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Solar Thermal Domestic Water Design

  • 1.  Solar Thermal Domestic Water Design

    Posted 12 days ago
    Can anyone point me to a design guide for solar thermal domestic water sizing? Say I have a nominal load of 300 gph. A 100 gal storage type heater with 120000 BTUh or 35 kW would work. How can I convert that to panel square footage?

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    Andrew Peter
    Piping Engineer
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  • 2.  RE: Solar Thermal Domestic Water Design

    Posted 11 days ago
    Hi Andrew,

    Here are a couple links to technical journals on the subject; not sure if they will answer your questions directly but they are very useful.
    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_3_0.pdf
    and
    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_6_0.pdf

    Best regards,
    Kevin

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    Kevin Freidt
    Director Product Management
    Caleffi North America
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  • 3.  RE: Solar Thermal Domestic Water Design

    Posted 11 days ago
    ASPE's Plumbing Engineering Design Handbook, 2006-2007 Volume 3 "Special Plumbing Systems", Chapter 10 is on Solar Energy. Also, the Solar Energy Systems CEU #263 posted in September 2018 in ASPE's Read, Learn, Earn program are good sources of information that are free to ASPE members.​

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    Michael Divens CPD
    Senior Mechanical Designer
    PDC Inc. Engineers
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  • 4.  RE: Solar Thermal Domestic Water Design

    Posted 10 days ago
    Andrew,

    A few things to keep in mind:
    While solar thermal domestic water heating systems can certainly be beneficial, (depending on your project area), they can quickly turn into a problem if they are oversized, (i.e. sized for the FULL domestic water load , what I recall as 'Solar Fraction').  I have typically designed these to be supplemental heating systems, (our peak HW loads don't usually match up well with the sun's peak output).  If you size the solar thermal system for the full load, you will definitely cut down on the clients Return On Investment, (ROI).  Also you would probably need to do a "drain back" type system to avoid overheating the storage tanks. 

    I would suggest doing your research first, then reaching out to a solar thermal rep to vet out your ideas.  Nothing worse than a closed loop solar thermal system overheating and having the fluid go acidic!

    Best of luck!

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    Christopher Sbarbaro , PE, CPD, GPD, LEED AP BD+C
    Plumbing & Fire Protection Eng
    Grumman Butkus Associates
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  • 5.  RE: Solar Thermal Domestic Water Design

    Posted 10 days ago
      |   view attached
    Andrew,

    You'll want to check the SRCC reports for the specific solar thermal collector (panel) you are interested in using. These OG-100 reports from the SRCC (https://secure.solar-rating.org/Certification/Ratings/RatingsSummaryPage.aspx?type=1) will have a table translating approximate number of BTUs per panel per day under specific use and radiation conditions. For example on the attached report, this panel being used for water heating ("Category C") in a medium radiation climate could produce 31,900 BTU per day. This would be a very quick back-of-envelope way to get you towards rough panel square footage/ number of panels.

    Some other good resources are:
         Dr. Ben's website: http://www.solarhotwater-systems.com/solar-water-heating-101/
         2016 ASHRAE Handbook ch 37
         Solar Water Heating by Bob Ramlow and Benjamin Nusz
         California Energy Commission's F-chart tool https://ww2.energy.ca.gov/title24/swh_calculator/
         And if you want to take a very deep dive, Solar Engineering of Thermal Processes by John Duffie and William Beckman is the industry bible

    I am a project engineer at a company that designs these systems, feel free to reach out and good luck!

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    Jason Morgan
    Project Engineer
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    Attachment(s)



  • 6.  RE: Solar Thermal Domestic Water Design

    Posted 10 days ago
    Thanks everyone. As usual your insights and references are immensely helpful.

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    Andrew Peter
    Piping Engineer
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