1. PSYCHROMETRICS ...WITHOUT TEARS Professor Eugene Silberstein, CMHE
SUFFOLK COUNTY COMMUNITY COLLEGE – BRENTWOOD, NY
CENGAGE DELMAR LEARNING – CLIFTON PARK, NY
HVAC EXCELLENCE INSTRUCTOR CONFERENCE LAS VEGAS, NEVADA
MARCH 20-22, 2011

2. What Makes Psychrometrics so Painful for our Students?
Unfortunately, most of the time it’s us!

3. How Do We Introduce the Topic?
You guys are going to hate this
This stuff is really difficult
This involves a ton of math
You’re not going to understand this but it’s okay because I don’t either
I hate it, so you will also

4. “This is really going to hurt!”

5. TEACHING PSYCHROMETRICS IS A LOT LIKE COMMERCIAL FISHING...

6. How Much Does the Air in this Room Weigh?
0 pounds? pounds? pounds?
100 pounds? pounds?
500 pounds? pounds? pounds?
THE ANSWER MIGHT SURPRISE YOU...
(I Hope It Does!)

7. Room Dimensions... Length: 66 feet Width: 46 feet
Ceiling Height: 20 feet
Room Volume: 66 x 46 x 20 = 60,720ft3
Based on this volume, the air in this room weighs approximately:
60,720 ft3 x lb/ft3 = 4,554 POUNDS

10. The First Four Things... Dry-Bulb Temperature Wet-Bulb Temperature
Absolute Humidity
Relative Humidity

11. TEMPERATURES: WET & DRY
Are all temperatures created equal?
Are all pressures created equal?
What is the difference between psia and psig?
How do we teach our students the difference?
How are wet/dry bulb temperatures similar?
How are wet/dry bulb temperatures different?
Can we create visual examples?

12. Dry Bulb Temperature Measured with a dry-bulb thermometer
Measures the level of heat intensity of a substance
Used to measure and calculate sensible heat and changes in sensible heat levels
Does not take into account the latent heat aspect
Room thermostats measure the level of heat intensity in an occupied space

13. DRY-BULB TEMPERATURE SCALE
As we move up and down, the dry bulb temperature does not change
As we move from left to right, the dry bulb temperature increases
As we move from right to left, the dry bulb temperature decreases
DRY-BULB TEMPERATURE

14. Wet Bulb Temperature Measured with a wet-bulb thermometer
Temperature reading is affected by the moisture content of the air
Takes the latent heat aspect into account
Used in conjunction with the dry-bulb temperature reading to obtain relative humidity readings and other pertinent information regarding an air sample

15. WET-BULB TEMPERATURE SCALE
As we move up and down along a wet-bulb temperature line, the wet bulb temperature does not change
The red arrow indicates an increase in the wet bulb temperature reading
The blue arrow indicates a decrease in the wet bulb temperature reading
WET BULB TEMPERATURE

16. WET-BULB, DRY-BULB COMBO
WET BULB TEMPERATURE
DRY-BULB TEMPERATURE

17. SLING PSYCHROMETER

18. 65 70 75
100% 75
80%
WET BULB TEMPERATURE
WET BULB TEMPERATURE 70 68
60% 65
DRY BULB TEMPERATURE

19. ---- HUMIDITY ---- ABSOLUTELY RELATIVE
There are two types of humidity
ABSOLUTE
RELATIVE
“AH” and “RH” are not the same
Cannot be used interchangeably
All humidities are not created equal

20. ABSOLUTE HUMIDITY Amount of moisture present in an air sample
Measured in grains per pound of air
7,000 grains of moisture = 1 pound
60 GRAINS
1 POUND

21. The moisture scale on the right-hand side of the chart provides information regarding the absolute humidity of an air sample

22. MOISTURE CONTENT SCALE
As we move from side to side, the moisture content does not change
As we move up, the moisture content increases
As we move down, the moisture content decreases
MOISTURE CONTENT (BTU/LBAIR)

23. WET-BULB, DRY BULB & MOISTURE CONTENT
DRY-BULB TEMPERATURE
WET BULB TEMPERATURE

24. RELATIVE HUMIDITY
Amount of moisture present in an air sample relative to the maximum moisture capacity of the air sample
Expressed as a percentage
Can be described as the absolute humidity divided by the maximum moisture-holding capacity of the air

25. RELATIVE HUMIDITY % FULL = 10 CARS 20 SPACES X 100% % FULL = # of CARS
Example #1
HOW FULL IS THE PARKING LOT?
% FULL =
10 CARS
20 SPACES X
100%
% FULL =
# of CARS
# of SPACES X
100%
% FULL = 0.5 X 100%
% FULL = 50%

26. RELATIVE HUMIDITY
Example #2

28. RELATIVE HUMIDITY Example #3
60 GRAINS
If capacity is 120 grains, then the relative humidity will be:
RH = (60 grains ÷ 120 grains) x 100% = 50%

29. RELATIVE HUMIDITY SCALE
As we move along a relative humidity line, the relative humidity remains the same
As we move up, the relative humidity increases
As we move down, the relative humidity decreases

30. WET-BULB, DRY BULB, MOISTURE CONTENT & RELATIVE HUMIDITY
DRY-BULB TEMPERATURE
WET BULB TEMPERATURE

31. The lines that represent constant wet-bulb temperature also represent the enthalpy of the air

32. ENTHALPY SCALE
As we move up and down along an enthalpy line, the enthalpy does not change
The red arrow indicates an increase in enthalpy
The blue arrow indicates a decrease in enthalpy

33. WET-BULB, DRY BULB, MOISTURE CONTENT, RELATIVE HUMIDITY & ENTHALPY
DRY-BULB TEMPERATURE

34. SPECIFIC VOLUME & DENSITY
Specific volume and density are reciprocals of each other
Density = lb/ft3
Specific volume = ft3/lb
Density x Specific Volume = 1
Specific volume can be determined from the psychrometric chart, density muse be calculated

35. LINES OF SPECIFIC VOLUME
As we move along a line of constant specific volume, the specific volume remains unchanged
As we move to the right, the specific volume increases
As we move to the right, the specific volume increases
ft3/lb

36. WET-BULB, DRY BULB, MOISTURE CONTENT, RELATIVE HUMIDITY & ENTHALPY
DRY-BULB TEMPERATURE

38. Return Air: 75ºFDB, 50% r.h.
Supply Air: 55ºFDB, 90% r.h.
Airflow: 1200 cfm
RETURN AIR
SUPPLY AIR

39. ΔT = Return Air Temp – Supply Air Temp
ΔT = 75ºF - 55ºF = 20ºF
ΔW = Return grains/lbAIR – Supply grains/lbAIR
ΔW = 64 Grains – 60 Grains = 4 grains/lbAIR
Return Air: 75ºFDB, 50% r.h.
Supply Air: 55ºFDB, 90% r.h.
Airflow: 1200 cfm
Δh = Return btu/lbAIR – Supply btu/lbAIR
Δh = 28.1 btu/lbAIR btu/lbAIR = 6.5 btu/lbAIR
h = 28.1 btu/lbAIR
h = 21.6 btu/lbAIR
RETURN AIR
64 grains/lb
60 grains/lb
SUPPLY AIR
55ºF ºF

40. Yeah, yeah, but where do they come from?
AIR FORMULAE
QT = QS + QL
QT = 4.5 x cfm x Δh
Qs = 1.08 x cfm x ΔT
QL = 0.68 x cfm x ΔW
Yeah, yeah, but where do they come from?

41. ON PLANET ENEGUE...

42. 100 x 24 x 365 x 5280 x 12 x 2.54 x 10 mm/year, which is....
100 MILES
24 HOURS
DAY
365 DAYS
YEAR
5280 FEET
MILE X X X
HOUR
100 x 24 x 365 x 5280 FEET
YEAR
12 IN FT
2.54 cm
INCH
10 mm cm X X X
So, my rate of speed was...
100 x 24 x 365 x 5280 x 12 x 2.54 x 10 mm/year, which is....
1,409,785,344,000 mm/year!

43. Try These Ideas for Your Students
If your car get 30 miles per gallon, how many inches per ounce will you be able to travel?
If you earn $15/Hour, how many pennies per year will you earn in a year if you work 40 hours per week and 50 weeks per year?
If air weight lb per cubic foot how many ounces per cubic inch is that?

44. Let Students Take Ownership
Ask the right questions
Let the students “create” a formula
Let students identify relevant factors that should be included in the formula
Let students identify relevant conversion factors that should be included

45. Total Heat Formula We all know QT = 4.5 x CFM x Δh
Where does the 4.5 come from?
Work with the units
QT (btu/hour)
What factors will contribute to get this result
Factors must be relevant to sensible heat
For example, grains/pound is not a relevant term as it applies to latent heat

46. Let the students “BUILD” the Sensible Heat Formula...
Total Heat Formula
QT (btu/hour)= 4.5 x CFM x Δh
Units on the right must be the same as the units on the left
Let the students “BUILD” the Sensible Heat Formula...

47. Heat Formulae Variables
So, ask your students what variables and factors will have an effect on the amount of heat transferred by the process
ΔW?
60 MIN = 1 HOUR?
CFM?
ΔT?
Δh?
SPECIFIC VOLUME?
SPECIFIC HEAT?

48. Total Heat Formula We have btu/hour on the left...
btu/hour = ? x ? x ? x ? x ?
Which factor, Δh, ΔW, or ΔT, is associated with the total heat?
btu/hour = Δh (btu/lbAIR) x ? x ? x ? x ?
Which other factors are associated with the total heat?

49. Total Heat Formula btu/hr = 60 x (btu x ft3)/hour x lbAIR x ?
btu/hr = Δh (btu/lbAIR) x ? x ? x ? x ?
Airflow
btu/hr = Δh (btu/lbAIR) x ft3/min x ? x ?
btu/hr = Δh (btu/lbAIR) x ft3/min x 60 min/hr
btu/hr = 60 x (btu x ft3)/hour x lbAIR x ?

50. Density btu/hr = 60 x (btu x ft3)/hour x lbAIR x ?
We need to get rid of the ft3 in the numerator and the lbAIR in the denominator...
What factor relating to air has ft3 in the denominator and lb in the denominator?
Density
btu/hr = 60 x (btu x ft3)/hour x lbAIR x lb/ft3

51. Total Heat Formula btu/hr = 60 x 0.075 btu/hour
Density = lb/ft3 at atmospheric conditions
btu/hr = 60 x btu/hour
QT (btu/hr) = 4.5 x Airflow x Δh

52. Sensible Heat Formula We all know QS = 1.08 x CFM x ΔT
Where does the 1.08 come from?
Work with the units
QS (btu/hour)
What factors will contribute to get this result
Factors must be relevant to sensible heat
For example, grains/pound is not a relevant term as it applies to latent heat

53. Sensible Heat Formula btu/hour = 4.5 x cfm x lb/hour x ? Specific Heat
Which factor, Δh, ΔW, or ΔT, is associated with sensible heat?
We already have some of our variables in place
btu/hour = cfm x 60 x x lb/hour x ?
btu/hour = 4.5 x cfm x lb/hour x ?
We need to add the “btu” to the right side and get rid of the “lb” on the right side
Specific Heat

54. Sensible Heat Formula btu/hour = 4.5 x lb/hour x 0.24 btu/lb
The specific heat of air is 0.24 btu/lb/ºF
btu/hour = 4.5 x lb/hour x 0.24 btu/lb
btu/hour = 1.08 x btu/hour
Adding in our other variable values gives us:
QS (btu/hr) = 1.08 x Airflow x ΔT

55. Challenges with the Sensible Heat Formula
It doesn’t always give accurate results
The 1.08 is only an estimate
The lb/ft3 is not correct most of the time
The density comes from the specific volume
Specific volume must be determined
Specific volume estimate is the average of the values before and after the heat transfer coil

56. Latent Heat Formula We all know QL = 0.68 x CFM x ΔW
Where does the 0.68 come from?
Work with the units
QL (btu/hour)
What factors will contribute to get this result
Factors must be relevant to latent heat
For example, grains/pound is definitely a relevant term as it applies to latent heat

57. Latent Heat Formula btu/hour = cfm x 60 x 0.075 x lb/hour x ?
Which factor, Δh, ΔW, or ΔT, is associated with sensible heat?
ΔW = Change in moisture in grains/lbAIR
We already have some of our variables in place
btu/hour = cfm x 60 x x lb/hour x ?
btu/hour = 4.5 x cfm x lbAIR/hour x ?
btu/hour = 4.5 x cfm x grains/hour x ?

58. Latent Heat Formula 1 pound of water contains 7000 grains
btu/hour = 4.5 x cfm x grains/hour x lb/7000 grains
btu/hour = (4.5 ÷ 7000) x cfm x lb/hour
We need to add the “btu” to the right side and get rid of the “lb” on the right side

59. SUPPLY AIR
RETURN AIR
Water Vapor at 75ºF
Water at 50ºF

60. STEAM TABLES ACCOMPLISH ONE THING!

62. Pertinent Enthalpy Information
TEMP °F
Saturated Vapor Btu/Lb
Saturated Liquid Btu/Lb

63. Latent Heat Formula QL (btu/hr) = 0.68 x Airflow x ΔW
btu/hour = (4.5 ÷ 7000) x cfm x lb/hour
We need to add the “btu” to the right side and get rid of the “lb” on the right side
From the steam table we get:
1094 btu/lb - 18 btu/lb btu/lb
btu/hour = [(4.5 x 1076) ÷ 7000] x cfm x lb/hour x btu/lb
QL (btu/hr) = 0.68 x Airflow x ΔW

64. You can find automated steam tables at:
Enter Temperature Here
Read Cool Stuff Here

65. MIXED AIR SYSTEMS Return air is mixed with outside air
Heat transfer coil does not see return air from the occupied space exclusively
Percentage of outside air changes with its heat content
Process is governed by an enthalpy control
The heat transfer coil sees only the mixture of the two air streams

66. LAW OF THE TEE Also known as nodal analysis
What goes into a tee, must go out!
Electric circuit applications
Water flow applications
Hot water heating applications
Mixed air applications

67. ?
5 AMPS
2 AMPS

68. ?
5 GPM
2 GPM

69. ?
5 100ºF
5 140ºF

70. ?
5 100ºF
3 140ºF

71. (5 GPM x 100ºF) + (3 GPM x 140ºF) = (8 GPM x YºF)
Here’s The Math...
(5 GPM x 100ºF) + (3 GPM x 140ºF) = (8 GPM x YºF)
= 8YºF
920 = 8YºF
Y = 115ºF

72. CLASSROOM DEMONSTRATION or EXPERIMENT
LAW OF THE TEE FOR WATER
CLASSROOM DEMONSTRATION or EXPERIMENT
40ºF
70ºF
1 CUP CUP
Have students predict final mixed temperature.... Then combine, mix, measure and confirm..... Then change the rules!

73. CLASSROOM DEMONSTRATION or EXPERIMENT
LAW OF THE TEE FOR WATER
CLASSROOM DEMONSTRATION or EXPERIMENT
THE RESULTS:
40ºF
70ºF
55ºF
15ºF

74. CLASSROOM DEMONSTRATION or EXPERIMENT
LAW OF THE TEE FOR WATER
CLASSROOM DEMONSTRATION or EXPERIMENT
40ºF
70ºF
2 CUPS CUP

75. CLASSROOM DEMONSTRATION or EXPERIMENT
LAW OF THE TEE FOR WATER
CLASSROOM DEMONSTRATION or EXPERIMENT
THE RESULTS:
10ºF
20ºF
40ºF
50ºF
70ºF

76. LAW OF THE TEE FOR MIXED AIR
OUTSIDE AIR
MIXED AIR
AIR HANDLER
RETURN AIR

77. LAW OF THE TEE FOR MIXED AIR
PERCENTAGE OF RETURN AIR + PERCENTAGE OF OUTSIDE AIR
100% of MIXED AIR
OUTSIDE
RETURN

78. LAW OF THE TEE FOR MIXED AIR
SAMPLE PROBLEM
AIR CONDITIONS: RETURN AIR (80%): 75ºFDB, 50%RH
OUTSIDE AIR (20%): 85ºFDB, 60%RH
MIXED AIR = 80% RETURN AIR + 20% OUTSIDE AIR
MIXED AIR = (.80) RETURN AIR + (.20) OUTSIDE AIR
MIXED AIR = (.80) (75ºFDB, 50%RH) + (.20) (85ºFDB, 60%RH)
MIXED AIR = 60ºFDB, 40%RH + 17ºFDB, 12%RH
MIXED AIR = 77ºFDB, 52%RH

79. Return Air: 75ºFDB, 50% r.h.
Outside Air: 85ºFDB, 60% r.h.
Mixed Air: 77ºFDB, 52% r.h.
OUTSIDE AIR
MIXED AIR
SUPPLY AIR
RETURN AIR

80. 917-428-0044 silbere@sunysuffolk.edu
Eugene Silberstein