1. Doug Jefferson, Business Development Engineer
Psychrometrics
Doug Jefferson, Business Development Engineer

2. Psychrometrics

3. Dry Bulb Temperature (DB, ºF)
Air temperature as measured by a thermometer with a dry sensing bulb

4. Relative Humidity (RH, %)
The moisture content of air expressed as a percent of the maximum moisture at the specified dry bulb temperature

5. Humidity Ratio (HR, gr/lb)
The ratio of the weight of the water to the weight of the dry air. ‘Grains’ of water vapor per pound of dry air.

6. Wet Bulb Temperature (WB, ºF)
Air temperature as measured by a thermometer with a wet sensing bulb

7. Dew Point Temperature (DP, ºF)
The temperature at which existing moisture will condense from the air (forming dew)

8. Enthalpy (h, Btu/lb)
The total energy of the air, equal to the sensible energy (temperature) plus the latent energy (originally used to evaporate the water in the air)

9. Vapor Pressure (VP, ″Hg)
The pressure exerted by the water vapor molecules on the surrounding environment

10. Specific Volume (ft3/lb)
Volume per pound of dry air.
Also referred to as inverse density: (ft3/lb)-1 = lb/ft3

11. Psychrometrics Problems

12. Psychrometric Quiz 1. Given the two conditions, find the remaining.70
°F DB 50
%RH
°F WB
°F DP
Gr/Lb
″Hg
Btu/Lb
Ft3/lb volume 65
°F DB
%RH
°F WB 20
°F DP
Gr/Lb
″Hg
Btu/Lb
Ft3/lb volume
16.3
58.5
50.7
45.7
54.7
0.37
14.9
0.10
25.3
13.5
17.9
13.3
122.3
°F DB
%RH 75
°F WB
°F DP 55
Gr/Lb
″Hg
Btu/Lb
Ft3/lb volume
10.1 75
°F DB
%RH 40
°F WB
°F DP
Gr/Lb
″Hg
Btu/Lb
Ft3/lb volume
50.6
0.37
38.1
14.9
2. What is the difference in Temperature, Gr/Lb and Energy between:
74°F DB, 69.3°F WB and °F DB, 100% RH 1 2
Delta
Temperature (°F ) 74 50
Humidity Ratio (gr/lb)
Energy / Enthalpy (Btu/lb)
Wet Bulb (°F)
69.3
Relative Humidity (%)
100 24
100
53.5
46.5
33.5
20.3
13.2 50
19.3
79.4
- 20.6

13. Psychrometric Quiz
3. What method of “Conditioning of air” to move between these points?
Cooling
4. Why do clouds float?
Psychrometric: recall psychrometric chart analysis Re: density
Chemical: (70% of air is Nitrogen)
N2 = 14x2 =28
H2O = 2 x (1) + 16 = 18
18 < 28 therefore clouds float