60670912 Refrigeration Fundamentals PPT

1

Refrigeration Fundamentals

& Sealed System Diagnosis

L2005-022PPT

2

Refrigeration

• Refrigeration is best defined as the movement of heat from a location where it is not wanted to a location where the added heat will not matter.

• Refrigeration works because there is a relationship between Heat and Pressure– Heat and pressure behave in a predictable ways– By controlling pressure, we can control heat

3

Heat

• Everything has heat

• Without heat, all molecular activity would stop (Absolute Zero)

• Heat is measured two ways– Heat Intensity (Thermometer)– Heat Quantity (BTU’s)

4

Heat

Heat Intensity (Temperature)

One BTU is equal to the heat generated

by burning common wooden kitchen

match

BTU (British Thermal Unit) Quantity

1 BTU

1 Lb.

+ 1 Degree

1 BTU

1 Lb.

+ 1 Degree

5

Heat Quantity

Wood Table Top

Metal Leg

Heat Packet

75º F Environment Even though two items can be at the same

temperature, some materials will contain more heat (heat packets) than others.

6

Heat Transfer

100º F

-15º F-5º F

50º F

Even in temperatures that we consider “cold,” heat still moves.

Heat travels from an area of higher heat concentration to an area of less heat. The great the temperature differential, the faster the heat transfer.

BTU

BTU

BTU

BTU

BTU

BTU

7

Heat Movement

Conduction

Heated air rises and is replaced with cooler air

Cooler air falls and repeats cycle.

Convection Gla

ssRadiation

8

BTU Transfer

Latent Heat of Fusion

Latent Heat of Vaporization

One BTU is = to heat generated by burning a common kitchen stick match

Super heated vapor

(only under pressure)

212º F

212º F

Intensity and Quantity

Even though both the water and steam are at 212 ºF, the steam has 970 BTU’s (per pound) more heat than the liquid (more heat packets)

212º F

Under pressure, the water and vapor temperatures will increase well beyond the normal 212 º F boiling point at sea level. Heat quantity rises as well.

Pressure Effect on Boiling points

Superheated vapor

11

Adding heat to a liquid causes it to vaporize Cooling the

vapor causes it to condense back into a liquid

12

Evaporation

WaterPorous ceramic

container

Water wicks through the porous ceramic to the exterior of the vessel. There, the water evaporates (changes state).

As the water changes from a liquid to a vapor, heat is absorbed. This cools the walls of the vessel which, in turn, cools the water.

Your body relies on this same principle to keep you cool. In a warm environment, your body sweats. The sweat evaporates and cools your skin.

13

Intensity and Quantity

• The key take aways from the boiling water example is:

In order for a change of state to occur, heat must be added or taken away. With water, 970 BTUs of heat must be absorbed to effect a change of state from a liquid to a vapor. Conversely, the same 970 BTUs of heat must be removed from that vapor before that vapor can change back into a liquid.

Boiling is just an exaggerated form of evaporation

14

Pressure

• Pressure is Relative– At sea level, pressure is 14.7 PSI– Pressure drops with Altitude

Boston

Pikes Peak

LA

Denver

Chicago

Altitude Pressure

15

To Vacuum Pump

212º F

75º F

212º F

75º F

Reducing the pressure over a liquid lowers its boiling point

16

Hg scale

Mercury (Hg) Tube

17

Hg Scale

As pressure is increased over the open Mercury, the level of liquid within the mercury tube rises

18

Hg Scale

Conversely, as pressure is reduced over the open Mercury, the level of liquid within the mercury tube falls

19

Hg Scale

By measuring the number of inches of Hg in the tube, we can determine the pressure over the liquid.

Normal Atmospheric pressure is 29.92” Hg

In weather reporting, atmospheric pressure is also known as barometric pressure. Changes in barometric pressure usually precedes a change in weather.

20

PSI Scale PSIA PSIG

96.7 82

77.592.2

14.7 0

28.9 29.2

.5 0

At Sea Level

Absolute Pressure

Gauge Pressure

Normal Atmospheric Pressure

14.7 PSIA

0.0 PSIG

21

PSI Scale PSIA PSIG

96.7 82

77.592.2

14.7 0

28.9 29.2

.5 0

At Sea Level

In refrigeration, pressure is relative. Since pressure is all around us, any measurements we make are referenced to normal atmospheric pressure.

Compound Gauge Set

At sea level, the normal 14.7 PSIG pressure that surrounds us becomes the zero reference point for our refrigeration gauges.

22

Positive and Negative Pressures PSIA PSIG

96.7 82

77.592.2

14.7 0

28.9 29.2

.5 0

At Sea Level

Po

sitive G

au

ge

Pre

ssure

Pressure that are greater than normal atmospheric pressure are called positive pressures and are measured in P.S. I. Gauge.

Ne

ga

tive

Ga

ug

e P

res

su

re

(Pa

rtial V

ac

uu

ms

)

Pressures that are less than normal atmospheric are called partial vacuums and are measured in Inches of Mercury (Hg).

Negative Pressure (Partial Vacuums)

A perfect vacuum is measured as Zero PSI on the absolute scale or negative 29.92 inches of mercury (Hg) on a refrigeration gauge

Measuring Pressure & Vacuums

Compound Gauge Set

Low side gauge

High side gauge

Low Side Hose (Blue)

Common Hose (Yellow)

High Side Hose (Red)

When hand valves are open, the manifold joins

all of the hoses to a common pressure

When hand valves are closed, the special

porting arrangement allows each gauge to

read the pressure on its corresponding hose

Low Side

Gauge

High Side

Gauge

Common Manifold

Low Side Hose

Common Hose

High Side Hose

When hand valves are open, the manifold joins

all of the hoses to a common pressure

When hand valves are closed, the special

porting arrangement allows each gauge to

read the pressure on its corresponding hose

Low Side

Gauge

High Side

Gauge

Common Manifold

Low Side Hose

Common Hose

High Side Hose

26

Measuring Pressure

Pressure

27

Gauge Markings

Low Side Gauge

R-134a

PSIG Pounds per Square Inch

Gauge

Negative Pressure

(Vacuums)

Atmospheric Pressure

28

Gauge Markings

Low Side Gauge

R-134a

Negative Pressure

(Vacuums)

This is read as 50 PSIG

This is read as a 20 Inch vacuum

Partial Vacuums Can also be Measured in Microns

A micron is a thousandth of an inch. A total of 29,920 microns of pressure would have to be removed to achieve a perfect vacuum (zero microns).

30

Charles Law

At a constant temperature, the volume of a gas varies directly with

pressure.

31

Charles LawAt a constant volume, the pressure

of a gas varies directly with temperature.

Liquid

Vapor

Liquid

This is know as the “Steady State” of a liquid in a storage vessel

Charles LawAt any given temperature, the contents of a cylinder will strike a balance between how much vapor and liquid exists within the tank

Temperature Pressure

Charles Law

Temperature Pressure

Charles Law

TemperaturePressure

Just as increasing pressure increases the temperature, decreasing pressure decreases temperature

Charles Law

36

Charles Law• Because of the pressure/temperature

relationship outlined in Charles’ law,– if we know the temperature of a liquid in a sealed

container, we can determine the pressure the liquid is under

• if we know the pressure, we can determine the temperature

– lowering the pressure reduces the boiling point of a liquid

– increasing the pressure raises the condensation point of a vapor

212º F

To Vacuum Pump

Under reduced pressure, water will boil at normal room temperatures or below

75º F

Pressure Affect on Boiling points

Pressure

20 PSIG0 PSIG

5 PSIG11.6

in Hg

29.92 in Hg

19.74

in Hg

Pressure Affect on Boiling Point of Water

34

84

134

184

234

284

334

2 6 10 14 18 22 26 30 34

PSIG

Tem

per

atu

re

At m

os

ph

er i

c P

r es

su

r e

10 PSIG 15 PSIG1.4 PSIG

At 0 PSIG, water boils at any temperature above 34º F and condenses at any temperature below 34º F

39

Class of chemicals with extremely low boiling and condensing points

Refrigerants

R-134a R-22

40

212º F

Because of its extremely low boiling point, R-134a boils normal room temperatures. The warmer the temperature, the more violently the refrigerant boils -16º F

75º F

R-134a

- At seal level, R134a boils at any temperature above -15º F

R-134a Boiling and Condensing Points

41

Refrigerant Temperature

PSIGR-12 R-22

R-134a

R-502

R-410A

0 -22 -41 -15 -50 -60

2 -16 -37 -10 -45 -58

4 -11 -32 -5 -40 -54

6 -7 -28 -1 -36 -50

8 -2 -24 3 -32 -46

10 2 -20 7 -29 -42

12 5 -17 10 -25 -39

14 9 -14 13 -22 -36

16 12 -11 16 -19 -33

18 15 -8 19 -16 -30

Refrigerant Temperature

PSIGR-12 R-22

R-134a

R-502

R-410A

105 93 62 90 54 34

110 96 64 93 57 36

115 99 67 96 59 39

120 102 69 98 62 41

125 104 72 100 64 43

130 107 74 103 67 45

135 109 76 105 69 47

140 112 78 107 71 49

145 114 81 109 73 51

150 117 83 112 75 53

Finding Steady State Pressures and Temperatures

T/P Gauge MarkingsLow Side Gauge

R-134a

Refrigerant Temperature Scales

43

How refrigerants make refrigeration possible

• Because refrigerants boil at very low pressure and temperatures, they absorb heat even in sub zero environments– Since R134a boils at any temperature above -15ºF

(0PSIG), it can remove heat from a freezer compartment that is at 0ºF

• Because of their pressure/temperature condensation points, they give up heat even in warm environments– Under normal sealed system operating conditions,

R134a will condense at any temperature below 100ºF

44

• By controlling pressure, we can control the boiling (evaporation) and condensation points of a refrigerant– Lowering pressure reduces the boiling point– Increasing pressure raises the condensation point

• By setting up pressure differentials within a Sealed System, we can control the temperatures at which the refrigerant will boil (evaporate) and condense

How refrigerants make refrigeration possible

45

Tying it all together

• In ANY refrigeration system, refrigerant is alternately evaporated, absorbing heat) and condensed (giving up the heat)– Evaporation occurs in low pressure side of the

system – Condensation occurs in high pressure side of

the system– Compressor and capillary set up pressure

differentials

46

Components of a Typical Sealed System

Evaporator

Condenser

Compressor

Filter Drier

Capillary Tube

Heat Exchanger

Suction line

How Compressor Increases Pressure

On the intake stroke, vapor refrigerant from

the low side of the system is pulled into

the compression chamber

On the exhaust stroke, the refrigerant is pushed out of the

compression chamber and into the high side

of the system

To Cond

To Cond

48

How Compressor Increases Pressure

To Cond

Cap Tube .030” or smaller

Fro

m C

on

den

ser

¼”

or

larg

er

How the Drier Creates a RestrictionT

o E

vapo

rator

As the liquid droplets enter the drier, the smaller cap tube restricts their flow into the condenser

50

Refrigerant Flow

Evaporator

Condenser

Compressor

Filter Drier

Capillary Tube

Heat Exchanger

Suction lineHigh Pressure

Low Pressure

51

How Refrigerant Absorbs Heat

Evaporator

High Pressure

Low Pressure

Refrigerant Boiling

Evaporator Coil

High Pressure

Low Pressure

Refrigerant Boiling

High Pressure

Low Pressure

Refrigerant Boiling

Evaporator Coil

52

How Refrigerant Absorbs HeatHigh

PressureLow

Pressure

Refrigerant Boiling

Evaporator Coil

High Pressure

Low Pressure

Refrigerant Boiling

High Pressure

Low Pressure

Refrigerant Boiling

Evaporator Coil

High pressure liquid travels from the condenser, through the capillary tube and enters the evaporator

The lower pressure of the evaporator drops the boiling point of the liquid and the refrigerant begins to evaporate (boil)

Hig

h p

res

su

re l

iqu

id f

rom

ca

p t

ub

e

53


PressureLow

Pressure

Refrigerant Boiling

Evaporator Coil

High Pressure

Low Pressure

Refrigerant Boiling

High Pressure

Low Pressure

Refrigerant Boiling

Evaporator Coil

As the refrigerant boils, it pulls heat from the coil and the vapor becomes Superheated (contains trapped heat)

When the coil in that area drops to -15ºF, the refrigerant can no longer exist as a vapor and condenses back into a -15ºF Liquid

Hig

h p

res

su

re l

iqu

id f

rom

ca

p t

ub

e

The latent heat that the refrigerant absorbed during evaporation is now trapped in the -15ºF liquid

54


PressureLow

Pressure

Refrigerant Boiling

Evaporator Coil

High Pressure

Low Pressure

Refrigerant Boiling

High Pressure

Low Pressure

Refrigerant Boiling

Evaporator Coil

As each section of the coil drops to -15ºF, the superheated vapor condenses back into a liquid

Hig

h p

res

su

re l

iqu

id f

rom

ca

p t

ub

e

55

How Refrigerant Absorbs Heat

This process continues until the entire coil is down to -15ºF and the evaporator is completely filled with liquid

This condition is referred to as a Flooded Evaporator

The -15ºF can now continue to absorb heat without any further evaporation taking place

56

Super Heated Vapor

Liquid

Heat Exchanger

Suction line

Cap Tube

Super Heated Vapor

Liquid

Heat Exchanger

Suction line

Cap Tube

How Refrigerant Absorbs HeatEventually, the only place where evaporation is taking place is the the very end of the coil (Evaporator outlet)

The super heated vapor now travels through the heat exchanger back to compressor

Vapor to Compressor

Liquid to Evaporator

Suction Line

Cap Tube

Heat Heat

Heat

HeatHeat

Vapor to Compressor

Liquid to Evaporator

Suction Line

Cap Tube

Heat Heat

Heat

HeatHeat

57

Heat Exchanger

Suction Line

Cap TubeVAPOR

To Compressor

From Condenser

LIQUID

Heat Exchanger

Heat

Heat

Heat

Heat

Heat

As the vapor travels through the suction line, it continues to absorb heat.

This cools the liquid refrigerant before it enters the evaporator.

It also warms the vapor and insures that no liquid enters the compressor.

58

Drier

Static Condenser

How Refrigerant Releases Heat

59

The combination of the higher condensing temperature and the cooler air moving across the coil causes the refrigerant to condense.

In the process, the refrigerant gives up its latent heat.


Liquid droplets travel to the drier

Cap Tube .030” or smaller

Fro

m C

on

den

ser

¼”

or

larg

er

How the Drier Creates a RestrictionT

o E

vapo

rator

As the liquid droplets enter the drier, the smaller cap tube restricts their flow into the condenser


Liquid begins to pool and backs up into the

condenser.

62


Once the drier fills with liquid, the liquid begins to pool back into the condenser

63


Eventually, the last few passes of the condenser are liquid filled.

This reservoir of liquid insures that there is enough refrigerant in the system to maintain a flooded evaporator

The condenser begins to fill with liquid

64

CondensersForced Air

Warm Wall Static

65

Evaporators

Tube an Fin

Roll Bond

Shelf

66

Gas Loops (Yoder lines)

Condenser Loop Refrigerant Flow

Post Condenser

Loop

68

General Refrigeration Rules

• Under normal conditions, low side and high side pressures follow one another.– If high side pressure goes up, low side

pressure follows– If low side pressure goes up, high side

pressure follows

69


• Heat load has greatest effect on low side pressure– As heat load increases, both low and high side

pressures go up– As heat load is decreased, pressures go down

• Ambient conditions has a greatest effect on high side pressures– As ambient temperature rises, condenser

temperatures increase– Higher condenser temperatures mean higher low side

temperatures and pressures and reduced ability to absorb heat

70


• Compressor running wattage reflects how much work the compressor is performing

• How much work the compressor is doing is dependent on heat load and ambient conditions

71

Sealed System Diagnosis

Constant State

Condenser

Evaporator

Normal Conditions

High Side (Condenser)

Pressure:

About 120 to130 PSIG

Low Side (Evaporator)

Pressure:

About 0 PSIG

(Ranges between 10” and 5-7 lb

PSIG)

Running Amperage

Approximately 1 amp

(Ranges from .6 to 1.4 Amps

depending on Compressor BTU rating)

Evaporator frosted from top to bottom

Liquid level varies but normally last couple of passes of condenser is filled with liquid when

running

74

Charging

1151101051009590858075

.5600

.6650

.7700

.8750

.9800

1.0850

1.2900

1.3950

1.41000

Amp Draw

BTU’s

.9

Amp Draw

Percent Correct Charge

(CoolingCapacity)

75

Refrigeration Diagnosis Do’s and Don’ts

• Don’t– Assume a system problem

unless you’ve eliminated all other possible causes

• Air flow• Heat load• Customer usage

– Tap into system unless you are absolutely sure that the problem is with the sealed system

• Do– Check internal and

external air flow– Check refrigerator and

freezer temperatures– Check for unusual heat

sources• Light staying on• Air leaks into freezer or

refrigerator sections– Check that defrost system

is working properly– Check current draw– Feel compressor,

condenser for proper temperatures

Ice ball on first pass (passes) of evaporator

Condenser

Evaporator

Low liquid level

Low Current Draw

Low Side Leak- Refrigerant still left in the system

LS Pressure: Lower than normal

Evap Temp: Warmer than normal

HS pressure: Depends on Air/Refrigerant ratio*

Cond Temp: Depends on Air/Refrigerant ratio*

* Condenser pressure and temperature will depend on volume of non-condensables absorbed into the system

Low Side Leak- Air in system

Condenser

Evaporator

High Current Draw

No frost on evaporator

No liquid

LS Pressure: Atmospheric

Evap Temp: Warm

HS pressure: Very high

Cond Temp: Very hot

Low Watts

Condenser

EvaporatorLiquid Level*

Current Draw **

Frost ***

High Side LeakLS Pressure: Lower than normal


HS pressure: Lower than normal*

Cond Temp: Cooler than normal*

* Liquid level will depend on how much refrigerant still left in system

**Compressor run wattage, pressures and temperatures of Evaporator and Condenser dependent on how much refrigerant is left in system.

***Frost on Evaporator and liquid level in condenser depends on how much refrigerant left in the system

Restriction

LS Pressure: Vacuum


HS pressure: Ambient

Cond Temp: Ambient

Low Current Draw

No Frost on evaporator

Condenser full of liquid

Condenser

Evaporator

Inefficient Compressor

LS Pressure: Higher than normal


HS pressure: Lower than normal

Cond Temp: Cooler than normal

Condenser

Evaporator

Low Current Draw

Little or o Frost on evaporator

Liquid level low or non existent

Inefficient compressor (defective exhaust valve)

To Cond

Because the condenser is under higher pressure than the dome of the compressor, most of the refrigerant is pulled back from the condenser on the down stroke

To Cond

Inefficient compressor (defective intake valve)

Because the condenser is under higher pressure than the dome of the compressor, most of the refrigerant is pushed back into the dome rather than the condenser

Undercharge

No frost on last pass (or passes) of evaporator

Condenser

Evaporator

Low liquid level

Low Current Draw

LS Pressure: Lower than normal




Overcharge


Evap Temp: Slightly Warmer than normal

HS pressure: Higher than normal

Cond Temp: Hotter than normal

Condenser

Evaporator

High Current Draw

Frosted suction line all the way back to

compressor

High liquid level

85

Conditions When Pressure/Temp/Watts Don’t Follow One Another

• Low Side Leak- Non-Condensables in high sideHigh side pressure- Low Side pressure- Watts-

• Inefficient CompressorHigh side pressure- Low Side pressure- Watts-

Indicators

Conditions WattsCondenser Temp

Condenser Liquid Level Frost Line

Capillary Tube Sound

Low Side Pressure

High Side Pressure

Pressure Equalization Rate

Overcharge

Undercharge

Low-Side Leak -Refrigerant in System

Low-Side Leak- NO Refrigerant in System

High Side Leak

Low Capacity Compressor

Restrictions

Capillary Tube (Complete)

Capillary Tube (Floating)

Sealed System Analysis

Indicators

Conditions WattsCondenser Temp

Condenser Liquid Level Frost Line


Low Side Pressure

High Side Pressure

Pressure Equalization Rate

Overcharge HighHigher than Normal

Higher than Normal

All the way back to suction line

Louder than Normal

Higher than Normal

Higher than Normal

Normal to slightly longer

Undercharge LowLower than Normal

Lower than Normal Partial Intermittent

Lower than Normal

Lower than Normal

Quicker than Normal

Low-Side Leak -Refrigerant in System High*

Normal to Slightly Higher *

Lower than Normal

Partial to Non existent (possible frost ball)

Intermittent to non existent

Normal to slightly higher*

Normal to slightly higher than Normal * Normal

Low-Side Leak- NO Refrigerant in System High High None Non existent None Atmospheric

Higher than Normal Normal

High Side Leak Low LowLow to non existent None None Vacuum Low

Quicker than Normal

Low Capacity Compressor Low Low Low

Partial to Non existent

Intermittent to non existent

Higher than normal

Lower than Normal

Quicker than Normal

Restrictions

Capillary Tube (Complete) Low Low

Higher than normal None None Vacuum Ambient

No equalization

Capillary Tube (Floating) Low Low

Higher than Normal Intermittent Intermittent

Intermittent Partial Vacuum

Intermittent lower than normal Intermittent

Sealed System Analysis

*Compressor run wattage and the pressures and temperatures of Evaporator and Condenser dependent on how much refrigerant is left in system.

Restricted Evaporator Air flow





CondenserCondenser

Evaporator

Low Current Draw

May be frosted all the way back to compressor

Low liquid level

Restricted Condenser Air Flow



HS pressure: Higher than normal

Cond Temp: Warmer than normal

Condenser

Evaporator

High Current Draw

Normal Frost PatternNormal liquid level

Indicators

Conditions WattsCondenser Temp Frost Line


Low Side Pressure

High Side Pressure

Fresh Food Temp

Freezer Temp

Plugged condenser

Blocked Cond. Fan

Blocked Evap Fan

Evap Iced up (defrost failure)

High heat load

High ambients

Damper failed closed

Damper failed open

Conditions that Mimic Sealed System Failures

Indicators

Conditions WattsCondenser Temp Frost Line


Low Side Pressure

High Side Pressure

Fresh Food Temp

Freezer Temp

Plugged condenser HighHigher than Normal Full Normal

Higher than Normal

Higher than Normal

Warmer than Normal

Warmer than Normal

Blocked Cond. Fan HighHigher than Normal Full Normal

Higher than Normal

Higher than Normal

Warmer than Normal

Warmer than Normal

Blocked Evap Fan LowLower than Normal

Frost back to compressor Normal

Lower than normal

Lower than Normal

Warmer than Normal

Warmer than Normal

Evap Iced up (defrost failure) Low

Lower than Normal

Frost back to compressor Normal

Lower than normal

Lower than Normal

Warmer than Normal

Warmer than Normal

High heat load HighHigher than Normal Full Normal

Higher than normal

Higher than normal

Warmer than Normal

Warmer than Normal

High ambients HighHigher than Normal Full Normal

Higher than normal

Higher than normal

Warmer than Normal

Warmer than Normal

Damper failed closed LowLower than Normal Full Normal

Lower than normal

Lower than normal

Warmer than Normal

Cooler than Normal

Damper failed open

Slightly higher than Normal Slightly higher Full Norma;

Lightly higher than normal

Slightly higher than normal

Cooler than Normal

Warmer than Normal

Conditions that Mimic Sealed System Failures

92

Be Aware, Be AlertAlways work safely.

On the Job, On the Road, In the Home

Every Time, All the Time

60670912 Refrigeration Fundamentals PPT

Documents

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pressure pressure

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