Air-to-air system problems can be traced to poor or improper air distribution
Why is understanding the air side so important?
Several years ago, Supply House Times changed the name of my monthly column to “The Air Side,” to differentiate it from Dan Holohan’s fine series that deals mostly with hydronic systems.
It’s not that I am unfamiliar with hydronics. As a former service/training manager for a large Carrier products wholesaler in the Mid-South, I dealt with many water-side problems on large equipment. However, it is a matter of location. Where Dan lives and works (the Northeast), there are a lot of boilers, radiators and steam systems. But in most of the places where I’ve worked and lived, the companies are nonunion and there are a lot of air-side components, even when that isn’t the best type of application for the job. Also understand that my areas are primarily in climates where cooling is important.
The trouble is air can’t be seen, so a lot of people in our business expect it to do ridiculous things. I’ve seen people trying to get enough air return for a five-ton system between the 16-in. centers of 2-by-4 studs in walls and other systems run with flex duct that looked like a plate of spaghetti for some giant. I’ve also seen vertical air handlers located in attics that didn’t have enough clearance at the top to allow for the use of a plenum, so the ductwork was connected in holes cut into the sides of the evaporator housing — and people expected this to work. After all, it’s only air! So yes, I think this is the most misunderstood part of our business to those who actually are doing the installing and servicing.
Why is understanding the air side so important? Many chronic problems with air-to-air systems can be traced to poor or improper air distribution. Either there’s not enough air (I’ve also seen problems with too much air), it’s poorly distributed throughout the facility or the air volume across the evaporator coil isn’t even, which results in low cooling output.
Am I saying air problems are one of the primary causes for equipment not meeting the efficiency ratings and for insufficient cooling? YES! And this is the weakest area for nonunion HVAC training.
One of the saddest things I see in residential and light-commercial applications is ductwork sized too small, and there are no balance dampers to ensure proper distribution throughout the facility. No, the dampers on grill faces are not designed to take their place since this interrupts the direction of flow and it creates greater noise. And besides, I haven’t known many companies that bother to balance the airflow on non-engineered jobs, so achieving comfort always is a problem in some areas and it costs more to operate the systems.
But the most grievous of air-side problems I see today is the use of flex duct throughout entire systems. What many don’t understand is flex duct was never created to replace fiberglass or sheet-metal ducts. It was made for the short runs between the solid mains and the nearby diffusers.
Air (like water) should be run in lines as straight as possible to reduce friction. There is no way to accurately calculate the losses in lines that are run like spaghetti.
Yes, to get the proper air to each area, the losses have to be calculated and the lines must be properly sized to deal with those losses.
In this industry, there is no substitute for proper training. Getting up to speed on the intricacies of the air side will only benefit your business and the customers you serve.
This article was originally titled “Airing it out” in the September 2016 print edition of Supply House Times.