US 3139735 A
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Description (OCR text may contain errors)
y 1964 H. MALKOFF ETAL VAPOR COMPRESSION AIR CONDITIONING SYSTEM OR APPARATUS AND METHOD OF OPERATING THE SAME Flled Aprll 16, 1962 3 Sheets-Sheet 1 Fig.1
H. MALKOFF ETAL VAPOR COMPRESSION AIR CONDITIONING SYSTEM OR July 7, 1964 APPARATUS AND METHOD OF OPERATING THE SAME Filed April 16, 1962 5 Sheets-Sheet. 2
y 7, 1964 H. MALKOFF ETAL 3,139,735
VAPOR COMPRESSION AIR CONDITIONING SYSTEM OR APPARATUS AND METHOD OF OPERATING THE SAME 1962 5 Sheets-Sheet 3 Filed April 16,
United States Patent ()fiFice 3,139,735 Patented July 7, 1964 This invention relates to a vapor compression air conditioning system or apparatus and method of operating the same especially designed and adapted for employment in situations, either domestic or industrial, where relative humidity is a critical factor, and has for a chief object the provision of means embodied in the system itself for reheating or raising the dry bulb temperature of the chamber or space being conditioned immediately following the reduction in temperature and absolute humidity due to the chilling effect of the cooling coil upon the air stream passing through it.
Another object consists in providing such a system which incorporates a secondary or auxiliary condenser that is, when needed, supplied with heat from the discharge of the compressor in the system, and serves to warm the air stream that is forced through the air cooling evaporator in the system for conditioning the chamber or space. 7
Another object consists in providing such a system which includes means for regulating the amount of heat supplied from the compressor discharge to the secondary or auxiliary condenser in order to avoid undesired rise of temperature within the chamber or space that is being conditioned while insuring adequate supply of heat for the re-heating function.
Another object consists in providing such a system in which the secondary or auxiliary condenser is constructed as a portion of the evaporator, with the two portions serving as the evaporator during normal cooling cycles and the secondary or auxiliary portion acting separately as a condenser during reheating.
Another object consists in providing such a system in which the re-heating means is constructed and arranged for cooperative functioning with means for maintaining a predetermined high side pressure regardless of ambient temperature at the condenser, or oversizing of the latter, or heat load at the evaporator.
A further object consists in providing certain improvements in the form, construction and arrangement of the several parts, and in the method of operation, whereby the above named, and other objects inherent in the invention, are efficiently attained.
Practical embodiments of the invention are represented in the accompanying drawings, in which FIG. 1 represents diagrammatically an air conditioning system of the vapor compression type with the secondary or auxiliary condenser for reheating shown as separately connected in the system with respect to the evaporator;
FIG. 2 represents a similar view in which the secondary or auxiliary condenser is shown as interconnected with the evaporator so as to serve as a part of the latter during cooling cycles of the system, while acting separately as a secondary condenser during reheating when necessary.
FIG. 3 represents a modification of the means shown in FIGS. 1 and 2, for maintaining a predetermined high side pressure in the system, and to insure re-starting after long off-cycles of the compressor without short cycling of its motor.
FIG. 4 represents diagrammatically an electric control circuit for the form of invention shown in FIG. 2; and
FIG. 5 represents diagrammatically an electric control circuit for the form of invention shown in FIG. 1.
In air conditioning for either human comfort or industrial purposes, where relative humidity is an important factor, the dehumidification of the air, which is accomplished by a cooling coil, usually requires the employment of a reheat coil, or the like, thereafter, in order to maintain a minimum desired dry bulb temperature in the chamber or space being conditioned, especially on relatively cool but humid days. Steam or hot water coils are commonly used for the reheat step. According to the present invention, heat of condensation of the air conditioning system is automatically employed for reheating. However, as the heat in the gas stream leaving the compressor discharge is substantially greater, say twenty percent, than the amount of heat which has been absorbed by the evaporator from its load, it will be evident that the use of all this heat in the reheating cycles would result in a constantly rising dry bulb temperature in the chamber or space, which is not desired. Furthermore, it is necessary, especially in a system having an air cooled condenser, that the latter be adequate in capacity for dissipating the maximum heat developed .at the evaporator during hot weather. Consequently, in properly attaining the functional purpose of using heat of condensation for reheating the air stream passing through the evaporator following the chilling and dehumidification step, it is requisite so to distribute or apportion the heat of compressor discharge as to accomplish the reheating of the air in the chamber or space while directing the remainder of the heat to be dissipated by the main air cooled condenser which feeds the evaporator during the cooling dehumidification step.
In brief summary, the invention comprehends the provision of a system with a secondary or auxiliary condenser that is operatively associated with the evaporator and functionally connected with the compressor in such manner as to receive from the latter sufficient heat for reheating steps and have its heat thus obtained dispersed throughout the chamber or space being conditioned by the air current or stream forced through the evaporator by the usual blower or fan, while leaving the remainder of the heat of compressor discharge for the main condenser; the whole operation being automatic and thermostatically or humidistatically controlled.
Referring now to the drawings, and specifically to FIG. 1, the system includes the usual closed circuit for refrigerant flow comprising a compressor, which may be of the hermetic suction cooled type, denoted by 1, connected by a conduit 2 with the inlet of an air cooled condenser 3 equipped with the usual fan 4. The outlet of the condenser communicates through a conduit 5 with a receiver 6, which, in turn, is connected by a conduit 7 with a thermostatic expansion valve 8, from which latter a pipe or tube 9 leads to the inlet of an evaporator 10. A suction conduit 11 connects evaporator outlet with compressor intake, thus completing the circuit. The expansion valve 8 is controlled by the customary feeler bulb 12. clasped to the suction conduit or, as is sometimes done, to a portion of the evaporator adjacent the suction conduit with its capillary tube 13 leading to the valve, while a suitable device, here shown as a blower 14, serves to force air through the evaporator for circulation within the chamber or space being conditioned. All the elements just described may be of any well known or approved form, construction and arrangement which calls for no further description. A solenoid valve 15 controls refrigerant flow through conduit 7.
A dominant feature of the present invention consists in the provision of a secondary or auxiliary condenser 16, which may be composed of coils as is usual in condensers, and is positioned in axial alignment with the evaporator at the side of the latter opposite the blower 14, so that the air stream from the latter will pass through both evaporator and secondary condenser, and thence out into the chamber or space being conditioned through the opening 17, which may be louvered, in the usual housing '18 that embraces the blower and evaporator.
A conduit 19 branches off from compressor discharge conduit 2 and leads to the inlet of the secondary or auxiliary condenser 16, and in this conduit 19 is fitted a solenoid valve 20, together with a pressure regulating valve 21 that is shown as positioned between the valve 2%) andthe auxiliary condenser 16 but could be located at the otherside of valve if desired. The solenoid valve 20 is thermostatically or humidistatically controlled, as will be hereinafter described, and it Will be clear that, when the secondary or auxiliary condenser is called upon to serve as a reheater, the opening of valve 20 will supply hot gas from the compressor thereto. This hot gas is condensed by the stream of cool air generated by the blower 14, and the condensate is fed through an outlet tube 22 to a second thermostatic expansion valve 23, and thence through a pipe 24 to pipe 9 at the inlet or" the evaporator I 10. Valve 23 is controlled by feeler bulb 25 and capillary tube 26, the bulb being clasped to the suction conduit 11 or, if desired, to a portion of the evaporator adjacent the suction conduit preferably at a point further down stream than bulb 12. The air stream which cools the condenser 16 is, in turn, warmed by the latter which thus serves as a reheater for the chamber or space being conditioned. Valve 21 is of the outlet pressure regulating type, which is well known and requires no description, that may be set for a predetermined reheat temperature of the auxiliary condenser 16.
In operation, when the degree of humidity within the chamber or space being conditioned is satisfactory, the system serves as a well known air conditioner, with the hot gas from the discharge of compressor 1 flowing to the I pansion valve 8 which sharply reduces refrigerant temperature so that it enters the evaporator 10 cold and mainly in liquid phase. As the low temperature refrigerant passes through the coils of the evaporator the air stream from the blower is chilled, and travels through the secondary or auxiliary condenser 16 (which is functionless at this stage) and out from the opening 17 in the housing 18 for circulation in the chamber or space being conditioned. The warmth of the air stream from the blower largely vaporizes the refrigerant passing through the evaporator coils and it exists from the latter mainly in gaseous phase and of elevated temperature to return to the compressor through the suction conduit 11, for re-cornpression and repeated circulation through the system.
The chilling by the air stream is effective to de-humidify the air within the chamber or space, but this step results in lowering of the dry bulb temperature therewithin to an uncomfortable or undesirable point which calls for activation of the reheater condenser 16. This is automatically accomplished by the humidistat or thermostat of the electric control circuit, to be hereinafter described, or a combination of both, which causes the solenoid valve 21) in the conduit to open and permit some of the hot gas from the compressor discharge to flow to the inlet of the secondary or auxiliary condenser 16, the amount of the flow being regulated by the setting of valve 21. This hot condenser, or the heat load of the evaporator.
gize the humidistat circuit while the compressor is in operation, which may actuate the valve 20 only if the humidistat is not satisfied.
As previously described, when the reheater condenser 16 is in operation its condensate is fed to the evaporator through the expansion valve 23 with the result that expansion valve 8 operates at minimum capacity, or may be entirely out of action. The locating of feeler bulb 25 down stream with respect to bulb 12, insures that the valve 23 operates at full capacity and that the auxiliary condenser 16 has a minimum of liquid flooding in order to insure a predetermined reheat temperature in the maximum portion of 16, so that valve 8 will be called upon only when the super-heat of the vapor at the outlet of the evaporator it) rises above a predetermined degree.
The cycles of dehumidification and reheating above described are automatically and sequentially performed as conditions in the chamber of space being conditioned require to maintain the air at desired degrees of humidity and temperature.
When constructing such systems for installations in which the main air cooled condenser 3 is to be subject to low ambient temperatures in some or all seasons of the year, e.g. 60 F. and lower down to below zero, it is highly desirable to equip the system for automatically maintaining a predetermined high side pressure in the condenser 3, receiver 6, and conduit '7, regardless of the ambient temperature at the said condenser, the size of the Such arrangements are shown and described in Us. Patents Nos. 2,564,310 and 2,963,877, issued respectively August 14, 1951 and December 13, 1960 which obviates the necessity of full description herein, it being deemed sufficient to note that from the compressor discharge conduit 2 a by-pass pipe or conduit 27 branches and leads to the outlet 28 of the condenser and to the conduit 5 which connects the condenser and the receiver which is adequately sized. In the by-pass 27 is fitted a valve 29 which is of a well known type that is designed and adapted to maintain an approximately constant pressure at its outlet side, is. its side that is toward the condenser outlet and the receiver. We prefer to use a constant outlet pressure modulating valve, but there may be substituted other devices such, for instance, as a constant pressure automatic expansion valve, or a solenoid valve combined with a pressure switch, or any other mechanism or combination thereof which will maintain its outlet or downstream pressure at the desired predetermined degree. Refrigerant flow restricting means 30 is positioned at the condenser outlet between the condenser itself and the junction of the by-pass 27 with the conduit 5. This is shown as a spring loaded check valve which permits flow from the condenser but restrains reverse flow, but there could be substituted other devices for the same purpose such as a serpentine restrictor tube or a valve (preferably modulating) with inlet pressure control.
When the ambient temperature at the condenser 3 is relatively warm, e.g. above 60 F., the valve 29 remains closed; but, if the'ambient falls below 60 F., or such other point as may have been selected by the setting of the valve for the opening thereof, the pressure at the outlet side of the valve will be reduced causing the valve to open and permit refrigerant flow toward the condenser outlet which raises the pressure at that point and causes the condenser to be gradually flooded by the condensation of gas flowing to its inlet through the conduit 2, thus reducing the condenser area of effective heat transfer surface and raising the high side pressure. When, the desired pressure has been attained, the valve 29 will close, and it will thus be seen that the eiiect of the said valve in maintaining a nearly constant pressure at its outlet side results in the maintenance of a nearly or approximately constant pressure throughout the high side from compressor discharge to expansion valve. In locations where the condenser ambient is warm, the valve 29 will remain closed and its associated parts will be without function. Hence, in these situations, this arrangement for maintaining high side pressure need not be incorporated in the system, but it is otherwise of substantial value, even in areas where seasonal temperature changes may call for its effect at only certain times of the year. And in this system, which embodies the secondary or auxiliary condenser acting as a reheater, it will be understood that, during the reheat cycles, the total condensing capacity of the main and reheat condensers may be materially in excess of the available heat load that is necessary to maintain a predetermined high side pressure, with the result that the reduction of the condensing capacity of the main condenser 3 by the activity of the valve 29 insures the supplying to the reheater condenser 16 of a proper amount of heat-carrying vapor for its functioning.
Referring to the modified form of the invention represented in FIG. 2, certain parts are the same as in FIG. 1, and will be given the same reference numerals. Thus, the condenser is 1, its discharge conduit 2, the air cooled main condenser 3, its fan 4, its outlet conduit 5, the receiver 6, the liquid supply conduit '7, its thermostatic expansion valve 8, the evaporator inlet pipe or tube 9, the suction conduit 11, the feeler bulb and capillary 12 and 13, the blower 14, the supply conduit solenoid valve 15, opening 17 in the housing 18 which encloses the blower, evaporator and reheater, the conduit 19 leading from the compressor to the reheater, its sol noid valve 2% and regulating valve 21, the reheater outlet tube 22, the second thermostatic expansion valve 23, its pipe connection 24 to pipe 9, the second feeler bulb and capillary tube 25 and 26, the by-pass 27, main condenser outlet 28, the constant pressure valve 29, and spring loaded check valve 30.
The modification in this form of FIG. 2 relates to the construction of evaporator and secondary or auxiliary condenser that performs as a reheater. Here, the evaporator proper is smaller than in the form of FIG. 1, and is denoted by 31, while the secondary or auxiliary condenser for reheating bears the numeral 32. These two elements of the system are so interconnected that the condenser reheater acts as part of the evaporator during the coolingdehumidification cycles. This is accomplished by connecting tube 22 and pipe 24 with a by-pass 33 in which is fitted a check valve 34 that permits flow from 24 to 22, by-passing valve 23, but prevents reverse flow, and by connecting conduit 19 with the suction conduit 11 by a tube 35 and locating a solenoid valve 36 in the said tube.
In the operation of this construction, when there is a high heat load, solenoid valve will be open and expansion valve 8 will be feeding refrigerant to both sections 31 and 32 of the evaporator, the supply to the latter moving through pipe 33 and check valve 34, for the cooling cycle, the outflow of vaporized refrigerant proceeding to the suction conduit 11, directly from section 31 of the evaporator and through tube 35 and solenoid vaive as (which is open) from the section 32. When this cycle has continued to a low temperature condition of the chamber or space being conditioned such that reheat is demanded, solenoid valve 15 may close, solenoid valve opens, and solenoid valve 36 closes. In this setting, hot gas from the compressor flows to section 32 of the evaporator which performs as a condenser and becomes the reheater for the air stream from blower 14, the condensate from the reheater passing to section 31 of the evaporator through expansion valve 23 as described in explaining the form of the invention illustrated in FIG. 1. As the section 31 of the evaporator in the form of FIG. 2 is smaller than the evaporator iii of PEG. 1, the refrigerant temperature, and consequent suction pressure, tall during the reheat cycle which reduces the system capacity and thus lessens the amount of total heat available at the compressor discharge, but the provision of the regulating valve 21 in conduit 19 insures a minimum temperature of the condenser reheater 32, in cooperation with the minimum head pressure control means consisting 6 of the components 27, 28, 29; or the corresponding means of FIG. 3, to be described.
Referring to both forms of the invention exhibited in FIGS. 1 and 2, and dealing particularly with the arrangement for maintaining a predetermined minimum high side pressure, there is shown in FIG. 3 a slight modification in which an inlet pressure regulating valve is positioned at the entrance to the condenser. Such a structure is illustrated and described in US. Patent No. 2,934,- 911, issued May 3, 1960, which obviates the necessity of a detailed explanation in this specification. Briefly touching the showing of FIG. 3, it is noted that the main condenser and its fan are denoted by the reference numerals 3 and 4, the receiver by 6, the compressor discharge conduit by 2 and the supply conduit for the evaporator by 7. In the discharge conduit is fitted a valve marked 37 which is of the constant inl t pressure type, while a constant outlet pressure valve 38, similar to the valve 29 of FIGS. 1 and 2, is located in a bypass 39, similar to the bypass 27 of said figures, which connects the discharge conduit 2 with the receiver. A check valve 49, serving the same purpose as the valve 313- of FIGS. 1 and 2, is in the condenser outlet conduit, here identified by 41. This arrangement is highly advantageous when the ambient temperature at the main condenser 33 is extremely low, and it provides means for preventing migration of refrigerant from evaporator and receiver to condenser during off-cycles of the compressor, as well as for imposing high compressor discharge pressure on the receiver immediately following the establishing of compressor oncycles and slightly in advance of imposing said pressure on the condenser whenever the receiver pressure is lower than the predetermined minimum normal refrigerating pressure in order to insure immediate flow of refrigerant at satisfactory operating pressure from the receiver to the expansion valve, as fully explained in said Potent No. 2,934,911. And, still referring to both forms of the invention shown in FIGS. 1 and 2, it will be understood that the effect hereinabove described as obtained by loeating feeler bulb 25 downstream from bulb 12, may also be obtained by relative adjustment of the two expansion valves 23 and 8 regardless of the relative location of the bulbs.
Two forms of electric control circuits are diagrammatically presented in FIGS. 4 and 5, and that of FIG. 4 will be first explained although particularly adapted to the form of the invention depicted in FIGS. 2.
In this showing of FIG. 4, the primary controlling element is a single pole, double throw thermostat 42 that is installed in the chamber or space being conditioned, although it might be installed in the air stream. On rise in temperature contact is made at 43 which breaks contact at 44 to deactivate the humidstat 45. The contact at 43 completes a circuit through solenoid valve 15 in the evaporator supply line 7', thus admitting refrigerant to the evaporator 31, 32. The resulting increase in evaporator pressure causes pressure switch 46 to close which energizes a starter coil 47 and thus activates a starter 48 and completes the circuit to the compressor 1. On further increase in the temperature of the chamber or space being conditioned, a second stage thermostat 49 makes contact to complete the circuit through solenoid valve 36 to open the same and establish flow communication between evaporator section 32 and the intake of compressor 1 through the suction conduit 11. At this point solenoid valve 2t? in conduit 19 is closed due to the act of thermostat 42 in breaking contact at 44, so that evaporator section 32 is not in flow communication with the compressor discharge 2.
When the temperature of the chamber or space falls, thermostat 49 breaks contact and closes solenoid valve 36. On further drop in temperature, the thermostat 42 switches from contact 43 to contact 44 which completes the circuit to the humidistat 45. If the degree of humidity in the chamber or space is now above the setting of the humidistat, a circuit will be made through the relay coil 50 which closes contacts 51 and 52, thus energizing both solenoid valves and 25. In this condition valve 15 admits liquid refrigerant to the evaporator section 31, while valve 29 connects the compressor discharge with the reheat section 32 of the evaporator, through conduits 2 and 19, the said section 32 being isolated from the cooling section 31 of the evaporator due to the fact that valve 36 is now closed.
When the humidistat 45 becomes satisfied, it opens and de-energizes relay coil 50, thus breaking contacts 51 and 52, which closes both valves 15 and 26. With these valves closed the operation of the compressor serves to evacuate the cooling section 31 of the evaporator and cause a drop in suction pressure that will bring about opening of the pressure switch 46 with the consequent deenergizing of the starter coil 47 and stopping of the compressor.
In the event of overloading or overheating of the compressor, a thermostat 53, which is built into the body of the compressor, opens contact, thus de-energizing the circuit to the starter coil 47 and to the control transformer 54, which de-energizes the entire control circuit with the result of de-activating the evaporator blower motor 55 and closing all solenoid valves which are operatively associated with the evaporator. The blower motor is controlled by a magnetic starter 56 that is equipped with a starter coil 57 provided with overload protectors under control of a manual switch 58 in the control circuit. Thus, when the compressor stops due to overload, or is manually stopped by breaking the switch 59, the transformer 54 is de-energized and starter coil 57 breaks the contacts in the magnetic starter 56 which halts the blower motor 55.
Turning now to the control circuit exhibited in FIG. 5, which is designed for operating the form of the invention shown in FIG. 1, it will be observed that, in many respects, there is correspondence with FIG. 4. Here, however, the primary controlling element is a humidistat 60 which, on rise of humidity within the chamber or space being conditioned, closes to complete the circuit through a relay 61 that, in turn, closes contacts 62 and 63 and opens solenoid valve 15 in evaporator supply line 7 as well as solenoid valve in the conduit 19 leading to the reheater condenser 16. This initiates the reheating cycle as previously explained. This step naturally causes a rise in the dry bulb temperature of the chamber or space, and this may be sufiicient to close the thermostat 64 and complete a second and parallel circuit through solenoid valve 15 in the evaporator supply conduit.
When the humidity within the chamber or space has been lowered to a degree that satisfies the humidistat 60, the latter opens with the effect of de-energizing relay 61 to break contacts 62 and 63 and close the solenoid valve 20. The solenoid valve 15 will remain open until the temperature satisfies the thermostat 64. The remaining functions of this form of control are as described in connection with FIG. 4, and the same reference numerals are applied to corresponding elements.
The elements shown at the upper left and right of both FIGS. 4 and 5, and denoted by 65 and 66 are fused disc switches, conventionally represented, which are deemed to require no explanation.
Although very similar in set-up and performance, it may be noted that the arrangement of FIG. 4 is designed particularly for employment in situations when maintenance of desired temperature is the predominant consideration and dehumidification takes place only when the thermostat is fully satisfied; such a condition being instanced by installations for cooling comfort when the outdoor dry bulb temperature is relatively low and there is a substantial latent heat load but a comparatively low sensible heat load. The control symbolized by FIG. 5, is, on the other hand, especially conceived for installations where control of humidity is the primary consideration and temperature is not required to be regulated Within close limits.
As the operation of the system has been included with the foregoing description of the parts and their arrangement, a full understanding of the invention is not thought to require an additional detailed recitation of the operation; but it may 0e helpful briefly to observe that there is provided an air conditioning system designed and adapted for sequentially and automatically supplying a stream of air which has been cooled below its dewpoint while passing through an evaporator, and, when necessary, reheated and returned to a chamber or space with accurate control of both humidity and temperature; the warming or heating following the cooling effect of dehumidification being accomplished through utilization of the heat of compressor discharge supplied in regulated amount to an element of the system that performs as a condenser and, in one form of the invention, also performs as a part or section of the evaporator.
It will be understood that various changes may be resorted to in the form and arrangement of the several parts of the apparatus and in the steps of the method without departing from the spirit and scope of the invention, hence, We do not intend to be limited to details herein shown or described unless included in the claims or required by disclosures of the prior art.
What we claim is:
1. An air conditioning system designed and adapted for automatic regulation of both temperature and humidity within a chamber or space, said system comprising a closed refrigerant circuit including a compressor, a main air cooled condenser, a liquid receiver, an evaporator, a supply conduit connecting the receiver with the evaporator inlet, a thermostatic expansion valve in the said supply conduit, a suction conduit connecting the evaporator outlet with the compressor intake, a feeler bulb operatively adjacent the outlet of the evaporator for controlling the expansion valve, means for causing a flow of air through the evaporator, a refrigerant condensing element disconnected from the main condenser and operatively connected to the evaporator for raising the temperature of said air flow in certain cycles of system operation, automatic means for refrigerant flow connection of the condensing element with and disconnection of it from the hot gas compressor discharge, and automatic pressure regulated means for controlling the flow from the compressor to the condensing element to maintain a predetermined temperature of the said condensing element.
2. A system as defined in claim 1, in which the automatic means for refrigerant flow connection of the condensing element with and disconnection of it from the compressor is thermostatically controlled.
3. A system as defined in claim 1, in which the automatic means for refrigerant flow connection of the condensing element with and disconnection of it from the compressor is humidistatically controlled.
4. A system as defined in claim 1, in which the automatic means for refrigerant flow connection of the condensing element with and disconnection of it from the hot gas compressor discharge and controlling the flow to the condensing element comprise a conduit connecting the compressor discharge with the condensing element, an automatic open and shut valve in said conduit, and an automatic pressure regulating valve also in said conduit.
5. A system as defined in claim 1, which also includes automatically controlled means for feeding condensate from the said condensing element to the evaporator, said means including a second feeler bulb controlled thermostatic expansion valve adapted to insure drainage of condensate from the said condensing element to attain a predetermined reheat temperature over the maximum portion thereof.
6. A system as defined in claim 5, in which the second expansion valve is adjusted to open before the first named expansion valve during the reheat cycle.
7. A system as defined in claim 1, which also includes automatically controlled means for feeding condensate from the said condensing element to the evaporator, said means including a second feeler bulb controlled thermostatic expansion valve with its bulb located further downstream than the bulb of the first named expansion valve to insure drainage of condensate from the said condensing element to attain a predetermined reheat temperature over the maximum portion thereof.
8. A system as defined in claim 7, in which the feeler bulbs of both expansion valves are on the suction conduit and the bulb of the second named expansion valve is positioned further away from the evaporator outlet than the bulb of the first expansion valve.
9. A system as defined in claim 1, which also includes automatic means for maintaining a minimum predetermined pressure in the system between the compressor discharge and the expansion valve regardless of the ambient temperature at the condenser or heat load in the evaporator.
10. A system as defined in claim 9, which also includes a second expansion valve operatively associated with the condensing element, and means for maintaining a predetermined minimum pressure between the compressor discharge and said second expansion valve.
11. A system as defined in claim 1, which also includes automatic means operatively associated with the condenser inlet and outlet for preventing: migration of refrigerant from the evaporator and receiver to the condenser during off-cycles of the compressor and for imposing high compressor discharge pressure on the receiver immediately following the establishing of compressor oncycles whenever the receiver pressure is lower than its predetermined minimum normal operating pressure.
12. A system as defined in claim 1, which also includes means for refrigerant flow connection of the condensing element with the supply from the receiver and with the return to the compressor, the said means for flow connection of the condensing element with the supply from the receiver including a pipe or tube fitted with a device for preventing reverse flow, and the means for flow connection with the return to the compressor including a pipe or tube fitted with an automatic open and shut valve.
References Cited in the file of this patent UNITED STATES PATENTS 1,837,798 Shipley .Dec. 22, 1931 2,195,781 Newton Apr. 2, 1940 2,451,385 Groat Oct. 12, 1948 2,679,142 McGrath May 25, 1954 2,715,320 Wright Aug. 16, 1955 2,961,844 McGrath Nov. 29, 1960 2,963,877 Malkoff Dec. 13, 1960