IT201900010572A1 - IMPROVED REFRIGERATION SYSTEM - Google Patents

Description

DESCRIPTION

of the invention entitled:

"Improved refrigeration system"

The present invention relates to an improved refrigeration system, in particular of the type which uses CO2 as the refrigerant fluid.

For some years the most advanced cooling systems have been using CO2 as a coolant. In particular, in these known systems (see fig. 1), the refrigerant fluid is compressed by a compressor 90, thus causing an increase in its pressure P and consequently in its temperature T, and subsequently, inside an exchanger heat at high pressure 91, the refrigerant fluid cools by exchanging heat with the air of the external environment. Normally a regulating valve 95 maintains the pressure in the tank 93 at a determined level. Subsequently, the refrigerant fluid is made to expand through a valve 92 inside a tank 93 thus reducing its pressure and temperature. Subsequently, the refrigerant fluid enters an evaporator 94 where it heats up by absorbing the heat from the air of the external environment and / or from an external body, which are therefore cooled.

However, these known plants are not fully satisfactory since CO2, although a gas that is simple to produce and use, in particular thanks to its non-toxicity and non-flammability, has thermodynamic properties that are not completely satisfactory for use in refrigeration systems. In particular, the critical temperature (Tc), i.e. the temperature above which condensation does not occur, is rather low, and in particular it is about 30-31 ° C, while its critical pressure (Pc), i.e. the pressure necessary to liquefy the gas at Tc is quite high, and in particular it is about 74bar.

In particular, given that in traditional systems the cooling of the CO2-based refrigerant fluid occurs mainly inside the high pressure exchanger 91 through a heat exchange with the outside air, on the hottest days these systems are found to work in conditions transcritical. This means that, if the external ambient temperature is higher than the critical CO2 temperature, a common situation in summer and / or in the hottest regions, the CO2 refrigerant fluid, even after having cooled down through the passage in the high pressure exchanger 91 , remains at a temperature higher than the critical one, and therefore remains in the gaseous state, without passing into the liquid, thus drastically reducing the efficiency of the refrigeration cycle compared to known systems in which synthetic refrigerant fluids or ammonia are used.

To remedy this drawback, various measures have already been proposed and, in particular, a method for recovering the expansion energy by means of an ejector, or with expanders, has been proposed (see G. Lorentzen, 1984).

However, these known methods are particularly expensive and sophisticated. Furthermore, in any case, all known systems have an upper limit to the ambient temperature at which the system itself can operate, as indeed for all refrigerant fluids. In fact, known plants are hardly capable of operating efficiently with particularly high ambient temperatures, for example above 40 ° C.

Cooling systems are known which provide for the accumulation of cold during the night hours, however, these are not fully satisfactory as they require an important consumption of energy to bring the second refrigerant fluid to a low temperature, and moreover, over time the second fluid tends anyway to warm up. Generally, this type of system can also be used efficiently up to external temperatures of about 40 ° C.

Plants are also known which make use of the mechanical subcooling process by means of a further separate refrigeration circuit. Basically, the refrigerant fluid leaving the condenser is further cooled by heat exchange with a refrigerant fluid circulating in a further refrigeration circuit. These systems are constructively more expensive and, moreover, require additional energy, supplied from the outside, to operate said additional refrigeration circuit. Generally this type of systems can be used up to outside temperatures of about 45 ° C.

The purpose of the invention is to propose a refrigeration system which overcomes the drawbacks of traditional solutions and which has a high efficiency even when the temperature in the installation environment of the system is particularly high, for example it is higher than about 40 ° C, even up to 50 ° C and above.

Another purpose of the invention is to propose a refrigeration system which accumulates heat during the coldest hours of the day and which then uses the heat thus accumulated during the hottest hours of the day.

Another purpose of the invention is to propose a circuit that has a high efficiency even using carbon dioxide as a refrigerant.

Another purpose of the invention is to propose a refrigeration system that allows to reduce energy consumption compared to traditional systems.

Another purpose of the invention is to propose a refrigeration system that has a high efficiency for all 24 hours of a day.

Another purpose of the invention is to propose a refrigeration system that uses heat transfer fluids that are non-polluting and easy to find.

Another purpose of the invention is to propose a highly flexible refrigeration system that can adapt promptly, correctly and independently to variations, even significant ones, of its operating conditions of use.

Another purpose of the invention is to propose a refrigeration system that is easily implemented and with low costs.

Another purpose of the invention is to propose a refrigeration system that is an alternative and / or improvement to the known systems.

Another purpose of the invention is to propose a refrigeration system that uses the day / night cycle to reduce energy consumption.

All these purposes, either alone or in any combination thereof, and others that will result from the following description are achieved, according to the invention, with a refrigeration system as defined in claim 1.

The present invention is further clarified hereinafter in some of its preferred embodiments reported for purely illustrative and non-limiting purposes with reference to the attached drawings, in which:

Figure 1 schematically shows a refrigerant circuit according to the state of the art,

Figure 2 shows a schematic view of the refrigeration system according to the invention in a first embodiment,

Figure 3 shows an entropic diagram of the first fluid circulating in the first circuit of the refrigeration system in fig. 2,

Figure 4 shows the exemplary trend of the external load to which the refrigeration system is subjected according to the invention during the 24 hours of a day,

Figure 5 shows an exemplary trend of the ambient temperature during the 24 hours of a day,

figure 6 shows in the same graph the trends, during the 24 hours of a day, of the load of fig. 4 (normalized with respect to the maximum daily load) and the temperature of fig. 5 (normalized to the maximum daily temperature),

Figure 7 shows a schematic view of the refrigeration system according to the invention in a second embodiment,

Figure 8 shows a schematic view of the air heat exchanger that can be used in the system of fig. 7,

Figure 9 schematically shows some variants implemented / implementable in the refrigeration system according to the invention.

As shown in Figure 2, the refrigeration system according to the invention, indicated as a whole with the reference 100, comprises: - a first refrigeration circuit 1 inside which a first refrigerant fluid flows, preferably CO2, and

- means configured to cause a first heat exchange between the first fluid circulating in the first circuit 1 and a second fluid, and at least a second heat exchange between said second fluid and a PCM phase change material (from the English "Phase change Material" ), i.e. of a material capable of accumulating and releasing heat thanks to the transition of state from the solid to the liquid phase, and vice versa.

Preferably, within the first circuit 1 CO2 circulates in the liquid state, in the vapor state and in the gaseous state, where the gaseous state means a state of dense gas, i.e. the state that the carbon dioxide CO2 assumes at a temperature higher than that criticism Tc.

Conveniently, as shown in fig. 2 and 9, said means for causing said first and second heat exchange can comprise a second fluid circulating in a second circuit 40 and a heat exchanger 22 in which said first heat exchange occurs between the first fluid circulating in the first circuit and the second fluid circulating in said second circuit 40. Conveniently, the second circuit 40 is also configured to cause at least a second heat exchange between said second fluid circulating in said second circuit 40 and a PCM phase change material present in the container 42 provided in said second circuit.

In particular, in this case, the second fluid circulating in the second circuit 40 can be any type of fluid that can be used for transporting heat, for example water, or a mixture of water and glycol or another fluid with a high thermal capacity. Preferably, the second fluid circulating in the second circuit 40 is water or another high thermal capacity fluid. Preferably, within the second circuit 40 the second fluid always and only circulates in the liquid state in order to maximize the heat capacity per unit of volume, or alternatively it can be air.

In addition and / or alternatively to said second circuit 40, as shown in fig. 7 and 8, said means for causing said first and second heat exchange can comprise an apparatus 25 comprising: - a first block 26 containing a PCM material and in which the heat exchange takes place between a second fluid and said PCM material.

- a second block 28 in which the heat exchange takes place between the first fluid circulating in the first circuit 1 and the second fluid coming from the first block 26.

In particular, in this case, the second fluid is the ambient air 29 which enters the first block 26 and which, after exchanging heat - cooling itself - with the PCM material inside said first block, enters the second block 28 where absorbs heat from the first refrigerant fluid. Conveniently, for this purpose, the first circuit 1 includes a section 68 that crosses said second block 28. Furthermore, suitably, the equipment 25 is configured so that the air can pass from the first block 26 to the second block 28.

Conveniently, the PCM material in the container 42 and / or in the equipment 25 can be organic, inorganic or hybrid, and preferably they are organic materials. The PCM material can comprise a derivative of paraffin, or other hydrocarbons and / or lipids, or hydrated salts, or inorganic eutectics, preferably at low melting temperatures.

Conveniently, the PCM material has a melting temperature (i.e. the temperature at which it passes from the solid to the liquid phase, and therefore accumulates heat while maintaining its temperature constant) which is lower than the maximum temperature that the air of the external environment TA it can reach, in a hot period / day of the year, during the coldest / coolest hours (that is, preferably during the night). Conveniently, as described in more detail below, in this way it is then possible to cool, during the hottest hours, the first refrigerant fluid leaving the high-pressure exchanger 4 and thus bring it to the temperature at which it could cool down during the night.

The first circuit 1 includes a compression unit 2 comprising at least one compressor 2 'and / or 2'. Preferably, when a variable refrigeration load is provided, the compression unit 2 can comprise a plurality of compressors in parallel with each other and configured so as to suck the first fluid in the vapor state 60 at the outlet from the evaporation unit 16.

The compression unit 2 is configured to suck and compress the first fluid, in the vapor state 62, which comes out of an evaporation unit 16 provided in said first circuit. In particular, the compression unit 2 is configured to increase - in a substantially isentropic and / or adiabatic way, as shown in the passage A-B of figure 3 - the initial pressure P1 (at the temperature T1-F1 of point A in figure 3) up to to bring it to a pressure P2 (at the temperature T2-F1 of point B in figure 3).

Conveniently, the compression of the first fluid carried out by the compression unit 2 causes an increase in the temperature of the fluid itself, and in particular the transition from the initial temperature T1-F1 to a temperature T2-

F1 which can also be about 120 ° C or more.

The first circuit 1 comprises at least one unit, for cooling the refrigerant fluid, which is connected downstream of the compression unit 2. In particular, the discharge port of the compression unit 2 is connected to the inlet of the unit cooling.

Preferably, the cooling unit comprises at least one high-pressure heat exchanger 4 which is configured so that the first high-pressure vapor state fluid 60 - as compressed by the compression unit 2 - is cooled and brought in the liquid or dense gas state.

In particular, in the high pressure exchanger 4 the first fluid cools by exchanging heat with the air present in the external environment. More in detail, the high pressure exchanger 4 is configured to allow a heat exchange between the first fluid (which is at the temperature T2-F1) and the air of the external environment (which is at a temperature TA which is lower than at the temperature T2-F1 of the first fluid entering the high pressure exchanger 4). Basically, by releasing heat to the air of the external environment (which thus heats up), the first fluid cools and its temperature decreases thus passing from T2-F1 to T3-F1 (corresponding to point C in Figure 3).

Conveniently, the temperature T3-F1 of the first fluid leaving the high-pressure exchanger 4 is slightly higher (at the same limit) than that of the air in the TA environment in which the exchanger itself and / or the entire system is installed. 100.

The first circuit 1 also comprises a first expansion valve 10 which is interposed between the outlet of the high pressure exchanger 4 and a first tank 12 which contains inside it the first fluid both in the liquid state 61 and in the vapor state 60. Conveniently, the first expansion valve 10 is configured to allow the first fluid leaving the high pressure exchanger 4 (and which has therefore been cooled and brought to the temperature T3-F1) to expand and, in particular, is configured to decrease the pressure of said first fluid until an intermediate pressure P3 is reached inside the first tank 12.

Preferably, the first expansion valve 10 is automatically controlled by an electric actuator. Advantageously, the pressure P3 of the first fluid inside the first tank 12 can be controlled:

- by means of a pressure regulating valve 14 'which is interposed between the compression unit 2 and the portion of the first tank 12 containing the first fluid in the vapor state 60, and / or

- by at least one dedicated compressor 2 '' which is provided inside the compression unit 2 and which is configured to work at a different (higher) suction pressure than that of the other compressor 2 'or of the other compressors of the unit itself.

Preferably, the pressure regulating valve 14 'is automatically controlled by an electric actuator. Conveniently, moreover, the contribution of the dedicated compressor 2 '' can be controlled by opening or closing a corresponding valve 14 provided between the inlet of the dedicated compressor 2 '' and that of the other compressor / s 2 '.

Conveniently, as mentioned, the fluidic connection between the first tank 12 and the suction port of the compression unit 2 is defined by a duct 15 which is associated with the first tank 12 so as to mainly collect the vapor 60 of the first fluid present in the latter, that is, it is positioned substantially in correspondence with the upper portion of the first tank 12.

Furthermore, the first evaporation unit 16 comprises at least one evaporator and is fluidically connected upstream with the portion of the first tank 12 containing the first fluid in the liquid state 61 and downstream with the inlet of the compression unit 2. Conveniently, the first evaporation unit 16 is fed with the first liquid in the liquid state 61, present in the first tank 12, by means of a section which is provided with a suitable control valve 17.

Conveniently, the pressure P1 of the first fluid entering the compression unit 2 substantially corresponds to the pressure of the first fluid leaving the first evaporation unit 16.

Conveniently, in the first evaporation unit 16, the first fluid in the liquid state 61 and at pressure P3 (corresponding to the pressure present inside the first tank 12) absorbs heat and becomes vapor. In particular, in the first evaporation unit 16 the first fluid evaporates by absorbing heat from the air to be cooled. Basically, by absorbing the heat from the air of the external environment (which thus cools it), the first fluid evaporates at a constant temperature, passing from the liquid state to the vapor state.

Conveniently, in an embodiment not shown here, a further evaporation unit can be provided comprising at least one evaporator configured to operate at a lower evaporation pressure. More in detail, said further evaporation unit is connected at the inlet to the zone of the first tank 12 containing the first fluid in the liquid state 61 and at the outlet connected to the zone of the circuit containing the first fluid in the vapor state 62. Furthermore, at the inlet an expansion valve is provided for said further evaporation unit, which is preferably controlled on the basis of superheating. Furthermore, at the outlet of said further evaporation unit there is a compressor configured to compress the steam leaving said unit until it reaches the intermediate pressure of the vapor present in the suction of the compressors 2.

As is known, for a first circuit 1 of the type described above, the efficiency of the refrigeration cycle depends on the temperature TA of the air of the external environment which, inside the high pressure exchanger 4, cools the first fluid (i.e. absorbs the heat released by the first refrigerant fluid).

In particular, based on the time of day and / or the period / season of the year and / or the geographical location and atmospheric conditions in which the refrigeration plant 100 is installed, the ambient air temperature TA external changes, for example according to the trend illustrated in fig. 5. More in detail, during the night the TA temperature is lower (typically about 10 ° C), compared to that reached during the central hours of the day (for example between 12-16).

Considering that generally the efficiency of a refrigeration circuit decreases as the temperature of the refrigerant fluid that leaves the cooling unit (i.e. from the high-pressure exchanger 4) increases, the efficiency of the circuit is minimal given that the temperature of the refrigerant fluid (and therefore its thermal load) is particularly high and this is precisely due to the fact that, inside the high pressure exchanger 4, the fluid temperature is not adequately cooled by the air from the external environment.

Conveniently, to solve this drawback the plant 100 according to the invention comprises means 40, 25 configured to cause:

- a first heat exchange between the first fluid circulating in the first circuit 1 and a second fluid, e

- at least a second heat exchange between said second fluid and a PCM phase change material.

As said, in the embodiment illustrated in figures 2 and 9, said means can comprise a second circuit 40 within which the second fluid flows.

Conveniently, in this case, the plant 100 comprises, between the high-pressure exchanger 4 and the expansion valve 10 of the first circuit 1, a first heat exchanger 22 in which the exchange of thermal energy between the first circulating fluid takes place in the first circuit 1 and the second fluid circulating in the second circuit 40.

Conveniently, the exchange of thermal energy between the first fluid in the liquid state that comes out of the high pressure exchanger 4 at the temperature T3-F1 takes place inside the first heat exchanger 22.

Advantageously, the first circuit 1 comprises a first branch 20 which crosses the first heat exchanger 22 and which is parallel with respect to the section 19 (of the first circuit) which directly connects the outlet of the high-pressure exchanger 4 with the first expansion valve 10.

Conveniently, the first branch 20 has two valves 21 and 23, positioned respectively upstream and downstream of the crossing of the first heat exchanger 22. Furthermore, suitably, in the section 19 in parallel with the first heat exchanger 22 a valve is provided 18. Conveniently, the valves 18, 21 and 23 are controlled so as to allow the passage of the first fluid either inside the section 19 (closing the valves 21 and 23, and opening the valve 18) or inside the first branch 20 (closing valve 18 and opening valves 21 and 23).

Preferably, the second fluid that flows / circulates in the second circuit 40 is water or in any case a fluid with a high thermal capacity. Preferably, within the second circuit 40, the second fluid is in the liquid state, to obtain a maximum heat capacity per unit of volume, obviously maintaining the ability to flow within the circuit unchanged.

Advantageously, the second circuit 40 comprises a container 42 containing the PCM material capable of accumulating heat thanks to the transition of state from the solid to the liquid phase.

Conveniently, in the embodiment of fig. 2, the container 42 is crossed by the second fluid circulating in the second circuit 40 so as to exchange heat with the PCM material contained in said container 42. In particular, the container 42 is configured so that, inside it, the second fluid exchanges heat with the PCM material, and this without ever coming into direct contact with each other.

Downstream of the container 42 there is a pump and / or compressor 41 to circulate the second fluid inside the second circuit 40. In particular, a pump is provided if the second fluid is a liquid (for example water) , or a fan if the second fluid is air or another gas.

The second circuit 40 also comprises, downstream of the pump and / or compressor 41, a three-way valve 44 which receives the second fluid coming from the container 42 at its inlet to direct it to the outlet alternatively:

- to a first branch 38 which crosses the first heat exchanger 22 and then returns inside the container 42,

- to a second branch 39 which crosses a second high pressure exchanger 46 and then returns inside the container 42.

Conveniently, in the first heat exchanger 22, the first fluid leaving the high pressure exchanger 4 (and therefore circulating in the first circuit 1) exchanges heat with the second fluid leaving the container 42 (and therefore circulating in the second circuit 40).

Conveniently, inside the first heat exchanger 22, the first and second fluids can transit, in their respective sides, in equi- or counter-current and preferably transit in counter-current in order to improve heat exchange.

Advantageously, therefore, the first fluid, in addition to being cooled by the air of the external environment inside the high pressure exchanger 4, is further cooled by transferring heat - inside the first heat exchanger 22 - to the second fluid coming from the container 42. Conveniently, said second fluid which enters and passes through the heat exchanger 22 is at a temperature T1-F2 which is lower (i.e. colder) than the temperature T3-F1 of the first fluid which, exiting the heat exchanger at a high pressure 4, crosses the other side of the exchanger and this against the fact that, inside the container 42, the second fluid has transferred heat to the PCM material, which, by heating up, has thus at least partially passed from the solid phase to the liquid (i.e. it has melted).

More in detail, suitably, the second fluid leaving the first exchanger 22 - which has been heated to the temperature T2-F2 following the absorption of the heat released by the first fluid - enters the container 42 where it transfers heat to the PCM material and, therefore , then leaves the container 42 at a temperature (T1-F2) which is suitably lower (and in any case suitable for heat exchange) than that (T3-F1) of the first fluid leaving the high pressure exchanger 4.

In particular, for example when the air temperature TA of the external environment is about 45 ° C (i.e. during the hottest daytime hours), the first fluid of the first circuit 1 can first be cooled inside the heat exchanger at high pressure 4 up to about 50 ° C and then it can be further cooled following the passage through the first exchanger 22 up to about 35 ° C. Preferably, in this case, the use of a PCM material with a high ability to absorb latent heat at about 28-30 ° C is envisaged.

Conveniently, in the second high pressure exchanger 46 the second fluid circulating in the second circuit 40 exchanges heat with the external environment. Preferably, said second high-pressure exchanger 46 can be provided with a fan.

In particular, when the second fluid enters the second branch 39, it cools inside the third high-pressure exchanger 46, releasing heat to the air of the external environment and then, entering the container, absorbs / receives the heat of the PCM material which, on cooling, thus passes at least partially from the liquid phase to the solid phase (i.e. solidifies).

For example, when the temperature TA of the air of the external environment is lower than about 28 ° C (i.e. during the night hours), the second fluid of the second circuit 40 is diverted by the valve 44 into the second branch 39 to thus cross the third high pressure exchanger 46; suitably, inside the latter, the second fluid cools by giving heat to the air of the external environment (which then heats up) and then reenters inside the container 42 where it absorbs the heat of the PCM material, thus causing the solidification of the latter.

Advantageously, the system 100 comprises a control unit (not shown) which acts on the second circuit 40 to make it work alternately in two different modes, and in particular:

- a first mode in which the second fluid leaving the container 42 enters the first branch 38 and therefore passes through the first exchanger 22, - a second mode in which the second fluid leaving the container 42 enters the second branch 39 and therefore crosses the second high pressure exchanger 46.

Conveniently, the second circuit 40 operates in said first mode during a first period of time (preferably during the day), while it operates in said second mode during a second period of time (preferably during the night). Conveniently, said first period of time and said second period of time are defined / expected within the same day (i.e. within 24 hours).

Conveniently, in said second operating mode, the second fluid substantially disposes of the heat accumulated by the PCM material during the first operating mode. Therefore, in essence, the second branch 39 substantially defines a disposal sub-circuit (defined as a whole with the reference "59") of the heat accumulated by the PCM material during the first operating mode.

Advantageously, the control unit controls the operation of the second circuit 40 in the first or second mode by correspondingly acting on the three-way valve 44. In particular, said control unit is configured to control the three-way valve 44 so that: - above a certain predefined temperature TA1 of the air of the external environment (for example during the hottest hours of a day), the second circuit works in said first mode; in particular, said valve 44 is switched so as to interrupt the connection with the second branch 39 to thus circulate the second fluid leaving the container 42 in the first branch 38,

- below a certain predefined temperature TA2 of the air of the external environment (for example during the night), the second circuit works in said second mode; in particular, said valve 44 is switched so as to interrupt the connection with the first branch 38 in order to circulate the second fluid leaving the container 42 in the second branch 39.

Preferably, the predefined temperature TA1 is equal to or higher than about 40-50 ° C.

Preferably, the predefined temperature TA2 is equal to or lower than the solidification temperature of the PCM material contained in the container 42. For example, the predefined temperature TA2 is set at approximately 28 ° C if a PCM material is used which has a solidification temperature of approximately 30 ° C or higher.

Basically, the operation of the system according to the invention is clearly evident from what has been described and, in particular, has two different modes of operation, one during the first period (daytime hours) and one during the second period (nighttime hours).

In particular, with reference to Figures 2 or 9, when the external ambient air temperature TA is lower than a predefined limit TA2 (and this preferably occurs during the second period of the day), the pump 41 (or the fan) is activated and the valve 44 is switched to circulate the second fluid leaving the container 42 in the second branch 39 and through the second high-pressure exchanger 46. Conveniently, in this way, the second fluid circulating in the second branch 39 is cooled until at a slightly higher temperature than the ambient air temperature. Subsequently, therefore, the second fluid returns to the container 42 where it cools the PCM material and thus causes the solidification of the latter (which conveniently occurs at a substantially constant temperature).

When the external ambient air temperature TA is higher than a predefined temperature limit TA1 (and this preferably occurs during a first period of the day), the pump 41 (or the fan) is activated and the valve 44 is switched to circulate the second fluid leaving the container 42 in the first branch 38 and thus make it pass through the first heat exchanger 22. Furthermore, the control unit conveniently switches the opening of the valves 21 and 23, and the closing of the valve 18 , to thus force the first high-pressure fluid leaving the high-pressure exchanger 4 to pass through the first heat exchanger 22.

Conveniently, inside the high-pressure exchanger 4, the air of the external environment at temperature TA (for example about 40 ° C) cools the first fluid up to, for example, bringing it to a temperature of about 45 ° C and, subsequently as it passes through the first exchanger 22, said first fluid is further cooled.

Advantageously, in addition or as an alternative to the first sub-circuit 59 - which is defined by the branch 39 with the second high-pressure exchanger 46 - for the disposal of the heat accumulated by the PCM material of the container 42, a second sub-circuit is provided for disposal of said heat (indicated as a whole with reference 54).

Preferably, therefore, the plant 100 can comprise the aforementioned second sub-circuit 54 for disposing of the heat accumulated by the PCM material of the container 42 and this in order to manage a situation in which the temperature of the external ambient air TA does not drop. never (i.e. not even during the second period, i.e. at night) below the predefined value TA2 (which preferably substantially corresponds to the solidification value of the PCM material) and, therefore, the operation of the second circuit 40 in the second mode does not start ( that is, the first disposal sub-circuit 59 which is defined by the branching 39 with the second high-pressure exchanger 46) is not activated / used.

In particular, advantageously, this second sub-circuit 54 comprises a third heat exchanger 53 in which there is an exchange of thermal energy between the first fluid (circulating in the first circuit 1) leaving the high pressure exchanger 4 and the second fluid coming from said container 42. Preferably, said third heat exchanger 53 is in countercurrent.

Conveniently, the first fluid, after passing through said third heat exchanger 53, returns to the first tank 12. Advantageously, between the outlet of the high pressure exchanger 4 and said further heat exchanger 53 an expansion valve 52 is provided.

Conveniently, the second fluid, after passing through said third heat exchanger 53, returns to the container 42. Advantageously, the circulation of the second fluid through said third heat exchanger 53 is obtained by operating a corresponding pump 51 provided in a corresponding section of inlet / outlet circuit to said third heat exchanger 53.

Preferably, the expansion valve 52 can be controlled so as to have a predetermined superheat at the inlet of the first fluid inside the first tank 12.

Conveniently, in said second disposal sub-circuit 54, the second fluid from the container 42 is cooled inside said third heat exchanger 53, giving heat to the first fluid that leaves the high-pressure exchanger 4. Then, therefore, the second fluid returns to the container 42 where it cools the PCM material and thus causes the latter to solidify. Basically, in this way, the PCM material transfers the previously accumulated heat to the second fluid and, suitably, said second fluid then transfers the heat - inside said third exchanger 53 - to the first fluid.

Conveniently, if (during operation in said second mode) it is foreseen that during subsequent operation in said first mode it will not be possible to accumulate sufficient heat in the PCM material, valve 14 can be closed and compressor 2 '' operated to cool thus - through the second disposal sub-circuit 54 and through said third heat exchanger 53 - the second fluid and the PCM material present in the container 42. In this case, there is a consumption of electrical energy for the operation of the compressor 2 '', however, the system 100 is in any case more efficient because the heat transfer temperature, and therefore the high pressure, will be lower than during the day (i.e. during the first period of the day), and therefore the system will work with greater efficiency.

Conveniently, in the embodiment shown in Figures 7 and 8, the plant 100 substantially has all the characteristics described above with the exception of the fact that in the apparatus 25 the heat exchange takes place between the first fluid and the air of the external environment, after the latter has been cooled by the PCM material. Basically, in this embodiment, the air of the external environment corresponds to the second fluid which, in the embodiment of fig. 2 and 9, circulates in the second circuit 40.

Conveniently, the operation of the system 100 of fig. 7 essentially remains the one described above and, in particular, the control unit acts on the equipment 25 to make it work alternately in two different modes, and in particular:

- a first mode - which operates during a first period of time (preferably during the daytime) - in which the air of the external environment, after exchanging heat in the first block 26 to regenerate the PCM material (in particular by cooling it), then enters the second block 28 to further cool the first fluid leaving the high pressure exchanger 4,

- a second mode - which operates during a second period of time (preferably during the night) - in which the air passes through only the first block 26 to thus dispose of the heat accumulated by the PCM material contained in said block.

In particular, preferably, the apparatus 25 is configured so that, in said first operating mode, there is a passage for the air between the first block 26 and the second block 28, while in said second operating mode this passage for air is blocked.

Advantageously, during the operation of the apparatus 25 in said first mode, the control unit switches the opening of the valves 21 and 23, and the closing of the valve 18, to thus force the first high-pressure fluid leaving the exchanger to high pressure 4 to enter the section 68 to thus pass through the second block 28 of the apparatus 25.

Conveniently, during the operation of the apparatus 25 in said second mode, the control unit switches the closure of the valves 21 and 23, and the opening of the valve 18, to thus force the first high-pressure fluid leaving the exchanger to high pressure 4 ad immediately passes through the expansion valve 10, without passing through the apparatus 25. However, advantageously, even during operation in said second mode and in particular below a certain predefined temperature TA2 of the air of the external environment (for example during the night), the control unit can switch the opening of the valves 21 and 23, and the closing of the valve 18, to thus force the first high-pressure fluid out of the high-pressure exchanger 4 to enter the section 68 to thus pass through the second block 28 of the apparatus 25, and thus improve the cooling of the first fluid by means of heat exchange with the air d in the external environment (air that is "fresh" given that it is below a certain predefined temperature TA2, for example about 28 ° C).

In a variant of the system 100, represented in Figure 9, the second circuit 40 is configured in such a way as to avoid corrosion problems of the pipes of the circuit itself in case of breakage of the containers (capsules) which, inside the container 42, contain the PCM material. In particular, the PCM material is generally not toxic, however it can be corrosive towards the materials, generally metallic, that make up the circuit.

In particular, for this purpose, the second circuit 40 comprises a sub-circuit 49 in which a third fluid flows which exchanges heat with the PCM material contained in the container 42 and which can be of the same or different type with respect to said second fluid which flows in the rest. part of the second circuit 40. For example, the third fluid circulating in the sub-circuit 49 can be water or another high heat capacity fluid.

Conveniently, said sub-circuit 49 is connected at the inlet and outlet to the container 42 and passes through an intermediate exchanger 43 in which the third fluid, circulating in said sub-circuit 49, exchanges heat with the second fluid circulating in the remaining part of the second circuit 40 (i.e. in the branches 38 and / or 39, as previously described).

Conveniently, a further pump 45 is also provided, and / or an additional fan, to circulate the third fluid within said sub-circuit 49.

In particular, one side of the intermediate exchanger 43 is crossed by the third fluid circulating in the sub-circuit 49, while the other side of said exchanger is crossed by the second fluid circulating then in the branch 38 in which the first exchanger 22 is provided for the exchange. thermal with the first fluid of the first circuit 1.

Conveniently, it is understood that the remaining part of the second circuit 40 corresponds to what has already been described above, with the difference that the second fluid does not pass through the container 42, and therefore does not exchange heat directly with the PCM material. In particular, in the variant of fig. 9, the second fluid exchanges heat indirectly with the PCM material contained in the container 42 through said third fluid, which instead exchanges heat directly both with the second fluid (inside the intermediate exchanger 43) and with the PCM material ( inside the container 42).

Therefore, in this way, even in the event of any breakage of a container of PCM material, the latter circulates at most within the sub-circuit 49 and not within the remaining part of the second circuit 40.

Conveniently in another variant of the system 100, again illustrated in Figure 9, the second disposal sub-circuit 54 can be configured to use the first heat exchanger 22, thus avoiding the use of the third dedicated exchanger 53.

In particular, in this variant, the first circuit 1 comprises at the outlet of the first heat exchanger 22 a second three-way valve 24 which receives the first fluid coming (at the outlet) from said exchanger 22 at the inlet to direct it to the outlet alternatively:

- to a zone of the first circuit 1 immediately upstream of the first expansion valve 10, or

- to an area of the first circuit 1 downstream of the first expansion valve 10, preferably directly inside the first tank 12.

In particular, the second three-way valve 44 substantially replaces the valve 23 provided in the embodiment of fig. 1.

Advantageously, a further valve 27 can also be provided which acts in parallel with respect to the valve 21 provided in the first branch 20 at the inlet of the first heat exchanger 22.

Conveniently, the plant control unit is configured to control the start-up / shutdown and / or modulate the operation of the compression unit 2, the valves and the compressor or pump 41 and / or 45 and / or 51.

Advantageously, the switching of the second circuit 40 and / or of the apparatus 25 from the first operating mode to the second operating mode - preferably with activation of the sub-circuit (s) 54 and / or 59 to dispose of the heat accumulated by the PCM material - it is controlled by the control unit on the basis of the measurement / detection of the energy stored in the PCM material.

Appropriately, the means of measurement include:

- a flow sensor installed in the sections of the second circuit 40 common to the first branch 38 and to the second branch 39 (for example in the section 37 'at the inlet to the container 42 or in the section 37' 'at the outlet from said tank), or two sensors flow rates installed respectively in the first branch 38 and in the second branch, to measure the mass or volumetric flow rate (M) of the second fluid circulating inside the container 42,

- two temperature gauges configured to detect the temperature difference of the second fluid entering (T1-F2) and leaving (T2-F2) from the container 42.

The measuring means are connected to the control unit (for example to a processor) which is configured to calculate the exchanged power P (in particular by means of the formula M x Cp x (T1-F2-T2-F2)) and the energy exchanged, during a certain time interval, between the second fluid and the PCM material present in the container 42. Conveniently, by calculating the exchanged energy, an indication of the heat accumulated by the PCM material is thus obtained.

Conveniently, the control unit is also configured so that: - below a first external air temperature threshold, the energy exchanged with the first circuit 1 is zero,

- above a second external air temperature threshold, the energy exchanged is maximum.

Advantageously, moreover, the control unit is also configured so that on the basis of the heat exchanged by the second fluid with the PCM material and / or the temperature of the external ambient air TA and / or the time of day and / or weather forecasts, the control unit itself commands the start-up of corresponding operating modes of the system 100, and in particular:

- a first operating mode in which the second circuit 40 is not activated (i.e. the pump or compressor 41 is not activated),

- a second operating mode in which the second circuit 40 is activated in the second operating mode (i.e. the second fluid passes through the first disposal sub-circuit 59), to thus disperse the heat accumulated in the PCM material (and subtracted to the first fluid of the first circuit 1), thus causing the solidification of said material,

- a third operating mode in which the second circuit 40 is activated in the first operating mode (i.e. the second fluid passes through the first heat exchanger 22), to thus absorb - through the second fluid - the heat of the first fluid leaving the exchanger at high pressure 4 and then transfer it to the PCM material which thus accumulates it, becoming liquid.

Conveniently, when the minimum temperature reached during the second period (i.e. during the night hours) is higher than the phase change temperature of the PCM material, a fourth operating mode can be provided - as an alternative to said second mode - in which the second disposal sub-circuit 54 to absorb the heat accumulated in the PCM material, in anticipation of activating the third mode during the following period.

Conveniently, it is understood that in all the above operating modes, the first circuit 1 is and remains always active.

Advantageously, the control unit itself can command the start-up of the aforementioned operating modes of the system 100 based on an estimate of the energy required for the following period. Conveniently, this estimate is made on the basis of the thermal load on the plant 1 and, preferably but not exclusively, can be defined by means of a predefined table, based on previous measurements or other known method.

Conveniently, the control unit may have a memory unit in which to store, for subsequent use, the data detected and / or calculated and this in order to use them to make future estimates.

Advantageously, the control unit can comprise wireless reception or transmission means, even at short range, or via cable. Conveniently in this way the control unit can be configured to independently obtain the weather forecast of the location in which the system is installed, and correspondingly control the operation of the system 100.

Preferably, the control unit includes and / or is associated with a user interface that is simple and intuitive to use, even for non-specialist personnel. Preferably, said user interface is constituted by a touch-screen type display or by a display associated with a keyboard or other input means.

Advantageously, the further cooling of the first fluid leaving the high pressure exchanger 4, obtained by exchanging heat with the second fluid - which then in turn exchanges heat directly or indirectly with a PCM material - allows to improve the efficiency of the plant 100, as shown in the diagram T - S of figure 3.

In particular, during the cooling obtained inside the high pressure exchanger 4, the first fluid can be cooled down to a temperature of about 50 ° C (assuming a temperature TA of the external ambient air of 45 ° C, temperature which is generally reached during the daytime hours of a hot day), which corresponds to point C of the diagram in figure 3. Conveniently, the passage of the first fluid inside the first heat exchanger 22 of the second circuit or inside the second blocking the apparatus 25 allows the first fluid to be further cooled, for example up to a temperature of 40 ° C (corresponding to point C '), or even 35 ° C (corresponding to point C' ').

This makes it possible to improve the efficiency of the system as in the face of a certain compression work necessary to pass from point A to point B, the decrease in temperature of the first fluid - which occurs as a result of the heat exchange between said first fluid and the second fluid (and corresponding to the passage from point C to point C 'or C' ') - thus allows to obtain a greater cooling effect, since the length of the section D' -E or D '' - E is greater than that of section D-E (see fig. 3).

Basically, in the present invention, the first refrigerant fluid leaving the high pressure exchanger 4 is further cooled by accumulating, through at least a second fluid, the heat released by said first fluid in a PCM material. Advantageously, then, when the load on the first circuit is lower (in particular when the temperature TA of the air of the external environment is below a certain value TA2, for example during the night) the heat accumulated in the PCM material can then be disposed of by transferring it to the external environment and / or to the first fluid of the first circuit.

As is clear from what has been described, the refrigerating system according to the invention is particularly advantageous in that:

- does not require any additional external energy supply, with the exception of the energy required for the pumps or fans,

- it is also suitable for use in installation contexts where the external ambient air reaches about 50 ° C,

- allows you to always operate the first circuit (i.e. the refrigerant circuit) at maximum efficiency,

- allows you to store heat efficiently,

- allows to reduce the load on the cooling circuit during peak hours,

- it allows to dissipate the heat accumulated during the hours of load substantially with an additional use of minimum energy.

The invention is particularly suitable for use with a first natural refrigerant fluid, such as in particular carbon dioxide (CO2 or R744), however it can also be used with other refrigerating fluids.

The present invention has been illustrated and described in one of its preferred embodiments, but it is understood that executive variations may be applied to it in practice, without however departing from the scope of protection of the present patent for industrial invention.

Claims (10)

CLAIMS 1. Refrigeration system (100) characterized in that it comprises a first cooling circuit (1) in which flows a first fluid, preferably CO2, said first circuit (1) comprising: - at least one compression unit (2) configured to compress said first fluid, - at least one cooling unit (4) positioned downstream of said compression unit (2) and fluidically connected to it, - an evaporation unit (16) positioned upstream of said compression unit (2) and fluidically connected to the inlet of said compression unit (2), and characterized in that it also comprises, downstream of said cooling unit (4) and upstream of said evaporation unit (16), means (40, 22, 25, 26, 28) configured to allow: - a first heat exchange between the first fluid circulating in the first circuit (1) and a second fluid, e - at least a second heat exchange between said second fluid and a PCM phase change material. 2. Plant according to claim 1, characterized in that it comprises a second circuit (40) inside which said second fluid flows, said second circuit (40) comprising: - a container (42) inside which said PCM material is contained and which is configured to allow said second heat exchange between said second fluid and said PCM material, - a first exchanger (22) which is positioned upstream with respect to the inlet to said container (42) and which is configured to allow said heat exchange between said second fluid and said first fluid of the first circuit (1), - a pump ( 41) or a fan for circulating the second fluid through said first exchanger (22) and through said container (42) of said second circuit (40). 3. Plant (1) according to one or more of the preceding claims characterized in that it comprises a first sub-circuit (59) configured to dispose of the heat accumulated by the PCM material present in said container (42), said first sub-circuit (59) ) of disposal being configured to allow an exchange of thermal energy between said second fluid circulating in said second circuit (40) and the air of the external environment. 4. Plant (1) according to one or more of the preceding claims characterized in that it comprises a second sub-circuit (54) configured to dispose of the heat accumulated by the PCM material present in said container (42), said second circuit (54) being configured to allow an exchange of thermal energy between said first fluid leaving said first cooling unit (4) and the second fluid circulating in said second circuit (40). 5. Plant (1) according to one or more of the preceding claims characterized in that said second circuit (40) comprises a sub-circuit (49) in which a third fluid circulates and which is connected at the inlet and outlet to said container (42) containing said PCM material, said sub-circuit (49) being configured to allow a heat exchange between said third fluid, circulating in said sub-circuit (49), and the second fluid circulating in the remaining part of the second circuit (40). 6. Plant according to one or more of the preceding claims characterized in that said second fluid is the air of the environment in which the plant itself is installed, and in that said means configured to allow said first and said second heat exchange comprise an apparatus (25) comprising: - a first block (26) containing a PCM material and configured to allow said second heat exchange between said second fluid and said PCM material, - a second block (28) configured to allow said first heat exchange between the first fluid circulating in the first circuit (1) and the second fluid coming from the first block (26). System (1) according to one or more of the preceding claims characterized in that it is configured so that the second circuit (40) operates alternatively in the following two modes: - a first mode, which operates during a first period of time, in which the second fluid leaving the container (42) passes through said first exchanger (22) to allow the heat exchange between said second fluid and said first fluid contained in the first circuit (1), thus further cooling said first fluid leaving the cooling unit (4), - a second mode, which operates during a second and distinct period of time, in which the second fluid leaving the container (42) passes through said at least one sub-circuit (54, 59) for the dissipation of the heat accumulated by the PCM material, or it is configured so that the equipment (25) works alternately in the following two modes: - a first mode, which operates during a first period of time, in which the second fluid leaving the first block (26) passes through said second block (28) to allow the heat exchange between said second fluid and said first fluid contained in the first circuit (1), thus further cooling said first fluid leaving the cooling unit (4), - a second mode, which operates during a second and distinct period of time, in which the second fluid only passes through said second block (28) for the disposal of the heat accumulated by the PCM material, 8. Plant according to one or more of the preceding claims characterized in that the first circuit (1) comprises, downstream of the cooling unit (4), an expansion valve (10) and a tank (12) containing said first fluid both in the liquid state (61) and in the vapor state (60), said tank (12) being fluidly connected with the inlet of the evaporation unit (16), said first circuit (1) also being characterized in that the The outlet of the cooling unit (4) is fluidically connected to the expansion valve (10) directly or by means of a section (20, 68) which crosses the first exchanger (22) of the second circuit (40). 9. Plant according to one or more of the preceding claims characterized in that said PCM material has a lower melting temperature than the maximum temperature reached by the ambient air TA, in which said plant is installed, during said second period of time, preferably corresponding to the night hours. Method for managing a plant (100) according to one or more of the preceding claims characterized in that on the basis of one or more of the following data: - air temperature of the external environment TA, - hour of the day, - forecast, - heat exchanged by the second fluid with the PCM material, the operation of the system itself is controlled according to one or more of the following operating modes: - a first operating mode in which said second circuit (40) is not activated, - a second operating mode in which the second fluid passes through the first disposal sub-circuit (59), to disperse the heat taken from the first fluid of the first circuit (1) and accumulated in the PCM material into the external environment, - a third operating mode in which the second fluid passes through the first heat exchanger (22), to thus absorb through the second fluid the heat of the first fluid leaving the cooling unit (4) and then transfer it to the PCM material which thus accumulates it.