A refrigerating apparatus for low-temperature refrigerated counters, particularly for frozen and deep-frozen products

Abstract

 A refrigerating apparatus is disclosed for refrigerated counters with a first (3) and at least one second (4,5) refrigeration circuit equipped with electric compressors of the sealed type (6;18a,b) being cascade connected together through a common heat exchanger (11a,b).

Description

[0001] This invention relates to a refrigerating apparatus for low-temperature refrigerated counters, particularly counters for frozen and deep-frozen products.

[0002] A most widely used refrigerating fluid in refrigerating systems for temperatures suiting the preservation of frozen or deep-frozen food is a mixture of isomers of chloro-fluorocarbons available commercially under the trade name of Freon R502. The use of Freon R502 is preferred on account of some thermodynamic features thereof. Specifically, it can withstand large pressure fluctuations, as are required to reach the low evaporation temperatures typical of display counters for deep-frozen food, without involving excessive end-of-compression temperatures. For instance, end-of-compression temperatures on the order of 180-200°C are met which do not affect the life span of the compressor equipping the refrigeration circuit.

[0003] However, Freon R502, due to it tending to combine chemically with ozone, is regarded as highly hazardous for the environment. In order to restrict this hazard, another mixture, called Freon R22, is preferred.

[0004] On the other hand, Freon R22 is less suited to high compressions from the thermodynamic standpoint, it producing, for example in traditional systems and for the same performance level as Freon R502, excessively high end-of-compression temperatures (around 230-240°C) for an acceptable life span of the compressor.

[0005] To obviate the technical problems brought about by the use of Freon R22, the current technology offers two alternative approaches, specifically intended for industrial type systems.

[0006] A first approach provides for the splitting of the target pressure fluctuation over a number of serially connected compressors using a technique of so-called multi-stage compression.

[0007] Another approach provides for the distribution of the target temperature fluctuation between the refrigerated space and the outside in a number of ranges each controlled by a respective refrigeration circuit. The circuits are operated at increasing temperature ranges and are cascade coupled thermodynamically by means of common heat exchangers wherein the refrigerating fluid of one circuit is condensed to a temperature close to the evaporation temperature of the other cascade-connected circuit.

[0008] This technology has been somewhat wanting in efficiency, especially because of the refrigerating fluid thermodynamic characteristics deteriorating when it is used for operation in temperature ranges other than the steady state ones, and especially so during the system starting transients.

[0009] These and other commonly encountered problems make it necessary to use electrical compressors of a comparatively sophisticated type, such as open-type or scroll-type compressors, wherein any heat transfer between the cooling system of the electric motor driving the compressor and the refrigerating fluid being processed is avoided.

[0010] However, open-type compressors are cumbersome, expensive and complicated, and therefore unsuited to such widely used articles as refrigerated counters. Accordingly, that technology is only of interest to industrial systems, where the cost for solving the problems posed by them can be more readily accommodated.

[0011] The technical problem addressed by this invention is that of fabricating refrigerated display counters adapted to preserve frozen and deep-frozen products, being cooled by a refrigerating apparatus which is conceived structurally and functionally to overcome the drawbacks with which the cited prior art is beset.

[0012] This problem is solved according to the invention by a refrigerating apparatus for refrigerated counters, characterized in that it comprises at least first and second refrigeration circuits cascade connected to each other through a common heat exchanger, each said circuit including at least one electric compressor of the sealed type.

[0013] Consequently, the invention stands, in a first and more general expression thereof, on the use of sealed compressors in cascade-connected circuits filled with fluids which have similar physical properties to those of Freon R22.

[0014] This circuit arrangement was regarded heretofore as unsuitable for use in relatively low-grade installations, as are refrigerated counters, where sealed compressors would be usually employed. This technical trend, which presently showed to be prejudicial, is also due to theoretical considerations of vulnerability of the efficiency in the terms set forth above; in fact, with sealed-type compressors, the refrigerating fluid is also intended to cool the motor of the electric compressor, which result in added detriment of the apparatus efficiency, especially during the cycle start transients. It has been found, however, that such compressors may be conveniently used, the resulting efficiency penalty being reasonable.

[0015] Vulnerability at the efficiency level of the apparatus, particularly during the start transient, may be further fought by coupling the first circuit in the cascade (in thermal contact with the refrigerated counter) both to the next circuit in the cascade and directly to the environment by means of an additional condenser.

[0016] The invention will be now described in detail with reference to a preferred embodiment thereof, shown by way of illustration and not of limitation in the accompanying drawings, where:

Figure 1 is a schematical representation of a refrigerating apparatus embodying this invention;

Figure 2 shows a partial cross-section through a display counter controlled by the apparatus of Figure 1.

[0017] In the drawing figures, generally shown at 1 is a refrigerating apparatus according to the invention, intended for cooling a refrigerated counter schematically shown at 2 and only partly shown in Figure 2. In that figure, denoted by 23 is a counter insulating structure which surrounds a vat 24 bordering the refrigerated space devoted to preserving the products.

[0018] The apparatus 1 comprises first, second, and third refrigeration circuits, respectively indicated at 3, 4 and 5.

[0019] The first circuit 3 comprises, serially connected together, a compressor 6 of the sealed type, a condenser 7 of the coil-in-air type, and a de-watering filter 8, from which there branch off two capillaries 9a and 9b in parallel, each supplying a respective evaporator 10a,b. The evaporators 10a,b form each a part of a respective heat exchanger, generally shown at 11a,b, wherethrough the first circuit 3 is cascade connected to the second and third circuits 4, 5, respectively. In a preferred embodiment of this invention, the heat exchangers 11a,b are thermally insulated externally using the same insulating structure 23 as the counter 2 in which they are embedded.

[0020] The second and third circuits 4, 5 form the low-pressure circuit portion of the apparatus 1 relatively to the comparatively high-pressure portion represented by the first circuit 3. They are cascade connected to the first circuit 3 through their respective heat exchangers 11a,b and are substantially identical with each other. Accordingly, only one of them will be described in detail, similar parts of the other being denoted by the same reference numerals with a suffix "a" for the second circuit and a suffix "b" for the third.

[0021] The second circuit comprises a sealed compressor 18a, a main condenser 12a, and an auxiliary condenser 13a wherebetween a de-watering filter 14a intervenes along with a capillary 15a, followed by first and second evaporators, respectively indicated at 16a and 17a.

[0022] The main condenser 12a is defined by an annular chamber of the heat exchanger 11a formed between the outer skirt of the evaporator 10a of the first circuit and a tubular conduit 19a extending coaxially outside it.

[0023] The auxiliary condenser 13a comprises a coil-in-air heat exchanger integral with the condenser 7 and using the same fin formation and the same cooling fans 22. Relatively to such fans and the airflow generated thereby, the condensers 13a,b locate downstream from the condenser 7 of the first circuit.

[0024] The first evaporator 16a comprises a tubular coil partway embedded in the insulating structure 23 of the counter 2 and being in heat transfer contact with the vat 24. Accordingly, it provides heat transfer mainly by conduction with the preserved products.

[0025] The second evaporator 17a is suspended in the space to be refrigerated and mainly intended for convective heat transfer. It is for this reason that it comprises a finned heat exchanger.

[0026] The steady state operation of the refrigerating apparatus according to the invention is as follows. The three refrigeration circuits 3, 4 and 5 are passed through by a refrigerating fluid such as Freon R 22 flowing in the direction of the arrows. That fluid is compressed, in the first circuit 3, by the compressor 6 from a pressure P1, whose value is related to the evaporation temperature, to a pressure P2 related to the condensation temperature.

[0027] The end-of-compression temperature reached by the refrigerating fluid is related to the pressure fluctuation P1-P2, and as such, it can be held within acceptable values for an adequate service life of the compressor 6.

[0028] The compressed and condensed refrigerating fluid is directed to its respective heat exchangers 11a,b through the capillaries 9a,b. Where, as in the example shown, two discrete circuit are used for the low-pressure circuit portion, the use of two separate capillaries connected in parallel is preferred because it has been found that this solution provide better balance of the thermal load on the low-pressure circuits.

[0029] The heat exchangers 11a,b are shared by the low-pressure circuit portion and the high-pressure portion of the apparatus 1, wherefor they perform the condenser and evaporator functions, respectively. Thus, the refrigerating fluid compressed by the compressors 18a,b will be condensed at a lower temperature than room temperature having a value close to the evaporation temperature in the evaporator of the first circuit 3.

[0030] As a result, as the condensed fluid is caused to evaporate in the evaporators 16a,b and 17a,b due to lamination through the respective capillaries 15a,b, it will cause the evaporators to cool to the target end temperature for preservation of the products introduced into the vat 24 of the counter 2.

[0031] The auxiliary condensers 13a,b bear little influence at this stage of the apparatus steady state operation, since the end-of-compression temperature reached by the refrigerating fluid at the outlet of the compressors 18a,b is comparatively close to the average temperature of air at the outlet of the condenser 7.

[0032] Such auxiliary condensers operate instead at full capacity during the starting transient of the apparatus, when the three circuits all operate at a starting temperature which is close to room temperature.

[0033] Under these conditions, the output from the refrigerating fluid, which is inherently related to the operating temperature, will deteriorate. This deterioration only appears in the low-pressure circuit portion, making the heat transfer rate achieved in the heat exchangers 11a,b insufficient, under the same pressure fluctuation and size of the remaining elements of each circuit, for the apparatus to gradually attain balanced operation of the high- and low-pressure circuit portions.

[0034] The auxiliary condensers serve to provide, during this starting transient of the apparatus, a further means of dissipating heat as necessary to accommodate this temporary loss of efficiency.

[0035] Among the principal advantages afforded by this apparatus is that it can ensure good refrigerating efficiency accompanied by adequate life of its components and improved environmental safeguard. Furthermore, the apparatus is suited to such widely used articles as refrigerated display counters. Advantageously, the proposed configuration affords appreciable savings in space, thereby the apparatus can find room beneath the insulating structure which borders the vat of a refrigerated counter. Contributive to such space savings is the embedding of the heat exchangers which interconnect thermally the low- and high-pressure circuit portions in said insulating structure. This has the added advantage of providing optimum insulation for said heat exchangers at no cost.

Claims

1. A refrigerating apparatus for refrigerated counters, characterized in that it comprises at least first (3) and second (4,5) refrigeration circuits cascade connected to each other through a common heat exchanger (11a,b), each said circuit including at least one electric compressor (6;18a,b) of the sealed type.

2. A refrigerating apparatus according to Claim 1, wherein said common heat exchanger comprises two coaxial pipes respectively forming the evaporator (10a,b) for said first refrigeration circuit and the condenser (12a,b) for said second circuit.

3. A refrigerating apparatus according to Claim 2, wherein the innermost pipe of said common heat exchanger is the evaporator for said first circuit and the outermost pipe is the condenser for said second circuit.

4. An apparatus according to Claim 1, wherein cascade connected to said first circuit (3) through respective heat exchangers (11a,b) are plural refrigeration circuits in parallel with one another (4,5), said first circuit comprising, for each heat exchanger in said cascaded refrigeration circuits, a respective discrete lamination means (9a,b).

5. An apparatus according to Claim 1, wherein said at least one second circuit comprises a main condenser (12a,b) and an auxiliary condenser (13a,b) in series with each other.

6. An apparatus according to Claim 5, wherein said auxiliary condenser (13a,b) in said second circuit is set close against a condenser (7) in the first circuit.

7. An apparatus according to Claim 6, wherein said condenser and auxiliary condenser are in-air condensers integral with a single finned sink.

8. A refrigerated display counter (2) cooled with a refrigerating apparatus according to one or more of the preceding claims.

9. A refrigerated display counter according to Claim 8, comprising an insulating structure (23) wherein said common heat exchanger (11a,b) is embedded at least partway.

Drawing