# The psychrometric chart

(1) Selection of the Coordinates

Horizontal coordinate — Enthalpy (155°)

Vertical coordinate — Humidity Ratio

(2) Dry Bulb Temperature

I = 1.0T + W(2501.3 +1.867) (SI Unit)

7 = const=>7 ocW

Isothermal lines are not parallel. Dry i? u!t temperature

(3) Relative Humiditx’

W = 0-622—~~ <P = — xl00%

P-(p Pv, s Wsp-Ps

Under a certain P, W = f{pv s) pv, = f(T)

From P587 Table A-lb. find W-T relationship

W

Approximately (J) « — x 100% (equal division) (4) Specific Volume

1 _____ L

P P„+Pv

Pv

Pa + Pr=-TZ +

RJ RJ T

Pa_ Pv

R. R.

(5) Wet-Balb Temperature

 Dry tu/t temperature ffj
 Go
 0OVP/WP

 <5O°P0/WP  I = (Cp, a + W Cp, v) Twet + W x 2501 when Twet= const, linear relationship

I = (Cp, a + w Cp, v) Twet + w x 2501 + W iw when <|> * 100%

(6) Sensible Heat /Total Heat

Enthalpy/Humidity ratio

See figure: Primary moist air parameter on the psychrometric chart. For specific pressure: Example

Repeat the previous problem by using the psychrometric chart. Given: Tdiy =30°C, Twet = 26°C

Find: Primary moist air parameter on psychrometric chart Solution: