MEANS OF SAID HEAT PUMP UNIT

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DESCRIPTION

Field of the invention

The present invention relates to the heat pump sector. In particular, the invention relates to a heat pump adapted to be used for cooling and/or heating spaces and for producing sanitary hot water with high performance in terms of energy efficiency and flexibility of use. The invention further relates to a method for cooling and/or heating which may be implemented by means of said heat pump. Background art

Heat pumps are an increasingly more popular solution for satisfying the cooling/heating needs of spaces and/or fluids. The reasons of such a success are mainly related to their high energy efficiency, to the possibility of using a single device for both cooling and heating (known as "reversible" heat pumps), to the flexibility in managing thermal users with different needs, and to the possibility, when used for heating, of drastically reducing the use of fossil fuel and consequently the emission of greenhouse gases which are harmful for the environment.

In order to make the use of heat pumps increasingly more competitive, the focus of designers and manufacturers has aimed to continual improvement of performance in terms of energy efficiency and flexibility of use (possibly of use for heating and cooling, possibility of satisfying several thermal users with different needs in terms of required heat/refrigerating power and/or working temperatures also simultaneously, capacity of working at partial loads also without energy efficiency decay etc.). The optimization need is particularly felt for high refrigerating/heat power heat pump units (e.g. >100kW), typically intended for use in large buildings with centralized thermal users, such as, for example, condos, hotels, hospitals, military quarters, sports centers, swimming pools etc.

In the case of gas compression heat pumps intended for heating, a known solution for improving energy efficiency consists in performing an undercooling of the operating fluid after its condensation and exploiting the undercooling heat power thus obtained for preheating the heat carrier fluid coming from a heat sink before sending it to the evaporator to determine the evaporation of the operating fluid. Documents DE 3311505 A1 and WO 2011/045752 A1 describe the use of the aforesaid solution, in particular, in irreversible type two-stage heat pumps intended for heating.

An additional heat exchanger connected downstream of the condenser and upstream of the expansion means in the circuit of each stage is present in the two- stage heat pumps described in such documents. The additional heat exchangers are further connected to a heat carrier fluid delivery line of a heat sink, upstream of the evaporator of the lower temperature stage. It is thus possible to preheat the heat carrier fluid coming from the heat sink before sending it to the lower temperature heat pump cycle evaporator by means of the heat power deriving from the undercooling of the operating fluids which perform the higher and lower temperature heat pump cycles. High COP can be obtained with this solution, in particular either equal to or higher than 3, also in two-stage heat pumps.

Summary of the invention

The technical problem underlying the present invention is improving the energy efficiency of heat pumps for cooling, which may be either irreversible heat pumps intended for cooling only or reversible heat pumps capable of either cooling or heating.

In particular, a heat pump is desired which can guarantee high EER (Energy Efficiency Ratio) values, in particular equal to or higher than 3, in a wide range of operating conditions, also in presence of thermal users with different needs in terms of refrigerating/heat power and/or required working temperatures.

The applicants thus realized the possibility of exploiting an undercooling after the condensation of the operating fluid in a heat pump cycle in order to obtain an improvement of the energy efficiency also in case of either irreversible or reversible heat pumps for cooling.

A first aspect of the invention thus relates to a heat pump unit comprising at least one circuit adapted to perform a heat pump cycle with a respective operating fluid, said at least one circuit comprising:

an evaporator adapted to perform the evaporation of the operating fluid at a lower pressure of said heat pump cycle and intended to be connected to an external circuit of a first thermal user installation in a cooling operating mode of said heat pump unit;

a condenser adapted to perform the condensation of the operating fluid at a higher pressure of said heat pump cycle and intended to be connected to an external circuit of a heat sink in a cooling operating mode of said heat pump unit, and

a first heat exchanger, adapted to perform an undercooling of the operating fluid at the higher pressure of said heat pump cycle after the condensation of the same,

characterized in that said first heat exchanger is selectively connectable to an external circuit of a second thermal user installation for transferring heat power released by said operating fluid during said undercooling thereto. Furthermore, the heat pump unit of the invention comprises switching means adapted to allow an exchange of the connections of the external circuits of said first thermal user installation and of said heat sink with said evaporator and said condenser, respectively.

In the scope of the present description and the appended claims:

the expression "heat pump cycle" means a generic inverted thermodynamic cycle, i.e. a thermodynamic cycle adapted to transfer heat power from a lower temperature means or installation to a higher temperature means or installation, for the purpose of either increasing or maintaining high the temperature of the higher temperature means or installation (heating operation) or for the purpose of either decreasing or maintaining low the temperature of the lower temperature means or system (cooling operation), and

the expression "heat sink" means a means or installation capable of surrendering or absorbing heat power without appreciable variations of its average temperature.

By virtue of the arrangement of a first heat exchanger with the aforesaid structural and functional features in the heat pump unit of the invention, the heat power subtracted from the operating fluid during its undercooling may be transferred to a second thermal user installation, and thus, in essence, disposed outside the heat pump unit without influencing the conditions of the heat carrier fluid in the external circuit which is connected to the evaporator of the heat pump unit, in particular in this case, the external circuit of a thermal cooling installation.

Advantageously, the undercooling of the operating fluid of the heat pump cycle results, in this case, into an increase of the evaporation enthalpy of the operating fluid in the heat pump cycle, i.e. of the performance in the case of an irreversible heat pump intended for cooling or of a reversible heat pump operating in cooling mode. As this occurs without any increase of electric power expended for compressing the operating fluid, the EER of the heat pump unit increases as a whole.

It is worth noting that, by virtue of the aforesaid features of the first heat exchanger, the heat power deriving from an undercooling of the operating fluid is treated in the heat pumps of the invention in manner entirely different from that which occurs in the heat pump units of the aforesaid prior art, in which the increase of the performance is obtained by recovering the undercooling heat power of the heat pump unit and exploiting it for preheating the heat carrier fluid in a lower temperature heat sink, before sending it to the evaporator. This solution is not adapted to heat pump units intended for cooling, because in this case the evaporator is intended to be connected to the external circuit of a heating thermal user, and the preheating of the heat carrier fluid of such a system would indeed act against the performance (refrigerating power) which is desirable to increase. It has been found that by appropriately choosing the operating fluid and the operating parameters, the heat pump unit of the invention allows to reach EER values equal to 3.5-4.0, with improvements in some cases even higher than 100% with respect to the performance of conventional heat pumps of equal type and power.

When the undercooling heat power is transferred to a second thermal user installation, e.g. an installation for the production of sanitary hot water at medium/low temperature, the heat pump unit of the invention is capable of providing an additional performance, again without any increase of electric compression power, with a further benefit of increasing the overall energy efficiency of the heat pump unit.

Furthermore, the technical features of the heat pump unit of the invention by means of which the aforesaid advantageous results can be obtained are compatible and easily integrated with the other technical solutions aimed at exploiting the undercooling thermal power of the operating fluid, in particular for the purpose of increasing energy efficiency also in a heating operating mode, when required, to the benefit for flexibility of use of the heat pump of the invention. Furthermore, the presence of the aforesaid switching means allows to obtain a reversible heat pump capable of cooling and heating. Advantageously, the choice of inverting the cycle by exchanging the external circuits of the thermal user(s) and of the heat sink with each other releases the switching of the two operating modes of the configuration specification of the heat pump unit.

In a preferred embodiment of the heat pump of the invention, the heat pump unit circuit comprises a first sub-circuit adapted to perform a higher temperature heat pump cycle with a respective operating fluid and a second sub-circuit adapted to perform a lower temperature heat pump cycle with a respective operating fluid, wherein said first and second sub-circuits are in cascading heat exchange relationship with each other so as to perform globally a two-stage heat pump cycle, and wherein said condenser is connected in said first sub-circuit and said evaporator and said first heat exchanger are connected in said second sub-circuit. Such a configuration allows to make a two-stage heat pump cycle, which is particularly advantageous when the heat pump unit of the invention must be used for cooling in very hot or torrid climates.

Indeed, higher heat pump cycle operating fluid condensation temperatures of about 80°C can be achieved in a two-stage heat pump cycle without needing to increase the operating fluid evaporation temperature in the lower heat pump cycle, and thus without negative repercussions on the cooling performance.

Condensation temperatures about 80 °C allow an easy disposal of the heat power released at the condenser of the higher temperature heat pump cycle also in case of external ambient temperatures of 50-60 °C, typical of torrid climates, without needing to use cooling towers or similar heat disposal systems.

Preferably, the first sub-circuit comprises a second heat exchanger adapted to perform an undercooling of the operating fluid at the higher pressure of said higher temperature heat pump cycle after the condensation of the same and selectively connectable to the external circuit of said second thermal user installation to transfer heat power released during said undercooling by the operating fluid of said higher temperature heat pump cycle thereto.

The use of a second heat exchanger with the aforesaid features allows to perform an undercooling of the operating fluid in the higher temperature heat pump cycle in a manner similar to that previously described with reference to the first heat exchanger.

This has repercussions on the lower temperature heat pump cycle performed in the second sub-circuit in two manners. Firstly, until the condensation at the condenser of the second sub-circuit is completed, the undercooling in the higher temperature heat pump cycle induces a further increase of the evaporation enthalpy at the evaporator of the second sub-circuit. When the condensation at the condenser of the second sub-circuit is complete, the aforesaid undercooling requires an increase of mass flow in the second sub-circuit in order to maintain the heat power balance exchanged between the condenser of the second sub-circuit and the evaporator of the first sub-circuit.

The further increase of the evaporation enthalpy in the second sub-circuit occurs without a further increase of a corresponding electric power expended for compressing the operating fluids in the higher and lower temperature heat pump cycles. The mass flow increase in the second sub-circuit implies a proportional increase of the electric power expended for compressing the operating fluid in the lower temperature heat pump, but no increase of the electric power expended for compressing the operating fluid in the higher temperature heat pump cycle. A considerable increase of the total EER of the heat pump is globally obtained.

Furthermore, by means of the aforesaid second heat exchanger, additional heat power is made available at temperature higher than that of the heat power released at the first heat exchanger to serve the second thermal user installation, when present.

Preferably, in the aforesaid embodiment of reversible type, in a heating operating mode of the heat pump unit, at least either said first heat exchanger or said second heat exchanger is further selectively connectable to the external circuit of said first heat sink so as to perform a preheating of a heat carrier fluid coming from said heat sink by means of heat power released by the operating fluid of at least either said lower temperature heat pump cycle or said higher temperature heat pump cycle during the respective undercooling.

Preferably, both the first heat exchanger and the second heat exchanger are selectively connectable to the external circuit of the heat sink. Preferably, in the latter case, the selective connection is such that heat exchangers may perform the respective preheating in reciprocally independent manner.

The heat power recovery deriving from the undercooling of the operating fluid of the lower and/or higher temperature heat pump cycle for preheating the heat carrier fluid of the heat sink allows to increase the COP of the heat pump unit of the invention when heating.

Preferably, the operating fluid of said heat pump cycle, i.e. the operating fluids of said higher temperature heat pump cycle and of said lower temperature heat pump cycle, respectively, are selected from the group consisting of: (E)-2-butene, (Z)-2-butene, 1-butylene, dimethyl ketone, methylacetylene, methyl alcohol, methylpentane, methylpropene, n-hexane, R1270, R290, R600, R600a, R601 , R601a, RE-170, tetramethylmethane or RC-270.

The aforesaid refrigerant fluids are characterized by H-p (specific enthalpy - pressure) diagram limit curves strongly inclined towards increasing enthalpies, with inclination increasing with pressure. This advantageously allows to perform also very extreme undercooling, which, as explained above, allows to enhance all the beneficial effects on total EER or COP of the heat pump unit obtainable by means of the embodiments described above.

In a second aspect thereof, the invention relates to a system for cooling/heating spaces and/or for the production of sanitary hot water comprising a heat pump unit having the features described above.

A third aspect of the invention relates to a method for cooling and/or heating by means of a heat pump unit adapted to perform at least one heat pump cycle with a respective operating fluid, said method comprising, in a cooling operating mode of said heat pump unit, the following steps: evaporating said operating fluid at a lower pressure of said heat pump cycle subtracting heat power from a first thermal user installation;

condensing said operating fluid at a higher pressure of said heat pump cycle releasing heat power to a first heat sink;

- undercooling said operating fluid at the higher pressure of said heat pump cycle after said step of condensing;

transferring the heat power released by said operating fluid during said undercooling step to a second thermal user installation.

Similarly to what is mentioned above with reference to the first aspect of the invention, by virtue of the undercooling of the operating fluid at the higher pressure of the heat pump cycle after the step of condensing and transferring the released undercooling heat power to a second thermal user installation, the enthalpy that the operating fluid can achieve in the step of evaporating can be increased, with a corresponding heat power increase, which can be subtracted from the first thermal user installation without any corresponding increase of electric power during the step of compressing.

The method of the invention thus allows to increase the performance of an irreversible heat pump unit intended for cooling or of a reversible heat pump unit for cooling. An overall improvement of EER of the heat pump unit results as such an effect is obtained without any additional electric power expenditure to implement the step of compressing of the operating fluid.

Brief description of the drawings

Further features and advantages of the present invention will be more apparent in the description of the following preferred embodiments, by way of indicative, non- limitative example, with reference to the accompanying drawings, in which:

Fig. 1 shows a circuit diagram of a first embodiment of the heat pump unit of the invention;

Fig. A diagrammatically shows the heat pump cycle performed in the heat pump unit of the invention in the embodiment in Fig. 1 in an H-p diagram;

- Fig. 2 shows a circuit diagram of a second embodiment of the heat pump unit of the invention;

Fig. 2A diagrammatically shows the heat pump cycles performed in the heat pump unit of the invention in the embodiment in Fig. 2 in an H-p diagram;

Fig. 3A and Fig. 3B show circuit diagrams of two operating configurations of a third preferred embodiment of the heat pump of the invention;

Fig. 4A and Fig. 4B show circuit diagrams of two operating configurations of a fourth preferred embodiment of the heat pump of the invention;

Fig. 5A and Fig. 5B show circuit diagrams of two operating configurations of a fifth preferred embodiment of the heat pump of the invention; and

Fig. 6 shows a circuit diagram of a sixth embodiment of the heat pump unit of the invention.

Detailed description of preferred embodiments of the invention

In the drawings, a heat pump unit in accordance with the invention is indicated by reference numeral 1 as a whole.

In such drawings, the heat pump unit 1 is shown as part of a system 100 for cooling/heating spaces and/or for producing sanitary hot water comprising an external circuit of a first thermal user installation 10, an external circuit of a heat sink 20 and an external circuit of a second thermal user installation 12, which are shown only diagrammatically.

In the case of a heat pump unit 1 for cooling (Fig. 2, 3A, 4A, 5A), the first thermal user installation 10 may be a system for cooling spaces and the second thermal user installation 12 may be a system for producing of medium/low temperature sanitary hot water.

In the case of a heat pump 1 for heating (Fig. 3B, 4B, 5B), the first thermal user installation 10 may be a first system for heating spaces, e.g. a high temperature heating system, and the second thermal user installation 12 may be a system for producing medium/low temperature or even a second heating system, e.g. a low temperature heating system.

In both cases, in situations of use of the heat pump unit 1 in which there are no thermal user installations 12 to be served, the function of such a system must be performed by an appropriate heat sink capable of disposing of the heat power which would otherwise be used by a second thermal system user.

Similarly, in conditions of use of the heat pump unit 1 in which both the production of heat and the production of cold are required at the same time, the heat sink 20 may be replaced by a further thermal user installation capable of using the heat or refrigerating power otherwise disposed of by such a heat sink.

Fig. 1 shows a first preferred embodiment of the heat pump unit 1 , in particular in a cooling configuration, comprising a circuit 2 for performing a heat pump cycle HPCM with a respective operating fluid.

The circuit 2 comprises: an evaporator S8 adapted to perform the evaporation of the operating fluid at a lower pressure of said heat pump cycle HPCM and intended to be connected, by means of a line FL2, to an external circuit of a first thermal user installation 10 in a cooling operating mode of the heat pump unit 1 ; a condenser S4 adapted to perform the condensation of the operating fluid at a higher pressure of the heat pump cycle HPCM and intended to be connected, by means of a line FL1 , to an external circuit of a first heat sink 20 in a cooling operating mode of said heat pump unit 1 ; a compressor C1 adapted to take the evaporated operating fluid to the pressure lower than the higher pressure of the heat pump cycle HPCM and expansion means L1 - e.g. a lamination valve or other functionally equivalent known device - adapted to expand the operating fluids at the pressure higher than the lower pressure of the heat pump cycle HPCM.

The circuit 2 further comprises a heat exchanger S6, connected downstream of the condenser S4 and upstream of the expansion means L1 , adapted to perform an undercooling of the operating fluid at the higher pressure of the heat pump cycle after condensation of the same in the condenser S4.

In the scope of the present description and of the appended claims, the expressions "downstream" and "upstream" refer to the directions of circulation of the fluid indicated in the figures by means of arrows and determined, in general, either by the compressors, in the case of heat pump cycle circuits, or by the circulation pumps, in the case of external thermal user installation and heat sink circuits, respectively.

The heat exchanger S6 is additionally selectively connectable to the external circuit of the second thermal user installation 12 to transfer the heat power released by the operating fluid during said undercooling thereto.

This is preferably obtained by means of a valve V9, preferably a modulating solenoid valve, arranged in a line FL3 for connecting to the external circuit of the second user system 12.

By means of the heat exchanger S6, the heat power subtracted from the operating fluid during the undercooling thereof may thus be disposed of outside the heat pump unit 1 without influencing the operating conditions of the first thermal user installation 10, thus obtaining a considerable increase of energy efficiency of the heat pump 1 , in particular of its EER. As mentioned above, such an increase is due to an increase of the refrigerating performance, determined by an increase of the evaporation enthalpy that the operating fluid may achieve at the evaporator S8, obtainable with an increase of electric compression power and/or collateral effects which contrast such a performance.

Fig. 1A diagrammatically shows in an H-p (specific enthalpy-pressure) diagram how a heat pump cycle of a conventional heat pump (solid line), free from the heat exchanger S6 with the aforesaid features, is modified (dashed line) in the case of the heat pump unit 1 of the invention.

In particular, in the heat pump cycle HPCM performed by the heat pump unit , the operating fluid undergoes, after the condensation C-D at the condenser S4, an undercooling D-E, performed in the heat exchanger S6. Such an undercooling positively impacts the steps of evaporating F-B performed in the evaporator S8. Indeed, by effect of the lower input enthalpy of the operating fluid in the evaporator S8, the evaporation enthalpy increases with respect to the conventional cycle by an amount (h _A -h _F ), corresponding to the enthalpy performed during the undercooling D-E.

By means of the heat pump unit 1 shown in Fig. 1 adapted to implement the heat pump cycle HPCM shown in Fig. 1A with a respective operating fluid, a cooling and/or heating method can be implemented, which in a cooling operating mode of the heat pump unit 1 comprises the steps described below.

During a first step, which occurs in the evaporator S8, the operating fluid is evaporated at a lower pressure of the heat pump cycle HPCM, putting it into heat exchange relationship with the first thermal user installation 10, in particular a cooling system from which heat power is thus subtracted.

During a later step, which occurs in the condenser S4, the operating fluid is condensed at a higher pressure of the heat pump cycle HPCM placing it in heat exchange relationship with the heat sink 20, to which the thermal condensation power is surrendered.

During a later step, which occurs in the heat exchanger S6, the operating fluid is subjected to an undercooling, preferably isobar.

During a further step, by means of the heat exchanger S6, the heat power released by the operating fluid during the step of undercooling is transferred to the second thermal user installation 12.

Fig. 2 shows a second preferred embodiment of the heat pump unit 1 , which differs from that of Fig. 1 for the type of circuit 2. In this case, such a circuit comprises a second sub-circuit 2a adapted to perform a higher temperature heat pump cycle HPCM_HT with a respective operating fluid and a second sub-circuit 2b adapted to perform a lower temperature heat pump cycle HPCM_LT with a respective operating fluid. The first and second sub-circuit 2a, 2b are connected to each other in cascading heat exchange relationship so as to perform a two-stage heat exchange cycle HPCM as a whole.

In this case, the first sub-circuit 2a comprises the condenser S4 described above with reference to the embodiment shown in Fig. 1 , expansion means L2, a compressor C2 and an evaporator. The second sub-circuit 2b comprises the evaporator S8, the heat exchanger S6, the compressor C1 and the evaporation means L1 described above with reference to the embodiment Fig. 1 , and a condenser in heat exchange relationship with the first sub-circuit 2a.

The condenser of the second sub-circuit 2b and the evaporator of the first sub- circuit 2a are preferably integrated in a single heat exchange device S7, for the purpose of greater constructive compactness and a better heat exchange efficiency. Embodiments in which such components are separated and placed in heat exchange relationship by means of an intermediate circuit for the circulation of an appropriate heat carrier fluid are not excluded in any case.

A two-stage configuration of the heat pump unit 1 is particularly advantageous in the case of use for cooling in very hot or torrid climates regions. Indeed, the heat condensation temperatures obtainable in this case at the condenser S4 allow in all cases an easy disposal of the condensation heat power in the outside environment, without needing to increase the evaporation temperature in the evaporator S8 and thus limiting the cooling performance.

As shown in Fig. 2, when the heat pump 1 of the invention has a two-stage configuration, a heat exchanger S5 connected downstream of the condenser S4 and upstream of the expansion means L2, with a function similar to that of the heat exchanger S6 in the second sub-circuit 2b, is preferably present also in the second sub-circuit 2a.

In particular, the heat exchanger S5 is adapted to perform an undercooling of the operating fluid of the higher temperature heat pump cycle HPCM_HT after condensation of the same and is connectable in selectable manner to the external circuit of the second thermal user installation 12 to transfer thereto the heat power released by the operating fluid during said undercooling.

The selective connection of the heat exchanger S5 to the external circuit of the second thermal user installation 12 is performed by means of a valve V12, preferably a modulating solenoid valve.

The undercooling of the operating fluid in the first sub-circuit 2a by means of the heat exchanger S5 advantageously contributes to a further increase of the enthalpy which can be implemented at the evaporator S8 and thus to improving the EER of the heat pump unit 1 .

Fig. 2A diagrammatically shows in an H-p (specific enthalpy-pressure) diagram how a two-stage heat pump cycle of a conventional heat pump (solid line), free from the heat exchangers S6 and S5 with the aforesaid features, is modified (dashed line) in the case of the embodiment shown in Fig. 2 by the heat pump unit 1 of the invention.

In particular, it is worth noting that the undercooling operations D'-E' and E-H, performed in the higher temperature heat pump cycle HPCM_HT by the heat exchanger S5 and in the lower temperature heat pump cycle HPCM_LT by the heat exchanger S6, determine an increase of the evaporation enthalpy performed at the evaporator S8 (G-B transformation) equal as a total to ( iA-hG) > (hA-hp), where (h _A -h _F ) is the increase of the evaporation enthalpy which would be obtained by performing an undercooling only of the higher temperature heat pump cycle HPCMJHT.

In the embodiments of the heat pump unit 1 with two stages and both heat exchangers S6 and S5 described above, as shown in Fig. 2, such heat exchangers are preferably arranged so as to transfer the respective undercooling heat powers to the second thermal user installation 12 independently from each other, i.e. by operating in parallel on two different heat carrier fluid flows of the second thermal user installation 12.

Additionally, preferably, in such embodiments, compressors C1 and C2 are variable flow rate compressors, e.g. capacity step compressors or with inverter. This guarantees a better adaptability of the heat pump unit 1 to possible heat exchange imbalances between the higher temperature heat pump cycle HPCM_HT and the lower temperature heat pump cycle HPCM_LT which may occur as a result of the undercooling operations. Such a greater adaptability has a positive influence on the total energy efficiency of the heat pump unit 1 , all other conditions being equal.

Fig. 3A and Fig. 3B show a third preferred embodiment of the heat pump unit 1 adapted for either cooling or heating, i.e. of the reversible type.

For this purpose, switching means are provided in this embodiment adapted to allow to exchange the external circuit connections of the first thermal user installation 10 and of the heat sink 20 with the evaporator S8 and the condenser S4, respectively. Preferably, such switching means comprise two four-way valves V1 and V2, preferably solenoid valves, appropriately arranged in the lines for connecting the aforesaid external circuits to the evaporator S8 and the condenser S4.

In particular, in the operating configuration shown in Fig. 3A, corresponding to a cooling operation, the external circuit of the first thermal user installation 10 is connected to the evaporator S8, while the external circuit of the heat sink 20 is connected to the condenser S4, in manner similar to the previously described embodiments.

In the operating configuration shown in Fig. 3B, corresponding to a heating operation, the external circuit of the first thermal user installation 10 is connected to the condenser S4, so as to provide the required heat power to such an installation, while the external circuit of the heat sink 20 is connected to the evaporator S8. Preferably, in the embodiment in Fig. 3A and Fig. 3B, and in general in all the embodiments in which an operation of the heat pump unit 1 also for heating is required, the heat exchanger S6 and/or the heat exchanger S5 are additionally selectively connectable to the external circuit of the heat sink 20 so as to perform, in the heating operating mode of the heat pump unit 1 , a preheating of the heat carrier fluid coming from said heat sink 20 by means of the heat power released by the operating fluid of the lower temperature heat pump cycle HPCM_LT and/or of the higher temperature heat pump cycle HPCM_HT during the respective undercooling operations.

Advantageously, in this manner, it is possible to exploit the undercooling heat power released at the heat exchangers S5 and S6 to improve the energy efficiency (COP) of the heat pump unit 1 also in case of heating operation.

In order to allow the connection of the heat exchangers S5 and/or S6 alternatively either to the external circuit of the second thermal user installation 12 (in the operating cooling configuration, Fig. 3A), or to the external circuit of the heat sink 20 (in the heating operating configuration, Fig. 3B), avoiding a mixing of the respective heat carrier fluids, switching means are provided, in particular a three- way valve V8, preferably a solenoid valve, adapted to connect the aforesaid heat exchangers alternatively either to line FL3 or to line FL2.

Preferably, when both heat exchangers S6 and S5 are selectively connectable to the external circuit of the heat sink 20, the connections are arranged so that the heat exchangers may preheat the heat carrier fluid of the heat sink 20 independently from each other, i.e. working in parallel on two different flows of a heat carrier fluid of the heat sink 20.

In particular, as shown in Fig. 3A and Fig. 3B, the heat exchanger S5 is connected to a first branch FL2' of the line FL2 for connecting to the external circuit of the heat sink 20. A valve V7, preferably a modulating solenoid valve, is present in the first branch FL2'. A heat exchanger S6 is instead connected to a second branch FL2", in parallel with the first branch FL2', of the line FL2. A valve V6, preferably a modulating solenoid valve, is present in the second branch FL2".

Preferably, line FL2 also comprises, in this case, a first manifold M1 connected upstream of the heat exchanger S6 and S5 and a second manifold M2 connected upstream of the evaporator S8 and downstream of the valves V6 and V7. Manifolds M1 and M2 are preferably connected by means of a bypass line BPL for bypassing the branches FL2' and FL2", provided with a valve V5, alstf preferably a modulating solenoid valve.

Preferably, a modulation or closing of the valve V6 and/or of the valve V7 is compensated by means of a corresponding modulation or opening of the valve V5, in order to maintain a constant flow of the heat carrier fluid of the heat sink 20 in the evaporator S8.

When the heat power released at the heat exchangers S5 and S6 must be transferred to the second thermal user installation 12 (cooling operating configuration, Fig. 3A), the three-way valve V8 is diverted to line FL3, valves V6 and V7 are all closed and valves V9 and V12 are either completely or partially open. An adjustment of the degree of opening of the valves V9 and V12 allows to adjust the heat power transferred to the heat carrier fluid of the second thermal user installation 12, and consequently the entity of the undercooling carried out in the heat exchangers S6 and S5.

When instead the heat power released at the heat exchangers S5 and S6 must be used for preheating the heat carrier fluid of the heat sink 20 (heating operating configuration, Fig. 3B), the three-way valve V8 is diverted to line FL2, valves V9 and V12 are all closed and valves V6 and V7 are either completely or partially open. An adjustment of the degree of opening of the valves V6 and V7 allows to adjust the heat power transferred to the heat carrier fluid 20 before it reaches the evaporator S8, and consequently the entity of the undercooling carried out in the heat exchangers S6 and S5.

In all embodiments in which pairs of two-way valves V6 + V9 and V7 + V12 are present, each of such pairs may be replaced by a three-way valve arranged so as to perform the functions of the corresponding two-way valves described above. Fig. 4A and Fig. 4B show a fourth preferred embodiment of the heat pump unit 1 which differs from that of Fig. 3A and Fig. 3B in that it can also serve in dedicated manner both in a cooling configuration (Fig. 4A) and a heating configuration (Fig. 4B), a further thermal user installation 13 for the production of sanitary hot water, in addition to the thermal user installations 10 and 12. This embodiment allows in particular to serve a thermal user installation for the production of hot temperature sanitary hot water. The production of high temperature hot water, in particular higher than 60 °C, is required in all cases in which the possible occurrence of Legionella must be prevented (hospitals, swimming pools and sports centers, military quarters etc.).

The embodiment shown in Fig. 4A and Fig. 4B includes, by way of example, that the heat exchange with the thermal user installation 13 occurs indirectly at a thermal accumulator (boiler) 13a, but other solutions known to a person skilled in the art to connect the heat pump unit 1 to the external circuit of such a thermal user installation are also possible.

With respect to the embodiment in Fig. 3A and Fig. 3B, connections for an external circuit of the thermal user installation 13 and of the two three-way valves V11 and V3, preferably solenoid valves, are additionally provided in this case.

The three-way valve V11 is provided so as to allow, in the cooling operating configuration (Fig. 4A), to connect line FL1 to the external circuit of the thermal user installation 13. In this manner, it is possible to exploit the heat power released by the condenser S4 to produce high temperature sanitary hot water instead of dispersing such a power at the heat sink 20.

The three-way valve V3 is provided so as to allow, in the heating configuration (Fig. 4B), to connect line FL1 alternatively to the external circuit of the thermal user installation 10 or to the external circuit of the thermal user installation 13. In this manner, it is possible to use the heat power released at the condenser S4 alternatively either for heating or for producing high temperature sanitary hot water.

Fig. 5A and Fig. 5B show a fifth preferred embodiment of the heat pump unit 1 , which, with respect to the embodiment shown in Fig. 4A and Fig. 4B, allows to satisfy low temperature sanitary hot water needs by means of the thermal user installation 13 in addition to the aforesaid production of sanitary hot water. The embodiment in Fig. 5A and Fig. 5B differs from that of Fig. 4A and Fig. 4B in particular for the presence of a further three-way valve V4, preferably a solenoid valve.

The three-way valve V4 is set so as to allow to selectively also connect the lines FL2' and FL2", in which the heat exchangers S5 and S6 are connected, to the external circuit of the thermal user installation 13 for the production of sanitary hot water in order to create a closed circuit therewith. In this manner, it is possible to use the heat power released at the two heat exchangers S5 and S6 alternatively to produce sanitary hot water, and in cooling configuration (Fig. 5A) and in heating configuration (Fig. 5B), or for preheating the heat carrier fluid of the heat sink 20, in the heating configuration.

For the optimal operation of this embodiment of the cooling configuration (Fig. 5A), it is further appropriate to provide means for bypassing the external circuit of the thermal user installation 10, intended for cooling in this operating configuration, outside the heat pump unit 1. Such means preferably comprise a three-way valve V13, preferably a solenoid valve, arranged between the external circuit of the thermal user installation 10 and the external circuit of the thermal user installation 13. The external three-way valve V13, in combination with the aforesaid three-way valve V11 of the heat pump unit 1 , allows to connect the line FL1 to the external circuit of the thermal user installation 13 bypassing the external circuit of the thermal user installation 10.

In particular, in the cooling operating configuration, the three-way valve V11 connects the line FL1 to the external circuit of the thermal user installation 13, while the external three-way valve V13 allows to bypass the external circuit of the thermal user installation 10. In this manner, it is possible to exploit the heat power released by the main condenser S4 to produce high temperature sanitary hot water instead of dispersing such a power at the heat sink 20. This operation mode requires circuit FL1 to be a closed circuit.

In all the described embodiments, the heat pump unit 1 preferably also comprises a programmable control unit (not shown in the figures). In particular, such a control unit may be appropriately programmed for controlling the opening/closing, the modulation or diversion of the valves, as well as the switching on/off, the capacity degree or rpm of the compressors present in each embodiment of the heat pump unit !

The operating fluids used in the heat pump cycles performed in the heat pump unit 1 may be reciprocally equal or different. Operating fluids which allow to combine the following features, advantageous for the operation of the heat pump unit 1 , are preferably chosen:

- limit curves, in particular the lower limit curve which are very inclined in the direction of increasing enthalpies in H-p diagrams;

- high specific heat of the operating fluid in liquid state with respect to the latent condensation/evaporation heat;

- high specific heat of the operating fluid in vapor state with respect to the latent condensation/evaporation heat.

The first two features mentioned above are particularly relevant for embodiments or operating conditions in which extreme undercooling is used, while the third is particularly relevant for all other embodiments or operating conditions in which extreme overheating is used.

In particular, the following operating fluids have proven to be particularly advantageous to obtain the best performance of the heat pump unit 1 : (E)-2- butene, (Z)-2-butene, 1-butylene, dimethyl ketone, methylacetylene, methyl alcohol, methylpentane, methylpropene, n-hexane, R1270, R290, R600, R600a, R601 , R60 a, RE- 70, tetramethylmethane or RC-270.

In addition to having at least one or more of the desired properties listed above, these operating fluids have the advantage of being so-called "natural" refrigerants, i.e. not harmful for the environment in terms of negative effects on atmospheric ozone nor from the point of view of greenhouse effect.

If the type of operating fluid chosen in particular for its hydrocarburic nature places problems of safety (risk of fire) and if the heat pump unit 1 must be installed in underground rooms or basements, the pump is preferably also provided with means for detecting and evacuating gas leaks.

Fig. 6 shows an embodiment of the heat pump unit 1 comprising a system for detecting and evacuating gas leaks. By way of example, the configuration of the represented heat pump unit 1 corresponds to the second embodiment described above with reference to Fig. 2.

The system for detecting and evacuating gas leaks comprises at least one gas detector 31 , positioned as close to the bottom of the heat pump unit 1 as possible and ventilation means 32, activatabie by the gas detector 31 and arranged so that their intake is also near the bottom of the heat pump unit 1 , while their delivery is connected to a gas evacuation pipe in communication with the outside environment/ Optionally, a specific control device 34 adapted to receive signals from the gas detector 31 and to control the ventilation means 32 as a consequence may be provided. The control device 34 may also control acoustic and/or light warning means 35, if provided, and/or may be configured to send alarm signals to a possible external monitoring/supervising system (not shown). The functions of the control device 34 may also be carried out by the programmable control unit of the heat pump unit 1.

Naturally, the person skilled in the art may exploit the technical features of the heat pump unit 1 of the invention presented with reference to the preferred embodiments described above also in different combinations, in order to satisfy specific, contingent application needs.