Patent Description:
A transportation refriegeration unit (TRU) is typically used in the transportation of perishable items. A TRU can be installed on a truck, for example, serves to maintain an environment within an interior of the trailer of the truck, in which perishable items are often stored, at a certain temperature range while the perishable items are being transported. Document <CIT> discloses a transportation refrigeration unit system according to the preamble of claim <NUM>.

Operations of the TRU can be based on the vapor compression cycle in which a fluid, such as refrigerant, is used to cool air that is driven into the trailer. In a vapor compression cycle, the refrigerant enters a compressor as a superheated vapor and is compressed within the compressor to a higher pressure and a higher temperature. The hot, compressed superheated vapor is then condensed within a condenser by air flowing across the coil or tubes of the condenser whereby heat is rejected from the system and carried away by the air. Next, the condensed refrigerant is routed as a saturated or subcooled liquid through an expansion valve where it undergoes an abrupt reduction in pressure resulting in an adiabatic flash evaporation of a part of the refrigerant and lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the interior of the trailer. The cold mixture is then routed through the coil or tubes in an evaporator whereupon a fan circulates warm air in the enclosed space across the coil or tubes carrying the cold liquid and vapor refrigerant mixture. The warm air evaporates the liquid part and the circulating air is cooled and thus lowers the temperature of the interior of the trailer. The refrigerant is then routed back toward the compressor as the superheated vapor.

Often TRUs operate at varying conditions. At low load conditions, current TRU designs need to frequently turn on and off to handle small loads. This can lead to lower energy efficiency, large fluctuations of cabin air temperatures and shortened component lives. For a TRU system that is driven at least in part by battery power, such lower efficiencies result in reduced work time of the battery and shortened battery life.

According to a first aspect of the present invention, a transportation refrigeration unit (TRU) system is provided according to claim <NUM> and includes an air supply chamber that includes a damper assembly configured to direct air flows through first or second pathways, a vapor compression cycle that includes an evaporator disposed in the first pathway, a coil element surrounded by phase change material (PCM) and disposed in the second pathway and a routing assembly configured to direct refrigerant through the evaporator or the coil element and a controller. The controller is configured to pre-cool the PCM and to control the damper and routing assemblies to respectively direct the air flows through the first pathway and the refrigerant through the evaporator when first conditions are met and to respectively direct the air flows through the second pathway when second conditions are met. The damper assembly includes first dampers at an outlet of the first pathway, second dampers at an outlet of the second pathway and third dampers between the first and second pathways.

Optionally, the controller pre-cools the PCM with grid or battery power, the first conditions are high-load conditions and the second conditions are low-load conditions.

Optionally, the controller closes the first, second and third dampers while the PCM is pre-cooled, opens the first dampers and closes the second and third dampers when the first conditions are met and closes the first dampers and opens the second and third dampers when the second conditions are met.

Optionally, the routing assembly includes first and second piping fluidly connecting an expansion valve with the evaporator and the evaporator with a compressor, respectively, first and second valves disposed along the first and second piping, respectively, third and fourth piping fluidly connecting the first piping with the coil element and the coil element with the second piping, respectively, and third and fourth valves disposed along the third and fourth piping, respectively.

Optionally, the controller closes the first and second valves and opens the third and fourth valves while the PCM is pre-cooled, opens the first and second valves and closes the third and fourth valves when the first conditions are met and closes at least the third and fourth valves when the second conditions are met.

Optionally, the controller closes the first, second and third dampers, closes the first and second valves and opens the third and fourth valves while the PCM is pre-cooled, opens the first dampers, closes the second and third dampers, opens the first and second valves and closes the third and fourth valves when the first conditions are met and closes the first dampers, opens the second and third dampers and closes at least the third and fourth valves when the second conditions are met.

Optionally, the coil element includes the PCM and refrigerant tubes extending through the PCM and through which the refrigerant, which is directed through the coil element, flows.

Optionally, the coil element includes a plurality of coil element slabs between which the air flows, which are directed through the coil element, proceed.

According to a second aspect of the present invention, a method of operating a transportation refrigeration unit (TRU) system is provided. The TRU includes a damper assembly configured to direct air flows through first or second pathways, an evaporator disposed in the first pathway, a coil element surrounded by phase change material (PCM) and disposed in the second pathway and a routing assembly configured to direct refrigerant through the evaporator or the coil element. The method includes pre-cooling the PCM, directing the air flows through the first pathway and the refrigerant through the evaporator when first conditions are met and directing the air flows through the second pathway when second conditions are met. The damper assembly includes first dampers at an outlet of the first pathway, second dampers at an outlet of the second pathway and third dampers between the first and second pathways.

Optionally, the pre-cooling of the PCM includes pre-cooling the PCM with grid or battery power, the first conditions are high-load conditions and the second conditions are low-load conditions.

Optionally, the pre-cooling of the PCM includes closing the first, second and third dampers, closing the first and second valves and opening the third and fourth valves, the directing when the first conditions are met includes opening the first dampers, closing the second and third dampers, opening the first and second valves and closing the third and fourth valves and the directing when the second conditions are met includes closing the first dampers, opening the second and third dampers and closing at least the third and fourth valves.

As will be described below, a transport refrigeration unit (TRU) system is provided in which a vapor compression cycle is provided with a coil element that is surrounded by phase change material (PCM). The PCM can be pre-cooled from a liquid phase to a solid phase by grid or battery power at an initial time. In this precooling process, the refrigerant can be flown from a compressor to a condenser, from the condenser to an expansion valve, from the expansion valve to an coil element and from the coil element back to the compressor. Subsequently, during high-load conditions, refrigerant can be flown from the compressor to the condenser, from the condenser to the expansion valve, from the expansion valve to an evaporator and from the evaporator back to the compressor. Alternatively, during low-load conditions, the vapor compression cycle is turned off and cabin air is cooled by the precooled PCM in the coil element.

With reference to <FIG>, a vehicle <NUM> is provided and may be configured as a truck. The vehicle <NUM> includes a cabin <NUM> sized to accommodate an operator and an engine, a truck bed <NUM> and a trailer <NUM> supported atop the truck bed <NUM>. The trailer <NUM> is formed to define an interior <NUM> in which perishable items can be stored for shipping. The vehicle <NUM> further includes a TRU system <NUM>. The TRU system <NUM> is installed at a front side of the trailer <NUM> and is configured to control environmental conditions within the interior <NUM>.

With continued reference to <FIG> and with additional reference to <FIG>, the TRU system <NUM> includes an air supply chamber <NUM> and a vapor compression cycle unit <NUM>. The air supply chamber210 includes a first pathway <NUM>, a second pathway <NUM> and a damper assembly <NUM>. The first pathway <NUM> and the second pathway <NUM> are both disposed to output cooled air into the interior <NUM> of the trailer <NUM>. The damper assembly <NUM> is configured to direct air flows through first pathway <NUM> or the second pathway <NUM>. The vapor compression cycle unit <NUM> includes a compressor <NUM>, a condenser <NUM>, which includes a condenser fan <NUM> and which is disposed downstream from the compressor <NUM>, and an expansion valve <NUM>, which is disposed downstream from the condenser <NUM>. The vapor compression cycle unit <NUM> further includes an evaporator <NUM>, which includes an evaporator fan <NUM> and which is disposed in the first pathway <NUM> and which is fluidly interposed between the expansion valve <NUM> and the compressor <NUM>, a coil element <NUM> and a routing assembly <NUM>. The coil element <NUM> is surrounded by PCM <NUM>, is disposed in the second pathway <NUM> and is fluidly interposed between the expansion valve <NUM> and the compressor <NUM>. The routing assembly <NUM> is configured to direct refrigerant through the evaporator <NUM> or the coil element <NUM>.

With continued reference to <FIG> and <FIG> and with additional reference to <FIG>, the TRU system <NUM> also includes a controller <NUM>. The controller <NUM> can include a processor <NUM>, a memory unit <NUM>, a servo control unit <NUM>, which is operably coupled to the various components of the vapor compression cycle unit <NUM>, the damper assembly <NUM> and the routing assembly <NUM>, and an input/output (I/O) unit <NUM> by which the processor <NUM>, the memory unit <NUM> and the servo control unit <NUM> are communicative with each other. The memory unit <NUM> has executable instructions stored thereon, which are readable and executable by the processor <NUM>. When the executable instructions are read and executed by the processor <NUM>, the executable instructions cause the processor <NUM> to instruct the servo control unit <NUM> to pre-cool the PCM <NUM> and to control both the damper assembly <NUM> and the routing assembly <NUM> to respectively direct the air flows through the first pathway <NUM> and the refrigerant through the evaporator <NUM> when first conditions are met (as will be discussed below) and to respectively direct the air flows through the second pathway <NUM> when second conditions are met (as will be discussed below).

The pre-cooling of the PCM <NUM> causes the PCM to change from a liquid state to a solid state and can be achieved prior to a normal operation of the TRU system <NUM> using power drawn from an electric grid (by, e.g., plugging the PCM <NUM> into a wall outlet or a charging station while the vehicle <NUM> is parked) and/or from a battery (e.g., the battery on board the vehicle <NUM>). Also, the first conditions are high-load conditions and can be characterized as cases in which cooling demands in the interior <NUM> of the trailer <NUM> are relatively high, and the second conditions are low-load conditions and can be characterized as cases in which cooling demands in the interior <NUM> of the trailer <NUM> are relatively low.

With reference back to <FIG>, features of the damper assembly <NUM> and the routing assembly <NUM> will now be described. The damper assembly <NUM> includes first dampers <NUM> at an outlet of the first pathway <NUM> to open or close the first pathway <NUM>, second dampers <NUM> at an outlet of the second pathway <NUM> to open or close the second pathway <NUM> and third dampers <NUM> between the first and second pathways <NUM> and <NUM> direct air flow through the first pathway 211or the second pathway <NUM>. The routing assembly <NUM> includes first piping <NUM> fluidly connecting the expansion valve <NUM> with the evaporator <NUM> and second piping <NUM> fluidly connecting the evaporator <NUM> with the compressor <NUM>. The routing assembly <NUM> further includes a first valve <NUM> disposed along the first piping <NUM>, a second valve <NUM> disposed along the second piping <NUM>, third piping <NUM> fluidly connecting the first piping <NUM> with the coil element <NUM>, fourth piping <NUM> fluidly connecting the coil element <NUM> with the second piping <NUM>, a third valve <NUM> disposed along the third piping <NUM> and a fourth valve <NUM> disposed along the fourth piping <NUM>.

The processor <NUM> of the controller <NUM> can instruct the servo control unit <NUM> to close the first, second and third dampers <NUM>, <NUM> and <NUM>, to close the first and second valves <NUM> and <NUM>, to open the third and fourth valves <NUM> and <NUM>, to activate the compressor <NUM> and the condenser fan <NUM> and to deactivate the evaporator fan <NUM> while the PCM <NUM> is pre-cooled.

When the first conditions are met and the TRU <NUM> is operated under high-load conditions, the processor <NUM> of the controller <NUM> can instruct the servo control unit <NUM> to open the first dampers <NUM>, to close the second and third dampers <NUM> and <NUM>, to open the first and second valves <NUM> and <NUM>, to close the third and fourth valves <NUM> and <NUM> and to activate the compressor <NUM>, the condenser fan <NUM> and the evaporator fan <NUM>. This will engage the evaporator <NUM>.

Here, the refrigerant enters the compressor <NUM> from the evaporator <NUM> along the second piping <NUM> via the open second valve <NUM> (the closed fourth valve <NUM> blocks the fourth piping <NUM>) as a superheated vapor and is compressed within the compressor <NUM> to a higher pressure and a higher temperature. The hot, compressed superheated vapor is then condensed within the condenser <NUM> by air being flown across the coil or tubes of the condenser <NUM> by the condenser fan <NUM>. Heat is rejected from the system and carried away by this air. Next, the condensed refrigerant is routed as a saturated or subcooled liquid through the expansion valve <NUM> where it undergoes an abrupt reduction in pressure resulting in an adiabatic flash evaporation of a part of the refrigerant and lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the interior <NUM> of the trailer <NUM>. The cold mixture is then routed to the evaporator <NUM> along the first piping <NUM> via the open first valve <NUM> (the closed third valve <NUM> blocks the third piping <NUM>) and through the coil or tubes in the evaporator <NUM> whereupon the evaporator fan <NUM> circulates warm air drawn from the interior <NUM> across the coil or tubes of the evaporator <NUM> within the first pathway <NUM> due to the first dampers <NUM> being open and the second and third dampers <NUM> and <NUM> being closed. The warm air evaporates the liquid part of the refrigerant mixture and the circulating air is cooled before returning to the interior <NUM> and thus lowering the temperature of the interior <NUM>. The refrigerant is then routed back toward the compressor <NUM> as the superheated vapor.

When the second conditions are met and the TRU <NUM> is operated under low-load conditions, the processor <NUM> of the controller <NUM> can instruct the servo control unit <NUM> to close the first dampers <NUM>, to open the second and third dampers <NUM> and <NUM>, to close at least the third and fourth valves <NUM> and <NUM>, to deactivate the compressor <NUM> and the condenser fan <NUM> and to activate the evaporator fan <NUM>. This will engage the coil element <NUM> with air flows generated by the evaporator fan <NUM> being directed over and around the PCM <NUM>. As long as the PCM <NUM> remains in the solid state and is cooler than the interior <NUM> of the trailer <NUM>, the PCM <NUM> will be able to provide cooling for the interior <NUM>.

With reference to <FIG>, the coil element <NUM> includes the PCM <NUM> and refrigerant tubes <NUM> through which refrigerant directed through the coil element <NUM> can flow. The refrigerant tubes <NUM> extend through the PCM <NUM>.

With reference to <FIG>, the coil element <NUM> can be provided as a plurality of coil element slabs <NUM> where each coil element slab <NUM> includes the PCM <NUM> and refrigerant tubes through which refrigerant directed through the coil element <NUM> can flow. As shown in <FIG>, air flows generated by the evaporator fan <NUM> can be directed between the coil element slabs <NUM> prior to entering the interior <NUM> of the trailer <NUM>. As such, separations between the coil element slabs <NUM> and the surface area of the coil element slabs <NUM> which is exposed to the air flows need to be weighed against each other to achieve sustained cooling capability without sacrificing mass flow rates.

The coil element <NUM> can be provided with an exterior encasement <NUM> (see <FIG>) to encase the PCM <NUM> in the liquid and the solid phases thereof. The exterior encasement <NUM> can be formed of highly thermally conductive material which is also at least one of compliant and deformable. As such, heat transfer across the exterior encasement <NUM> is possible while the PCM <NUM> is permitted to vary in shape and size as it transitions between the liquid and solid phases. In addition, the compliance and deformability of the exterior encasement <NUM> permits the coil element <NUM> to be designed in various overall shapes and sized as described above with reference to <FIG>.

The coil element <NUM> can be removably installed in the TRU system <NUM> and can be charged in an installed or non-installed condition. In either case, the coil element <NUM> includes a charging element <NUM> (see <FIG>) that can be coupled to a power source, such as an electrical grid or a battery, so that the coil element <NUM> can be charged.

With reference to <FIG>, a method of operating the TRU <NUM> described herein is provided. As shown in <FIG>, the method includes pre-cooling the PCM (<NUM>) with electric grid or battery power, directing the air flows through the first pathway and the refrigerant through the evaporator when first conditions are met or high-load conditions are in effect (<NUM>) and directing the air flows through the second pathway and the refrigerant through the coil element when second conditions are met or low-load conditions are in effect (<NUM>).

Benefits of the features described herein are the reduction of on/off refrigeration system cycles at low loads and/or low ambient temperatures. This will help increase energy efficiency by reducing cycling and operation of compressor and condenser fans, decrease fluctuations in cabin air temperatures and improve component life spans. For systems driven by battery power, continuous operation times and battery life will be increased.

Claim 1:
A transportation refrigeration unit (TRU) system (<NUM>), comprising:
an air supply chamber (<NUM>) comprising a damper assembly (<NUM>) configured to direct air flows through first (<NUM>) or second pathways (<NUM>);
a vapor compression cycle (<NUM>) comprising an evaporator (<NUM>) disposed in the first pathway (<NUM>), a coil element (<NUM>) surrounded by phase change material (PCM) (<NUM>) and disposed in the second pathway (<NUM>) and a routing assembly (<NUM>) configured to direct refrigerant through the evaporator (<NUM>) or the coil element (<NUM>); and
a controller (<NUM>) configured to pre-cool the PCM (<NUM>) and to control the damper (<NUM>) and routing assemblies (<NUM>) to respectively direct:
the air flows through the first pathway (<NUM>) and the refrigerant through the evaporator (<NUM>) when first conditions are met, and
the air flows through the second pathway (<NUM>) when second conditions are met;
characterised in that the damper assembly (<NUM>) comprises:
first dampers (<NUM>) at an outlet of the first pathway (<NUM>);
second dampers (<NUM>) at an outlet of the second pathway (<NUM>); and
third dampers (<NUM>) between the first (<NUM>) and second pathways (<NUM>).