Musings of an Energy Nerd

UPDATED 12/20/2012

Most green builders include some type of mechanical ventilation system in every home they build. That’s good. Since green buildings usually have very low levels of air leakage, mechanical ventilation is usually essential.

Unfortunately, several research studies have shown that a high number of mechanical ventilation systems are poorly designed or installed.

For thousands of years, the chimney has been closely associated with our concept of home. Upon spying smoke curling from a distant chimney, the weary traveler ends his journey with lightened steps.

When I built my house in Vermont, as a much younger man than I am today, I designed a house with two chimneys. The house has a cellar, first floor, second floor, and attic; because I wanted the chimneys to rise five feet above the ridge, they had to be 40 feet tall.

More and more designers of high-performance homes are buzzing about a superinsulation standard developed in Germany, the PassivhausA 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. standard. The standard has been promoted for over a decade by the Passivhaus Institut, a private research and consulting center in Darmstadt, Germany.

UPDATED March 28, 2013

The average new home is so poorly built, it’s enough to make an environmentalist weep.

Windows are routinely installed without any consideration of orientation. As a result, south windows fail to take full advantage of free solar heat during the winter, while west windows worsen summer overheating. Windows are often installed in unshaded walls, even in hot climates. In the absence of legal requirements for high-performance windows, builders regularly choose windows with appalling U-factors and solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. coefficients (SHGCs).

Question: What do the following homes have in common?

• An 11,000-square-foot home in St. Charles, Ill., touted as “one of the greenest homes in the Chicago area.”
• A 5,100-square-foot home at Live Oaks Estates in San Rafael, Calif., marketed as green by an Eco-Broker.
• A 6,100-square-foot home in West Vancouver, British Columbia, aiming for LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. Gold certification.
• A 3,000-square-foot home on Block Island, R.I., aiming for LEED for Homes Silver certification.

Builders in northern states and Canada often specify exterior wall foam for new construction as well as for residing jobs on existing houses. Installing rigid foam on exterior walls reduces thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. through studs and (as long as the foam is thick enough) greatly reduces the chances of condensation in wall cavities. Current trends favor thicker and thicker foam; many cold-climate builders now routinely install 4 or 6 inches of EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest., XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation., or polyisoPolyisocyanurate foam is usually sold with aluminum foil facings. With an R-value of 6 to 6.5 per inch, it is the best insulator and most expensive of the three types of rigid foam. Foil-faced polyisocyanurate is almost impermeable to water vapor; a 1-in.-thick foil-faced board has a permeance of 0.05 perm. While polyisocyanurate was formerly manufactured using HCFCs as blowing agents, U.S. manufacturers have now switched to pentane. Pentane does not damage the earth’s ozone layer, although it may contribute to smog. on exterior walls.

Over a thousand home performance contractors, weatherization experts, HERS raters, and energy nerds are gathered in Kansas City, Missouri, this week to attend the ACI Home Performance conference (formerly known as the Affordable Comfort conference).

At one well-attended workshop, energy consultant Michael Blasnik and Shaun Hassel of Advanced Energy Corporation shared a roundup of data on the performance of Energy Star homes — data which are unlikely to be happily received at the U.S. Environmental Protection Agency (EPA). Among the findings presented by Blasnik and Hassel:

In the U.S. and Canada, many residential builders use the word “sustainable” as a synonym for “green.” We hear about sustainable development, sustainable homes, and sustainable building products.

Now that the word “sustainable” has become ubiquitous — even at the GreenBuildingAdvisor Web site, where a new $736,000 home on the coast of Maine is described as a “sustainable spec house” — it’s time to take a step back and consider the word’s history.

In 1977, a group of Canadian researchers built a demonstration house in Regina. Called the Saskatchewan Conservation House, the nearly airtight building had triple-glazed windows, R-40 wall insulation, R-60 roof insulation, and one of the world’s first heat-recovery ventilators.

The home’s design and engineering team included Robert Besant, Oliver Drerup, Rob Dumont, David Eyre, and Harold Orr. That same year, Gene Leger, a Massachusetts builder, finished a similar superinsulated house in Pepperell, Mass.

Designers of energy-efficient homes — especially homes aiming for net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. use — must inevitably grapple with the question of simplicity versus complexity.

Residential designers can choose from an array of sophisticated appliances that improve comfort and help homeowners reduce energy use. Examples include heat-recovery ventilators (HRVs), condensing boilers, ground-source heat pumps, solar hot water systems, on-demand water heaters, heat-pump water heaters, photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. modules, and co-generation systems.