Patent Description:
Traditional refrigerated cargo trucks or refrigerated tractor trailers, such as those utilized to transport cargo via sea, rail, or road, is a truck, trailer or cargo container, generally defining a cargo compartment, and modified to include a refrigeration system located at one end of the truck, trailer, or cargo container. Refrigeration systems typically include a compressor, a condenser, an expansion valve, and an evaporator serially connected by refrigerant lines in a closed refrigerant circuit in accord with known refrigerant vapor compression cycles. A power unit, such as a combustion engine, drives the compressor of the refrigeration unit, and may be diesel powered, natural gas powered, or other type of engine. In many tractor trailer transport refrigeration systems, the compressor is driven by the engine shaft either through a belt drive or by a mechanical shaft-to-shaft link. In other systems, the engine of the refrigeration unit drives a generator that generates electrical power, which in-turn drives the compressor.

With current environmental trends, improvements in transportation refrigeration units are desirable particularly toward aspects of environmental impact. With environmentally friendly refrigeration units, improvements in reliability, cost, and weight reduction is also desirable.

<CIT> discloses a HVAC and battery thermal management system for a vehicle having a HVAC portion and a battery portion.

<CIT> discloses a technique of estimating, with high accuracy, state of supply of cooling medium to electrical equipment connected to a medium passage having a plurality of routes.

<CIT> discloses a system to suppress the energy consumption of a battery temperature control device.

<CIT> discloses a transport refrigeration system including a tractor or vehicle, a container and an engineless transportation refrigeration unit.

Viewed from a first aspect, the present invention provides a transport refrigeration system including a tractor or vehicle, a container, and an engineless transportation refrigeration unit, the engineless transportation refrigeration unit comprising: a compressor configured to compress a refrigerant; a compressor motor configured to drive the compressor; an evaporator heat exchanger operatively coupled to the compressor; an energy storage device for providing power to the compressor motor; and an evaporator fan configured to provide return airflow from a compartment of the container through a return air intake and flow the return airflow over the evaporator heat exchanger; wherein the engineless transportation refrigeration unit is configured to provide conditioned supply airflow to the compartment; wherein the engineless transportation refrigeration unit is configured to divert a selected amount of the return airflow from the return air intake to the energy storage device to thermodynamically adjust a temperature of the energy storage device, and wherein the engineless transport refrigeration unit comprises a barrier configured to direct the selected amount of return airflow through the energy storage device and towards the evaporator heat exchanger, wherein the engineless transportation refrigeration unit is configured such that upon exiting the energy storage device the selected amount of return airflow mixes with non-bypassed return airflow from the compartment before entering the evaporator heat exchanger.

In addition to one or more of the features described above, or as an alternative, further embodiments may include a regulating device located proximate the return air intake and configured to divert the selected amount of the return airflow to the energy storage device.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the energy storage device includes a battery system.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the selected amount of the return airflow is diverted around the energy storage device.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the selected amount of the return airflow is diverted through the energy storage device.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the barrier divides the energy storage device into at least two compartments.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the energy storage device includes a right-hand side and a left-hand side, and the barrier stretches from the right-hand side of the energy storage device to the left-hand side of the energy storage device.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the energy storage device includes a front side and a back side, and the barrier stretches from the front side of the energy storage device to the back side of the energy storage device.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the barrier is located upstream of the energy storage device.

In addition to one or more of the features described above, or as an alternative, further embodiments may include a flow adjustment device to adjust the selected amount of return airflow to the energy storage device using at least one of a controller and a booster fan.

In addition to one or more of the features described above, or as an alternative, further embodiments may include: a heating element located in an airflow path of the selected amount of the return airflow being diverted from the regulating device.

Viewed from a second aspect, the present invention provides a method of operating a engineless transportation refrigeration unit of a transportation refrigeration system, the transportation refrigeration system comprising a tractor or vehicle, a container, and the engineless transportation refrigeration unit, the method comprising: powering a compressor motor of the engineless transportation refrigeration unit using an energy storage device; providing conditioned supply airflow to a cargo compartment of the container using the engineless transportation refrigeration unit; and regulating a temperature of the energy storage device using return airflow from the cargo compartment, wherein a selected amount of the return airflow is diverted from a return air intake to the energy storage device using a barrier to thermodynamically adjust the temperature of the energy storage device, wherein the selected amount of return airflow is directed towards an evaporator heat exchanger using the barrier, and wherein upon exiting the energy storage device the selected amount of return airflow mixes with non-bypassed return airflow from the compartment before entering the evaporator heat exchanger.

Viewed from a third aspect, the present invention provides a computer program product tangibly embodied on a computer readable medium, the computer program product including instructions that, when executed by a processor, cause the processor to perform operations comprising: powering a compressor motor of a engineless transportation refrigeration unit of a transport refrigeration system using an energy storage device, the transportation refrigeration system comprising a tractor or vehicle, a container, and the engineless transportation refrigeration unit; providing conditioned supply airflow to a cargo compartment of the container using the engineless transportation refrigeration unit; and regulating a temperature of the energy storage device using return airflow from the cargo compartment by: diverting a selected amount of the return airflow from a return air intake to the energy storage device to thermodynamically adjust the temperature of the energy storage device, and adjusting the selected amount of return airflow with a flow adjustment device using at least one of a controller and a booster fan; wherein the selected amount of return airflow is directed to an evaporator heat exchanger, and wherein upon exiting the energy storage device the selected amount of return airflow mixes with non-bypassed return airflow from the compartment before entering the evaporator.

Technical effects of embodiments of the present disclosure include utilizing return air from a transportation refrigeration unit to thermodynamically adjust the temperature of an energy storage device configured to power the transportation refrigeration unit.

The subject matter which is regarded as the disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification.

With reference to the accompanying drawings, like elements are numbered alike.

Referring to <FIG>, a transport refrigeration system <NUM> of the present disclosure is illustrated. In the illustrated embodiment, the transport refrigeration systems <NUM> may include a tractor or vehicle <NUM>, a container <NUM>, and an engineless transportation refrigeration unit (TRU) <NUM>. The container <NUM> may be pulled by a vehicle <NUM>. It is understood that embodiments described herein may be applied to shipping containers that are shipped by rail, sea, air, or any other suitable container, thus the vehicle may be a truck, train, boat, airplane, helicopter, etc..

The vehicle <NUM> may include an operator's compartment or cab <NUM> and a combustion engine <NUM> which is part of the powertrain or drive system of the vehicle <NUM>. The container <NUM> may be coupled to the vehicle <NUM> and is thus pulled or propelled to desired destinations. The trailer may include a top wall <NUM>, a bottom wall <NUM> opposed to and spaced from the top wall <NUM>, two side walls <NUM> spaced from and opposed to one-another, and opposing front and rear walls <NUM>, <NUM> with the front wall <NUM> being closest to the vehicle <NUM>. The container <NUM> may further include doors (not shown) at the rear wall <NUM>, or any other wall. The walls <NUM>, <NUM>, <NUM>, <NUM>, <NUM> together define the boundaries of a cargo compartment <NUM>. Typically, transport refrigeration systems <NUM> are used to transport and distribute cargo, such as, for example perishable goods and environmentally sensitive goods (herein referred to as perishable goods). The perishable goods may include but are not limited to fruits, vegetables, grains, beans, nuts, eggs, dairy, seed, flowers, meat, poultry, fish, ice, blood, pharmaceuticals, or any other suitable cargo requiring cold chain transport. In the illustrated embodiment, the TRU <NUM> is associated with a container <NUM> to provide desired environmental parameters, such as, for example temperature, pressure, humidity, carbon dioxide, ethylene, ozone, light exposure, vibration exposure, and other conditions to the cargo compartment <NUM>. In further embodiments, the TRU <NUM> is a refrigeration system capable of providing a desired temperature and humidity range.

Referring to <FIG> and <FIG>, the container <NUM> is generally constructed to store a cargo (not shown) in the compartment <NUM>. The engineless TRU <NUM> is generally integrated into the container <NUM> and may be mounted to the front wall <NUM>. The cargo is maintained at a desired temperature by cooling of the compartment <NUM> via the TRU <NUM> that circulates airflow into and through the cargo compartment <NUM> of the container <NUM>. It is further contemplated and understood that the TRU <NUM> may be applied to any transport compartments (e.g., shipping or transport containers) and not necessarily those used in tractor trailer systems. Furthermore, the transport container may be a part of the of the vehicle <NUM> or constructed to be removed from a framework and wheels (not shown) of the container <NUM> for alternative shipping means (e.g., marine, railroad, flight, and others).

The components of the engineless TRU <NUM> may include a compressor <NUM>, an electric compressor motor <NUM>, an electric energy storage device <NUM>, a condenser <NUM> that may be air cooled, a condenser fan assembly <NUM>, a receiver <NUM>, a filter dryer <NUM>, a heat exchanger <NUM>, a thermostatic expansion valve <NUM>, an evaporator <NUM>, an evaporator fan assembly <NUM>, a suction modulation valve <NUM>, and a controller <NUM> that may include a computer-based processor (e.g., microprocessor). Operation of the engineless TRU <NUM> may best be understood by starting at the compressor <NUM>, where the suction gas (e.g., natural refrigerant, hydro-fluorocarbon (HFC) R-404a, HFC R-134a. etc) enters the compressor at a suction port <NUM> and is compressed to a higher temperature and pressure. The refrigerant gas is emitted from the compressor at an outlet port <NUM> and may then flow into tube(s) <NUM> of the condenser <NUM>.

Air flowing across a plurality of condenser coil fins (not shown) and the tubes <NUM>, cools the gas to its saturation temperature. The air flow across the condenser <NUM> may be facilitated by one or more fans <NUM> of the condenser fan assembly <NUM>. The condenser fans <NUM> may be driven by respective condenser fan motors <NUM> of the fan assembly <NUM> that may be electric.

By removing latent heat, the gas within the tubes <NUM> condenses to a high pressure and high temperature liquid and flows to the receiver <NUM> that provides storage for excess liquid refrigerant during low temperature operation. From the receiver <NUM>, the liquid refrigerant may pass through a sub-cooler heat exchanger <NUM> of the condenser <NUM>, through the filter-dryer <NUM> that keeps the refrigerant clean and dry, then to the heat exchanger <NUM> that increases the refrigerant sub-cooling, and finally to the thermostatic expansion valve <NUM>.

As the liquid refrigerant passes through the orifices of the expansion valve <NUM>, some of the liquid vaporizes into a gas (i.e., flash gas). Return air from the refrigerated space (i.e., cargo compartment <NUM>) flows over the heat transfer surface of the evaporator <NUM>. As the refrigerant flows through a plurality of tubes <NUM> of the evaporator <NUM>, the remaining liquid refrigerant absorbs heat from the return air, and in so doing, is vaporized.

The evaporator fan assembly <NUM> includes one or more evaporator fans <NUM> that may be driven by respective fan motors <NUM> that may be electric. The air flow across the evaporator <NUM> is facilitated by the evaporator fans <NUM>. From the evaporator <NUM>, the refrigerant, in vapor form, may then flow through the suction modulation valve <NUM>, and back to the compressor <NUM>. A thermostatic expansion valve bulb sensor <NUM> may be located proximate to an outlet of the evaporator tube <NUM>. The bulb sensor <NUM> is intended to control the thermostatic expansion valve <NUM>, thereby controlling refrigerant superheat at an outlet of the evaporator tube <NUM>. It is further contemplated and understood that the above generally describes a single stage vapor compression system that may be used for HFCs such as R-404a and R-134a and natural refrigerants such as propane and ammonia. Other refrigerant systems may also be applied that use carbon dioxide (CO<NUM>) refrigerant, and that may be a two-stage vapor compression system.

A bypass valve (not shown) may facilitate the flash gas of the refrigerant to bypass the evaporator <NUM>. This will allow the evaporator coil to be filled with liquid and completely 'wetted' to improve heat transfer efficiency. With CO<NUM> refrigerant, this bypass flash gas may be re-introduced into a mid-stage of a two-stage compressor.

The compressor <NUM> and the compressor motor <NUM> may be linked via an interconnecting drive shaft <NUM>. The compressor <NUM>, the compressor motor <NUM> and the drive shaft <NUM> may all be sealed within a common housing <NUM>. The compressor <NUM> may be a single compressor. The single compressor may be a two-stage compressor, a scroll-type compressor or other compressors adapted to compress HFCs or natural refrigerants. The natural refrigerant may be CO<NUM>, propane, ammonia, or any other natural refrigerant that may include a global-warming potential (GWP) of about one (<NUM>).

Referring to <FIG> and <FIG>, the energy storage device <NUM> may be configured to selectively power the compressor motor <NUM>, the condenser fan motors <NUM>, the evaporator fan motors <NUM>, the controller <NUM>, and other components <NUM> (see <FIG>) that may include various solenoids and/or sensors via, for example, electrical conductors <NUM>. The controller <NUM> through a series of data and command signals over various pathways <NUM> may, for example, control the electric motors <NUM>, <NUM>, <NUM> as dictated by the cooling needs of the TRU <NUM>. In one embodiment, the energy storage device <NUM> may be contained within the structure <NUM> of the TRU (see <FIG>). The operation of the energy storage device <NUM> may be managed and monitored by an energy storage management system <NUM>. The energy management system <NUM> is configured to determine a status of charge of the energy storage device <NUM>, a state of health of the energy storage device <NUM>, and a temperature of the energy storage device <NUM>.

Examples of the energy storage device <NUM> may include a battery system (e.g., a battery or bank of batteries), fuel cells, and others capable of storing and outputting electric energy that may be direct current (DC). The battery system may contain multiple batteries organized into battery banks through which cooling air may flow for battery temperature control, as described in <CIT>.

The engineless TRU <NUM> may include a DC architecture without any of the components requiring alternate current (AC), or a mechanical form of power, to operate (i.e., the motors <NUM>, <NUM>, <NUM> may be DC motors). If the energy storage device <NUM> includes a battery system, the battery system may have a voltage potential within a range of about two-hundred volts (200V) to about six-hundred volts (600V). The use of these batteries may include a step-up or step-down transformer as needed (not shown). Generally, the higher the voltage, the greater is the sustainability of electric power which is preferred. However, the higher the voltage, the greater is the size and weight of, for example, batteries in an energy storage device <NUM>, which is not preferred when transporting cargo. Additionally, if the energy storage device is a battery <NUM>, then in order to increase either voltage and/or current, the batteries need to be connected in series or parallel depending upon electrical needs. Higher voltages in a battery energy storage device <NUM> will require more batteries in series than lower voltages, which in turn results in bigger and heavier battery energy storage device <NUM>. A lower voltage and higher current system may be used, however such a system may require larger cabling or bus bars.

The engineless TRU <NUM> may further include a renewable power source <NUM> configured to recharge the batteries of the energy storage device <NUM>. One embodiment of a renewable power source <NUM> may be solar panels mounted, for example, to the outside of the top wall <NUM> of the container <NUM> (also see <FIG>). Another embodiment of a renewable power source <NUM> may include a regenerative braking system that derives electric power from the braking action of the wheels of the transport refrigeration system <NUM>. An additional embodiment of a renewable power source <NUM> may include axle generators located in the axles of the transport refrigeration system <NUM> that are used to recover rotational energy when the transport refrigeration system <NUM> is in motion and convert that rotational energy to electrical energy, such as, for example, when the axle is rotating due to acceleration, cruising, or braking.

The combustion engine <NUM> of the vehicle <NUM> may further include an alternator or generator <NUM> for recharging the batteries <NUM>. Alternatively or in addition to, the engineless TRU <NUM> may include a rectifier <NUM> and other components that facilitate recharging of the batteries <NUM> from an alternating current source <NUM> such as, for example, a remote power station or receptacle that receives power from a public utility grid.

Benefits of the present disclosure when compared to more traditional systems include lower fuel consumption, and a refrigeration unit that emits less noise and is lighter in weight. Yet further, the present disclosure includes an energy storage device that is conveniently and efficiently recharged to meet the power demands of the refrigeration unit.

Referring now to <FIG> with continued reference to <FIG>. <FIG> illustrates airflow through the TRU <NUM> and the cargo compartment <NUM>. Airflow is circulated into and through the cargo compartment <NUM> of the container <NUM> by means of the TRU <NUM>. A return airflow <NUM> flows into the TRU <NUM> from the cargo compartment <NUM> through a return air intake <NUM>, and across the evaporator <NUM> via the fan <NUM>, thus conditioning the return airflow <NUM> to a selected or predetermined temperature. The conditioned return airflow <NUM>, now referred to as supply airflow <NUM>, is supplied into the cargo compartment <NUM> of the container <NUM> through the refrigeration unit outlet <NUM>, which in some embodiments is located near the top wall <NUM> of the container <NUM>. The supply airflow <NUM> cools the perishable goods in the cargo compartment <NUM> of the container <NUM>. It is to be appreciated that the TRU <NUM> can further be operated in reverse to warm the container <NUM> when, for example, the outside temperature is very low.

The return airflow <NUM> may be at a temperature relatively lower than an air temperature outside of the cargo compartment <NUM> and may be diverted in order to cool the energy storage device <NUM> once the return airflow <NUM> has entered the return air intake <NUM>. A regulating device <NUM> may be located proximate the return air intake <NUM> and configured to divert a selected amount of the return airflow <NUM> to the energy storage device <NUM>. The selected amount of return airflow <NUM> thermodynamically adjusts the temperature of the energy storage device <NUM>. For example, the selected amount of return airflow <NUM> may be utilized to reduce the temperature of the energy storage device <NUM> by absorbing heat. The regulating device <NUM> may adjust the selected amount of return airflow <NUM> diverted to the energy storage device <NUM> in real-time in response to a current temperature of the energy storage device <NUM>. As shown in <FIG>, the selected amount of return airflow <NUM> is diverted to the air energy storage device <NUM> such that the selected amount of return airflow <NUM> is in thermal contact with the energy storage device <NUM>. For example, the selected amount of return airflow <NUM> may be diverted through and/or around the energy storage device <NUM>. The energy storage device <NUM> includes a barrier 162a-b which may be inserted in the energy storage device <NUM>, as seen in <FIG>. The barrier 162a-b is configured to separate the energy storage device <NUM> into at least two distinct paths including one path for return airflow <NUM> entering into the energy storage device <NUM> and the other path for return airflow exiting the energy storage device <NUM>. The barrier 162a-b may be part of the energy storage device <NUM>, as seen in <FIG> or the barrier (i.e., divider baffle <NUM>) may be external to the energy storage device <NUM> bypassing a selected amount of return airflow <NUM> to the energy storage device <NUM>, as shown in <FIG>. The barrier 162a-b is configured to direct the selected amount of return airflow <NUM> through the energy storage device <NUM> and upon exiting the energy storage device the bypassed return airflow mixes with the non-bypassed return air from the cargo compartment <NUM> before entering the evaporator <NUM>. As seen in <FIG>, the barrier 162a-b may segment the energy storage device <NUM> into at least two compartments 67a-d and create a flow path for the selected amount of return airflow <NUM> to flow through the energy storage device <NUM>.

<FIG> illustrate a barrier 162a in a side-to-side orientation that stretches from a right-hand side <NUM> of the energy storage device <NUM> to a left-hand side <NUM> of the energy storage device <NUM>. The barrier 162a separates the energy storage device <NUM> into two compartments 67a-b for the selected amount of return airflow <NUM> to flow through the energy storage device <NUM>. The barrier 162a separates the energy storage device <NUM> into a front compartment 67a and a back compartment 67b. The front compartment 67a and is fluidly connected to the back compartment 67b. It is understood that there may be multiple barriers 162a to create more than two compartments within the energy storage device <NUM>.

<FIG> illustrate a front-to-back barrier 162b that stretches from a front side <NUM> of the energy storage device <NUM> to a back side <NUM> of the energy storage device <NUM>. The front-to-back barrier 162b separates the energy storage device <NUM> into two compartments 67c-d for the selected amount of return airflow <NUM> to flow through the energy storage device <NUM>. The front-to-back barrier 162b separates the energy storage device <NUM> into a left-hand compartment 67c and a right hand compartment 67d. The left-hand compartment 67c is fluidly connected to the right hand compartment 67d. It is understood that there may be multiple front-to-back barriers 162b to create more than two compartments 67c-d within the energy storage device <NUM>. It is also understood that the embodiments disclosed herein are not limited to the side-to-side or front-to-back orientations of the barriers and the energy storage device <NUM> may contain any number of different barriers in different orientations.

Referring now to <FIG> with continued reference to <FIG>. It is understood that embodiments disclosed herein may be incorporated on TRUs <NUM> other than the specific TRU <NUM> illustrated in <FIG>. For example, <FIG> illustrates a truck unit TRU <NUM> that diverts a selected amount of return airflow <NUM> to an energy storage device <NUM> within the truck unit TRU <NUM>. In the embodiment illustrated in <FIG>, the TRU <NUM> utilizes a regulating device <NUM> to divert a selected amount of the return airflow <NUM> to the energy storage device <NUM>. The regulating device <NUM> in <FIG> is composed of a divider baffler <NUM> to split the return airflow <NUM> between the energy storage device <NUM> and the evaporator <NUM> and a flow adjustment device <NUM> to adjust the amount of airflow to the energy storage device <NUM>. The divider baffler <NUM> is located upstream of the energy storage device <NUM> and configured to divert a selected amount of return airflow <NUM> through the energy storage device <NUM>. The flow adjustment device <NUM> can include a control motor (i.e., a stepper motor) that would be used to fully open, partially open or fully close the flow openings depending upon the temperature setting inside the energy storage device <NUM>. A temperature sensor (i.e., thermistor or RTD) can be placed in the air stream inside the energy storage device <NUM> and when the temperature rises above or below a pre-determined temperature setpoint defined in the TRU controller <NUM>, the opening would be opened or closed accordingly. Additionally, a heating element <NUM> (e.g., electrical heater) can be placed in the airflow path to provide heat when the temperature setting is above one or more of the TRU controlling temperatures (e.g., Return Air Temperature and/or Ambient Air Temperature). In an embodiment, the heating element <NUM> is located in an airflow path of the selected amount of the return airflow being diverted from the regulating device <NUM>, as seen in <FIG>. In another embodiment, the heating element <NUM> may be placed inside the energy storage device <NUM>. The flow adjustment device <NUM> may also include a booster fan to augment circulation into and out of the energy storage device <NUM>. This operation of the booster fan could also be controlled based upon the temperature sensor located inside the energy storage device <NUM> through on/off or variable speed operation.

Referring now also to <FIG> with continued reference to <FIG>. <FIG> shows a flow diagram illustrating a method <NUM> of operating a TRU <NUM>, according to an embodiment of the present disclosure. At block <NUM>, the TRU <NUM> is powered using an energy storage device <NUM>. At block <NUM>, conditioned supply airflow <NUM> is provided to a cargo compartment <NUM> using the TRU <NUM>. At block <NUM>, a temperature of the energy storage device <NUM> is regulated using return airflow <NUM> from the cargo compartment <NUM>.

Embodiments can also be in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into an executed by a computer, the computer becomes a device for practicing the embodiments.

Claim 1:
A transport refrigeration system (<NUM>) including a tractor or vehicle, a container (<NUM>), and an engineless transportation refrigeration unit (<NUM>), the engineless transportation refrigeration unit comprising:
a compressor (<NUM>) configured to compress a refrigerant;
a compressor motor (<NUM>) configured to drive the compressor;
an evaporator heat exchanger (<NUM>) operatively coupled to the compressor;
an energy storage device (<NUM>) for providing power to the compressor motor; and
an evaporator fan (<NUM>) configured to provide return airflow (<NUM>) from a compartment (<NUM>) of the container through a return air intake (<NUM>) and flow the return airflow over the evaporator heat exchanger;
wherein the engineless transportation refrigeration unit (<NUM>) is configured to provide conditioned supply airflow (<NUM>) to the compartment (<NUM>);
wherein the engineless transportation refrigeration unit is configured to divert a selected amount of the return airflow from the return air intake (<NUM>) to the energy storage device (<NUM>) to thermodynamically adjust a temperature of the energy storage device, and wherein the engineless transport refrigeration unit comprises a barrier (<NUM>) configured to direct the selected amount of return airflow through the energy storage device (<NUM>) and towards the evaporator heat exchanger, wherein the engineless transportation refrigeration unit is configured such that upon exiting the energy storage device the selected amount of return airflow mixes with non-bypassed return airflow from the compartment (<NUM>) before entering the evaporator heat exchanger (<NUM>).