HEAT EXCHANGE APPARATUS

Abstract

A heat exchange apparatus includes a heat exchange circuit which is provided with an evaporator which is connected in output to a condenser, which is connected, in output, by way of the interposition of expansion elements to the evaporator and in which there is at least one regenerative exchanger between the evaporator and the condenser. The apparatus includes adjustment valve elements between the outlet of the condenser and the inlet of the evaporator. Sensor elements are further provided which are adapted to measure at least one thermodynamic parameter of the exchange fluid at preset points of the circuit and control elements are further provided which are connected to the sensor elements and are configured to calculate, using measurements supplied by the sensor elements, the instantaneous efficiency and a reference efficiency of the regenerative exchanger.

Claims

1-16. (canceled)

17. A heat exchange apparatus comprising: a heat exchange circuit which is passed through by a heat exchange fluid and is provided with an evaporator which is connected in output, by way of the interposition of a compressor, to a condenser, which is connected in output, by way of the interposition of expansion means, to said evaporator, between said evaporator and said condenser there being at least one regenerative exchanger for an exchange of heat between a vapor-phase exchange fluid that exits from said evaporator and a liquid-phase exchange fluid that exits from said condenser, and further comprising, between an outlet of said condenser and an inlet of said evaporator, adjustment valve means for a flow of said exchange fluid, sensor means being provided which are adapted to measure at least one thermodynamic parameter of said exchange fluid at preset points of said circuit and control means being provided which are connected to said sensor means and are configured to calculate, using measurements supplied by said sensor means, an instantaneous efficiency of said regenerative exchanger and a reference efficiency of said regenerative exchanger, said control means being adapted to act on said adjustment valve means in order to vary their degree of opening, at least on the basis of a difference between the instantaneous efficiency and the reference efficiency of said regenerative exchanger.

18. The apparatus according to claim 17, wherein said circuit comprises at least one liquid line which connects the outlet of said condenser with the inlet of said evaporator and passes through said regenerative exchanger, said expansion means comprising at least one adjustable expansion valve, which is interposed along said liquid line between said regenerative exchanger and said evaporator, said adjustment valve means comprising at least one first adjustment valve which is constituted by said at least one adjustable expansion valve.

19. The apparatus according to claim 18, wherein said adjustment valve means comprise at least one second adjustment valve which is adapted to adjust the flow of the liquid-phase exchange fluid that passes through said regenerative exchanger.

20. The apparatus according to claim 19, wherein said at least one second adjustment valve is interposed along said liquid line.

21. The apparatus according to claim 19, further comprising a bypass line which connects a first section of said liquid line located upstream of said regenerative exchanger to a second section of said liquid line located downstream of said regenerative exchanger, said at least one second adjustment valve being interposed along said bypass line.

22. The apparatus according to claim 21, wherein said second adjustment valve comprises a variable-aperture three-way valve which is connected, with two ways, along said liquid line and, with a third way, to said bypass line.

23. The apparatus according to claim 21, wherein said at least one second adjustment valve comprises a variable-aperture two-way valve interposed along said bypass line.

24. The apparatus according to claim 21, wherein said at least one second adjustment valve comprises a two-way valve interposed along said liquid line, upstream of said regenerative exchanger.

25. The apparatus according to claim 17, wherein said circuit comprises at least one steam line which connects the outlet of said evaporator with the inlet of said condenser and passes through said regenerative exchanger, said compressor being interposed along said steam line, between said regenerative exchanger and said condenser, said sensor means comprising a first temperature sensor which is arranged along said steam line between said regenerative exchanger and said compressor, a second temperature sensor arranged along said liquid line upstream of said regenerative exchanger, a third temperature sensor arranged along said liquid line downstream of said regenerative exchanger, and a pressure sensor arranged along said steam line between said evaporator and said compressor.

26. The apparatus according to claim 25, wherein said sensor means comprise a fourth temperature sensor which is arranged along said steam line between said evaporator and said regenerative exchanger.

27. The apparatus according to claim 17, wherein said control means are configured to calculate said reference efficiency, by requiring a superheating of said exchange fluid at said evaporator to be comprised substantially between 0 and 5 K.

28. The apparatus according to claim 18, wherein said control means are configured to actuate said adjustable expansion valve on the basis of the difference between the instantaneous efficiency and the reference efficiency of said regenerative exchanger.

29. The apparatus according to claim 19, wherein said control means are configured to actuate said adjustable expansion valve, on the basis of the difference between actual superheating of said heat exchange fluid at the outlet of said evaporator or at the inlet of said compressor, which is determined using the measurements of said sensor means, and a preset reference value for the superheating of said exchange fluid at said evaporator, and to actuate said second adjustment valve, on the basis of the difference between the instantaneous efficiency and the reference efficiency of said regenerative exchanger.

30. A method for adjusting a heat exchange apparatus of the type comprising a heat exchange circuit which is passed through by a heat exchange fluid and is provided with an evaporator which is connected in output, by way of the interposition of a compressor, to a condenser, which is connected in output, by way of the interposition of expansion means, to said evaporator and with the interposition, between said evaporator and said condenser, of at least one regenerative exchanger for heat exchange between the vapor-phase exchange fluid that exits from said evaporator and the liquid-phase exchange fluid that exits from said condenser, and further comprising the steps of performing a measurement of at least one thermodynamic parameter of said exchange fluid at preset points of said circuit, calculating, using the measurements made, an instantaneous efficiency and a reference efficiency of said regenerative exchanger, calculating a difference between a calculated value of the instantaneous efficiency of said regenerative exchanger and a calculated value of the reference efficiency of said regenerative exchanger, and varying a degree of opening of adjustment valve means interposed between an outlet of the condenser and an inlet of the evaporator on the basis of a calculated value of the difference between the instantaneous efficiency and the reference efficiency of said regenerative exchanger.

31. The method according to claim 30, wherein the instantaneous efficiency is calculated using the measurement at least of a temperature of said liquid-phase exchange fluid in input to said regenerative exchanger and of a temperature of said vapor-phase exchange fluid in output from said regenerative exchanger.

32. The method according to claim 30, wherein the reference efficiency of said regenerative exchanger is calculated by requiring a superheating of said exchange fluid at said evaporator to be comprised between 0 and 5 K.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further characteristics and advantages of the disclosure will become better apparent from the description of preferred, but not exclusive, embodiments of the heat exchange apparatus according to the disclosure, which are illustrated for the purposes of non-limiting example in the accompanying drawings wherein:

[0016] FIG. 1 is a diagram of the apparatus according to the disclosure in a first embodiment;

[0017] FIG. 2 is a diagram of the apparatus according to the disclosure, in a second embodiment;

[0018] FIG. 3 is a diagram of the apparatus according to the disclosure in a third embodiment;

[0019] FIG. 4 is a schematic diagram of a fourth embodiment of the apparatus according to the disclosure;

[0020] FIG. 5 is a graph of the trend of the flow of the liquid-phase exchange fluid passing through a regenerative exchanger as a function of the degree of opening of a second adjustment valve provided in the apparatus, for the embodiment of FIG. 1;

[0021] FIG. 6 is a graph of the trend of the flow of the liquid-phase exchange fluid passing through the regenerative exchanger as a function of the degree of opening of the second adjustment valve, for the embodiment of FIG. 3;

[0022] FIG. 7 is a graph of the trend of the flow of the liquid-phase exchange fluid passing through the regenerative exchanger as a function of the degree of opening of the second adjustment valve, for the embodiment of FIG. 4; and

[0023] FIG. 8 is a general diagram of a portion of the apparatus according to the disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0024] With reference to the figures, the heat exchange apparatus according to the disclosure, generally designated by the reference numeral 1, comprises a heat exchange circuit 2 which is passed through by a heat exchange fluid, such as for example refrigerant fluid R134a.

[0025] In particular, the circuit 2 has an evaporator 3, preferably of the dry expansion type, in which the exchange fluid exchanges heat with a first temperature source, in so doing heating up and thus transiting from the liquid phase to the vapor phase.

[0026] The evaporator 3 is connected in output to a compressor 4 which receives the vapor-phase exchange fluid and compresses it in order to send it in input to a condenser 5, in which the exchange fluid is cooled, by exchanging heat with a second temperature source, kept at a temperature that is lower than the first source, and thus transiting from the vapor phase to the liquid phase.

[0027] The output of the condenser 5 is, in turn, connected to the evaporator 3 via the interposition of expansion means 6, the function of which is to lower the pressure of the liquid-phase exchange fluid, before it enters the evaporator 3.

[0028] The circuit 2 is further provided, between the evaporator 3 and the condenser 5, with at least one regenerative exchanger 7 which enables the heat exchange between the vapor-phase exchange fluid exiting from the evaporator 3 and the liquid-phase exchange fluid exiting from the condenser 5.

[0029] More specifically, the circuit 2 is provided with at least one liquid line 2a, through which the liquid-phase exchange fluid flows and which connects the outlet of the condenser 5 with the inlet of the evaporator 3 and passes through the regenerative exchanger 7, and at least one steam line 2b, through which the vapor-phase exchange fluid flows and which, in turn, connects the outlet of the evaporator 3 with the inlet of the condenser 5, also passing through the regenerative exchanger 7.

[0030] As illustrated, the compressor 4 is interposed along the steam line 2b, between the regenerative exchanger 7 and the condenser 5.

[0031] According to the disclosure, the circuit 2 is provided, between the outlet of the condenser 5 and the inlet of the evaporator 3, with adjustment valve means for adjusting the flow of the exchange fluid in the circuit 2.

[0032] Also according to the disclosure, there are furthermore sensor means, described in more detail below, which make it possible to measure at least one thermodynamic parameter of the exchange fluid at preset points of the circuit 2 in order to allow the calculation of the efficiency of the regenerative exchanger.

[0033] The sensor means are connected to control means 8, which are constituted, preferably, by a programmable electronic controller.

[0034] In particular, the control means 8 are configured to calculate, using the measurements supplied by the sensor means, the instantaneous efficiency of the regenerative exchanger 7 and a reference efficiency or set-point efficiency of said regenerative exchanger.

[0035] The thermal efficiency () of the regenerative exchanger 7 is defined by the general formula, per se known:

[00001]$=\frac{\max \left[\left(T_{\mathrm{Vout}}-T_{\mathrm{Vin}}\right),\left(T_{\mathrm{Lin}}-T_{\mathrm{Lout}}\right)\right].}{T_{\mathrm{Lin}}-T_{\mathrm{Vin}}}$

where: T.sub.Vout is the temperature of the vapor-phase exchange fluid in output from the regenerative exchanger 7, T.sub.Vin is the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7, T.sub.Lin is the temperature of the liquid-phase exchange fluid in input to the regenerative exchanger 7 and T.sub.Lout is the temperature of the liquid-phase exchange fluid in output from the regenerative exchanger 7.

[0036] The instantaneous efficiency is calculated by the control means 8 by substituting the variables T.sub.in, T.sub.out, T.sub.Lin, T.sub.Vin appearing in the formula with the values measured using the sensor means, while the reference efficiency is instead calculated, again by the control means 8, using the same formula, but requiring that the superheating at the evaporator 3 of the exchange fluid be substantially comprised between 0 and 5 K and, more preferably, between 0 and 3 K, as will be better explained below.

[0037] The control means 8 furthermore compare the calculated values of the instantaneous efficiency and of the reference efficiency of the regenerative exchanger 7 and calculate the difference between them, and are designed to actuate the adjustment valve means, in order to vary the degree of opening thereof, at least on the basis of the calculated difference between the instantaneous efficiency and the reference efficiency of the regenerative exchanger 7.

[0038] Advantageously, the expansion means 6 are constituted by at least one expansion valve 9, with adjustable opening, which is interposed along the liquid line 2a between the regenerative exchanger 7 and the evaporator 3.

[0039] The cited adjustment valve means comprise at least one first adjustment valve which can be constituted by said expansion valve 9.

[0040] According to possible embodiments of the disclosure, better described below, the adjustment valve means can also comprise, in addition to the first adjustment valve constituted by the expansion valve 9, at least one second adjustment valve 10, also interposed along the liquid line 2a, which makes it possible, in particular, to vary the flow rate of the liquid-phase exchange fluid that is made to pass through the regenerative exchanger 7.

[0041] Advantageously, the sensor means supplied for calculating the instantaneous efficiency and the reference efficiency of the regenerative exchanger 7 comprise at least one first temperature sensor 11, arranged along the steam line 2b between the regenerative exchanger 7 and the compressor 4, at least one second temperature sensor 12, arranged along the liquid line 2a upstream of the regenerative exchanger 7, and at least one third temperature sensor 13, arranged along the liquid line 2a downstream of the regenerative exchanger 7.

[0042] In particular, the first temperature sensor 11 measures the temperature value of the vapor-phase exchange fluid in output from the regenerative exchanger 7 (T.sub.Vout), which corresponds, basically, to the temperature of the exchange fluid in input to the compressor 4 (T.sub.Suction), the second temperature sensor 12 measures the temperature value of the liquid-phase exchange fluid in input to the regenerative exchanger 7 (T.sub.Lin), while the third temperature sensor 13 measures the temperature value of the liquid-phase exchange fluid in output from the regenerative exchanger 7 (T.sub.Lout).

[0043] Conveniently, the sensor means also comprise a pressure sensor 14 arranged along the steam line 2b, between the evaporator and the compressor 4, for measuring the evaporation pressure value of the exchange fluid exiting from the evaporator 3 (p.sub.EVout), with which the control means 8 can calculate the saturation temperature of the exchange fluid in output from the evaporator 3, as will also be better explained below.

[0044] Optionally, the sensor means can further comprise a fourth temperature sensor 15, arranged along the steam line 2b, between the evaporator 3 and the regenerative exchanger 7, for measuring the temperature of the exchange fluid in input to the regenerative exchanger 7 (T.sub.Vin), which is equal to the temperature of the exchange fluid in output from the evaporator 3 (T.sub.EVout).

[0045] Alternatively, if, for reasons of the apparatus's construction, it should not be possible to install the fourth temperature sensor 15 between the evaporator and the regenerative exchanger 7, as in the case where the regenerative exchanger 7 is integrated with the evaporator 3, the temperature value of the exchange fluid in output from the evaporator 3 and in input to the regenerative exchanger 7 (T.sub.Vin) can also be estimated by the control means 8 by way of measurements supplied by the other temperature sensors, as will be better described below.

[0046] It should be noted that, according to possible embodiments of the apparatus according to the disclosure, on the liquid line 2a there can be a bypass line 2c of the regenerative exchanger 7, which connects a first section of the liquid line 2a, located upstream of the regenerative exchanger 7, with a second section of the liquid line 2a, located downstream of the regenerative exchanger 7.

[0047] In this case, the second adjustment valve 10 is interposed along the bypass line 2c.

[0048] Turning now to describe the apparatus according to the disclosure in more detail, it can be noted, with reference to a first embodiment, shown in FIG. 1, that the second adjustment valve 10 can be constituted by a variable-aperture two-way valve, interposed along the bypass line 2c.

[0049] With this embodiment, the flow rate ({dot over (m)}.sub.L) of the exchange fluid that passes through the regenerative exchanger 7 can be modulated, on the basis of the degree of opening of the second adjustment valve 10, between a minimum value ({dot over (m)}.sub.Lmin), greater than zero, and a maximum value equal to the total flow rate value ({dot over (m)}.sub.LTOT) of the exchange fluid exiting from the condenser 5, as can be observed from the graph of FIG. 5.

[0050] The minimum flow value ({dot over (m)}.sub.Lmin) depends on the configuration of the circuit and in particular on the flow resistances along the liquid line 2a and the bypass line 2c.

[0051] In a second embodiment, simpler than the first, shown in FIG. 2, it can be noted that both the bypass line 2c and the second adjustment valve 10 are absent and only the expansion valve 9 is present to provide the adjustment valve means for adjusting the flow of the exchange fluid.

[0052] In this case, since the second adjustment valve 10 is not present, the ratio between the flow of the liquid-phase exchange fluid that passes through the regenerative exchanger 7 and the flow of the vapor-phase exchange fluid that passes through the regenerative exchanger 7 is always equal to 1, while, by varying the degree of opening of the expansion valve 9, the only thing that can be varied is the total flow rate of the exchange fluid that circulates inside the circuit 2.

[0053] According to a preferred embodiment, shown in FIG. 3, the second adjustment valve 10 is provided via a variable-aperture three-way valve, which is connected, with two ways, along the liquid line 2a, for example downstream of the regenerative exchanger 7, and, with a third way, to the bypass line 2c.

[0054] In this embodiment, by varying the degree of opening of the second adjustment valve 10 it is possible to vary the flow ({dot over (m)}.sub.L) of liquid-phase exchange fluid that passes through the regenerative exchanger 7 from zero to the total flow rate value ({dot over (m)}.sub.LTOT) of the exchange fluid exiting from the condenser 5, as the graph of FIG. 6 shows.

[0055] A fourth possible embodiment is shown in FIG. 4 and in it the second adjustment valve 10 is provided by a two-way valve interposed along the liquid line 2a, upstream of the regenerative exchanger 7, and there is a bypass line 2c bypassing the regenerative exchanger 7.

[0056] In this case, by varying the degree of opening of the second adjustment valve 10 it is possible to modulate the flow ({dot over (m)}.sub.L) of the liquid-phase exchange fluid that passes through the regenerative exchanger 7 between zero and a maximum value ({dot over (m)}.sub.Lmax), which is less than the total flow rate value ({dot over (m)}.sub.LTOT) of the exchange fluid exiting from the condenser 5, as the graph of FIG. 7 shows.

[0057] The maximum value of the flow rate of the liquid-phase exchange fluid that can pass through the regenerative exchanger 7 ({dot over (m)}.sub.Lmax) in this embodiment is determined by the flow resistances along the liquid line 2a and along the bypass line 2c.

[0058] The operation of the apparatus according to the disclosure is the following.

[0059] With reference to the embodiment of FIG. 1, the flow rate of the liquid-phase exchange fluid that passes through the regenerative exchanger 7 ({dot over (m)}.sub.L) varies between a fraction p and 100% of the total flow rate of the exchange fluid exiting from the condenser 5, according to the degree of opening of the second adjustment valve 10.

[0060] The sensor means and in particular the temperature sensors 11, 12, 13, 15 and the pressure sensor 14 transmit, to the control means 8, the respective measurement signals IS.sub.1, IS.sub.2, IS.sub.3, IS.sub.4, IS.sub.5, at each instant i.e. at every time interval of preset length.

[0061] The control means 8 then calculate, at each instant, the instantaneous efficiency of the regenerative exchanger 7 using the general formula given above for the thermal efficiency of the regenerative exchanger 7, using the measurements taken by the sensor means and, in particular, by the temperature sensors 11, 12, 13, 15, which supply the control means 8 with respectively the temperature of the vapor-phase exchange fluid in output from the regenerative exchanger 7 (T.sub.Vout), the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7 (T.sub.Lin), the temperature of the liquid-phase exchange fluid in output from the regenerative exchanger 7 (T.sub.Lout) and the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7 (T.sub.Vin).

[0062] In particular, in proceeding to calculate the instantaneous efficiency, the control means 8 initially determine, using the general formula given above, using the measurements of the temperature probes 11, 12, 13 and 15, the difference between the temperature of the vapor-phase exchange fluid in output from the regenerative exchanger 7 and the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7, as well as the difference between the temperature of the liquid-phase exchange fluid in input to the regenerative exchanger 7 and the temperature of the liquid-phase exchange fluid in output from the regenerative exchanger 7 and to compare the values of the two differences thus calculated, in order to establish which of these two differences is the greatest.

[0063] More specifically, in the more general case where the greater difference between the two is the difference between the temperature of the vapor-phase exchange fluid in output from the regenerative exchanger 7 and the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7, the formula for calculating the instantaneous efficiency used by the control means 8 becomes:

[00002]$=\frac{T_{\mathrm{Vout}}-T_{\mathrm{Vin}}}{T_{\mathrm{Lin}}-T_{\mathrm{Vin}}}$

where: T.sub.Vout is the temperature of the vapor-phase exchange fluid in output from the regenerative exchanger 7 and T.sub.Vin is the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7.

[0064] Otherwise, if the greater difference between the two is the difference between the temperature of the liquid-phase exchange fluid in input to the regenerative exchanger 7 and the temperature of the liquid-phase exchange fluid in output from the regenerative exchanger 7, then the formula for calculating the instantaneous efficiency becomes:

[00003]$=\frac{T_{\mathrm{Lin}}-T_{\mathrm{Lout}}}{T_{\mathrm{Lin}}-T_{\mathrm{Vin}}}$

where: T.sub.Lin is the temperature of the liquid-phase exchange fluid in input to the regenerative exchanger 7 and T.sub.Lout is the temperature of the liquid-phase exchange fluid in output from the regenerative exchanger 7.

[0065] It should be noted that if it is not possible to obtain the measurement of the fourth temperature probe 15, then the control means 8 proceed to estimate the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7 T.sub.Vin using the following formula:

[00004]${\stackrel{.}{m}}_L{c}_{\mathrm{PL}}\left(T_{\mathrm{Lin}}-T_{\mathrm{Lout}}\right)={\stackrel{.}{m}}_V{c}_{\mathrm{PV}}\left(T_{\mathrm{Vout}}-T_{\mathrm{Vin}}\right)$

which expresses an energy balance within the regenerative exchanger 7 by equalizing the heat exchanged by the vapor-phase exchange fluid inside the regenerative exchanger 7 with the heat exchanged by the liquid-phase exchange fluid, also inside the regenerative exchanger, and from which is obtained:

[00005]$T_{\mathrm{Vin}}=T_{\mathrm{Vout}}-\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\frac{c_{\mathrm{PL}}}{c_{\mathrm{PV}}}\left(T_{\mathrm{Lin}}-T_{\mathrm{Lout}}\right)$

[0066] The temperature values to be inserted in the formula shown above to calculate the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7 T.sub.Vin, i.e. the values of the temperature of the vapor-phase exchange fluid in output from the regenerative exchanger 7 T.sub.Vout, of the temperature of the liquid-phase exchange fluid in input to the regenerative exchanger T.sub.Lin and of the temperature of the liquid-phase exchange fluid in output from the regenerative exchanger 7 T.sub.Lout, are, respectively, measured by the temperature probes 11, 12 and 13, while the specific heat values c.sub.pV and c.sub.pL of the vapor-phase exchange fluid and of the liquid-phase exchange fluid at the temperatures of said exchange fluid are determined by the control means 8 from the relations that link these specific heat values c.sub.pV and c.sub.pL to the temperatures of said exchange fluid, i.e.:

[00006]$c_{\mathrm{PV}}=c_{\mathrm{PV}}\left(T_{\mathrm{Vout}}\right)$$c_{\mathrm{PL}}=c_{\mathrm{PL}}\left(\frac{T_{\mathrm{Lin}}+T_{\mathrm{Lout}}}{2}\right)$

which depend on the exchange fluid used and which are per se known.

[0067] The value of the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V between the flow rate of the liquid-phase exchange fluid passing through the regenerative exchanger 7 and the flow rate of the vapor-phase exchange fluid passing through the regenerative exchanger 7, also present in the same formula used to calculate the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7 T.sub.Vin, is obtained by the control means 8 using the liquid-side characteristic curve of the regenerative exchanger 7, which is obtained from previous measurements once only and which supplies the measurement of the flow resistance on the liquid side of the regenerative exchanger 7, and using the characteristic curve of the second adjustment valve 10, which is supplied by the maker of said valve.

[0068] In more detail, reference can be made to the general diagram in FIG. 8, which shows the liquid line 2a and, more specifically, the section of the latter, indicated with L, that passes through the heat exchanger 7, and which also shows in schematic form the presence of the regenerative exchanger 7 and of the second adjustment valve 10. Also in FIG. 8, the branch BP that connects the ends of the section L represents the bypass line 2c.

[0069] In particular, it must be noted that, generally, the equation that expresses the liquid-side characteristic curve of the regenerative exchanger 7 is constituted by a relation between the flow resistance on the section L of the liquid line 2a that passes through the regenerative exchanger 7 and the product of the hydraulic characteristic on the liquid side of the regenerative exchanger 7 and the square of the flow rate of the liquid-phase exchange fluid that passes through said regenerative exchanger.

[0070] The hydraulic characteristic of the liquid side of the regenerative exchanger 7, C.sub.IHX, can be easily obtained for each model of regenerative exchanger 7 via initial mapping of the characteristic curve with a minimum of three measurement points, i.e. by conducting tests with different flow rates of fluid so as to identify at least three points of the parabola that represents the characteristic curve of the regenerative exchanger 7.

[0071] The mapping can be carried out with an easily-obtained and easily-managed liquid, such as water, and then scale it to the density of the coolant liquid considered. That is to say, given that C.sub.IHX depends on the type of coolant used, if mapping with water results in determining the characteristic C.sub.IHX, WATER, then the value of the sought characteristic is obtained from:

[00007]$C_{\mathrm{IHX}}=\frac{{}_{\mathrm{WATER}}}{{}_L}{C}_{\mathrm{IHX},\mathrm{WATER}}$

where .sub.L is the density of the liquid-phase exchange fluid and .sub.WATER is the density of the liquid water, both calculated in the same temperature interval.

[0072] More specifically, the hydraulic characteristic of the liquid side of the regenerative exchanger 7, C.sub.IHX, depends not only on the type of coolant used, but also on the geometry of the regenerative exchanger 7 and on the preset interval of temperatures within which the regenerative exchanger is intended to operate, and is defined by the relation:

p.sub.L,IHX=C.sub.IHX{dot over (m)}.sub.L.sup.2

where: {dot over (m)}.sub.L is the flow rate of the liquid-phase exchange fluid that passes through the regenerative exchanger 7, C.sub.IHX is the hydraulic characteristic of the liquid side of the regenerative exchanger 7, and p.sub.L is the flow resistance through the regenerative exchanger 7 i.e. along the section L of the liquid line 2a that passes through the regenerative exchanger 7.

[0073] It is also possible to consider the effect of any non-negligible hydraulic resistances that are present, in addition to the second adjustment valve 10, if any, along the liquid line 2a, such as resistances determined by bends, choking and the like, and schematically represented in FIG. 8 by the box indicated with C.sub.L.

[0074] In particular, if the type and the geometry of the hydraulic resistances are known, their effect is easily determined, in a manner that is per se known, using the theory.

[0075] For example, for a valve of the on/off type, i.e. with only two working conditions, respectively a completely open condition and a completely closed condition, and therefore without the ability to adjust the degree of opening, its characteristic indicated with K.sub.L, according to the theory the effect of its hydraulic resistance can be expressed as follows:

[00008]$C_L^{}=\frac{1}{{}_L^2{K}_L^2}$

where: .sub.L is the density of the liquid-phase exchange fluid.

[0076] If, on the other hand, the type and geometry of the hydraulic resistances are not known, their effect can be measured by way of a preliminary mapping, i.e. by carrying out experimental tests by making different flow rates pass through the hydraulic resistance.

[0077] By defining the hydraulic characteristic of the liquid side of the regenerative exchanger 7, not connected to the second adjustment valve 10, as the sum, indicated with C.sub.L, of the hydraulic characteristic of the liquid side of the regenerative exchanger 7 C.sub.IHX and the effect C.sub.L of any non-negligible hydraulic resistances that are present along the liquid line 2a, not including the second adjustment valve 10, i.e.:

[00009]$C_L=C_{\mathrm{IHX}}+C_L^{}$

then the flow resistance on the section L of the liquid line 2a that passes through the regenerative exchanger 7, not connected to the second adjustment valve 10, can be expressed as follows:

p.sub.L=C.sub.L{dot over (m)}.sub.L.sup.2

where: p.sub.L is the flow resistance, not connected to the second adjustment valve 10, on the section L of the liquid line 2a that passes through the regenerative exchanger 7, C.sub.L is the hydraulic characteristic of the section L of the liquid line 2a that passes through the regenerative exchanger 7, not connected to the second adjustment valve 10, and 111 is the flow rate of the liquid-phase exchange fluid that passes through the regenerative exchanger 7.

[0078] According to the embodiment, along the section L of the liquid line 2a that passes through the regenerative exchanger 7, the second adjustment valve 10 can be absent, as in the embodiments of FIGS. 1 and 2, or it can be present, as in the embodiment of FIG. 4 or as in the embodiment of FIG. 3, in which it is present with one of its parts.

[0079] If the second adjustment valve 10 is present along the section L of the liquid line 2a that passes through the regenerative exchanger 7, then we consider the flow resistance p.sub.v,L through the second adjustment valve 10, such that:

[00010]${\stackrel{.}{m}}_L={}_L{K}_{v,L}{p}_{v,L}^{1/2}$

or:

[00011]$p_{v,L}=\frac{{\stackrel{.}{m}}_L^2}{{}_L^2{K}_{v,L}^2}$

where: p.sub.V,L is the flow resistance through the second adjustment valve 10, .sub.L is the density of the liquid-phase exchange fluid, {dot over (m)}.sub.L is the flow rate of the liquid-phase exchange fluid that passes through the second adjustment valve 10, and K.sub.v,L is a characteristic coefficient of the second adjustment valve 10 which is supplied by the maker of said valve.

[0080] The above formula, which expresses the value of the flow resistance through the second adjustment valve 10, continues to be valid even if the second adjustment valve 10 is absent, simply by having:

K.sub.v,L.fwdarw.

both in the embodiment of FIG. 2 and in the embodiment of FIG. 1, given that the corresponding absence of the adjustment valve 10 is equivalent to assuming the flow resistance through it is nil, which can happen only with a hydraulic resistance of nil and, therefore, with value of the characteristic tending towards infinity.

[0081] The flow resistance total p.sub.L on the section L of the liquid line 2a that passes through the regenerative exchanger 7 is, therefore, equal to the sum of the flow resistance on the section L of the liquid line 2a, not connected to the second adjustment valve 10, that passes through the regenerative exchanger 7 and the flow resistance through the second adjustment valve 10, i.e:

[00012]$p_L=p_L^{}+p_{v,L}$

and, as a consequence, by substituting in the above equation the previous relations for the flow resistance on the section L of the liquid line 2a that passes through the regenerative exchanger 7, not connected to the second adjustment valve 10, and for the flow resistance through the second adjustment valve 10, and inserting the term {dot over (m)}.sub.L, we have:

[00013]$p_L=\left(C_L+\frac{1}{{}_L^2{K}_{v,L}^2}\right){\stackrel{.}{m}}_L^2$

[0082] Similarly to the section L of the liquid line 2a, it is necessary to consider the effect of non-negligible hydraulic resistances that are present, in addition to those associated with the second adjustment valve 10, if any, along the bypass line 2c, such as resistances determined by bends, choking and the like, and schematically represented in FIG. 8 by the box indicated with C.sub.BP.

[0083] In particular, if the type and the geometry of the hydraulic resistances are known, their effect is easily determined, in a manner that is per se known, using the theory. For example, for a valve of the on/off type, i.e. with only two working conditions, respectively a completely open condition and a completely closed condition, and therefore without the ability to adjust the degree of opening, its characteristic indicated with K.sub.BP, according to the theory the effect of its hydraulic resistance can be expressed as follows:

[00014]$C_{\mathrm{BP}}=\frac{1}{{}_L^2{K}_{\mathrm{BP}}^2}$

where .sub.L is the density of the liquid-phase exchange fluid.

[0084] If, on the other hand, the type and geometry of the hydraulic resistances are not known, their effect can be measured by way of a preliminary mapping, i.e. by carrying out experimental tests by making different flow rates pass through the hydraulic resistance. The flow resistance on the branch BP of the bypass line 2c, not connected to the second adjustment valve 10, can be expressed as follows:

p.sub.BP=C.sub.BP{dot over (m)}.sub.BP.sup.2

where {dot over (m)}.sub.BP is the flow rate of the liquid-phase exchange fluid that passes through the branch BP.

[0085] According to the embodiment, along the branch BP of the bypass line 2c, the second adjustment valve 10 can be absent, as in the embodiments of FIGS. 2 and 4, or it can be present, as in the embodiment of FIG. 1 or as in the embodiment of FIG. 3, in which it is present with one of its parts.

[0086] If the second adjustment valve 10 is present along the branch BP of the bypass line 2c, then we consider the flow resistance p.sub.v,BP through the second adjustment valve 10, such that:

[00015]$p_{v,\mathrm{BP}}=\frac{{\stackrel{.}{m}}_{\mathrm{BP}}^2}{{}_L^2{K}_{v,\mathrm{BP}}^2}$

where: p.sub.v,BP is the flow resistance through the second adjustment valve 10, .sub.L is the density of the liquid-phase exchange fluid, {dot over (m)}.sub.BP is the flow rate of the liquid-phase exchange fluid that passes through the second adjustment valve 10, and K.sub.v,BP is a characteristic coefficient of the second adjustment valve 10 which is supplied by the producer of said valve. The above formula, which expresses the value of the flow resistance through the second adjustment valve 10, continues to be valid even if the second adjustment valve 10 is absent, simply by having:

K.sub.v,BP.fwdarw.

in the embodiment of FIG. 4, given that the corresponding absence of the adjustment valve 10 is equivalent to assuming the flow resistance through it is nil, which can happen only with a hydraulic resistance of nil and, therefore, with value of the characteristic tending towards infinity. The embodiment of FIG. 2, by contrast, simulates the absence of the branch BP with a corresponding fixed hydraulic resistance tending towards infinity, i.e., with reference to FIG. 8:

C.sub.BP.fwdarw.

and therefore the characteristic of the second adjustment valve 10 on the branch BP K.sub.v,BP can assume any value between zero and infinity:

K.sub.v,BP[0,)

[0087] The flow resistance on the section L of the liquid line 2a must be equal to the flow resistance in the branch BP of FIG. 8, such that:

p.sub.L=p.sub.BP

and as a consequence:

[00016]$\left(C_L+\frac{1}{{}_L^2{K}_{v,L}^2}\right){\stackrel{.}{m}}_L^2=\left(C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}\right){\stackrel{.}{m}}_{\mathrm{BP}}^2$

[0088] Considering then that the total flow rate of the exchange fluid {dot over (m)} is, by the principle of continuity, equal to the flow rate of the vapor-phase exchange fluid passing through the regenerative exchanger 7 {dot over (m)}.sub.V, then the flow rate of the refrigerant fluid through the branch BP is equal to:

[00017]${\stackrel{.}{m}}_{\mathrm{BP}}=\stackrel{.}{m}-{\stackrel{.}{m}}_L={\stackrel{.}{m}}_V-{\stackrel{.}{m}}_L$

[0089] From the above formulas, we obtain the following general formula which is valid for the general diagram of FIG. 8:

and this general formula enables the control means 8 to calculate the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V between the flow rate of the liquid-phase exchange fluid that passes through the regenerative exchanger 7 and the flow rate of the vapor-phase exchange fluid that passes through the regenerative exchanger 7, and to obtain, from this ratio and the measurements supplied to the control means 8 by the temperature probes 11, 12 and 13, the temperature value of the vapor-phase exchange fluid in input to the regenerative exchanger 7.

[0090] The general formula shown above for calculating the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V between the flow rates of the liquid-phase exchange fluid and of the vapor-phase

[00018]$\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}=\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}$

exchange fluid which pass through the regenerative exchanger 7 will take a different form depending on the different embodiments of the apparatus.

[0091] Turning, in particular, to the case of the first embodiment of FIG. 1, since the second adjustment valve 10 is, in this case, absent along the section L of the liquid line, we can consider the second adjustment valve 10 as if it were present along the section L, always in the completely open condition, without offering any resistance, such that;

K.sub.v,L.fwdarw.

and the formula for calculating the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V becomes:

[00019]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{Emb}.\mathrm{Fig}\text{.1}}=\underset{K_{v,L}.fwdarw.}{\lim }\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}=\frac{1}{1+\sqrt{\frac{C_L}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}$

[0092] From this formula we determine the limit values, minimum and maximum, for the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V in the case of the first embodiment.

[0093] In particular, when, in the first embodiment of FIG. 1, the second adjustment valve 10 we have:

K.sub.v,BP=0

thus obtaining:

[00020]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{MAX},\mathrm{Emb}.\mathrm{Fig}\text{.1}}=\underset{K_{v,\mathrm{BP}}.fwdarw.0}{\lim }\frac{1}{1+\sqrt{\frac{C_L}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}=1$

[0094] When, on the other hand, again in the embodiment of FIG. 1, the second adjustment valve is open to the maximum, we have:

K.sub.v,BP=K.sub.v,MAX

where K.sub.v,MAX is the characteristic of the second adjustment valve supplied by the producer of the valve, and, as a consequence, the following relation is obtained:

[00021]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{MIN},\mathrm{Emb}.\mathrm{Fig}\text{.1}}=\frac{1}{1+\sqrt{\frac{C_L}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{MAX}}^2}}}}>0$

which confirms that, in the embodiment of FIG. 1, {dot over (m)}.sub.L can assume all the values between a minimum value threshold and {dot over (m)}.sub.V, as shown by the graph of FIG. 5.

[0095] From the above relations, the control means 8 are able to determine, for the embodiment of FIG. 1, the value of the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V between the flow rates of the liquid-phase exchange fluid and of the vapor-phase exchange fluid which pass through the regenerative exchanger 7 and, from this ratio, the temperature value of the vapor-phase exchange fluid in input to the regenerative exchanger 7 T.sub.Vin, using the formulas given above.

[0096] At every instant, the control means 8 also calculate the reference efficiency of the regenerative exchanger 7.

[0097] In particular, for the calculation of the reference efficiency of the regenerative exchanger 7, the control means 8 again use the general formula for the efficiency of the regenerative exchanger 7, but starting from the assumption that the difference T.sub.EVsup between the temperature of the vapor-phase exchange fluid in input to the regenerative exchanger 7 (T.sub.Vin) and the saturated evaporation temperature (T.sub.EVsat) of the exchange fluid, i.e. the superheating at the evaporator 3, has a preset reference value or set-point value T.sub.EVsup,SETPOINT, chosen in advance and preferably comprised between 0 and 5 K and more preferably between 0 and 3 K.

[0098] For example, to maximize the benefits of the regenerative exchanger 7 the control means 8 can be programmed to assume that, in the calculation of the reference efficiency, the value of superheating at the evaporator 3 T.sub.EVsup is considered equal to 0 K i.e. that T.sub.EVsup,SETPOINT=0 K.

[0099] In this manner, the reference efficiency is calculated by the control means 8 using the following formula:

[00022]$=\frac{{.Math.T_{\mathrm{in}}-T_{\mathrm{out}}.Math.}_{\max }}{T_{\mathrm{Lin}}-T_{\mathrm{EV},\mathrm{sat}}-T_{\mathrm{EVsup},\mathrm{SETPOINT}}}$

with

[00023]${.Math.T_{\mathrm{in}}-T_{\mathrm{out}}.Math.}_{\max }=\max .Math.\left(T_{\mathrm{Vout}}-T_{\mathrm{EV},\mathrm{sat}}-T_{\mathrm{EVsup},\mathrm{SETPOINT}}\right),\left(T_{\mathrm{Lin}}-T_{\mathrm{Lout}}\right).Math.$

[0100] The saturation temperature T.sub.EVsat that appears in the formulas shown above is, as known, a unique function of the evaporation pressure p.sub.EV.

[0101] Therefore, in order to determine the reference efficiency, the control means 8 use, in the first embodiment, four parameters: T.sub.Lin, T.sub.Lout, T.sub.Vout, p.sub.EV.

[0102] It must be noted that, for the same reason that measuring the temperature of the vapor-phase exchange fluid in output from the evaporator and in input to the regenerative exchanger is problematic, measuring the evaporation pressure is also difficult. However, given that in general the regenerative exchanger 7 is designed to minimize the flow resistance on the vapor side (otherwise the advantages of using it are lost), it is possible to use the measurement of the pressure of the vapor-phase exchange fluid downstream of the regenerative exchanger 7 for calculating the reference efficiency, thus positioning the pressure sensor 14 between the regenerative exchanger 7 and the compressor 4, as shown in FIG. 1, instead of measuring the pressure of the vapor-phase exchange fluid upstream of the regenerative exchanger 7, with a negligible error in the determination of T.sub.EVsat, by virtue of calculating the flow resistance on the steam line 2b.

[0103] At this point, once the instantaneous efficiency and the reference efficiency are calculated, the control means 8 proceed to adjust the apparatus by following the per se known -NTU theory, whereby the efficiency of the exchanger is a function of the flow rate of the vapor-phase exchange fluid that passes through the regenerative exchanger 7, which corresponds, in practice, to the overall flow rate of the exchange fluid in the circuit 2, and to the flow rate of the liquid-phase exchange fluid that passes through the regenerative exchanger 7, which in the embodiment of FIG. 1 varies with the extent of opening of the second adjustment valve 10, i.e.:

[00024]$=\left({\stackrel{.}{m}}_V,{\stackrel{.}{m}}_L\right)=\left(\stackrel{.}{m},{\stackrel{.}{m}}_L\right)$

with {dot over (m)} controlled by the expansion valve 9 and with {dot over (m)}L controlled instead, as mentioned, by the second adjustment valve 10.

[0104] It is thus possible to efficaciously adjust two parameters: the efficiency of the regenerative exchanger 7 and the superheating at the evaporator or the efficiency of the regenerative exchanger 7 and the superheating at the suction line of the compressor 4.

[0105] More specifically, the control means 8, using the measurement signals received from the sensor means, determine the difference between the actual superheating of the exchange fluid at the outlet of the evaporator 3 or at the inlet of the compressor 4 and the preset reference value for the superheating of the exchange fluid (T.sub.supT.sub.sup,SET) and based on this difference said control means generate a first command signal OS.sub.1 to control the degree of opening of the expansion valve 9, by way of which the degree of opening of the expansion valve 9 is adjusted so as to ensure that the actual superheating at the evaporator 3 is substantially equal to the preset reference value, i.e. between 0 and 5 K and more preferably between 0 and 3 K.

[0106] Once the difference between the previously-determined instantaneous efficiency and reference efficiency is calculated, the control means 8, as a function of the difference between the instantaneous efficiency and the reference efficiency, also generate a second command signal OS.sub.2 to control the degree of opening of the second adjustment valve 10, so as to vary the degree of opening of the second adjustment valve 10 until the value of the instantaneous efficiency of the regenerative exchanger 7 is brought to the value of the reference efficiency.

[0107] It must be noted that the control means 8 are, conveniently, configured to keep the interaction between the two signals OS and OS under control, for the purpose of reaching a condition of stable control.

[0108] The operation of the embodiments of FIGS. 3 and 4 is similar to that described for the embodiment of FIG. 1, with the exception that the relations that enable the control means 8 to determine the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V between the flow rates of the liquid-phase exchange fluid and of the vapor-phase exchange fluid which pass through the regenerative exchanger 7 change, so as to calculate the temperature value of the vapor-phase exchange fluid in input to the regenerative exchanger 7 T.sub.Vin, if the fourth temperature sensor 15 is not present or cannot be installed in the apparatus.

[0109] In particular, in the embodiment of FIG. 3, the control means 8 proceed to calculate the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V from the general formula obtained for the diagram of FIG. 8 i.e:

[00025]$\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}=\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}$

[0110] This formula makes it possible to determine the limit values of the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V and, in the embodiment of FIG. 3, when the bypass line 2c is closed by acting on the second adjustment valve 10, we have:

[00026]$K_{v,L}=K_{v,\mathrm{MAX}};K_{v,\mathrm{BP}}=0$

obtaining from the formula:

[00027]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{MAX},\mathrm{Emb}.\mathrm{Fig}\text{.3}}=\underset{\underset{K_{v,\mathrm{BP}}.fwdarw.0}{K_{v,L}.fwdarw.K_{v,\mathrm{MAX}}}}{\lim }\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}=1$

while, when the section of the liquid line 2a that passes through the regenerative exchanger 7 is closed, again by acting on the second adjustment valve 10, we have:

[00028]$K_{v,L}=0;K_{v,\mathrm{BP}}=K_{v,\mathrm{MAX}}$${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{MIN},\mathrm{Emb}.\mathrm{Fig}\text{.3}}=\underset{\underset{K_{v,\mathrm{BP}}.fwdarw.K_{v,\mathrm{MAX}}}{K_{v,L}.fwdarw.0}}{\lim }\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}=0$

obtaining from the formula:
which confirms that, in the embodiment of FIG. 3, {dot over (m)}.sub.L can assume values between zero and {dot over (m)}.sub.V, as shown by the graph of FIG. 6.

[0111] With reference, instead, to the embodiment of FIG. 4, to calculate the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V between the flow rates of the liquid-phase exchange fluid and of the vapor-phase exchange fluid which pass through the regenerative exchanger 7 we still start from the general formula, considering however that, in this particular case, the bypass line is as if it were always open without offering any resistance.

[0112] Therefore, in the embodiment of FIG. 4, we have:

K.sub.v,BP.fwdarw.

and as a consequence the general formula for calculating the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V becomes:
from which we can obtain the limit values, minimum and maximum, of the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V in the embodiment of FIG. 4.

[0113] In particular, in the embodiment of FIG. 4, when the second MO

[00029]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{Emb}.\mathrm{Fig}\text{.4}}=\underset{K_{v,\mathrm{BP}}.fwdarw.}{\lim }\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}=\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}}}{C_{\mathrm{BP}}}}}$

adjustment valve 10 is closed, we have:

K.sub.v,L=0

such that:

[00030]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{MIN},\mathrm{Emb}.\mathrm{Fig}\text{.4}}=\underset{K_{v,L}.fwdarw.0}{\lim }\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}}}}=0$

while, by contrast, when the second adjustment valve 10 is open to the maximum, we have:

K.sub.v,L=K.sub.v,MAX

such that:

[00031]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{MAX},\mathrm{Emb}.\mathrm{Fig}\text{.4}}=\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,\mathrm{MAX}}^2}}{C_{\mathrm{BP}}}}}<1$

confirming that, in the embodiment of FIG. 4, 111 can assume values between zero and a limit value less than {dot over (m)}.sub.V, as shown in the graph of FIG. 7.

[0114] Turning now to the embodiment of FIG. 2, in this case the adjustment is simplified, as we can act on the expansion valve 9 only and adjust only the efficiency of the regenerative exchanger 7 on a reference value or set-point value.

[0115] With this embodiment, the control means 8 operate on the basis of three parameters, since, there being no second adjustment valve 10 to vary the flow of the liquid-phase exchange fluid that passes through the regenerative exchanger 7, the two flow rates of the liquid-phase exchange fluid and of the vapor-phase exchange fluid that pass through the regenerative exchanger 7 are always the same, which is why, in this case, it is always the vapor-phase exchange fluid that has the maximum jump in temperature and, as a consequence, the efficiency of the regenerative exchanger can be determined from:

[00032]$=\frac{T_{\mathrm{Vout}}-T_{\mathrm{Vin}}}{T_{\mathrm{Lin}}-T_{\mathrm{Vin}}}$

[0116] The temperature value of the vapor-phase exchange fluid in input to the regenerative exchanger 7 (T.sub.Vin) can be calculated by the control means 8 using the formula:

[00033]$T_{\mathrm{Vin}}=T_{\mathrm{Vout}}-\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\frac{c_{\mathrm{PL}}}{c_{\mathrm{PV}}}\left(T_{\mathrm{Lin}}-T_{\mathrm{Lout}}\right)$

using the measurement of the temperature value of the liquid-phase exchange fluid in output from the regenerative exchanger 7 (T.sub.Lout) provided by the third temperature sensor 13 and considering that in this case {dot over (m)}.sub.L/{dot over (m)}.sub.V=1.

[0117] In fact, if we wished to apply the general formula for calculating the ratio {dot over (m)}.sub.L/{dot over (m)}.sub.V, then, in the embodiment of FIG. 2, no second adjustment valve 10 is present along the section of the liquid line 2a that passes through the regenerative exchanger 7, and so it is as if on the section L of the diagram of FIG. 8 there were present a hypothetical valve, always open, without offering any resistance, such that:

K.sub.v,L.fwdarw.

and, furthermore, the bypass line is also absent, such that the hydraulic characteristic of the branch BP is as if it were infinite, i.e:

C.sub.BP.fwdarw.

with the consequence that, for any value of C:

[00034]${\left(\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}\right)}_{\mathrm{Emb}.\mathrm{Fig}\text{.2}}=\underset{\underset{K_{v,L}.fwdarw.}{C_{\mathrm{BP}}.fwdarw.}}{\lim }\frac{{\stackrel{.}{m}}_L}{{\stackrel{.}{m}}_V}=\underset{\underset{K_{v,L}.fwdarw.}{C_{\mathrm{BP}}.fwdarw.}}{\lim }\frac{1}{1+\sqrt{\frac{C_L+\frac{1}{{}_L^2{K}_{v,L}^2}}{C_{\mathrm{BP}}+\frac{1}{{}_L^2{K}_{v,\mathrm{BP}}^2}}}}=\frac{1}{1}=1$

such that the formula confirms that, in the embodiment of FIG. 2, {dot over (m)}.sub.L={dot over (m)}.sub.V.

[0118] In practice, in this embodiment, the value of the instantaneous efficiency or real efficiency (.sub.real) of the regenerative exchanger 7 is obtained by the control means 8 by way of the measurement, supplied by the pressure sensor 14, of the pressure value of the exchange fluid in output from the evaporator p.sub.EVout or, alternatively, in input to the compressor 4 (said pressure value making it possible, if the superheating is nil, to directly obtain T.sub.Vin, otherwise the measurement of T.sub.Lout), the temperature of the vapor-phase exchange fluid in output from the regenerative exchanger 7 and in input to the compressor 4 T.sub.Vout, and the temperature of the liquid-phase exchange fluid in input to the regenerative exchanger 7 T.sub.Lin are also required.

[0119] In this case too, the reference efficiency or set-point efficiency (.sub.set) is calculated by the control means 8 by setting a preset value for the superheating at the evaporator, as explained previously.

[0120] Given that, according to the -NTU theory, in the embodiment of FIG. 2, the efficiency of the regenerative exchanger 7 is a function solely of the flow rate of the exchange fluid that passes through the circuit 2, since this corresponds to the value of the flow rate of the liquid-phase exchange fluid that passes through the regenerative exchanger 7, i.e. =({dot over (m)}), then in the embodiment of FIG. 2, by varying the opening of the expansion valve 9 it is possible to vary the flow rate of the exchange fluid that passes through the regenerative exchanger 7, so that the instantaneous efficiency .sub.real reaches the value of the reference efficiency .sub.set.

[0121] In particular, in the embodiment of FIG. 2, the control means 8, based on the calculated value of the difference between the instantaneous efficiency and the reference efficiency of the regenerative exchanger 7, generate a command signal OS.sub.1 to control the degree of opening of the expansion valve 9, so as to be able to vary the flow rate of the exchange fluid that passes through the regenerative exchanger 7 and therefore the efficiency of said regenerative exchanger.

[0122] More specifically, in the embodiment in FIG. 2, if the control means 8 detect that the instantaneous efficiency is less than the reference efficiency, they send a command signal OS.sub.1 to the expansion valve 9 to reduce the degree of opening of said expansion valve and consequently reduce the flow rate {dot over (m)} of the exchange fluid that passes through the circuit 2 and therefore the regenerative exchanger 7, until the value of the instantaneous efficiency is brought to the value of the reference efficiency.

[0123] Also in the embodiment of FIG. 2, if instead the control means 8 detect that the instantaneous efficiency is greater than the reference efficiency, they send a command signal OS.sub.1 to the expansion valve 9 to increase the degree of opening of said expansion valve, so as to increase as a consequence the flow rate 1 ml of the exchange fluid that passes through the circuit 2 and so bring the instantaneous efficiency to the same value as the reference efficiency.

[0124] In practice it has been found that the disclosure fully achieves the intended aim and objects and in particular attention is drawn to the fact that the apparatus according to the disclosure makes it possible to keep the superheating of the exchange fluid at the evaporator within a minimum range, preferably between 0 and 5 K and more preferably between 0 and 3 K.

[0125] It must also be emphasized that the disclosure, by virtue of the type of adjustment used, which is based on the calculation of the difference between the instantaneous thermal efficiency of the regenerative exchanger and a reference efficiency of said regenerative exchanger, makes it possible to obtain a more efficient use of the exchange area of the evaporator and of the condenser, in particular under partial workload conditions. This brings a benefit with an increase in the seasonal efficiency of the refrigeration cycle.

[0126] The disclosure thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.

[0127] In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and to the state of the art.