Building Science

Is NIST Serious About Net-Zero-Energy Homes?

Posted on June 19, 2013 by Allison A. Bailes III, PhD, GBA Advisor

The National Institute of Standards and Technology (NIST) still handles a lot of our basic numbers work, keeping lasers, hunks of metal, and atomic clocks that determine our standards of length, mass, and time. But it turns out they also have an interest in net-zero-energy (NZE) homes.

They’ve built and outfitted an amazing NZE research facility, and they also have convened meetings of experts to develop guidelines for NZE homes. But there’s something about their latest report I just don’t understand.

Taking a 20-Year-Old Florida House to Net Zero

Posted on June 12, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Steve Larson, a builder and home energy rater in Florida, sent me an e-mail with his energy bills for February through July of 2012. When you subtract out the monthly service charges, he paid only $5.35 for electricity during those six months. That's right — less than a dollar a month for electricty... and then $9.88 a month for the service charge.

A 3-Ton Air Conditioner Will Rarely Give You 3 Tons of Cooling

Posted on June 5, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Today I'm going to give you three reasons why your 3 ton air conditioner isn't really a 3 ton air conditioner. Of course, there are more than three reasons, starting with the fact that it's not 3 tons in weight. That unit refers to cooling capacity and harkens back to the days of ice.

Why Do We Measure Air Conditioner Capacity in Tons?

Posted on May 29, 2013 by Allison A. Bailes III, PhD, GBA Advisor

A few years ago, a 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 student in a class I taught told a funny story. He was an HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. contractor and said he was installing a new air conditioner for an elderly woman. As he was explaining things to her, he mentioned that they would be installing a 4-ton unit. "Oh, my," she said. "How are you going to get something so big into my back yard?"

Does a Composting Toilet Stink Up Your House?

Posted on May 22, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Ten years ago I was building a green home. It had passive solar features, was built out of structural insulated panels, sent all the greywater out to the back yard to water fruit trees, and was going to be super energy efficient. One feature above all others, though, captured people’s attention when I described the house to them — the composting toilet.

Does Your Air Barrier Work in Both Directions?

Posted on May 15, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Do you want a good air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. on your house? Of course you do. No one who knows anything at all about building science believes that old myth that a house needs to breathe. We want airtight houses, but then we want mechanical ventilation to bring in fresh air from outside (well, at least as fresh as you can get from your outside).

A PhD and an Architect Build a Net-Zero Home

Posted on May 8, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Amy Musser has a PhD in Architectural Engineering and, like me, used to be a college professor. Her husband, Matthew Vande, is an architect with an MS in Architectural Engineering. He is also a treehugger (see the black and white photo below). Together, they founded Vandemusser Design, a firm that provides green design, certification, and consulting.

All About Climate Zones

Posted on May 1, 2013 by Allison A. Bailes III, PhD, GBA Advisor

One of the fundamental principles of building science is that buildings must be suited to their climate. When they're not, problems can ensue. Maybe it's just that they're not as efficient as they should be. Maybe it's worse.

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!

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