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```					WARNING
THIS MATERIAL IS

PROTECTED
PSYCHROMETRICS
A. Psychrometric
Information
1. Psychrometric
psychro – meaning ‘cold’

metrics – meaning ‘measure of’
Actually, psychrometrics is
more than the measurement
of cold. It is a study of all
the properties of moist air.
AIR
DRY               WET
78% Nitrogen     78% Nitrogen
20.9% Oxygen     20.9% Oxygen
1% Argon         1% Argon
.1% Other
.1% Other         Gases
Gases
PLUS
Water Vapor
2. Atmospheric Air
The weight of air pushing down on the
earth is referred to as atmospheric
pressure.

At sea level, the pressure of 70o dry air
is 14.696 lbs/in2(psi).
3. Standard Air
At a barometric pressure of 29.921
inches of mercury (14.696 psi),
one pound of 70o dry air will
occupy 13.33 cubic feet.    Air at
these conditions is known as
standard air.
4. Specific Density
1
Specific Density = ------------------------
Specific Volume

1
= --------- = .075 lbs/ft3
13.33
5. Relationship between Specific
Volume and Specific Density
5. Relationship between Specific
Volume and Specific Density
Specific
Volume

Specific
Density
6. Sensible Heat
If we wish to calculate the Btu’s
needed to raise the temperature of
dry air, we would use the sensible
heat formula.
Sensible Heat Formula
Btu/hr = Sp. Heat x Sp. Density x
60 min/hr x cfm x ΔT

Btu/hr = .24 x .075 x cfm x ΔT

Btu/hr = 1.08 x cfm x ΔT
7. BUT
Moisture is almost always present
in air and has a heat content of its
own.
This is known as latent heat.
8. Total Heat
is

Sensible Heat + Latent Heat
9. Enthalpy
is
the term used to indicate the
total heat content
of one pound of air.
Enthalpy
is
measured with a
wet bulb
thermometer.
10. Total Heat Formula
We use the total heat formula for
changes in BOTH sensible and
latent heat AND it is useful to
determine the capacity of an air
conditioning system.
Total Heat Formula
Btu/hr = Sp. Density x 60 min/hr x
cfm x ΔH

Btu/hr = .075 x 60 x cfm x ΔH

Btu/hr = 4.5 x cfm x ΔH
11. Relative Humidity
is a ratio of the amount of
moisture present in the air to
the amount it can hold at
saturation.
12. Specific Humidity
The amount of moisture present
in the air expressed in grains of
moisture per pound of dry air.
7,000 grains of moisture in
one pound of water.
13. Dew Point
The temperature at which the
water vapor in the air becomes
saturated    and    starts    to
condense into water droplets.
In Summary:

air has the following properties:
• Density(dry or wet)
• Volume
• Sensible Heat
• Latent Heat
and the following measurements can be
found:

• Density
• Volume
• Temperature
• Dry bulb
• Wet bulb
• Dew Point
• Relative Humidity
And now to the

Psychrometric
Chart
The    psychrometric   chart   is
simply a tool that can be used to
determine the properties of moist
air.
Construction

of the

Chart
C. PROCESSES
• Sensible Heat
• Sensible Heat plus Humidification
• Chemical Dehydration
• Sensible Cooling
• Cooling and Dehumidification
• Evaporative Cooling
1. SENSIBLE HEAT PROCESS
Entering Conditions:   69oF dry bulb
o
(return air)     55 F wet bulb

Determine: grains ________(specific humidity)
SENSIBLE HEAT PROCESS
Entering Conditions:   69oF dry bulb
o
(return air)     55 F wet bulb

Determine: grains ___42___(specific humidity)
SENSIBLE HEAT PROCESS
Entering Conditions:   69oF dry bulb
o
(return air)     55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ________oF
SENSIBLE HEAT PROCESS
Entering Conditions:   69oF dry bulb
o
(return air)     55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
SENSIBLE HEAT PROCESS
Entering Conditions:   69oF dry bulb
o
(return air)     55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy ________Btu/lb
SENSIBLE HEAT PROCESS
Entering Conditions:    69oF dry bulb
o
(return air)      55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy __23.22__Btu/lb
SENSIBLE HEAT PROCESS
Entering Conditions:    69oF dry bulb
o
(return air)      55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy __23.22__Btu/lb
relative humidity ______%
SENSIBLE HEAT PROCESS
Entering Conditions:    69oF dry bulb
o
(return air)      55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy __23.22__Btu/lb
relative humidity __40__%
SENSIBLE HEAT PROCESS
Entering Conditions:    69oF dry bulb
o
(return air)      55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy __23.22__Btu/lb
relative humidity __40__%
specific volume ________Ft3/lb.
SENSIBLE HEAT PROCESS
Entering Conditions:    69oF dry bulb
o
(return air)      55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy __23.22__Btu/lb
relative humidity __40__%
specific volume __13.45__Ft3/lb.
SENSIBLE HEAT PROCESS
Entering Conditions:    69oF dry bulb
o
(return air)      55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy __23.22__Btu/lb
relative humidity __40__%
specific volume __13.45__Ft3/lb.
specific density _______lbs/ft3
SENSIBLE HEAT PROCESS
Entering Conditions:     69oF dry bulb
o
(return air)       55 F wet bulb

Determine: grains ___42___(specific humidity)
dew point ___44___oF
enthalpy __23.22__Btu/lb
relative humidity __40__%
specific volume __13.45__Ft3/lb.
specific density __.074__lbs/ft3
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains _______(specific humidity)
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point ______oF
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy ______Btu/lb
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity ______%
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity __18__%
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity __18__%
specific volume ______Ft3/lb.
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity __18__%
specific volume __14.1__Ft3/lb.
SENSIBLE HEAT PROCESS
Leaving Conditions:     95oF dry bulb
(supply air)      64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity __18__%
specific volume __14.1__Ft3/lb.
specific density ______lbs/ft3
SENSIBLE HEAT PROCESS
Leaving Conditions:      95oF dry bulb
(supply air)       64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity __18__%
specific volume __14.1__Ft3/lb.
specific density __.071__lbs/ft3
SENSIBLE HEAT PROCESS
Leaving Conditions:      95oF dry bulb
(supply air)       64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity __18__%
specific volume __14.1__Ft3/lb.
specific density __.071__lbs/ft3
sensible heat factor ______
SENSIBLE HEAT PROCESS
Leaving Conditions:      95oF dry bulb
(supply air)       64.5oF wet bulb

Determine: grains __42__(specific humidity)
dew point __44__oF
enthalpy __29.68__Btu/lb
relative humidity __18__%
specific volume __14.1__Ft3/lb.
specific density __.071__lbs/ft3
sensible heat factor __1.00__
Btu/hr = 1.08 x cfm x ΔT

Btu/hr = 1.08 x 1000 x (95 – 69)

Btu/hr = 1.08 x 1000 x 26

Btu/hr = 28,080
2. COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains _______(specific humidity)
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point ______oF
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy ______Btu/lb
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy __28.94__Btu/lb
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy __28.94__Btu/lb
relative humidity ______%
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy __28.94__Btu/lb
relative humidity __40__%
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy __28.94__Btu/lb
relative humidity __40__%
specific volume ______ Ft3/lb.
COOLING and
DEHUMIDIFICATION
Entering Conditions:    80oF dry bulb
o
(return air)      63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy __28.94__Btu/lb
relative humidity __40__%
specific volume __13.78__ Ft3/lb.
COOLING and
DEHUMIDIFICATION
Entering Conditions:     80oF dry bulb
o
(return air)       63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy __28.94__Btu/lb
relative humidity __40__%
specific volume __13.78__ Ft3/lb.
specific density ______ lbs/ft3
COOLING and
DEHUMIDIFICATION
Entering Conditions:     80oF dry bulb
o
(return air)       63.5 F wet bulb

Determine: grains __61___(specific humidity)
dew point __53.5__oF
enthalpy __28.94__Btu/lb
relative humidity __40__%
specific volume __13.78__ Ft3/lb.
specific density __.073__ lbs/ft3
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains _______(specific humidity)
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point ______oF
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy ______Btu/lb
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity ______%
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity __67__%
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity __67__%
specific volume ______Ft3/lb.
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity __67__%
specific volume __13.24__Ft3/lb.
COOLING and
DEHUMIDIFICATION
Leaving Conditions:     60oF dry bulb
o
(supply air)      53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity __67__%
specific volume __13.24__Ft3/lb.
specific density ______lbs/ft3
COOLING and
DEHUMIDIFICATION
Leaving Conditions:      60oF dry bulb
o
(supply air)       53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity __67__%
specific volume __13.24__Ft3/lb.
specific density __.076__lbs/ft3
COOLING and
DEHUMIDIFICATION
Leaving Conditions:      60oF dry bulb
o
(supply air)       53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity __67__%
specific volume __13.24__Ft3/lb.
specific density __.076__lbs/ft3
sensible heat factor ______
COOLING and
DEHUMIDIFICATION
Leaving Conditions:      60oF dry bulb
o
(supply air)       53.5 F wet bulb

Determine: grains __51__(specific humidity)
dew point __48__oF
enthalpy __22.30__Btu/lb
relative humidity __67__%
specific volume __13.24__Ft3/lb.
specific density __.076__lbs/ft3
sensible heat factor __.75__
Sensible Heat Removed
Btu/hr = 1.08 x cfm x ΔT

Btu/hr = 1.08 x 1600 x (80 – 60)

Btu/hr = 1.08 x 1600 x 20

Btu/hr = 34,560 Btu/hr
TOTAL Heat Removed
Btu/hr = 4.5 x cfm x ΔH

Btu/hr = 4.5 x 1600 x (28.94 – 22.30)

Btu/hr = 4.5 x 1600 x 6.64

Btu/hr = 47,808
qs
SHR = --------
QT

34,560
SHR = -----------
47,808

•SHR = .73
IF
1. You extend the process line through
the 100% saturation line, then
2. the air would be completely saturated
as it leaves the coil, thus
3. the air temperature would be equal to
the coil temperature.
What is that temperature?

o
43 F
a. APPARATUS DEW POINT

The temperature of the air at
which it leaves the coil saturated.

100% RH
What is the temperature at which
the air left our coil?
o
60 F
WHY?
b. BYPASS AIR
Because some of the air was
bypassed and unaffected by the
coil temperature.
This is known as

Bypass Factor
c. Conditions which affect the
BYPASS FACTOR
1. Fin Spacing
2. Number of Rows & Depth of
Coil
3. Type of Fin
4. Velocity of Air
5. If Coil is Wet or Dry
6. Conditions of System
D. NOW
application of

PSYCHROMETRICS
APPLICATION 1

new unit installed in
existing building
3 TON
Day 1 Conditions
o       o
• Entering Air - 80 DB, 73 WB, 72%RH
o   o
• Leaving Air - 68 DB, 65 WB, 85%RH
• Determine:
• Sensible heat
• Latent heat
• Sensible Heat Ratio
Locate these two conditions
on the Psychrometric Chart

o      o
Entering Air - 80 DB, 73 WB
o      o
Leaving Air - 68 DB, 65 WB
Draw a line connecting the two
points.
Draw a vertical line down from the
entering conditions.
Draw a line horizontally to the
right from the leaving conditions.
At the intersection of these two
lines, draw a line upwards
following the wet bulb line until it
crosses the line connecting the
two points.
• NOTE that the VERTICAL            line
• NOTE that the HORIZONTAL line
Where does this point of crossing
occur, in terms of distance from
either point?
SO
Use the SWAG method to determine
the approximate amount of sensible
Another method to determine
the amount of sensible heat to
latent heat is:
1. Locate the 80DB, 67WB reference dot.
2. Place your pencil point on the dot.
3. Lay a straight edge against the pencil
point and use the dot as a pivot point.
4. Rotate the straight edge until it is
5. Read the sensible heat percentage on
the far right of the chart.
NOW
Let us do it again for the ‘Day 2’
conditions.
Day 2 Conditions
o       o
• Entering Air - 80 DB, 67 WB
• Leaving Air - 63oDB, 58oWB
• Determine:
• Sensible heat
• Latent heat
• Sensible Heat Ratio
Locate these two conditions
on the Psychrometric Chart

o      o
Entering Air - 80 DB, 67 WB
o      o
Leaving Air - 63 DB, 58 WB
Draw a line connecting the two
points.
Draw a vertical line down from the
entering conditions.
Draw a line horizontally to the
right from the leaving conditions.
At the intersection of these two
lines, draw a line upwards
following the wet bulb line until it
crosses the line connecting the
two points.
• NOTE that the VERTICAL            line
• NOTE that the HORIZONTAL line
Where does this point of crossing
occur, in terms of distance from
either point?
SO
Use the SWAG method to determine
the approximate amount of sensible
Another method to determine
the amount of sensible heat to
latent heat is:
1. Locate the 80DB, 67WB reference dot.
2. Place your pencil point on the dot.
3. Lay a straight edge against the pencil
point and use the dot as a pivot point.
4. Rotate the straight edge until it is
5. Read the sensible heat percentage on
the far right of the chart.
NOW
Let us do it again for the ‘One
Week Later’ conditions.
One Week Later Conditions
o       o
• Entering Air - 78 DB, 62 WB
o       o
• Leaving Air - 53 DB, 51 WB
• Determine:
• Sensible heat
• Latent heat
• Sensible Heat Ratio
Locate these two conditions
on the Psychrometric Chart

o      o
Entering Air - 78 DB, 62 WB
o      o
Leaving Air - 53 DB, 51 WB
Draw a line connecting the two
points.
Draw a vertical line down from the
entering conditions.
Draw a line horizontally to the
right from the leaving conditions.
At the intersection of these two
lines, draw a line upwards
following the wet bulb line until it
crosses the line connecting the
two points.
• NOTE that the VERTICAL            line
• NOTE that the HORIZONTAL line
Where does this point of crossing
occur, in terms of distance from
either point?
SO
Use the SWAG method to determine
the approximate amount of sensible
Another method to determine
the amount of sensible heat to
latent heat is:
1. Locate the 78DB, 62WB reference dot.
2. Place your pencil point on the dot.
3. Lay a straight edge against the pencil point
and use the dot as a pivot point.
4. Rotate the straight edge until it is parallel
5. Read the sensible heat percentage on the
far right of the chart.
Comparison of Critical Data

DAY 1         DAY 2       ONE WEEK
Temperature   Temperature     LATER
Difference    Difference   Temperature
Difference

12            17            25
Comparison of Critical Data

DAY 1        DAY 2      ONE WEEK
Sensible     Sensible      LATER
Heat Ratio   Heat Ratio    Sensible
Heat Ratio

.43         .62           .86
Comparison of Critical Data

DAY 1         DAY 2       ONE WEEK
Temperature   Temperature     LATER
Difference    Difference   Temperature
Difference

12            17            25
CFM REQUIREMENTS

Temperature DROP
For

COOLING
1. Temperature DROP
o      o
18 – 22
o
Minimum = 15
o
Maximum = 25
2. Application

HIGH
Should the temperature drop be closer
to 15 or 25?
2. Application

HIGH
Should the temperature drop be closer
to 15 or 25?
3. Cooling
Temperature
Splits
(temperature drops)
Outdoor   Indoor   Indoor DB   Indoor DB   Indoor DB
DB      WB oF       75oF        78oF        80oF

59         22          24          25
85oF      63         19          21          23
67         15          17          19

59         21          23          24
95oF      63         18          20          22
67         15          17          19

63         17          20          21
105oF     67         14          17          18
71         11          13          15

63         17          19          21
115oF     67         13          16          17
A17

71         10          13          14
APPLICATION 2
MIXTURE
TEMPERATURES
Mix outdoor air (OA)

with Return Air (RA)

THEN
The Mixture Air (MA)

passes over the coil
QUESTION:

What should be the
temperature of the mixed air?
Problem
Outdoor Ambient Temperature = 95 DB
Return Air Temperature = 78 DB
Required to have:
25% OA
75% RA
Two Methods

1. Formula
2. Psychrometric Chart
Formula
TEMPMA = (%OA x TEMPOA) + (%RA x TEMPRA)

TEMPMA = (.25 x 95) + (.75 x 78)

TEMPMA = 23.75 + 58.5

TEMPMA = 82.25oF
Psychrometric

Chart
1. Plot the following two points on the
chart.
OUTDOOR AIR
95DB, 83WB

RETURN AIR
78DB, 65WB
2. Draw a line between the two points.

3. Locate a point approximately 25%
from the condition which has the
MOST air. Use the SWAG method.

4. That   will    be   the   mixed   air
temperature.
Question:

What if you want to check the
%OA on an existing job?
Problem
Outdoor Ambient Temperature = 95 DB
Return Air Temperature = 78 DB
Mixed Air Temperature = 82.25 DB
Formula

TMA - TRA
%OA = -----------------
TOA - TRA
TMA - TRA
%OA = -----------------
TOA - TRA

82.25 - 78
= ----------------- = .25 or 25%
95 - 78

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