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What's the best velocity for moving air through ducts?
Posted by Allison Bailes on June 26, 2019
The first thing to know about the velocity of air moving through ducts is that the slower you get the air moving, the better it is for air flow.  That was the main point of my last article.  In fact, the title asked the question, "Is Low Velocity Bad for Air Flow in Ducts?”  And the answer was that...
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What is the best velocity for air moving in ducts?
Posted by Allison Bailes on June 12, 2019
It's obvious that moving air too quickly through ducts can be a problem.  Faster air means more turbulence, more resistance, and more noise.  But I run into people who think that low velocity also can be a problem in ducts.  Just recently I heard someone talking about how low velocity causes "...
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What criteria should you use to determine when is the best time to change the filter in your HVAC system?
Posted by Allison Bailes on May 20, 2019
One of the topics I've hammered on for years is the inadequacy of using rules of thumb for sizing air conditioners.  The standard one ton of air conditioning capacity for each 400 to 600 square feet of conditioned floor area just doesn't work.  We know that a load calculation based on how a...
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A dirty air conditioner coil can create bad odors
Posted by Allison Bailes on May 3, 2019
I never read Robert Fulghum's book, All I Ever Needed to Know I Learned in Kindergarten, but I have a clear memory of learning about one thing in the book:  Most of the dust floating around our homes is actually made up of skin flakes.  Now, I don't know if that memory is accurate (maybe it wasn't...
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Using a high-MERV filter doesn't have to result in a large pressure drop
Posted by Allison Bailes on April 23, 2019
Last August I began a series of articles on filtration and indoor air quality.  You can find the list of them at the bottom of this article but let's do a quick review here:  We spend a lot of our time in buildings.  A lot of indoor pollutants are generated in the kitchen and not removed by the...
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A heat pump is an air conditioner with a reversing valve
Posted by Allison Bailes on March 29, 2019
So we've looked at a simple way to estimate the heat pump balance point.  If you also read the comments of that article, you should be aware that there's more to the actual balance point than what I wrote in the article.  Today, though, let's look at two factors that can affect the balance point....
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At the balance point, a heat pump can supply the same amount of heat as a house needs
Posted by Allison Bailes on March 26, 2019
As the outdoor temperature drops on a cold day, a home's heating load increases.  At the same time, decreasing temperature means less heat in the air for a heat pump to pump indoors.  And at one special temperature, the capacity of a heat pump equals the heating load in the house.  That temperature...
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The 2019 Home Performance Coalition national conference is in Chicago. Be there!
Posted by Allison Bailes on February 22, 2019
My first conference after I officially left academia and got into the world of home performance and building science was in 2004.  Since then I've been to a whole lot of conferences.  There are even more building science conferences I could have gone to.  But fifteen years down the road now, I have...
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A heat pump pumping heat in winter
Posted by Allison Bailes on February 19, 2019
Since more people are using heat pumps these days, even in cold climates, let's spell out the three different types of heat that conventional heat pumps provide.  Why not!  We've just recently covered the three main sources of home heating and then stepped back and looked another group of three...
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Low indoor relative humidity in winter is common
Posted by Allison Bailes on February 15, 2019
I'm going to go out on a limb and make what you may think is an outrageous statement:  Water is the most interesting substance in the world.  Some of you may immediately respond, "Oh, yeah!  What about beer?"  (Or wine or Sidecars, Negronis, or Sazeracs or whatever your drink of choice is.) ...
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