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Aprilaire high-MERV filter with carbon
Posted by Allison Bailes on November 9, 2018
What is a hair's breadth?  A strand of the finest human hair is about 20 micrometers (also called microns) in diameter.  Take a piece and slice it in half.  Then take one of those halves and slice it in half again...and then one more time.  Now you've got a sliver of hair that's 2.5 microns wide. ...
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What happens to the air flow in ducts when the size changes?
Posted by Allison Bailes on October 29, 2018
As we continue our study of indoor air quality and filtration, we now come back to duct design.  Today's lesson is on an interesting bit of physics that applies to anything that flows.  It could be heat or particles or electromagnetic energy.  In our case, it's air, a fluid, and the physics we're...
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Filter bypass because of incorrectly installed filter
Posted by Allison Bailes on October 24, 2018
Indoor air quality (IAQ) researchers have established that little bitty invisible pieces of stuff that float around in the air are bad for human health.  Of course, being scientists, they don't call it little bitty invisible pieces of stuff.  They call it particulate matter (PM) or particulates. ...
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Friction rate is the wronge name
Posted by Allison Bailes on October 12, 2018
Last year I wrote some articles on duct design and one of the topics I covered was this thing called friction rate.  At the end of that article, I discussed "How to think about friction rate."  It confuses a lot of people because it's the wrong name.  First I'll tell you why and then I'll tell you...
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HVAC School logo
Posted by Allison Bailes on August 24, 2018
I love to share good resources and here's one you need to know about if you're interested in the nitty gritty of HVAC systems.  I'm talking about HVAC School, with their various channels like their daily Tech Tips email, YouTube videos, quizzes, and a podcast.  It's all free. Bryan Orr (shown below...
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Zone dampers in a duct system
Posted by Allison Bailes on August 2, 2018
Last year I wrote five articles in a series on duct design and ever since, I keep getting requests to continue it.  Well, those of you looking for more in this area, you're getting your wish.  I've listed and linked the others in the series below so you can go back and read them first if you'd like...
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Good HVAC design is 99% invisible.  (Photo of living room by Ceylon Tea Trails from flickr.com, used under a Creative Commons license.)
Posted by Allison Bailes on July 3, 2018
Sometimes people are bothered by how things look.  They don't want a return grille showing in that location or they'd rather have the supply registers low on the wall or they just can't stomach the thought of a wall-mounted ductless mini-split anywhere.  We all have our preferences about how things...
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Staying cool with air conditioning
Posted by Allison Bailes on June 11, 2018
It's getting hot out there. Here in the Southeast, we love our air conditioning.  In fact, without air conditioning, far fewer people would live in places like Houston, Hattiesburg, and Sopchoppy.  And that's true for the hot, dry places, too, like Phoenix, El Paso, and Boron. So if we're going to...
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Oversized air conditioner
Posted by Allison Bailes on May 8, 2018
Many people seem to think HVAC design means you get a load calculation (Manual J in the ACCA protocols) so you know what size system to put in. Hey, that's a great start. It's way better than just using a rule of thumb or Manual E (for eyeball). You don't really want to end up with a ginormous...
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air conditioner heat pump furnace supply vent register
Posted by Allison Bailes on March 28, 2018
When you embark on the project of educating yourself about building science, one of the first things you encounter is the concept of heating and cooling loads. Every building has them. (Yes, even Passive House projects.) That's why we do heating and cooling load calculations. We enter all the...
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