Volume 35, Number 9, September 2000



Electricity Restructuring

deregulation opens glass industry windows

 by Dariush Arasteh

Consumers are now beginning to experience the negative effects of electricity deregulation in the states leading the transition from a rate-regulated industry to one in which markets set prices. As with the phone industry in the early 1980s, consumers now can choose among a variety of providers and tailor service options to best meet their needs. However, customers are finding themselves ill-equipped to deal with high electricity costs when supplies are scarce. Seasonal price spikes made headlines earlier this summer when consumers in San Diego received electricity bills more than double their normal summer bills due to unexpectedly high power costs in the previous month.

What does electricity restructuring have to do with the glass industry? Plenty. Electricity demand is greatest on hot summer afternoons when offices and homes require the most air conditioning. On these days, up to 50 percent of a building’s electricity demand may be powering air conditioners. Of this 50 percent, up to half of these requirements are accounted for by the removal of solar heat gains through the window. As a result of market pricing, the hourly cost of electricity can be hundreds of times greater than it is during periods of low demand.

Over the past decade the glass industry has developed low-emissivity coatings which can significantly reduce solar gains—by 40 to 50 percent—without altering visible clarity or total visible transmittance. Generically termed “spectrally-selective” low-E or low-solar gain low-E, these coatings may be placed on clear or tinted glass and thus do not limit architectural appearances. They work by reflecting half of the incoming solar energy, which is invisible to the human eye, called solar infrared. Clear and tinted glass typically pass all or much of this energy into buildings, which must then be removed as unwanted heat. What’s more, because it also has greater insulating value, low-E glass slows down the transmission of heat into air conditioned spaces. Low-solar gain or high performance tints combined with conventional low-E glass are another effective alternative.

By reducing unwanted solar gains while still passing visible light into buildings, these glazings can be combined with daylighting instead of electric lighting within the building. Using daylighting controls to turn off electric lights further reduces electricity demands at peak times, both in direct reductions in electricity use for lighting and in secondary reductions in air conditioning that is no longer needed to remove the heat produced by electric lighting.

With the incremental cost for such coatings on the order of $1-$2 per square-foot, low-solar gain low-E coatings are among the most cost-effective ways to lower expensive peak power costs. These incremental costs, when balanced off against real time pricing, pay for themselves over the course of one heat wave.

From a societal perspective, widespread use of these coatings will avert brownouts and reduce the need to start-up reserve generating units, which often have a disproportionately high environmental impact.

Low-solar gain low-E is used in less than 20 percent of all potential applications today. With virtually all office buildings suffering from excess heat all or most of the year and with more and more homes being built with air conditioning, these products have a market potential for applications 80 to 90 percent of the time.

Commercial buildings with large glazed curtainwall may sometimes be better off using low shading coefficient or low solar heat gain coefficient reflective glass, which combats excessive solar gains with a slightly different technology. Residential buildings in climates without significant cooling loads should consider high solar gain low-E coatings in order to take advantage of free solar heat during the winter season. In all other cases, specifying low-solar gain low-E glass will save money, stabilize energy bills and keep occupants cool.

Dariush Arasteh is a staff scientist for Lawrence Berkeley National Laboratory in Berkeley, Calif.

Fenestration Focus appears monthly with rotating columnists.


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