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Weather

Weather data, solar position and Perez coefficients for the site

FastSmoothBuildings.BoundaryConditions.Weather, model (source)

Purpose

The weather bus of a model: the weather data, given as inputs (the top-level inputs of the CasADi model), with the site, the solar position and the coefficients of the Perez sky model computed from them, without table or event.

Equations

Solar position, with t the model time in seconds, the standard clock time from the beginning of the year:

  • declination δ = asin(−sin 23.45° cos(2π (t/86400 + 10)/365.25));
  • equation of time E = 60 (9.87 sin 2B − 7.53 cos B − 1.5 sin B) s, B = π ((t + 86400)/86400 − 81)/182;
  • solar time tsol = t − timZon + lon 43200/π + E, hour angle ω = 2π (tsol/3600 − 12)/24;
  • cos ζ = cos φ cos δ cos ω + sin φ sin δ.

Perez model, with ζ the zenith angle:

  • relative air mass m = exp(−0.0001184 alt) / (cos ζ' + 0.15 (93.9 − ζ')−1.253), ζ' = min(ζ, 90°), in degrees in the second term;
  • sky brightness Δ = min(Hdif,hor m / (1366.1 (1 + 0.033 cos(2π (tsol/86400 + 1)/365))), 1);
  • sky clearness ε = ((Hdir,nor + Hdif,hor) / Hdif,hor + κ ζ3) / (1 + κ ζ3), κ = 5.534·10−6 (ζ in degrees), limited to [1, 8];
  • with ak the weight of the clearness bin k of eight (edges 1.065, 1.23, 1.50, 1.95, 2.80, 4.50 and 6.20) and ζ in radians, F1 = max(0, Σk ak (F11,k + F12,k Δ + F13,k ζ)), F2 = Σk ak (F21,k + F22,k Δ + F23,k ζ).

Smoothing

Each bin weight is the difference of two regStep over 0.01 at its edges: the weights sum to 1 and pass from one bin to the next continuously. The minima, maxima and limits are smooth (smoothMin, smoothMax, smoothLimitInside), and Hdif,hor is bounded below by 0.5·10−4 W/m2 in the clearness.

Parameters

  • lat, lon, timZon: the site and its time zone, Uccle by default.
  • alt: the altitude of the site, in the relative air mass.
  • pAtm: the atmospheric pressure on the bus, constant, the default of Buildings; the runnable model takes the pressure of the altitude of the site when the YAML reads the pressure from the weather file.

Relation to Buildings

The solar position of Buildings.BoundaryConditions.SolarGeometry and the Perez coefficients of Buildings.BoundaryConditions.SolarIrradiation.BaseClasses.

Use

TiltedSurface computes the irradiance on each surface from its bus; Examples.BaseClasses.SyntheticWeather gives it clear days.

Parameters

Parameter Type Unit Default Description
lat Real rad 0.8868 Latitude (Uccle by default)
lon Real rad 0.0760 Longitude (Uccle by default)
timZon Real s 3600 Time zone (offset of the standard time from UTC)
alt Real m 100 Altitude of the site
pAtm Real Pa 101325 Atmospheric pressure, constant (Buildings' default; the runnable model takes the pressure of the site's altitude when the YAML reads the pressure from the weather file)

Revisions

  • October 2026: moved from trano's FastModel.BoundaryConditions.