The document discusses psychrometry, which is the study of moist air properties. It outlines 7 fundamental parameters of moist air including total pressure, vapor pressure, specific humidity, relative humidity, enthalpy, specific volume, and degree of saturation. It then describes 5 common psychrometric processes: sensible heating, sensible cooling, cooling and dehumidifying, heating and humidifying, and humidifying. It also discusses adiabatic mixing, sensible heat factor, apparatus dew point, and load ratio line which are important concepts in air conditioning design.

1. Psychrometry
It is the study of the properties of Moist Air or a mixture
of dry air and water vapor.
Fundamental Parameters:
1. TOTAL PRESSURE
P = Pa + Pv KPa
2. VAPOR PRESSURE
Pv = Pw − PA(t d − t w ) KPa
where
A = 6.66 x 10 −4 → For tw equal or greater than 0°C
A = 5.94 x 10 −4 → For tw equal or less than 0°C

2. 3. SPECIFIC HUMIDITY OR HUMIDITY RATIO
0.622Pv kg moisture
W=
P − Pv kgdryair
4. RELATIVE HUMIDITY
Pv
φ=
x 100%
Pd
5. ENTHALPY
KJ
h = 1.0045t d + W(2501 .3 + 1.86t d )
kg dryair

3. 6. SPECIFIC VOLUME
0.287(t d + 273) m3
υ=
(P − Pv )
kgda
7. DEGREE OF SATURATION
 P − Pd 

µ = φ
P − P 
v 

Where
P – total pressure in KPa
Pw – saturation pressure corresponding tw, KPa
Pv – vapor pressure or saturation pressure corresponding
the dry bulb temperature of the water vapor in the
mixture.
Pa – partial pressure of dry air, KPa

4. Pd – saturation pressure corresponding td in KPa
td – dry bulb temperature, °C
tw – wet bulb temperature,°C
φ - relative humidity
W – humidity ratio or specific humidity, kgm/kgda
h – enthalpy, KJ/kgda
υ- specific volume, m3/kgda
µ - degree of saturation

5. Psychrometric Chart
φ
P = 101.325 KPa
h
tW
tdP
W
υ
td

7. Psychrometric Processes or Air conditioning
Processes
1. Sensible Heating – it is addition of heat to moist air
without the addition of moisture. It follows a constant
humidity ratio line on the psychrometric chart.
Q
m
1
t1
h1
m
2
t2
h2

8. h2
h1
1
t1
2
W1 = W 2
t2
Q = m(h2 - h1) → 1
Q = mCp(t2 - t1) → 2
Cp = 1.0045 + 1.86W KJ/kg-C → 3

9. 2. Sensible Cooling: It is the removal of heat from moist air
without the removal of moisture. It also follows a constant
W on the psychrometric chart.
Q
m
1
t1
h1
m
2
t2
h2

10. h1
h2
2
t2
1
W1 = W2
t1
Q = m(h1 – h2) → 1
Q = mCp(t1 – t2) → 2
Cp = 1.0045 + 1.86W KJ/kg-C → 3

11. 3. Cooling and Dehumidifying: It is the removal of heat and
moisture from moist air, it involves sensible and latent
heat transfer.
Q
m
1
t1
h1
m
2
t2
h2
mw
hw

12. h1
1
ha
W1
h2
2
t2
a
t1
Q = m(h1 – h2) - mwhw → 1
mw = m(W1 – W2)→ 2
Q = Q s + QL → 3
W2

13. Qs = mCp(t1 – t2) → 4
Cp = 1.0045 + 1.86W2 → 5
Qs = m(ha – h2) → 6
QL = m(W1 – W2)hfg → 7
QL = m(h1 – ha) → 8
Where:
Qs – sensible heat
QL – latent heat
For air conditioning design
Cp = 1.02 KJ/kg-°C
hfg = 2500 KJ/kg

14. 4. Heating and Humidifying: It is the addition of heat and
moisture to moist air, it also involves sensible and latent
heat transfer.
Q
m
1
t1
h1
m
mw
hw
2
t2
h2

15. h2
2
ha
W2
h1
1
t1
a
t2
Q = m(h2 – h2) - mwhw → 1
mw = m(W2 – W1)→ 2
Q = Q s + QL → 3
W1

16. Qs = mCp(t2 – t1) → 4
Cp = 1.0045 + 1.86W1 → 5
Qs = m(ha – h1) → 6
QL = m(W2 – W1)hfg → 7
QL = m(ha – h1) → 8

17. 5. HUMIDIFYING – It is the addition of moisture to moist
air without the addition of heat.
m
1
t1
h1
m
mw
hw
2
t2
h2

18. hw = h g @ t 1
hw < h g @ t 1
hw = hf @ tw1 or tw2
2
2
2
2
1
m(h2 – h2) = mwhw → 1
mw = m(W2 – W1)→ 2
hw > h g @ t 1

19. h2 − h1
hw =
→3
W2 − W1
. ADIABATIC MIXING – It is the mixing of two streams of
moist air without the addition of heat.
h2
W2
m2
2
m1
1
h1
W1
3
m3
h3
W3

21. m1 + m2 = m3 → 1
m1h1 + m2h2 = m3h3→ 2
m1W1 +m2W2 = m3W3→ 3
m1 h2 − h3 W2 − W3 t 2 − t 3
=
=
=
→4
m2 h3 − h1 W3 − W1 t 3 − t 1
m1 h2 − h3 W2 − W3 t 2 − t 3
=
=
=
→ 5
m 3 h2 − h 1 W 2 − W1 t 2 − t 1
m2 h3 − h1 W3 − W1 t 3 − t 1
=
=
=
→ 6
m 3 h2 − h1 W 2 − W1 t 2 − t 1

22. SENSIBLE HEAT FACTOR
Sensible Heat factor is the ratio of the sensible heat to
the total heat transfer for a process.
QS
SHF =
Q
QS
SHF =
QS +Ql

23. APPARATUS DEW POINT
COOLING AND DEHUMIDIFYING
PROCESS
1
2
tADP
t ADP – apparatus dew point

24. LOAD RATIO LINE
Room air condition
Supply air condition
2
1
For air conditioning design, supply air temperature is within 3°C to 11°C lower
than the room condition.

25. By: ENGR. YURI G. MELLIZA