In our field we frequently deal with applications where we use wall penetrations to relieve and intake air. It could be the need for bathroom exhaust, makeup air intake, emergency purge exhaust, or even general building pressure intake or relief. For this case-study, it is for emergency generator intake and exhaust at a new-construction project for the Erie County Medical Center. If the building loses power and the emergency generators are required to kick on, the dampers will open to allow combustion airflow into the space. 

For this application the dampers will be closed 99% of the time. The space within is still conditioned (heated and cooled) and energy loss through wall penetrations can be great if not properly considered with a preventative approach. This was a legitimate concern for the design engineers. The wall cavity sections at ECMC are large - roughly 100 square feet a piece. They know that in order to maintain a high-performing energy system they will need to minimize all wasted energy through this area.

Define: High Vs. Low Performing Dampers (PLUS: De-Coding Industry Terminology)

In order to obtain a grasp on what a damper does for your building, you need to understand all types of control dampers and how the industry classifies them (WARNING: EDUCATIONAL CONTENT ENSUES).

Air Movement and Control Association International, Inc. (known as AMCA) is the industry standard for defining, categorizing, and establishing ratings for fans, louvers, dampers, and other airflow devices. By definition, "
AMCA International publishes and distributes standards, references, and application manuals for specifiers, engineers, and others with an interest in air systems to use in the selection, evaluation, and troubleshooting of air system components." 

AMCA publication511-10 focuses on general control ventilation products. I've summarized the definitions from AMCA below:
  • Volume control damper: Device that varies the flow of air, broken down into Class 1A, 1, 2, and 3 classification levels
  • Ultra-low Leakage Rating: A damper device that leaks 6.93 CFM/ft^2 or less under a 12 inch static pressure differential. 
  • Bubble tight dampers: zero leakage dampers that are used in laboratory ventilation (desnt't concern us with this application)
For all intensive purposes the following statement is valid: as the leakage rating of a damper increases, the energy efficiency decreases. The less a damper seals from space-to-space, the greater the transfer of hot or cold energy.

The table below defines the 4 classification ratings for volume control dampers. For your clarification, Class 1A is the most stringent to obtain and Class 3 being the least:

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Source: AMCA 511-10 page 13

How To Get Low Leaking Dampers

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Damper manufacturers utilize a few different methods for their control products. They are made typically from either galvanized steel or extruded aluminum material. Galvanized is cheaper and used for non-critical environment, but can rust and deteriorate over time. Aluminum is stronger and has greater rust preventing characteristics.

The blade seals are located at the tips of the blades and seal when the damper is shut. The jamb seals are located between the internal frame edge and the sides of the blades. Blade seals are made typically of PVC and upgradeable options are usually a form of rubber or silicone. Standard jamb seals are made of compressible metals, such as stainless steel. Upgradeable options are also silicone or similar materials. 

Common problems seen with compression type seals are that over time they will rust or crack. In colder climates they can compress and, again, crack under damper sealing. These are important items to consider when looking at dampers because once the seals crack the dampers are no longer doing their job and maintenance workers have a hard time spotting damper failures since often times they are located inside the ductwork.

The material property benefits of rubber type blade and jamb seals are as follows:
they have a greater resistance to colder climates and don't compress as much as metal; leakage rates drastically improve with these seals (many times required to obtain ultra-low leak ratings); seal failures are less likely to occur.

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These seals are used versus typical metal seals to increase leakage performance and prevent cracking --- significantly increasing the life of the damper

Adding Insulation and Thermal Breaks

Low leak dampers are critical to minimize airflow penetration through the wall cavity, but adding thermal resistance and thermal breaks to these dampers can drastically improve the building's energy performance. Buffalo sees a wide range of temperatures throughout the four seasons. In the winter it can get below zero, while the summer months can reach temperatures in the ninety's. The severity of temperature difference in the winter between the building and outdoors is a big reason to consider insulated blades, frames, and thermal breaks to minimize infiltration through the wall penetration.

Thermally insulated blades and frames provide an improvement in insulation than that of standard galvanized or aluminum control dampers. The insulation rating, given by an R-value, is a measure of thermal resistance. The greater the R-value, the better the insulation. The damper chosen had an R-Value of 2.29. Much better than a value of 0.

Thermal breaks allow for complete isolation of the two environments from each other. Typical dampers are constructed of all aluminum or all galvanized material and are high conductors of thermal energy transfer because of the continuous metal material throughout the product. If it is divided, however, by a thermal break that is less conductive than the temperature transfer decreases. Thermal breaks are commonly used in windows, doors, air handling units, and yes... dampers.
Never seen a thermal break before? Don't worry, you're not alone...

Afterword

The dampers specified incorporates all of the above features. For areas in which the dampers are closed the majority of the time and where the building owner wants their building to perform at it's best, the TAMCO thermally insulated and thermally broken blade and frame control damper was the best option to satisfy and impress the end user. At a Class 1A leakage rating the dampers are best in class. All aluminum construction ensures a long lasting damper with strength and rigidity. Silicone blade and jamb seals prevent the event of cracking and allow for an ultra low leakage seal.

I have created a two-page PDF version of this case study that can be found here.
To read more about Tamco's capabilities, browse here.
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Installed in the wall louvers and the roof vents
 - Joel Erway, 01/15/12
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