Musings of an Energy Nerd

Owners of older homes often contact GBAGreenBuildingAdvisor.com and ask, “What can I do to make my home more energy-efficient?” My standard answer goes something like this: “The first step is to hire a certified rater to perform an energy auditEnergy audit that also includes inspections and tests to assess moisture flow, combustion safety, thermal comfort, indoor air quality, and durability. of your home. The audit report will include a tailor-made list of retrofit measures to address your home’s specific problems.”

For years, the English-language website of the Passivhaus Institut in Germany provided this definition: “A 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. is a building in which a comfortable interior climate can be maintained without active heating and cooling systems. The house heats and cools itself, hence ‘passive.’”

What’s the deal with thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. ? Since manufacturers of materials that incorporate concrete often exaggerate the benefits of thermal mass, it’s easy to get cynical and conclude that the buzz around thermal mass is all hype. But in many climates, it’s actually useful to have a lot of thermal mass inside your house. Just keep in mind that thermal mass may not be as beneficial as its boosters pretend.

Why are the smallest available American furnaces rated at about 40,000 Btuh? Back in the 1960s, a house in a cold climate may have needed such a powerful furnace — or even one rated at 60,000 or 80,000 Btuh. But these days, many new homes have design heating loads that are much smaller — as low as 10,000 to 20,000 Btuh. Over the past 30 years, building envelopes have become tighter and better insulated, but U.S. furnace manufacturers haven’t kept up with the times. For mysterious reasons, they don’t offer furnaces that are small enough for today’s energy-conscious builders.

Green building websites can be confusing. One site might tell you that a green home should include spray foam insulation, a tankless water heater, and a geothermal heating system. After you’ve absorbed this advice, you visit another website, where you learn that spray foam is a dangerous petrochemical, tankless water heaters are overpriced gadgets, and “geothermal” systems aren’t really geothermal.

There are lots of ways to insulate a low-slope roof, and most of them are wrong. In older buildings, the usual method is to install fiberglass batts or cellulose on top of the leaky ceiling, with a gap of a few inches (or sometimes a few feet) between the top of the insulation and the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . In some cases, but not all, there is an attempt to vent the air space above the insulation to the exterior.

My grandfather, William L. Holladay, was a refrigeration and cooling engineer. Decades ago, he wrote a pioneering, speculative article on ground-source heat pumps, “The Heat Pump: What it does, and what it may do someday.” The article appeared in the October 1948 issue of Engineering and Science Monthly. (For a basic explanation of how a heat pump works, and the difference between an air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps. and a ground-source heat pump, see Heat Pumps.)

Stuffy homes are unhealthy homes, while homes with plenty of fresh air are healthy. That’s been a commonly held belief for at least 200 years. In the mid-19th century, the connection between ventilation and human health was championed by sanitarians, a group of health experts who blamed the spread of bubonic plague and cholera on “miasma.”

There are lots of reasons to attend conferences. At a good conference, we get a chance to network with colleagues, to learn about recent research, to see new products, and to talk with manufacturers' reps. I've had the good fortune, over the last six weeks, to attend three conferences focusing on green building and residential energy:

Twenty years ago, very few residential builders knew what a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. was. These days, however, it’s no longer unusual to see siding being installed on vertical furring strips or a plastic drainage mat. As rainscreens become more common, mainstream builders are beginning to ask, “What’s a rainscreen? How do I know if I need one?”

This article will pull together information to answer the most common questions about rainscreen gaps between siding and sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. .