. Adiabatic humidification is essential for optimizing use of air-side economizers for data centers. Otherwise the humidification needs in the winter may create a serious energy requirement. Computers are being manufactured now to meet a specification that requires tolerance of a wider range of humidity and temperatures, so the savings from air-side economizers are greater for these new computers. In existing databases (retrofit of air-side economizers), savings depend heavily on ability of mechanical cooling equipment to unload efficiently so that an integrated economizer strategy can be used effectively when the outside air temperature lies somewhere between the supply air temperature required and the return air temperature. The effectiveness of an air-side economizer is enhanced by separation of hot and cold aisles because that separation allows use of a higher supply air temperature set point.
Impact on humidity control is always a concern.
High efficiency filters will be required to minimize dust accumulation. This technology should also consider indirect evaporative cooling.
This is standard practice and required by code in Washington State. I don't think it can be considered emerging technology.

Technical Score Details

TAG Technical Score: 3.2 out of 5

How significant and reliable are the energy savings?
Energy Savings Score: 4.2 Comments:

For facilities with dedicated cooling systems and access to perimeter or roof of building.
In the Northwest this is a good option

How great are the non-energy advantages for adopting this technology?
Non-Energy Benefits Score: 2.4
Comments:

Economizers can significantly extend the useful life of cooling equipment - an additional non-energy benefit that is not often appreciated.
Using air economizers rather than chillers improves reliability. I also provides some level of backup when chillers are operating
Costs, air contaminants, humidity and reliability concerns may outweigh energy savings.

How ready are product and provider to scale up for widespread use in the Pacific Northwest?
Technology Readiness Score: 4.1
Comments:

Nothing new here!
Well proven technology
With new digital economizers and FDD

How easy is it to change to the proposed technology?
Ease of Adoption Score: 2.3
Comments:

May be very difficult to implement in an existing facility. Air side economizers require more maintenance in order to function effectively. A facility using air side economization requires a competent facility staff in order to maintain the economizer's functionality and ensure persistence of savings.
Depends - could be very difficult to adopt depending on the location of the data center.
In rare instances very good; in most instances okay or poor. Payback periods after incentives are still typically quite long (three or four years).
It may be costly to implement in traditional closed data centers.
Not usually an easy retrofit measure

Considering all costs and all benefits, how good a purchase is this technology for the owner?
Value Score: 3.1
Comments:

Air side economization is often not cost-effective in existing data centers in commercial facilities. It is a great measure when the data center is located adjacent to exterior walls or a ceiling.
Varies widely depending on the amount of work required to install ductwork.
But...it would be somewhat difficult to design a prescriptive rebate for the measure. I suppose you could assume a typical supply air specification and offer a prescriptive rebate based on the ton rating of the equipment, but you'd be taking quite a bit of technical risk on the claimed savings (i.e what is the actual heat load in the data center?)
Where feasible this is a good option. Should not be implemented near pulp and paper mills however

Completed:
9/21/2010 4:19:00 PM
Last Edited:
12/4/2013 3:52:06 PM

2009 HVAC TAG (#2)

Technical Advisory Group: 2009 HVAC TAG (#2)
TAG Ranking:
Average TAG Rating:
TAG Ranking Date:
TAG Rating Commentary: