Date: 2021-11-01 14:21:51
The mission-critical nature of information-technology equipment demands precise control of temperature, humidity, and airflow inside data centers to prevent costly and potentially catastrophic failures.
By MICHAEL J. BULZOMI, AMCA North America Region Air Control Advocacy Committee
Housing applications and information vital to the way the world works, collaborates, and socially interacts, data centers operate 24 hours a day, seven days a week, 365 days a year. The processors, servers, and other information-technology (I.T.) equipment they contain generate an exorbitant amount of heat. If that heat and resultant humidity is not controlled, the equipment will be at great risk of failure, which can lead to costly downtime, lost data, and lost revenue. HVAC systems for data centers, thus, are designed for year-round cooling with precise monitoring and control of ventilation.
This article will provide a foundational understanding of the various types of control dampers available for use in data-center ventilation and present recommendations for specific performance requirements.
As defined in ANSI/AMCA Standard 500-D, Laboratory Methods of Testing Dampers for Rating, a damper is a device mounted in a duct or opening that varies the volume of air flowing through the duct or opening. A damper may be operated manually or mechanically and have a single blade or multiple blades. Ventilation of a space includes the integration of dampers to control the volume of outside air, return air, and exhaust air.
If controlled mechanically with an actuator, dampers can modulate open or closed to achieve a desired position or flow via a signal from a building management system. Employing modulating actuated dampers with specific control strategies allows the owner to take advantage of free cooling—that is, the use of outdoor air at ambient temperature, rather than the refrigeration process, to reject heat—and air-side economization—defined in ANSI/ASHRAE/IES 90.1-2019, Energy Standard for Buildings Except Low-Rise Residential Buildings, as the use of outdoor air, through a duct-damper arrangement and automatic control system, to reduce the need for mechanical cooling—when the outdoor temperature and humidity are mild. Selecting the most appropriate damper for a system design is critical in ensuring system performance and optimizing data-center-equipment functionality.
There are several styles and methods of construction of volume-control dampers and numerous options that can provide additional value to a ventilation strategy. Understanding the differences enables designers to properly specify, design, and maximize the benefits of systems utilizing control dampers. Selection of the appropriate modulating actuator, along with the correct blade rotation (parallel or opposed), is vital to optimal system operation.
Volume-control dampers are used when it is necessary to control flow, pressure, humidity, or temperature in an air system. Specifying and selecting the appropriate damper for a ventilation strategy requires consideration of various performance factors, such as static-pressure loss, leakage, and thermal efficiency.
Static-pressure loss. Per ASHRAE, static-pressure loss is the difference in pressure between two points in a flow system, usually resulting from frictional resistance to fluid flow. Blade design and construction greatly affect static-pressure-loss performance. Increased static-pressure loss translates to greater energy and load required to operate a system. Standard volume-control dampers used to regulate flow in a system commonly are constructed with one of three types of blades: triple V, formed airfoil, or extruded airfoil.
Because of its aerodynamic shape, a formed airfoil blade typically will have considerably less static-pressure loss in the fully open position than a triple-V blade. This has been shown in air-performance testing performed in accordance with ANSI/AMCA Standard 500-D.
Because of the smoother shapes that can be achieved via the extruding process, an extruded-aluminum “true” airfoil blade will have a lower static-pressure drop than a formed-steel airfoil blade. Additionally, it will have a longer service life because of less corrosion. Although an extruded-aluminum damper can be costlier, in a system with velocities greater than 2,000 fpm (10 m/s), it should be the first choice to minimize static-pressure loss and possibly reduce the fan energy required to operate the system.
Leakage. Where a damper is required for air shutoff, the amount of air leakage through the damper should be considered. Leakage is expressed as the volume of air through a damper per square area of damper at a specific static pressure for a given closing torque in the closed position. Control dampers with excessive air leakage reduce system efficiency, requiring system fans to work harder to compensate, resulting in wasted fan energy. This wasted energy increases operational costs and can have a negative effect on the performance of other HVAC equipment.
To achieve the lowest leakage ratings, blade-edge and jamb seals typically are employed. A variety of seal materials, some more suitable for specific application requirements than others, are available. General-purpose seals constructed of polyvinyl chloride (PVC) and similar materials provide adequate leakage characteristics and performance at temperatures up to 140°F to 180°F (60°C to 82°C). For more stringent applications, where temperatures can fluctuate from -50°F to -70°F (-46°C to -57°C) and 200°F to 250°F (93°C to 121°C), silicone and ethylene-propylene-diene-monomer (EPDM) rubber seals can be utilized.
Opposed-blade galvanized-steel control damper.
Parallel-blade extruded-aluminum control damper.
Insulated control damper with thermally broken blades and frame. Above photographs courtesy of Greenheck Fan Corp.
The compression requirement for tight shutoff varies based on seal material, which will affect the torque requirements for operating a damper. Dampers with stainless-steel jamb seals can have a higher torque requirement for opening and closing than dampers with silicone or EPDM jamb seals, possibly resulting in the need for an actuator with a higher torque rating. Larger torque-rated actuators consume more energy and cost more. Seals made with silicone and EPDM tend to have a longer service life than seals made with other materials.
Air-leakage testing usually is conducted in accordance with ANSI/AMCA Standard 500-D. The maximum allowable leakage is defined in AMCA Publication 511, Certified Ratings Program Product Rating Manual for Air Control Devices (Table 1).
Thermal efficiency. Typically constructed of extruded aluminum, with blades and a frame featuring a thermal break component and insulation enabling performance in extremely cold environments, thermally efficient dampers, also known as thermal break dampers, provide extremely low leakage as well as exceptional air control in medium-to-high-pressure-and-velocity applications. Thermally efficient dampers reduce or eliminate the transfer of heat and cold and lessen the potential for condensation.
When designing for resilience, thermally efficient dampers offer a level of protection against the elements that standard control dampers do not. Their design typically includes low-pressure-drop airfoil blades and ultra-tight closure for AMCA Class 1A leakage. Dampers rated for AMCA Class 1A leakage are the optimal choice for shutoff and help to reduce costs attributed to wasted fan energy or the infiltration of extreme-temperature outside air. When balancing performance, cost, and overall resilience, thermally efficient dampers are the premium choice for airflow-, pressure-, and temperature-control ventilation strategies.
Damper Performance and Certification
Subsequent to being tested in accordance with ANSI/AMCA Standard 500-D, dampers can be certified for air performance in accordance with AMCA Publication 511 as part of the AMCA Certified Ratings Program (CRP). The purpose of the CRP is to assure buyers, specifiers, and users of air-control devices that published ratings are accurate and reliable. At the same time, the CRP assures manufacturers that competitors’ ratings are based on standard test methods and procedures and subject to periodic checks by an impartial authority. (For more on the AMCA CRP, see “Inside the AMCA Laboratory and Certified Ratings Program.”)
Understanding differences in the construction and performance of control dampers allows designers and owners to specify features that are essential and beneficial to damper operation. Specifying the correct type of control dampers for your data-center ventilation strategy will ensure system design requirements are met and provide an environment conducive to the efficient operation of I.T. equipment. Validating the performance of dampers ensures systems will operate within parameters to achieve the overall design intent.
About the Author
Michael J. Bulzomi is director of marketing, louvers and dampers, for Nailor Industries Inc. and a member of the AMCA North America Region Air Control Advocacy Committee.
General damper-blade types. Source: AMCA Publication 502-06 (R2009), Damper Application Manual for Heating, Ventilating, and Air Conditioning
TABLE 1. Allowable air leakage to achieve classification. Source: AMCA Publication 511-21, Certified Ratings Program Product Rating Manual for Air Control Devices