Designing a forced-air system for proper air movement and efficiency is a challenge faced by multiple players in the HVAC industry. The first sector to square off with this challenge is the OEMs.

“We design our products to be the quietest, most efficient products they can be,” said Blake Edwards, senior product marketing manager, Controls and Indoor Air Quality, Lennox. “We also work with the direct dealer base that puts our products in the home.”

In their testing laboratories, manufacturers create efficient equipment under ideal conditions. It is up to the HVAC contractor to install and maintain the equipment as close to that level of efficiency for every different installation application attempted.

 “Efficiency is a byproduct of comfort,” said David Richardson, curriculum developer and trainer for the National Comfort Institute Inc. (NCI). “There are a lot of systems out there, though, that are rated efficient in the laboratory, but because they’re not installed correctly, or there are different variables, they aren’t yielding the efficiency promised.”

He pointed out that this issue can stem from contractors and technicians who consider the system to be just the primary unit as opposed to the combination of all the different components that work with it, i.e. ductwork, grilles, refrigerant drain lines, etc. According to Richardson, measuring a system based on its actual performance, as opposed to its capacity, can be a solution that provides maximum comfort and efficiency.

“For example, a 3-ton air conditioner could only be yielding 1.5 tons of cooling in the occupied part of the house,” he said. “The rest is being lost in a crawl space or an attic; but when we measure and then do a comparison, that’s where comfort and efficiency are found.

“If you don’t measure, you’re just guessing,” he added.



Taking the lab-rated equipment and installing it in less-than-ideal applications while trying to achieve optimal comfort and efficiency can be overwhelming for contractors. In fact, Richardson compared the beginning of the performance-based contracting journey to the idea of eating an elephant.

“You can’t try to do it all at once, and where to start is one of the biggest barriers to most technicians,” he said. “I also like to use the analogy of a lion tamer with a four-legged stool. The lion doesn’t move, not because it is intimidated by the stool, but because in trying to focus on all four legs at a time, it can’t focus on any single one and becomes paralyzed.”

According to Richardson, the four legs of performance-based system installation are static pressure, airflow, temperature, and Btu. He suggests that technicians sequentially implement best practices in regard to these topics, starting with static pressure. Considered the cornerstone of system performance by NCI, static pressure can be measured by a manometer. Richardson also suggests contractors invest in an air balancing hood to measure airflow in and out of the system, an anemometer for hard-to-access registers and grilles, and a thermometer to measure the temperature coming out of the ductwork.

“The goal is to see what is actually being delivered to the rooms in a home and make adjustments from there,” he said. “If you have these tools and know how to use them properly, you are on your way.”

However, Richardson cautioned those who have these tools and do not know how to use them.

“You can draw some very false conclusions or end up coming up with some really bad assumptions, and that’s just as bad as not measuring” he said. “A lot of times, our industry is looking for a silver bullet. Technicians tend to want to gravitate toward one measurement instead of keeping in mind that it is really just a piece of the puzzle. All of these pieces have to work together to paint a complete picture of performance.”



Installation and system issues affect comfort and efficiency, but so does IAQ and regional outdoor conditions.

“More and more, homes are needing different types of airflow, and the equipment itself isn’t likely going to meet 100 percent of the desired needs,” said Edwards. “There are a lot of accessories and different solutions that can come into play, and ventilation is one of them.”

He explained that the tightness of newer buildings is pushing an increased demand for fresher, cleaner air. This, combined with the high-efficiency equipment, is producing more of what homeowners want.

“Best practices in regard to this topic are job-specific and require the technician truly knowing and understanding the needs of the home,” said Edwards. “Some of it just plain comes down to geography. For example, if you’re in the South or Southeast, there are certain ventilation requirements as compared to being in the North and Northeast of the nation.”



The commercial sector of the industry also faces off with comfort and efficiency, and there are many different technologies that improve these measurements in commercial applications. According to Tom Kolsun, strategic accounts manager, Aircuity, some of the more common items are demand control ventilation systems that operate on multiple parameters, reverse bipolar ionization for air cleaning, systems with feedback loops that report ventilation performance to the occupants, and dedicated outdoor air systems (DOAS) when used to decouple the ventilation load from the heating/cooling.

“We highly recommend a design that delivers measured and verified ventilation that follows the criteria prescribed by the International Well Building Institute, or some similar organization,” said Kolsun.

In looking closer at the commercial use of DOAS in regard to air movement efficiency and design, the design is critical because the fan runs 100 percent of the time during occupied mode.

“For a building owner, a poor design of the supply fan can mean high operating costs,” said Dennis Mueller, building HVAC systems engineering manager, Modine Mfg. Co. “An important best practice during design is the decoupling of the ventilation load from terminal equipment through the use of a DOAS unit. This ensures effective and efficient dehumidification and conditioning of the building.”

He also suggests that those in the commercial sector utilize a building management system to ensure that the DOAS and terminal units aren’t fighting against each other.

Publication date: 5/13/2019

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