Ongoing Commissioning of Economizers in a Data Center
Data Center Economizer Maintenance: Ongoing Commissioning vs. Conventional
A maintenance protocol/program to verify performance and make corrections to the air or water side economizers in a data center
Item ID: 486
HVAC--Rooftop Units & Air Handling Units
Technical Advisory Group: 2013 Information Technology TAG (#8)
Average TAG Rating: 3.38 out of 5
TAG Ranking Date: 10/25/2013
TAG Rating Commentary:
- Not emerging - simply good maintenance practice - if economizers are installed, they should be kept in working order ·
- Especially for air side economizers. Seattle Energy code requires their installation, but often they do not work b/c the facility staff does not know how to correctly maintain and operate them.
- Always need to be sure economizers are in operation.
- But this isn't new or emerging.
- Not an ET.
Dampers and valves, and the associated controls on economizers, have been shown to need inspection and calibration typically semi-annualy, to assure optimal performance. If the economizers are not performing optimally, they are not performing at peak efficiency. Sensors and controllers, regardless of the application, need to be inspected routinely.
Baseline Description: No calibration of economizers
Baseline Energy Use: 810 kWh per year per square foot
Baseline and energy savings is 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 1500 kWh/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:
"Typical" Savings: 10%
Savings Range: From 1% to 100%
Savings will depend on how out of calibration the economizer system is. For the purpose of this analysis, we assume the equipment gets recalibrated when it is 10% out of calibration. This conservative assumption provides a payback of less than 6 months, making a semi-annual expense a viable project. However, economizer controls and actuators can be completely broken, eliminating any useful energy savings from the equation. Therefore, we use up to 100% as the maximum.
Best Estimate of Energy Savings:
"Typical" Savings: 10%
Energy Savings Reliability: 2 - Concept validated
We expect a commissioning program to be adopted for the economizer on a semi-annual basis. If the equipment is out of calibration by only 10%, the payback is less than 6 months, making this a viable program for the IT Manager to implement.
Energy Use of Emerging Technology:
729 kWh per square foot per year
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.))
10% savings over baseline is used for a conservative estimate of energy savings.
Potential number of units replaced by this technology:
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. Furthermore, we will assume that 50% of data centers are equipped with economizers, yielding a total of 2,181,350 sf.
Regional Technical Potential:
0.18 TWh per year
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)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $7.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.00
Baseline Technology Unit Cost (Equipment Only): $0.00
The baseline is to not provide any commissioning of economizers, and allow them to float out of calibration. This is a function that is better if added to the routine maintenance and not a special visit. A standard maintenance agreement would occur twice a year at the beginning of the heating and cooling seasons. This would include verification of refrigerant levels, filters, coil cleaning, etc. Having a technician that has the tools to recalibrate is possible and would make this a viable ET. The technician would need to make sure that the dampers go to an appropriate minimum in non-economizer mode, and go to full open at the correct OSA temperatures. The technician would also need to assure the mechanical cooling is properly interlocked. We estimate this adding about $10/ton, or about $600 per year for the twice annually inspections for each 60-ton system (or $7.00/sf).
Simple payback, new construction (years): 1.0
Simple payback, retrofit (years): 1.0
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.
Since this is a strategy, and maintenance should be performed on a periodic basis, the numbers above may be misleading. The ET is to implement a routine commissioning process to an existing economizer system. Therefore, the numbers are the same for retrofit and new construction. With a measure life of 0.6 years and a simple payback of 1 year for the twice annually maintenance, the building managers essentially break even and may not be willing to fund the level of maintenance/commissioning that maximizes on-site and regional energy savings.
Controls and actuators on water and air side economizers need to be inspected and calibrated regularly to assure optimal performance. Ideally, this attention would be included in the semi-annual inspection of the mechanical equipment. Many facilities get the HVAC equipment installed and forgotten, unit there is a problem. Uniquely, economizers may be out of calibration or even non-functional for years and not noticed.
Economizers are no exception to needing to be commissioned regularly. Commissioning of economizers includes (PECI, 2013 Pg Section 3.2.1)
- Verify that the control process provides reliable free cooling when conditions are appropriate under all building and system operating modes (including automatic and manual control modes) and under all climate conditions including seasonal extremes outside the statistical design envelope.
- Verify the cycle is integrated properly with other building processes and systems in both normal and emergency control modes. Building processes and systems include, but are not limited to, building pressurization requirements, zone pressurization requirements, minimum outdoor air requirements, normal and emergency operating modes, and scheduled operation.
- Verify that interlocks return the economizer dampers and/or valves to safe and efficient positions when the air handling system is shut down.
- Verify that interlocks disable the economizer cycle when it no longer provides energy savings benefit. The set points of these interlocks are appropriate for the loads served and the local environmental conditions.
- Verify that interlocks protect the air handling system and building areas served by the economizer from damage in the event of a failure of the economizer control process or a component of the system. These interlocks include low temperature cut-outs, high and low static pressure cut-outs, pressure relief doors, and limit switches.
- Verify that alarms are provided to alert the operating staff to economizer operating conditions that indicate an economizer control failure that could lead to energy waste and/or the failure or unscheduled shut down of the air handling system served by the economizer.
Standard practice is to not address the economizer after initial startup unless there is a noticeable problem, like poor air quality (dampers failed closed), inability to provide adequate heat (dampers failed open), etc.
Recalibration of the economizer controls and actuators to fit actual conditions/loads should be a maintenance item that should be highlighted and emphasized with building owners. Economizers may not be fully understood by the industry. It is not uncommon to find economizers with no barometric relief, rendering the economizer function useless as the fan rides the curve to deadhead position, even on packaged RTU's. It is also not uncommon to find the damper actuators slipping on the shaft. This ET would be an excellent topic for general discussion across all sectors, including Contractors, Service Technicians, Building Operators, Building Owners, etc.
Equipment that is out of calibration does not function at peak performance. Compromises to the HVAC system include poor air quality and poor temperature control.
End User Drawbacks:
This requires a higher level of knowledge from the maintenance technician.
Operations and Maintenance Costs:
Baseline Cost: $200.00
per: square foot per year
Emerging Technology Cost: $220.00
per: square foot per year
In addition to commissioning the HVAC equipment, cleaning coils, filters and drain pans/traps, checking refrigerant charge, filters, etc. the controls and actuators on the economizer should also be given attention. Since this commissioning function is part of a bigger commissioning project, the added cost is marginal.
Anticipated Lifespan of Emerging Technology: 0.5 years
The life of this ET is the same for the baseline. Per ASHRAE, the theoretical life is about 15 years. The equipment life does not change. However, with this being a commissioning action, estimated to occur semi-annually, the life is given as 6 months.
This is a strategy or maintenance ET, therefore, the competition might be considered as, to do nothing.
Reference and Citations:
The Green Grid,
Free-Cooling Estimated Savings Calculator
A calculator to show the energy savings based on a number of variables for both air and water side economizers.
Data Center Projects: Commissioning
Hydeman, Seidl, Shalley,
Data Centers: Staying On-Line: Data Center commissioning
Data Center Energy Management
Lawrence Berkeley National Laboratory
Section 2: Mechanical air handler Systems
Economizers and Mixed Air
Standard Energy Usage Numbers for E3TNW
Washington State University Energy Program
Global Data Center Space 2013