// Calculate manages calculations that need to be run for each time step
public void Calculate
(
double HGlo // Horizontal Global Irradiance [W/m2]
, double NExtra // Extraterrestrial Normal Irradiance [W/m2]
, double SunZenith // The Zenith position of the sun with 0 being normal to the earth [radians]
)
{
clearnessIndex = Sun.GetClearnessIndex(HGlo, NExtra, SunZenith);
// Clearness correction is treated as a loss for consistency, but made negative so that it has the effect of a gain
clearnessCorrection = -1 * Interpolate.Linear(ClearnessIndexArr, ClearnessCorrectionArr, clearnessIndex);
}
// Calculation method
// There are 6 ways to call the Calculate method; for each, only some of the parameters are required to calculate global, beam and diffuse. The inputs can be
// 1. global horizontal
// 2. global horizontal and diffuse horizontal
// 3. global horizontal and direct horizontal
// 4. global horizontal and direct normal
// 5. diffuse horizontal and direct horizontal
// 6. diffuse horizontal and direct normal
public void Calculate
(
double Zenith // zenith angle of sun [radians]
, double _HGlo = double.NaN // global horizontal irradiance [W/m2]
, double _HDif = double.NaN // diffuse horizontal irradiance [W/m2]
, double _NDir = double.NaN // direct normal irradiance [W/m2]
, double _HDir = double.NaN // direct horizontal irradiance [W/m2]
, double NExtra = double.NaN // normal extraterrestrial irradiance [W/m2]
)
{
// Set all values to an invalid
// Check that at least some of the radiation inputs are properly defined
try
{
// Either HGlo has to be defined, or HDif and one of the two direct components
if (double.IsNaN(_HGlo) && (double.IsNaN(_HDif) || (double.IsNaN(HDir) && double.IsNaN(NDir))))
{
throw new CASSYSException("Splitter: insufficient number of inputs defined.");
}
// If global is defined, cannot have both diffuse and direct defined
if (!double.IsNaN(_HGlo) && !double.IsNaN(_HDif) && ((!double.IsNaN(_HDir)) || !double.IsNaN(_NDir)))
{
throw new CASSYSException("Splitter: cannot specify both diffuse and direct when global is used.");
}
// Cannot have direct normal and direct horizontal defined
if (!double.IsNaN(_HDir) && !double.IsNaN(_NDir))
{
throw new CASSYSException("Splitter: cannot specify both direct normal and direct horizontal.");
}
// If global is defined but neither diffuse and direct are defined,
// then additional inputs are required to calculate them
if (!double.IsNaN(_HGlo) && !double.IsNaN(_HDif) && !double.IsNaN(_HDir) && !double.IsNaN(_NDir))
{
if (NExtra == double.NaN)
{
throw new CASSYSException("Splitter: Extraterrestrial irradiance is required when only global horizontal is specified.");
}
}
}
catch (CASSYSException cs)
{
ErrorLogger.Log(cs, ErrLevel.FATAL);
}
// Calculate cos of zenith angle
double cosZ = Math.Cos(Zenith);
// First case: only global horizontal is defined
// Calculate diffuse using the Hollands and Orgill correlation
try
{
// If only HGlo is specified this case is used, first check the values provided in the program:
if (!double.IsNaN(_HGlo) && double.IsNaN(_HDif) && double.IsNaN(_NDir) && double.IsNaN(_HDir))
{
// Initialize value of HGlo
HGlo = _HGlo;
// If sun below horizon, direct is zero and diffuse is global
// Changed this to sun below 87.5° as high zenith angles sometimes caused problems of
// high direct on tilted surfaces
if (Zenith > 87.5 * DTOR || HGlo <= 0)
{
HDif = HGlo;
HDir = NDir = 0;
}
// Compute diffuse fraction
else
{
double kt = Sun.GetClearnessIndex(HGlo, NExtra, Zenith);
double kd = Sun.GetDiffuseFraction(kt);
kd = Math.Min(kd, 1.0);
kd = Math.Max(kd, 0.0);
// Compute diffuse and direct on horizontal
HDif = HGlo * kd;
HDir = HGlo - HDif;
NDir = HDir / cosZ;
}
// Limit beam normal to clear sky value
// ASHRAE clear sky model (ASHRAE Handbook - Fundamentals, 2013, ch. 14) with tau_b = 0.245, taud = 2.611, a_b = 0.668 and a_d = 0.227
// (these values are from Flagstaff, AZ, for the month of June, and lead to one of the highest beam/extraterrestrial ratios worldwide)
double AirMass = Astro.GetAirMass(Zenith);
double NDir_cs = NExtra * Math.Exp(-0.245 * Math.Pow(AirMass, 0.668));
NDir = Math.Min(NDir, NDir_cs);
HDir = NDir * cosZ;
HDif = HGlo - HDir;
}
// Second case: global horizontal and diffuse horizontal are defined then this
else if (_HGlo != double.NaN && _HDif != double.NaN)
{
// If sun below horizon, direct is zero and diffuse is global
// Changed this to sun below 87.5° as high zenith angles sometimes caused problems of
// high direct on tilted surfaces
if (Zenith > 87.5 * DTOR || _HGlo <= 0)
{
HGlo = _HGlo;
HDif = _HGlo;
HDir = NDir = 0;
}
else
{
HGlo = _HGlo;
HDif = Math.Min(_HGlo, _HDif);
HDir = HGlo - HDif;
NDir = HDir / cosZ;
}
}
// Third case: global horizontal and direct horizontal are defined
else if (_HGlo != double.NaN && _HDir != double.NaN)
{
HGlo = _HGlo;
HDir = Math.Min(_HGlo, _HDir);
HDif = HGlo - HDir;
NDir = HDir / cosZ;
}
// Fourth case: global horizontal and direct normal are defined
else if (_HGlo != double.NaN && _NDir != double.NaN)
{
HGlo = _HGlo;
HDir = Math.Min(HGlo, NDir * cosZ);
HDif = HGlo - HDir;
NDir = HDir / cosZ;
}
// Fifth case: diffuse horizontal and direct horizontal are defined
else if (_HDif != double.NaN && _HDir != double.NaN)
{
HDif = _HDif;
HDir = _HDir;
HGlo = HDif + HDir;
NDir = HDir / cosZ;
}
// Sixth case: diffuse horizontal and direct normal are defined
else if (_HDif != double.NaN && _NDir != double.NaN)
{
HDif = _HDif;
NDir = _NDir;
HDir = NDir * cosZ;
HGlo = HDif + HDir;
}
// Other cases: should never get there
else
{
throw new CASSYSException("Splitter: unexpected case encountered.");
}
}
catch (CASSYSException ex)
{
ErrorLogger.Log(ex, ErrLevel.FATAL);
}
}
