Building Science

The Hidden Flaw in Some High-Efficiency Furnaces

Posted on April 19, 2017 by Allison A. Bailes III, PhD

You can tell how energy-efficient a furnace is by its official efficiency rating, the Annual Fuel Utilization Efficiency(AFUE) Widely-used measure of the fuel efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation. AFUE is always lower than combustion efficiency. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment. (AFUEAnnual Fuel Utilization Efficiency. Widely-used measure of the fuel efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation. AFUE is always lower than combustion efficiency. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment. ). It's a measure of how much of the heat originally in the fuel that's being burned is available for delivery to the home. The more heat that gets lost up the flue or through the cabinet, the lower the AFUE.

But that rating doesn't capture all the ways a furnace can lose efficiency. Some, like how well the heat gets distributed to the house, aren't related to the furnace itself. But there's one big one that is related to the furnace.

Five Ways to Do Balanced Ventilation

Posted on April 12, 2017 by Allison A. Bailes III, PhD

Ventilation is a great thing. Bringing outdoor air into the home and exhausting stale indoor air improves indoor air quality. Well, most of the time, anyway. Sometimes the outdoor air quality is worse than indoor air. Sometimes you bring in too much humidity and start growing mold. And sometimes you bring in the wrong outdoor air. But the issue of outdoor air vs. indoor air is a topic for another article.

The Home Performance Forum Has Launched!

Posted on March 29, 2017 by Allison A. Bailes III, PhD

The Internet age has made it easy to find information. Occasionally you can find some that's even true. That's where it becomes helpful to have someone more knowledgeable than yourself to be able to ask for advice and input on stuff you read online, get feedback on ideas you'd like to try on a project, or discover what cool things other home energy pros are doing.

Pete’s Puzzle: Fanciful Fuel

Posted on March 16, 2017 by Peter Yost

A new client called me, saying that his insulation contractor urged him to contact me about some moisture problems in the home before they actually embarked on a major energy upgrade. (That was gratifying.) The home was actually moved many years ago off of a failing rubble foundation to a new concrete masonry unit (CMUConcrete masonry unit. Precast concrete block used to build walls. CMUs have hollow cores that can be filled with concrete onsite for additional reinforcement. The use of stronger, more lightweight types of concrete such as autoclaved aerated concrete (AAC) is becoming increasingly popular in CMU manufacture. ) foundation on a different site.

Image #2 (bottom of page) shows the home from the front. Image #3 shows the bare CMU on the above-grade portion of CMU foundation.

But it is Image #1 (right) that is the real puzzle. Here are the puzzle pieces:

Does a Bigger Volume Mean More Heating and Cooling Load?

Posted on March 15, 2017 by Allison A. Bailes III, PhD

What happens to the heating and cooling loads when you encapsulate an attic? With the insulation and 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. at the ceiling below the attic, you're excluding the attic space. That volume of air up there isn't involved in the conditioning of the home. But when you move the enclosure to the roofline (usually by installing spray foam insulation beneath the roof deck), now the attic's volume is included in the conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .

Occasionally I hear people say the loads will be higher because of the extra volume. Does having more air inside really increase the loads?

Manual J Doesn’t Tell You Equipment Capacity

Posted on March 8, 2017 by Allison A. Bailes III, PhD

Here's a little conundrum for you. To get the right amount of heating and cooling to each room in your home, you need a load calculation. Rules of thumb don't work. But if you do a load calculation, the result isn't the size of 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., furnace, or boiler you need. It's only the first step to sizing your system.

Do you know why? Let's take a look.

Building Enclosure Commissioning

Posted on February 23, 2017 by Peter Yost

I have been advising architects and builders on high-performance design, materials, and construction — particularly for residential buildings — for many years. But to do this work on commercial buildings, a building science training and credentialing program seemed really important (yet elusive).

This past November I bit the bullet and spent three days in class, a half day in exams, and several thousand dollars, and fulfilled the requirements for these two certifications:

  • Building Enclosure CommissioningProcess of testing a home after a construction or renovation project to ensure that all of the home's systems are operating correctly and at maximum efficiency. Process Provider (BECxP)

This Radiative Cooling Material Could Supplant Traditional Air Conditioners

Posted on February 22, 2017 by Allison A. Bailes III, PhD

When it's hot out, we want cold. At night, we like to be able to turn on the lights. During the daytime, it can be hard to find the darkness.

All these things — hot and cold, day and night, light and dark — can seem like opposites. Chinese philosophy suggests, however, that these opposing forces, known collectively as the yin and the yang, aren't separate. And science has proved it. Let me tell you about the latest yin and yang science and how it could revolutionize air conditioning.

Buried Ducts Allowed in 2018 Energy Code

Posted on February 15, 2017 by Allison A. Bailes III, PhD

Water vapor from the air condenses on air conditioning ducts in humid climates. It's as normal as poorly insulated bonus rooms making occupants uncomfortable or cigarettes causing lung cancer. Condensation on ducts is most common in crawl spaces and basements, where the air is more likely to have a higher dew point.

Should Balanced Ventilation Be Required?

Posted on February 8, 2017 by Allison A. Bailes III, PhD

"You know where this is going, right? Codes will eventually require balanced ventilationMechanical ventilation system in which separate, balanced fans exhaust stale indoor air and bring in fresh outdoor air in equal amounts; often includes heat recovery or heat and moisture recovery (see heat-recovery ventilator and energy-recovery ventilator). ." I've heard people say this more than once in the past year or so. As someone who has been attending the semiannual meeting of the ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. committee, I've been skeptical. Then I read the new Aspen energy code and saw the first evidence that this really could happen.

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