FR2738331A1 - Compressor-type refrigerating unit with optimised energy control - Google Patents

Abstract

The working fluid, e.g. Freon (RTM), passes (2) from the compressor (20) to a condenser (21) with ambient air heat-exchange, and thence (3), via a float-type expansion valve (22), to the reservoir or buffer tank (23), containing fluid, in the gaseous phase, in equilibrium over the liquid. Liquid passes (5,6) to parallel-connected evaporators (25), each with an expansion valve (24) and a return connection (1) to the compressor. The evaporator heat-exchange medium is again air. Reservoir gas pressure is controlled (5A) by an electrically operated valve (26), supplemented by a manual valve (28), connected to the compressor inlet (6A).

Description

ENERGETIC OPTIMIZATION DEVICE OF A SET OF
COMPRESSION AND DIRECT EXPANSION REFRIGERATION
The present invention relates to a compression refrigeration device and expansion of a refrigerant.

 The technical field of the invention is that of the manufacture of refrigeration installation by compression and expansion of a refrigerant.

 The invention applies to refrigeration installations using the compression and expansion of a refrigerant such as, for example, a chloro fluoro carbon (CFC) fluid.

 The present invention applies to such installations which comprise, in a known manner, successively connected in series on a refrigerant circulation circuit (which essentially consists of pipes connecting the various main components) one or more compressors, one or more condensers, a buffer tank, one or more regulators, one or more evaporators.

 The invention applies to such installations in which the compression of the refrigerant is single-stage, as well as the expansion valve, or to so-called bi or multi-stage installations and possibly with several expansion points.

Such an example of a two-stage compression refrigeration installation is for example described in patent EP424003 (General Electric
Company) which relates to a refrigeration installation for a refrigerator equipped with a freezing compartment and a compartment for fresh products (which must be kept at different temperatures).

 The object of the present invention is to improve compression and direct expansion refrigeration installations.

 The present invention more particularly aims to allow energy savings and to facilitate the adaptation and operation of such installations when external conditions vary; in fact, in such installations, the heat produced by the condensation of the refrigerant, which is evacuated by an external fluid thanks to a heat exchange between the external fluid and the refrigerant at the level of the condenser (s), requires the adaptation of installation under external conditions, in particular in the case where the external fluid used is air, and in this case in particular due to climatic variations of greater or lesser amplitude and period.

 The present invention applies in particular to refrigeration installations which are used to maintain cold rooms at low temperature in which is arranged one (or more) evaporator which allows by heat exchange between the refrigerant circulating in the evaporator and the air from the cold room, to cool these.

 The invention also applies to refrigeration installations for supermarkets and large surfaces which make it possible to supply refrigerant to display windows for food products in particular, which each include an evaporator for cooling the air circulating therein. interior of refrigerated display cabinets or units.

 A problem existing in such installations is that the regulators arranged upstream of the evaporators and making it possible to regulate the flow of refrigerant fluid introduced into the evaporator (in particular the thermostatic regulators), are subjected to variable operating conditions when the temperature of the the outdoor air used for example for the evacuation of condensing heat from the refrigerant varies.

 More particularly, such regulators are equipped with adjustment means which make it possible to adapt them to operating conditions situated within a certain range in which these regulators must operate stably to maintain a substantially constant evaporation pressure.

 Climatic variations, in particular variations in the external air temperature used for condensation, between winter and summer periods, are likely to cause significant variations in the pressure difference to which the regulator is subjected and consequently cause malfunctions of these regulators; the consequence is that one generally maintains in winter a condensing pressure identical to that for a correct operation during the summer periods, which requires to provide (in winter) a work of compression which is useless and consuming energy .

The invention overcomes the aforementioned drawbacks by providing a compression refrigeration device and direct expansion of a refrigerant, which comprises
- one or more condensers for the condensation of said refrigerant compressed by heat exchange with a first external fluid
- one or more tanks or bottles for the accumulation or buffer storage of said condensed refrigerant
- a large capacity expansion device which is arranged between the outlet of said condenser and the inlet of said tank
- a pressure regulating member prevailing in said tank.

In other words, the invention provides a refrigeration device for compression and expansion of a refrigerant, which comprises, successively connected in series on a circulation circuit of said refrigerant.
- one or more compressors for the compression of said refrigerant in the gaseous state
- one or more condensers for the condensation of said refrigerant compressed by heat exchange with a first external fluid
- one or more tanks or bottles for the accumulation or buffer storage of said condensed refrigerant
- one or more regulators for the expansion of said refrigerant supplied by said tank or bottle
- one or more evaporators for the evaporation of said refrigerant by heat exchange with a second external fluid
- an expansion member of said refrigerant which is disposed on a pipe of said circulation circuit of said refrigerant, between the outlet of said condenser and the inlet of said tank
a pressure regulating member prevailing in said reservoir which maintains a substantially constant pressure,
a condensing pressure regulating member, which varies this pressure as a function of external conditions (temperature of the fluid used for condensation) by lowering it as much as possible, in winter in particular to a value slightly greater than the pressure in the tank.

According to preferred embodiments
- said expansion member is a float regulator
- Said pressure regulating member is essentially constituted by a valve disposed on a degassing pipe which connects an upper part of said tank to an orifice or an inlet or suction pipe of said compressor
The opening of said pressure regulation valve is controlled as a function of the pressure prevailing upstream of said valve, that is to say as a function of the pressure prevailing in said tank by a pilot or pressure regulator integrated into said valve
- Several evaporators are connected in parallel on said refrigerant circulation circuit, which are each equipped with a respective individual expansion valve; ;
- at least two compressors are connected in series and provide multi-stage compression, for example two-stage compression
- The device comprises an economizer exchanger which is supplied with liquid refrigerant supplied by said tank via a pressure reducer, and the outlet of which is connected to a suction or inlet orifice (intermediate) of a compressor preferably via a non-return valve
- Said pressure regulating member prevailing in said tank or bottle is adjusted to maintain in said tank a pressure of the refrigerant corresponding to a saturation temperature between 10-C and 2O0C, for example close to 15'C
- said first external fluid or condensing fluid is air
- Said second external fluid or evaporation fluid is air.

 The invention makes it possible to ensure optimum and correct operation of the pressure reducers (in particular thermostatic) supplying the evaporators of a refrigeration installation, whatever the climatic conditions which cause variations in the condensing pressure.

 The invention in particular has the result of making it possible to maintain a constant supply pressure of the regulators and consequently, because they generally provide a constant evaporation pressure, to make these regulators "operate" under a pressure difference substantially constant and therefore ensure stable operation and avoid malfunctions of the installations.

 The invention also has the result of allowing significant energy savings by making it possible to lower the condensation pressure when the external fluid allows it and consequently by making it possible to lower the energy necessary for the compression of the refrigerant.

 The numerous advantages provided by the invention will be better understood through the following description which refers to the appended drawings which illustrate without any limiting character preferred embodiments of refrigeration installation according to the invention.

 FIG. 1 schematically illustrates a circuit comprising the main components of a refrigeration installation according to the invention, in which the compression and expansion are carried out with a single stage, and in which circuit are provided several evaporators connected in parallel on this circuit.

 FIG. 2 is an enthalpy diagram schematically illustrating the principle of operation during the winter period of the installation represented in FIG. 1 and more particularly illustrating the thermodynamic cycle followed or carried out by the refrigerant circulating in the installation of FIG. 1.

 FIG. 3 schematically illustrates, in the same manner as FIG. 2, a stage compression refrigeration installation, which is further provided with an economizer exchanger.

 FIG. 4 is an enthalpy diagram which illustrates, similar to that of FIG. 2, the thermodynamic cycle followed by the refrigerant circulating in the installation of FIG. 3.

 Figure 5 illustrates in sectional view through a general plane of symmetry of the device, a particular embodiment of a float regulator fitted to an installation according to the invention.

 On the enthalpy diagrams represented in FIGS. 2 and 4, the abscissa axis represents the enthalpy of the refrigerant and the ordinate axis represents the pressure of the refrigerant which by way of example may be Freon (registered trademark of Dupont de Nemours) sold under the name "R22".

 It is recalled that for such fluids, inside the curve 7 of saturation of this fluid, the isobars correspond to isotherms and therefore, inside this curve 7, in the central part of these figures, the transformations of the refrigerant constituted by condensation and evaporation, which are supposed to take place at constant pressure (respectively marked 48 and 45 and for example respectively close to 106 Pascal and 105 Pascal in the case of FIG. 4), s' also perform and therefore at constant temperature (for example respectively around 20-C and minus 30-C).

 With reference to FIGS. 1 and 3, the installation comprises one or more compressors 20, the outlet of which is connected by a section of pipe 10 to the inlet of one or more condensers 21 allowing the condensation of the refrigerant circulating in the circuit by heat exchange with an external fluid such as air.

 The condensed refrigerant leaving the condenser is conveyed by a second section of pipe 10 to a reservoir 23 forming a buffer bottle containing in the lower part the liquid refrigerant and in the upper part the gaseous refrigerant in equilibrium with the liquid phase.

 The liquid refrigerant supplied by the bottle 23 is conveyed by a pipe 10 to a pressure reducer 24 supplying an evaporator 25 in which the liquid refrigerant evaporates by heat exchange with an external fluid such as air.

 The evaporated refrigerant leaving the evaporator is then returned to the compressor by another section 10 of pipe.

 In FIGS. 1 and 2, corresponding to an installation with a single stage of compression and expansion (of measurement as in FIGS. 3 and 4 corresponding to a two-stage compression), reference marks 1, 2, 3 have been identified, 4, 5, 6, the successive states of the refrigerant circulating in the main refrigeration circuit and carrying out a thermodynamic refrigeration cycle.

 These marks (as well as the marks SA, 6A, 7, 8, 7A, 8A) are shown in FIGS. 1 and 3 in the vicinity of the portions of the circuit where these different states are observed.

 As illustrated in FIG. 2, the gaseous fluid in state 1 is compressed by the compressor to pass to a compressed gaseous state 2.

 Condensation of the fluid from state 2 to state 3 is obtained by the condenser.

 The transition from state 3 to state 4 of the refrigerant is obtained by expansion in the float regulator (marked 22 in Figure 1) which is interposed between the outlet of the condenser 21 and the inlet of the fluid reservoir 23 refrigerant (mainly liquid).

 A (main) part of the refrigerant having passed through the float regulator 22 is completely condensed (in the liquid state in the reservoir 23) which is represented by the passage from the state marked 4 to the state marked 5 on the Figure 2, state 5 corresponding to a substantially saturated state of the liquid refrigerant.

 The liquid forming the major part of the refrigerant then undergoes expansion in the pressure reducer (reference 24 in FIG. 1) which takes it from the state marked 5 in FIG. 2 to the state marked 6 in this figure, before evaporating ( in the evaporator at pressure 45) to return to the initial state 1 of the cycle.

 As illustrated in FIG. 1, a line 9 connects the upper part of the liquid reservoir 23 to the inlet of the compressor 20, which line 9 successively comprises a solenoid valve 26 provided with a pilot regulating the degassing flow passing through the valve 26 and circulating in the line 9, to maintain a constant pressure inside the liquid reservoir 23; an additional manual adjustment member 27 can be provided on the line 9.

 The transformation (shown in Figure 2 in broken lines) undergone by the refrigerant in the gas phase which is taken in the SA state inside the tank 23 also shown in Figure 2, is an expansion in the organs 26, 27 passing the gaseous refrigerant circulating in the pipe 9, from the state SA to the state 6A close to the gaseous state 1 corresponding to the conditions of suction of the refrigerant by the compressor.

 With reference to Figures 3 and 4, the operation of the installation is similar to that already explained with reference to Figures 1 and 2; however in the case of FIGS. 3 and 4 the compression is carried out in two stages and comprises an intermediate state 2 (at an intermediate pressure 49 or medium pressure) between state 1 of the refrigerant at the suction of the first stage and the state 3 of the refrigerant compressed and leaving the compression device 20.

 The refrigerant in state 2 corresponding to the outlet of the first compression stage of the compressor 20 undergoes a slight cooling by contact with the gaseous refrigerant delivered in state 8A; this marked state 8A corresponds to the outlet on the one hand from the degassing pipe 9 of the bottle 23 comprising, in the same way as shown in FIG. 1, the piloted solenoid valve 26 and the manual adjuster 27; the state marked 8A also corresponds to the outlet of a non-return valve 30 disposed on a pipe 8 into which is inserted an economizer exchanger 28 supplied by the bottle 23 via a pressure reducer 29.

 In the transformation undergone by the refrigerant in this pipe 8 (which is represented by broken lines in FIG. 4), the refrigerant passes from state 6 corresponding to the outlet of the liquid reservoir 23 to state 7A by following expansion in the regulator 29, then goes from state 7A to state 8A by evaporation in the economizer 28; this evaporation thus causes cooling, also called under cooling, (transition from state 6 to state 7), of the main part of the refrigerant which passes through the pipe 10 and into the other part of the economizer, before trigger in the main regulator 24 of the installation.

 The invention makes it possible, when the outside air (external fluid used for the condensation) is at a temperature for example close to 5 ° C. corresponding to a pressure marked 46, by maintaining a pressure 47 in the reservoir 23 (by the regulation means) corresponding for example to a temperature in the region of 15in, to lower the condensation pressure 48 to a value, for example greater than 105 Pascal only at pressure 47.

 In the case of two-stage compression, the intermediate pressure 49 is for example close to the geometric mean of the suction (evaporation) 45 and discharge (condensation) pressures 48, in order to ensure a compression rate per stage substantially identical.

 With reference to FIG. 5, the regulator 22 with float may essentially consist of a cylindrical body or ferrule 33 closed at one end by a convex bottom 34, for example welded to the body 33.

 The device or reservoir thus formed can be closed at its second end by a removable flat bottom 41 capable of being fixed to the body 33 by bolts and by means of a flange welded to the body 33.

On the flat bottom 41 closing the container, holes are provided
inlet and outlet communicating with inlet 40 and outlet 39 connections of the regulator 22 to float.

 The refrigerant entering through the orifice 40 in the body of the regulator 22, causes the displacement of the float 35 mounted at the end of an arm 36 pivoting along an axis 37 perpendicular to the plane of the figure; the pivoting of this arm 36 causes the displacement of an outlet valve cooperating with an outlet nozzle or outlet 38; the float device thus makes it possible to cause an expansion of the refrigerant passing through the regulator 22.

Claims (10)

 1. Compression and expansion refrigeration device for a refrigerant, which comprises  one or more condensers (21) for the condensation of said compressed refrigerant by heat exchange with a first external fluid,  - one or more tanks (23) or bottles for the accumulation or buffer storage of said condensed refrigerant, characterized in that it further comprises  a large capacity expansion member (22) which is arranged between the outlet of said condenser (21) and the inlet of said tank (23),  - A member (26) for regulating the pressure prevailing in said reservoir (23).  2. Device according to claim 1 wherein said expansion member (22) is a float regulator (35).  3. Device according to any one of claims 1 to 2 wherein said member (26) for pressure regulation is essentially constituted by a valve (26) disposed on a pipe (9) which connects an upper part of said tank (23) at the input of a compressor (20).  4. Device according to claim 3 wherein the opening of said valve (26) is controlled as a function of the pressure prevailing upstream of said valve, by a pilot or pressure regulator (43) integrated into said valve (26).  5. Device according to any one of claims 1 to 4 comprising several evaporators (25) connected in parallel on said refrigerant circulation circuit, which are each equipped with a respective individual expansion valve (24).  6. Device according to any one of claims 1 to 5 comprising at least two compressors (20) connected in series and ensuring a multi-stage compression.  7. Device according to claim 6 further comprising an economizer exchanger (28) supplied with liquid refrigerant supplied by said tank (23) via a pressure reducer (29), and the outlet of which is connected to the inlet a compressor (20).  8. Device according to any one of claims 1 to 7 wherein said pressure regulating member prevailing in said tank or bottle (23) is adjusted to maintain in said tank a pressure (47) of the refrigerant corresponding to a temperature saturation between 100C and 200C.  9. Device according to any one of claims 1 to 8 wherein said first external fluid or condensing fluid is air.  10. Device according to any one of claims 1 to 9 wherein said second external fluid or evaporation fluid is air.