HIGH PERFORMANCE HEAT PUMP UNIT

Abstract

A heat pump unit (1) comprises at least one main circuit (2) adapted to perform a main heat pump cycle with a respective operating fluid, which comprises: a main condenser (S4) adapted to perform the condensation of the operating fluid of the main heat pump cycle and intended to be connected to an external circuit of a first thermal user plant (10) in a heating operating mode of said heat pump unit (1), a first heat exchanger (S2), connected downstream of the main condenser (S4) and upstream of expansion means (L2) of said the main circuit (2), adapted to perform an undercooling of the operating fluid of the main heat pump cycle after the condensation of the same in the main condenser (S4), and a main evaporator (S8) adapted to perform the evaporation of the operating fluid of the main heat pump cycle and intended to be connected to an external circuit of a heat sink (20) in a heating operating mode of said heat pump unit (1). The heat pump unit (1) further comprises a secondary circuit (3) adapted to perform a secondary heat pump cycle with a respective operating fluid, which comprises: a secondary evaporator (S2) adapted to perform at least the evaporation of the operating fluid of the secondary heat pump cycle and in heat exchange relationship with the first heat exchanger (S2) to transfer heat power released by the operating fluid of the main heat pump cycle during said undercooling to the operating fluid of the secondary heat pump cycle, and a secondary condenser (S1) adapted to perform the condensation of the operating fluid of said secondary heat pump cycle (HPCS) and intended to be connected to the external circuit of the first thermal user plant (10) or to an external circuit of a second thermal user plant, different from the first thermal user plant (10).

Description

FIELD OF THE INVENTION

The present invention relates to the field of heat pumps. In particular, the invention relates to a heat pump unit adapted to be used for heating/cooling environments and for producing sanitary hot water with high performance in terms of energy efficiency and use flexibility.

PRIOR ART

Heat pumps are an increasingly widespread technical solution for meeting the requirements of heating/cooling environments and/or fluids. The reasons for such a success are mainly to be ascribed to the high energy efficiencies, to the possibility of using a single device for both heating and cooling (so-called “reversible” heat pumps), to the flexibility in managing thermal users with different requirements and to the possibility, in case of use for heating, of considerably reducing the use of fossil fuels and thus the output of harmful carbon harmful to the environment.

In order to make the use of heat pumps increasingly competitive, the focus of designers and manufacturers is on a constant improvement of the performance thereof, both in terms of energy efficiency and in terms of use flexibility (possibility of use for both heating and cooling, possibility of meeting multiple different requirements of multiple thermal users, even concurrently, in terms of heating/cooling power and/or operating temperatures, capability of operating at partial loads without energy efficiency degradation, etc.). The optimization need is especially felt for heat pump units having a high heating/cooling power (for example >100 kW), typically intended to be used in large buildings with centralized thermal users, such as blocks of flats, hotels, hospitals, barracks, sports centers, swimming pools, etc.

In the case of gas compression heat pumps a intended for heating, a known method for improving the COP (Coefficient of Performance) consists in performing an undercooling of the operating fluid after the condensation thereof and in using the undercooling heat power thus obtained for preheating the heat carrier fluid coming from a heat sink before sending it to the evaporator for determining the evaporation of the operating fluid.

Documents DE 3311505 A1 and WO 2011/045752 A1 describe the use to the above solution in particular in so-called “high temperature” gas compression heat pumps. Such heat pumps allow condensation temperatures of 80-85° C. to be achieved—required for the operation of conventional high temperature heating plants which typically require a delivery temperature of the heat carrier fluid of at least 80° C.—even when a heat sink is provided, the average temperature thereof does not exceed 7-10° C., as it normally happens with groundwater. Two stage heat pumps are typically needed in order to operate with so large differences, which however usually have relatively low COP.

In two stage heat pumps described in the above documents there is provided an additional heat exchanger connected downstream of the condenser and upstream of the expansion means in the circuit of each stage. The additional heat exchangers are further connected to a delivery line of a heat carrier fluid of a heat sink, upstream of the evaporator of the lower temperature stage. Therefore, the heat carrier fluid coming from the heat sink can be preheated before sending it to the evaporator of the lower temperature heat pump cycle through the heat power resulting from the undercooling of the operating fluids that perform the higher and lower temperature heat pump cycles. Due to such a configuration, COP can be obtained so as to be equal to or higher than 3 even in two stage heat pumps.

SUMMARY OF THE INVENTION

The technical problem at the basis of the present invention consists in providing a heat pump having improved performance as compared to the heat pumps having the same power and type of the prior art. In particular, a heat pump is desired which is capable of ensuring a high energy efficiency, with COP in case of heating or EER (Energy Efficiency Ratio) in case of cooling equal to or higher than 3, in a wide range of operating conditions, also in the presence of thermal users with different requirements in terms of heating/cooling power and/or operating temperatures required.

The Applicants have perceived the possibility of solving such a technical problem using the heat power resulting from an undercooling subsequent to the condensation of the operating fluid in a heat pump cycle in an alternative and more effective manner with respect to the solution presented in the prior art described above.

The invention therefore relates to a heat pump unit comprising at least one main circuit adapted to perform a main heat pump cycle with a respective operating fluid, said at least one main circuit comprising:

• • a main condenser adapted to perform the condensation of the operating fluid of said main heat pump cycle and intended to be connected to an external circuit of a first thermal user plant in a heating operating mode of said heat pump unit;
  • a first heat exchanger, connected downstream of said main condenser and upstream of expansion means of said at least one main circuit, adapted to perform an undercooling of the operating fluid of said main heat pump cycle after the condensation of the same in said main condenser, and
  • a main evaporator adapted to perform the evaporation of the operating fluid of said main heat pump cycle and intended to be connected to an external circuit of a heat sink in a heating operating mode of said heat pump unit,
    characterized by comprising a secondary circuit adapted to perform a secondary heat pump cycle with a respective operating fluid, said secondary circuit comprising:
  • a secondary evaporator adapted to perform at least the evaporation of the operating fluid of said secondary heat pump cycle and in heat exchange relationship with said first heat exchanger to transfer heat power released by the operating fluid of said main heat pump cycle during said undercooling to the operating fluid of said secondary heat pump cycle, and
  • a secondary condenser adapted to perform the condensation of the operating fluid of said secondary heat pump cycle and intended to be connected to the external circuit of said first thermal user plant or to an external circuit of a second thermal user plant, different from said first thermal user plant.

Within the scope of the present description and in the following claims

• • the expression “heat pump cycle” is understood to indicate a generic inverted thermodynamic cycle, i.e. a thermodynamic cycle adapted to transfer heat power from a means or system at lower temperature to a means or system at higher temperature, or in order to increase or keep the temperature of the means or system at higher temperature high (heating operation), or in order to decrease or keep the temperature of the means or system at lower temperature low (cooling operation), and
  • the expression “heat sink” is understood to indicate a means or system capable of yielding or absorbing heat power without considerable variations of the average temperature thereof.

In the heat pump unit of the invention, due to the performance of a secondary heat pump cycle with the above features, the heat power released during the undercooling of the operating fluid of the main heat pump cycle can be advantageously brought substantially to the same temperature at which the condensation heat power in the main condenser is released. Thereby, also the undercooling heat power of the main operating fluid may be transferred to the thermal user plant served by the main heat pump cycle or to another thermal user plant operating at similar temperatures, increasing the overall useful heat power that can be provided by the heat pump unit.

The Applicants have surprisingly found that, unlike what happens for example in the case of the cascading coupling of two heat pump cycles according to the prior art, in this case the increase of the above useful heat power leads to an improvement of the overall COP. This is essentially related to the fact that such an increase in the useful heat power may be achieved with a minimum additional use of energy, in particular electrical energy for compressing the operating fluid in the secondary heat pump cycle. It has been determined that with a suitable selection of the operating fluids and of the operating parameters, an increase in the COP up to 20% can be advantageously obtained as compared to the values obtainable in conventional heat pumps of the same type and power.

In fact, it should be noted that the undercooling of the operating fluid of the main heat pump cycle takes place, due to its nature, with a temperature variation. The heat power released during the undercooling of the operating fluid of the main heat pump cycle therefore allows not only the evaporation but also a strong overheating of the operating fluid of the secondary heat pump cycle, to be obtained.

The overheating degree obtainable on the operating fluid of the secondary heat pump cycle, which is stronger as the thermal gradient of the operating fluid of the main heat pump cycle is wider during the undercooling, has two important effects that contribute to a considerable reduction of the electrical compression power in the secondary heat pump cycle.

In the first place, there occurs an increase in the enthalpy jump undergone by the operating fluid of the secondary heat pump cycle in the heat exchange with the main operating fluid in the undercooling step. Having established the heat power to transfer between the two fluids, such an enthalpy jump allows a corresponding reduction in the mass flow rate of the operating fluid of the secondary heat pump cycle so that less compression work is required.

In the second place, the overheating distances the operating fluid of the secondary heat pump cycle from the saturation conditions and therefore allows the use of compressors with higher isentropic yields, without the risk of intersecting the higher limit curve (i.e. saturation curve in vapor conditions) during the compression.

Both aspects mentioned contribute to a reduction in the electrical power used for the compression of the operating fluid of the secondary heat pump cycle and thus, according to what explained above, to the increase in the overall COP of the heat pump unit of the invention.

The heat pump unit of the invention with the above features, moreover, provides a considerable use flexibility. In fact, if no additional heat power at the higher temperature is required, or in case of cooling operation when this option is provided, the secondary heat pump cycle can be easily deactivated and the heat power resulting from the undercooling of the main operating fluid can be released to the external environment or used for other purposes.

To this end, it should also be noted that the use of the secondary heat pump cycle in the heat pump unit of the invention is compatible and easily integrated with other technical solutions aimed to use the undercooling heat power of the main operating fluid, such as for example the preheating of the heat carrier fluid of the heat sink carried out in the prior art devices.

In a preferred embodiment of the heat pump unit of the invention, both said main condenser and said secondary condenser are intended to be connected to the external circuit of said first thermal user plant and are connected to one another so as to be in series in said external circuit of said first thermal user plant.

This embodiment advantageously allows the use of both the condensation heat power and of the undercooling heat power of the main operating fluid for the same thermal user plant.

A situation of interest for the use of this embodiment therefore is in combination with high temperature heating plants which envision high temperature differences between delivery and backflow of the respective heat carrier fluid.

Advantageously, moreover, due to the possibility of performing the heating of the heat carrier fluid of the thermal user plant in two steps that occur in a sequence in the secondary condenser and in the main condenser, with this embodiment it is possible to further improve the overall COP of the heat pump unit. In fact, since in this case the secondary condenser must only contribute to a part of the heating, the heat power to transfer to the thermal user plant being equal, it is possible to decrease the condensation temperature in the secondary heat pump cycle, obtaining a simultaneous decrease of the compression work required in such a cycle and in the practice, an increase in the overall COP of the heat pump unit.

In another preferred embodiment, said main circuit comprises a first sub-circuit adapted to perform a higher temperature main heat pump cycle with a respective operating fluid and a second sub-circuit adapted to perform a lower temperature main heat pump cycle with a respective operating fluid, in which said first and second sub-circuits are in cascading heat exchange relationship with each other to perform globally a two-stage main heat pump cycle, and in which said main condenser and said first heat exchanger are connected in said first sub-circuit and said main evaporator is connected in said second sub-circuit.

Such a configuration of the main circuit allows a two-stage main heat pump cycle to be performed, and thus the operation with thermal gradients significantly higher than those obtainable through a single-stage heat pump cycle. Due to this, the heat pump unit of the invention can be advantageously used with thermal user plants operating at a high temperature (for example radiator heating plants which normally require delivery temperatures around 80° C.) also when a heat sink is available which consists of water or environmental fluids at low temperature (for example groundwater or running water on the surface or in depth, seawater or lake water, waterworks water, wastewaters, etc., with average temperatures typically not lower than about 7° C.).

Preferably, said first sub-circuit comprises a second heat exchanger connected downstream of said first heat exchanger and upstream of expansion means of said first sub-circuit, said second heat exchanger being adapted to perform an undercooling of the operating fluid of said higher temperature main heat pump cycle after the condensation thereof and being selectively connectable to the external circuit of said heat sink so as to perform a preheating of a heat carrier fluid coming from said heat sink by means of heat power released during said undercooling by the operating fluid of said higher temperature main heat pump cycle.

The recovery of heat power resulting from the undercooling of the operating fluid of the higher temperature main heat pump cycle for preheating the heat carrier fluid of the heat sink when the heat pump unit of the invention is active in heating implies a further improvement of the overall COP.

Preferably, said second heat exchanger is further selectively connectable to an external circuit of a third thermal user plant.

Thereby, the heat power resulting from the undercooling of the operating fluid of the higher temperature main heat pump cycle may be used for serving a further medium/low temperature thermal user, for example a heating plant with floor or ceiling radiating panels, fan coils, etc. The possibilities of use and the overall energy efficiency of the heat pump unit of the invention therefore are advantageously increased.

Preferably, said second sub-circuit comprises a third heat exchanger connected downstream of said first heat exchanger and upstream of expansion means of said second sub-circuit, said third heat exchanger being adapted to perform an undercooling of the operating fluid of said lower temperature main heat pump cycle after the condensation thereof and being selectively connectable to the external circuit of said heat sink so as to perform, preferably independently of said second heat exchanger, a preheating of a heat carrier fluid coming from said heat sink by means of heat power released during said undercooling by the operating fluid of said lower temperature main heat pump cycle.

Preferably, said third heat exchanger is further selectively connectable to the external circuit of said third thermal user plant.

These embodiments replicate, in the second sub-circuit for performing the lower temperature main heat pump cycle, what described above with reference to the first sub-circuit for performing the higher temperature main heat pump cycle, advantageously allowing the increase of the heat power available for preheating the heat carrier fluid of the heat sink or a medium/low temperature thermal user to be served.

In a preferred embodiment, said first sub-circuit comprises a fourth heat exchanger connected downstream of said main condenser and upstream of said first heat exchanger, said fourth heat exchanger being adapted to perform an undercooling of the operating fluid of said higher temperature main heat pump cycle after the condensation of the same and being selectively connectable to the external circuit of said first thermal user plant so as to be in series with said main condenser in said external circuit of said first user plant.

This embodiment advantageously allows the use of heat power resulting from an undercooling of the operating fluid of the main heat pump cycle (i.e. of the higher temperature main heat pump cycle in the case of two-stage main heat pump cycle) for preheating the heat carrier fluid of the first thermal user plant before it reaches the main condenser, with a positive effect on the overall COP of the heat pump unit.

It should be noted that the advantages on the COP obtainable by this solution are related to the undercooling heat power fraction actually usable with respect to the theoretically available one, which is determined by the minimum temperature achievable with the undercooling, i.e. the evaporation temperature of the operating fluid of the main heat pump cycle (or of the higher temperature main heat pump cycle).

Since the undercooling heat power usable is greater as the backflow temperature of the heat carrier fluid to be heated is lower, the above embodiment is especially advantageous for an operation of the heat pump unit in all those operating conditions in which a drop of the temperature level in the thermal user plant is acceptable with the same heat power transferred thereto. Such a situation occurs, for example, in high temperature heating plants in autumn and spring.

In general, therefore, this embodiment finds an advantageous use in combination with high temperature heating plants which provide for the possibility of changing the backflow temperature of the heat carrier fluid in order to optimize the operation of the heating plant.

Preferably, the heat pump unit according to the invention comprises switching means, adapted to allow an exchange of connections of the external circuits of at least said first thermal user plant and said heat sink respectively with at least said main condenser and with said main evaporator.

This allows a reversible heat pump unit to be obtained, capable of operating both for heating and for cooling. Advantageously, the choice to perform the cycle reversal by exchanging the external circuits of the thermal user(s) and of the heat sink, respectively, releases the switching between the two operating modes from the specific configuration of the heat pump unit (main circuit with one or two stages, number of heat exchangers connected to a same delivery line of the thermal user plant(s), etc.).

Preferably, the operating fluid of said main heat pump cycle, or the operating fluids of said higher temperature main heat pump cycle and said lower temperature main heat pump cycle respectively, and the operating fluid of said secondary heat pump cycle 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 above cooling fluids are characterized by limit curves in diagram h-p (specific enthalpy—pressure) strongly inclined towards the increasing enthalpies, with increasing inclination as pressure increases. This advantageously allows even strong undercooling to be performed which, as already explained, allows all the advantageous effects on the overall energy efficiency that can be obtained by the above embodiments of the heat pump unit to be enhanced.

The invention also relates to a system for heating/cooling environments and/or for producing sanitary hot water comprising a heat pump unit having the features described above

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the present invention will appear more clearly from the following description of some preferred embodiments thereof, made by way of a non-limiting example with reference to the annexed drawings, in which:

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

FIG. 1A schematically shows a diagram h-p of the heat pump cycles performed in the heat pump unit of the invention in the embodiment in FIG. 1;

FIG. 2 shows a circuit diagram of a second preferred embodiment of the heat pump unit of the invention;

FIG. 2A schematically shows a diagram h-p of the heat pump cycles performed in the heat pump unit of the invention in the embodiment in FIG. 2;

FIG. 3 shows a circuit diagram of a variant of the embodiment in FIG. 2;

FIG. 4 shows a circuit diagram of a third preferred embodiment of the heat pump unit of the invention;

FIG. 5 shows a circuit diagram of a fourth preferred embodiment of the heat pump unit of the invention;

FIG. 6 shows a circuit diagram of a fifth preferred embodiment of the heat pump unit of the invention;

FIGS. 7A and 7B show circuit diagrams of two operating configurations of a sixth preferred embodiment of the heat pump unit of the invention;

FIGS. 8A and 8B show circuit diagrams of two operating configurations of a seventh preferred embodiment of the heat pump unit of the invention;

FIGS. 9A and 9B show circuit diagrams of two operating configurations of an eighth preferred embodiment of the heat pump unit of the invention;

FIGS. 10A and 10B show circuit diagrams of two operating configurations of an ninth preferred embodiment of the heat pump unit of the invention, and

FIG. 11 shows a circuit diagram of a tenth preferred embodiment of the heat pump unit of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the figures, a heat pump unit according to the invention is globally indicated with reference numeral 1.

In such figures, the heat pump unit 1 is shown as a part of a system 100 for heating/cooling environments and/or for producing sanitary hot water, comprising at least one external circuit of a thermal user plant 10 and an external circuit of a heat sink 20, which are only schematically shown.

In situations of use of the heat pump unit 1 in which both heat production and cold production are concurrently required, the heat sink 20 may therefore be replaced by a further thermal user plant capable of using the cooling or heating power otherwise disposed of through such a heat sink.

FIG. 1 shows a first preferred embodiment of the heat pump unit 1, in particular for heating, comprising a main circuit 2 and a secondary circuit 3 adapted to perform respective heat pump cycles in heat exchange relationship with each other, with respective operating fluids.

The main circuit 2 for performing a main heat pump cycle HPCM comprises: a main condenser S4 adapted to perform the condensation of the operating fluid at a higher pressure of the main heat pump cycle HPCM and intended to be connected to the external circuit of the thermal user plant 10 in a heating operating mode of the heat pump unit 1; a main evaporator S8 adapted to perform the evaporation of the operating fluid at a lower pressure of the main heat pump cycle HPCM and intended to be connected to the external circuit of the heat sink 20 in a heating operating mode of the heat pump unit 1; a compressor C2 adapted to bring the evaporated operating fluid from the lower pressure to the higher pressure of the main heat pump cycle HPCM, and expansion means L2—for example a lamination valve or other functionally equivalent known device—adapted to perform the expansion of the operating fluid from the higher pressure to the lower pressure of the main heat pump cycle HPCM.

The main circuit 2 further comprises a heat exchanger connected downstream of the main condenser S4 and upstream of the expansion means L2, adapted to perform an undercooling of the operating fluid after the condensation of the same in the main condenser S4 and in heat exchange relationship with the secondary circuit 3.

Within the scope of the present description and of the following claims, the expressions “upstream” and “downstream” are to be understood with reference to the directions of fluid circulation indicated in the figures by arrows and in general determined by the compressors, in the case of circuits for performing heat pump cycles, and by the circulation pumps in the case of the external circuits of the thermal user plants and of the heat sink, respectively.

Likewise, the secondary circuit 3 for performing a secondary heat pump cycle HPCS comprises: a secondary condenser S1 adapted to perform the condensation of the operating fluid at a higher pressure of the secondary heat pump cycle HPCS and intended to be connected to the external circuit of the thermal user plant 10 or to the external circuit of another separate thermal user plant (see thermal user plant 11 in FIG. 3); a secondary evaporator adapted to perform at least the evaporation of the operating fluid at a lower pressure of the secondary heat pump cycle HPCS and in heat exchange relationship with said heat exchanger of the main circuit 2 for transferring heat power released by the operating fluid of the main heat pump cycle HPCM during said undercooling to the operating fluid of the secondary heat pump cycle HPCS; a compressor C3 adapted to bring the evaporated operating fluid from the lower pressure to the higher pressure of the secondary heat pump cycle HPCS, and expansion means L3—for example a lamination valve or another functionally equivalent known device—adapted to allow the expansion of the operating fluid from the higher pressure to the lower pressure of the secondary heat pump cycle HPCS.

In the preferred embodiments shown in the figures, said heat exchanger of the main circuit 2 and the secondary evaporator of the secondary circuit 3 are integrated in a single heat exchanger device S2 for greater construction compactness and a better heat exchange efficiency. In any case, embodiments in which such components are separate and placed in thermal exchange relationship by an intermediate circuit for the circulation of a suitable heat carrier fluid are not excluded.

Compressor C3 preferably is a variable flow rate compressor, for example a cut-off or step or inverter compressor. This allows the extent of the operating fluid undercooling in the main heat pump cycle HPCM at the heat exchanger device S2 and accordingly, the heat power that can be provided at the secondary condenser S1 to be controlled without stressing the compressor with an excessive repetition of on-off cycles.

Through the secondary circuit 3 and the related secondary heat pump cycle HPCS described above, it is possible to raise the temperature level of the heat power released upon the undercooling of the operating fluid in the main heat pump cycle HPCM, thus making also such a heat power usable by the thermal user plant 10 or by another and separate thermal user plant operating at medium or high temperature. Due to the fact that such a result may be obtained minimizing the additional energy consumption related to compressor C3, as already explained above, the increase in the useful heat power leads to an increase in the overall COP of the heat pump unit 1.

FIG. 1A schematically shows a diagram h-p (specific enthalpy-pressure) of the main HPCM and secondary HPCS heat pump cycles that may be performed in the heat pump unit 1 in FIG. 1.

In particular, it can be seen that in the main heat pump cycle HPCM, after condensation C′-D′ performed in the main condenser S4, the operating fluid undergoes an undercooling D′-E′, performed in the heat exchanger device S2. Through the heat exchanger device S2, the heat power released during the undercooling D′-E′ is transferred to the secondary heat pump cycle HPCS. Such a heat power is used for performing evaporation A″-F″ of the operating fluid of the secondary heat pump cycle HPCS and also a substantial overheating F″-B″ of the same. As already explained above, the possibility of performing such a high overheating has advantageous effects on the secondary heat pump cycle HPCS, which in turn lead to an improvement in the overall COP of the heat pump unit 1. The heat powers released during the condensation step C′-D′ in the main heat pump cycle HPCM at the main condenser S4 and during the condensation step C″-D″ in the secondary heat pump cycle HPCS at the secondary condenser S1, respectively, as said, may both be transferred to the same thermal user plant or to two separate thermal user plants.

As shown in FIG. 1, when both the main condenser S4 and the secondary condenser S1 are intended to serve the same thermal user plant, they are reciprocally connected in series, with the secondary condenser S1 upstream, in a line FL1 arranged in the heat pump unit 1 for the connection to the external circuit of such a thermal user plant. Thereby, the secondary condenser S1 can be used for performing a preheating of the heat carrier fluid of the thermal user plant, and the main condenser S4 for completing the heating up to reaching the required delivery temperature.

As already explained above, since in this case the secondary condenser S1 must only contribute to a part of the heating, the heat power to transfer to the thermal user plant being equal, it is possible to decrease the condensation temperature in the secondary heat pump cycle HPCS, obtaining a simultaneous decrease of the compression work required in such a cycle and thus, a further improvement of the overall COP of the heat pump unit 1.

According to the minimum temperature of the heat sink 20 available, the embodiment of the heat pump unit 1 shown in FIG. 1 may be used with low/mean or high temperature thermal user plants.

For example, if a heat sink 20 is available with a mean temperature of no less than 7° C., as it happens for example in the case of groundwater or running water on the surface or in depth, seawater or lake water, waterworks water, wastewaters, etc., it is possible to serve thermal user plants that require temperatures up to 60-65° C., for example heating plants operating at low/mean temperature, such as plants with floor or ceiling radiating panels, fan coils, etc., or plants for the production of sanitary hot water.

On the other hand, if a heat sink 20 is available with a higher mean temperature (at least 30-35° C.), for example waste/cooling heat from industrial processes, hot spring, etc., it is possible to serve thermal user plants which require temperatures even higher than 60-65° C., for example heating plants operating at high temperature, such as plants with radiators, fan heaters, etc. which typically require delivery temperatures of 80° C. or higher, or plants for the production of sanitary hot water in all those situations where the hot water must be produced at temperatures considerably higher than 60° to prevent the possible occurrence of legionella (hospitals, swimming pools and sports centers, barracks, etc.).

The Applicant has therefore noted that through the heat pump unit according to the invention, the “useless” enthalpy of the operating fluid is advantageously changed into “useful” enthalpy. Through a strong undercooling of the operating fluid of the main circuit 2, the same operating fluid at the output from compressor C2 has an overall enthalpy given by the sum of a “useful” enthalpy, obtainable by the de-overheating followed by the condensation of the operating fluid through the main condenser S4, and by the “useful” enthalpy obtainable by the undercooling of the operating fluid through the first heat exchanger S2. The term “useful” indicates the possibility of transferring high temperature heat power (i.e. at temperatures close to those of condensation) to a heat carrier fluid, whereas the term “useless” indicates the possibility of transferring heat power only at temperatures strongly lower than those of condensation. According to the present invention, the “useless” enthalpy is used to evaporate an operating fluid circulating in the secondary cycle HPSC which, by means of a secondary compressor C3, is able to condensate at a temperature corresponding to the useful enthalpy. In order to obtain this result, the operating fluid circulating in the main circuit is strongly undercooled, i.e. so as to bring the same fluid from an initial temperature close to the condensation temperature up to a temperature close to the evaporation one. FIG. 2 shows a second preferred embodiment of the heat pump unit 1, which differs from that in FIG. 1 in the type of main circuit 2. In this case, the main circuit 2 comprises a first sub-circuit 2a adapted to perform a higher temperature main heat pump cycle HPCM_HT with a respective operating fluid and a second sub-circuit 2b adapted to perform a lower temperature main heat pump cycle HPCM_LT with a respective operating fluid. The first and second sub-circuits 2a, 2b are in cascading heat exchange relationship with each other to perform globally a two-stage main heat pump cycle HPCM.

In this case, the first sub-circuit 2a comprises the main condenser S4, the heat exchanger device S2, the expansion means L2 and compressor C2 described above with reference to the embodiment in FIG. 1, and an evaporator. The second sub-circuit 2b comprises the main evaporator S8, already described above as well with reference to the embodiment in FIG. 1, a compressor C1, a condenser in heat exchange relationship with the evaporator of the first sub-circuit 2b and the expansion means L1.

In the preferred embodiments shown herein, the condenser of the second sub-circuit 2b and the evaporator of the first sub-circuit 2a are integrated in a single heat exchanger device S7 for greater construction compactness and a better heat exchange efficiency. In any case, embodiments where such components are separate and placed in thermal exchange relationship by an intermediate circuit for the circulation of a suitable heat carrier fluid are not excluded.

The embodiment of the heat pump unit 1 with two-stage main heat pump cycle HPCM finds an advantageous use in all those situations in which it is necessary to serve thermal user plants operating at a high temperature but having a low temperature heat sink available.

FIG. 2A schematically shows a diagram h-p of the main HPCM and secondary HPCS heat pump cycles that may be performed in the heat pump unit 1 in FIG. 2. In this case, the main heat pump cycle HPCM consists of the two main heat pump cycles at higher temperature HPCM_HT and at lower temperature HPCM_LT, respectively, in cascading heat exchange relationship with each other. In particular, through the heat exchanger device S7, the heat power released during condensation C-D of the operating fluid of the lower temperature main heat pump cycle HPCM_LT is transferred to the operating fluid of the higher temperature main heat pump cycle HPCM_HT for performing the evaporation (and optional overheating) A′-B′ thereof.

The relationship between the higher temperature main heat pump cycle HPCM_HT and the secondary heat pump cycle HPCS is totally similar to that already described with reference to the diagram in FIG. 1A.

As indicated above, it has been seen that through the heat pump unit according to the invention, the “useless” enthalpy resulting from the undercooling of the operating fluid is advantageously converted into enthalpy useful for heating the heat carrier fluid of the external circuit of the first user plant 10. Considering for example a “cascading” cycle like that in FIG. 2, where Isobutane -R600 is used as operating fluid for the main circuit 2 and for the secondary one 3, it has been seen that against the 34 KW required for the operation of compressors C1, C2 of sub-circuits 2a and 2b, the operating fluid of the main circuit has an enthalpy useful for the main condenser S4 capable of transferring a power of 100 thermal KW at 80° C. to the heat carrier fluid of the external circuit. The same operating fluid also has an enthalpy “useless” for the first heat exchanger S2 capable of transferring a heat power of 38 thermal KW at 40° C. to evaporator S1 of the secondary cycle 3. Compressor C3 of the secondary cycle 3, against the 8 electrical KW used, is capable of transferring an additional heat power of 46 thermal KW at 80° C. to the heat carrier fluid circulating in the external circuit that adds up to the 100 thermal KW of enthalpy useful for the main exchanger S4 of the main circuit 2. Overall, it has therefore been seen that the heat carrier fluid receives 146 thermal KW at 80° C. against a use of 42 KW.

In order to provide the same 146 thermal KW at 80° C. to the heat carrier fluid without making the “useless” enthalpy “useful”, the option may be to increase the mass flows rate of the operating fluids related to the dual cascading cycle by 46%. However, thereby, the electrical power used by the compressors would increase proportionally and the COP would remain unchanged (equal to 2.94). Moreover, thereby it would be necessary to also increase the flow rate of cold fluid to the evaporator of the second sub-circuit 2b by 46%. On the other hand, the heat pump unit allows 46% of the electrical power used and 46% of the flow rate of cold fluid to the evaporator of the second sub-circuit 2b to be saved, the yielded heat power at 80° C. being the same.

FIG. 3 shows a variant of the embodiment in FIG. 2, in which the main condenser S4 and the secondary condenser S1 are intended to be connected to external circuits of two separate thermal user plants 10, 11. This variant, which may be implemented in a similar manner also in embodiments of the heat pump unit 1 with single-stage main heat pump cycle HPCM (FIG. 1), is advantageous in all those situations in which it is necessary to serve two medium/high temperature thermal user plants having different operating requirements (different operating temperatures, different operating periods, etc.).

FIG. 4 shows a third preferred embodiment of the heat pump unit 1 which differs from that in FIG. 2 essentially by the provision, in the first sub-circuit 2a for performing the higher temperature main heat pump cycle HPCM_H, of a further heat exchanger S5 connected downstream of the heat exchanger device S2 and upstream of the expansion means L2.

Heat exchanger S5 is adapted to perform an undercooling of the operating fluid of the higher temperature main heat pump cycle HPCM_HT after the condensation thereof in the main condenser S4, and optionally after a first undercooling in the heat exchanger device S2, and is selectively connectable to the external circuit of the heat sink 20 so as to perform a preheating of the heat carrier fluid coming from the latter by means of the heat power released during said undercooling.

In particular, a first end of the heat exchanger S5 is connected in the first sub-circuit 2a as described above and a second end of the heat exchanger S5 is connected upstream of the main evaporator S8 in a line FL2 arranged in the heat pump unit 1 for the connection to the external circuit of the heat sink 20. In such a line FL2 there is also provided a valve V7, preferably a modulating solenoid valve, for adjusting the flow rate of heat carrier fluid of the heat sink 20 which crosses the heat exchanger S5, and thus the extent of the undercooling of the operating fluid in the higher temperature main heat pump cycle HPCM_HT. Line FL2 preferably also comprises a first manifold M1 connected upstream of the heat exchanger S5 and a second manifold M2 connected upstream of the main evaporator S8 and downstream of valve V7. Preferably, manifolds M1 and M2 are also connected by a bypass line BPL for bypassing the heat exchanger S5, provided with a valve V5, also preferably a modulating solenoid valve.

This further embodiment of the heat pump 1 therefore allows the heat power obtained with the undercooling of the operating cycle of the higher temperature main heat pump cycle HPCM_HT to be used for preheating the heat carrier fluid of the heat sink 20, in addition or as an alternative to the use through the secondary heat pump cycle HPCS that may be performed in the secondary circuit 3 described above.

In particular, when compressor C3 of the secondary circuit 3 is off, the undercooling is carried out only in heat exchanger S5. When compressor C3 is cut off or operates at a reduced number of revolutions, the undercooling is partly carried out in the heat exchanger device S2 and partly in heat exchanger S5. In this case, valve V7 is correspondingly cut off. When compressor C3 operates at full load, preferably all the undercooling heat power available is used in the heat exchanger device S2 and heat exchanger S5 is disabled by closing valve V7. Preferably, in order to keep a constant flow rate of the heat sink 20 heat carrier fluid in the main evaporator S8, a modulation or closure of valve V7 is compensated through a corresponding modulation or opening of valve V5. Preferably, in this embodiment and in those described hereinafter, compressors C1 and C2 are variable flow rate compressors, for example cut-off step or inverter compressors. This ensures higher adaptability of the heat pump unit 1 to the possible unbalances in the thermal power exchange between higher temperature main heat pump cycle HPCM_HT and lower temperature main heat pump cycle HPCM_HT which may happen due to the undercooling. Such a higher adaptability has a positive influence on the overall energy efficiency of the heat pump unit 1, all the other conditions being equal.

FIG. 5 shows a fourth preferred embodiment of the heat pump unit 1 which differs from that in FIG. 4 by the provision, in the second sub-circuit 2b for performing the lower temperature main heat pump cycle HPCM_LT, of a further heat exchanger S6 connected downstream of the heat exchanger device S7 and upstream of the expansion means L1.

Similar to heat exchanger S5, heat exchanger S6 is adapted to perform an undercooling of the operating fluid of the lower temperature main heat pump cycle HPCM_LT after the condensation thereof in the heat exchanger device S7, and is selectively connectable to the external circuit of the heat sink 20 so as to perform a preheating of the heat carrier fluid coming from the latter by means of the heat power released during said undercooling.

Preferably, heat exchanger S5 and heat exchanger S6 are arranged so as to perform the preheating of the heat carrier fluid of the heat sink 20 independently of one another, i.e. operating in parallel on two separate flows of such a heat carrier fluid.

In particular, as shown in FIG. 5, the heat exchanger S5 and valve V7 are connected in a first branch FL2′ of line FL2 for the connection to the external circuit of the heat sink 20 and heat exchanger S6 is connected in a second branch FL2″, in parallel with the first branch FL2′, of line FL2. In such a line FL2″ there is also provided a valve V6, preferably a modulating solenoid valve, for adjusting the flow rate of heat carrier fluid of the heat sink 20 which crosses the heat exchanger S6. Similar to what mentioned with reference to valve V7, also the modulation or closing of valve V6 may be compensated through a corresponding intervention on valve V5 in the bypass line BPL in order to keep a constant flow rate of the heat sink 20 heat carrier fluid in the main evaporator S8.

This embodiment of the heat pump 1 allows an undercooling of the operating fluid to be performed also in the lower temperature main heat pump cycle HPCM_LT after the condensation thereof and the heat power thus released to be used for preheating the heat carrier fluid of the heat sink 20.

FIG. 6 shows a fifth preferred embodiment of the heat pump unit 1 which differs from that in FIG. 5 in that the heat exchangers S5 and S6 are further selectively connectable to an external circuit of a further thermal user plant 12, in particular a thermal user plant operating at mean/low temperature, for example a heating plant with floor or ceiling radiating panels, a plant for the production of sanitary hot water, etc.

This is preferably obtained using a three-way valve V8, preferably a solenoid valve, and two valves V9 and V12, preferably modulating solenoid valves, arranged so as to allow the connection of the second end of heat exchangers S5 and S6 alternately to the external circuit of the heat sink 20 or to the external circuit of the thermal user plant 12.

In particular, when the heat power released at the heat exchangers S5 and S6 must be used for serving the thermal user plant 12, the three-way valve V8 is diverted towards the external circuit of such a plant, valves V6 and V7 are fully closed and valves V9 and V12 are fully or partly open. An adjustment of the opening degree of valves V9 and V12 allows the heat power transferred to the thermal user plant 12 to be adjusted.

On the contrary, when the heat power released at the heat exchangers S5 and S6 must be used for preheating the heat sink 20 heat carrier fluid, as in the embodiments described above with reference to FIGS. 4 and 5, the three-way valve V8 is diverted towards the external circuit of the heat sink, valves V9 and V12 are fully closed and valves V6 and V7 are fully or partly open.

In all the embodiments where the pairs of two-way valves V6+V9 and V7+V12 are provided, each of such pairs may be replaced by a three-way valve arranged so as to perform the functions described above of the corresponding two-way valves.

FIGS. 7A and 7B show a sixth preferred embodiment of the heat pump unit 1 adapted to operate for both heating and cooling, i.e. of the reversible type.

To this end, in this embodiment there are provided switching means adapted to allow an exchange of connections of the external circuits of the thermal user plant 10 and of the heat sink 20 respectively with the main condenser S4 and with the main evaporator S8. Preferably, such switching means comprise two four-way valves V1 and V2, preferably solenoid valves, suitably arranged in the lines for the connection of the above external circuits to the main condenser S4 and the main evaporator S8.

In particular, in the operating configuration shown in FIG. 7A, corresponding to a heating operation (winter or autumn and spring), the external circuit of the thermal user plant 10 is connected to the main condenser S4 (and to the secondary condenser S1), whereas the external circuit of the heat sink 20 is connected to the main evaporator S8 in a manner totally similar to the embodiments described above.

In the configuration shown in FIG. 7B, corresponding to a cooling operation (summer), the external circuit of the thermal user plant 10 is connected to the main evaporator S8 so as to provide such a plant with the required cooling power whereas the external circuit of the heat sink 20 is connected to the main condenser S8.

It is noted that in the cooling operation, the use of heat exchangers S5 and S6 for the undercooling of the operating fluid respectively in the higher temperature main heat pump cycle HPCM_HT and in the lower temperature main heat pump cycle HPCM_LT allows a substantial increase of the useful cooling power without a corresponding increase of electrical power used, to the advantage of the overall energy efficiency. Numerical simulations carried out have shown that this embodiment of the heat pump unit 1 when operating for cooling allows EER values to be reached that are equal to 3.5-4.0, against a value of about 2.2 in the absence of undercooling.

The undercooling heat power released in this operating configuration at the heat exchangers S5 and S6 may advantageously be used for example for the production of sanitary hot water in a dedicated plant (schematized in FIG. 7B by the thermal user plant 12). If the undercooling heat power cannot be used, this shall be suitably disposed to the external environment.

In case of cooling operation, the secondary circuit 3 for performing the secondary heat pump cycle HPCS typically is not active (compressor C3 off). Alternatively, for example in use situations in which the production of large amounts of sanitary hot water is required even in hot seasons, it is possible to provide also for the transfer of the power released at the secondary condenser S1 to a plant for the production of sanitary hot water.

FIGS. 8A and 8B show a seventh preferred embodiment of the heat pump unit 1 which differs from that of FIGS. 7A and 7B in that it can also serve, in a dedicated manner, both in a heating operating configuration (FIG. 8A), and in a cooling operating configuration (FIG. 8B), a thermal user plant 13 for the production of sanitary hot water, in addition to the thermal user plants 10 and 12 and optionally 11, already mentioned. This embodiment in particular allows a thermal user plant for the production of high temperature (higher than 60° C. to prevent the possible occurrence of legionella) sanitary hot water to be served.

The embodiment shown in FIGS. 8A and 8B, by way of an example, envisions that the heat exchange with the thermal user plant 13 indirectly takes place at a heat accumulator (boiler) 13a, but other solutions known by the man skilled in the art are also possible for connecting the heat pump unit 1 to the external circuit of such a thermal user plant.

With respect to the embodiment of FIGS. 7A and 7B, connections are further provided in this case for an external circuit of the thermal user plant 13 and two three-way valves V3 and V11, preferably solenoid valves.

The three-way valve V3 is arranged so as to allow, in the heating operating configuration (FIG. 8A), the connection of line FL1, in which the main condenser S4 and the secondary condenser S1 are connected, alternately to the external circuit of the thermal user plant 10 or to the external circuit of the thermal user plant 13. Thereby, the heat power released at the main condenser S4 (and at the secondary condenser S1 when the secondary circuit 3 is active) can be alternately used for heating or producing high temperature sanitary hot water.

The three-way valve V11 is arranged so as to allow, in the cooling operating configuration (FIG. 8B), the connection of line FL1 alternately to the external circuit of the thermal user plant 13. Thereby, the heat power released by the main condenser S4 (and of the secondary condenser S1 when the secondary circuit 3 is active, a condition which may also occur during the cooling operation to meet a high hot water requirement) can be used for producing high temperature sanitary hot water rather than dispersing such a power at the heat sink 20.

FIGS. 9A and 9B show an eighth preferred embodiment of the heat pump unit 1 which, as compared to the embodiment of FIGS. 8A and 8B, in addition allows also low temperature sanitary hot water requirements to be met through the thermal user plant 13 for the production of sanitary hot water already mentioned. The embodiment of FIGS. 9A and 9B differs from that of FIGS. 8A and 8B in particular by the presence of a further three-way valve V4, preferably a solenoid valve.

The three-way valve V4 is arranged so as to allow the selective connection of lines FL2′ and FL2″, in which the heat exchangers S5 and S6 are connected, also to the external circuit of the thermal user plant 13 for the production of sanitary hot water, so as to create a closed circuit therewith. Thereby, the heat power released at the two heat exchangers S5 and S6 can be alternately used for producing sanitary hot water both in the heating operating configuration (FIG. 9A) and in the cooling operating configuration (FIG. 9B), or for preheating the heat sink 20 heat carrier fluid in the heating operating configuration.

For an optimum operation of this embodiment in the cooling operating configuration (FIG. 9B) it is suitable to provide, externally to the heat pump unit 10, means for bypassing the external circuit of the thermal user plant 10, intended for cooling in this operating configuration. Such means preferably comprise a three-way valve V13, preferably a solenoid valve, arranged between the external circuit of the thermal user plant 10 and the external circuit of the thermal user plant 13. The external three-way valve V13, together with the already described three-way valve V11 of the heat pump unit 1, allows line FL1 to be connected to the external circuit of the thermal user plant 13 bypassing the external circuit of the thermal user plant 10.

In particular, in the cooling operating configuration shown in FIG. 9B, the three-way valve V11 connects line FL1 to the external circuit of the thermal user plant 13 whereas the external three-way valve V13 allows the external circuit of the thermal user plant 10 to be bypassed. Thereby, the heat power released by the main condenser S4 (and by the secondary condenser S1 when the secondary circuit 3 is active, a condition which may also occur during the cooling operation to meet a high hot water requirement) can be used for producing high temperature sanitary hot water rather than dispersing such a power at the heat sink 20. This operating mode requires circuit FL1 to be a closed circuit.

FIGS. 10A and 10B show a ninth preferred embodiment of the heat pump unit 1 which differs from that of FIGS. 9A and 9B mainly in that it comprises a further heat exchanger S3 in the first sub-circuit 2a for performing the higher temperature main heat pump cycle HPCM_HT.

In particular, the heat exchanger S3 is connected downstream of the first sub-circuit 2a so as to be downstream of the main condenser S4 and upstream of the heat exchanger device S2 and of the heat exchanger S5 and is adapted, as the latter, to perform an undercooling of the operating fluid of the higher temperature main heat pump cycle HPCM_HT after the condensation of the same in the main condenser S4.

The heat exchanger S3 is further selectively connectable in line FL1 for the connection to the external circuit of the thermal user plant 10, in which the main condenser S4 and the secondary condenser S1 are also connected. This is preferably obtained by means of a three-way valve V10, preferably a modulating solenoid valve, arranged in line FL1 so as to allow the connection in such a line alternately of the heat exchanger S3 or of the secondary condenser S1.

The heat exchanger S3, in the heating operating configuration (FIG. 10A) allows the use of the heat power resulting from an undercooling of the operating fluid of the higher temperature main heat pump cycle HPCM_HT for preheating the heat carrier fluid of the first thermal user plant 10 before it reaches the main condenser S4. As explained above, this leads to a significant improvement of the overall COP of the heat pump unit 1 in particular in operating conditions in which a decrease in the temperature level of the thermal user plant 10 is acceptable, the heat power transferred thereto being equal, as it may happen for example in a high temperature heating plant in spring and autumn.

Therefore, with reference to the heating operating configuration (FIG. 10A) of the ninth embodiment described above, in operating conditions in which the temperature level in the thermal user plant 10 must be maximum (for example in full winter), the three-way valve V10 is preferably diverted so as to connect the secondary condenser S1 in line FL1 and exclude the heat exchanger S3. Advantageously, the heat power provided by the undercooling of the operating fluid of the higher temperature main heat pump cycle HPCM_HT can thus be transferred to the thermal user plant 10 at a higher temperature, due to the secondary heat pump cycle HPCS performed in the secondary circuit 3 (active compressor C3), as already described with reference to the above embodiments. In operating conditions in which the temperature level in the thermal user plant 10 may be reduced, the backflow of heat carrier fluid from the thermal user plant is partly or totally diverted towards the heat exchanger S3 through the three-way valve V10. In case of partial diversion, the secondary circuit 3 may be deactivated or not (compressor C3 cut off or off), whereas in case of full diversion, the secondary circuit 3 is deactivated (compressor C3 off). In case of full diversion towards the heat exchanger S3, the heat power available from the undercooling of the operating fluid of the higher temperature main heat pump cycle HPCM_HT is transferred to the thermal user plant 10 directly, without heat increase, through the heat exchanger S3. The adjustment of the delivery temperature for the thermal user plant 10 takes place through the modulation of the three-way valve V10. A further advantage may be obtained by shutting or reducing the number of revolutions of compressors C1 and C2 in order to reduce the heat power delivered.

In the heating operating configuration shown in FIG. 10A, the use level of the heat exchanger S5, i.e. the fraction of undercooling heat power used therein with respect to the total available, depends on the corresponding use level of the heat exchanger device S2 and of heat exchanger S3.

In particular, the use level of heat exchanger S5 is maximum when the three-way valve V10 is diverted so as to exclude the heat exchanger S3 and the secondary circuit 3 is not active (compressor C3 off). On the contrary, the use level is null when all the undercooling heat power is used in the heat exchanger device S2 (for example in full winter operating conditions) or in heat exchanger S3 (for example in autumn and spring operating conditions). In this case, the heat exchanger S5 is excluded from line FL1 by closing valve V7. In intermediate situations, the use level of the heat exchanger S5 is partial and valve V7 must modulate accordingly. In the cooling operating configuration (FIG. 10B) of the ninth preferred embodiment of the heat pump unit 1, the use of the heat exchanger S3 is not generally required and the three-way valve V10 is therefore diverted so as to exclude such a heat exchanger from line FL1.

In all the embodiments described, the heat pump unit 1 preferably comprises also a programmable control unit not shown in the figures. In particular, such a control unit may be suitably programmed for controlling the opening/closing, the modulation or diverting of the valves as well as the switching on/off, the shutting degree or the number of revolutions of the compressors present in each embodiment of the heat pump unit 1.

The operating fluids used in the various heat pump cycles performed in the heat pump unit 1 may be equal to or different from, each other.

Operating fluids are preferably selected that allow the following advantageous features to be combined for the operation of the heat pump unit 1:

• • limit curves, and in particular lower limit curve, in diagrams h-p highly inclined in the direction of the increasing enthalpies;
  • high specific heat of the operating fluid at the liquid state with respect to the latent condensation/evaporation heat;
  • high specific heat of the operating fluid at the vapor state with respect to the latent condensation/evaporation heat.

The first two features mentioned above are particularly important for embodiments or operating conditions that use strong undercooling whereas the third one is particularly important for all the embodiments or operating conditions that use strong overheating.

In particular, in order to obtain the best performance of the heat pump unit 1, the following operating fluids have proven to be particularly advantageous: (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.

Besides having at least one or more of the desired features listed above, these operating fluids have the advantage of being so-called “natural” cooling fluids, i.e. not harmful for the environment from the viewpoint of negative effects on the stratospheric ozone, or from the viewpoint of the greenhouse effect.

If the type of operating fluid selected, in particular for its hydrocarbon nature, poses safety issues (fire hazard) in the cases in which the heat pump unit 1 must be installed in underground or basement rooms, the latter is preferably provided also with means for the detection and evacuation of gas leaks.

FIG. 11 shows an embodiment of the heat pump unit 1 comprising a system for the detection and evacuation of gas leaks. By way of example, the configuration of the heat pump unit 1 shown corresponds to the first embodiment described above with reference to FIG. 1.

The system for the detection and evacuation of gas comprises at least one gas detector 31, positioned as close as possible to the bottom of the heat pump unit 1 and ventilation means 32, which can be activated by the gas detector 31 and arranged so that the suction thereof is also close to the bottom of the heat pump unit 1, whereas the delivery thereof is connected to a gas evacuation conduit in communication with the external environment. Optionally, there may be provided a dedicated control device 34 adapted to receive signals from the gas detector 31 and to control the ventilation means 32 accordingly. The control device 34 may also control sound and/or light warning means 35, if provided, and/or be configured for sending alarm signals to an optional external monitoring/supervision 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.

A man skilled in the art may obviously use the technical features of the heat pump unit 1 of the invention disclosed with reference to the preferred embodiments described above also in different combinations in order to meet specific and contingent application requirements.

Numerical simulations were carried out in order to determine the improvement in the energy efficiency that may be obtained with the heat pump unit 1 as compared to a heat pump unit of the prior art with similar configuration.

Table 1 shows the comparative results of simulations related to a single-stage configuration, in the case of the invention corresponding to the first preferred embodiment described above with reference to FIGS. 1 and 1A.

TABLE 1
Single-stage heat pump unit
	Invention	Prior art
HPCM
useful heat power [kW]	100	138.1
mass flow rate [kg/s]	0.337	0.466
	h [kJ/kg]	Tin [° C.]	Tout [° C.]	h [kJ/kg]	Tin [° C.]	Tout [° C.]
evaporation +	347.5	40.0	45.0	247.7	40	45
overheating (S8)
compression (C2)	48.9	45.0	81.8	48.9	45	81.8
de-overheating +	296.6	81.8	80.0	296.6	81.8	80
condensation (S4)
undercooling (S2)	99.9	80.0	43.0	—	—	—
HPCS
useful heat power [kW]	38.1	—
mass flow rate [kg/s]	0.101	—
evaporation +	334	40.0	79.0	—	—	—
overheating (S2)
compression (C3)	44	79.0	107	—	—	—
de-overheating +	378	107	73.0	—	—	—
condensation (S1)
Overall cycle
useful heat power [kW]	138.1	138.1
electrical power [kW]	20.9	22.8
COP	6.61	6.07

Table 2 shows the comparative results of simulations related to a two-stage configuration, in the case of the invention corresponding to the second preferred embodiment described above with reference to FIGS. 2 and 2A.

The tables show, for each heat pump cycle performed in the specific heat pump unit (HPCM, i.e. HPCM_HT and HPCM_LT, HPCMS), the useful heat power, the mass flow rate and, for each cycle transformation, the specific enthalpy variation (h) and the operating fluid temperatures at the beginning (Tin) and at the end (Tout) of the transformation. Finally, the overall useful heat power, the electrical power and the COP of the heat pump unit considered are shown (overall cycle). With reference to the circuit diagram of FIGS. 1 and 2, for each transformation, the component at which it is performed is also shown in brackets.

TABLE 2
Two-stage heat pump unit
	Invention	Prior art
HPCM_LT
heat power [kW]	118.1	114.0
mass flow rate [kg/s]	0.339	0.331
	h [kJ/kg]	Tin [° C.]	Tout [° C.]	h [kJ/kg]	Tin [° C.]	Tout [° C.]
evaporation +	293.2	10.0	15.0	285.4	10.0	15.0
overheating (S8)
compression (C1)	55.2	15.0	52.5	59.1	15.0	55.3
de-overheating +	348.5	52.5	47.0	344.5	55.3	50.0
condensation (S7)
HPCM_HT
useful heat power [kW]	100.0	136.4
mass flow rate [kg/s]	0.337	0.460
evaporation +	350.8	44.0	49.0	247.7	40	45
overheating (S7)
compression (C2)	43.6	49.0	82.0	48.9	45	81.8
de-overheating +	297.1	82.0	80.0	296.6	81.8	80
condensation (S4)
undercooling (S2)	97.3	80.0	44.0	—	—	—
HPCS
useful heat power [kW]	36.4	—
mass flow rate [kg/s]	0.098	—
evaporation +	333	44.0	79.0	—	—	—
overheating (S2)
compression (C3)	38	79.0	104.9	—	—	—
de-overheating +	370	104.9	73.0	—	—	—
condensation (S1)
Overall cycle
useful heat power	136.4	136.4
electrical power	37.1	42.0
COP	3.68	3.25

R600 has been considered as operating fluid. In the configurations which provide for multiple heat pump cycles, the operating fluid was the same for all cycles.

The simulations were carried out with the same useful heat power of the heat pump unit (overall cycle), equal to 138.1 kW in the simulations related to single-stage configurations and to 136.4 kW in the simulations related to two-stage configurations, respectively.

As it may be seen, the COP of the heat pump units of the invention is higher than that of the heat pump unit of the prior art having similar configuration. In particular, there occurs an increase of about 9% in the COP for a single-stage configuration, and of about 13% for a two-stage configuration.

Moreover, it is noted that in the case of the heat pump units of the invention, the mass flow rates of operating fluid in the secondary heat pump cycles HPCS are substantially lower than the mass flow rates of operating fluid in the main heat pump cycles HPCM, i.e. HPCM_HT and HPCM_HT. In particular, the ratio between the above flow rates is about 1:3. As already explained above, the possibility of performing the secondary heat pump cycles HPCS with minimum mass flow rates of operating fluid is one of the main factors to which the improvement in the COP which can be obtained with the heat pump units of the invention can be ascribed.

Claims

1. Heat pump unit comprising at least one main circuit adapted to perform a main heat pump cycle with a respective operating fluid, said at least one main circuit comprising: characterized by comprising a secondary circuit adapted to perform a secondary heat pump cycle with a respective operating fluid, said secondary circuit comprising:

a main condenser adapted to perform the condensation of the operating fluid of said main heat pump cycle and intended to be connected to an external circuit of a first thermal user plant in a heating operating mode of said heat pump unit;

a first heat exchanger, connected downstream of said main condenser and upstream of the expansion means of said at least one main circuit, adapted to perform an undercooling of the operating fluid of said main heat pump cycle after the condensation of the same in said main condenser, and

a main evaporator adapted to perform the evaporation of the operating fluid of said main heat pump cycle and intended to be connected to an external circuit of a heat sink in a heating operating mode of said heat pump unit,

a secondary evaporator adapted to perform at least the evaporation of the operating fluid of said secondary heat pump cycle and in heat exchange relationship with said first heat exchanger to transfer heat power released by the operating fluid of said main heat pump cycle during said undercooling to the operating fluid of said secondary heat pump cycle, and

a secondary condenser adapted to perform the condensation of the operating fluid of said secondary heat pump cycle and intended to be connected to the external circuit of said first thermal user plant or to an external circuit of a second thermal user plant, different from said first thermal user plant.

2. Heat pump unit according to claim 1, wherein both said main condenser (S4) and said secondary condenser are intended to be connected to the external circuit of said first thermal user plant and are connected to each other so as to be in series in said external circuit of said first thermal user plant.

3. Heat pump unit according to claim 1, wherein said main circuit comprises a first sub-circuit adapted to perform a higher temperature main heat pump cycle with a respective operating fluid and a second sub-circuit adapted to perform a lower temperature main heat pump cycle with a respective operating fluid, wherein said first and second sub-circuits are in cascading heat exchange relationship with each other in order to perform globally a two-stage main heat pump cycle, and wherein said main condenser and said first heat exchanger are connected in said first sub-circuit and said main evaporator is connected in said second sub-circuit.

4. Heat pump unit according to claim 3, wherein said first sub-circuit comprises a second heat exchanger connected downstream of said first heat exchanger and upstream of expansion means of said first sub-circuit said second heat exchanger being adapted to perform an undercooling of the operating fluid of said higher temperature main heat pump cycle after the condensation thereof and being selectively connectable to the external circuit of said heat sink in order to perform a preheating of a heat carrier fluid coming from said heat sink by means of heat power released during said undercooling by the operating fluid of said higher temperature main heat pump cycle.

5. Heat pump unit according to claim 4, wherein said second heat exchanger is further selectively connected to an external circuit of a third thermal user plant.

6. Heat pump unit according to claim 4, wherein said second sub-circuit comprises a third heat exchanger connected downstream of a condenser and upstream of expansion means of said second sub-circuit, said third heat exchanger being adapted to perform an undercooling of the operating fluid of said lower temperature main heat pump cycle after the condensation thereof and being selectively connectable to the external circuit of said heat sink so as to perform, preferably independently with respect to said second heat exchanger, a preheating of a heat carrier fluid coming from said heat sink by means of heat power released during said undercooling by the operating fluid of said lower temperature main heat pump cycle.

7. Heat pump unit according to claim 6, wherein said third heat exchanger is further selectively connectable to the external circuit of said third thermal user plant.

8. Heat pump unit according to claim 3, wherein said first sub-circuit comprises a fourth heat exchanger connected downstream of said main condenser and upstream of said first heat exchanger, said fourth heat exchanger being adapted to perform an undercooling of the operating fluid of said higher temperature main heat pump cycle after the condensation of the same and being selectively connectable to the external circuit of said first thermal user plant so as to be in series with said main condenser in said external circuit of said first user plant.

9. Heat pump unit according to claim 1, comprising switching means adapted to allow an exchange of connections of the external circuits of at least said first thermal user plant and said heat sink respectively with at least said main condenser and with said main evaporator.

10. Heat pump according to claim 1, wherein the operating fluid of said main heat pump cycle, or the operating fluids of said higher temperature main heat pump cycle and said lower temperature main heat pump cycle respectively, and the operating fluid of said secondary heat pump cycle 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, 8290, R600, R600a, R601, R601a, RE-170, tetramethylmethane or RC-270.

11. Heat pump unit according to claim 1, comprising means for detecting and evacuating gas leaks.

12. System for heating/cooling environments and/or for producing sanitary hot water comprising a heat pump unit according to claim 1.

13. Heat pump unit according to claim 5, wherein said second sub-circuit comprises a third heat exchanger connected downstream of a condenser and upstream of expansion means of said second sub-circuit, said third heat exchanger being adapted to perform an under-cooling of the operating fluid of said lower temperature main heat pump cycle after the condensation thereof and being selectively connectable to the external circuit of said heat sink so as to perform, preferably independently with respect to said second heat exchanger, a preheating of a heat carrier fluid coming from said heat sink by means of heat power released during said undercooling by the operating fluid of said lower temperature main heat pump cycle.

14. Heat pump unit according to claim 7, wherein said third heat exchanger is further selectively connectable to the external circuit of said third thermal user plant.