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Measuring solar radiation absorption coefficients

Jam

Hi all,

We're doing some thermal calculations for a some existing equipment and as it's outside need to quantify the solar gain. This obviously depends on the absorption coefficient, which in turn depends on colour, finish, cleanliness etc.

Is anyone able to recommend / point us in the direction of a portable device that could measure the absorption coefficient in the field, or perhaps suggest a method for getting a reasonable estimate?

We don't need to be accurate to the nth degree, just enough to quantify where we lie between "white" or "light grey" (as the standards we're using refer to them).

Jam

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    There isn’t really a handheld “absorption coefficient meter.” In practice, you estimate solar absorption from published tables (ASHRAE, ISO 8995, CIBSE, NREL) which give typical absorptivity values by colour/finish (e.g. ~0.2–0.3 for white/very light grey, ~0.6–0.9 for dark colours).

    If you want a field method:

    • Use a portable reflectometer or spectrophotometer (many coatings/paint QA instruments exist) → measure solar reflectance, then absorptivity ≈ 1 − reflectance.

    • For rough design work, visual comparison to standard colour charts (e.g. RAL shades) and applying tabulated absorptivity is usually acceptable.

    In your case, best approach is either:

    • Use tabulated values for “white/light grey” vs “dark” as in ASHRAE/CIBSE, or

    • Hire/borrow a portable reflectometer (commonly used in building/roofing industries) for a quick field measurement.

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  • 0

    There isn’t really a handheld “absorption coefficient meter.” In practice, you estimate solar absorption from published tables (ASHRAE, ISO 8995, CIBSE, NREL) which give typical absorptivity values by colour/finish (e.g. ~0.2–0.3 for white/very light grey, ~0.6–0.9 for dark colours).

    If you want a field method:

    • Use a portable reflectometer or spectrophotometer (many coatings/paint QA instruments exist) → measure solar reflectance, then absorptivity ≈ 1 − reflectance.

    • For rough design work, visual comparison to standard colour charts (e.g. RAL shades) and applying tabulated absorptivity is usually acceptable.

    In your case, best approach is either:

    • Use tabulated values for “white/light grey” vs “dark” as in ASHRAE/CIBSE, or

    • Hire/borrow a portable reflectometer (commonly used in building/roofing industries) for a quick field measurement.

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