The heat paradox

Scientists eager to show us how to make homes, offices comfortable while saving money and the planet.

By TOMER SPINNER
September 8, 2009 10:48

 
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Everybody complains about the heat, but only a handful of green architects are doing something about it. Most designers disregard climate and energy considerations. The result: Modern buildings consume vast amounts of energy for cooling, heating and lighting - almost half of a nation's total energy budget.



Sustainable design (and retrofit of existing buildings) may significantly mitigate this huge energy waste. "Bio-climatic architecture enhances life quality using natural resources, but it's also considered the most economic way to cut energy consumption," asserts Edna Shaviv, professor of architecture and urban design at the Technion.



One of these sweltering days the electricity is going to die on us again. Suddenly the air conditioner will suffocate in a menacing hiss and the soothing stream of cool air will succumb to an ugly little heat wave.



We'll likely curse the utility company and on the evening news watch its executives clash with Treasury officials over the $2.5 billion urgently needed for a fourth coal power plant to meet the country's soaring energy demands.





The chilling truth, however, is that air conditioners consume some 50 to 60 percent (utility company estimates) of peak summer electricity production. Our highly inefficient homes and offices are the main culprit in this energy crisis.



"A lot of buildings in Israel, public and private, are climatic catastrophes" says Dr. Oded Potcher, a climatologist from Tel Aviv University and Beit Berl College. "Energy-hungry buildings may demand twice, even more, the amount of cooling or heating than would similar-size green buildings."



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Hi-tech "crystal palaces" may appear "cool" or "green," but their shiny transparent glamour comes with a punishing energy toll: "Large glass curtain walls create an intense greenhouse effect indoors," says Potcher. "In many hi-tech buildings and malls featuring large windows, even massive air conditioning systems fail to combat heat buildup in summer.



"Take, for example, the western glass wall of the Seven Stars Mall in Herzliya. It receives blazing sun during afternoon hours, so they put in drapes to stop the glare. But they mainly block the view and heat still pours in. So what do we have? A huge window that functions as a heater in summer... drapes that block natural light and necessitate artificial lighting... This is what you might call anti-ecological architecture."



AT A bio-climatic architecture lecture, Shaviv once paused to give a live demonstration of just how inefficient the elegant conference hall was. "Heavy dark inner curtains block all incoming natural light, yet intense heat persists near the windows despite excellent air-conditioning. In fact the waste here is threefold: First, we cut off natural light, which is the most pleasant and energetically efficient. Second, inner dark shading converts a large portion of incoming light into harmful heat radiation, and third, since we've darkened the room, artificial lighting is required, which further increases energy waste. That's quite absurd when pleasant natural light is so abundant in Israel."



"To minimize summer 'greenhouse effect,' external light-colored shades are far more effective," says Shaviv, who developed the computerized model SunShades as early as 1975. "The challenge was to model minimal external shading devices that block harsh direct summer sun, while allowing natural 'soft' daylighting and maximum exposure to the much desired winter sun.



"It's too bad the good old Israeli blind [fell from] grace. The shading panes can be rotated to block direct radiation, but can also reflect indirect soft sky-light into the room, reducing the need for artificial lighting."



When asked whether double-glazed reflective glass can replace outer blinds, she responds: "Smart glazing - such as 'low-e' glass with special coatings that is translucent to the visible light but not so much to heat radiation - can provide a prescribed amount of shading to reduce heat, while allowing entrance of pleasant natural light. This is practical in office buildings, where daylight is important. These advanced glazings are rather expensive, and are not ideal for large west- or east-facing windows without the addition of external shading devices or internal shading to avoid glare from the low sun that penetrates deep into the room. This glazing may have a drawback in winter: Its shading effect considerably reduces desired solar heating, especially in residential buildings."



MANY OF us dream of breezy west windows, overlooking the sea, and tend to forget the inferno they pour in during summer afternoons. Here is how it really works: The sun rises in the east and sets in the west, but observe that it goes over the southern horizon, high in summer and low in winter.



This celestial marvel is at the heart of solar architecture: shading against high summer sun while endorsing low winter sun.



It's an age old natural wisdom harnessed successfully by the ancient Greeks and Romans, but largely neglected in modern architecture, armed with the almighty air conditioner.



Around noon in summer the sun is almost overhead, above the southern window and hitting it relatively lightly. But in the afternoon, summer sun travels west (and a bit north), bombarding the western window with furious radiation.



A visit to a prestigious Herzliya gym sporting a giant, dark-bluish western glass wall made the point radiantly clear. The powerful air-conditioning system was running at full throttle, but was no match for the western inferno striking at about 600 watts per square meter. At around 3 p.m. the heat was so intense that trainees had to abandon equipment within a few meters of the transparent killing zone. So contrary to common belief west - not east - is hottest in summer. East and west windows get almost double summer sun radiation than does south.



In winter the balance reverses: Low winter sun warms a southern window roughly twice as much as it does east and west windows.



South is the ideal window orientation for both winter and summer," concludes Shaviv.





SO IF any smart contractor tries to sell you a "winter sun-porch" facing north, don't fall for it.



East or west porches enjoy only a meager amount of winter sun. In looking for an apartment (or designing your own home), follow the wisdom of Roman noblemen who were fanatic about their southern solarium's "sun rights" in winter. Roman architects took care that buildings did not obscure winter sun from each other's southern windows.



Shaviv's colleagues Dr. Avraham Yezioro and Dr. Guedi Capeluto developed this Roman "sun art" into state-of-the-art software. Capeluto's SustArc model enables architects to design year-round economical solar envelopes, while Yezioro's SHADING allows evaluating the exact amount of solar exposure, thus maximizing winter sun-rights even in densely built areas where buildings compete for every winter ray.



Green architecture has a clever shading trick that works well only for southern exposures: For a south-facing window one meter high, a fixed 40-centimeter horizontal "casquette" hung 50 cm. above the window blocks direct summer sun yet allows winter sun in.



Architects Ruth Lahav, Tony Rigg and Prof. Len Warshaw used shaded, recessed low-e double-glazed southern windows that do just that in the Government Administration Center of Beersheba. The complex is one of a few energy-conscious green buildings in Israel and won the 2005 Azrieli award for sustainable urban planning.



"The site stretches 230 meters from north to south, so it naturally had undesired long east and west elevations [facades]," explains Lahav. "To maximize southern exposures we 'sliced' the 76,000 sq.m. complex into a series of five office buildings facing north-south, with courtyards between them. This orientation [with minimum east and west elevations] gives controlled access of sun in winter, allows natural daylighting, yet blocks direct summer radiation."







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