R/psychrometric-graph-sat-w-press.R

In jinlee86/bems_analysisr_package: EDAS System R Package

#' Satuated water vapour pressure (p_ws)
#'
#' Calculates the satuated water vapour pressure over water and ice.
#' Eq.5 & 6 - ASHRAE Fundamentals Handbook 2002, Psychrometrics.
#' @param temp.air Vector of air temperatures [degC].
#' @family PsychrometricGraph
#' @return Returns a vector of satuated water pressure over water and
#'  ice [kPa].
#' @export
#' @examples
#' sat_w_press(temp.air = 25)
#' @author Christoffer Rasmussen
sat_w_press <- function(temp.air) {
  
  
  temp.air <- temp.air + 273.15
  
  # Coefficients for calculating the satuated pressure over water and ice
  c <- c(-5674.5359, 6.3925247, -0.009677843, 6.22157E-07, 2.07478E-09,
         -9.48402E-13, 4.1635019, -5800.2206, 1.3914993, -0.048640239,
         4.17648E-05, -1.44521E-08, 6.5459673)
  
  # Calculate satuated pressure over ice (Eq. 5) and water (Eq. 6)
  sat.w.press <- ifelse(temp.air < 273.15,
                        exp(c[1] / temp.air +
                              c[2] +
                              c[3] * temp.air +
                              c[4] * temp.air ** 2 +
                              c[5] * temp.air ** 3 +
                              c[6] * temp.air ** 4 +
                              c[7] * log(temp.air)),
                        exp(c[8] / temp.air +
                              c[9] +
                              c[10] * temp.air +
                              c[11] * temp.air ** 2 +
                              c[12] * temp.air ** 3 +
                              c[13] * log(temp.air)))
  
  # Return pressure in kPa
  return(sat.w.press / 1000)
}