Humidity
Robert Fehr
Professor Emeritus
Department of Biosystems and Agricultural Engineering
University of Kentucky
WATER VAPOR PROPERTIES
WATER
(liquid state)
144 btu/lb
970 btu/lb
sublimation
ICE
(solid state)
1223 btu/lb
VAPOR
(gas state)
Definitions
Humidity: The amount of water vapor in the air
Relative humidity: The amount of water vapor
actually in the air divided by the amount of
water vapor the air can hold.
Saturation of air: The condition under which the
amount of water vapor in the air is the
maximum possible at the existing temperature
and pressure. 100% Relative Humidity
Definitions
Wet bulb temperature: The lowest temperature
that can be obtained by evaporating water into
the air at constant pressure.
Dew point: the temperature air would have to
be cooled to in order for saturation to occur.
Psychometrics Basic Concepts
Saturation Line
PSYCHROMETRIC CHART
Lexington, Kentucky USA
210
BAROMETRIC PRESSURE 28.874 inches of Mercury
200
190
180
170
160
140
130
120
110
Staturation Line
100
90
80
70
60
50
40
30
20
10
0
5
10
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
65
DRY BULB TEMPERATURE - °F
70
75
80
85
90
95
100
105
110
115
120
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
Constant Dry Bulb Temperature
PSYCHROMETRIC CHART
Lexington, Kentucky USA
210
BAROMETRIC PRESSURE 28.874 inches of Mercury
200
190
180
170
160
140
130
Constant Dry Bulb Temperature
120
110
100
90
80
70
60
50
40
30
20
10
0
5
10
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
65
DRY BULB TEMPERATURE - °F
70
75
80
85
90
95
100
105
110
115
120
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
Constant Relative Humidity
PSYCHROMETRIC CHART
Lexington, Kentucky USA
210
BAROMETRIC PRESSURE 28.874 inches of Mercury
200
190
180
170
160
140
130
Constant Relative Humidity
120
110
100
90
%
90
%
80
%
80
70
60
70
60
%
50
50
%
40
40
%
30
30%
20
20%
HUMIDITY
LATIVE
10% RE
0
5
10
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
65
DRY BULB TEMPERATURE - °F
70
75
10
80
85
90
95
100
105
110
115
120
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
Constant Humidity Ratio
PSYCHROMETRIC CHART
Lexington, Kentucky USA
210
BAROMETRIC PRESSURE 28.874 inches of Mercury
200
190
180
170
160
140
130
Constant Humidity Ratio
120
110
100
90
80
70
60
50
40
30
20
10
0
5
10
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
65
DRY BULB TEMPERATURE - °F
70
75
80
85
90
95
100
105
110
115
120
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
Constant Humidity Ratio
PSYCHROMETRIC CHART
Lexington, Kentucky USA
210
BAROMETRIC PRESSURE 28.874 inches of Mercury
200
190
180
170
160
Saturation Line
Constant Humidity Ratio
Dew
Point
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
5
10
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
65
DRY BULB TEMPERATURE - °F
70
75
80
85
90
95
100
105
110
115
120
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
Constant Wet Bulb Temperature
Dew Point
Dew Point
Humidity Ratio
Psychometrics of Heating
Psychometrics of Cooling
180
85
W
ET
B
Annual Hourly Outside Air Conditions – Lexington KY
UL
B
80
170
TE
MP
ER
AT
U
RE
160
-°
F
140
75
130
1 5 .0
75
120
70
110
70
100
65
90
90
%
80
55
70
%
30
35
25
10
10% RELA
MIDITY
TIVE HU
10
1 2 .5
5
15
10
5
0
0
20
10
20
20%
1 3 .0
25
15
5
30%
30
20
0%
30
1 3 .5
40
40
IR
4
35
%
50
A
RY
50
45
60
FD
/lb O
%
50
1 4 .0
60
45
70
ft³
ME
50
40
60
OLU
IC V
55
80
CI F
SPE
%
60
1 4 .5
65
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
DRY BULB TEMPERATURE - °F
65
70
75
80
85
90
95
100
105
110
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
80
180
85
W
ET
B
Annual Hourly Outside Air Conditions – Lexington KY
UL
B
80
170
TE
MP
ER
AT
U
RE
160
-°
F
140
75
130
1 5 .0
75
120
70
110
70
100
65
90
90
%
80
55
70
%
30
35
25
10
10% RELA
MIDITY
TIVE HU
10
1 2 .5
5
15
10
5
0
0
20
10
20
20%
1 3 .0
25
15
5
30%
30
20
0%
30
1 3 .5
40
40
IR
4
35
%
50
A
RY
50
45
60
FD
/lb O
%
50
1 4 .0
60
45
70
ft³
ME
50
40
60
OLU
IC V
55
80
CI F
SPE
%
60
1 4 .5
65
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
DRY BULB TEMPERATURE - °F
65
70
75
80
85
90
95
100
105
110
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
80
180
85
W
ET
B
Annual Hourly Outside Air Conditions – Lexington KY
UL
B
80
170
TE
MP
ER
AT
U
RE
160
-°
F
140
75
130
1 5 .0
75
120
70
110
70
100
65
90
90
%
80
55
70
%
30
35
25
10
10% RELA
MIDITY
TIVE HU
10
1 2 .5
5
15
10
5
0
0
20
10
20
20%
1 3 .0
25
15
5
30%
30
20
0%
30
1 3 .5
40
40
IR
4
35
%
50
A
RY
50
45
60
FD
/lb O
%
50
1 4 .0
60
45
70
ft³
ME
50
40
60
OLU
IC V
55
80
CI F
SPE
%
60
1 4 .5
65
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
DRY BULB TEMPERATURE - °F
65
70
75
80
85
90
95
100
105
110
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
80
180
85
W
ET
B
Annual Hourly Outside Air Conditions – Lexington KY
UL
B
80
170
TE
MP
ER
AT
U
RE
160
-°
F
140
75
130
1 5 .0
75
120
70
110
70
100
65
90
90
%
80
55
70
%
30
35
25
10
10% RELA
MIDITY
TIVE HU
10
1 2 .5
5
15
10
5
0
0
20
10
20
20%
1 3 .0
25
15
5
30%
30
20
0%
30
1 3 .5
40
40
IR
4
35
%
50
A
RY
50
45
60
FD
/lb O
%
50
1 4 .0
60
45
70
ft³
ME
50
40
60
OLU
IC V
55
80
CI F
SPE
%
60
1 4 .5
65
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
DRY BULB TEMPERATURE - °F
65
70
75
80
85
90
95
100
105
110
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
80
180
85
W
ET
B
Annual Hourly Outside Air Conditions – Lexington KY
UL
B
80
170
TE
MP
ER
AT
U
RE
160
-°
F
140
75
130
1 5 .0
75
120
70
110
70
100
65
90
90
%
80
55
70
%
30
35
25
10
10% RELA
MIDITY
TIVE HU
10
1 2 .5
5
15
10
5
0
0
20
10
20
20%
1 3 .0
25
15
5
30%
30
20
0%
30
1 3 .5
40
40
IR
4
35
%
50
A
RY
50
45
60
FD
/lb O
%
50
1 4 .0
60
45
70
ft³
ME
50
40
60
OLU
IC V
55
80
CI F
SPE
%
60
1 4 .5
65
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
DRY BULB TEMPERATURE - °F
65
70
75
80
85
90
95
100
105
110
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
80
180
85
W
ET
B
Annual Hourly Outside Air Conditions – Lexington KY
UL
B
80
170
TE
MP
ER
AT
U
RE
160
-°
F
140
75
130
1 5 .0
75
120
70
110
70
100
65
90
90
%
80
55
70
%
30
35
25
10
10% RELA
MIDITY
TIVE HU
10
1 2 .5
5
15
10
5
0
0
20
10
20
20%
1 3 .0
25
15
5
30%
30
20
0%
30
1 3 .5
40
40
IR
4
35
%
50
A
RY
50
45
60
FD
/lb O
%
50
1 4 .0
60
45
70
ft³
ME
50
40
60
OLU
IC V
55
80
CI F
SPE
%
60
1 4 .5
65
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
DRY BULB TEMPERATURE - °F
65
70
75
80
85
90
95
100
105
110
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
80
App for Air Properties
Moisture Balance
Moisture Added
People, Animals, Plants,
Foundation
Outside Air Entering
@ Outside Conditions
Moisture Stored
Fabric, Carpet, Wood
Moisture Removed
Dehumidifier
Inside Air Leaving
@ Inside Conditions
Winter Moisture Balance
Moisture Added
People, Animals, Plants,
Foundation
Outside Air Entering
@ Outside Conditions
32F 85% = 78 lbw/day
0.80 ACHn
Moisture Stored
Fabric, Carpet, Wood
Moisture Removed
Dehumidifier
134 lbw/day drying potential
Inside Air Leaving
@ Inside Conditions
70f 60% = 212 lbw/day
Winter Moisture Balance
Moisture Added
People, Animals, Plants,
Foundation
Outside Air Entering
@ Outside Conditions
53F 85% = 174 lbw/day
0.80 ACHn
Moisture Stored
Fabric, Carpet, Wood
Moisture Removed
Dehumidifier
38 lbw/day drying potential
Inside Air Leaving
@ Inside Conditions
70f 60% = 212 lbw/day
Winter Moisture Balance
Moisture Added
People, Animals, Plants,
Foundation
Outside Air Entering
@ Outside Conditions
53F 85% = 85 lbw/day
0.40 ACHn
Moisture Stored
Fabric, Carpet, Wood
Moisture Removed
Dehumidifier
21 lbw/day drying potential
Inside Air Leaving
@ Inside Conditions
70F 60% = 106 lbw/day
Summer Moisture Balance
Moisture Added
People, Animals, Plants,
Foundation
Outside Air Entering
@ Outside Conditions
85F 50% = 283 lbw/day
0,80 ACHn
Moisture Stored
Fabric, Carpet, Wood
Moisture Removed
Dehumidifier
27 lbw/day added
Inside Air Leaving
@ Inside Conditions
76F 60% = 256 lbw/day
Sources of Moisture
• People
– Respiration
– Transpiration
•
•
•
•
Pets
Plants
Showers and Bathing
Dishwashing, and Cooking
– 0.1 lb of water per ft3 of NG
Sources of Moisture
• Foundations
– Difficult to quantify
Effect of Humidity on Moisture Production
Sources of Moisture - People
Design Residential Moisture Generation Rates
(TenWolde and Walker 2001)
Number of Number of Moisture Generation Rate
Bedrooms Occupants lb/h lb/day gallon/day
1
2
0.7 16.8
2.01
2
3
1.1 26.4 `
3.17
3
4
1.3 31.2
3.74
4
5
1.4 33.6
4.03
Additional +1
+0.1 2.4
0.29
per bedroom
Sources of Moisture - Plants
• Potted flowers: 0.011–0.022 lb/h
• Potted plants: 0.015–0.033 lb/h
• Medium-size rubber plant: 0.022–0.044 lb/h
Sources of Moisture - Pets
It is a function of the weight of the animal.
• A medium-size dog weighing 22 lb contributes
about 0.015 lb/h, 0.36 lb/day, 0.043
gallons/day
Sources of Moisture – Showers and Baths
• 5.7 lb/h for showers
– 5 minute shower = 0.475 lbs
– 15 minute shower = 1.425 lbs
• 1.5 lb/h for baths
– 5 minute bath = 0.125 lbs
– 15 minute bath = 0.375 lbs
Suggested Dehumidifier Size
Pints per day of Dehumidifier Capacity
Source: Association of Home Appliance Manufacturers
Humidity Level vs Ventilation Rate
The Effect of Indoor Humidity on
Water Vapor Release in Homes
Anton TenWolde Crystal L. Pilon
ASHREA 2007
Older House
0.8 ACHn
0.4 ACHn
New House
0.35 ACHn
0.20 ACHn
Recommended Humidity Levels
Soruce: American Society of Heating, Refrigerating
and Air Conditioning Engineers (ASHRAE).
Surface Condensation
• Occurs when surface is cooler than the dew
point of the surrounding air
• Temperature of interior surfaces is dependent
on:
– Air temperatures on both inside and outside
– Heat transmittance of assembly
Surface Condensation
• Raising the R value of a assembly
– Increases the inside surface temperature
– Reduces the condensation hazard
Concealed Condensation
• In cold temperatures, production of vapor
inside an occupied building normally raised
the vapor pressure
– Difference for interior pressure to exterior
pressure cause vapor diffusion into exterior walls
and ceilings
– Vapor has no where to escape
• As the temperature drops, condensation begins.
When is Condensation an Issue
• Cooler climates in occupied, heated buildings
• Humid, warm climates in air-conditioned
buildings
Why is Condensation an Issue
Water is the
DEATH
of a building
…after a FIRE
Window Temperature Profile
70
60
66%
50
44%
40
30
20
14%
10
0
Single Pane
Double Pane
Double Pane, low-E, Argon
Uninsulated Wall Temperature Profile
70
60
50
40
30%
30
20
10
0
Brick
OSB Wall Cavity
Air Space
Gypsum Board
Insulated Wall Temperature Profile
70
60
50
40
30
20
10
0
9%
Brick
OSB Cavity Insulation
Air Space
Gypsum Board
Vapor Retarders & Barriers
• Impedes the passage of water vapor into a
building assembly before it can condense into a
liquid
• Prevents water vapor from penetrating into
concealed space of exterior construction
• Used on roofs, wall, and concrete slabs
Moisture Migration Into Walls
Source:
Building Science Corporation
Rain Event Creates Vapor Pressures
Exterior Conditions
Temperature 80 °F
Relative Humidity 75%
Vapor Pressure 2.49 kPa
Conditions within Cavity
Temperature 100 °F
Relative Humidity 100%
Vapor Pressure 6.45 kPa
Interior Conditions
Temperature 75 °F
Relative Humidity 60%
Vapor Pressure 1.82 kPa
Solar radiation strikes wall
Brick veneer is saturated
with rainwater
1-inch air space
Felt paper
Fiberboard sheathing
Vapor is driven both
inward and outward by a
high vapor pressure
differential between the
brick and the interior and
the brick and the exterior
Fiberglass insulation
Polyethylene
Interior gypsum board
Source:
Building Science Corporation
Measuring Air Moisture Content
•
•
•
•
•
•
Chilled mirror dew point hygrometers
Capacitive humidity sensors
Resistive humidity sensors
Thermal conductivity humidity sensors
Physical change sensors
Psychrometers
– (Wet and Dry Bulb Thermometers)
Human Hair Hygrometer
Swing Psychrometer
Sling Psychrometer Scale
Wet Bulb Depression Table
Relative Humidity - RH (%)
Dry Bulb Temperature - Tdb (oF)
Difference
Between Dry
Bulb
and Wet Bulb
Temperatures
Tdb - Twb
(oF)
1
2
3
4
5
6
7
8
9
10
60
64
68
72
76
80
84
88
94
90
84
78
73
68
63
58
54
49
95
90
85
80
75
70
66
61
57
52
95
90
85
81
76
72
67
63
59
55
95
91
86
82
78
73
69
65
61
57
96
91
87
83
79
75
71
67
63
59
96
92
88
84
80
76
72
68
65
61
96
92
88
84
80
77
73
70
66
63
96
92
89
85
81
78
74
71
68
64
Temperature and RH Logger
Using a Room Dehumidifier
Large Room
Dehumidifier
Using a Room Dehumidifier
Inside Duct
Large Room Dehumidifier
Dehumidification
• Primary – Air Conditioner
– Size
• Runtime
– SHR (Sensible Heat Ratio)
• Varies with Web Bulb Temperature (RH)
– Two Speed
• Typically 1 ton less at low speed
Air Sealing and Runtime
0.80 ACHn
0.40 ACHn
Psychometrics of Cooling
Whole House Dehumidifier
Homeywell TrueDRY™
Dehumidifier Performance
Capacity:
• 21 pints/day (60 ºF [15.6 ºC], 60 %RH) = 21.9 lbw/day
• 42 pints/day (70 ºF [21.1 ºC], 60 %RH) = 43.8 lbw/day
• 65 pints/day (80 ºF [26.7 ºC], 60 %RH) = 67.8 lbw/day
Energy Performance:
• 4.7 pints per kilowatt hour (KWH)
– 4.903 pounds per KWH
Dehumidifier Components
Source:
Homeywell TrueDRY™
Whole House Dehumidifier Installation Options
Source:
Homeywell TrueDRY™
Desiccant Dehumidifier
Source:
Novelaire ComfortPlus™ 300
Combined Desiccant and DX Cooling
Desiccant Dehumidifier
Source:
Novelaire ComfortPlus™ 300
Evaporator
Condenser
Economizers for Humidity Control
Ventilation for Moisture Control
180
85
W
ET
B
Annual Hourly Outside Air Conditions – Lexington KY
UL
B
80
170
TE
MP
ER
AT
U
RE
160
-°
F
140
75
130
1 5 .0
75
120
70
110
70
100
65
90
90
%
80
55
70
%
30
35
25
10
10% RELA
MIDITY
TIVE HU
10
1 2 .5
5
15
10
5
0
0
20
10
20
20%
1 3 .0
25
15
5
30%
30
20
0%
30
1 3 .5
40
40
IR
4
35
%
50
A
RY
50
45
60
FD
/lb O
%
50
1 4 .0
60
45
70
ft³
ME
50
40
60
OLU
IC V
55
80
CI F
SPE
%
60
1 4 .5
65
15
20
25
Linric Company Psychrometric Chart, www.linric.com
30
35
40
45
50
55
60
DRY BULB TEMPERATURE - °F
65
70
75
80
85
90
95
100
105
110
HUMIDITY RATIO - GRAINS OF MOISTURE PER POUND OF DRY AIR
150
80
QUESTIONS