April, 27, 2021
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Using a Data Center Water Side Economizer on an existing facility to reduce water and energy usage
​By: Gardson Githu, PE
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EYP Mission Critical Facilities, Part of Ramboll (EYP MCF, Part of Ramboll) worked with the client to reduce the power and water consumption of their fully operational data center(s). Considering different variables including cost, code compliance, maintaining existing reliability, space, and constructability while the data center is fully operational, the clients can obtain up to 25% of energy savings, and 7% on Water Usage Savings
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Rising Realty Partners, owner of West 7 Center, formerly known as the Garland Center, a premier purposed-built mission-critical, co-location, and data center facility located at 1200 W.7th Street in downtown Los Angeles is one of the most energy-efficient data center following their recent central plant retrofit project. At a full load of 12-megawatt of data center load, the projected energy saving is approximately 6,900,000kWh per year after the retrofit project. With annualized mechanical partial PUE of 1.37, this data center at full load is among the top tier of its kind in the middle of downtown Los Angeles business district. The data center is located on the subterranean levels of a nine-story office building, it comprises of three subterranean levels. The bottom floor on lower level 3 is reserved for the critical mechanical and electrical infrastructure while the two top levels of lower level 1 and lower level 2 are the data center white space.
EYP MCF, Part of Ramboll performed an energy audit and made recommendations on improving energy usage in the data center and the lowering of PUE (Power Usage Efficiency). Upon completion of the audit, EYP MCF, Part of Ramboll recommended the installation of a water side economizer to the existing 4400-ton water-cooled chiller plant for energy savings and for the plant to be compliant with California Energy Code (Title 24). The existing central plant is an (N+1) chiller plant which consists of four (1100-ton) Trane centrifugal water-cooled chillers, four (3300 GPM) condenser water Pump, four (2600GPM) primary chilled water pumps, cooling towers, and multiple secondary chilled water pumps.
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Energy Analysis and Benchmarking
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The West 7 Center facility operations provided central plant energy usage trends from the Building Management System (BMS), water usage trending, and utility bills. During the study, the total building cooling load demand was approximately 761-tons, so at the time only one of the four chillers was required to meet the cooling demand for the building. Upon completion of benchmarking process, the data was analyzed, and the table and chart below represent the breakdown of the energy usage. (Figure 1)
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Figure 1 Central Plant Energy and water Usage Summary
Full Build Data Center Projected Energy Savings
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The energy base model was created using Trane Trace Energy Modeling tool. The base model was calibrated and tested using actual field measurements and power consumption of the mechanical equipment at the site. The calibrated base model was then used to model future data center load profile and power and energy consumption. Figure 1 above represents the data center’s full load energy usage without an economizer system and chilled water supply set point of 43-degree Fahrenheit.
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The economizer system allows the chilled water system to operate at higher chilled water temperatures above the current design setpoint. Chilled water setpoint for economizer base model was set at 65-degree Fahrenheit driven by current Energy Code requirement and industry projected future trends. Figure 2 below represents the data center’s full load energy usage with an economizer system and a chilled water supply set point of 65-degree Fahrenheit.
Figure 2 Full Build Data Center Energy Consumption with Economizer.
The projected annual energy savings of 1,563,145 kWh and water savings of 1.8-million gallons at the current load condition was computed and complied as summarized in Figure 3. However, the projected full implementation of the economizer will result in 6,944,371 kWh, and water usage savings of approximately 7-million gallons per year at full load.
Figure 3 Energy Savings summary
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Economizer Design Considerations
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EYP Mission Critical Facilities, Part of Ramboll (EYP MCF, Part of Ramboll) in corroboration with Rising Realty Partners considered several factors in the design of the economizer retrofit project. Those factors included cost, code compliance, maintaining the reliability of the existing system, space availability, and constructability while the data center was still fully operational. Of all these factors, constructability and reliability were the two most important factors for Rising Realty Partners and EYP MCF, Part of Ramboll. The original design intent was for chillers to operate in line-up formation of a primary pump, condenser pump, and cooling tower, connected to a common header, however, none of the pumps or the towers are dedicated to any chiller. EYP MCF, Part of Ramboll recommended and designed an economizer system that was consistent with the original design intent. The economizer heat exchanger was to be connected in series with the chiller on both sides of chilled water and condenser water systems. Figure 4 below represents one line economizer heat exchanger connection diagram. As indicated both chilled water and condenser water are connected in series thus eliminating the cost of additional pumps. The system is designed for an economizer system to provide partial cooling to the chilled water and the chiller providing trim cooling to meet the setpoint. On the condenser side, the system is designed to maintain condenser water temperature through the chiller within the recommended manufacturer’s range. This is accomplished by passing through warm water from the heat exchanger exit through the chiller and by modulating a 3-way valve controlled by the chiller control system.
Figure 4 Heat Exchanger High-Level connection diagram
Successful Project Completed During Shutdown
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In the fall of 2019, the economizer retrofit construction commenced followed by vigorous balancing and testing, control system upgrade, and system functional testing. The project was completed in the fall of 2020. Figure 5 is a photo of one of the heat exchanger installations at the site while figure 6 is a photo of piping modification at the site.
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Figure 5 Heat Exchanger installation photo
Figure 6 Economizer Piping Modified Installation Photo
Conclusion
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The West 7 Center economizer retrofit project, is a sample case study of a successful retrofit project. It is projected to yield energy savings and maintain the operational reliability of the system. Projected annual energy and water savings and partial mechanical PUE of 1.37 makes this data center one of the most efficient data centers in downtown Los Angeles. This data center design by EYP Mission Critical Facilities, Part of Ramboll (EYP MCF, Part of Ramboll) provides operational flexibility as the information technology industry continues to evolve.
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