Building Science

Does a Heat Pump Condenser Need to Go Outdoors?

Posted on April 24, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Occasionally I get asked if it's OK to put the condensing unit of an air conditioner or 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. in a garage or other room that's a buffer space. The thinking is that since the temperature may not be as hot in summer or as cold in winter, the system will operate more efficiently.

I saw recently that this same question came up in a column in Home Power magazine, so I thought this would be a good time to cover this issue (once and for all?) here.

ACCA vs. BPI: The Brouhaha Over Energy Audit Standards

Posted on April 17, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Probably the biggest news I heard at the 2013 RESNET conference this year was that the Air Conditioning Contractors of America (ACCA) and 12 other organizations had asked the American National Standards Institute (ANSI) to have the Building Performance Institute's (BPI) accreditation as a Standards Development Organization (SDO) revoked. Really!

Embarking on the Building Science Learning Curve

Posted on April 10, 2013 by Allison A. Bailes III, PhD, GBA Advisor

I just returned from Arizona, where I spoke at this year's conference of the Structural Insulated Panel Association. Since the conference was in Tucson, I also took the opportunity to visit with my friend David Butler of Optimal Building Systems.

Vented Crawl Spaces and the Psychrometric Chart Are Not Friends

Posted on April 3, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Really, the argument about whether you should vent a crawl space in a humid climate is over. Advanced Energy's research project from 2002 proved that closed crawl spaces outperform vented crawl spaces.

A quick look at the psychrometric chart below shows that the argument should never have existed in the first place. (Click the image to see an enlarged version.)

The Mad Hatter, Isaac Newton, and That Old Thermostat

Posted on March 27, 2013 by Allison A. Bailes III, PhD, GBA Advisor

I was a kid a long, long time ago. Seems like it was another century ... another millennium even. Wait a minute — it was another millennium!

That was back in the day when we used to ride bicycles without helmets, apply mercury to our wounds, move seat belts out of the way (if the car even had them), and put our tongue on steel poles in the middle of winter. Of course, in Texas and Louisiana we just ended up with a bad taste in our mouth from those steel poles and wondered why people made such a big deal about it.

The Tail-Wagging Labradors of RESNET

Posted on March 20, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Labradors? James Brown? What do either of those have to do with the RESNET conference?! Be patient, my friend. All will be revealed shortly. The 2013 conference sponsored by the Residential Energy Services Network (RESNET) in Orlando a few weeks ago was fantastic. It and Building Science Summer Camp are my two favorite events of the year, and this year RESNET was better than ever.

How to Install Flex Duct Properly

Posted on March 13, 2013 by Allison A. Bailes III, PhD, GBA Advisor

I've written a lot about duct problems (especially those in flex duct) because they're so abundant. A couple of years ago, I even wrote an article in the Energy Vanguard Blog about whether or not flex duct should be banned. My answer was no — but that we need better quality control.

The Science of Global Warming Is Older Than Quantum Mechanics

Posted on March 6, 2013 by Allison A. Bailes III, PhD, GBA Advisor

I'm new to global warming. I didn't hear about it until 1983. Even thirty years ago, the science behind the greenhouse effect and global warming was well known. French Physicist and mathematician Joseph Fourier is generally credited with being the first to hypothesize that the earth is warmed by its atmosphere and even that we humans can change the climate. That goes all the way back to 1827.

Should the Paper Facing of Batt Insulation Face the Inside or Outside?

Posted on February 27, 2013 by Allison A. Bailes III, PhD, GBA Advisor

If you install fiberglass batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. * with a kraft paper vapor retarder in a home, which way do you face the vapor retarder? To the inside of the home or the outside of the home? For many building science questions, the answer is, “It depends.” For this one, however, the answer is clear.

SPOILER ALERT: The answer is in the next paragraph — so if you'd rather wait and find out when you see the movie in the theater, don't read any further.

Air Leakage at Electrical Switches and Outlets

Posted on February 20, 2013 by Allison A. Bailes III, PhD, GBA Advisor

One thing that invariably surprises people when I walk them through a house during their first blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. is how much air leaks in through the electrical switches and receptacles. On a recent Friday, we went out to do the last home energy rating in our latest HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. rater class, and we got to see something even better. But first, let's talk about that air leakage. We have a number of surprises waiting.

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