Operation; Introduction; Everfresh Air And Gas Flow - Carrier EverFRESH Operation, Service And Parts Manual

3.1

Introduction

This section addresses the operating requirements for the EverFRESH
parameters are not changed except for EverFRESH settings. For information pertaining to the operation of the
refrigeration system, refer to the Operation and Service Manual for your particular model.
3.2

Operation

The EverFRESH option offers enhanced functionality to help slow the ripening process of perishable cargo by
controlling Carbon Dioxide (CO2) and Oxygen (O2) levels to specified setpoints. This enables the fresh transport of
perishables on longer voyages. The system controls the container atmosphere with a Nitrogen Membrane, a Fresh
Air Solenoid and an optional CO2 Injection kit.
During the nitrogen control mode, CO2 and O2 are replaced with nitrogen proportionally. EverFRESH also utilizes
the cargo's natural respiration to control CO2 and O2 levels. Additionally, opening and closing a Fresh Air Valve
allows for raising O2 levels and controlling CO2 for high respiring cargos. An O2 sensor monitors O2 levels and
allows the system to prevent O2 levels from dropping below the lower setpoint. A CO2 sensor provides CO2 levels
to the controller to allow the control algorithm to activate the required EverFRESH components. For low respiring
cargoes requiring high CO2 setpoints, an optional CO2 Injection system can be used to maintain CO2 levels.
While the EverFRESH option is operating, the process of removing ethylene needs to be per-
formed with an external ethylene scrubber (part # 30-50344-00).
3.3

EverFRESH Air and Gas Flow

The EverFRESH system (see
refrigeration unit to increase the pressure of the air inside the system. The warm, moisture laden air exits the
compressor and is brought inside the refrigerated space and passed through a condensing loop, consisting of a
single piece of copper tubing located above the fan deck. As the compressed air is exposed to the cooler
temperature of the cargo space, moisture condenses and is carried out to the filter assembly.
The filter assembly consists of a Water Separator and two Particulate Filters. Any condensed moisture is first
removed at the Water Separator and then at the first of two Particulate Filters, which removes debris and also any
additional moisture. Any condensate and solid material settles to the bottom of the filter assembly and is blown out
of the line when the Water Drain Valve (WDV) opens. The water drips onto the evaporator coil and down the
defrost drain line. The WDV energizes during the initial unit startup when the air compressor starts. It also opens
periodically during air compressor operation to remove accumulated condensate and again before the air
compressor is disengaged.
The compressed air then passes through a second Particulate Filter, to drain any remaining moisture from the
system through the EverFRESH Air Valve (EA) solenoid. This opens after the WDV operates for draining moisture
and when fresh air is required in the system. The EA maintains the desired oxygen levels inside the cargo space.
When the controller detects that oxygen levels are dropping below the threshold setting, it opens the EA valve to
force clean, dry, pressurized, air into the cargo space. Since this air contains 21% oxygen, it increases the
concentration of oxygen available for respiration. Located before the EA is the Membrane Pressure Transducer
(MPT) where the controller monitors system pressure and can determine if the Nitrogen Membrane Separator is
maintaining good flow. When the EA is closed, the clean, dry air exits the Particulate Filter and enters the bottom of
the Nitrogen Membrane Separator. Inside the Separator, the air enters thousands of tiny hollow fibers. The smaller,
faster molecules of oxygen and carbon dioxide passes through the walls of the membrane fibers, exits the
Separator through a port on the side, and then are exhausted out the front of the refrigeration unit to the
atmosphere. The larger, slower nitrogen molecules stay trapped in the fibers until they exit the top of the Separator.
As the nitrogen leaves the Separator, it is piped above the fan deck to the nitrogen orifices. The orifices provide a
restriction that helps control the gas flow. The Nitrogen Supply orifice will regulate the flow of nitrogen out to the air
stream where the evaporator fans will blow it across the evaporator and down into the t-slots where it will enter the
Section 3
Operation
Figure 3.1) uses an EverFRESH Air Compressor (EAC) mounted to the front of the
®
Controlled Atmosphere option. Operating
3–1 T-374