Psychrometrics Psychrometrics Dry Bulb Temperature DB ºF Air temperature as measured by a thermometer with a dry sensing bulb Relative Humidity RH The moisture content of air expressed as a percent of the maximum moisture at the specified dry bulb temperature ID: 680066
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Slide1
Doug Jefferson, Business Development Engineer
PsychrometricsSlide2
PsychrometricsSlide3
Dry Bulb Temperature (DB, ºF)
Air temperature as measured by a thermometer with a
dry
sensing bulbSlide4
Relative Humidity (RH, %)
The moisture content of air expressed as a percent of the maximum moisture at the specified dry bulb temperatureSlide5
The ratio of the weight of the water to the weight of the dry air.
‘Grains’ of water vapor per pound of dry air.
Humidity Ratio (HR, gr/lb)Slide6
Wet Bulb Temperature (WB, ºF)
Air temperature as measured by a thermometer with a
wet
sensing bulbSlide7
Dew Point Temperature (DP, ºF)
The temperature at which existing moisture will condense from the
air (
forming dew)Slide8
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)Slide9
Vapor Pressure (VP,
″
Hg)
The pressure exerted by the water vapor molecules on the surrounding environmentSlide10
Volume per pound of dry air.
Also referred to as inverse density: (ft
3
/lb)
-1
= lb/ft
3
Specific Volume (ft
3
/lb)Slide11
Psychrometrics ProblemsSlide12
Psychrometric Quiz
1. Given the two conditions, find the remaining.
70
°F DB
50
%RH
°F WB
°F DP
Gr/Lb
″Hg
Btu/Lb
Ft
3
/lb volume
°F DB
%RH
75
°F WB
°F DP
55
Gr/Lb
″Hg
Btu/Lb
Ft
3
/lb volume
75
°F DB
%RH
40
°F WB
°F DP
Gr/Lb
″Hg
Btu/Lb
Ft
3
/lb volume
65
°F DB
%RH
°F WB
20
°F DPGr/Lb″HgBtu/LbFt3/lb volume
58.5
54.7
25.3
50.7
0.37
13.5
45.7
14.9
17.9
16.3
0.10
13.3
122.3
38.1
10.1
50.6
0.37
14.9
2. What is the difference in Temperature, Gr/Lb and Energy between:
74°F DB, 69.3°F WB and 50°F DB, 100% RH
12DeltaTemperature (°F )7450Humidity Ratio (gr/lb)Energy / Enthalpy (Btu/lb)Wet Bulb (°F)69.3Relative Humidity (%)100
24
46.5
13.2
50
100
53.5
33.5
20.3
79.4
19.3
- 20.6Slide13
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)
N
2
= 14x2 =28
H
2
O = 2 x (1) + 16 = 18
18 < 28 therefore clouds float