Section 3

DESCRIPTION

3.1General Description

3.1.1Refrigeration Unit - Front Section

The unit is designed so that the majority of the components are accessible from the front (see Figure 3.1). The unit model number, serial number and parts identification number can be found on the unit nameplate to the left of the receiver or water-cooled condenser on the back wall of the condenser section.

Figure 3.1  Refrigeration Unit - Front Section

1)Access Panel (Evaporator Fan #1)

2)Fork Lift Pockets

3)Control Box

4)Compressor

5)Ambient Sensor (AMBS)

6)Economizer

7)Filter Drier

8)Receiver or Water Cooled Condenser

9)Unit Nameplate (Serial Number, Model Number and Parts Identification (PID) Number)

10)Power Cables and Plug location

11)Condenser Fan

12)Autotransformer location

13)TransFRESH Communications Connector

14)Interrogator Connector (Front left)

15)Temperature Recorder

16)Lower Fresh Air Makeup Vent location

17)TIR (Transports Internationaux Routiers) Sealing Provisions - Typical All Panels

18)Upper Fresh Air Makeup Vent or eAutoFresh (Automatic Vent) panel

19)Access Panel (Evaporator Fan #2)

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3.1.2Fresh Air Makeup Vent

The function of the upper or lower fresh air makeup vent is to provide ventilation for commodities that require fresh air circulation. A manually operated venting system is located in the upper left access panel. The optional eAutoFresh vent system moderates the atmospheric level in the container in response to cargo respiration. When transporting fro­zen cargo loads, the vent will be closed. The upper left access panel contains the vent slide and motor assembly. It may be removed to allow entry into the evaporator section where the CO₂ sensor and drive pack are located.

3.1.3Evaporator Section

The evaporator section (see Figure 3.2) contains the return temperature sensor (RTS), humidity sensor (HS), elec­tronic expansion valve (EEV), dual speed evaporator fans (EM1 and EM2), evaporator coil and heaters, defrost tem­perature sensor (DTS), heat termination thermostat (HTT) and evaporator temperature sensors (ETS1 and ETS2).

Figure 3.2  Evaporator Section

1)Evaporator Fan #1

2)Return Recorder Sensor (RRS) / Return Tempera­ture Sensor (RTS)

3)Humidity Sensor (HS)

4)Evaporator Fan #2

5)Evaporator Coil

6)Evaporator Coil Heaters

7)Heat Termination Thermostat (HTT)

8)Defrost Temperature Sensor (DTS)

9)Electronic Expansion Valve (EEV)

10)Evaporator Temperature Sensors (ETS1 & ETS2)

11)Air Filter

12)CO₂ Sensor Sensing Line

13)CO₂ Sensor (COS)

14)CO₂ Sensor Outlet Line

15)Stepper Motor Drive (SD)

16)Stepper Motor (AF)

17)Interrogator Connector Rear (ICR)

18)USDA Probe Receptacle PR2

19)USDA Probe Receptacle PR1

20)USDA Probe Receptacle PR3

21)Cargo Probe Receptacle PR4

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The evaporator fans circulate air through the container by pulling it in the top of the unit, directing it through the evaporator coil, where it is heated or cooled, and discharging it at the bottom.

If the unit is equipped with eAutoFresh, system components are mounted in addition to the standard refrigeration unit components. The stepper motor component is installed in the vent; the air filter, CO₂ sensor, stepper motor drive and CO₂ sensing lines are installed on the rib of the upper grill.

Most evaporator components are accessible by removing the upper rear panel or by removing the evaporator fan access panels (see Figure 3.1, Items 1 and 19).

3.1.4Compressor Section

The compressor section (see Figure 3.3) includes the compressor, digital unloader valve (DUV), high pressure switch, discharge pressure transducer (DPT), evaporator pressure transducer (EPT) and the suction pressure transducer (SPT). The supply temperature sensor (STS), supply recorder sensor (SRS), and ambient sensor are located to the left of the compressor.

Figure 3.3  Compressor Section

1)Compressor

2)Discharge Temperature Sensor (CPDS) location

3)Discharge Connection

4)Suction Connection Location

5)Compressor Terminal Box

6)Oil Drain location

7)Economizer Connection

8)Discharge Pressure Transducer (DPT)

9)Suction Pressure Transducer (SPT)

10)Digital Unloader Valve (DUV)

11)Evaporator Pressure Transducer (EPT)

12)Discharge Service Valve

13)High Pressure Switch (HPS)

14)Warning Label

15)Suction Service Valve

16)Supply Temperature Sensor (STS) / Supply Recorder Sensor (SRS)

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3.1.5Air-Cooled Condenser Section

The air-cooled condenser section (see Figure 3.4) consists of the condenser fan, condenser coil, receiver, liquid line service valve, filter drier, fusible plug, economizer, economizer expansion valve (EXV), economizer solenoid valve (ESV), and sight glass / moisture indicator. The condenser fan pulls air from around the coil and discharges it horizontally through the condenser fan grille.

Figure 3.4  Air-Cooled Condenser Section

1)Grille and Venturi Assembly

2)Condenser Fan

3)Key

4)Condenser Fan Motor

5)Condenser Coil

6)Condenser Coil Cover

7)Receiver

8)Sight Glass

9)Filter Drier

10)Economizer

11)Economizer Solenoid Valve (ESV)

12)Economizer Expansion Valve (EXV)

13)Warning Label location

14)Service Access Valve

15)Liquid Level / Moisture Indicator

16)Fusible Plug

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3.1.6Water-Cooled Condenser Section

The water-cooled condenser section (see Figure 3.5) consists of a water-cooled condenser, sight glass, rupture disc, filter drier, water couplings, water pressure switch, economizer, economizer expansion valve, economizer solenoid valve (ESV), and moisture / liquid indicator. The water-cooled condenser replaces the standard unit receiver.

Figure 3.5  Water-Cooled Condenser Section

1)Water-Cooled Condenser

2)Rupture Disc

3)Moisture / Liquid Indicator

4)Filter Drier

5)Economizer

6)Economizer Solenoid Valve (ESV)

7)Economizer Expansion Valve (EXV)

8)Coupling (Water In)

9)Liquid Line Service Valve / Connection

10)Self Draining Coupling (Water Out)

11)Water Pressure Switch (WP)

12)Sight Glass

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3.1.7Control Box Section

The control box (see Figure 3.6) includes: the manual operation switches, circuit breaker (CB-1), compressor, fan and heater contactors, control power transformer, fuses, keypad, display module, current sensor module, controller module and the communications interface module.

Figure 3.6  Control Box Section

1)Compressor Contactor (CH)

2)Compressor Phase A Contactor (PA)

3)Compressor Phase B Contactor (PB)

4)Heater Contactor (HR)

5)Display Module

6)Communications Interface Module

7)Controller / DataCORDER Module

8)Keypad

9)Remote Monitoring Receptacle

10)Start-Stop Switch (ST)

11)Controller Battery Pack standard Location

12)Interrogator Connector box location

13)Control Transformer

14)High Speed Evaporator Fan Contactor (EF)

15)Low Speed Evaporator Fan Contactor (ES)

16)Condenser Fan Contactor (CF)

17)Circuit Breaker 460V

18)Current Sensor Module

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3.1.8Communications Interface Module

The communications interface module is a slave module which allows communication between the refrigeration unit and a ship system master central monitoring station. The module will respond to communication and return information over the ships main power line. Refer to the master system technical manual for further information.

3.2Refrigeration System Data

3.3Electrical Data

3.4Safety and Protective Devices

Unit components are protected from damage by safety and protective devices listed in Table 3–1. These devices moni­tor the unit operating conditions and open a set of electrical contacts when an unsafe condition occurs.

Open safety switch contacts on either or both of devices IP-CP or HPS will shut down the compressor.

Open safety switch contacts on device IP-CM will shut down the condenser fan motor.

The entire refrigeration unit will shut down if one of the following safety devices open: (a) circuit breaker(s); (b) fuse (F3A/F3B, 7.5A); or (c) evaporator fan motor internal protector(s) - (IP).

3.5Refrigeration Circuit

3.5.1Standard Operation

Starting at the compressor (see Figure 3.7) the suction gas is compressed to a higher pressure and temperature.

The refrigerant gas flows through the discharge line and continues into the air-cooled condenser. When operating with the air-cooled condenser active, air flowing across the coil fins and tubes cools the gas to saturation tempera­ture. By removing latent heat, the gas condenses to a high pressure / high temperature liquid and flows to the receiver, which stores the additional charge necessary for low temperature operation.

When operating with the water-cooled condenser active (see Figure 3.8), the refrigerant gas passes through the air-cooled condenser and enters the water-cooled condenser shell. The water flowing inside the tubing cools the gas to saturation temperature in the same manner as the air passing over the air-cooled condenser. The refrigerant condenses on the outside of the tubes and exits as a high temperature liquid. The water-cooled condenser also acts as a receiver, storing refrigerant for low temperature operation.

The liquid refrigerant continues through the liquid line, the filter drier (which keeps refrigerant clean and dry) and the economizer (not active during standard operation) to the electronic expansion valve (EEV).

As the liquid refrigerant passes through the variable orifice of the EEV, the pressure drops to suction pressure. In this process some of the liquid vaporizes to a gas (flash gas), removing heat from the remaining liquid. The liquid exits as a low pressure, low temperature, saturated mix. Heat is then absorbed from the return air by the balance of the liquid, causing it to vaporize in the evaporator coil. The vapor then flows through the suction tube back to the compressor.

On systems fitted with a water pressure switch, the condenser fan will be off when there is sufficient pressure to open the switch. If water pressure drops below the switch cut out setting, the condenser fan will automatically start.

During the standard mode of operation, the normally closed digital unloader valve (DUV) controls the system refrig­erant flow and capacity by loading and unloading the compressor in frequent discrete time intervals. If the system capacity has been decreased to the lowest allowable capacity with the DUV, the unit will enter a trim heat mode of operation, during which the controller will pulse the evaporator heaters in sequence with the compressor digital sig­nal in order to absorb the excess capacity.

3.5.2Economized Operation

In the economized mode (see Figure 3.9) the frozen and pull down capacity of the unit is increased by sub-cooling the liquid refrigerant entering the electronic expansion valve. Overall efficiency is increased because the gas leaving the economizer enters the compressor at a higher pressure, therefore requiring less energy to compress it to the required condensing conditions.

Liquid refrigerant for use in the economizer circuit is taken from the main liquid line as it leaves the filter drier. The flow is activated when the controller energizes the economizer solenoid valve (ESV).

The liquid refrigerant flows through the ESV to the expansion valve internal passages, absorbing heat from the liq­uid refrigerant flowing to the electronic expansion valve. The resultant “medium” temperature/pressure gas enters the compressor at the economizer port fitting.

When the control air temperature falls to 2.0°C (3.6°F) above set point, the DUV unloads the compressor’s scroll and begins to reduce the capacity of the unit. Percentage of the unit capacity is accessed through code select 01 (Cd01). For example, if Cd01 displays 70, it indicates that the compressor is operating unloaded with the DUV engaged 30% of the time.

3.5.3Electronic Expansion Valve

The microprocessor controls the superheat leaving the evaporator via the electronic expansion valve (EEV), based on inputs from the evaporator pressure transducer (EPT). The microprocessor transmits electronic pulses to the EEV stepper motor, which opens or closes the valve orifice to maintain the superheat set point.

Figure 3.7  Refrigeration Circuit Schematic - Standard Operation

1)Compressor

2)Discharge Service Valve

3)Discharge Temperature Sensor (CPDS)

4)Discharge Pressure Transducer (DPT)

5)Condenser

6)Receiver

7)Receiver Sight Glass

8)Receiver Liquid Level / Moisture Indicator

9)Liquid Line Service Valve

10)Filter Drier

11)Economizer

12)Economizer TXV

13)Economizer Solenoid Valve (ESV)

14)Economizer TXV Sensing Bulb

15)Electronic Expansion Valve (EEV)

16)Evaporator

17)Evaporator Temperature Sensors (ETS1 & ETS2)

18)Digital Unloader Valve (DUV)

19)Evaporator Pressure Transducer (EPT)

20)Suction Pressure Transducer (SPT)

21)Suction Service Valve

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Figure 3.8  Refrigeration Circuit Schematic - Standard Operation with Water-Cooled Condenser

1)Compressor

2)Discharge Service Valve

3)Discharge Temperature Sensor (CPDS)

4)Discharge Pressure Transducer (DPT)

5)Condenser

6)Water-Cooled Condenser (WCC)

7)Sight Glass

8)Moisture Indicator

9)Liquid Line Service Valve

10)Filter Drier

11)Economizer

12)Economizer TXV

13)Economizer Solenoid Valve (ESV)

14)Electronic Expansion Valve (EEV)

15)Evaporator

16)Evaporator Temperature Sensors (ETS1 & ETS2)

17)Digital Unloader Valve (DUV)

18)Evaporator Pressure Transducer (EPT)

19)Suction Pressure Transducer (SPT)

20)Suction Service Valve

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Figure 3.9  Refrigeration Circuit Schematic - Economized Operation

1)Compressor

2)Receiver

3)Liquid Line Service Valve

4)Economizer

5)Economizer TXV

6)Economizer Solenoid Valve (ESV)

7)Economizer TXV Sensing Bulb

8)Electronic Expansion Valve (EEV)

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