Musings of an Energy Nerd

Rethinking Durability

Posted on October 23, 2015 by user-756436

Does durability matter? Most green building advocates seem to think that green builders should always aim to build durable structures. My own opinion differs; in fact, as I explained in a 2009 article on the topic, it’s hard to see any correlation between durability and “greenness.”

I recently had an opportunity to reconsider the advantages and disadvantages of durability when my wife and I visited the Pont du Gard in Languedoc-Roussillon, France.

Ductless Minisplits May Not Be As Efficient As We Thought

Posted on October 16, 2015 by user-756436

A recent monitoring study of ductless minisplits installed in seven New England homes found that these heating appliances had lower airflow rates and lower coefficients of performance (COPs) than expected. The average COP of these air-source heat pumps ranged from 1.1 at the house with the least-efficient minisplit to 2.3 at the house with the most-efficient minisplit.

The results of the study raise at least as many questions as they answer. Perhaps the most useful outcome of the study is that it sets up a framework for recommendations that could enhance minisplit efficiency.

GBA Prime Sneak Peek: Reassessing Passive Solar Design Principles

Posted on October 9, 2015 by user-756436 Prime subscribers have access to many articles that aren't accessible to non-subscribers, including Martin Holladay's weekly blog series, “Musings of an Energy Nerd.” To whet the appetite of non-subscribers, we occasionally offer non-subscribers access to a “GBA Prime Sneak Peek” article like this one.

Reassessing Passive Solar Design Principles

Posted on October 9, 2015 by user-756436

Everybody loves passive solar design. Back in the 1970s, “passive solar” was the essential first step for cold-climate builders. It was considered an approach with obvious advantages over complicated “active solar” schemes that required pumps, fans, and electronic controls.

Naming Building Parts is Tricky

Posted on October 2, 2015 by user-756436

This blog is directed to homeowners. If you are a builder or an architect, you should probably click on a different article.

Homeowners who send questions to GBA sometimes don't know what to call the parts of their building. (If it's a diffuserIn a forced-air heating/cooling system, the diffuser is a register or grille attached to ducting through which heated or air conditioned air is delivered to the living space. In a tubular skylight or an electric light fixture, the diffuser is a cover plate through which scattered light is delivered., grille, register, or duct termination, there's a fair chance that someone will decide to just call it a "vent.") I've rounded up some of the most confusing terms used by builders and architects and clarified their definitions.

Since a drawing can be a handy way to clarify a definition, I made some quick sketches to illustrate my points.

Air Leakage Through Spray Polyurethane Foam

Posted on September 25, 2015 by user-756436

Many builders use spray polyurethane foam as an 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., raising the question: How thick does the spray foam layer have to be to stop air flow? There's a follow-up question, of course: Is the answer different for open-cell spray foam than for closed-cell spray foam?

As with most building science questions, there is a short answer and a long answer. The short answer is that closed-cell spray foam needs to be at least 1 or 1.5 inch thick to act as an air barrier, while open-cell spray foam needs to be between 3.0 and 5.5 inches thick to act as an air barrier.

Quality Issues With Brick Buildings

Posted on September 18, 2015 by user-756436

The design of brick buildings and the quality of brick construction have declined dramatically in the last 100 years. While this statement is debatable, I'll try to defend it with evidence. If my evidence is compelling, it raises questions about why certain technologies advance in sophistication while other technologies decline.

Before I return to the topic of brick buildings, I'd like to take a detour to look at an example of technological evolution.

Flash-and-Batt Insulation

Posted on September 11, 2015 by user-756436

Closed-cell spray polyurethane foam insulation has several desirable characteristics. It’s an excellent 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., an excellent vapor retarder, and it has a high insulating value per inch (about R-6). Unfortunately, it’s also expensive.

Cold-Weather Performance of Polyisocyanurate

Posted on September 4, 2015 by user-756436

The ability of insulation products to resist the flow of heat changes with temperature. Most insulation products — including fiberglass batts, extruded polystyrene (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.), and expanded polystyrene (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.) — perform better at low temperatures than high temperatures. At lower temperatures, there is less conductionMovement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow., less convection, and less radiation — so insulation materials usually work better than they do at warmer temperatures.

Hygrothermal Software Sometimes Yields False Results

Posted on August 28, 2015 by user-756436

Building designers and researchers have begun to realize that computer modeling programs, including WUFI, sometimes falsely predict that certain common wall assemblies — wall assemblies that have been used successfully for years — should be failing. (WUFI is a so-called “hygrothermal” modeling program — that is, a program that calculates heat and moisture flows through building assemblies. For more information on WUFI, see “WUFI IS Driving Me Crazy.”)

Yet experienced builders know that these wall assemblies aren’t failing. So what’s going on?

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