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A Trane Air Conditioning Clinic
Psychrometry
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Psychrometry
period one
The Psychrometric Chart
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
PsychrometricChart
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Properties of Air
Dry-bulb temperature
Wet-bulb temperature
Dew-point temperature
Relative humidity
Humidity ratio
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Dry-Bulb Thermometer
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Wet-Bulb Thermometer
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Condensation Occurs at Dew Point
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Fog Occurs When Air Is Saturated
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Relative Humidity
RelativeHumidity
Amount of moisture that a given
amount of air is holding=
Amount of moisture that a given
amount of air can hold
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
50% 100%(saturated)
Relative Humidity
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Humidity Ratio
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Properties of Air
Dry-bulb temperature
Wet-bulb temperature
Dew-point temperature
Relative humidity
Humidity ratio
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Summer Design Conditions
95°F DB (dry bulb)
78°F WB (wet bulb)
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Point of Intersection
95°F
78°F
72°F
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
25°F
30°F
35°F
40°F
45°F
50°F
55°F
19.14
24.19
29.94
36.51
44.34
53.63
64.63
60°F
65°F
70°F
75°F
80°F
85°F
90°F
77.61
92.89
110.82
131.83
156.38
185.03
218.42
dry-bulbtemp.
humidityratio
dry-bulb temp.
humidityratio
Properties of Saturated Air
030
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
Plotting Saturation Points218.42
185.03
156.38
131.83
110.82
92.89
77.61
64.63
53.63
44.34
36.5129.94
24.1919.14
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Saturation Curve
100% relative humidity curve
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Dry Bulb, Wet Bulb and Dew Point
60°Fdew point
60°Fwet bulb
A B C D
dry bulb 60°F 62°F 75°F 90°F
wet bulb 60°F 60.8°F 65.2°F 70°F
dew point 60°F 60°F 60°F 60°F
rel humidity 100% 92% 60% 37%
DCB
A
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Adding Sensible Heat
100% saturation
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
60°Fdew point
60°Fwet bulb
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Relative Humidity Curves
relative humidity
0%30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Properties of Air
humidity ratio
dry bulbrelative humidity
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Determining Wet-Bulb Lines
A
BI
CI
DI
B C D
AI
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Properties of Air
wet bulb
dew point
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
humidity ratio
dry bulbrelative humidity
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Specific Volume
specific volume lines
(cubic feet / pound of dry air)
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Effect of Adding Sensible Heat
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Effect of Removing Sensible Heat
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Effect of Adding Moisture
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Effect of Removing Moisture
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Removing Sensible Heat and Moisture
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Removing Sensible Heat and Moisture
A
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Psychrometry
period two
Air Mixtures
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
supplyfan
mixture outdoorair (OA)
recirculated air (RA)
A
C
B
coolingcoil
Determining Entering Air Conditions
80°F95°F
Determining Entering Air Conditions
B
A
outdoor air
recirculated air
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
1,000 cfm
4,000 cfm = 0.25
OA
RA
mixture
=
=
=
25%
75%
100%
A
C B
4,000 cfmmixed air
1,000 cfmOA
3,000 cfmRA
Determining Entering Air Conditions
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
95°F × 0.25 = 23.75°F
80°F × 0.75 = 60.00°F
mixture = 83.75°F
Determining Entering Air Conditions
83.75°F
70°F
Determining Entering Air Conditions
B
80°F
95°F
C
A
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Psychrometry
period three
Sensible Heat Ratio
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Effect of Removing Sensible Heat
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Effect of Removing Latent Heat
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Removing Sensible and Latent Heat
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
supply air
sensible
heat
latent
heat
return air
Heat and Moisture Transfer
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Removing Sensible and Latent Heat
cooler & damper
warmer & drier
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Heat Gain
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
SHRSensible Heat Gain
Sensible Heat Gain + Latent Heat Gain=
Sensible Heat Ratio (SHR)
78°F DB
65°F WB
index point
Sensible Heat Ratio Scale
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Drawing an SHR Line
A
index point
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
A
SHR Dictates Supply Air Condition
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
C
D
B
80°F
Drawing an SHR Line
index point
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Psychrometry
period four
Air Quantity
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
coil curves
Coil Curves
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
80,000 Btu/hr sensible heat gain
20,000 Btu/hr latent heat gain
STEP 1: Calculate the sensible heat ratio (SHR)
Determining Supply Airflow
= 0.8080,000 Btu/hr
100,000 Btu/hrSHR =
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
room — 78°F DB, 50% RH
outdoor air (OA) — 95°F DB, 78°F WB
ventilation — 25% OA
Determining Supply Airflow
95°F × 0.25 = 23.75°F
78°F × 0.75 = 58.50°F
mixture = 82.25°F
Determining Supply AirflowSTEP 2: Plot room, outdoor, and entering conditions
A
C
B
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
56.5°F 78°F
STEP 3: Identify supply air conditions
A
C
B
D
Determining Supply Airflow
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Sensible Heat Gain
1.085 × (Room DB – Supply DB)
SupplyAirflow
=
STEP 4: Solve the supply airflow equation
Determining Supply Airflow
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
80,000 Btu/hr
1.085 × (78°F – 56.5°F)3,430 cfm=
STEP 4: Solve the supply airflow equation
Determining Supply Airflow
D
A
C B
3,430 cfm
56.5°F DB
55.2°F WB
RA
OA
82.2°F DB
68.6°F WB
mixture
Determining Supply Airflow
SA
56.5°F
DA
C
B
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
47,000 Btu/hr sensible heat gain
20,000 Btu/hr latent heat gain
= 0.7047,000 Btu/hr
67,000 Btu/hrSHR =
Arbitrarily Using 55°F Supply Air
A
C
B
D
55°F
DI
AI
Arbitrarily Using 55°F Supply Air
49°F
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Psychrometry
period five
Tons of Refrigeration
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
What is Enthalpy?
Enthalpy (h) = Sensible Heat + Latent Heat
The total heat energy in one pound of air
(Btu/lb) at its present condition.
Determining Tons of RefrigerationSTEP 1:
Find enthalpies
entering and
leaving coil
A
B
C
D
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Determining Tons of Refrigeration
STEP 2: Solve the total refrigeration load equation
4.5 × Supply Airflow × (h1 – h2)Refrigeration Load (Btu/hr)
=
h1 = enthalpy of air entering coil (Btu/lb)
h2 = enthalpy of air leaving coil (Btu/lb)
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
= 11.8 tons of refrigeration
Determining Tons of Refrigeration
STEP 2: Solve the total refrigeration load equation
4.5 × 3,430 cfm × (32.7 – 23.5) = 142,000 Btu/hr
142,000 Btu/hr
12,000 Btu/hr/ton
Sensible and Latent Coil Loads
A
B
C
D
sensibleload
latentload
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
4.5 × 3,430 cfm × (29.6 – 23.5) = 94,150 Btu/hr
7.8 tons of refrigeration (sensible)
Sensible and Latent Coil Loads
4.5 × 3,430 cfm × (32.7 – 29.6) = 47,850 Btu/hr
4.0 tons of refrigeration (latent)
Psychrometry
period six
Psychrometric Analyses
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
SHR at Full-Load Conditions
56.5°F 78°F
DA
B
C
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
80,000 Btu/hr
80,000 Btu/hr + 20,000 Btu/hr
Full-Load SHR:
= 0.80
47,000 Btu/hr
47,000 Btu/hr + 20,000 Btu/hr = 0.70
SHR Changes with Room Load
Part-Load SHR:
D
A
B
C
SHR at Part-Load Conditions
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
DA
B
CAI
DI
47,000 Btu/hr
1.085 × (78°F – Supply DB)= 3,430 cfm
Supply DB = 65.4°F
65.4°F
SHR at Part-Load Conditions
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
constant quantity of variable-temperature air
OA
RASA
B
D C
A
modulatingcooling coil
Constant-Volume System
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
reheat coil
coolingcoil
roomthermostat
adding reheat improves humidity control
B
E
DC
A
Constant-Volume with Reheat
A
C
B
47,000 Btu/hr
1.085 × (78°F – Supply DB)= 3,430 cfm
Supply DB = 65.4°F
Effect of Adding Reheat
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
D E
65.4°F56.5°F
D E
65.4°F56.5°F
Effect of Adding Reheat
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
A
C
B
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
mixed-air bypass improves humidity control
OA
RA
SA
B
D C
A
face-and-bypass
dampers
Mixed-Air Bypass
Effect of Mixed-Air Bypass
D
A
C
B
E
82.25°F × 0.455 = 37.4°F
51.40°F × 0.545 = 28.0°F
mixture = 65.4°F
65.4°F51.4°F
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Effect of Mixed-Air Bypass
A
C
B
AI
65.4°F51.4°F
D
E
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
OA
RA
SA
B
D
A
C
variable quantity of constant-temperature air
variable-speed drive
Variable-Air-Volume (VAV) System
DA
C
B
47,000 Btu/hr
1.085 × (78°F – 56.5°F)= 2,015 cfm
AI
55.5°F
Calculating Part-Load Airflow
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Software Tools
Psychrometry
period seven
Review
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
Properties of Air
30
Dry-Bulb Temperature (°F)
Hum
idity
Rat
io (
grai
ns/lb
of d
ry a
ir)
25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
20
40
60
80
100
120
140
160
180
200
220
wet bulb
dew point
humidity ratio
dry bulbrelative humidity
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
80°F
95°F
83.75°F
70°F
C
B
A
Determining Mixed-Air Conditions
95°F × 0.25 = 23.75°F
80°F × 0.75 = 60.00°F
mixture = 83.75°F
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
A
Determining Sensible Heat Ratio
SHR = Sensible Heat Gain
Sensible Heat Gain + Latent Heat Gain
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
A
C
B
D
coil curve
Sensible Heat Gain
1.085 × (Room DB – Supply DB)
SupplyAirflow
Determining Coil Leaving Conditions
=
supply DB
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
A
C
B
D
Determining Tons of RefrigerationRefrigeration Load = 4.5 × Supply Airflow × (h1 – h2)
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999
C
OA
RA
B
A
D
SA
PsychrometricAnalysis
A
BCD
Air Conditioning Clinic TRG-TRC001-EN© American Standard Inc. 1999