Shah (1981) showed that the analogy for heat and mass
transfer is reliable provided the airflow is fully turbulent and
exceeds 5.6 mph (2.5 m/s) at any air-to-water temperature
difference. At lower airflow rates, the analogy is accurate
provided the air-to-water temperature gradient exceeds about
27°F (15°C). Unfortunately, during the late twilight hours of
any summer day, both the roof-to-air temperature gradient and
the wind speed are usually below these limits. Shah (1981)
checked the predictive accuracy of mass-transfer algorithms