Building Science

How Your Thermostat Can Grow Mold and Make You Uncomfortable

Posted on September 10, 2014 by Allison A. Bailes III, PhD, GBA Advisor

I've been experimenting with my family lately. Or is it, experimenting on my family? In either case, I've got the data to confirm something I wrote in a 2011 article.

But before I tell you what I did, first let me show you what happened. In the graph at right, you can see Exhibit A: a moisture mystery. What do you think happened to cause the humidity (blue data) in the air in our condo to rise like that?

How to Tell If Your Air Conditioner Is Oversized

Posted on September 3, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Back in 2009, I had a new air conditioner installed our condo. The previous one was an ancient 25 years old and barely limping along. It wasn't cooling much, and the summer electric bills had risen.

Is Oriented Strand Board as Impermeable as They Say?

Posted on August 27, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Oriented strand board (OSB) gets blamed for a lot of problems that are really the fault of the designers and builders. Part of the problem, of course, is the perrenial confusion between correlation and causality. OSB hit the market as we really started getting serious about insulation and air sealing.

The Passive House Conference in California Is Where It’s At!

Posted on August 20, 2014 by Allison A. Bailes III, PhD, GBA Advisor

The 9th annual North American Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Conference is less than a month away. You knew it's going to be in California, right?

It's unfortunate that the other Passivhaus group has chosen to use the same name that the Passive House Institute U.S. (PHIUS) has been using since 2006, but I've already discussed that confusion. (Full disclosure: I am on the board of directors of PHIUS.)

Using the Pen Test for Control Layers

Posted on August 13, 2014 by Allison A. Bailes III, PhD, GBA Advisor

I listened to the IAQ Radio podcast a few weeks ago when they interviewed Lew Harriman and Terry Brennan, who were discussing the new moisture control guide published by the EPA last year. Brennan is the lead author of the document, and it's a really great resource full of useful information about indoor air quality, fundamental building science principles, and how to control moisture.

The Achilles’ Heel of Zoned Duct Systems

Posted on August 6, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Last week I wrote about what happens when you try to save energy by closing air conditioning registers in unused rooms. In the end, I recommended not doing it because you won’t save money and you may create some big problems for yourself, like freezing up the coil and killing your compressor.

At the end of the article, I mentioned that zoned duct systems do close off registers, and that doing so can be OK with the right kind of equipment and design. But there’s one thing often done in zoned duct systems that’s rarely done well.

Is It OK to Close Air Conditioner Vents in Unused Rooms?

Posted on July 30, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Your air conditioner, heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump., or furnace probably uses a lot of energy. Heating and cooling makes up about half of the total energy use in a typical house. For air conditioners and heat pumps using electricity generated in fossil-fuel fired power plants, the amount you use at home may be only a third of the total.

How Duct Leakage Steals Twice

Posted on July 23, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Duct leakage is a big deal. It's one of the top three energy wasters in most homes (air leakage and cable TV set-top boxes being the other two). Researchers at Lawrence Berkeley National Lab found that duct systems leak on average about 10% of the supply air they move and 12% of the return air. (Download pdf and also see Dana Dorsett's comment below, #1.) In far more homes than you might suspect, the main culprit is a disconnected duct, as shown in the photo at right, but a typical duct system has a lot of other leaks, too.

Energy Efficiency Requires More Than an App on Your Smartphone

Posted on July 16, 2014 by Allison A. Bailes III, PhD, GBA Advisor

When it comes to air conditioning, there are a lot of bad products and bad ideas out there. Here are a few: You can buy a cover for your condenser that could kill your compressor.

Four Ways to Find the Size of Your Air Conditioner

Posted on July 9, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Do you know what size your air conditioner is? In the world of building science, you'll hear a lot of talk about why oversized air conditioners are a bad idea. Why? Briefly, they don't dehumidify as well, short-cycling wears them out quicker, and your home will probably be less comfortable if the air conditioner is too big. But to know if your AC is oversized, first you have to know what size it is.

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