Reflective roofs

Researchers have simulated the impact of the urbanwidc application ot reflective roofs on cooling-energy use and smog in the Los Angeles Basin. They... 

Akbari, H., ed. (1998). Energy Savings of Reflective Roofs. ASHRAE Technical Data Bulletin 14(2). 

Please note that those figures do not reflect roof insulation, which this year represents a potential of more than 3 billion board feet of one-inch fiberboard equivalent to 1.25 billion board feet of one-inch urethane. Ely mid-decade, we anticipate the market to grow to U billion board feet or 1.66 billion board feet of one-inch urethane. 

Reflective Roofs. Reflective or white roofs are often considered to be the most cost effective and easily implemented SRM method of reducing global temperatures. The concept relies on reflecting solar radiation back into space by using white materials (or paint) on the surfece of building roofs. 

Although sound pressure level drops with distance from the somce (this can be one way of reducing noise exposure), the drop or sound pressme level reduction will not be as great in a shed or workshop with reflecting roof, floor and/or walls. 

Texas, and Florida. [2 3] One significant advantage to these programs is that the Cool Roof specifications mentioned above are guidelines for new construction (Table 24.2). The rebates provide incentive for converting existing low reflectance roofs to the higher standard. 

Very often the environment is reflected in the composition of corrosion products, eg, the composition of the green patina formed on copper roofs over a period of years. The determination of the chemical composition of this green patina was one of the first systematic corrosion studies ever made (see Copper). The composition varied considerably depending on the location of the stmcture as shown in Table 2 (26,27). 

Calculate the beating due to solar radiation on the flat concrete roof of a building, 8 nr by 9 m. if the surface temperature of the roof is 330 K. What would be the effect of covering the roof with a highly reflecting surface such as polished aluminium ... 

In an alkaline solution, the cuticle—the outermost layer of a strand of hair—swells up, softens, and becomes rougher. The cuticle is made up of translucent, flattened cells that line the hair shaft like shingles on a roof. The cuticle gets rougher when the cells do not lay flat. When the raised cuticle cells of one piece of hair get stuck on the raised cuticle cells of another piece of hair, the hair tangles. The raised cells also reflect light differently than smooth, flat cells, making the hair appear dull. 

Increased Parkland through zoning, and incentives for buildings to have Green Roofs with water retention and heat reflection. 

As the wave front moves forward, the reflected overpressure on the face of the structure drops rapidly to the side-on overpressure, plus an added drag force due to the wind (dynamic) pressure. At the same time, the air pressure wave bends or "diffracts" around the structure, so that the structure is eventually engulfed by the blast, and approximately the same pressure is exerted on the sides and the roof. The front face, however, is still subjected to wind pressure, although the back face is shielded from it. 

The loads from external near-surface burst explosions are based on hemispherical surface burst relationships. Peak pressure (P psi) and scaled. impulse Ci/W psi/lb ) are plotted vs. scaled distance (R/W ft/lb ). Roof and sidewall elements, side-on to the shock wave, see side-on loads (P and i ). The front wall, perpendicular to the shock wave, sees the much higher reflected shock wave loads (P and i ). An approximate triangular pressure-time relationship is shown in Figure 5a. The duration, T, is determined from the peak pressure and impulse by assuming a triangular load. Complete load calculations include dynamic loads on side-on elements, the effect of clearing times on reflected pressure durations, and load variations on structural elements due to their size and varying distance from the explosive source. 

For a building with a flat roof (pitch less than 10°) it is normally assumed that reflection does not occur when the blast wave travels horizontally. Consequently, the roof will experience the side-on overpressure combined with the dynamic wind pressure, the same as the side walls. The dynamic wind force on the roof acts in the opposite direction to the overpressure (upward). Also, consideration should be given to variation of the blast wave with distance and time as it travels across a roof element. The resulting roof loading, as shown in Figure 3.8, depends on the ratio of blast wave length to the span of the roof element and on its orientation relative to the direction of the blast wave. The effective peak overpressure for the roof elements are calculated using Equation 3.11 similar to the side wall. 

The shape of (he rear wall loading is similar to that for side and roof loads, however the rise time ami duration arc influenced by a not well understood pattern of spillover from the roof and side walls and from ground reflection effects. The rear wall blast load lags that for the front wall by L/U, the lime for the blast wave to travel the length, L, of the building. The effective peak overpressure is similar to that for side walls and is calculated using Equation 3.11 (Ph is normally used to designate the rear wall peak overpressure instead of P,). Available references indicate two distinct values for the rise lime and positive phase duration. 

Another possible protective scheme, although rarely used in the petrochemical industry, is a blast resistant barrier wall. A barrier wall can be used to provide protection from fragments and reduce reflected wall loads. However, it will not reduce overpressures on the roof and unprotected side walls. 

Some reduction of reflected overpressure results within a horizontal distance of about twice the barrier wall height. Beyond this distance, the effects of a barrier wail is virtually nil. Quantification of the pressure reduction is difficult and often times requires sophisticated computer modeling. Normally, it is more cost effective to upgrade the strength of the structure to be protected than it is to construct a barrier wall. This is especially true when the structure of interest does not have sufficient blast capacity in the roof to resist the blast load. 

The downward force from the overpressure on the roof is applied simultaneously with the horizontal force from the peak reflected pressure on the front wall, However, the compensating effects of blast forces acting on the rear wall may be conservatively neglected. 

So then everyone had to have a look. "No " Herman said, but (hey took a vote and it was unanimous. One by one, members of the Living Flag went up to the roof and admired it. It was marvelous It brought tears to the eyes, it made one reflect... 

Ti02/Mica IR-reflective IR-reflecting plastic sheets, e.g. for domed and continuous roof lights [5.236]... 

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