page_title: John I. Yellott
section_title: Solar engineering
hierarchical_section_title: John I. Yellott / Solar engineering
caption_attribution_description: English: This is a sketch of the roofpond experimental apparatus at Trinity University Texas, using the "Skytherm System," an illustration which accompanied an article in the Vol. 4 No. 3 of the Passive Solar Journal.
context_page_description: John I. Yellott was a scientist internationally recognized as a pioneer in passive solar energy, and an inventor with many patents to his credit. In his honor the American Society of Mechanical Engineers Solar Division confers a biannual "John I. Yellott Award" which "recognizes ASME members who have demonstrated sustained leadership within the Solar Energy Division, have a reputation for performing high-quality solar energy research and have made significant contributions to solar engineering through education, state or federal government service or in the private sector."
context_section_description: Yellott's early interest, the source of much consulting work, was on the transparency and transmissivity of glass.  In 1960s he helped to develop the solar heat gain factor (SHGF) method of calculating the passive thermal role of glass, now the standard method accepted by the American Society of Heating, Refrigerating and Air-Conditioning Engineers.  He served as a consultant to  major industrial concerns such as Corning Glass,  PPG Industries, Libbey-Owen-Ford Glass company, Shatterprufe Glass Company of Port Elizabeth, South Africa; and Pilkington Brothers Glass Company of Great Britain. One of Yellott's clients was Northrup, Inc. whose founder Leonard L. Northrup Jr. was introduced to solar technology by Yellott, and whose company went on to develop some of the first solar air conditioning systems and heliostats, under Yellott's on-going advice.
  According to his Illinois Institute of Technology Hall of Fame entry, Yellott's work resulted in more than fifty patents, such as an electric locomotive with a coal fired gas turbine using pulverized coal directly injected into a combustion chamber; a film-type solar water heater  and a transparent cover to heat swimming pools by trapping solar radiation  Yellott's pool cover idea remains in commercial use to this day.  He also contributed his solar expertise to civic projects such as the landmark Carefree Sundial in Carefree, Arizona.
    Yellott pioneered passive solar cooling as a field parallel to solar heating, with particular attention to water spray and controlled evaporation.  As with any innovator, not all experiments met with success.
  Yellott's collaboration with solar entrepreneur Harold Hay on developing an evaporative solar system called a roofpond, which Yellott considered "the simplest system which can accomplish both heating and cooling with the same equipment,” proved to be not so simple.  The experiments at Yellott's laboratory encountered obstacles such as the unexpected "healthy growth of 'wrigglers' within plastic-enclosed water" from the city mains; then "a pair of nesting birds was attracted to the comfort of a projecting portion of the roofpond.  . . ." (The researchers eliminated the unwelcome  'wrigglers' as well as a prolific growth of algae with chemical treatment; they considered the “cheerfulness of the birds a pleasant relief from the drudgery of data-collection,” but recommended “preventive measures for those not wanting such company.”)
  Yellott's and Hay's experiments did prove the roofpond concept technically feasible, later confirmed with expanded testing on dormitory roofs at Trinity University in Texas. Nonetheless, in the words of solar scientist Kenneth Haggard of the San Luis Obsispo Solar Group, implementation of the idea of maintaining a large puddle of water on one's roof to cool the interior "awaits the next period of blossoming of passive solar architecture." (Hay defended roofponds, acknowledging that while a roofpond design error proved "highly expensive to a young architect and his client," nonetheless there is an "unnecessary fear of having bodies of water overhead."  Hay also noted that a review of all roofpond installations in the United States concluded the roofpond "outperforms any other single passive system in both heating and cooling modes" and opined "It may be DOE's best kept-secret buried under hundreds of reports.")
  Yellott's achievements particularly in the area of glazing and solar radiation capture have stood the test of time.  According to Dr. Jeffrey Cook, College of Architecture and Design, Arizona State University, writing the introduction to the Passive Solar Journal's John I. Yellott Memorial issue, "he made major contributions in areas of basic research, instrumentation, analytic methods, applications, collaboration, education, and demonstration." Cook also wrote: "[h]e published no definitive book," but "[a]rticles bearing Yellott's name will remain classics in solar energy literature;" he "developed no distinctive demonstration, no outrageous solar machine, and no landmark building or award winning engineerin
caption: Sketch of full scale roofpond apparatus experiment at Trinity University, Texas
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