Today when many projects are lining up at the “green” window, it is hard to know what is really meant by “green.”

The intent of the green initiative is to encourage the use of energy efficient products and practices that also have a positive impact on the environment. This concept has expanded to include all energy used to create products and deliver them to the jobsite.

Energy efficiency has a direct link with the environment because for every kilowatt hour of electricity that buildings consume, there is a measurable amount of pollution emitted into the atmosphere.

Every aspect of a construction project is under closer scrutiny today, especially the HVAC system, which is often the single largest energy consuming component in a building. The HVAC industry, ASHRAE, and national and local codes are pushing energy improvements—and there are real opportunities for those who endeavour to find new ways to capitalize on them.

Legislation in the past several years has resulted in the development of higher-efficiency HVAC equipment and higher SEER ratings, but poor installations cause equipment to work harder and run longer—often reducing the very efficiency we are trying to attain.

Proper duct design is critical to HVAC performance, yet far too many projects do not maximize the positive effect created by good duct design practices. While a bad duct system may deliver air to the conditioned space, it increases the static pressure losses, which lowers the system efficiency and cheats the owner out of the performance and value that they paid for.

When it comes to proper ductwork design and installations there are a wide range of factors that can impact the system. Here are four common mistakes that can affect HVAC system performance along with suggestions for good practice:

Selecting duct materials: Flexible duct is the least expensive duct material to purchase and install, but is also by far the least efficient. Even when installed correctly, flexible duct has twice the static pressure loss of round metal duct. With installation of proper wye fittings and other components in accordance with SMACNA duct construction standards, the most efficient duct system can be installed.

Using proper load calculations instead of load averages: If installers use load averages such as CFM/sq. ft. instead of accurate load calculation, they may oversize and / or undersize the equipment and / or ductwork. In addition, load averaging does not account for various climate zones. Accurate calculations by a qualified industry person should always be done to guarantee a properly designed HVAC system.

Inadequately sizing ducts: Ducts should be sized in accordance with ASHRAE guidelines and other recognized authorities. Airflow and pressure loss measurements should be made by the testing and balancing contractor and in turn be reviewed by the engineer to see that all the intended efficient design criteria are met. If not, have it redone properly.

Failing to design and install to maximize system performance: The most efficient ducts are straight, smooth, and short. Sections of flexible duct that are used should be stretched tight. Failure to do this will compress the core and dramatically increase static pressure losses. The design focus should always be on performance. Proper sizing and installation of a duct system is essential to maximize system performance. This is what the client is expecting.

Funding and programs from organizations such as NRCan and Live Smart are available to help develop and promote energyefficient HVAC practices. HVAC designers and installers who utilize good practices will come up with systems that use the least amount of energy/CFM thus enabling the greenest possible solution for a particular HVAC system. NG

Reference for chart: Source: National Energy Savings Potential From Addressing HVAC Installation Problems(1999) by Chris Neme, Vermont Energy Corporation; John Proctor, Proctor Engineering Group: and Steve Nadel, American Council for an Energy Efficient Economy.