Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The optical depth estimages in ASHRAE climatic data were calculated using a high performance clear sky radiation model called REST2, developed by Chris Gueymard. The REST2 model was used to calculate radiation data for the various locations in the ASHRAE climatic data and then a 2 parameter regression model was fitted to the results to derive the revised clear sky model.
The ASHRAE research project notes that the optical depths are more appropriately called "pseudo" optical depths (because optical depth is typically employed when the air mass = 1). Gueymard further states that aerosol optical depths are very sensitive to water vapor content and are not recommended for use; rather he suggests the use of the Angstrom coefficients, which it appears is what ASHRAE has tabulated as the beam and diffuse optical depths.
Gueymard, Chris. (2004). High performance model for clear-sky irradiance and illuminance.
Thevenard, D & Gueymard, Chris. (2010). Updating the ASHRAE climatic data for design and standards. ASHRAE Trans.. 116(2). 444-459.
| | 2 | No.2 Revision |
The optical depth estimages estimates in ASHRAE climatic data were calculated using a high performance clear sky radiation model called REST2, developed by Chris Gueymard. The REST2 model was used to calculate radiation data for the various locations in the ASHRAE climatic data and then a 2 parameter regression model was fitted to the results to derive the revised clear sky model.
The ASHRAE research project notes that the optical depths are more appropriately called "pseudo" optical depths (because optical depth is typically employed when the air mass = 1). Gueymard further states that aerosol optical depths are very sensitive to water vapor content and are not recommended for use; rather he suggests the use of the Angstrom coefficients, which it appears is what ASHRAE has tabulated as the beam and diffuse optical depths.
Gueymard, Chris. (2004). High performance model for clear-sky irradiance and illuminance.
Thevenard, D & Gueymard, Chris. (2010). Updating the ASHRAE climatic data for design and standards. ASHRAE Trans.. 116(2). 444-459. 444-459.
