Modern Refrigeration and

1
Modern Refrigeration and Air Conditioning
Althouse Turnquist Bracciano
PowerPoint Presentation by Associated
Technical Authors
PublisherThe Goodheart-Willcox Company,
Inc.Tinley Park, Illinois
2
Chapter 13
Commercial Systems
3
Learning Objectives

• Explain the differences between the mechanism of
  commercial refrigeration systems and domestic
  systems.
• Compare the differences between various
  commercial mechanisms.
• Describe how each mechanism (condenser,
  evaporator, and compressor) operates.
• Discuss the theory and operation of control
  devices.
• Follow approved safety procedures.

4
Modules

• Commercial Systems
• Commercial SystemsControls

5
Chapter 13
COMMERCIAL SYSTEMS MODLULE
6
Construction ofRefrigeration Components
13.1

• Varies from domestic systems in the following
  ways
• Number of evaporators connected to a single
  condenser.
• Electrical voltage.
• Compressor design and size.
• Condenser unit designs and size.
• Motor controls (both temperature and pressure).
• Refrigerant controls (liquid and vapor).

7
Construction ofRefrigeration Components
13.1

• Varies from domestic systems in the following
  ways
• Piping.
• Evaporator designs.
• Defrosting systems.
• Variety of refrigerants used.

8
Refrigeration Components
13.2

• Hermetic compressors used on small commercial
  systems such as beverage dispensers, ice cube
  makers, and ice cream machines.
• Semihermetic compressors are used on larger
  commercial applications such as multiple
  evaporator storage rooms, large fresh-food cases,
  and multiple compressor units.
• Commercial systems are either packaged or split
  systems.

9
Refrigeration Componentscontinued
13.2

• Packaged systems are designed, built, and shipped
  by manufacturer and include all components needed
  for a complete system.
• Split systems are site engineered. Components
  are assembled on site. These systems are often
  custom designed for specific applications.

10
Packaged Commercial System Components
13.3

• High-pressure side includes
• Compressor, usually hermetic.
• Condenser, usually air-cooled.
• Liquid receiver, when TXV or AXV are used.
• High-pressure safety motor control.
• Liquid line with drier and sight glass.
• NoteThe refrigerant control is the division
  point between the low side and the high side of
  the system. It consists of an AEV or capillary
  tube.

11
Packaged Commercial System Componentscontinued
13.3

• Low-pressure side includes
• Evaporator.
• Low-pressure or temperature motor control.
• Suction linesome with filter-driers and surge
  tanks.

12
Packaged System withMultiple Evaporators
13.3

• High-pressure side includes
• Compressor, often with an oil separator.
• Condenser water- or air-cooled.
• Liquid receiver.
• High-pressure motor control.
• Liquid lines with a drier and a sight glass.
• Water valve, used with a water-cooled unit.

13
Packages System withMultiple Evaporators
13.3
14
Packages System withMultiple Evaporatorscontinue
d
13.3

• NoteThe refrigerant control is the division
  point between the high-pressure side and the
  low-pressure side.
• Low-pressure side includes
• Refrigerant controls (two or more)usually
  thermostatic expansion valves.
• Evaporators (two or more)may be natural
  convection, forced convection, or submerged.
• Motor controlusually operated by pressure.
• Suction lines with drier and suction pressure
  regulator.

15
Packages System withMultiple Evaporatorscontinue
d
13.3

• Low-pressure side includes (continued)
• Two-temperature valves for multiple temperature
  installation.
• Surge tanks for reducing rapid pressure changes.
• Check valves for multiple temperature
  installations.

16
Subcooling
13.3

• Used on low-temperature units such as display
  cases, freezers, etc.
• The process reduces the refrigerant temperature
  in the liquid line below the saturated
  temperature. The lower the temperature in the
  liquid line, the greater the systems heat
  removal capacity, resulting in a more efficient
  system.
• Accomplished by refrigerating the liquid line on
  a low-temperature system. A high-temperature
  system is used since it removes Btus three times
  more efficiently than low-temperature
  refrigeration systems. Together the two systems
  increase overall efficiency of the refrigeration
  process.

17
Subcooling
13.3
18
Subcoolingcontinued
13.3
External drive unit Condensers are mounted on
steel base. Motor is mounted outside the
compressor. Motor drives the compressor either
directly or with one or more belts.
19
Subcoolingcontinued
13.3
Hermetic unit Motor is connected directly to
compressor. Crankcase and system pressures are
equalized on start-up, preventing oil from
leaving the compressor during start-up.
20
Subcoolingcontinued
13.3

• Compressors may be named after their cylinder
  arrangementvertical single, horizontal single,
  vertical two cylinder, V-type four cylinder, etc.
• Shown is a serviceable six-cylinder W-type
  compressor.

21
Commercial Hermetic Units
13.3.1

• Units with bolted assembly are referred to as
  field serviceable or accessible. Both have
  service valves. Some units are sealed in a welded
  casing. These units may be connected to any type
  of evaporator.
• Advantage of hermetics in commercial field is the
  elimination of crankshaft seals and belts.
  Moisture and dirt must be kept out of system
  during servicing.

22
Commercial Hermetic Unitscontinued
13.3.1
Outdoor hermetically sealed air-cooled condenser
has a fan condenser, shroud, and service valve.
23
Commercial Hermetic Unitscontinued
13.3.1
Inside of four cylinder welded hermetic motor
compressor used for air conditioning, heat pump,
and commercial condensers.ACrankshaft.BConnect
ing rod.CPiston.DMotor windings.EElectrical
terminals.FSuction and discharge openings.
24
Commercial Hermetic Unitscontinued
13.3.1
Smaller units have single-phase motors. Units
over 5 hp generally have three-phase motors.
Rotor
Stator
25
Commercial Hermetic Unitscontinued
13.3.1

• Condensers may be installed in different rooms or
  outside the building.
• Manufacturer-assembled condensing unit can be
  matched with an evaporator assembly and
  precharged refrigeration lines, to meet a wide
  range of cooling needs.

26
Commercial Hermetic Unitscontinued
13.3.1

• For large installations, two-motor compressors
  may be used.
• Tandem assembly motor compressor Connects two
  motor compressors together at the motor end.
  These units can be run separately for low load or
  together for full load.

27
Commercial Hermetic Unitscontinued
13.3.1

• For large installations, two-motor compressors
  may be used.
• Parallel assembly motor compressors Connects two
  or more units in parallel by piping. The units
  also require a compressor oil piping system to
  ensure all compressors have the correct oil
  amount in each crankcase while operating.

28
Outdoor Air-CooledCondensing Units
13.3.2

• Save space when air conditioning commercial
  buildings and homes.
• Save cost of plumbing for water circuits.
• Useful when chemicals in water make water-cooling
  impractical.
• May be mounted on the roof, outside wall, or at
  ground level.

29
Outdoor Air-CooledCondensing Unitscontinued
13.3.2

• Four major provisions to using outdoor air-cooled
  condensing units
• Must be a head pressure control if unit is
  exposed to outdoor weather below the operating
  cabinet temperature.
• Method of preventing short cycling must be
  designed into the system.
• Means provided to prevent dilution of the
  compressor oil by liquid refrigerant.
• Completed condenser must be constructed and
  installed so it is virtually weatherproof.

30
Outdoor Air-CooledCondensing Unitscontinued
13.3.2

• Low ambient temperatures will cause low head
  pressures, which may stop flow of refrigerant. To
  maintain pressure
• Partially fill condenser with liquid refrigerant.
• Stop or slow condenser fans.
• Partially or completely close ambient air
  louvers.
• Heat the condenser.

31
Dual-Compressor Model
13.3.2

• Contains two completely separate refrigeration
  systems.
• Range from 6 tons to 35 tons and provide a
  partial standby system.

32
Dual-Compressor Modelcontinued
13.3.2

• Basic operation similar to two-stage compressor.
  Each compressor is activated individually from a
  two-stage space thermostat.
• Provides two-stage heating and two-stage cooling
  with automatic changeover.

33
Operation ofDual-Compressor Model
13.3.2

• System No. 1 turns on first stage of the
  thermostat.
• If load is light, system No. 1 carries the load.
  The compressor cycle is on and off at the call of
  the thermostat.
• If system No. 1 is not adequate to handle the
  load, the room thermostat automatically turns on
  the second compressor.

34
Operation ofDual-Compressor Modelcontinued
13.3.2

• It will signal on and off to carry the rest of
  the load, while compressor No. 1 runs constantly,
  removing moisture from the air.
• When the load drops and the facility temperature
  is lowered, compressor No. 2 shuts down and
  compressor No. 1 cycles to carry the reduced load.

35
Maintaining Condensing Pressures by Design Change
13.3.2

• When using outdoor units, it is important to
  maintain full operating capacity at the
  thermostatic expansion valve during cold weather.
• Capacity depends on pressure difference across
  the valve. If condensing pressure is reduced,
  valve capacity will drop and not enough liquid
  refrigerant will flow. The fixture temperatures
  may rise too high. The unit will short cycle.

36
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2
A design change can alleviate this problem. The
unit is made to nearly fill the condenser tubes
with liquid. Just enough condensing surface is
left to maintain the pressure.
37
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2

• Installation specifications must be carefully
  checked. The receiver must hold enough liquid
  refrigerant to flood most of the condenser in the
  winter. It must also safely hold the refrigerant
  during the warm season.
• The check valve and limiter valve ensure good
  condensing pressure during cold weather.
• Another method of maintaining pressures is to
  install a pressure-sensitive device connected to
  the condenser tubing. This head pressure device
  will move the rod out as pressures increase,
  opening the louvers.

38
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2

• The adjustable louvers will close as head
  pressure decreases. A system may also use a
  fan-cycling pressure control to sense condenser
  pressure.
• Controls lower the fan speed when the head
  pressure drops. Electrically controlled modulated
  fan speeds are used for this purpose.

39
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2

• The system operates with a thermistor on the
  condenser and a special fan motor.
• Electric heating elements are often placed in or
  around the receiver in an effort to keep receiver
  temperature warmer than cabinet temperature. If
  the receiver became too cold, it would act like a
  condenser.

40
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2
Systems may use a bypass from the compressor to
the receiver. The bypass feeds hot refrigerant
vapor to the receiver to keep it warm. The bypass
has a check valve mounted in it to ensure one-way
refrigerant flow.
41
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2

• Compressor is kept warm by electric heating
  elements that surround it. They are
  thermostatically operated to energize the heating
  element at about 50ºF (10ºC). The heater usually
  has a 100W to 200W capacity.
• Windy conditions can prevent damper and fan
  operation. The unit must be installed in a
  position to avoid high-velocity cold winds. It
  should be as weatherproof as possible with walls
  built around all four sides.
• Head pressure control valves that are thermostat
  operated are often used. A check valve in the
  condenser outlet prevents the flow of refrigerant
  to the cold receiver.

42
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2

• A system with a pressure-control valve will open
  as the receiver pressure falls. Hot gas is
  allowed to bypass into the receiver (at about 20
  psi pressure difference), raising the receiver
  pressure and increasing the flow of liquid
  refrigerant to the evaporators.

43
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2
44
Maintaining Condensing Pressures by Design
Changecontinued
13.3.2

• The valve has two openings, B and C. As one
  closes, the other opens. Valves must be sized to
  capacity of system.
• System is charged with twice as much refrigerants
  as without the condenser flooding feature. A
  receiver that can store all extra refrigerant
  during the summer is needed. For service
  purposes, the receiver should be twice the normal
  size.
• The compressor may collect small amounts of
  liquid refrigerant during the off cycle. A trap
  may be needed in the compressor discharge line.

45
The Compressor
13.3.3

• Commercial compressors are either external drive
  or hermetic.
• There are several types of commercial hermetic
  compressors. A bolted hermetic compressor uses
  temperature limit controls and an oil pressure
  sensing safety control.

46
The Compressorcontinued
13.3.3
Large units may have winter hydraulic or electric
unloading devices to control the number of
cylinders pumping. The higher the load, the more
cylinders used to pump the vapor.
47
The Compressorcontinued
13.3.3

• A welded hermetic motor compressornot field
  serviceableis built in sizes from 1/6 hp to 20
  hp. Design varies with size and manufacturer.
  Some are spring mounted internally others use
  outside mounting springs. Smaller units have one
  cylinder. Larger units have two or more
  cylinders. Small units may be either two or
  four-pole (single phase). Three-phase motors are
  used in larger units.

48
The Compressorcontinued
13.3.3

• Each compressor has a minimum and maximum
• Revolutions per minute (rpm) for efficiency.
• Compression ratio (a maximum pressure difference
  between low side and high side).
• Discharge temperature.
• Volume of gas it can pump.
• Prior to using a compressor, check the
  manufacturers operating specifications.

49
Cascade Systems
13.3.3

• Used in many low-temperature systems.
• First stage compressor may be reciprocating unit,
  but rotary units are also used. Rotary compressor
  pressure limit is about 45 psi across the
  compressor. Works well with a compression ratio
  of 41. Also works well with a discharge
  temperature of about 200ºF (93ºC).
• Rotary has a high volumetric efficiency. A check
  valve is usually placed in the discharge to
  prevent backup of refrigerant during off cycle.
  Check valve should also be placed in the oil
  lines.

50
Cascade Systemscontinued
13.3.3
Compressors may have from one to twelve
cylinders. There are numerous cylinder
arrangements.
51
Cascade Systemscontinued
13.3.3

• Internal unloaders are usually operated by oil
  pressure. A spring holds the intake valve open
  until oil pressure builds up, causing all intake
  valves to operate. This also reduces pumping
  capacity during low-load conditions. Solenoid
  valves are mounted in the oil lines to unloaders.
  When the solenoid closes, the oil pressure drops
  in the unloader. The intake valves are kept open.

52
Cascade Systemscontinued
13.3.3

• Low-side pressure switches operate the solenoids.
  A timer bypass pressure switch operates the
  system at full capacity for a minute each hour or
  two. External unloaders use a bypass to the
  evaporator inlet ensuring suction vapor is cool.
  (De-superheating.)

53
Air-Cooled Condenser
13.3.4

• Common in large commercial systems. May be cooled
  by a big fan built onto the motor or into the
  compressor flywheel on external drive units.

54
Air-Cooled Condensercontinued
13.3.4
Placing a metal shroud around the air-cooled
condenser may increase fan efficiency. More than
one fan may be used. Air is drawn and forced
through the condensers.
55
Air-Cooled Condenser
13.3.4
The condensers have fins and frequently use a
double or triple row of tubes. A variety of fin
arrangements and constructions may be used.
56
Outdoor Air-Cooled Condensers
13.3.5

• Motor compressor and liquid receiver may be
  located indoors and the air-cooled condenser
  located outdoors.
• The compressor discharge line carries the hot
  high-pressure vapor to the outdoor air-cooled
  condenser.
• The condensed liquid is piped back into the
  building.

57
Water-Cooled Condenser
13.3.6

• Large commercial refrigerating units often use
  water-cooled condensers. They are built in three
  styles
• Shell and tube.
• Shell and coil.
• Tube-within-a-tube.

58
Shell and Tube Condenser
13.3.6

• Cylinders usually made of steel with copper tubes
  inside. Water circulates through the tubes
  condensing hot vapors in the cylinder into a
  liquid.
• The bottom part of the shell serves as a liquid
  receiver.

59
Shell and Tube Condenser
13.3.6
60
Shell and Tube Condenser
13.3.6
Advantages include compact, needs no fans, and
combines condenser and receiver in one. When
manifold ends are removed, water tubes can easily
be cleaned of deposits.
61
Shell and Coil Condenser
13.3.6

• Very similar to shell and tube water-cooled
  condenser.
• Has a coil of water tubing inside the shell
  rather than a straight tube.
• Often used in smaller commercial units.

62
Tube-within-a-Tube Condenser
13.3.6

• Popular because it is easy to construct.
• Water passing through the inside tube cools the
  refrigerant in the outer tube. The outer tubing
  is cooled by air in the room. Double cooling
  improves efficiency.

63
Tube-within-a-Tube Condensercontinued
13.3.6
This type of condenser may be constructed in a
cylindrical, spiral, or rectangular style.
64
Tube-within-a-Tube Condensercontinued
13.3.6
The inner tube shows a six-lead and an eight-lead
grooved inner tube that is designed to increase
heat transfer.
65
Tube-within-a-Tube Condensercontinued
13.3.6
A double-walled inner tube with a grooved design
achieves venting of refrigerant vapor in the
event of a leak.
66
Tube-within-a-Tube Condensercontinued
13.3.6

• The tube-within-a-tube design has water entering
  the condenser at the refrigerant outlet. The
  water leaves the condenser at the point where the
  hot vapor from the compressor enters. This is
  called a counterflow design. The warmest water is
  adjacent to the warmest refrigerant and the
  coolest refrigerant is next to the coolest water.

67
Cooling Towers
13.3.7

• Water-cooling towers save on water consumption.
  The towers serve the same purpose as the spray
  towers in large systems.
• There are a variety of cooling tower designs.
• Cooling towers generate excessive noise due to
  their large fans and water sprays. Therefore,
  they should be located away from areas such as
  offices, restaurants, and residences.
• Cooling towers are made of corrosion-resistant
  materials, including steel, copper, stainless
  steel, plastic, and treated wood.

68
Cooling Towers
13.3.7
69
Cooling Towerscontinued
13.3.7

• The more water surface in contact with the air
  flowing through the cooling tower, the more
  efficient the cooling action.
• The following factors impact performance of a
  cooling tower
• Design conditions.
• Humidity requirements.
• Tower heat load.
• Design wet bulb temperature.
• Water quality.

70
Cross-Flow Cooling Tower
13.3.7

• A cross-flow cooling tower takes the water from
  the heat source through an inlet on the side of
  the unit to the hot water distribution basins on
  each side.
• Gravity flow nozzles distribute the water evenly
  over the wet deck surface. Air is drawn through
  the air inlet louvers and across the wet deck,
  causing some water to evaporate, removing heat
  from the remaining water.

71
Cross-Flow Cooling Towercontinued
13.3.7

• Cooled water flows into the lower sump and
  returns to the heat source. Cooled water collects
  in the bottom of the enclosure and passes through
  a screen removing foreign material. The water is
  then re-circulated through the condenser.
• A float-controlled valve in the lower water pan
  adds water as needed.
• A drain continually bleeds some water out of the
  pan to keep water hardness to a minimum.
  Chemicals are added to retard rust, algae,
  fungus, and bacteria.

72
Cross-Flow Cooling Tower
13.3.7
73
Fills
13.3.7

• A fill is a material that allows water to flow
  over materials in thin films, ensuring increased
  contact with the airflow and more efficient
  cooling action.
• Fills are made of many materials metal fins,
  wood slats, plastic, etc.
• The shapes of the surfaces vary with the most
  popular being cellular (honeycomb).
• The distribution system (nozzles, troughs,
  V-notches) must be kept clean and must distribute
  water evenly to prevent scale buildup.

74
PreventingCooling Tower Freezing
13.3.7

• Normally no danger of freezing while in
  operation. Electric heat in the form or immersion
  and convection heaters can keep water temperature
  up during shutdowns.
• An electric heater may be installed in the pump
  circuit to prevent freezing.
• Hot water or steam may be used to prevent
  reservoir freeze-up. Pipes may require insulation
  or electric heater tape.

75
Screens for Cooling Towers
13.3.7

• Use only coarse screens on pump inlets. All
  suction lines must be below water level in the
  cooling tower or air may enter the suction line,
  causing drop in pump volume and damage.
• Pump outlets require fine screens. The water pump
  should push water through the system to prevent
  low water pressures in the condenser tubes or
  pipes.
• See manufacturers literature for details of
  tower sizes and capacities.

76
Cooling Towers andLegionnaires Disease
13.3.7

• Legionella Pneumophila is a bacterium that causes
  Legionnaires disease.
• First found in 1976 at a Legionnaires convention
  in Philadelphia.
• During convention, over two hundred people became
  ill and thirty-four people died.
• Symptoms include headache, high fever, and
  respiratory problems.
• Disease is caused by contaminated cooling water
  from a cooling tower. Bacteria grow in stagnant
  cooling-tower water and are then transferred from
  the water sprays into the buildings air
  conditioning ductwork.

77
Cooling Towers andLegionnaires Diseasecontinued
13.3.7

• Preventive measures include placing cooling
  towers downwind from buildings and ductwork, and
  periodic disinfecting of cooling towers.
• When bacteria count is high, action must be taken
  to reduce levels.
• Check state and local requirements for testing
  procedures.

78
Evaporative Condensers
13.3.8

• The evaporative condenser system carries
  refrigerant into a condenser.
• An enclosure much like a cooling tower, and is
  usually mounted outdoors.
• Water is sprayed or drips over the condenser,
  cooling it.
• Water cycle is in the condenser cabinet only.

79
Evaporative Condenserscontinued
13.3.8

• Variety of systems are available including one
  that pumps water to a trough above the condenser.
• The water drips over coils as air is forced
  through them. A thermostat can be used to control
  the water flow.
• A fan blows air over the condenser whenever the
  condenser is operating.
• The condenser is cooled by air alone until the
  condenser temperature reaches 80ºF (26.7ºC) or
  more. A thermostat then initiates water cooling.

80
Evaporative Condenserscontinued
13.3.8

• One method subcools the refrigerant as it leaves
  the receiver.
• The liquid line goes through the evaporative
  condenser.
• Temperature of the refrigerant can be dropped
  10ºF (6ºC) by subcooling.
• When the temperature reaches 45ºF (7.2ºC) or
  lower, the water is shut off.
• The condenser can still carry the load as an
  air-cooled condenser.

81
Liquid Receiver
13.3.9

• The liquid receiver is a welded steel tank with
  two service valves.
• One service valve is mounted between the liquid
  receiver and the condenser. The other is located
  between the receiver and the liquid line.
• Receivers should have safety devices, minimally a
  thermal release plug. Some receivers should have
  both thermal and pressure releases. A special
  line should be installed on relief valves to the
  refrigerant recovery system.

82
Liquid Receivercontinued
13.3.9

• Receivers may be mounted vertically or
  horizontally. The horizontal style hangs
  underneath the compressor and motor frame.
• Some receivers have a sight glass, magnet floats,
  or valves for determining level of liquid
  refrigerant. The receiver should be able to hold
  the entire refrigerant charge in the system.

83
Liquid Receiver
13.3.9
84
Commercial Evaporators
13.4

• Divided into two main groups
• Those used for cooling air in turn, the air
  cools the contents of the cabinet.
• Those submerged in a liquid, such as brine or a
  beverage.
• Evaporators for cooling are of two primary types
• Natural convection.
• Forced convection.

85
Commercial Evaporatorscontinued
13.4

• Natural air convection evaporators
• Air circulation depends on gravitational or
  thermal circulation.
• Three classes of natural convection, air cooling
  evaporators
• Frosting.
• Defrosting.
• Nonfrosting.
• Conditions (temperature range, temperature
  difference between evaporator and cabinet) under
  which an evaporator must work determine its
  classification.

86
Frosting Evaporators
13.4.1

• Frequently used in low temperature and frozen
  food fixtures.
• Builds up frost continuously when operating.
• Operates at 5ºF (15ºC) refrigerant temperature
  cut-in.
• Machine must shut down from time to time to get
  rid of frost.
• Frost on evaporator comes from moisture in air.
  Therefore, air in cabinet is dry.
• As frost grows thicker, cooling efficiency of
  evaporator is reduced.

87
Defrosting Cycle Evaporators
13.4.2

• While condenser is running, temperature of the
  evaporator is low, causing frost to accumulate on
  it.
• When compressor shuts off, the coil warms above
  32ºF (0ºC). The frost melts.
• While compressor is running, the evaporator will
  remain at 20ºF to 22ºF (6.6ºC to 5.6ºC).

88
Defrosting Cycle Evaporatorscontinued
13.4.2

• This defrosting process is called air defrosting.
  It clears the evaporator surfaces of frost and
  provides efficient heat transfer.
• It maintains a high relative humidity of 9095.
  
• This sacrifices temperature differences between
  the evaporator refrigerant and the air in the
  cabinet.
• Greater evaporator area is needed to make up for
  this loss.

89
Defrosting Cycle Evaporatorscontinued
13.4.2

• Often present problems. Top of evaporator may
  defrost and moisture flows down the surface,
  freezing on the lower parts of the evaporator.
• This ice accumulation will block air circulation
  around the evaporator and interfere with proper
  refrigeration.
• The drier coil prevents blockage.

90
Nonfrosting Evaporators
13.4.3

• Operate at temperatures not much below 32ºF
  (0ºC), so frost does not form on evaporator.
• Evaporators operate at temperature of 33ºF
  (0.6ºC) to 34ºF (1.1ºC). Refrigerant temperature
  inside the evaporator will be around 20ºF
  (6.7ºC) to 22ºF (5.6ºC).
• Since they do not frost over, little moisture
  from inside the cabinet is lost. Therefore, a
  relative humidity (RH) of 75 to 85 can be
  maintained in cabinet, keeping produce fresh.

91
Nonfrosting Evaporatorscontinued
13.4.3
Fin-Type
Plate-Type
Two types of evaporator construction are used.
92
Forced Circulation Evaporator
13.4.4

• A compact arrangement of refrigerant-cooled tubes
  and fins. A fan driven by an electric motor blows
  air over them.
• Evaporator and fan are usually enclosed in a
  metal housing.

93
Forced Circulation Evaporatorcontinued
13.4.4

• Forced circulation evaporators tend to cause
  rapid dehydration of food. Drying can be
  minimized if the evaporator is large.
• It should operate at a small temperature
  difference 10ºF to 12ºF (6ºC to 7ºC).
• Air should be circulated slowly.

94
Forced Circulation Evaporatorcontinued
13.4.4
Fan motor can be any size and may run
continuously. Refrigerant temperature is usually
kept quite low. Rapid air circulation keeps
evaporator from frosting up. Considerable
sweating occurs so drainage must be provided.
95
Forced Circulation Evaporatorcontinued
13.4.4

• Blower evaporators operated at low refrigerant
  temperatures need special defrosting care. Frost
  or ice may interfere drastically with heat
  transfer.
• A microprocessor controls the operation of the
  expansion valve, defrost system, and fan.

96
Forced Circulation Evaporatorcontinued
13.4.4
A condensate pump may be used to remove
condensate. The pump is mounted on the drain and
is self-priming. It uses 10W and operates
continuously. It may also be used for pumping
slightly acidic condensate produced by
high-efficiency gas furnaces.
97
Forced Circulation Evaporatorcontinued
13.4.4
Many evaporators use a hot gas bypass system. It
maintains above-freezing temperatures when
cooling load is decreased. Hot gas is provided to
prevent evaporator frosting during low head
conditions.
98
Liquid-Cooling Evaporator
13.4.5

• Used to refrigerate drinks, water, and beverages.
• Three types of cooling evaporators are used
• Bottled liquids.
• Liquids under atmospheric pressure.
• Liquids under pressure.

99
Immersed Evaporator (Brine)
13.4.5

• Evaporator mounted inside the liquid being cooled
  is referred to as an immersed evaporator.
• Usually a small, plain tube evaporator is used.
• Immersion makes the evaporator more efficient.
  Liquids transfer heat to metals faster than air.
  An efficiency ratio of 501 to 1001 is common.
• A submerged evaporator can remove 50 to 100 Btu
  per hour, per degree temperature difference, per
  square foot of evaporator surface.
• Air-cooling evaporators can only remove 1 Btu
  under the same conditions.

100
Immersed Evaporator(Sweet Water)
13.4.5

• Immerses the evaporator in ordinary tap water
  called a sweet water bath.
• Allows the sweet water to freeze around the
  evaporator during the nonload period.
• Light ice accumulation acts as a reserve of
  refrigeration.

101
Immersed Evaporator(Sweet Water)continued
13.4.5

• Usually have a thermostatic expansion valve
  refrigerant control. Evaporator should reach
  bottom if the bath temperature is to be less than
  39.1ºF (3.9ºC).
• Water, as it cools from 39.1ºF to 32ºF (3.9ºC to
  0ºC) expands and rises. Therefore, the coldest
  water is on top.

102
Pressure (Beverage) Evaporators
13.4.5

• Liquid refrigerant is carried in a tube submerged
  in the beverage to be cooled. The beverage itself
  is under pressure. The temperature of the
  beverage must never be low enough to freeze to
  any extent.
• An all-metal beverage evaporator takes advantage
  of the high heat conductivity of aluminum. Two
  separate copper tubes are coiled in a helix
  (spiral) design. They are then molded in a hollow
  cylinder of aluminum.
• Refrigerant is evaporated in one coil. Heat will
  then flow from the liquid in the other coil.
  Coolers may have three or more separate tubes
  enclosed by aluminum when more than one liquid
  must be cooled.

103
Ice Cube Maker Evaporator
13.4.6

• To create flaked ice, the following process
  occurs
• Water is made to flow over an evaporator shaped
  like a cylinder. The evaporator surface is cold,
  9ºF (12.7ºC), so the water freezes rapidly.

104
Ice Cube Maker Evaporatorcontinued
13.4.6

• To create flaked ice, the following process
  occurs (continued)
• A heavy steel auger is driven by an electric
  motor. It cuts and scrapes the ice from the
  surface.

105
Ice Cube Maker Evaporatorcontinued
13.4.6

• To create flaked ice, the following process
  occurs (continued)
• Float level control of the water is provided. A
  shutoff mechanism is located in the storage bin
  halts ice making when bin is full.

106
Ice Cube Maker Evaporatorcontinued
13.4.6
Square or cylindrically shaped cubes may be
formed by using a tube-within-a-tube.
107
Ice Cube Maker Evaporatorcontinued
13.4.6
The water and ice circuit of an automatic ice
cube maker includes an inlet water strainer,
water valve, evaporators, and ice forming tubes.
108
Ice Cube Maker Evaporatorcontinued
13.4.6

• Ice is harvested when a hot gas solenoid valve is
  energized allowing high-pressure vapor to
  enterthe evaporator.

109
Ice Cube Maker Evaporatorcontinued
13.4.6

• Small commercial ice cube makers are often used
  in fast-food restaurants.
• Basic components
• Evaporator.
• Automatic expansion valve.
• Gearbox.
• Water reservoir.

110
Ice Cube Maker Evaporatorcontinued
13.4.6
111
Ice Cube Maker Evaporatorcontinued
13.4.6

• Process for small commercial ice cube maker
• Water enters at water inlet and goes through
  water supply assembly.
• Water enters the bottom of the evaporator and
  freezes on the evaporator cylinder.
• The auger inside the freezer evaporator moves the
  ice upward into the storage bin.
• When the bin is filled, the ice-making switch
  shuts off the flow of ice.

112
Ice Cube Maker Evaporatorcontinued
13.4.6

• Caution It is very important to follow the
  plumbing code in piping away the drain water. A
  loss of water pressure in the buildings water
  supply could cause reverse siphoning. This may
  result in contamination of the drinking water in
  the building.

113
Freezing Dispenser Evaporators
13.4.8
The freezing evaporator is a cylinder in which a
motor-driven dasher churns the mix. The
refrigerant then travels to a premix storage
compartment.
114
Freezing Dispenser Evaporatorscontinued
13.4.8
A serviceable hermetic motor compressor, a
water-cooled condenser, and a freezer-mixing
blade drive motor, are components of a
freezer-dispenser.
115
Evaporator Defrosting
13.4.9

• Many evaporators operate at temperatures below
  freezing. Low temperatures and small fin spacing
  make frequent defrosting necessary.
• Defrosting is usually automatic.
• Some evaporators defrost during each off part
  of the cycle.
• Others use a timer control.

116
Evaporator Defrostingcontinued
13.4.9

• Six defrosting methods
• Hot refrigerant vapor system.
• Nonfreezing solution system.
• Water system.
• Electric heater system.
• Reverse cycle defrost system.
• Warm air system.
• These defrosting methods either heat the
  evaporator from the inside or outside to melt the
  frost. It is important to clean the evaporator,
  drain pans, and drain lines frequently.

117
Hot Gas Defrost System
13.4.9

• Hot refrigerant vapor is pumped directly through
  the evaporator tubing. System has a refrigerant
  line running directly from the compressor
  discharge line to the evaporator.
• Line may be connected between the thermostatic
  expansion valve or the capillary tube and the
  evaporator.
• Line is opened and closed by a solenoid shutoff
  valve.

118
Hot Gas Defrost Systemcontinued
13.4.9

• At a predetermined time, when the system is not
  in use, a timer closes the circuit.
• Compressor starts, opens the solenoid valve, and
  stops the evaporator fan motors.
• Hot compressed vapor rushes through the
  evaporator and warms it.
• It then returns to the compressor along the
  suction line.

119
Hot Gas Defrost Systemcontinued
13.4.9
120
Hot Gas Defrost Systemcontinued
13.4.9

• Defrost process usually takes 5 to 10 minutes.
• Defrost water must be kept from freezing in the
  drain pan and tube.
• A hot gas defrost line may be installed under the
  drain pan and pipe or a small electric heater can
  be installed here.

121
Evaporation of Condensate during Defrost Cycle
13.4.9

• A defrost bypass places some hot gas into the
  suction line to vaporize any liquid refrigerant.
• A TEV is mounted on a line between the liquid
  line and the suction line.
• The sensing bulb is mounted on the suction line.
• If gas returning to compressor becomes warm, TEV
  will open.
• Liquid refrigerant mixes with hot bypass gas.
• Mix is kept between 45ºF and 65ºF (7.2ºC and
  18.3ºC).
• A solenoid valve in the bypass TEV inlet shuts
  off the TEV when the system is operating normally
  or on a full load.

122
Evaporation of Condensate during Defrost
Cyclecontinued
13.4.9

• Heat is applied to vaporize the returning
  refrigerant.
• A blower-evaporator may be installed in
  connection with suction line, allowing only vapor
  to return to the compressor.
• The blower only works when unit is on defrost. An
  accumulator mounted in the suction line will trap
  liquid refrigerant and vaporize it prior to it
  reaching the compressor.

123
Evaporation of Condensate during Defrost
Cyclecontinued
13.4.9
124
Evaporation of Condensate during Defrost
Cyclecontinued
13.4.9

• Sometimes hot gas is fed backwards into the
  evaporator.
• Condensed refrigerant bypasses the TEV by means
  of a check valve, forcing the liquid into the
  receiver by way of the liquid line.

125
Evaporation of Condensate during Defrost
Cyclecontinued
13.4.9
126
Hot Gas Cooling Cycle
13.4.9

• Refrigerant that condenses during the defrost
  cycle should be evaporated.
• During the defrost cycle, hot gas from the
  compressor and receiver travel back to the
  evaporator by way of the suction line.
• Condensed liquid refrigerant is traveling around
  TEVs by way of check valve and is returning to
  the receiver through the liquid line.
• A heater in the receiver provides more hot gas
  for defrosting.

127
Hot Gas Bypass Valves
13.4.9

• Pressure Operated
• Connected to the suction line.
• Valve is adjusted by low-side pressure of the
  vapor going to the compressor.
• Opens wider as suction pressure drops and starts
  to close as low-side pressure rises.

128
Hot Gas Bypass Valvescontinued
13.4.9

• Pilot Controlled Valve
• Dependent on suction line pressure.

129
Multiple Systems withSeveral Evaporators
13.4.9

• Evaporators should be defrosted one at a time.
• Others are used to evaporate the liquid from the
  defrosting evaporator.
• This ensures no liquid refrigerant will reach the
  low side of the motor compressor.

130
Multiple Systems withSeveral Evaporators
13.4.9
131
Multiple Systems withSeveral Evaporatorscontinue
d
13.4.9

• Valve may be used in place of two suction line
  valves on each evaporator.
• Evaporator gas at point A travels into valve
  during normal operation. Hot gas travels out of
  valve at A during defrosting.
• When pilot solenoid valve at A is energized, it
  opens, allowing high-pressure gas from discharge
  connection to push down on the double valve.
• This closes the top valve B, stopping flow from
  evaporator into suction line, opening bottom
  valve C. High-pressure hot gas flows from
  discharge connection up into the evaporator.

132
Multiple Systems withSeveral Evaporatorscontinue
d
13.4.9
133
Nonfreezing SolutionDefrost System
13.4.9

• The hot fluid defrost system has a container in
  which brine is stored.
• Refrigerant vapor from the compressor is pumped
  through heat storage container then into the
  condenser.
• The brine may be electrically heated during the
  normal running part of refrigerating cycle.
• When system shuts off, the defrost timer closes a
  solenoid valve. This is the beginning of the
  defrost cycle. The evaporator fan is usually shut
  off.
• The brine solution is pumped through its own
  piping along the drain line, drain pan, and
  evaporator. It then returns to its container.

134
Nonfreezing SolutionDefrost System
13.4.9
135
Water Defrost Systems
13.4.9

• Runs warm tap water over evaporator when system
  is off. Done manually or automatically.
• Water may be sprayed over evaporator, or fed to a
  pan located over the evaporator. Holes in the pan
  feed the water evenly over the evaporator.
  During the operation, evaporator louvers are
  closed.
• Water lines must be completely drained before
  unit is turned on, or water will freeze. Electric
  timer provides automatic operation.
• Pump may be employed to recirculate brine.
  Eliminator plates are needed to prevent brine
  spray from passing into the refrigerated space.

136
Water Defrost Systems
13.4.9
137
Electric Heater Defrost System
13.4.9

• Popular for defrosting low-temperature
  evaporators. Heating coils are installed in the
  evaporator, around it, or within the refrigerant
  passages.
• May use resistance wire heating elements mounted
  underneath the evaporator, under the drain pan,
  and along the drainpipe.
• A timer stops the refrigeration unit and closes
  the liquid line.
• It then pumps the refrigerant out of the
  evaporator. Blowers and electric heaters are
  turned on.
• Heaters melt the frost from the evaporator and
  water drains away.

138
Pump Down
13.4.9

• A control system.
• An extra relay is wired into the compressor
  circuit in parallel to the normal relay. It is
  connected to the thermostat circuit. The extra
  relay operates the start button on the normal
  starting relay. The compressor cannot restart
  until the thermostat points close.
• The thermostat operates a solenoid in the liquid
  line. At same time, a low-pressure switch
  operates the compressor, to prevent flow of
  liquid refrigerant from the evaporator to the
  compressor.

139
Pump Downcontinued
13.4.9

• When thermostat is satisfied, it opens and liquid
  line solenoid closes.
• Compressor continues to run, removing refrigerant
  vapor from the evaporator and suction line.
• When proper low-side pressure is reached,
  low-pressure switch opens and the compressor
  stops. Crankcase heaters may be needed to drive
  the refrigerant during the off cycle.

140
Optional ElectricDefrost Systems
13.4.9

• An immersion electric heater heats a separate
  charge of refrigerant. The warm refrigerant
  circulates in the evaporator while the unit is
  turned off, defrosting the system.

141
Optional ElectricDefrost Systemscontinued
13.4.9

• In a double tube evaporator system, refrigerant
  passes through the passageway between the tubes
  during normal refrigeration.
• Electric heating elements are inserted in the
  center tube.
• In the defrost operation, the system is stopped
  and the electric heating elements are turned on.
  The evaporator tubes cause defrosting from the
  inside.

142
Reverse Cycle Defrost System
13.4.9

• Evaporators are defrosted by reversing the flow
  of refrigerant, causing the evaporator to become
  the condenser and the condenser an evaporator.
• The evaporator, functioning as a condenser, melts
  the frost. A four-way valve handles the reversing.

143
Warm Air Defrosting
13.4.9

• Cabinet air is used for defrosting if it is at
  the correct temperature.
• Cycles must be frequent enough and long enough to
  defrost the evaporator completely.
• Outside air may be used for defrosting, using a
  controlled duct system with blowers and a fan.

144
Heat Exchangers
13.4.10

• Heat exchanger mounted in the suction and liquid
  line has three advantages
• Subcools the liquid refrigerant and increases
  operating efficiency.
• Reduces flash gas in the liquid line.
• Reduces liquid refrigerant in the suction line.

145
Heat Exchangerscontinued
13.4.10
Heat is transferred from the warmer liquid in the
liquid line to the cool vapor coming from the
evaporator.
146
Heat Exchangerscontinued
13.4.10

• Reduces flash vapor (flash gas). Liquid cooled by
  10ºF to 20ºF (5ºC to 11ºC) at prevailing head
  pressure absorbs more latent heat. This occurs as
  it changes to a vapor in the evaporator. This
  subcooled liquid reduces the chance of flash gas
  forming in the liquid line.
• Prevents sweat backs or frost backs on the
  suction line. Low-temperature liquid refrigerant
  in the returning suction vapor will evaporate in
  the heat exchanger, as the refrigerant absorbs
  heat from the liquid line.

147
Questions

• What is subcooling and where does it take place
  in a refrigeration system?

Subcooling is lowering the temperature of a
liquid below its saturation temperature. It takes
place at the end of the condenser and in the
liquid line.

• What special provisions must be made to outdoor
  refrigeration condensing units?

They must have a head pressure control and a
crankcase heater.

• Name three types of head pressure controls.

Airflow louvers, cycling of condenser fans, and a
head pressure control valve.
148
Questionscontinued

• How does a head pressure control valve maintain
  high-side pressures?

It bypasses hot gas into the receiver and floods
the condenser.

• Name three types of water-cooled condensers.

Tube-within-a-tube, shell and tube, and shell and
coil.

• How does the counter-flow principle work for a
  tube-within-a-tube condenser?

The coldest (entering) water is in contact with
the coldest (leaving) refrigerant.
149
Questionscontinued

• Name two factors that affect the operation of a
  cooling tower.

Wetbulb temperature and water quality.

• What is the purpose of a float control valve in a
  cooling tower?

It is used to add makeup water to the system when
needed.

• If cooling towers are not properly maintained,
  certain bacteria in the water can cause a fatal
  disease called _________________.

Legionnaires disease
150
Questionscontinued

• Which type of condenser uses both airflow and
  water flow for heat transfer?

An evaporative condenser.

• What is the purpose of a receiver?

It is a storage tank that holds the systems
refrigerant charge.

• Name two types of direct expansion evaporators.

Natural and forced convection evaporators.
151
Questionscontinued

• Name two types of defrost systems.

Electric and hot gas defrost.

• On a hot gas defrost system, which component must
  be de-energized during the defrost mode?

The evaporator fans.

• Which component must be added to the suction line
  on a hot gas defrost system?

An accumulator.
152
Questionscontinued

• With an automatic pumpdown system, which
  component does the temperature control operate?

The liquid line solenoid.

• On an automatic pumpdown system, which component
  does the low-pressure control operate?

The compressor.

• Which type of defrost system uses a four-way
  solenoid valve?

A reverse cycle defrost system.
153
Questionscontinued

• What is the purpose of a heat exchanger?

It is used to subcool the liquid refrigerant
before the expansion valve to increase system
efficiency.
154
Chapter 13
COMMERCIAL SYSTEMSCONTROLS MODULE
155
Refrigerant Controls
13.5

• Refrigerant Controls
• A single evaporator and condenser system
  typically use one of the following refrigerant
  controls
• Thermostatic expansion valves.
• Automatic expansion valves.
• High-side floats.
• Low-side floats.
• Capillary tubes.
• Systems with more than one evaporator usually use
  multiple thermostatic expansion valves or
  low-side floats.

156
Motor Controls
13.6

• Commercial refrigeration uses two basic types
• Thermostatic.
• Pressure.
• Large systems use magnetic starters operated by
  motor controls.

157
Motor Controlscontinued
13.6

• In multiple evaporator commercial systems,
  pressure motor controls are often used because
• Low-side pressure is an indication of the
  temperature in the evaporators.
• One control works well regardless of the number
  of evaporators connected to it.
• Pressure motor controls provide variety of range
  and differential adjustments.

158
Motor Controlscontinued
13.6
159
Motor Controlscontinued
13.6
There are recommended average pressure motor
control settings.
160
Pressure Motor Control
13.6.1

• Usually mounted on the condenser.
• Operated by low-side pressure.
• Control should be placed about 10' to 15' (3m to
  4.6m) from the compressor.
• Range settings vary with application. Cut-out
  pressure should be set about 10ºF (6ºC) below the
  desired evaporator outside surface temperature.
  Cut-in pressure should be about the same as the
  highest allowable evaporator temperature.

161
Pressure Motor Control
13.6.1
162
Pressure Motor Controlcontinued
13.6.1

• Differential setting will vary, depending on the
  temperature accuracy required.
• A wide pressure difference will allow some
  variation in cabinet temperature and lengthen the
  operating cycle interval of the condenser. (The
  compressor will not run as often.)
• A differential set to close limits will maintain
  a more uniform cabinet temperature, and will
  shorten the cycling interval of the condenser.
  (The unit will run more often.)

163
Pressure Motor Controlcontinued
13.6.1

• Pressure difference between cut-in and cut-out
  point varies with the refrigerant used.
• Common pressure difference is 20 psi for R-12,22
  psi for R-22, 16 psi for R-500, and 25 psi for
  R-502.

164
Thermostatic Motor Control
13.6.2

• Similar to pressure motor control in design, but
  sensing bulb and capillary tube are different.
• Used in large single installations.
• If used in multiple evaporator system, is used to
  sense warmest evaporator case.

165
Thermostatic Motor Controlcontinued
13.6.2

• Sized so when the unit shuts off the compressor,
  there is sufficient cooling in the colder
  conditioned space. Allows each separate cabinet
  in a multiple installation to be controlled.
• May have a very close differential, such as 1ºF
  (0.5ºC), in display cases, frost alarms, liquid
  chillers, and refrigerated trucks.
• May have double-throw contacts and operate other
  devices (fans, defrost systems).

166
Safety Motor Controls
13.6.3

• Commercial systems may use high-pressure safety
  cutout and oil pressure safety cutout.
• High-pressure safety device
• A bellows built into the control and connected to
  the high-pressure side of the system.
• Often connected to cylinder head for easy
  disconnecting of the control from the system.

167
Safety Motor Controlscontinued
13.6.3

• High-pressure safety device
• A bellows built into the control and connected to
  the high-pressure side of the system.
• Often connected to cylinder head for easy
  disconnecting of the control from the system.

168
Safety Motor Controlscontinued
13.6.3

• High-pressure safety device
• When head pressure becomes too high, bellows will
  expand. The bellows are attached to plunger that
  is pushed against the switch, shutting off the
  motor.
• High-pressure safety device prevents buildup of
  dangerous pressures with the system.
• Usually set to cut out at 20 above normal head
  pressure.
• R-12 set at 150-160 psi, R-22 set at 260-270 psi,
  R-502 set at 280-290 psi, and R-500 set at
  190-200 psi.

169
Safety Motor Controlscontinued
13.6.3

• Oil pressure safety cutout
• Shuts off electrical power if oil pressure fails
  or drops below normal.
• A differential control, using two bellows.
• One bellows responds to crank pressure, the other
  to oil pressure.
• Oil pressure must always be above the crank
  pressure for oil to flow.

170
Safety Motor Controlscontinued
13.6.3

• Oil pressure safety cutout (continued)
• Control opens circuit if pressure difference
  between two bellows drops below required oil
  pressure.
• Used in large commercial systems. Control points
  may be in compressor motor circuit or through a
  bimetal strip.

171
Safety Motor Controlscontinued
13.6.3

• Oil pressure safety cutout (continued)
• Refrigerant level kept within safe limits by
  float switch. If level is too high, float switch
  closes an electrical circuit. If level is too
  low, actuates a circuit allowing refrigerant to
  flow into the system.

172
Motor Contactors
13.6.4

• Allows commercial controls to handle larger
  motors (larger loads) using a magnetic starter
  (contactor).
• An electromagnetic device whose magnetism is
  controlled by the electricity that flows through
  the motor control.
• Magnetism attracts an armature. The armature
  moves, closing large contact points.

173
Motor Contactorscontinued
13.6.4

• Contact points safely carry large current flow
  needed for large motors.
• Mounted in an approved metal box with safety
  access door. May incorporate manual shutoff
  switch, fuses, and overload thermal safety
  breaker switch.

174
Motor Contactorscontinued
13.6.4

• Mounted in an approved metal box with safety
  access door. May incorporate manual shutoff
  switch, fuses, and overload thermal safety
  breaker switch.
• Safety switch operated by heating element in
  motor circuit black lead inside the contactor box
  or starter.

175
Motor Contactorscontinued
13.6.4
If motor demands too m