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Rain on the Roof-Evaporative Spray Roof Cooling
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This paper describes evaporative spray roof cooling systems, their components, performance and applications in various climates and building types. The evolution of this indirect evaporative cooling technique is discussed. Psychrometric and sol-air principles are covered and a simplified method of evaluation presented. A life cycle energy savings example is discussed. Benefits of roof life and roof top equipment efficiency and maintenance are covered as well as water consumption and performance trade-offs with alternate methods of roof heat gain control. Testimonials and case studies are presented. The gradual migration of business, industry, and populace to the southern United States was largely brought on by the advent of the practical air-conditioner, cheap electricity, and the harshness of northern winters. But while "wintering at Palm Beach" has been replaced by "Sun Belt industries" ; the compression-refrigeration cooling cycle is about the only thing separating millions of southerners (native and adopted) from August heat stroke and the Detroit News employment ads. This migration has been spurred by economic recessions which hit harder at the competitively populated northern centers than at the still growing industries of the south. These trends are important illustrations of the concern for efficient cooling strategies. Not only are homes in hot climates vulnerable to the now not-so-low cost of electricity but large, compact. and heavily occupied buildings (offices, schools, hospitals, theaters, etc.) often must air-condition year-around. In 1968. air-conditioning was 3% of U.S. end energy consumption compared to 18% for space heating and 25% for transportation. By 1980, according to Electric Power Research Institute's Oliver Yu, air-conditioning use was 12.5% of all electricity generated and by the year 2000 is projected to reach 16.7% "as migration slows and the GNP reaches a stable 3% growth rate" (EPRI 1982 to 1986 Overview and Strategy). Of further significance is the effect of air-conditioning loads on the peak generating requirements of electrical utilities. Because utilities must build generating capacity to meet peak requirements, they normally charge a higher summer kWh rate (for residential) and levy a peak kW demand charge on a monthly or even annual "ratchet" rate (for larger service customers). The June '83 cover of Houston City Magazine, in reference to future electrical rates, promised: "Pay or Sweat". Typical of many cooling or heat gain prevention strategies being employed on "innovative" buildings in warm climates, evaporative spray roof cooling (ESRC) systems (not to be confused with roof ponds) are not new. Like ventilated structures, ice house roofs, enhanced ventilation, masonry walls, night sky radiation and ground contact cooling, evaporative cooling in many forms has been around for centuries. (See Solar Age, July '82 and February '81 for related articles). Even the development of roof spray systems is not as newly founded as one might suspect.
Bachman, L. R. (1985). Rain on the Roof-Evaporative Spray Roof Cooling. Energy Systems Laboratory (http://esl.tamu.edu); Texas A&M University (http://www.tamu.edu). Available electronically from