GetTDewPointFromVapPres: Return dew-point temperature given dry-bulb temperature and...

In psychrolib: Psychrometric Properties of Moist and Dry Air

Description

Return dew-point temperature given dry-bulb temperature and vapor pressure.

Usage

GetTDewPointFromVapPres(TDryBulb, VapPres)

Arguments

TDryBulb	A numeric vector of dry-bulb temperature in degreeF [IP] or degreeC [SI]
VapPres	A numeric vector of partial pressure of water vapor in moist air in Psi [IP] or Pa [SI]

Value

A numeric vector of dew-point temperature in degreeF [IP] or degreeC [SI]

Note

• The dew point temperature is solved by inverting the equation giving water vapor pressure at saturation from temperature rather than using the regressions provided by ASHRAE (eqn. 37 and 38), which are much less accurate and have a narrower range of validity.

• The Newton-Raphson (NR) method is used on the logarithm of water vapour pressure as a function of temperature, which is a very smooth function.

• Convergence is usually achieved in 3 to 5 iterations.

• TDryBulb is not really needed here, just used for convenience.

References

ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn. 5 and 6

Examples

SetUnitSystem("IP")
GetTDewPointFromVapPres(70:80, seq(0.0149, 0.0249, 0.001))

SetUnitSystem("SI")
GetTDewPointFromVapPres(70:80, 12581:12591)

psychrolib documentation built on May 29, 2021, 9:11 a.m.