# PSYCHROMETRICS ...WITHOUT TEARS Professor Eugene Silberstein, CMHE

## Presentation on theme: "PSYCHROMETRICS ...WITHOUT TEARS Professor Eugene Silberstein, CMHE"— Presentation transcript:

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

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

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

“This is really going to hurt!”

TEACHING PSYCHROMETRICS IS A LOT LIKE COMMERCIAL FISHING...

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!)

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

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

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?

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

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

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

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

WET-BULB, DRY-BULB COMBO
WET BULB TEMPERATURE DRY-BULB TEMPERATURE

SLING PSYCHROMETER

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

---- 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

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

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

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)

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

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

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%

RELATIVE HUMIDITY Example #2

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%

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

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

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

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

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

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

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

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

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

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

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?

ON PLANET ENEGUE...

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!

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?

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

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

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...

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?

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?

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 ?

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

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

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

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

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

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

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

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 ?

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

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

STEAM TABLES ACCOMPLISH ONE THING!

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

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

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

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

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

? 5 AMPS 2 AMPS

? 5 GPM 2 GPM

? 5 100ºF 5 140ºF

? 5 100ºF 3 140ºF

(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

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!

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

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

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

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

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

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

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

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