Randall Lamb Association

INsight: Data Centers

November 9, 2010

Data Centers: Success with Air-side Economizers

By: Brad Hollub, PE, LEED AP – Senior Associate
The world of HVAC design for critical facilities seems to be evolving by the minute. However, in a world of endless design options (e.g. indirect/direct evaporative cooling, air/water-side economizers, in-row cooling, hot/cold aisle containment, supply/room temperature set-point adjustment, etc.), finding a common ground that makes economic sense and pleases both owners and operators is paramount. We’re always faced with the same question when hearing new design theories: How do you balance a client’s need of proven reliability with new energy-saving solutions?

This is a challenge that Randall Lamb has faced on two recent data center expansions. What’s important to note in the last sentence is the word “expansion.” This means we’re expected to provide solutions that meet the facilities’ needs and their operators in a live, critical environment. The benefits of incorporating air-side economizers in the projects profiled below simply could not be ignored. We understood the potential savings associated with these systems, and fortunately for us, so did our clients. Despite the obvious advantages of utilizing free cooling by means of outside air, this topic remains in debate by specialists throughout the industry due to the risk of introducing pollutants and humidity control issues into the data center. Ultimately, we were able to meet the team’s goals without compromising our dedication to energy conservation and our client’s bottom line.


Colocation size: 3,200 SF, Critical Load Requirement: 3.0 KW/Cabinet

We targeted implementing an HVAC design that maximized the energy savings associated with using the mild bay area climate. Located in San Francisco, the mechanical design is comprised of split-DX CRAC units with overhead ducted supply distribution. This particular co-location site was on the top floor of a 2-story building, and the subject of connecting an air-side economizer to the overhead distribution from the roof became the main focus during our design development phase. We were able to introduce a rooftop modulating economizer system that best fit the needs of this speculative data center environment. Seven (7) 26-ton units were designed to condition the space at full capacity, with the economizer system able to meet the demand of the space in increments, as tenants began to populate the room with cabinets. Room contamination of outdoor pollutants was mitigated by the use of a filtration system on the intake side of the economizer fan. A custom housing fitted with 4” deep ASHRAE Standard 52.2 MERV 11 filters was installed to protect the indoor environment. Working with our local utility provider PG&E, an early energy analysis estimated the annual savings with the economizer design at 964,000 kWh/yr at peak load. With an estimated annual energy cost savings of $115,000 and simple payback of less than two years, this option became immediately desirable to our client. Participating in PG&E’s incentive program, an incentive of 50% of the installation cost of the economizer and controls is available to the Owner, thus reducing their final project cost and their payback to less than one year.

Client: Confidential Data Center Expansions, Seattle, Washington,
Colocation size: 18,000 SF, Critical Load Requirement: Present = 3.0 KW/Cabinet, Future = 5.0 KW/Cabinet

This data center expansion was located on the top floor of a 3-story building with dedicated rooftop space for mechanical equipment. Working concurrently with the building’s engineers, multiple equipment manufacturers and the client, we were able to propose a layout for the 650-ton cooling system using manifolded packaged A/C units. Collaborating with the unit manufacturer, we selected units that included custom features to meet our space constraints. Through a streamlined design process, the client was able to pre-purchase the equipment prior to construction document completion, thus keeping the project on schedule and on budget. The units, shipped from the factory complete with comparative enthalpy modulating economizer control, exceeded our client’s expectations. The system also included “adiabatic humidification” as opposed to the traditional isothermal humidifiers that vaporizes water to humidify, consuming significant amounts of energy. The humidification equipment, coupled with a building management system that monitored humidity throughout the data center, ensured the space environment met the operator’s needs. With the inclusion of the air-side economizer, this data center is expected to see a 60-70% reduction in HVAC operating costs. Upon completion of the Level 4 Integrated Systems Testing (IST), the client is hoping to report significant energy savings and a low Power Usage Effectiveness (PUE).

Posted in Project Insights