Function solveForWetBulb

src/utilities/filetypes/EpwFile.cpp:105–146

Using equation 35/37 in ASHRAE Fundamentals 2009 Ch. 1: W = (A W*_s - B)/C where A, B, C, and W*_s are all function of wet bulb t Solve for the root of f = W C - A W*_s + B To make things even more opaque, lets use A = a0 + a1 t B = b (t - t*) C = c0 + c1 t + c2 t

//  C = c0 + c1 t + c2 t*
//
static boost::optional<double> solveForWetBulb(double drybulb, double p, double W, double deltaLimit, int itermax) {
  const double Bp = -1.006;
  const double b = 1.006;
  const double c1t = 1.86 * drybulb;
  double a0 = 2501;
  double a1 = -2.326;
  double c0 = 2501;
  double c2 = -4.186;
  double Ap = -2.326;
  double Cp = -4.186;
  if (drybulb < 0) {
    a0 = 2830;
    a1 = -0.24;
    c0 = 2830;
    c2 = -2.1;
    Ap = -0.24;
    Cp = -2.1;
  }

  int i = 0;
  double tstar = drybulb;
  while (i < itermax) {
    i++;
    const double A = a0 + a1 * tstar;
    const double B = b * (drybulb - tstar);
    const double C = c0 + c1t + c2 * tstar;
    const double pwsstar = psat(tstar);
    const double pwsstarp = psatp(tstar, pwsstar);
    const double deltap = p - pwsstar;
    const double Wsstar = 0.621945 * pwsstar / deltap;
    const double Wsstarp = (0.621945 * pwsstarp * deltap + 0.621945 * pwsstar * pwsstarp) / (deltap * deltap);
    const double f = W * C - A * Wsstar + B;
    const double fp = W * Cp - A * Wsstarp - Ap * Wsstar + Bp;
    const double delta = -f / fp;
    tstar += delta;
    // std::cout << i << " " << tstar << " " << delta / (273.15 + tstar) << '\n';
    if (std::fabs(delta / (273.15 + tstar)) <= deltaLimit) {
      return {tstar};
    }
  }
  return boost::none;
}

// Using equation 38 in ASHRAE Fundamentals 2009 Ch. 1:
//