US3589139A

US3589139A - Refrigerated shipping container

Info

Publication number: US3589139A
Authority: US
Inventors: Reginald L Arthur
Original assignee: Electronic Assistance Corp
Current assignee: Electronic Assistance Corp
Priority date: 1969-11-07
Filing date: 1969-11-07
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29
Also published as: AU2873671A; DE2054722A1; GB1262832A; FR2082965A5

Abstract

Perishable goods are transported by air by placing them in a portable, insulated container including a refrigerating unit. Electric service is supplied to the refrigerating unit at 60 p.s.i. when the container is at an air terminal at 400 p.s.i. when the container is on board an aircraft. An unskilled attendant can effect the necessary electrical connection by plugging in the refrigerating unit terminal plug to whatever electrical outlet socket is available. The frequency of the supplied electric service is automatically sensed, and an electric signal is generated that depends on the sensed frequency. There is established in the refrigerating unit in response to the electric signal a selected one of two possible configurations such that the operating speed of the refrigerating unit is rendered substantially independent of the frequency of the electric service supplied thereto.

Description

United States Patent 1 1 3,589,139 [72] Inventor Reginald L. Arthur 2,532,234 I 1/1950 Kimble 62/457 Loveland, Ohio 2,747,146 5/1956 McDonald... 307/129 [2!] Appl. No. 874,931 2,761 ,03l 8/1956 McDonald... 307/129 gg f 9 Primary ExaminerWilliam J. Wye [73} Assignee Electronic Assistance Corporation Anamey Brumbaugh Graves Donohue & Raymond Red Bank, NJ.

[54] REFRIGERATED SHIPPING CONTAINER ABSTRACT: Perishable goods are transported by air by placing them in a portable, insulated container including a refrigerating unit. Electric service is supplied to the refrigerating unit at 60 p.s.i. when the container is at an air terminal at 400 p.s.i. when the container is on board an aircraft. An unskilled attendant can effect the necessary electrical connection by plugging in the refrigerating unit terminal plug to whatever clectrical outlet socket is available. The frequency of the supplied electric service is automatically sensed, and an electric signal is generated that depends on the sensed frequency. There is established in the refrigerating unit in response to the electric signal a selected one of two possible configurations such that the operating speed of the refrigerating unit is rendered substantially independent of the frequency of the electric service supplied thereto.

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\---"' SOLENOID THERMOSTAT COMPRESSOR INVliN'l'UR. REGINALD L. ARTHUR BY W MW MHQ REFRIGERATED SHIPPING CONTAINER BACKGROUND OF THE INVENTION This invention relates to refrigerated shipping containers and, more particularly, to novel and highly effective refrigerated shipping containers for storing goods at a first facility provided with electric service at a first frequency and at a second facility provided with electric service at a second frequency.

In shipping perishable goods such as fruits, vegetables, dairy products, eggs, meats and seafoods, refrigeration is necessary to prevent spoilage. Different temperatures are necessary for short term and long term storage and quick freezing of a given product. For example, for short term storage of asparagus, a temperature of about 40 F. is indicated, as compared to a temperature of about 32 F. for long term storage. The freezing point of asparagus is about 30 F., and, for quick-freezing asparagus, a temperature of about 30 F. is indicated.

Often, ranges of temperatures are specified for the various purposes. In the case of strawberries, for example, the short term storage temperature range is from 42 F. to 45 F., the long term storage range is from 31 F. to 32 F., the freezing point is 30 F., and the quick-freezing temperature is F.

Control of humidity is also important. Thus, in the case of califlower, the relative humidity should be maintained between 85 percent and 90 percent, whereas, in the case of melons, the relative humidity should be within the range of 75 percent to 85 percent.

Evidently, the requirements for optimum control of temperature and humidity during shipment of perishable foodstuffs and the like are stringent. One factor that makes it extremely difficult to meet the requirements is that, during shipment, the electric service that is available at successive facilities is not standardized.

In shipping by air, for example, the electric service available at the air terminal where the cargo is stored prior to loading on board an aircraft, is likely to have a frequency of substantially 60 c.p.s. When the cargo is loaded on board the aircraft, the only electric service available is likely to have a frequency of 400 c.p.s. At the destination air terminal, where the cargo may be stored again for a period of time, the available electric service is again likely to have a frequency of 60 c.p.s.

The various expedients for controlling the temperature of perishable foodstuffs during shipment that have been adopted heretofore have not been entirely successful.

One expedient is to employ a medium, such as frozen carbon dioxide, or dry ice, that is capable of effecting temporary cooling without connection to a source of power. This expedient is unsatisfactory in that it does not permit adequate control of the temperature of the commodity being shipped and in that the dry ice soon evaporates so that the commodity can not be refrigerated for long.

A more sophisticated expedient is to employ in effect two refrigeration systems, one adapted to operate when connected to electric service having a frequency of 60 c.p.s. and the other adapted to operate when connected to electric service having a frequency of 400 c.p.s. This expedient is also unsatisfactory in that it requires a certain amount of time and skill on the part of those who are handling the shipment in order to make the right connections at the various facilities en route and in that the apparatus tends to be expensive.

Still another expedient is to provide a vehicle-carried refrigeration system that includes provision for standby operation by plugging into 60-cycle power available at a shipping terminal and a variably responsive refrigeration system operated from the vehicle electrical system when the vehicle is in motion. The vehicle drive is such that the output frequency of the AC generator varies with the speed, and switch means is provided for changing the pole configuration of the motor at an intermediate point in the speed range. Consequently, the speed range of the refrigerator motor is maintained within an optimum compressor speed range. Manual switching is required to select either standby or vehicle operation. Switching between the two pole configurations of the motor may be effected by a frequency responsive relay. This system leaves much to be desired because its operation is tied directly to the speed of the vehicle in which it is mounted.

It is also conventional to provide a portable refrigerator operating from a standard -cycle source where available or from a 6-volt DC source such as may be found in an automotive vehicle. Switching is effected upon plugging in the appropriate source by virtue of the internal wiring of the plug. Such a system is of limited use in a modern distribution system in which aircraft are extensively employed in feeding foodstuffs to the market.

It is also conventional to provide a portable refrigeration unit operable from power available dockside and while aboard a vehicle and that freezes a quantity of eutectic fluid at dockside. A fan operable from the vehicle electrical system circulates air over the eutectic fluid to maintain the temperature. This expedient is not a full solution to the problem, because of insufficientchoice in establishing the temperature and because the unit is effected for only a limited period of time without refreezing the fluid.

SUMMARY OF THE INVENTION An object of the invention is to remedy the deficiencies of prior art methods and apparatus noted above. In particular, an object of the invention is to provide for the shipment of perishable products such as foodstuffs from any source to any market, the product being maintained at an optimum temperature during the entire shipping process. Another object of the invention is to accomplish the shipping process while placing minimum demands on the time and skill of the persons responsible for accomplishing the shipping.

The foregoing and other objects of the invention are accomplished by the provision of a portable housing for housing the goods to be shipped and a fluid circuit attached to the housing. A compressor, evaporator and condenser are mounted in series in the fluid circuit, and a terminal is provided for connection to electric service at either of two frequencies. A compressor motor that drives the compressor has a first configuration in which it runs at a desired speed in response to actuation at one of the frequencies and a second configuration in which it runs substantially at the same speed in response to actuation at the other of the two frequencies. Frequency-responsive means connected to the terminal generates an output that depends on the frequency of the electric service to which the terminal is connected. Means actuated by the frequency-responsive means establishes in the compressor motor the appropriate configuration to run at the desired speed irrespective of the frequency to which the terminal is connected.

Fan motors driving an evaporator fan and a condenser fan, respectively, likewise have two configurations the appropriate one of which they automatically assume in response to the detected frequency of the electric service to which the terminal is connected.

BRIEF DESCRIPTION OF THE DRAWING An understanding of additional aspects of the invention may be gained from a consideration of the following detailed description of a representative embodiment thereof, taken in conjunction with the accompanying figures of the drawing, wherein:

FIG. 1 is a perspective view in front elevation of a portion of apparatus constructed in accordance with the invention;

FIG. 2 is a schematic diagram of certain electrical components of apparatus constructed in accordance with the invention; and

FIG. 3 is a schematic diagram of certain electric and fluidconduit means constructed in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows apparatus constructed in accordance with the invention. The apparatus 10 respectively, rectangular floor 12, a generally rectangular left sidewall 14, and a generally rectangular right sidewall 16. It also has a left rectangular sloping roof portion 18 and a right rectangular sloping roof portion 20 meeting 60-cyclc peak rectangular roof portion 22. In addition, it has a back wall 24 closing the back of 60and a front wall (not shown) that is removable to facilitate loading and unloading of the container.

A refrigerating unit 26 is mounted in the container for the purpose of refrigerating the container. The refrigerating unit 26 includes a plurality of hoses 28 for distributingrefrigerated air throughout the volume of the container so that all of the produce stored therein is effectively cooled. Typically, eight hoses are employed, but only two are illustrated in FIG. I, in order to simplify the drawing.

The overall shape of the container facilitates transportation in an airplane with the axis of the container (which is parallel to the peels l2, l4, l6, 18, 20 and 22 and perpendicular to the panel 24 and the front panel) parallel to the axis of the aircraft fuselage. The container is formed of a material or composite of materials having good heat insulating qualities in order to reduce the load on the refrigerating unit 26.

The refrigerating unit 26 is adapted to be connected to electric service such as a power supply 30 (FIG. 2) having a frequency of 60 c.p.s. or 400 c.p.s. by means of a terminal plug 32. The terminal 32 is connected to five branch leads 34, 36, 38, 40 and 42. The branch leads 38, 40 and 42 are adapted to be connected to conventional

electric motors

44, 46 and 48, respectively. Each electric motor has two configurations, identified very schematically as 44-1 and 44-2 in the case of the motor 44, as 46-] and 46-2 in the case of the motor 46, and as 48-1 and 48-2 in the case of the motor 48. The first configuration of each motor is the configuration in which the motor is adapted to respond to electric service at a frequency of 60 c.p.s., and the second configuration of each motor is a configuration in which the motor is adapted to respond at substantially the same operating speed to electric service having a frequency of 400 c.p.s.

Switch means 50, 52 and 54 are associated with the

motors

44, 46 and 48, respectively, for selectively connecting the motors with the power source in either of the two configurations. In the positions of the switches shown, the lead 38 is connected to the motor 44 in the 60-cycle configuration by a lead 56, the lead 40 is connected to the motor 46 in the 60-cycle configuration by a lead 38 is connected to the motor 44 in the 60-cycle configuration by a lead 56, the lead 40 is connected to the motor 46 in the 60-cycle configuration by a lead 58, and the lead 42 is connected to the motor 48 in the 60-cycle configuration by a lead 60. When the switches are reversed, the lead 38 is connected to the motor 44 in the 40-cycle configuration by a lead 62, the lead 40 is connected to the motor 46 in the 40-cycle configuration by a lead 64, and the lead 42 is connected to the motor 48 in the 40-eycle configuration by a lead 66.

The

switches

50, 52 and 54 are controlled by relays R-l and R-2 (switch 50), R-3 and R-4 (switch 52), and R-5 and R-6 (switch 54). The relays R-l, R-3 and R-S are connected to a common lead 68 which in turn is connected to the lead 34 through a 60-cycle pass filter 70, and the relays R-2, R-4 and R-6 are connected to a common lead 72 that in turn is connected to the lead 36 through a 400-cycle pass filter 74. The 60-cycle pass filter 70 passes current within the range of, say slightly less than 50 c.p.s. to slightly more than 60 c.p.s., which is to say the current available at virtually every air terminal facility throughout the world. In the U.S., 60 c.p.s. is the usual frequency, and in Europe, for example, 50 c.p.s. is conventionally employed. The 60-eycle pass filter blocks current having a frequency that is close to 400 c.p.s.

On the other hand, the 400 cycle pass filter 74 passes current substantially at a frequency of 400 c.p.s. and the blocks current having a frequency close to 60 c.p.s.

The operation of the circuitry of FIG. 2 is as follows: the terminal 32 is connected to whatever power supply is available at an air terminal or on board an aircraft, regardless of whether the frequency of the power supply is 60 c.p.s. or 400 c.p.s. Initially, the

switches

50, 52 and 54 are in the positions shown in FIG. 2 or in the reverse positions described above. In either case, only the odd-numbered relays R-l, R-3 and R-5 or only the even-numbered relays R-2, R-4 and R-6 will be energized. That is because only one of the filters 70 and 74 passes the current supplied by the power supply.

Electric power is supplied to the

motors

44, 46 and 48 in the 60-cycle configuration or the 400-cycle configuration depending on whether the odd-numbered relays or the even-numbered relays are energized through the filters 70 and 74. If the odd-numbered relays R-I, R-3 and R-S are energized, then the

motors

44, 46 and 48 are energized in the 60-cycle configuration, as indicated in FIG. 2. If the even-numbered relays R-2, R-4 and R-6 are energized, the

motors

44, 46 and 48 are energized in the 400-cycle configuration. The

motors

44, 46 and 48 are suitably designed so that their operating speeds in the 60-cycle configuration are substantially the same as their respective operating speeds in the 400-cycle configuration. This relationship can be obtained by, for example, effectively employing two poles in the (SO-cycle configuration and I2 poles in the 400-cycle configuration. With the usual slippage at full load, this might yield a shaft speed of about 3,450 rotations per minute at full load in the 60-cycle configuration and about 3,700 rotations per minute at full load in the 400-cycle configuration.

The

motors

44,46 and 48 are employed in accordance with the invention to drive a compressor 80, an evaporator fan 82, and a condenser fan 84, respectively. It is evident from the preceding description that each of the latter three components runs at substantially the same speed irrespective of the frequency of the electric service to which the terminal 32 is connected.

FIG. 3 shows how the compressor 80, evaporator 82' and condenser 84 are connected in a fluid circuit 86. The compressor compresses a refrigerant substantially adiabatically so that its temperature rises sharply. The compressed refrigerant is delivered through a line 88 to the condenser 84, wherein a heat exchange takes place. The heat exchange in the condenser 84 involves a flow of heat from the refrigerant to the ambient atmosphere, because the refrigerant is at a higher temperature than the ambient atmosphere. The condenser fan 84 circulates ambient air over the condenser 84' to facilitate the heat exchange. The refrigerant then flows through a line 90 in its cooled state through a throttling valve 92, a two-way controlled by a solenoid 94 so that it communicates selectively with a line 96 or a line 98.

The solenoid 94 is controlled by a thermostat 100 connected to a power source 102. The power source 102 can be a battery, as indicated, or it can be drawn from the electric service to which the terminal 32 is connected.

Thethermostat is conventional per se and is set to maintain a desired temperature. So long as the thermostat 100 is not satisfied, the solenoid 94 establishes communication between the line 90 and the line 96 through the two-way throttling valve 92. This permits the refrigerant to flow through the line 96 and into the evaporator 82. The refrigerant in the evaporator 82 is at low pressure so that it evaporates. Evaporation is a I cooling process, and the evaporator, which is located within the container 10 (FIG. I), extracts heat from the interior of the container. The heat exchange is facilitated by the evaporator fan 82 (FIG. 2). The refrigerant then flows through a line 104 back to the compressor 80, and the cycle is repeated.

When the thermostat 100 is satisfied, it reverses the solenoid, so that the valve 92 shunts the refrigerant through the shunt line 98, thus bypassing the evaporator 82', while permitting the compressor 80 to continue to operate at its rated load.

It is within the scope of the invention to employ means making it unnecessary to phase the incoming power (which may be three phase), such as a phase reversal switch; power factor correction capacitors; magnetic-hydraulic circuit breakers for overcurrent protection; a transformer for stepping down the supplied current to a lower voltage,'such as 28 v.; and indica tor means such as a light for indicating improper phasing of the power. It is also within the scope of the invention to employ rectifier means for converting the alternating current to direct current and to employ means other than filters (such as frequency sensing relay means) for sensing the high or low frequency and energizing the proper motor control devices.

It is further contemplated that automatic defrosting means may be employed including a hot gas solenoid that is energized upon dropping out of the liquid solenoid and an electric clock governing the defrost cycle. The defrost mode of operation includes provision for shutting down the evaporator fan and flooding the evaporator with hot gas for deicing the evaporator coil.

Thus there is provided in accordance with the invention novel and highly effective methods and apparatus facilitating the shipping of perishable products 'by air. This'system is designed to operate from a conventional power source that may be, for example, three phase having a voltage within the range of 200 to 250 and a frequency of either 50 to 60 c.p.s. or 400 c.p.s. Spoilage of perishable products due to delays in transit and at origin and destination are obviated.

Many modifications of the representative embodiment disclosed herein will readily occur to those skilled in the art. For example, provision may be made in accordance with the principles of the invention for automatic adaptation to electric service at more than two frequency ranges. Moreover, one of the frequency ranges can be direct current (which may be regarded as alternating current having a frequency of Further, the power supply can include a gasoline driven generator or a fixed-frequency solid-state inverter. Many other modifications of the representative embodiment disclosed herein will readily occur to those skilled in the art, and the invention is to be construed as including all of the embodiments thereof within the scope of the appended claims.

lelaim:

1. Apparatus for storing goods at a first facility provided with electric service at a first frequency and at a second facility provided with electric service at a second frequency, comprising portable housing means for housing said goods; fluid circuit means attached to said housing means; compressor means, evaporator means and condenser means in series in said fluid circuit means; terminal means for connection to said electric service at either of said frequencies; compressor motor means connected to said terminal means for driving said compressor means, said compressor motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; frequencyresponsive means connected to said terminal means for providing an output that depends on the frequency of the electric service to which said terminal means is connected; and means actuated by said frequency-responsive means for establishing in said compressor motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency.

2. Apparatus according to claim 1 comprising evaporator fan means for blowing air over said evaporator means to facilitate heat exchange; evaporator fan motor means connected to said terminal means for driving said evaporator fan means, said said evaporator fan motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; and means actuated by said frequency-responsive means for establishing in said evaporator fan motor means said first configuration in in response to connection of said terminal means to electric service at said 6' first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency.

3. Apparatus according to claim 1 comprising condenser fan means for blowing air over said condenser means to facilitate heat exchange; condenser fan motor means connected to said terminal means for driving said condenser fan means, said condenser fan motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; and means actuated by said frequency-responsive means for establishing in said condenser fan motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency.

4. Apparatus according to claim 1 comprising shunt means in said fluid circuit means in parallel with said evaporator means and valve means in said fluid circuit means, whereby fluid flowing in said fluid circuit means in response to operation of said compressor means can be made selectively to pass through said evaporator means or to bypass said evaporator means and pass through said shunt means.

5. Apparatus according to claim 4 comprising thermostat means mounted in said housing means for indicating whether the temperature in said housing means is below a predetermined temperature and solenoid means responsive to said thermostat means for adjusting said valve means so that fluid flowing in said fluid circuit means bypasses said evaporator means when and only when the temperature in said housing means is below said predetermined temperature.

6. Apparatus for storing goods at a storage depot provided with electric service at a first frequency and in a vehicle provided with electric service at a second frequency, comprising portable housing means for housing said goods; fluid circuit means attached to said housing means; compressor means, evaporator means and condenser means in series in said fluid circuit means; terminal means for connection to said electrical service at either of said frequencies;

compressor motor means connected to said terminal means for driving said compressor means, said terminal means for driving said compressor means, said compressor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; frequency-responsive means connected to said terminal means for providing an output that depends on the frequency of the electric service to which said terminal means is connected; and means actuated by said frequency-responsive means for establishing in said compressor motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency;

evaporator fan means for blowing air over said evaporator means to facilitate heat exchange; evaporator fan motor means connected to said terminal means for driving said evaporator fan means, said evaporator fan motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; and means actuated by said frequency responsive means for establishing in said evaporator fan motor means said first configuration in response to connection of said .terminal means to electric service at said first frequency and said second configuration in response to connection of saidterminal means to electric service at said second frequency;

condenser fan means for blowing air over said condenser means to facilitate heat exchange; condenser fan motor means connected to said terminal means for driving said condenser fan means, said condenser fan motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; and means actuated by said frequency-responsive means for establishing in said condenser fan motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency;

shunt means in said fluid circuit means in parallel with said evaporator means and valve means in said fluid circuit means, whereby fluid flowing in said fluid circuit means in response to operation of said compressor means can be made selectively to pass through said evaporator means or to bypass said evaporator means and pass through said shunt means; and

thermostat means mounted in said housing means for indicating whether the temperature in said housing means is below a predetermined temperature and solenoid means responsive to said thermostat means for adjusting said valve means so that fluid flowing in said fluid circuit means bypasses said evaporator means when and only when the temperature in said housing means is below said predetermined temperature.

7. A method of transporting perishable goods by air, comprising the steps of placing said goods in a portable, insulated housing means, mounting a refrigerating unit on said housing means, supplying electric service to said refrigerating unit at substantially 60 c.p.s. when said housing means is at an air ter minal and at substantially 400 c.p.s. when said housing means is on board in aircraft, sensing the frequency of the electric service so supplies, generating an electric signal that depends on the frequency of the electric service so supplied, and establishing in said refrigerating unit in response to said electric signal a selected one of two possible configurations such that the operating speed of said refrigerating unit is rendered vice supplied thereto.

Claims

1. Apparatus for storing goods at a first facility provided with electric service at a first frequency and at a second facility provided with electric service at a second frequency, comprising portable housing means for housing said goods; fluid circuit means attached to said housing means; compressor means, evaporator means and condenser means in series in said fluid circuit means; terminal means for connection to said electric service at either of said frequencies; compressor motor means connected to said terminal means for driving said compressor means, said compressor motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; frequency-responsive means connected to said terminal means for providing an output that depends on the frequency of the electric service to which said terminal means is connected; and means actuated by said frequency-responsive means for establishing in said compressor motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency.

2. Apparatus according to claim 1 comprising evaporator fan means for blowing air over said evaporator means to facilitate heat exchange; evaporator fan motor means connected to said terminal means for driving said evaporator fan means, said said evaporator fan motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; and means actuated by said frequency-responsive means for establishing in said evaporator fan motor means said first configuration in in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency.

6. Apparatus for storing goods at a storage depot provided with electric service at a first frequency and in a vehicle provided with electric service at a second frequency, comprising portable housing means for housing said goods; fluid circuit means attached to said housing means; compressor means, evaporator means and condenser means in series in said fluid circuit means; terminal means for connection to said electrical service at either of said frequencies; compressor motor means connected to said terminal means for driving said compressor means, said terminal means for driving said compressor means, said compressor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; frequency-responsive means connected to said terminal means for providing an output that depends on the frequency of the electric service to which said terminal means is connected; and means actuated by said frequency-responsive means for establishing in said compressor motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency; evaporator fan means for blowing air over said evaporator means to facilitate heat exchange; evaporator fan motor means connected to said terminal means for driving said evaporator fan means, said evaporator fan motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; and means actuated by said frequency responsive means for establishing in said evaporator fan motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency; condenser fan means for blowing air over said condenser means to facilitate heat exchange; condenser fan motor means connected to said terminal means for driving said condenser fan means, said condenser fan motor means having a first configuration in which it runs at a desired speed in response to actuation at said first frequency and a second configuration in which it runs substantially at the same speed in response to actuation at said second frequency; and means actuated by said frequency-responsive means for establishing in said condenser fan motor means said first configuration in response to connection of said terminal means to electric service at said first frequency and said second configuration in response to connection of said terminal means to electric service at said second frequency; shunt means in said fluid circuit means in parallel with said evaporator means and valve means in said fluid circuit means, whereby fluid flowing in said fluid circuit means in response to operation of said compressor means can be made selectively to pass through said evaporator means or to bypass said evaporAtor means and pass through said shunt means; and thermostat means mounted in said housing means for indicating whether the temperature in said housing means is below a predetermined temperature and solenoid means responsive to said thermostat means for adjusting said valve means so that fluid flowing in said fluid circuit means bypasses said evaporator means when and only when the temperature in said housing means is below said predetermined temperature.

7. A method of transporting perishable goods by air, comprising the steps of placing said goods in a portable, insulated housing means, mounting a refrigerating unit on said housing means, supplying electric service to said refrigerating unit at substantially 60 c.p.s. when said housing means is at an air terminal and at substantially 400 c.p.s. when said housing means is on board in aircraft, sensing the frequency of the electric service so supplies, generating an electric signal that depends on the frequency of the electric service so supplied, and establishing in said refrigerating unit in response to said electric signal a selected one of two possible configurations such that the operating speed of said refrigerating unit is rendered substantially independent of the frequency of the electric service supplied thereto.