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					WARNING
THIS MATERIAL IS

COPYRIGHT
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__
  Sensible Heat Added
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
  represents the latent load, and
• NOTE that the HORIZONTAL line
  represents the sensible load.
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
load and latent load you have.
 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
  parallel to your original line.
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
  represents the latent load, and
• NOTE that the HORIZONTAL line
  represents the sensible load.
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
load and latent load you have.
 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
  parallel to your original line.
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
  represents the latent load, and
• NOTE that the HORIZONTAL line
  represents the sensible load.
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
load and latent load you have.
 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
   to your original line.
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
   Building with Sensible Load

               HIGH
Should the temperature drop be closer
            to 15 or 25?
        2. Application
    Building with Latent Load

               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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posted:3/29/2013
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