This work is initially focused on tropical and subtropical climates. In tropical climates, cooling is nearly always desired. Thus a cool roof can be built directly on a dwelling without the need for a ceiling or insulation. In subtropical climates there are cool nights; some method for disabling radiative cooling may be needed if the site is occupied at night. This can be accomplished by unrolling a (infrared) reflective shade over or under the roof. The roof described in Optics for Passive Radiative Cooling can be switched off using reflective louvers.
While simulations of low-slope roofs during temperate summers should be reasonably accurate, for temperate or arctic simulations the following issues would need to be addressed.
Fundamental differences [between TMY3 and TMY2] are measurement units, which are SI or equivalent in the TMY3, the addition of three new fields for surface albedo and liquid precipitation, and the removal of the fields for present weather, snow-depth, and days since last snowfall that were present in the TMY2. These fields were removed because of incompatible changes in the nature of the source data or because the source data were not available.
Clouds and high humidity are the primary atmospheric phenomena inhibiting radiative cooling. The measure of how much water vapor is contained by the atmosphere is its precipitable-water. The only collection of Typical-Meteorological-Year data for widespread locations including precipitable-water is the (TMY2 and) TMY3 datasets from the United States National Renewable Energy Laboratory Renewable Resource Data Center.
The NSRDB update subdivided stations by class: Class I sites are those with the lowest uncertainty data, Class II sites have higher uncertainty data, and Class III sites have an incomplete period of record.
SimRoof simulations using tropical class-III sites produced strange artifacts. Bug reports involving class-III sites will have low priority. The latitudes in the List of Class-I and Class-II Sites in Order of Increasing Latitude span the range from 13 to 72 (Guam to Alaska).
The site pages linked below have scatter-graphs of precipitable-water versus dry-bulb-temperature for each location, along with minimum and maximum values for all the TMY3 parameters used in simulation. The "Ceiling-Unlimited Opaque Sky Coverage Hours" statistic is explained in Ceiling.
Note: In a scatter-plot two points at identical locations look no different from one point at that location. In order to reduce this effect, SimRoof dithers Typical Meteorological Year (TMY3) data values by up to half their resolution (as measured when the TMY3 file is read).
On the maps, Class-II sites are marked with a black +. Class-I sites are marked with gold diamond.
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