humidity cal.

[Alex C. Peper]

//humidity equations units inHg and F

double satH20pres(double temp)
{
 double
 c[6]={-4.14483e-3,5.76645e-3,-6.32788e-5,2.12294e-6,-7.85415e-9,6.552
 63e-11};
 double q;
  q = poly( (double)temp,5,c);
  return (q);
 }

double Ferrel(double Tw, double Td, double Pb)
{
       double Pw,Pv,A;

       A = 3.67e-4 * ( (1+ (0.00064 * (Tw-32) ) ) );
       Pw = satH20pres(Tw);
       Pv = Pw-(A * Pb * (Td-Tw));
       return (Pv);
}

double absHum(double Tw, double Td, double Pb)
{
 double H,Pv;

 Pv = Ferrel(Tw,Td,Pb);
 H = (4347.8 * Pv) / (Pb - Pv);
 return (H);
 }

double HumCf(double Tw, double Td, double Pb)
{
 double H,Kh;

       H = absHum(Tw,Td,Pb);
       Kh = 1/( 1- ( 0.0047 * (H-75) ) );
       return (Kh);
}

double relHum(double Tw, double Td, double Pb)
{
 double Pv, Pd,R;

 Pv = Ferrel(Tw,Td,Pb);
 Pd = satH20pres(Td);
 R = Pv / Pd * 100;
 return (R);
}

Alex C Peper
http://www.obd-2.com