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 serial plate on the back wall of the condenser section.

3.1.2Fresh Air Makeup Vent

The function of the upper or lower makeup air 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 is used to moderate 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.

Figure 3.1  Refrigeration Unit - Front Section

1.Access Panel (Evap. Fan #1)

2.Fork Lift Pockets

3.Control Box

4.Unit Display

5.Key Pad

6.Remote Monitoring Receptacle

7.Start-Stop Switch, ST

8.Compressor

9.Supply Temperature Supply/Recorder Sensor Assembly (STS/SRS)

10.Economizer

11.Ambient Temperature Sensor (AMBS)

12.Power Cables and Plug (Location)

13.Autotransformer

14.Condenser Grille

15.Upper Fresh Air Makeup Vent Panel (Evap. Fan #2)

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3.1.3Evaporator Section

The evaporator section is shown below. 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 provisioned for XtendFRESH or 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 (as shown in the illustration) or by removing the evaporator fan access panels (see Figure 3.2).

Figure 3.2  Evaporator Section

1.Evaporator Fan Motor #1 (EM1)

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

3.Humidity Sensor (HS)

4.Evaporator Fan Motor #2 (EM2)

5.Evaporator Coil Heaters (Underside of Coil)

6.Evaporator Coil

7.Electronic Expansion Valve (EEV)

8.Evaporator Temperature Sensors (Location) (ETS1 & ETS2)

9.Interrogator Connector (Rear) (ICR)

10.USDA Probe Receptacle PR2

11.USDA Probe Receptacle PR1

12.USDA Probe Receptacle PR3

13.Cargo Probe Receptacle PR4

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3.1.4Compressor Section

The compressor section includes the compressor, digital loader valve (DLV), digital unloader valve (DUV), high pressure switch (HPS), discharge pressure transducer (DPT), evaporator pressure transducer (EPT) and the suc­tion pressure transducer (SPT).

The supply temperature sensor and supply recorder sensor are located to the left of the compressor.

Figure 3.3  Compressor Section

1.Compressor

2.Compressor 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.DUV/DLV Connection

10.Digital Loader Valve (DLV)

11.Suction Pressure Transducer (SPT)

12.Evaporator Pressure Transducer (EPT)

13.High Pressure Switch (HPS)

14.Discharge Service Valve

15.Suction Service Valve

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

17.Warning Label

18.Digital Unloader Valve (DUV)

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3.1.5Air-Cooled Condenser Section

The air-cooled condenser section consists of the condenser fan, condenser coil, receiver, liquid line service valve, filter drier, fusible plug, economizer, economizer expansion valve, 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.Condenser Coil Cover

4.Condenser Coil

5.Condenser Fan Motor

6.Receiver

7.Sight Glass

8.Filter Drier

9.Economizer

10.Economizer Solenoid Valve (ESV)

11.Economizer Expansion Valve

12.Warning Label (location)

13.Service Access Valve

14.Liquid Level/Moisture Indicator

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3.1.6Control Box Section

The control box (Figure 3.5) includes: the manual operation switches, circuit breaker (CB-1), compressor, fan and heater contactors, control power transformer, fuses, key pad, display module, current sensor module, controller module and the communications interface module.

3.1.7Communications 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.

Figure 3.5  Control Box Section

1.Compressor Contactor - CH

2.Compressor Phase A Contactor - PA

3.Compressor Phase B Contactor - PB

4.Heater Contactor - HR

5.Controller/DataCORDER Module (Controller)

6.Remote Monitoring Receptacle

7.Start-Stop Switch, ST

8.Controller Battery Pack (Standard Location)

9.Control Transformer

10.High Speed Evaporator Fan Contactor - EF

11.Low Speed Evaporator Fan Contactor - ES

12.Condenser Fan Contactor - CF

13.Circuit Breaker - 460V

14.Current Sensor Module

15.Condenser Fan Low Speed - LC

16.Condenser Fan (High Speed Shorting) - FS

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3.2Refrigeration System data

3.3Electrical System 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 3.6, upper schematic) 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.

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.

During the standard mode of operation, the normally closed valves, digital loader valve (DLV) and digital unloader valve (DUV), control the system refrigerant flow and capacity by loading and unloading the compressor in frequent discrete time intervals. The DLV and DUV operate in opposition to each other such that when the DLV is closed the DUV is open and vice versa. The valves cycle on a fixed duty cycle so that maximum capacity occurs when the DLV is open 100% of the time and the DUV is open 0% and minimum capacity is when the DLV is open 0% of the time and the DUV 100% of the time. If the system capacity has been decreased to the lowest allowable capacity, 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 3.7) 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 economizer 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.

3.5.3Economizer Expansion Valve

The microprocessor controls the superheat leaving the economizer expansion valve (EXV). From the EXV the refrigerant flows through the internal passages of the economizer heat exchanger, absorbing heat from the refriger­ant flowing to the EEV. The resultant “medium” temperature/pressure gas enters the compressor at the economizer port fitting.

Figure 3.6  Refrigeration Circuit Schematic - Standard Operation

Figure 3.7  Refrigeration Circuit Schematic - Economized Operation