text: // EnergyPlus, Copyright (c) 1996-2019, The Board of Trustees of the University of Illinois,
  // The Regents of the University of California, through Lawrence Berkeley National Laboratory
  // (subject to receipt of any required approvals from the U.S. Dept. of Energy), Oak Ridge
  // National Laboratory, managed by UT-Battelle, Alliance for Sustainable Energy, LLC, and other
  // contributors.
  // Copyright (c) 2019, Jason W. DeGraw
  // All rights reserved.
  //
  // NOTICE: This Software was developed under funding from the U.S. Department of Energy and the
  // U.S. Government consequently retains certain rights. As such, the U.S. Government has been
  // granted for itself and others acting on its behalf a paid-up, nonexclusive, irrevocable,
  // worldwide license in the Software to reproduce, distribute copies to the public, prepare
  // derivative works, and perform publicly and display publicly, and to permit others to do so.
  //
  // Redistribution and use in source and binary forms, with or without modification, are permitted
  // provided that the following conditions are met:
  //
  // (1) Redistributions of source code must retain the above copyright notice, this list of
  //     conditions and the following disclaimer.
  //
  // (2) Redistributions in binary form must reproduce the above copyright notice, this list of
  //     conditions and the following disclaimer in the documentation and/or other materials
  //     provided with the distribution.
  //
  // (3) Neither the name of the University of California, Lawrence Berkeley National Laboratory,
  //     the University of Illinois, U.S. Dept. of Energy nor the names of its contributors may be
  //     used to endorse or promote products derived from this software without specific prior
  //     written permission.
  //
  // (4) Use of EnergyPlus(TM) Name. If Licensee (i) distributes the software in stand-alone form
  //     without changes from the version obtained under this License, or (ii) Licensee makes a
  //     reference solely to the software portion of its product, Licensee must refer to the
  //     software as "EnergyPlus version X" software, where "X" is the version number Licensee
  //     obtained under this License and may not use a different name for the software. Except as
  //     specifically required in this Section (4), Licensee shall not use in a company name, a
  //     product name, in advertising, publicity, or other promotional activities any name, trade
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  //     similar designation, without the U.S. Department of Energy's prior written consent.
  //
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  // IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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  // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  // OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  // POSSIBILITY OF SUCH DAMAGE.
  #ifndef PROPERTIES_HPP
  #define PROPERTIES_HPP
  
  #include <algorithm>
  #include <cmath>
  
  namespace airflownetwork {
  
  namespace properties{
  
  struct EnergyPlus
  {
    static constexpr double temperature_0 = 20.0;
    static constexpr double pressure_0 = 101325.0;
    static constexpr double humidity_ratio_0 = 0.0;
    static constexpr double R_0 = 287.0; // Should check that this is used everywhere
  
    static double density(double P, double T, double w)
    {
      return P / (287.0 * (T + 273.15) * (1.0 + 1.6077687 * std::max(w, 1.0e-5)));
    }
  
    static double viscosity(double T)
    {
      return 1.71432e-5 + 4.828E-8 * T;
    }
  };
  
  struct AIRNET
  {
    static constexpr double temperature_0 = 20.0;
    static constexpr double pressure_0 = 101325.0;
    static constexpr double humidity_ratio_0 = 0.0;
    static constexpr double R_0 = 287.055; // Maybe should adjust this to match better
  
    static double density(double P, double T, double)
    {
      return 0.0034838* P / (T + 273.15);
    }
  
    static double viscosity(double T)
    {
      return 1.71432e-5 + 4.828E-8 * T;
    }
  };
  
  struct CONTAM
  {
    static constexpr double temperature_0 = 20.0;
    static constexpr double pressure_0 = 101325.0;
    static constexpr double humidity_ratio_0 = 0.0;
    static constexpr double R_0 = 287.055;
  
    static double density(double P, double T, double)
    {
      return P / (R_0 * (T + 273.15));
    }
  
    static double viscosity(double T)
    {
      return 3.7143e-6 + 4.9286e-8 * T;
    }
  };
  
  struct Fixed
  {
    static constexpr double temperature_0 = 20.0;
    static constexpr double pressure_0 = 101325.0;
    static constexpr double humidity_ratio_0 = 0.0;
    static constexpr double R_0 = 287.055; // Maybe should adjust this to match better
    
    static double density(double, double, double)
    {
      return 1.2041;
    }
  
    static double viscosity(double)
    {
      return 0.0000181625;
    }
  
    static double kinematic_viscosity(double, double, double)
    {
      return 0.0000181625/1.2041;
    }
  };
  
  }
  
  namespace reference {
  const double P = 101325.0;
  const double T = 293.15;
  const double R = 287.055;
  }
  
  /** Density calculated from the ideal gas equation of state
  */
  double ideal_gas_density(double p,  /**< pressure (in Pa) */
    double T, /**< temperature (in K) */
    double w  /**< humidity ratio */
  );
  
  /** Density as calculated by AIRNET
  */
  inline double airnet_density(double P, /**< pressure (in Pa) */
    double T, /**< temperature (in K) */
    double w  /**< humidity ratio */
  );
  
  double airThermConductivity(double T // Temperature in Celsius
  );
  
  /** Sutherland's law for the dynamic viscosity of air
  */
  double sutherland_dynamic_viscosity(double T /**< temperature (in C) */
  );
  
  double airDynamicVisc(double T // Temperature in Celsius
  );
  
  double airKinematicVisc(double T, // Temperature in Celsius
    double W, // Humidity ratio
    double P  // Barometric pressure
  );
  
  //double airThermalDiffusivity(double T, // Temperature in Celsius
  //  double W, // Humidity ratio
  //  double P  // Barometric pressure
  //);
  
  //double airPrandtl(double T, // Temperature in Celsius
  //  double W, // Humidity ratio
  //  double P  // Barometric pressure
  //);
  
  
  //auto& density{ ideal_gas_density };
  //auto& dynamic_viscosity{ sutherland_dynamic_viscosity };
  
  template <typename P> struct State
  {
    State() : temperature(P::temperature_0), pressure(P::pressure_0), humidity_ratio(P::humidity_ratio_0),
      density(P::density(pressure, temperature, humidity_ratio)), sqrt_density(std::sqrt(P::density(pressure, temperature, humidity_ratio))),
      viscosity(P::viscosity(temperature))
    {}
  
    State(double pressure, double temperature, double humidity_ratio) : temperature(temperature), pressure(pressure), humidity_ratio(humidity_ratio),
      density(P::density(pressure, temperature, humidity_ratio)), sqrt_density(std::sqrt(density)),
      viscosity(P::viscosity(temperature))
    {}
  
    void update()
    {
      density = P::density(pressure, temperature, humidity_ratio);
      sqrt_density = std::sqrt(density);
      viscosity = P::viscosity(temperature);
    }
  
    double temperature{ P::temperature_0 };
    double pressure{ P::pressure_0 };  // absolute pressure
    double humidity_ratio{ P::humidity_ratio_0 };
    double density{ P::density(P::pressure_0, P::temperature_0, P::humidity_ratio_0) };
    double sqrt_density{ sqrt(P::density(P::pressure_0, P::temperature_0, P::humidity_ratio_0)) };
    double viscosity{ P::viscosity(P::temperature_0) };
  };
  
  }
  
  #endif // !PROPERTIES_HPP
  