Improper air-flow design will create havoc
From the title of this article, you might assume this is something religion- or metaphysical-related.
But what I’m talking about is something that is all around us – air! Because it’s something that can’t be seen, many people don’t think that you have to worry much about its flow in heating/cooling systems — even in our very advanced scientific society.
For example, look at your own bedroom. Unless you have a return air duct there (most houses don’t anymore), how does the air get back to the HVAC system? Oh yes, the 600 cubic feet per minute or so slips through the tiny crack between the door and the carpet when the door is closed, right?
No, it probably just shuts off most of the airflow and it gets too stuffy in your bedroom whenever the door is closed.
You see? You can’t see it, so you don’t have to worry about it!
This is one of the sad truisms about our business. In an effort to cut installation costs, the once-common practice of installing returns in every room has largely been abandoned in even multimillion-dollar homes! And this is done at the expense of comfort.
Back when this poor practice was coming into vogue, many articles were written about how much bedroom doors had to be undercut to provide enough air return, which conscientious contractors followed to the letter. That is until homeowners complained about the size of the gap. And then came wall-to-wall carpeting to make matters worse.
I’d hate to tell you about all the bad jobs I’ve seen where the air returns and even the discharge ducts and vents were horribly undersized. I’ve also looked at many jobs where furnaces were sooted up, creating carbon monoxide because someone had stopped up the combustion-air intakes.
Let me ask this: How many of the air vents have you closed in your own home or how much air does that high-efficiency air filter you installed let through? But you don’t really have to worry about it because you can’t see it. It’s just air!
Experts in air design and research use smoke pellets to make air become visible. If you could do this in your own home it would worry you. First, you’d see how much conditioned air is being blown outdoors and wasted in attics because of cracks in ducts and over- and under-pressurized rooms.
In many commercial buildings, the situation is even worse. For example, the use of many vent fans often creates a negative pressure in the structure, which makes it hard to open exterior doors and hinders the work of those same bathroom and cooking fans, thus creating air-quality problems.
If I had more space I could go on for pages describing all the common airflow problems I’ve seen related to wrong duct designs and the wrong numbers used to calculate them. But then few would read it because I’m just talking about the unseen.
Yet, with all that is being said about achieving higher energy efficiencies in our very advanced technical society, the biggest problem with achieving it can’t be reached by designing better compressors or setting higher equipment standards.
Instead, we must pay far more attention to airflow design.