Musings of an Energy Nerd

In Search of a DIY Guide to Rooftop PV

Posted on January 27, 2017 by Martin Holladay

Most new grid-tied 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. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) systems are installed by solar contractors. Here’s what usually happens: the homeowners call up a few local solar companies; representatives come to the house to make a site assessment; the homeowners choose the contractor whose quote sounds reasonable and sign a contract for the work. The homeowners don’t even have to put up a ladder; all they have to do is sign a check.

Slow Progress on New Blowing Agents for Polyiso

Posted on January 20, 2017 by Martin Holladay

R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. tests by the National Roofing Contractors Association and the Building Science Corporation have revealed that the thermal performance of polyisocyanurate is greatly reduced at cold temperatures. While the R-value of polyiso at a mean temperature of 75°F might be about R-5.7 per inch, the effective R-value of the polyiso drops to about R-4.8 per inch at a mean temperature of 25°F.

Building Science Information for Builders

Posted on January 13, 2017 by Martin Holladay

Jacob Deva Racusin, a Vermont builder and educator, has just written a book called Essential Building Science. The book aims to provide builders — especially so-called “natural builders” — with a basic understanding of the ways that heat and moisture flows affect residential buildings. (The book is available from New Society Publishers for $34.95.)

Windwashing in Exterior Mineral Wool

Posted on January 6, 2017 by Martin Holladay

Fibrous insulation materials like mineral wool do not stop air flow. Unlike rigid foam (which is a pretty 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., as long as the seams between panels are taped), mineral wool can only slow down air flow, not stop it.

So what happens when builders install mineral wool insulation on the exterior side of wall 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. ? Is the thermal performance of the mineral wool degraded by wind?

R-Value Scammers Sued By the FTC

Posted on December 30, 2016 by Martin Holladay

Here at GBAGreenBuildingAdvisor.com, we received our first inquiry concerning Insultex housewrap on July 31, 2015, when Marcus Sheffer questioned the validity of Insultex’s R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. claims.

Insultex is a plastic housewrap distributed by Innovative Designs of Pittsburgh, Pennsylvania. The company offers two versions of its housewrap, at a price that is from two to nine times higher than the price of ordinary housewrap. One version is 1 mm (0.0384 inch) thick; according to Innovative Designs, this product has an R-rating of R-3. That’s R-78 per inch.

Songs for Christmas 2016

Posted on December 23, 2016 by Martin Holladay

Donald Trump’s Song

Oh, the weather outside is frightful,
But the new AC is delightful,
I’ll tell you what I’ve always felt:
Let it melt! Let it melt! Let it melt!

Polar bears these days are thinking
That the ice cap seems to be shrinking,
I’ll tell you what I’ve always felt:
Let it melt! Let it melt! Let it melt!

The heat shows no signs of stopping,
And the corn in the fields is popping,
I’ll tell you what I’ve always felt:
Let it melt! Let it melt! Let it melt!

We expect a most wild ride,
Because it’s so hot outside,

A Caribbean Island Transitions to PV

Posted on December 16, 2016 by Martin Holladay

Most of the electricity generated in the U.S. comes from power plants that burn coal or natural gas. Although an increasing percentage of our electricity comes from 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. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) arrays and wind turbines, there are two problems with these renewable energy sources. First, electricity generated by PV arrays or wind turbines is still somewhat more expensive than electricity generated by fossil fuel plants (although the cost of solar and wind continue to drop).

Green Building in the Trump Era

Posted on December 9, 2016 by Martin Holladay

Most green building advocates are concerned about global climate change. So what are we to make of the election of Donald Trump?

Well, there is bad news and good news.

The bad news is that Trump is ignorant about basic economic facts relevant to the energy industry and is disdainful of scientific consensus. There’s more bad news:

  • Trump believes that climate change is a hoax;
  • Trump has promised to withdraw from (or, as he puts it, to “cancel”) the Paris Climate Agreement;
  • Trump has ridiculed supporters of renewable energy;
  • Worries About Trapping Moisture

    Posted on December 2, 2016 by Martin Holladay

    A significant number of questions posted by readers on the GBAGreenBuildingAdvisor.com site are variations of, “Will this wall detail (or roof detail) trap moisture?”

    When I entered “trap moisture” into the GBA search box, I got 182 results. The search terms “trapping moisture” yielded another 104 results. Clearly, there is a high level of concern around the issue.

    Cold Floors and Warm Ceilings

    Posted on November 25, 2016 by Martin Holladay

    During the winter, the air near your floor is cold, while the air near your ceiling is hot. Similarly, during the summer, the air conditioner keeps your first floor comfortable, while the rooms on the second floor are unbearably hot. What’s going on?

    The usual answer is, “Heat rises.” But that explanation isn’t quite accurate. (It’s true that hot air rises by convection. But heat travels in all directions, including sideways and downward, by 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. and radiation.)

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