Abstract:
A method of operating a hybrid temperature control system. The method provides an evaporator, which has a discharge line, a supply line, and a evaporator coil. The evaporator coil is in fluid communication with the discharge line and the supply line. The method also provides a microprocessor, which regulates a supply of a heat absorbing fluid to the evaporator. The method further couples a sensor module to the microprocessor. The sensor module is near the evaporator, senses a temperature of a gas exiting the evaporator, and sends a temperature to the microprocessor. The method also turns off the supply of the heat absorbing fluid to the evaporator when the microprocessor determines that the temperature of the gas exiting the evaporator reaches a predetermined temperature.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to a provisional patent application serial No. 60/293,481, filed on May 25, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a temperature control system for pulling down the temperature in a conditioned space to a set point temperature, and for maintaining the set point temperature of the conditioned space; and more particularly the invention relates to a hybrid temperature control system that includes a first evaporator coil which utilizes a first heat absorbing fluid to provide primary temperature control of the conditioned space air and a second evaporator coil adjacent to, a distance from, or integrated with, the first evaporator coil where the second evaporator coil utilizes a second heat absorbing fluid to provide supplemental temperature control of the conditioned space air. 
     Mobile temperature control units are typically mounted on one end of trailers, trucks or containers to maintain the cargo transported in the trailer, truck, or container conditioned space at a desired set point temperature during shipment. Known temperature control units may be mechanical units which utilize a hydroflurocarbon-based refrigerant to maintain the conditioned space ambient fluid at the desired set point temperature. As illustrated schematically in FIG. 1, prior art mechanical temperature control unit  10  is generally comprised of a compressor  11  that raises the pressure of a known refrigerant gas, a condenser  12  flow connected to the compressor to condense the high pressure refrigerant gas to a liquid, and an expansion valve  13  for controlling the refrigerant flow to an evaporator  14 . The evaporator  14  includes evaporator coils  17  which are enclosed by an evaporator housing  20  having an evaporator inlet  16  through which conditioned space air enters the evaporator and an evaporator discharge  18  through which conditioned space air reenters the conditioned space. 
     Warm conditioned space air flows into the evaporator inlet  16 , continues across the evaporator coils  17  and is discharged through evaporator discharge  18 . The refrigerant that flows through the evaporator coils  17  absorbs heat from the conditioned space air, and in this way pulls down the temperature of the conditioned space air to a predetermined set point temperature and thereby maintains the conditioned space at the set point temperature. 
     In operation, high cooling capacities are needed to pull down a higher temperature conditioned space to the desired lower set point temperature in a relatively short time. After the conditioned space has been pulled down to the desired set point temperature, the cooling capacities required to maintain the conditioned space set point temperature are modest relative to the required pull down cooling capacities. 
     Conventional mechanical temperature control units provide the required variable cooling capacities by utilizing a compressor prime mover (not shown in FIG. 1) that drives the compressor at high and low speeds to provide high and low cooling capacities. However, even known mechanical temperature control units that utilize multi-speed prime movers cannot provide the cooling capacities required during peak demand periods. For example, during transportation of cargo, the doors to the trailer or truck are typically left open while the cargo is unloaded from the conditioned space. The temperature of the cargo conditioned space increases as the warm outside ambient air flows into the trailer conditioned space. The doors may be left open for an hour or more during unloading. After the delivery has been made and the doors are again closed, the conditioned space is pulled down to reestablish the conditioned space set point temperature. If the temperature of the conditioned space is not pulled down quickly, the load can spoil. Known mechanical units cannot provide the cooling capacity needed to quickly initially pull down the conditioned space or reestablish the set point temperature after cargo unloading. 
     In order for known mechanical units to achieve the desired pull down capacities, the size of conventional mechanical refrigeration units would need to be increased considerably. However this is not a realistic alternative since such units would be too large to be effectively used in the trailer, truck or container applications and such larger capacity mechanical units would be higher in cost, would be less efficient, would weigh more and would be noisier than conventional mechanical units. 
     A non-mechanical temperature control unit has been developed to meet the peak cooling demands at initial pull down and during pull down to reestablish the set point temperature in the conditioned space. Such non-mechanical temperature control units utilize a cryogen fluid to produce the desired cooling in the conditioned space. FIG. 2 schematically illustrates a prior art cryogen-based temperature control system  30  that includes a supply of cryogen liquid in cryogen tank  32  and the cryogen may be liquid carbon dioxide LCO 2  for example. An electronic expansion valve  34  or other valve means regulates the supply of cryogen through the evaporator coil  38  of evaporator  36 . A microprocessor  37  adjusts the expansion valve position by sending a signal to the valve in response to the sensed temperature at the evaporator unit  36 . A vapor motor  40  drives a fan  45  that draws conditioned space air through the evaporator  36  and across the evaporator coil  38 . The rotating vapor motor turns alternator  41  which charges a temperature control unit battery (not shown). 
     The higher temperature conditioned space air is drawn into the evaporator and across coil  38 . The cryogen liquid flowing through the evaporator coil absorbs heat from the conditioned space air and the lower temperature air is discharged from the evaporator  36  into the conditioned space in the direction of arrows  43 . The cryogen is vaporized as it absorbs heat from the conditioned space air. The cryogen vapor flows out of the evaporator and drives the vapor motor  40 . The spent cryogen vapor is exhausted from the vapor motor to atmosphere through exhaust  42  and muffler  39 . 
     The liquid cryogen can provide the cooling capacity required to quickly pull down the conditioned space. However, there are limitations associated with nonmechanical, cryogenic based temperature control units. First, cryogen units are limited by how fast one wants to drop the cargo temperature and by practical considerations so that fresh loads such as produce are not frozen. The supply of cryogen typically only lasts one to three days and when the cryogen supply is exhausted the tank must be refilled. It may be difficult to locate a cryogen filling station. If the cryogen units are to provide defrost and heating capability, a heating fuel and necessary heating components must be provided. 
     Hybrid mechanical and non-mechanical temperature control systems have been developed. These systems directly spray a volume of cryogen into the conditioned space during pull down of the conditioned space to the set point temperature. As a result, the conditioned space air is displaced and the conditioned space is comprised primarily of cryogen, which is undesirable for most applications. The cryogen is not breathable and can negatively affect some foods. 
     The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, this is accomplished by providing a hybrid temperature control system including a mechanical temperature control system that includes a primary evaporator having a first evaporator coil with a first heat absorbing fluid adapted to flow through the first coil to absorb heat from the conditioned space air and provide primary cooling of the conditioned space air. The hybrid temperature control system further includes a supplemental evaporator located adjacent to, a distance from, or integrated with the first evaporator coil. The supplemental evaporator includes a supplemental evaporator coil with a second heat absorbing fluid adapted to flow through the supplemental evaporator coil to provide supplemental cooling of the conditioned space air. 
     The first heat absorbing fluid is a conventional refrigerant and the second heat absorbing fluid is a cryogen. 
     By the present invention supplemental cooling of the conditioned space air by the supplemental evaporator is controlled by a microprocessor or by the unit operator so that supplemental cooling is only provided when required such as during initial pull down of the conditioned space or during pull down to reestablish the conditioned space set point temperature. 
     The supplemental evaporator coil may be made integral with the mechanical refrigeration unit evaporator housing with the supplemental evaporator coil located immediately adjacent to the primary evaporator discharge. Additionally, the supplemental evaporator coil may be located adjacent to, a distance from, or integrated with the mechanical evaporator discharge by locating the coil on a panel of the conditioned space, such as the ceiling; or along side the primary evaporator coil. 
     The invention may be utilized in both a conditioned space to be maintained at a single set point temperature and also in multi-temperature applications having a first conditioned space to be maintained at a first temperature with a first primary evaporator and a first supplemental evaporator adjacent to, a distance from, or integrated with or along side the first primary evaporator; and second conditioned space at a second set point temperature with a second primary evaporator, and a second supplemental evaporator adjacent to, a distance from, or integrated with the second primary evaporator. 
     When the present invention is used in a multi-temperature application with a number of conditioned spaces, any of the conditioned spaces may be maintained at the lowest set point temperature. 
    
    
     The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a schematic representation of a conventional mechanical temperature control system; 
     FIG. 2 is a schematic representation of a conventional non-mechanical, cryogen-based temperature control system; 
     FIG. 3 is a systematic representation of a first embodiment of the hybrid temperature control system of the present invention; 
     FIG. 4 is a longitudinal sectional view of a conventional trailer including the hybrid temperature control unit of FIG. 3; 
     FIG. 4A is a longitudinal sectional view of a conventional trailer including the hybrid temperature control unit of FIG. 3 with the exhaust line in the front; 
     FIG. 5 is a systematic representation of a second embodiment of the hybrid temperature control system of the present invention; 
     FIG. 6 is a longitudinal sectional view of a conventional trailer including the second embodiment hybrid temperature control system of FIG. 5; 
     FIG. 7 is a longitudinal section view of a conventional trailer illustrating a third embodiment hybrid temperature control system of the present invention. 
     FIG. 8 is a systematic representation of a fourth embodiment hybrid temperature control system of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     Turning now to the drawings wherein like parts are referred to by the same number throughout the several views, FIGS. 3 and 4 illustrate a first embodiment of the hybrid temperature control system  50  of the present invention. As shown in FIG. 3, the hybrid temperature control system  50  is comprised of the mechanical temperature control system  10  as previously described hereinabove and supplemental cooling unit  52  adjacent to, a distance from, or integrated with mechanical evaporator coil  17 . 
     As the description proceeds, the supplemental cooling unit  52  will be described as being manually actuated. It should be understood that it is also contemplated that a microprocessor or other suitable electronic means will actuate the unit  52 . 
     As illustrated in FIG. 3 the evaporator housing  20  of FIG. 1 may be extended and the extended housing is identified at  54 . The housing includes inlet  16  and discharge opening  55 . A supplemental evaporator coil  56  is located in the housing extension adjacent to, a distance from, or integrated with the evaporator coil  17 . Although one row of cryogen evaporator coils  56  is shown in FIGS. 3 and 4 it should be understood that additional rows of coils  56  may be provided. 
     The heat absorbing fluid in supplemental cooling unit  52  is a cryogen liquid that is stored in cryogen tank  32 . The cryogen liquid flows through the supplemental evaporator coil and is vaporized in the supplemental coil during operation of unit  50 . The supply of liquid cryogen through the supplemental evaporator coil  56  is controlled by valve  58  flow connected along the length of the inlet line  60  that flow connects the cryogen tank and the cryogen evaporator coil  56 . The valve  58  may be any suitable valve well known to one skilled in the art such as a manually actuated butterfly valve or may be an electronic expansion valve for example. However, the suitable valve  56  permits for selectively supplying cryogen to coil  56  and adjusting the volume of cryogen provided to the coil. A conventional back pressure regulator  62  is located in exhaust line  64 . The regulator  62  may be an electronically a manually or a spring actuated back pressure valve. The inlet line  60  is located in a front trailer panel  81 , a bottom panel  84  and passes through the bottom panel  84 . See FIG.  4 . 
     It should be understood that valves  58  and  62  and associated lines  60 ,  64  are shown schematically in FIGS. 3 and 4 for illustrative purposes only and the valves may be located in unit  50  with associated flow lines located in the trailer panels. 
     FIG. 4 illustrates the first embodiment hybrid temperature control unit of the present invention  50  mounted for use on the nose of trailer  80 . The trailer includes front  81 , top  82 , rear  83 , bottom  84 , and side panels  85  that define a conditioned space  88 . The cryogen tank  32  and the fuel tank  33  for the compressor prime mover are mounted on the bottom side of the trailer in a conventional manner. The exhaust line  64  extends through the trailer top panel  82 , side panel  85 , and the flow line  64  passes through the bottom panel  84 . The exhaust line  64 , in the preferred embodiment shown in FIG. 4A, extends through the cryogenic unit  50  in the front. A conventional fuel supply line  75  flow connects fuel tank  33  and the prime mover (not shown) of mechanical unit  10 . 
     Although conditioned space  88  is shown and described as being defined by a trailer, it should be understood that the conditioned space could be defined by a truck, container, bus, railway car, warehouse, storage facility, repository, storehouse or other enclosed volume or space, mobile or stationary, requiring the temperature in the enclosed conditioned space to be maintained at a predetermined set point temperature. 
     Operation of the first embodiment hybrid temperature control unit  50  of the present invention will now be described. When the mechanical unit is in high speed cool mode, it signals that supplemental cooling by supplemental evaporator coil  56  is needed to provide rapid pull down of the air in the conditioned space  88 . Then after a period of time, valve  58  is opened either electronically or manually to permit liquid cryogen to flow from tank  32  through line  60  to supplemental evaporator coil  56 . The mechanical temperature control unit  10  is started before the valve  58  is opened. 
     Higher temperature conditioned space air is drawn through inlet  16  and across the primary evaporator coils  17 . The refrigerant flowing through the coils  17  absorbs heat from the conditioned space air and thereby provides primary cooling to the conditioned space air. The lower temperature conditioned space air continues across supplemental evaporator coils  56 . The cryogen flowing through the supplemental coils absorbs additional heat from the already cool conditioned space air. After passing the coils  56  the cooled ambient air is discharged from housing  54  through opening  55  back into conditioned space  88 . The vaporized cryogen is exhausted out exhaust  64  to atmosphere. None of the vaporized cryogen enters the conditioned space. 
     The supplemental cooling can be stopped manually or with a timer to automatically shut off the flow of cryogen. The valve “on” time varies for each particular application and is generally dependent on the ambient conditions, cargo, and required conditioned space set point temperature. The supplemental cooling may be shut off by a temperature switch. 
     The supplemental evaporation provided by supplemental evaporator coil  56  provides rapid pull down of conditioned space  88 . Because the cryogen is released to atmosphere the cargo in the space  88  is not exposed to cryogen gas. The application of supplemental cooling may be selectively applied to meet peak demand such as during pull downs. Therefore, frequent refills of the cryogen tank are not required. 
     A second embodiment hybrid temperature control unit  90  is illustrated in FIGS. 5 and 6. The second embodiment unit  90  includes mechanical unit  10  as previously described hereinabove and also includes supplemental cooling unit  92 . The supplemental cooling unit is adapted for use with trailer  80  also previously described. 
     The supplemental cooling unit is comprised of cryogen tank  32  with flow of the cryogen from the tank being regulated by valve  58 . A supplemental evaporator  93  is mounted on the interior of trailer roof panel  82  in conditioned space  88  adjacent to, a distance from, or integrated with the evaporator  17  of mechanical temperature control unit  10 . The evaporator  93  may also be located along side evaporator  14 . The supplemental evaporator is mounted on the roof panel in a conventional manner. The supplemental evaporator  93  has a supplemental evaporator coil  94  that is flow connected to supply line  95  and discharge line  96  that extends through roof  82  to atmosphere. Valve  58  is connected to supply line  95  outside the conditioned space. The supply line passes through the bottom panel of the trailer  80 . The back pressure regulator  62  is located in the discharge line  96  outside the trailer conditioned space. Although line  96  is shown extending in panel  88  and line  95  extending through panel  85  and bottom panel  84  with valves  58  and  62  located outside the trailer, the lines and valves may assume any suitable configuration and location. 
     It is easy to retrofit existing mechanical temperature control units with supplemental cooling units  92  by mounting the supplemental evaporator adjacent to, a distance from, or integrated with evaporator  14  in the flow path of the mechanical unit evaporator, and by connecting the associated supply and discharge flow lines to the supplemental evaporator coil. 
     The second embodiment hybrid temperature control system operates in the manner previously described in conjunction with the first embodiment hybrid temperature control system. 
     FIG. 7 illustrates a third embodiment hybrid temperature control unit  100  that includes the trailer  80 , mechanical temperature control unit  10  and supplemental cooling units  92  previously described in conjunction with first and second embodiments  50  and  90 , however the third embodiment unit  100  is related to a multitemperature control unit. 
     As illustrated in FIG. 7, the conditioned space  88  is further divided into first conditioned space  88   a  by lateral partition  86  and is divided into second and third conditioned spaces  88   b  and  88   c  by lateral partition  87 . Primary and supplemental cooling is supplied to conditioned spaces  88   a  and  88   b  however primary and supplemental cooling could be provided to third conditioned space  88   c  as well if desired. One or more of the conditioned spaces may be provided with supplemental cooling units. In operation either the first or second spaces  88   a ,  88   b  may have the lowest set point temperature. 
     Primary mechanical evaporator  101  is flow connected to mechanical unit in a manner well known to one skilled in the art so that during operation the refrigerant is supplied from unit  10  through evaporators  14  and  101 . Flow lines  102   a  and  102   b  flow connect supplemental evaporator coils  94  to tank  32 . Lines  102   a  and  102   b  extend through the side panel  85  and bottom panel  84  of the trailer but like other lines previously described may assume any suitable configuration. 
     Third embodiment hybrid temperature control unit operates in the manner previously described except that the supplemental cooling may be provided to a conditioned space independent of other supplemental cooling units. For example, if the second conditioned space is partially unloaded, once the doors to the center space are closed, the supplemental cooling may be selectively provided only to the second conditioned space to pull down the second conditioned space and no supplemental cooling is provided to the first conditioned space  88   a . In this way the cryogen is not used unnecessarily. 
     As illustrated in FIG. 8, the fourth embodiment hybrid temperature control unit  110  operates in the manner previously described. In the fourth embodiment, the hybrid unit  110  includes the mechanical unit  10  as previously described hereinabove and also includes a supplemental cooling unit  112 . The supplemental cooling unit  112  is adapted for use with the trailer  80  also previously described. 
     The supplemental cooling unit  112  is comprised of a cryogen tank  32  with flow of the cryogen from the tank being regulated by a valve  58 . In the fourth embodiment, the valve  58  is controlled by a microprocessor  114 . The microprocessor  114  receives a signal  115  from the mechanical compressor unit  11  typically via a relay or speed solenoid (not shown), corresponding to the compressor speed. When the mechanical compressor  11  is in high speed cool, the microprocessor  114  sends a signal  117  to open the valve  58 , allowing the cryogen liquid to flow through the supplemental evaporator coils  94  to provide supplemental pull down of the conditioned area  88  (see FIG.  6 ). The valve  58  will be closed if the signal  115  received from the mechanical compressor  11  indicates that any of the following conditions occur: the mechanical compressor enters low speed cool, the unit is off, the unit is in high or low speed heat or the unit is in defrost mode. 
     The valve  58  will also close if the microprocessor  114  receives a signal  116  that the door to the conditioned area (not shown) is open. In this way, the cryogen is not wasted by cooling air that will escape from the trailer. The valve  58  is further controlled by a separate temperature sensor module  118  that will send signals  120  to the microprocessor  114  which will turn off the valve  58  if the temperature of the gas that exits the supplemental evaporator coils  94  reaches just above the freezing point of the cryogen, thus inhibiting the formation of dry ice in the supplemental evaporator coil  94 . 
     The present invention hybrid temperature control system provides many benefits and advantages over present mechanical and cryogenic temperature control units. The hybrid temperature control system of the present invention boosts the cooling capacity of a conventional cooling unit, and provides maximum capacity as needed, especially during initial pull-down and for quick recovery to load set point temperature after door openings. By the present invention the operator may locate the coldest cargo in any conditioned space, there is no requirement to place the coldest cargo in the front conditioned space. Mechanical components can be designed to meet the more steady state cooling needs with the supplemental evaporator providing cooling during peak loads. As a result of the present invention the unit is quieter than equivalent mechanical units and weighs less than mechanical units. The physical size of the hybrid unit of the present invention is smaller than a conventional mechanical unit with the same cooling capacity. This is an important benefit since mechanical units are typically mounted on the front of the trailer, truck or container where space is at a premium. The lower weight unit also lowers the center of gravity of the vehicle. Engine/compressor speed can be lowered and thereby increase their useful lives. Mechanical system can be simplified to have a single speed to handle steady state operation. This simplifies the control system and also increases unit reliability. The present invention provides airflow, heating, defrost, and cooling for extended periods and very high cooling capacities for rapid pull down and temperature recovery after door openings. 
     While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth. 
     Various features and advantages of the invention are set forth in the following claims.