HVACR NOTES
01/20/2021 – Shop II
Absolute 0 is -459.67F or -273.15C (Theoretical)
Absolute scale is: 0 ---->
Plank temperature (?)
Heat transfer
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Conduction (Transfer)
Convection (Transfer through air or water)
Radiation (Transfer directly from source)
Specific Heat
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The amount of heat required to raise the temperature of one pound of a substance
one-degree Fahrenheit
Doesn’t apply when the substance undergoes a change of state
All substances have a specific heat. It varies from material
o Water: 1.0
o Air: 0.24
o Alcohol: 0.58
o Iron: 0.11
Sensible heat – Causes a change in temperature
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Heat that can be felt
The effects are measured with a thermometer
Latent Heat – Heat that is absorbed or released when a substance changes its physical state
without causing a temperature change
Three physical states of matter
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Solid
Liquid
Gas
Change of state – Most substance can exist as a solid, liquid, or gas depending on their
temperature and the pressure.
Five types of latent heat:
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Fusion
Vaporization
Condensation
Solidification
Sublimation
Superheat Vapor - A gas that has been heated to a temperature above its saturation point
(boiling point)
Subcooling – Any liquid that is cooled below its saturation temperature
BTU -> Tons
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2000 lbs. ice in 24 hours. Weight x Latent heat
1200 BTU/H is 1 Ton of Air conditioning
TEMPATURE – “The intensity of heat”
Represents the speed of motion of the molecules within a substance. Based on water freezing
at 32F or boiling at 212F
Fahrenheit scale
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Developed by Daniel Gabriel Fahrenheit
Defined by 2 pts.
o Water freezing point 32F
o Water boiling point 212F
Celsius Scale
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Developed by Anders Celsius
Was known as Centigrade
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1.8 difference or 180/100
Water -> Celsius
Air -> Fahrenheit
F vs C
Absolute Zero
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Rankine
Kelvin
(There are no negative numbers)
Absolute:
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The Fahrenheit absolute scale is known as Rankine (R)
The Celsius absolute scale is known as Kelvin (K)
Conversion of scales:
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Fahrenheit = (C x 1.8) x 32
Celsius = (F – 32) / 1.8
Conversion of Absolute scales
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F = (R - 460)
C = (K - 273)
R = (F + 460)
K = (C + 273)
K = (R / 1.8)
R = (K x 1.8)
Ambient Temperature – Refers to the temperature surrounding an object.
Dry Bulb Temperature – Refers to the sensible eat level of air and is measured with a n ordinary
thermometer (Ambient air temperature)
Wet Bulb temperature – Refers to the lowers temp. obtained by the process evaporation
moisture. It is measured using a special thermometer covered with a wet cloth, using distilled
water. Wet Bulb temperature is the thermodynamic process.
Dew Point Temperature – The temp. at which moisture begins to condense from the air. Also
known as saturation temperature. The dew point temperature of air varies on the moisture
content. When the air is saturated, the dry bulb temperature, the wet bulb temperature, and
dew point temperature will all be the same.
Saturation Temperature – Referred to as the boiling point. The point when a substance begins
to turn into vapor or condense into a liquid.
Thermometers
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Liquid filled
o A temperature-measurement device whose operation is based on the
thermal expansion of a liquid
Electronic
o Temperature-sensing instrument that is easy to use, with digital display
Thermocouple
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o Voltage devices that indicate temperature by measuring a change in voltage
Resistive
o A resistor temperature detector (RTD) is a temperature sensor, which
operates on the principle that a material’s electrical resistance varies with
temperature change.
Infrared
o Measures the electromagnetic radiation emitting from a surface.
 They don’t sense through glass
 Only measures surface
 May require adjustments
 Can be affected by the environment
Bimetal
o Designed to indicate temperature changes when the metal in the base
expands and contracts
Psychrometers (Digital/Sling)
o Tools for measuring wet and dry bulb temperature
o The wet bulb temperature measure the temperature effect of evaporation
o Wet bulb is precisely related to relative humidity
01/25/2021 – Fundamentals of Refrigeration
Heat, Temperature, and Pressure
PSIG – Is pounds per square inch gauge (0 = atmosphere)
PSIA – Is pounds per square inch atmosphere (14.7)
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Heat energy moves from one substance to another as well as between the molecule
of a single substance
When we need to be more specific than “hot” or “cold”, we refer to temperature
“Heat” and “temperature” are not the same
System pressures are obtained by using a refrigeration gauge manifold
Absolute zero – “Temperature at which all molecular movement stops (-460F)
Heat
o Is the motion of molecules
o Cannot be created or destroyed
o Can be measured and accounted for
o Can be transferred from one substance to another
o Travels from a warmer substance to a cooler substance
Conduction
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o Heat energy travels from molecule to molecule within a substance
o Heat energy travels from one substance to another
o Heat does not conduct at the same rate in all materials
Convection
o Transfers through a fluid from one substance to another
o Natural convection utilizes natural fluid flow, such as the rising of warm air
and the falling of cooler air
o Forced convection uses fans of pimps to move fluids from one point to
another
Radiation
o Radiant heat passes though air, heating the first solid object with which the
heat comes in contact
o Can travel through space without heating it
01/25/2021 – Shop II
Matter and Energy
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Matter
o Defined as any substance that occupies and has mass
o Is made up of atoms
o Exists as a solid, liquid, or a gas
o The state of the matter is determined by the heat content of the matter
Solids
o Exerts all pressure download
Liquids
o Exerts pressure outward and downward
Gases
o Exerts pressure in all directions at random
Mass
o The property of matter that responds to gravitational attraction
Weight
o Force that matter applies to a supporting surface when it is at rest
Density
o Mass to volume relationship
 Water has a density of 62.4 lb/ft3
Specific gravity: Density of a substance divided by the density of water
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Density of water = 62.4 lb/ft3
Density of aluminum = 171 lb/ft3
Specific gravity is unitless
Specific volume: volume of one pound of a gas (Measured in ft3/lb)
01/26/2021 – Fundamentals of Refrigeration
Sensible Heat
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Heat transfer that results in a change in temperature of a substance
Can be measured with a thermometer
Example:
o Changing the temperature of a sample of water from 68F to 69F
Latent Heat
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Transfers result in a change of state of a substance with no change in temperature
o Also referred to as hidden heat
o Cannot be measured with a thermometer
o Terms
 Latent Heat of Vaporization
 Latent Heat of Condensation
 Latent Heat of Fusion
Specific Heat
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Defined as the number of BTU’s required…
Sizing heating equipment: Q = Weight x Specific Heat x Temperature Difference – Q
*Q = Quantity of heat needed for the temperature change
Pressure
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Defined as the force per unit area
Often expressed in pounds per square inch
Atmospheric Pressure
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The atmosphere exerts a pressure of 14.696 psi at sea level
14.696psi at sea level is known as the standard condition
Barometer
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Mercury (Hg) Barometer
o Inches in Mercury
o 14.696psi = 29.92 inches of Mercury
Pressure Gauges
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Bourden Tube
o Measures pressure in a closed system
o Reads 0 psi when opened to the atmosphere
01/27/2021 – Fundamentals of Refrigeration
Introduction to Refrigeration
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Cooling preserves products and provides comfort
o 1900’s were the beginnings of mechanical refrigeration systems
o Refrigeration process… (?)
Refrigeration
o Process of transferring heat from a place where it is objectionable to where it
makes little or no difference
Heat Leakage
Rating Refrigeration Equipment
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The refrigeration process
o Heat is pumped from a cool box to a warm room
 Similar to water
Air Conditioning
o Air conditioners pump heat from the inside to the outside
 Inside temperature 75oF; outside temperature 95oF
 Cooling (Indoor) coil temp. 40oF
 Condenser (Outdoor) coil temp. 125oF
 Indoor heat travels to the indoor coil
 System heat flows from the outdoor coil to the outside air
01/27/2021 – Shop II
Gas Laws
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Always use absolute pressures and temperatures when working with gas laws
o Boyle’s Law: relates to pressure (P) and volume (V)
 P1 x V 1 = P2 x V2
o Charles’s Law: relates to volume (V) and temperature (T)
 V1/T1 = V2/T2
o General’s Law of Perfect Gas: relates pressure (P), volume (V), and
temperature (T)
 P1 x V1 / T1 = P2 x V2 / T2
o Dalton’s Law (of Partial Pressures): relates pressures of gases in a mixture
 The total pressure is the sum of the individual pressures of each gas
*Absolute pressure = psig + 14.696
01/29/2021 – Fundamentals of Refrigeration
Refrigeration Components
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Evaporator: Absorbs heat from area to be cooled
Compressor: Creates pressure difference needed to facilitate refrigerant flow
through the system
Condenser: Rejects system heat
Metering device: Regulates refrigerant flow to the evaporator
Evaporator
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Heat exchange surface used to absorb heat
o Located on low-pressure side of system
o Operates at temperatures lower than the medium being cooled or
conditioned
o Absorbs heat by boiling a low temperature liquid into a low temperature
vapor
Evaporator and Refrigerant
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Refrigerant typically enters the evaporator a s a liquid/vapor mix
o 75% liquid; 25% vapor
Superheat (Found using a thermo-couple)
o The heating of a vapor above its saturation temperature
o Ensures the no liquid refrigerant enters the compressor
o Equal to the evaporator outlet temperature minus the evaporator saturation
temperature
o Design superheat is typically between 8oF and 12oF
Superheated vapor does not follow a pressure/temperature relationship
The Compressor
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Pumps heat-laden vapor from the evaporator to the condenser by increasing the
refrigerant pressure
Reduces pressure on the low-side of the system
Increases pressure on the high-side of the system
Types:
o Common compressor types include the scroll, reciprocating, and the rotary
o Positive displacement compressors require that the compressed gas be
moved to the condenser
Toilet papering a house
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Pack rocks into the tube
o
Makes it easier to throw over tree limbs
o
Makes it easier to throw on the top of houses
o
Makes it easier to throw under cars
Have an escape vehicle
o
Makes you free from jail
o
Makes you free from bullets
01/28/2021 – Shop II
FAQ video
Q: Is this a drop in refrigerant?
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No
o It is a violation to mix refrigerants in a system
o You are really creating a new refrigerant
o There are ways to put different refrigerants in the same system. You need to
follow the guidelines.
o The new (Mixed) refrigerant has no service chart
o Financial – You are destroying any refrigerant reclaim value the old
refrigerant had
02/03/2021 – Fundamentals of Refrigeration
Refrigerants
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R-12
o Primarily for high/medium temperature refrigeration applications (Banned in
1996)
R-22
o Primarily in air conditioning application (slated for total phase-out in 2020)
R-500 and R-502
o Banned in 1996
R-134a
o Replacement for R-12 with retrofit
Replacements for R-22 include R-410a and R-407c
Refrigerants must be safe
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Designed to protect people from sickness, injury, and death
Proper ventilation is required
Refrigerants can displace oxygen if permitted to accumulate
Modern refrigerants are non-toxic
When burned, toxic/corrosive gasses are created
Refrigerants must be detectable
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Methods used for detecting refrigerant leaks
o Soap bubble solution: Pinpoints leaks
o Halide leak detector: Uses an open flame
o Electronic leak detectors: General area leaks
o Ultraviolet leak detectors: Pinpoints leaks
o Ultrasonic leak detectors: Uses sound waves
General Refrigerant Notes
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Should boil at low temperatures at atmospheric pressure
Is illegal to intentionally vent refrigerant to the atmosphere (Stiff fines for violations)
Mandatory certification for technicians
Refrigerant phase-out schedules set by EPA
Refrigerant cylinders/drums color-coded
Recovery, Recycling, and Reclaiming refrigerants
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Refrigerant recovery is mandatory using service and installation operation
Intended to reduce the emission of CFC, HCFC, and HFC refrigerants
Recovery equipment must be used according to manufacturer’s instructions
Plotting the Refrigerant Cycle
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Pressure-enthalpy chart
o Creates graphical representation of system
o Pressure scales on the vertical axis (psia)
o Enthalpy scale along bottom
o …
o …
…
02/05/2021 – Shop II
Pressure Enthalpy without Tears (Pt.1)
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Magic square
o Each side represents 4 cycles of the refrigeration cycle
 Top Left – High Pressure/High Temperature – Liquid
 Top Right – High Pressure/High Temperature – Vapor
 Bottom Left – Low Pressure/Low Temperature – Liquid
 Bottom Right – Low Pressure/Low Temperature – Vapor
o Major System Components
 Bottom Right -> Top Right: Compressor
 Superheated Vapor
 Top Right -> Top Left: Condenser
 Saturated Liquid
 Subcooled Liquid (Top Right Corner)
 Top Left -> Bottom Left: Metering Device
 Bottom Left -> Bottom Right: Evaporator
Pressure Enthalpy without Tears (Pt.2)
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What is enthalpy?
o Enthalpy is a fancy word for heat content
o Is expressed in BTU
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Horrible story about a youth pastor that lost his job
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Made giant twister board in gym
o Co-ed twister game
 LOST HIS JOB