R/psychrometric-graph-hum-ratio-enthalpy.R

In jinlee86/bems_analysisr_package: EDAS System R Package

#' Humidity ratio for enthalpy lines
#'
#' Calculates the humidity ratio based on the enthalpy.
#' Eq. 32 - ASHRAE Fundamentals Handbook 2002, Psychrometrics.
#' @param enthalpy Vector of enthalpies [kJ/kg].
#' @param temp.db Vector of dry bulb temperatures [degC].
#' @family PsychrometricGraph 
#' @return Returns a vector of humidity ratios [kg/kg].
#' @keywords internal
#' @export
#' @examples
#' hum_ratio_enthalpy(enthalpy = 30, temp.db = 25)
#' @author Christoffer Rasmussen

hum_ratio_enthalpy <- function(enthalpy, temp.db, alt = 0) {
 
  # Humidity ratio (eq. 32, solved for W)
  w <- -0.557341 * (temp.db - 0.994036 * enthalpy) / (temp.db + 1385.6)
  
  cut.profile <- sat_hum_ratio(temp.db, alt)
  
  w <- ifelse(w > cut.profile, NA, ifelse(w < 0, NA, w))
  
  return(w)
  
}