The sol-air temperature expression includes the long-wave correction term defined as the product of (the hemispherical emittance of the surface) and (the difference between long-wave radiation incident on the surface from sky and surroundings and radiation emitted by a blackbody at the outdoor air temperature) devided by (the coefficient of heat transfer by long-wave radiation and convection at the outer surface).
It is common practice (from reference ASHRAE) to assume this correction term equal to 0K for vertical surfaces and equal to 4K for horizontal surfaces.
Could anyone help me with a more precise model to estimate this correction term?
According to ASHRAE, the correction term for the vertical surfaces is 0C (not 0K) and for horizontal surfaces is -3.9C (not 4K). This is according to Bliss (I attached his original paper for more details). Other authors suggest -11.6C for arid climates with clear skies, -13.8C for humid climates with clear skies and -17.7C for cloudy skies conditions (see, e.g., Baruch Givoni, 1997: Climate Considerations in Buildings and Urban Design, New York: Van Nostrand Reinhold).
Regarding some recent models used to calculate this correction, check the attached thesis. I hope you will find it useful.
Thank you M. Sergei for your help.
In my question, the positive value of 4K corresponds to the term that I defined and wich is preceded by a minus sign in the sol-air temperature expression. So, as you noted, the correction itself is -4K.
The unit can be Kelvin or °C since it comes from the heat transfer coefficient unit and is related to a difference of temperature.
one simple answer to the question in the Wikipedia at http://en.wikipedia.org/wiki/Sol-air_temperature. Naturally, better answers to apply to specific situations would be in the state-of-the-knowledge research papers on the subject.
might be useful for you to get an idea of how to calculate sol-air temperature please check this:
Conference Paper Assessment of the thermal performance of plastering mortars ...
Thank you M. Kheradmand for your response.
My question was about the estimation of the correction term (ΔR) included in the expression of the sol-air temperature, which is defined from ASHRAE as :
Tsol-air=Tair + α*Ig/he - ε*ΔR/he
In your publication, this correction term is assumed to be equal to zero, because you have considered a vertical wall.
However, in the case of a horizontal surface, this correction term should be included in the calculation of the sol-air temperature.
- Badges
- Science topic
- Similar topics
- Engineering
- Thermal Engineering
- Thermofluid
- Heat Transfer