This paper describes evaporative spray roofcooling systems, their components, performance andapplications in various climates and building types.The evolution of this indirect evaporative coolingtechnique is discussed. Psychrometric and sol-airprinciples are covered and a simplified method ofevaluation presented. A life cycle energy savingsexample is discussed. Benefits of roof life androof top equipment efficiency and maintenance arecovered as well as water consumption and performancetrade-offs with alternate methods of roof heat gaincontrol. Testimonials and case studies arepresented.The gradual migration of business, industry,and populace to the southern United States waslargely brought on by the advent of the practicalair-conditioner, cheap electricity, and the harshnessof northern winters. But while "wintering atPalm Beach" has been replaced by "Sun Belt industries" ; the compression-refrigeration cooling cycleis about the only thing separating millions ofsoutherners (native and adopted) from August heatstroke and the Detroit News employment ads. Thismigration has been spurred by economic recessionswhich hit harder at the competitively populatednorthern centers than at the still growing industries of the south.These trends are important illustrations of theconcern for efficient cooling strategies. Not onlyare homes in hot climates vulnerable to the nownot-so-low cost of electricity but large, compact.and heavily occupied buildings (offices, schools,hospitals, theaters, etc.) often must air-conditionyear-around. In 1968. air-conditioning was 3% ofU.S. end energy consumption compared to 18% forspace heating and 25% for transportation. By 1980,according to Electric Power Research Institute'sOliver Yu, air-conditioning use was 12.5% of allelectricity generated and by the year 2000 isprojected to reach 16.7% "as migration slows and theGNP reaches a stable 3% growth rate" (EPRI 1982 to1986 Overview and Strategy).Of further significance is the effect ofair-conditioning loads on the peak generatingrequirements of electrical utilities. Becauseutilities must build generating capacity to meetpeak requirements, they normally charge a highersummer kWh rate (for residential) and levy a peak kWdemand charge on a monthly or even annual "ratchet"rate (for larger service customers). The June '83cover of Houston City Magazine, in reference tofuture electrical rates, promised: "Pay or Sweat".Typical of many cooling or heat gain preventionstrategies being employed on "innovative" buildingsin warm climates, evaporative spray roof cooling(ESRC) systems (not to be confused with roof ponds)are not new. Like ventilated structures, ice houseroofs, enhanced ventilation, masonry walls, nightsky radiation and ground contact cooling, evaporativecooling in many forms has been around forcenturies. (See Solar Age, July '82 and February'81 for related articles). Even the development ofroof spray systems is not as newly founded as onemight suspect.
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