rdi product training
DESCRIPTION
RDI Product Training. Refrigeration 101. Table of Contents. Refrigeration 101 3-68 What is Refrigeration? 4 BTU5 Latent & Sensible Heat6 Latent Heat7-12 Saturation Temperature13 Superheat14 Sub-cooled Liquid15 Refrigerants16-17 - PowerPoint PPT PresentationTRANSCRIPT
RDI
1
RDI Product
Training
RDI
2
Refrigeration 101
RDI
3
Table of Contents
Refrigeration 101 3-68
What is Refrigeration? 4
BTU 5
Latent & Sensible Heat 6
Latent Heat 7-12
Saturation Temperature 13
Superheat 14
Sub-cooled Liquid 15
Refrigerants 16-17
Refrigeration Capacity 18
Pressure to Control 19
Refrigeration Cycle 20-68
Compression System 21
Basic System 22
Heat Rejection 23
Compressors 25-29
Oil Separator 30-31
Condenser 32-33
Headmaster Valve 34-36
Liquid Receiver Tank 37-38
Filter/Drier 39-40
Sight Glass 41-42
Solenoid Valve 43-44
Pump-Down 45
TXV 46-49
Superheat 50-52
Evaporators 53-56
EPR & CPR Valve 57-62
Suction Accumulator 63-65
Suction Filter 66-67
RDI
4
What is Refrigeration?
Process of Heat Removal
Heat ALWAYS travels from a warm object to
a colder objectHeat travels from the air or product inside a walk-
in to the refrigerant inside the evaporatorHeat travels from the refrigerant in the condenser
to the air surrounding the condenser
RDI
5
BTU
British Thermal UnitEnergy required to increase temperature of 1 pound
of water 1 degree FahrenheitApproximately equal to energy of one wooden
match
RDI
6
Latent Heat & Sensible Heat
Latent HeatHeat that has the effect of changing the state of a
substance without changing its temperatureHidden heat; heat that cannot be sensed with a
thermometer
Sensible Heat Heat that causes a change in the temperature of a
substanceA rise in temperature that can be sensed with a
thermometer
RDI
7
Latent Heat
Latent Heat of Vaporization Liquid to VaporThe amount of heat that must be added to 1 lb. of liquid
at its boiling point to change it into 1 lb. of vapor
Latent Heat of CondensationVapor to Liquid The amount of heat that must be released by 1 lb. of
vapor at its boiling point to change it into 1 lb. of liquid
This is the Essence of Modern Refrigeration
RDI
8
Latent Heat
RDI
9
Latent Heat
RDI
10
Latent Heat
RDI
11
Latent Heat
RDI
12
Latent Heat
When one pound of water boils it absorbs 970 BTU’s at a constant temperature of 212° F
When one pound of steam condenses into water, 970 BTU’s must be extracted constant temperature of 212° F
RDI
13
Saturation Temperature
A saturated liquid or vapor is one at its boiling point; for water at sea level, the saturation temperature is 212° F
At higher pressures, the saturation temperature
increases, and with a decrease in pressure, the saturation temperature decreases
RDI
14
Superheated Vapor
The amount of sensible heat over a vapors evaporation point
Water At Sea Level at 220° F has 8° F of Superheat
RDI
15
Sub-cooled Liquid
Any liquid which has a temperature lower than the saturation temperature corresponding to its pressure is said to be sub-cooled
Water at any temperature less than its boiling temperature (212°F at sea level) is sub cooled
RDI
16
Refrigerants
The ability of liquids to absorb enormous quantities of heat as they vaporize is the basis of the mechanical refrigeration system
R-22Liquid at +25°F and 48.8 psig has a Latent Heat of
Vaporization of 90.3 BTU/lb.
R-404ALiquid at -20°F and 16.3 psig has a Latent Heat of
Vaporization of 81.6 BTU/lb
RDI
17
Alternative Refrigerants
We are constantly looking for new technology and continue to pursue alternative refrigerants
Look for possible refrigerant modifications in the future
RDI
18
Refrigeration Capacity
Measured in BTUs or in Tons Not HP
Ton= energy needed to freeze one ton of ice
Each pound of water has a latent heat of fusion of 144 BTU
Ton = 2000 (LBS)*144 (LHF) = 288,000 BTU
288,000/24 = 12,000 BTU/HR
RDI
19
Pressure to Control State
At Sea Level Water Saturation Point 212°
At 10,000 Feet Water Saturation Point 193°
RDI
20
The Refrigeration Cycle
RDI
21
Compression System
There are two pressures existing in a compression system
1. Evaporating or low pressure2. Condensing or high pressure
The refrigerant acts as a transportation medium to move heat from the evaporator to the condenser where it is given off to the ambient air
The change of state from liquid to vapor and back to liquid allows the refrigerant to absorb and discharge large quantities of heat efficiently
RDI
22
Basic System
Flow
Flow
Flow
Flow
High Pressure Gas
Low Pressure Liquid
High Pressure Liquid
Low Pressure Gas
RDI
23
Heat Rejection
The condenser is the exit door for the heat that the refrigerant has absorbed in the evaporator and compressor
RDI
24
Refrigeration System Components
RDI
25
Compressor
RDI
26
Compressor
Forces (pumps) the refrigerant through the refrigeration system
Compresses the refrigerant from a low pressure gas to a high pressure gas First it removes the refrigerant vapor from the
evaporator and reduces the pressure in the evaporator to a point where the desired evaporating temperature can be maintained
Second, the compressor raises the pressure of the refrigerant vapor to a level high enough so that the saturation temperature is higher than the temperature of the cooling medium (air or water) used for condensing the refrigerant vapor to a liquid refrigerant
We use Reciprocating and Scroll Compressors
RDI
27
Hermetic Compressor
Most Prevalent in Smaller Systems
Costs Less
Refrigerant Acts as Coolant
Simple Replacement
Cannot be Repaired in Field
RDI
28
Semi-Hermetic Compressor
More Robust
The “Old Standard”
Reputation of Quality
More Expensive
RDI
29
Scroll
Hermetic System
Different Compression System
More Expensive than Standard Hermetic
Less Expensive than Semi-Hermetic
Limited to Larger Systems
RDI
30
Oil Separator
RDI
31
Oil Separator
RDI
32
Condenser
RDI
33
Condenser
As heat is given off by the high temperature high pressure vapor, its temperature falls to the saturation point and the vapor condenses to a liquid, hence the name condenser
Air Cooled vs. Water Cooled
RDI
34
Headmaster Valve
RDI
35
Headmaster Valve
Designed to maintain head pressure during low ambient conditions
Limits the flow of liquid refrigerant from the condenser while at the same time regulating the flow of hot gas around the condenser to the receiver
The two primary controlling pressures are the dome pressure, opposed by the discharge pressure which bleeds around the pushrods to the underside of the diaphragm
RDI
36
Headmaster Valve
Pressure Pre-Set
Not Adjustable
Liquid
Gas
Mixture
Maintains
High Pressure
RDI
37
Liquid Receiver Tank
RDI
38
Liquid Receiver Tank
Liquid storage tank for refrigerant which is not in circulation
Contain high pressure liquid refrigerant and some high pressure refrigerant gas
CVD Technology uses the gas here for defrost mode
RDI
39
Filter/Drier
RDI
40
Filter/Drier
The liquid line filter/drier absorbs moisture, acid and sludge/varnish
It also filters (collects) small foreign particles from the system
RDI
41
Sight Glass
RDI
42
Sight Glass
Also know as the “liquid level moisture indicator”
Provides a visual means to determine if the refrigerant charge is low
Bubbles or foaming in the sight glass indicate a shortage in the flow of refrigerant
Provides a visual means to determine the approximate moisture level within the system GREEN – Moisture level should be at acceptable range YELLOW – Moisture level too high. The sight glass
should be located in the liquid line after the liquid line filter drier
RDI
43
Solenoid Valve
RDI
44
Solenoid Valve
Located in the liquid line just before the expansion valve inside the evaporator housing
Used in conjunction with the thermostat (temperature control) and a low pressure control in order to achieve an automatic pumpdown
RDI
45
Pump-Down
Sequence1. The thermostat senses that the interior walk-in temperature has
become cool enough. The thermostat opens, de-energizing the normally closed liquid solenoid valve
2. The solenoid valve closes (stops the flow of refrigerant at the valve). The compressor continues to run. The pressure in the low side of the system is reduced and all remaining liquid in the evaporator changes to vapor
3. When the low-side pressure has dropped to satisfy the low pressure control setting, the electrical circuit through the low pressure control opens and turns off the compressor
Purpose1. It removes the refrigerant from the low side, making it impossible for
the oil to become diluted with liquid refrigerant. (Refrigerant vapor will always migrate to the coldest point of the system)
2. It prevents the compressor from having to start-up with a high suction pressure that could overload the compressor motor
RDI
46
TXV
RDI
47
TXV
The Thermostatic Expansion Valve (TXV) controls the flow of refrigerant to the evaporator and also reduces the high pressure liquid to a low pressure liquid and gas
Intelligent device that modulates in order to allow the correct amount of refrigerant to enter the evaporator
Senses the pressure and the temperature of the refrigerant leaving the evaporator, and determine the number of degrees of superheat
RDI
48
TXV
Liquid
Liquid
(Starting to Boil)
Sensing
Superheat
RDI
49
TXV
Sensing
Superheat
RDI
50
Superheated Vapor
The amount of sensible heat over a vapors evaporation point
Water At Sea Level at 220° F has 8° F of Superheat
RDI
51
Superheat
A vapor that is at a temperature higher than its saturation (boiling) temperature
How to Determine Evaporator Superheat:1. Measure the temperature of the suction line at the point the bulb
is clamped2. Obtain the suction pressure that exists in the suction line at the
bulb location3. Convert the pressure obtained in 2 above to saturated
evaporator temperature by using a temperature-pressure chart4. Subtract the two temperatures obtained in 1 and 3 (1 minus 3).
The difference is the evaporator superheat
RDI
52
Calculating Super Heat
R-22Temperature at bulb is 33°F Pressure is 49 PSIG Super Heat Equals
33°F
-25°F 8°F
RDI
53
Evaporator
RDI
54
Evaporator
Condenser Evaporator
RDI
55
Evaporator
The cold refrigerant is allowed to absorb heat from the warmer material that needs to be cooled
In our design application: The air inside the walk-in absorbs heat from its surroundings. Some
possible heat sources are:Product being stored (if above walk-in design temperature)Heat transferred through the insulated walls from the exterior of the
walk-inPeople entering the walk-inWarm exterior air through wall penetrations not sealed properlyHeat generated by other sources inside the walk-in (lights, fan motors,
heaters, forklifts, etc.) The evaporator coil surface absorbs heat from the air The refrigerant flowing inside the evaporator absorbs heat from the
evaporator coil surface
REMEMBER: Heat ALWAYS travels from a warm object to a colder object
RDI
56
Evaporator TD
Difference in temperature between the temperature of the air entering the evaporator, usually taken as the walk-in interior design temperature, and the saturation temperature of the refrigerant corresponding to the pressure at the evaporator outlet
EXAMPLE:WALK-IN DESIGN TEMP. 35 °FSuction Pressure at EvapOutlet is 49PSIG 25 °F
(Refrigerant R-22) _____EVAPORATOR TD 10 °F
The most important factor governing the humidity in the refrigerated space is the evaporator TD The smaller the difference in temperature between the evaporator and
the space, the higher is the relative humidity in the space Likewise, the greater the evaporator TD, the lower is the relative
humidity in the space The colder the surface of an object, the more moisture it will attract
RDI
57
EPR or CPR Valve
RDI
58
EPR Valve
The Evaporator Pressure Regulating (EPR) Valve prevents the evaporator pressure from falling below the predetermined value for which the EPR valve has been set
By controlling the evaporator pressure, the evaporator temperature is also controlled
An EPR valve modulates from fully open to fully closed, closing on a fall in inlet pressure
Located in the suction line near evaporator outlet
RDI
59
EPR Valve
Some typical applications where an EPR valve might be used:On multiple evaporator applications where each
evaporator is intended to operate at a different temperature
On multiple evaporator installations where evaporators vary in size, style and capacity
RDI
60
EPR Valve
Flow
Flow
RDI
61
CPR Valve
The Crankcase Pressure Regulating (CPR) Valve limits the suction pressure at the compressor below a preset limit to prevent overloading of the compressor motor
The CPR valve modulates from fully open to fully closed. The valve responds to outlet pressure, closing on a rise in outlet pressure
A CPR valve is typically used to prevent motor overloading on low temperature units during start-up after a defrost cycle or on systems in applications where high back pressures might be encountered during pulldown
RDI
62
CPR Valve
Flow
Flow
RDI
63
Suction Accumulator
RDI
64
Suction Accumulator
Primary purpose is to intercept liquid refrigerant before it can reach the compressor
Prevents slugging the Compressor
RDI
65
Suction Accumulator
RDI
66
Suction Filter
RDI
67
Suction Filter
Protects the refrigeration compressor by collecting all foreign material and preventing it from entering the compressor where it could damage the internal working parts
Must be on remote systems with long lines
The filter will collect any dirt that is in the evaporator or suction line at start up, and thus protect the new compressor
Any field built up system which requires cutting and/or brazing of lines needs the protection of a suction filter
RDI
68
Refrigeration System Components