Co2 reversible heat pump and method for operating same

Abstract

The invention relates to a reversible heat pump, in which the refrigerant is CO2, and to a method for operating such a pump. The invention is characterized in that the heat pump comprises a hot water distribution circuit (1) provided with a hot exchanger (9), a chilled water distribution circuit (2) provided with a cold exchanger (11), a tank (3) for CO2 in the gaseous and / or liquid state, a compressor (4) and one or more combined blocks (5-1, 5-2), each combined block comprising a gas cooler (6) and an air evaporator (7), the heat pump having a plurality of operating modes, namely a cooling operating mode only in which the heat pump produces chilled water, a heating operating mode only in which the heat pump produces hot water, and a heating and defrosting operating mode in which a hot gas from the hot exchanger (9) is used for defrosting.

Description

[0001]REVERSIBLE CO2 HEAT PUMP AND OPERATING METHOD FIELD OF THE INVENTION The present invention relates to a reversible heat pump, in which the refrigerant is CO2. It further relates to a method of operating such a pump. PRIOR ART There are several types of heat pumps. These are - air / air heat pumps, for which thermal energy is transferred from the air constituting a first medium, to the air constituting a second medium; - air / water heat pumps, for which thermal energy is transferred from the air constituting one medium, to the water constituting another medium; water / air heat pumps, for which thermal energy is transferred from the water constituting one medium, to the air constituting another medium; and - water / water heat pumps,for which thermal energy is transferred from water constituting one medium to water constituting another medium. Heat pumps according to the prior art use refrigerants from the petroleum industry commonly called FreonTM. However, refrigeration and / or air conditioning units are known, which use so-called CO2 (carbon dioxide) technology. This technology has been known since the 1920s, but was developed in the early 2000s, then put on the market, particularly in mass distribution, from 2008. CO2 is a natural fluid, which has the particularity of no longer condensing above a temperature of 33°C. This fluid operates at pressures much higher than those of the fluids used in conventional systems. In practice, for CO2, the so-called working pressures are between 10 and 100 bars, whereas, for the fluids used in conventional systems,these pressures are between 0 and 33 bars. In some refrigeration applications using CO2, such as refrigeration applications implemented in warehouses or supermarkets, the heat produced by the refrigeration system is recovered to heat premises, such as offices, the sales area, work premises. However, there is still cold production. In practice, to date, there is no reversible CO2 heat pump. Indeed, in the case of a conventional reversible heat pump according to the prior art, using conventional refrigerants, during the changes, the function of the exchangers is reversed, and the evaporator becomes a condenser and vice versa. Due to the high pressures required for a CO2 machine, there is no control equipment or accessory capable of reversing the refrigeration cycle and this,especially since it is necessary to add to this a so-called trans-critical operation of the machine with a calorie production stage at 100 bars, an intermediate stage at 60 bars, and a cold production stage at 40 bars. SUMMARY OF THE INVENTION In view of the above, a problem that the invention proposes to solve is to produce a heat pump in which the refrigerant is CO2, as well as a method of operating such a heat pump. The solution of the invention advantageously proposes, in response to this problem, the original implementation of a combined hot / cold battery formed by a gas cooler, which forms the hot part of the battery, and an air evaporator, which forms the cold part of this battery. During defrosting, the fluid comes from the CO2 / water exchanger,which makes it possible not to affect the resilience of the materials. The proposed solution of the invention to this problem posed has as its first object a reversible heat pump, in which the refrigerant is CO2, the reversible heat pump comprising a hot water distribution circuit provided with a hot exchanger, a chilled water distribution circuit provided with a cold exchanger, a CO2 reservoir in the gaseous and / or liquid state, a compressor and one or more combined blocks, each combined block comprising a gas cooler and an air evaporator, the heat pump having a plurality of operating modes, an air conditioning only operating mode in which the heat pump produces chilled water, a heating only operating mode in which the heat pump produces hot water, and a heating and defrosting operating mode,in which a hot gas from the hot exchanger is used for defrosting. Advantageously, - the heat pump also has an air conditioning operating mode with heat recovery; - in the operating mode the tank is connected to the compressor by a fluid inlet pipe in said compressor, provided with an expansion valve, the compressor is connected to the gas coolers by a pipe on which are arranged a first and a second three-way valve, the first three-way valve being a valve which receives the compressed fluid from the compressor and directs it, as the case may be, to the hot exchanger or to the second three-way valve, the second three-way valve directing the fluid received either from the hot exchanger or from the compressor, through the first three-way valve, to, as the case may be, the fluid supply pipe from the gas coolers to the tank,or to the coolers; - in the air conditioning only operating mode, the CO2 fluid is expanded in the evaporator(s), then sucked in by the compressor; - in the heating only operating mode, the air evaporators evaporate the CO2 fluid, this fluid having previously been expanded by means of the expansion valves; and - in the heating and defrosting operating mode, cold production is stopped in the evaporator by closing an expansion valve, a hot gas three-way valve is opened, as well as a valve of the gas cooler corresponding to the evaporator to be defrosted. The solution of the invention has as a second object a method of operating a heat pump in which the refrigerant is CO2, according to which a reversible heat pump is provided comprising a hot water distribution circuit provided with a hot exchanger, a chilled water distribution circuit provided with a cold exchanger,a CO2 reservoir in the gaseous and / or liquid state, a compressor and one or more combined blocks (5-1, 5-2), each combined block comprising a gas cooler (6) and an air evaporator (7), the heat pump operating according to a plurality of operating modes, an air conditioning only operating mode (figure 2) in which the heat pump produces chilled water, a heating only operating mode (figure 4) in which the heat pump produces hot water, and a heating and defrosting operating mode (figure 5), in which a hot gas from the hot exchanger (9) is used for defrosting. BRIEF DESCRIPTION OF THE FIGURES The invention will be better understood from reading the following non-limiting description, drawn up with reference to the appended drawings, in which: figure 1 illustrates a heat pump according to the invention; figure 2 illustrates the heat pump according to the invention,in the air conditioning only operating mode; Figure 3 illustrates the heat pump according to the invention, in the air conditioning with heat recovery operating mode; Figure 4 illustrates the heat pump according to the invention, in the heating only operating mode; and Figure 5 illustrates the heat pump according to the invention, in the heating and defrosting operating mode. DETAILED DESCRIPTION OF THE INVENTION As shown in Fig. 1, the heat pump according to the invention comprises a hot water distribution circuit 1, a chilled water distribution circuit 2, a CO2 fluid reservoir 3, a compressor 4 and one or more combined blocks 5-1, 5-2 also called a battery, each combined block comprising a gas cooler 6 and an air evaporator 7. The hot water distribution circuit 1 comprises a water inlet pipe, a pump 8 for pumping water into this pipe,a hot exchanger 9 and a hot water distribution pipe. The chilled water distribution circuit 2 comprises a water inlet pipe, a pump 8 for pumping water into this pipe, a cold exchanger 11 and a chilled water distribution pipe. The combined block(s) 5-1, 5-2 are physically unitary blocks and form a single assembly composed of two integral and nested functional elements, namely a gas cooler 6 and an air evaporator 7. Nested in these blocks / batteries is a high-pressure circuit, of the order of 100 bars, for the evacuation of calories in summer, and a low-pressure battery – 33 bars -, which captures the calories in winter. The tank 3 is connected to the cold exchanger 11 by a fluid inlet pipe in said exchanger 11, on which an expansion valve 12 is arranged. It is also connected to the air evaporators 7 of the combined blocks 5-1,5- 2 by fluid inlet pipes in said evaporators, on which are arranged expansion valves 13. Furthermore, the gas coolers 6 are themselves connected to the tank 3 by a fluid inlet pipe in said tank, on which is arranged a pump and an expansion valve 14. The tank 3 is finally connected to the compressor 4 by a fluid inlet pipe in said compressor, provided with an expansion valve 15. The compressor 4 is connected to the gas coolers by a pipe on which are arranged two three-way valves 16, 17. The first three-way valve 16 is a valve which receives the compressed fluid from the compressor 4 and directs it, as the case may be, to the hot exchanger 9 or to the second three-way valve 17. This second three-way valve 17 directs the fluid received either from the hot exchanger 9 or from the compressor 4, through the first three-way valve, to, as the case may be,the fluid supply line from the gas coolers 6 to the tank 3, or to said coolers 6. The different operating modes of the heat pump according to the invention are shown in Figures 2, 3, 4 and 5. It should be noted that the pressures and temperatures specified in the remainder of the description vary depending on the external conditions, the conditions of use - the load to be supplied being variable -, the regulation. In Figure 2, the heat pump operates in air conditioning mode only, or air conditioning only. Operation in air conditioning only makes it possible to produce chilled water, namely water at temperatures between approximately 7°C and approximately 12°C, in practice when the outside ambient temperature is high, for example above 25°C, that is to say, generally, in summer. As shown in Figure 2,the CO2 fluid is expanded in the evaporator(s) 7 via the expander. The fluid pressure then increases from 56 bars – the pressure at which the fluid is in the liquid state – to a pressure of around 35 bars, in which the fluid is in a mixed liquid / gas state. After complete evaporation of the fluid in the evaporator(s) 7, the gas is, at the outlet of said evaporators, in the gaseous state, at 100%. The CO2 is sucked in, at a pressure of around 35 bars, by the compressor 4. The pressure at the outlet of the compressor 4 is around 90 bars, and the temperature, around 90°C. In transcritical mode, the fluid pressure is greater than approximately 31°C, and the pressure is around 72 bars. The fluid is then cooled by the gas cooler(s) 6, at a pressure of 90 bars. However, the temperature is then approximately equal to 2°C above the ambient air temperature, i.e. for an air temperature equal to 35°C,a gas temperature equal to 37°C. The cooled gas is then expanded by the expansion valve, to a pressure for example of the order of 56 bars. As a result, there is, in the tank 3, approximately 60% of CO2 fluid in the liquid state and 40% of CO2 fluid in the gaseous state. The liquid CO2 fluid located in the lower part of the tank 3 is sent to the expansion valve 12 for expansion and production of cold by the circuit 2. The gas located in the upper part of the tank 3 is sucked in by the compressor 4, after expansion by the valve 15 so that the pressure is lowered from 56 bars to 35 bars. In the case where the condensation pressure is lower than 72 bars (temperature of 31°C), the CO2 is condensed in the gas cooler 6. There is then 100% liquid in the tank 3 and there is no reinjection of gas into the compressor 4. This operating mode is called subcritical. In figure 3,the heat pump operates in air conditioning mode with heat recovery. This operating mode is identical to the air conditioning only operating mode. However, in the air conditioning with heat recovery operating mode, the following operations are implemented in addition to the operations implemented in the air conditioning only mode. First of all, the hot fluid at the compressor discharge, whose temperature is around 90°C, and whose pressure is around 90 bars in transcritical mode, and whose temperature is around 70°C and whose pressure is less than 72 bars in subcritical mode, is sent directly to the hot exchanger 9 via the three-way valves 16. Then, the hot exchanger 9 recovers the heat to heat the water in the hydraulic heating network,using circuit 1. The fluid is then directed to the gas cooler 6 to finish being cooled and continue its cycle. The air conditioning mode with heat recovery is generally used in spring and autumn when it is necessary to both heat part of a building and air condition another part of this building according to the needs of each, for example in the case where premises are oriented differently. The priority in this operating mode is air conditioning. In Figure 4, the heat pump operates in heating only mode. In this operating mode, which is mainly implemented in winter, the air “evaporator” batteries 7, which are nested in the gas coolers 6 are used. These evaporator batteries 7 make it possible to evaporate the CO2 fluid, at a pressure of around 25 bars, this fluid having previously been expanded by means of the expansion valves 13,the pressure of the upstream fluid in the liquid state being of the order of 56 bars. The CO2 fluid in the gaseous state is then sucked in by the compressor. The discharge gases, at a pressure of the order of 99 bars and at a temperature of the order of 90°C, are then sent to the hot exchanger 9 for heating the hot water distribution circuit 1, the water temperature being between 45 and 65°C. The fluid leaving the exchanger 9 is directed to the expansion valve 14, which allows the pressure to be reduced from approximately 99 bars to approximately 56 bars. The expanded fluid produces 60% liquid and 40% gas. The liquid is sent to the expansion valves 13 to be injected into the air evaporator batteries 7. The gas part, in the upper part of the tank 3, is expanded via the expansion valve 15, which allows the gas pressure to drop from approximately 56 bars to approximately 25 bars. The gas is then re-aspirated by the compressor 4. Thus,in this situation, the system is forced to operate in transcritical mode, with high pressures, which allow the water to be heated to a high temperature, up to 90°C. In Figure 5, the heat pump operates in heating and defrosting mode. When cold is produced at an evaporation temperature below 0°C, frost forms on the evaporator coils 7. Frost is an insulator, which impairs the operation of the system. This is why defrosting is carried out cyclically. To carry out these defrosting operations, the production of cold in the evaporator is stopped by closing the expansion valve 12. The hot gas three-way valve 16 is then opened, as is the valve of the gas cooler 6 corresponding to the evaporator 7 to be defrosted. The injection of hot gas into the gas cooler 6 allows, by conduction, to melt the ice. The fans are off. When the battery is completely defrosted,the fans are restarted to dry it. Following this, the evaporator 7 is powered again and then restarted. In the advantageous case where several gas coolers 6 / evaporators 7 are connected in parallel, defrosting takes place in turn. Ultimately, the recovery of warm gases from the heating exchanger to defrost the evaporators 7 / gas coolers 6 makes it possible to avoid having too great a temperature difference during phase changes which could affect the resistance of materials which are very sensitive to rapid temperature changes. Finally, in summer, only the hot battery is used to evacuate the calories. In winter, the cold battery is used to capture the calories. When the outside temperature is low,frost forms on the exchanger. Defrosting is then carried out by stopping the cold coil and starting the hot coil which melts the ice. The fans are stopped during this phase called "defrosting". The hot gases used for this cycle are those coming from the outlet of the heat production exchangers so as not to create too large a temperature difference and make the metals work on too great a resilience. If the hot gases produced directly by the compressors were used, there would be a rupture of the exchange coils. Another advantage is that conventional heat pumps produce water at a maximum temperature of 50°C. In the case of a CO2 heat pump according to the invention, these maximum temperatures can be 85°C, which makes it possible to replace combustion boilers. In the invention,the air battery is nested with two circuits where there is the hot "gascooler" for the evacuation of calories in summer and the cold evaporator to capture calories in winter. This makes it possible to use the hot "gascooler" to defrost the cold evaporator battery in winter. This is not possible in the heat pumps of the prior art, because the elements are dissociated. In the invention, we advantageously have a heat pump having several batteries. Thus, it is possible to defrost them without stopping production. In the case of the heat pumps of the prior art, the system switches to cycle inversion to defrost and, therefore, no longer produces heating. To date,There is no high-power equipment to perform cycle inversion with a four-way valve. The invention proposes such equipment by circumventing the principle of reversibility by designing a battery with two circuits ("gascooler" and evaporator). With the addition of recovering the hot gases at the outlet of the hot water production gascooler to inject warm gas into the air gascoolers during defrosting. This makes it possible not to have too large a temperature difference and to be at the limit of resistance of the metal (resilience of materials). This phenomenon is known in particular in CO2 installations where there are high pressures and significant temperature differences, which destroys the exchangers. The invention proposes a solution to this particular technical problem.,

Claims

CLAIMS 1. Reversible heat pump, in which the refrigerant is CO2, the reversible heat pump comprising a hot water distribution circuit (1) provided with a hot exchanger (9), a chilled water distribution circuit (2) provided with a cold exchanger (11), a CO2 reservoir in the gaseous and / or liquid state (3), a compressor (4) and one or more combined blocks (5-1, 5-2), the combined block(s) being physically unitary blocks and forming a single assembly composed of two integral and nested functional elements, namely a gas cooler (6) and an air evaporator (7), the heat pump having a plurality of operating modes, an air conditioning only operating mode in which the heat pump produces chilled water, a heating only operating mode in which the heat pump produces hot water, and a heating and defrosting operating mode,in which a hot gas from the hot exchanger (9) is used for defrosting.

2. Heat pump according to claim 1, characterized in that it further has an air conditioning operating mode with heat recovery.

3. Heat pump according to one of claims 1 or 2, characterized in that, in the operating mode, the reservoir (3) is connected to the compressor (4) by a fluid inlet pipe in said compressor (4), provided with an expansion valve (15), the compressor (4) is connected to the gas coolers (6) by a pipe on which are arranged a first and a second three-way valve (16, 17), the first three-way valve (16) being a valve which receives the compressed fluid from the compressor (4) and directs it, as the case may be, to the hot exchanger (9) or to the second three-way valve (17), the second three-way valve (17) directing the fluid received either from the hot exchanger (9) or from the compressor (4),through the first three-way valve (16), to, as the case may be, the fluid supply line from the gas coolers (6) to the tank (3), or to the coolers (6).

4. Method of operating a heat pump according to one of the preceding claims, in which the refrigerant is CO2, according to which a reversible heat pump is provided comprising a hot water distribution circuit (1) provided with a hot exchanger, (9), a chilled water distribution circuit (2) provided with a cold exchanger (11), a CO2 reservoir in the gaseous and / or liquid state (3), a compressor (4) and one or more combined blocks (5-1, 5-2), the combined block(s) being physically unitary blocks and forming a single assembly composed of two integral and nested functional elements, namely a gas cooler (6) and an air evaporator (7), the heat pump operating according to a plurality of operating modes, an air conditioning only operating mode in which the heat pump produces chilled water, a heating only operating mode in which the heat pump produces hot water, and a heating and defrosting operating mode, in which a hot gas from the hot exchanger (9) is used for defrosting. 5.Method according to claim 4, characterized in that, in the air conditioning only operating mode, the CO2 fluid is expanded in the evaporator(s) (7), then sucked in by the compressor (4).

6. Method according to one of claims 4 or 5, characterized in that, in the heating only operating mode, the air evaporators (7) evaporate the CO2 fluid, this fluid having previously been expanded by means of the expansion valves (13).

7. Heat pump according to one of claims 4 to 6, characterized in that, in the heating and defrosting operating mode, cold production is stopped in the evaporator (7) by closing an expansion valve (12), a hot gas three-way valve (16) is opened, as well as a valve of the gas cooler (6) corresponding to the evaporator (7) to be defrosted.

Images