Transcript Read Document - Southern Ice

RDI
RDI Product
Training
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RDI
Refrigeration 101
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Table of Contents
Refrigeration 101
What is Refrigeration?
BTU
Latent & Sensible Heat
Latent Heat
Saturation Temperature
Superheat
Sub-cooled Liquid
Refrigerants
Refrigeration Capacity
Pressure to Control
Refrigeration Cycle
Compression System
Basic System
Heat Rejection
Compressors
Oil Separator
Condenser
Headmaster Valve
Liquid Receiver Tank
Filter/Drier
Sight Glass
Solenoid Valve
Pump-Down
TXV
Superheat
Evaporators
EPR & CPR Valve
Suction Accumulator
Suction Filter
3-68
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5
6
7-12
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14
15
16-17
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19
20-68
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22
23
25-29
30-31
32-33
34-36
37-38
39-40
41-42
43-44
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46-49
50-52
53-56
57-62
63-65
66-67
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What is Refrigeration?
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 Process of Heat Removal
 Heat ALWAYS travels from a warm object to
a colder object
 Heat travels from the air or product inside a walkin to the refrigerant inside the evaporator
 Heat travels from the refrigerant in the condenser
to the air surrounding the condenser
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BTU
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British Thermal Unit
 Energy required to increase temperature of 1
pound of water 1 degree Fahrenheit
 Approximately equal to energy of one wooden
match
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Latent Heat & Sensible Heat
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Latent Heat
 Heat that has the effect of changing the state of a
substance without changing its temperature
 Hidden heat; heat that cannot be sensed with a
thermometer
Sensible Heat
 Heat that causes a change in the temperature of a
substance
 A rise in temperature that can be sensed with a
thermometer
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Latent Heat
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Latent Heat of Vaporization
 Liquid to Vapor
 The 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 Condensation
 Vapor 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
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Latent Heat
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Latent Heat
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Latent Heat
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Latent Heat
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Latent Heat
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 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
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Saturation Temperature
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 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
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Superheated Vapor
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 The amount of sensible heat over a vapors
evaporation point
 Water At Sea Level at 220° F has 8° F of
Superheat
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Sub-cooled Liquid
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 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
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Refrigerants
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 The ability of liquids to absorb enormous quantities
of heat as they vaporize is the basis of the
mechanical refrigeration system
R-22
 Liquid at +25°F and 48.8 psig has a Latent Heat of
Vaporization of 90.3 BTU/lb.
R-404A
 Liquid at -20°F and 16.3 psig has a Latent Heat of
Vaporization of 81.6 BTU/lb
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Alternative
Refrigerants
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 We are constantly looking for new
technology and continue to pursue
alternative refrigerants
 Look for possible refrigerant modifications
in the future
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Refrigeration Capacity
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 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
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Pressure to Control State
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 At Sea Level Water Saturation Point 212°
 At 10,000 Feet Water Saturation Point 193°
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The Refrigeration Cycle
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Compression System

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There are two pressures existing in a
compression system
1. Evaporating or low pressure
2. 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
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Basic System
High Pressure Liquid
Flow
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High Pressure Gas
Flow
Flow
Low Pressure Liquid
Flow
Low Pressure Gas
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Heat Rejection
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 The condenser is the exit door for the heat
that the refrigerant has absorbed in the
evaporator and compressor
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Refrigeration System
Components
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Compressor
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Compressor
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 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
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Hermetic Compressor
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 Most Prevalent in Smaller
Systems
 Costs Less
 Refrigerant Acts as Coolant
 Simple Replacement
 Cannot be Repaired in Field
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Semi-Hermetic Compressor
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 More Robust
 The “Old
Standard”
 Reputation of
Quality
 More
Expensive
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Scroll
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 Hermetic System
 Different Compression System
 More Expensive than Standard
Hermetic
 Less Expensive than SemiHermetic
 Limited to Larger Systems
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Oil Separator
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Oil Separator
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Condenser
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Condenser
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 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
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Headmaster Valve
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Headmaster Valve
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 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
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Headmaster Valve
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Pressure Pre-Set
Not Adjustable
Gas
Mixture
Maintains
High Pressure
Liquid
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Liquid Receiver Tank
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Liquid Receiver Tank
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 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
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Filter/Drier
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Filter/Drier
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 The liquid line filter/drier absorbs moisture,
acid and sludge/varnish
 It also filters (collects) small foreign particles
from the system
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Sight Glass
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Sight Glass
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 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
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Solenoid Valve
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Solenoid Valve
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 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
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Pump-Down
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Sequence
1.
2.
3.
The thermostat senses that the interior walk-in temperature has
become cool enough. The thermostat opens, de-energizing the
normally closed liquid solenoid valve
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
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
Purpose
1.
2.
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)
It prevents the compressor from having to start-up with a high
suction pressure that could overload the compressor motor
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TXV
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TXV
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 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
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TXV
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Sensing
Superheat
Liquid
Liquid
(Starting to Boil)
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TXV
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Sensing
Superheat
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Superheated Vapor
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 The amount of sensible heat over a vapors
evaporation point
 Water At Sea Level at 220° F has 8° F of
Superheat
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Superheat
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 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 clamped
2. Obtain the suction pressure that exists in the suction line at the
bulb location
3. Convert the pressure obtained in 2 above to saturated
evaporator temperature by using a temperature-pressure chart
4. Subtract the two temperatures obtained in 1 and 3 (1 minus 3).
The difference is the evaporator superheat
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Calculating Super Heat
 R-22
 Temperature at bulb is
 Pressure is 49 PSIG
 Super Heat Equals
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33°F
33°F
-25°F
8°F
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Evaporator
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Evaporator
Condenser
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Evaporator
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Evaporator
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 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-in
 People entering the walk-in
 Warm exterior air through wall penetrations not sealed properly
 Heat 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
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Evaporator TD
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 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.
Suction Pressure at Evap
Outlet is 49PSIG
(Refrigerant R-22)
EVAPORATOR TD
35 °F
25 °F
_____
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
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EPR or CPR Valve
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EPR Valve
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 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
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EPR Valve
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 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
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EPR Valve
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Flow
Flow
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CPR Valve
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 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
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CPR Valve
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Flow
Flow
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Suction Accumulator
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Suction Accumulator
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 Primary purpose is to intercept liquid
refrigerant before it can reach the compressor
 Prevents slugging the Compressor
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Suction Accumulator
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Suction Filter
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Suction Filter
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 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
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Refrigeration System
Components
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