Function psat

src/utilities/filetypes/EpwFile.cpp:21–45

namespace openstudio {

static double psat(double T) {
  // Compute water vapor saturation pressure, eqns 5 and 6 from ASHRAE Fundamentals 2009 Ch. 1
  // This version takes T in C rather than Kelvin since most of the other eqns use C
  T += 273.15;
  constexpr double C1 = -5.6745359e+03;
  constexpr double C2 = 6.3925247e+00;
  constexpr double C3 = -9.6778430e-03;
  constexpr double C4 = 6.2215701e-07;
  constexpr double C5 = 2.0747825e-09;
  constexpr double C6 = -9.4840240e-13;
  constexpr double C7 = 4.1635019e+00;
  constexpr double C8 = -5.8002206e+03;
  constexpr double C9 = 1.3914993e+00;
  constexpr double C10 = -4.8640239e-02;
  constexpr double C11 = 4.1764768e-05;
  constexpr double C12 = -1.4452093e-08;
  constexpr double C13 = 6.5459673e+00;
  double rhs = 0.0;
  if (T < 273.15) {
    rhs = C1 / T + C2 + T * (C3 + T * (C4 + T * (C5 + T * C6))) + C7 * std::log(T);
  } else {
    rhs = C8 / T + C9 + T * (C10 + T * (C11 + T * C12)) + C13 * std::log(T);
  }
  return exp(rhs);
}

static double psatp(double T, double psat) {
  // Compute the derivative of the water vapor saturation pressure function (eqns 5 and 6 from