Tassel ears showing up in fields

first_imgShare Facebook Twitter Google + LinkedIn Pinterest While scouting fields this time of year it is common to find a few strange looking ears. Corn is a monecious plant, which means it has separate male (the tassel) and female (the ear) flowers. In some cases, both male and female structures form as a combination in the same plant structure.“Tassel-ears” often form on the tillers or “suckers” of a corn plant. Corn experts and agronomists believe that tassel ears are the result of some kind of environmental occurrence, however, the exact event that causes their development is unknown. The number of kernels that form on the tassel ear are limited. Without a husk to protect them, these kernels are exposed to environmental conditions and are usually damaged by the time harvest occurs.According to Bob Nielsen from Purdue University, “The male and female reproductive organs of a corn plant are contained in physically separate unisexual flowers (a flowering habit called “monoecious” for you trivia fans.) The tassel represents the male flower on a corn plant, while the ear shoots represent the female flowers. Interestingly, both reproductive structures initiate as perfect (bisexual) flowers, containing both male and female reproductive structures. During the normal course of development, the female components (gynoecia) of the tassel and the male components (stamens) of the ear shoots abort, resulting in the unisexual flowers we come to expect.“Once in a while, the normal development of the tassel alters such that it becomes partly or mostly female reproductive structures, often resulting in actual kernel development. The physiological basis for the survival of the female floral parts on the tassel is likely hormonally-driven, but the environmental “trigger” that alters the hormonal balance is not known.“A “tassel-ear” is an odd-looking affair and is found most commonly on tillers or “suckers” of a corn plant along the edges of a field or in otherwise thinly populated areas of a field. It is very uncommon to find tassel-ears that develop on the main stalk of a corn plant.”last_img read more

Do Window Shades Save Energy?

first_img_Yes, but high-performance windows and exterior shading may save more_While it’s theoretically impossible for anything to actually save energy, interior window shades can indeed keep summer heat out and winter heat in. The real questions then become: How well do they perform, and under what circumstances?In the summer, shades keep out heat, but they also block lightInterior shades (and drapes, blinds, and the like) can reflect light energy back out that would otherwise be converted to heat energy inside the home. According to the authors of the best resource on the topic, Residential Windows (Carmody, Selkowitz, Arasteh, and Heschong), “drapes can reduce the solar heat gain coefficient of clear glass from 20 to 70 percent.” That’s a pretty big range. How well drapes exclude heat depends on the shade’s color (silver would be the best, black would be worst) and their proper use. They can’t block anything if they are not closed, and when they are closed, you of course can’t see anything out of the window, and you need to turn on a light inside (so, laws of thermodynamics notwithstanding, are they really saving energy?).Exterior shading, on the other hand, performs better all around: It can deflect 100% of the direct solar gain, does not depend on occupant operation, and does not eliminate views. So, interior shades do work to reduce direct solar heat gain, they just do it rather poorly in the grand scheme of things.In the winter, shades reduce radiant heat lossYou will see claims of up to R-8 by some manufacturers of interior shades in terms of reducing heat loss. Just as with insulation in a wall cavity, the insulating value of a window shade depends on a continuous air barrier being right next to it. How many of these interior thermal shades have an airtight seal around their perimeter? None that I have seen; instead, convective currents short-circuit the shades’ thermal performance. It is hard to say just exactly what their performance is, because there is no standardized third-party testing of window shades, as there is for windows. But be happy with a couple or so Rs, not R-8. And once again, you have to operate the shades to get their best performance. Leave them down or closed on a day that turns sunny, and you have a net loss of energy. Open or up at night—oops.Interior shades can make rooms more comfortable. They have been shown to boost thermal comfort (raise the mean radiant temperature) by as much as 5°F. But just as with overall energy efficiency, improvements in thermal comfort with interior shades depend on how well the windows work to begin with. Improvements are highest and most noticeable with older, poorly performing windows. That bears repeating: Improvements are highest and most noticeable with older, poorly performing windows. Or put another way, good windows work better than shades.So, interior shades can keep your house cooler in the summer (during the day) and warmer in the winter (at night). But for real energy savings and overall performance, go with high-performance windows and exterior shading, and relegate interior shading to handling privacy. After all, you put those holes in your walls for the views and the free light!—Peter Yost is Director-Residential Services atGreenBuildingAdvisor and BuildingGreen.last_img read more

Highlighting the Benefits of Light-Colored Roofs

first_imgOne of the oldest, simplest, and least expensive ways to reduce the heat absorbed by a sun-exposed roof or other exterior surface is, as Department of Energy Secretary Steven Chu recently put it, to “make it white.”As noted in a story about white roofs in Thursday’s New York Times, Chu made that observation during a July 21 appearance on Comedy Central’s The Daily Show.True, most of Chu’s chat with the show’s host, Jon Stewart, focused on the merits of the cap-and-trade provisions of the American Clean Energy and Security Act. But near the end of the conversation, Chu briefly discussed the energy-saving potential of white roofs (and white roads). And the topic seemed to strike a chord with folks who heard Chu’s remarks: almost all of the viewers who posted comments on The Daily Show Web page featuring the Chu segment focused on the benefits of white roofs and roads.Chu’s comments were timely. A draft presentation on the subject was released on Wednesday by the Lawrence Berkeley National Laboratory, in a document titled “Cool Roof Q&A.”A primer on roof colorThe Q&A offers both consumer-oriented information and technical descriptions of the ways roofing materials and their color affect their “radiative” properties – their ability to reflect solar radiation (on a scale of 0 to 1) and emit thermal radiation (on a scale of 0 to 1) – when exposed to sunlight. The coolness rating of a material, known as its solar reflective index, is often compared to that of a reference black roof, which is assigned an SRI of 0, and that of a reference white roof, whose SRI is 100. That doesn’t rule out the possibility, however, that some materials may earn index values above or below the references.The Q&A cites as an example a roof with a clean, smooth bright white surface that reflects about 85% of incident sunlight (giving it a reflective, or “R,” value of 0.85) and emits thermal radiation with 90% efficiency (giving it an emittance, or “E,” value of 0.90). This surface, the document explains, has an SRI of 107 and will be only 9°F warmer than the outside air on a typical summer afternoon. Meanwhile, the surface of a standard gray roof that has the same emittance value but reflects only about 20% of incident sunlight (R = 0.20, E = 0.90) would have an SRI of just 19 and a surface temperature elevation (surface temperature minus outside air temperature) of 69°F.Rosenfeld’s big pictureThe document does note that exposure to weather over a three-year period typically does not change the thermal emittance but does reduce the reflectance of a low-sloped bright white roof to about 65%, pushing its SRI down to 79. After similar exposure, the reflectance and thermal emittance of a standard gray roof remain unchanged – but so does the roof’s relatively poor SRI.California Energy Commission member Arthur Rosenfeld, who, the Times notes, is one of Secretary Chu’s heroes and a longtime advocate of cool roofs, recently wrote an opinion piece for the Huffington Post that cited one of his favorite illustrations of cool-roof efficiency.“From a global perspective,” Rosenfeld wrote, “replacing dark roofs with cool ones would be equivalent to taking half the world’s cars – 300 million vehicles – off the road for 20 years, or reducing 24 billion tons of CO2 emissions for the same period.”last_img read more