KR20140123968A - Cascade refrigeration system - Google Patents

Abstract

The present invention is directed to cooling a fluid or a body by a first vapor compression circuit (10) containing at least a first heat exchange fluid and a second vapor compression circuit (20) containing at least a second heat exchange fluid, Lt; RTI ID = 0.0 >
- measuring the temperature of the surrounding water; And
- Set the temperature of the second heat-exchange fluid for evaporation, depending on the temperature of the external ambient water.
The invention also relates to an installation suitable for carrying out such a method.

Description

CASCADE REFRIGERATION SYSTEM < RTI ID = 0.0 >

The present invention relates to a cascaded cooling system designed to operate optimally and to a cooling method performed in such a system.

Cooling systems typically include fluid evaporation at low pressure where the fluid absorbs heat; Compression of the evaporating fluid to high pressure; Condensation of the evaporating fluid to produce liquid at high pressure, wherein the fluid emits heat; And a thermodynamic cycle involving pressure reduction of the fluid to complete the cycle.

The choice of the heat-exchange fluid (which may be a pure compound or mixture of compounds) depends, on the one hand, on the thermodynamic properties of the fluid and on the other, by further constraints. Therefore, an important criterion is the influence of the fluid considered in the environment. In particular, chlorinated compounds (chlorofluorocarbons and hydrochlorofluorocarbons) have the disadvantage of damaging the ozone layer. Thus, non-chlorinated compounds such as hydrofluorocarbons, fluoroethers and fluoroolefins are generally preferred in the future.

Another environmental constraint is the Global Warming Potential (GWP). Therefore, it is essential to develop heat-exchange compositions that exhibit as low a GWP as possible and good energy performance.

Some special cooling systems are based on the use of several cooling circuits and in particular two circuits connected together: high temperature circuit and low temperature circuit: these systems are referred to as "cascaded" systems. The two circuits generally comprise different heat-exchange fluids.

Cascaded systems represent a number of safety-related benefits. In particular, for cost or performance reasons, another heat-exchange fluid may be used that uses a particular heat-exchange fluid in the high temperature circuit and is less flammable or less toxic in the low temperature circuit. Thus, the total charge of the most flammable or most toxic heat-exchange fluid is minimized, and this most flammable or most toxic heat-exchange fluid is contacted with the public or individuals at the unconfined region and / It is limited to areas where there is no danger.

For example, carbon dioxide is a heat-exchange fluid that is highly advantageous in terms of its non-flammability and environmental aspects. However, due to its low critical point, it is generally less effective than conventional heat-exchange fluids (hydrocarbons, hydrofluorocarbons, etc.). The optimum solution may consist of using a cascaded system comprising carbon dioxide in the low temperature circuit and a conventional heat-exchange fluid in the high temperature circuit.

The documents WO 2008/150289 and WO 2011/056824 provide examples of cascaded cooling systems.

The thesis by Dopazo et al., Applied Thermal Engineering, 29, 1577-1583 (2009), a CO ₂ -NH ₃ cascade refrigeration system for low temperatures, and also International Journal of Refrigeration, 32, 1358-1365 2009) describes the performance of cascaded systems using ammonia in carbon dioxide and high temperature circuits in low-temperature circuits, and the performance of the NH ₃ / CO ₂ cascade refrigeration system with twin-screw compressors have.

However, there is still a need to improve the performance and efficiency of cascaded cooling systems, and there is in particular a need to minimize the overall energy consumption and also the associated environmental impact of such systems.

The present invention firstly relates to a method of cooling a fluid or a body by means of at least one second vapor compression circuit comprising at least one first vapor compression circuit comprising a first heat exchange fluid and a second heat exchange fluid The method comprising: < RTI ID = 0.0 >

In the first vapor compression circuit:

Partial evaporation of a portion of the first heat-exchange fluid by heat exchange with the fluid or body;

■ First heat - compression of the exchange fluid;

A second heat - a portion of the first heat-exchange fluid is condensed by heat exchange with the exchange fluid;

■ First heat - pressure reduction of the exchange fluid;

In the second vapor compression circuit:

■ first heat - partial evaporation of the second heat-exchange fluid by exchange of heat with the exchange fluid;

■ second heat - compression of the exchange fluid;

■ second heat by heat exchange with the external medium - condensation of at least some of the exchange fluid;

■ second heat - pressure reduction of the exchange fluid;

The method also includes:

- measuring the temperature of the external medium; And

- temperature control of the second heat-exchange fluid during evaporation, as a function of the temperature of the external medium.

According to embodiments, temperature control of the second heat-exchange fluid upon evaporation is performed continuously or more than once per hour.

According to one embodiment, the method includes the detection of a change in temperature of the external medium, wherein the temperature control of the second heat-exchange fluid upon evaporation is such that, when an increase in temperature of the external medium is detected, And a temperature decrease of the second heat-exchange fluid upon evaporation when a temperature decrease of the external medium is detected.

According to one embodiment, the method comprises calculating the optimum evaporation temperature as a function of the temperature measurement of the external medium.

According to one embodiment, the temperature of the second heat exchange fluid at the time of evaporation is adjusted to the optimum evaporation temperature.

According to one embodiment, the optimum evaporation temperature corresponds to a vaporization temperature at which the total coefficient of performance of the first vapor compression circuit and the second vapor compression circuit is at a maximum.

According to one embodiment, the optimum evaporation temperature is defined by the formula T _opt = A x T _ext + B, where T _ext is the external medium temperature to C, A is the dimensionless constant, and B is the constant to C °.

According to one embodiment, the constant A has a value of from 0.3 to 0.6, preferably from 0.4 to 0.45, and the constant B has a value of from -50 캜 to 0 캜, preferably from -30 캜 to -20 캜.

According to one embodiment, the fluid or body is cooled to a temperature of -50 to -15 占 폚, preferably -40 to -25 占 폚.

According to one embodiment:

The first heat exchange fluid is selected from carbon dioxide, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably carbon dioxide; And / or

The second heat exchange fluid is selected from ammonia, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably tetrafluoropropene, more particularly preferably 2, 3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene.

According to one embodiment, the compression of the second heat-exchange fluid is performed by one or more compressors, and the temperature control of the second heat-exchange fluid upon evaporation is performed by control of the compressor.

According to one embodiment, the control of the compressor comprises adjusting the rotational speed of the compressor or is performed by continuous start and shutdown of the compressor.

According to one embodiment, the method is a method of cooling a compartment containing a product, preferably a food product (which is highly refrigerated or frozen).

The invention also relates to a facility for cooling a fluid or a body, at least comprising:

A first vapor compression circuit comprising a first column-exchange fluid;

A second vapor compression circuit comprising a second column-exchange fluid;

A cascaded heat exchanger suitable for exchanging heat between the first heat exchange fluid and the second heat exchange fluid;

Said first vapor compression circuit comprising:

A first evaporator suitable for exchanging heat between the first heat exchange fluid and the fluid or body;

At least one first compressor;

A first expansion device;

Said second vapor compression circuit comprising:

At least one second compressor;

A second condenser suitable for exchanging heat between the second heat exchange medium and the external medium;

A second expansion device;

The facility also includes:

A device for measuring the temperature of the external medium; And

Means for controlling the evaporation temperature in a cascaded heat exchanger as a function of the temperature measurement of the external medium.

According to one embodiment, the facility also includes a module for calculating the optimum evaporation temperature as a function of the external medium temperature measurement.

According to one embodiment, the means for controlling the evaporation temperature in a cascaded heat exchanger is suitable for controlling the evaporation temperature of the cascaded heat exchanger to the optimum evaporation temperature.

According to one embodiment, the optimum evaporation temperature corresponds to a vaporization temperature at which the total coefficient of performance of the first vapor compression circuit and the second vapor compression circuit is at a maximum.

According to one embodiment, the optimal evaporation temperature is defined by the formula T _opt = A x T _ext + B, where T _ext is the external medium temperature to C, A is the dimensionless constant, and B is the constant to C do.

According to one embodiment, the constant A has a value of from 0.3 to 0.6, preferably from 0.4 to 0.45, and the constant B has a value of from -50 캜 to 0 캜, preferably from -30 캜 to -20 캜.

According to one embodiment, the installation is suitable for cooling the body or fluid to a temperature of -50 to -15 占 폚, preferably -40 to -25 占 폚.

According to one embodiment:

The first heat exchange fluid is selected from carbon dioxide, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably carbon dioxide; And / or

The second heat exchange fluid is selected from ammonia, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably tetrafluoropropene, more particularly preferably 2 , 3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene.

According to one embodiment, the means for regulating the evaporation temperature in the cascaded heat exchanger comprises control means of the second compressor.

According to one embodiment, the control means of the second compressor is suitable for regulating the rotational speed of the second compressor or is suitable for the continuous start and shutdown of the second compressor.

According to one embodiment, the installation comprises a compartment suitable for receiving a product, preferably a food product (which is frozen or frozen).

The present invention makes it possible to satisfy the requirements felt in the state of the art. More particularly, it provides a refrigeration process and corresponding equipment that minimizes overall energy consumption and environmental impact.

This is achieved by adjusting the evaporation temperature of the heat-exchange fluid of the hot circuit as a function of the external temperature (ambient temperature). It has been found that the adjustment allows to optimize the overall performance of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an illustration of a plant according to the invention.

2 is a graph showing the following: (1) a change in ambient temperature during the representative blade taken as an example (white circle, left axis of ordinate, value in C); And (2) an example of a typical change in refrigeration capacity (black square, right axis of ordinate, value in kW) required to preserve frozen foods for this representative day; This is as a function of the time of the day (axis of abscissa).

Figure 3 shows the heat exchange fluid of the high temperature circuit: (1) HFO-1234yf (white square); (° C, axis of ordinate) as a function of ambient temperature (° C, axis of abscissa), with respect to a cascaded cooling system which is a HFO-1234ze (black circle) .

Fig. 4 is a graphical representation of the effect of the cooling system on the performance of the system according to the invention (gray bars, the evaporation temperature of the hot, heat-exchange fluid conditioned as a function of the ambient temperature) (KWh) of the cooling system for a representative day, depending on the temperature (e.g., evaporation temperature). The two sets of data correspond to (1) when the heat-exchange fluid of the high temperature circuit is HFO-1234yf, and (2) when the heat-exchange fluid of the high temperature circuit is HFO-1234ze.

5 is a graph illustrating the TEWI index of a cascaded cooling system for a representative day in various scenarios: a typical cooling system and HFO-1234yf (R1234yf rod) in a high temperature circuit; A cooling system and HFO-1234yf (opti R1234yf rod) according to the invention in a high temperature circuit; Conventional cooling systems and HFO-1234ze (R1234ze rod) in high temperature circuits; A cooling system and HFO-1234ze (opti R1234ze rod) according to the invention in a high temperature circuit. This value corresponds to the percentage of the TEWI index for reference conditions (typical cooling system in high temperature circuits and HFO-1234yf). A typical system is one in which the evaporation temperature of the hot heat-exchange fluid is set at -10 DEG C, and the system according to the present invention is a system in which the evaporation temperature of the hot heat-exchange fluid is regulated as a function of ambient temperature.

Fig. 6 is a graph equivalent to the graph of Fig. 4 , but uses a conventional system in which the evaporation temperature of the hot heat-exchange fluid is set at -18 占 폚.

Fig. 7 is a graph equivalent to the graph of Fig. 5 , but uses a conventional system in which the evaporation temperature of the hot heat-exchange fluid is set at -18 deg.

The present invention will now be described in more detail, but is not limited to the following detailed description.

Each of the terms "heat-exchange compound" or "heat-exchange fluid" (or refrigerant) is capable of absorbing heat by evaporation at low and low pressure in a vapor compression circuit and capable of releasing heat by condensation at high and high pressure Quot; is understood to mean a compound or fluid, respectively. Generally, the heat-exchange fluid may comprise only one, two, three or more than three heat-exchange compounds.

The term "heat-exchange composition" is understood to mean a composition comprising a heat-exchange fluid and optionally one or more additives which are not heat-exchange compounds for the anticipated application.

The present invention aims at a facility for the cooling of fluids or bodies and an associated cooling process. Such a facility may be a stationary or mobile air conditioning installation or preferably a stationary or mobile cooling and / or refrigeration and / or cryogenic installation.

Referring to Figure 1 , in accordance with one embodiment, a facility in accordance with the present invention includes a first vapor compression circuit 10 (or low temperature circuit) comprising a first heat-exchange fluid, and a second heat- A second vapor compression circuit 20 (or a high temperature circuit). The cascaded heat exchanger 30 (or the evaporator-condenser or refrigerant-to-refrigerant heat exchanger) provides thermal coupling between the two vapor compression circuits.

The first vapor compression circuit 10 includes at least one first evaporator 11, at least one first compressor 12, and at least one first expansion device 14. [ Between the first compressor 12 and the first expansion device 14, the circuit passes through a cascaded heat exchanger 30 serving as a condenser (first condenser) for this first circuit.

A fluid transport line is provided between all parts of the circuit.

The vapor compression circuit 10 operates according to a conventional vapor compression cycle. The cycle is a change in the state of the first heat-exchange fluid from the liquid phase (or liquid / vapor two-phase system) to the vapor phase (at the first evaporator 11) (Condensation) of the heat-exchange fluid from the vapor phase to the liquid phase (at the cascaded heat exchanger 30) at relatively high pressures, 14) to reduce the pressure for resumption of the cycle.

The second vapor compression circuit 20 includes one or more second compressors 22a, 22b, 22c, one or more second condensers 23, and one or more second expansion devices 24.

Between the second expansion device 24 and the second compressors 22a, 22b, 22c, the circuit is connected to a cascaded heat exchanger 30 (second evaporator) ).

A fluid transport line is provided between all parts of the circuit.

The second vapor compression system 20 operates similarly to the first.

An accumulator (27) may be provided in the circuit to form a reservoir of fluid in the liquid state. The level of liquid in the accumulator varies as a function of the conditions of use and on the requirements of the installation.

The first heat-exchange fluid receives heat from a portion of the fluid or body that is cooled in the first evaporator (11). For example, when the body to be cooled is made up of one or more frozen or high frozen products (especially food), the body has at least a portion of the wall in direct contact with (or at least part of) 1 evaporator 11). ≪ / RTI >

Alternatively, the heat exchange between the cooled fluid or body and the first heat-exchange fluid may be accomplished through a supplemental circuit comprising a heat-exchange fluid such as air or other glycol compound (with or without a change in state) . As a result, the first heat-exchange fluid is desorbed from the cascaded heat exchanger 30 providing the coupling between the two circuits to the second heat-exchange fluid. The exchange of heat from the first heat-exchange fluid to the second heat-exchange fluid yields, on the one hand, the condensation of the first heat-exchange fluid and, on the other hand, evaporation of the second heat-exchange fluid.

Finally, the second condenser 23 allows the second heat-exchange fluid to take heat away from the external medium. The external medium is preferably enclosed air.

The heat exchange between the second heat-exchange fluid and the external medium may be performed either directly or through an auxiliary circuit of the heat-exchange fluid (with or without a change of state).

Particularly in the above-mentioned circuit, the use of a single-stage or multi-stage centrifugal compressor or a centrifugal small compressor as a compressor can be made. Rotary, piston or axial compressors may also be used. The compressor may be driven by a gear or by a gas turbine or an electric motor (for example, for a mobile application, supplied by exhaust gas from an automobile).

As a heat exchanger for the practice of the present invention, the use of a co-current heat exchanger or preferably a reverse heat exchanger can be made. Micro channel exchangers can also be used.

Each of the items of the apparatus (condenser, expansion device, evaporator, compressor) may consist of a plurality of devices arranged in series and / or parallel or a single device. When several parallel apparatuses are used, a fractionator 25 and a collector 26 are provided as needed, as in the case of the second compressors 22a, 22b, 22c in Figure 1 , Distribute to various devices and collect fluids generated from various devices.

Several first vapor-compression (low temperature) circuits connected to a single second vapor compression (high temperature) circuit or several second vapor compression (high temperature) circuits connected to a single first vapor compression (low temperature) circuit may also be provided.

The first heat-exchange fluid is preferably selected from carbon dioxide, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins, and mixtures thereof. This may in particular be carbon dioxide.

The second heat-exchange fluid is preferably selected from ammonia, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins, and mixtures thereof. (HFO-1234yf) or 1,3,3,3-tetrafluoropropene (HFO-1234ze) and more particularly 2,3,3,3-tetrafluoropropene (In the form of cis or trans form or mixture of cis and trans form).

According to one embodiment, the first heat-exchange fluid is carbon dioxide and the second heat-exchange fluid is HFO-1234yf.

According to another embodiment, the first heat-exchange fluid is carbon dioxide and the second heat-exchange fluid is HFO-1234ze.

Other possible examples for the second heat-exchange fluid are:

A mixture of HFO-1234yf and HFC-134a (1,1,1,2-tetrafluoroethane), which is preferably a two-component mixture, preferably 50% to 65% HFO-1234yf and ideally about Includes 56% of HFO-1234yf.

A mixture of HFO-1234ze and HFC0-134a, which is preferably a two-component mixture and preferably comprises 50% to 65% HFO-1234ze and ideally about 58% HFO-1234ze.

A mixture of HFO-1234yf and HFO-1234ze, which is preferably a two-component mixture, preferably comprising 35% to 65% HFO-1234yf and ideally about 50% HFO-1234yf.

A mixture of HFO-1234yf, HFO-1234ze and HFC-134a, which is preferably a three-component mixture and preferably contains 40% to 45% HFC-134a, 35% to 50% HFO-1234ze and 5% % HFO-1234yf.

A mixture of HFO-1234yf and ammonia, which is preferably a two-component mixture and preferably contains from 15% to 30% ammonia.

A mixture of HFO-1234yf, HFC-152a (1,1-difluoroethane) and HFC-134a, which is preferably a three-component mixture and preferably contains 2% to 15% HFC-134a, 2% to 20% % HFC-152a and 65% to 96% HFO-1234yf.

A mixture of HFO-1234ze, HFC-134a and HFO-1336mzz (1,1,1,4,4,4-hexa-fluorobut-2-ene), which is preferably a three-component mixture.

In this range, the proportion of the different compounds is the ratio by weight.

Various additives may be added to the heat-exchange fluid in the context of the present invention in a vapor compression circuit. This may in particular be a lubricant, a stabilizer, a surfactant, a tracer, a fluorescent agent, a perfume and a solubilizing agent.

The stabilizer (s), when present, preferably represent up to 5% by weight of the heat-exchange composition. Among the stabilizers, mention may be made of nitromethane, ascorbic acid, terephthalic acid, azoles such as tolurriazole or benzotriazole, phenolic compounds such as tocopherol, hydroquinone, t-butylhydroquinone or 2,6-di- (tert- Methylphenol, epoxide (alkyl (optionally fluorinated or perfluorinated) or alkenyl or aromatic) such as n-butyl glycidyl ether, hexanediol diglycidyl ether, allyl glycidyl ether or butylphenyl glycidyl ether Cydyl ethers, phosphites, phosphonates, thiols and lactones can be mentioned.

Deuterated or unhydrogenated hydrofluorocarbons, deuterated hydrocarbons, perfluorocarbons, fluoroethers, brominated compounds, iodinated compounds, alcohols, aldehydes, ketones, nitrogen oxides, and combinations thereof as tracers Can be mentioned. The tracer is different from a compound that produces a heat-exchange compound or a heat-exchange fluid.

As solubilizers there may be mentioned hydrocarbons, dimethyl ethers, polyoxyalkylene ethers, amides, ketones, nitriles, chlorocarbons, esters, lactones, aryl ethers, fluoroethers and 1,1,1-trifluoroalkanes . Solubilizers are different from compounds that produce heat-exchange compounds or heat-exchange fluids.

As the fluorescent agent, mention may be made of naphthalimide, perylene, coumarin, anthracene, phenanthracene, xanthene, thiosanthene, naphthoxyne, fluorensine and derivatives and combinations thereof.

As the fragrance, it is possible to use, as an aromatic compound, at least one selected from the group consisting of alkyl acrylates, allyl acrylates, acrylic acid, acrylic esters, alkyl ethers, alkyl esters, alkynes, aldehydes, thiols, thioethers, disulfides, allyl isothiocyanates, alkanoic acids, Boranen derivatives, cyclohexene, aromatic heterocyclic compounds, ascariol, o-methoxy (methyl) phenol, and combinations thereof.

Particularly, as a lubricant or a lubricating oil, it is possible to use an oil of mineral origin, silicone oil, paraffin of natural origin, naphthene, synthetic paraffin, alkylbenzene, poly (alpha-olefin), polyol ester, polyalkylene glycol and / The compound to be selected can be selected. Polyol esters and polyvinyl ethers are preferred. Polyalkylene glycols are very particularly preferred.

The present invention is particularly suitable for cooling a fluid or a body to a temperature of -50 to -15 占 폚, preferably -40 to -25 占 폚. The temperature of the external medium typically varies from -10 to 50 占 폚, especially from 0 to 40 占 폚, very particularly from 10 to 35 占 폚.

The evaporation temperature (the temperature of the first evaporator 11) of the first heat-exchange fluid is preferably -60 to -20 占 폚, more particularly -50 to -25 占 폚.

The temperature at which the second heat-exchange fluid is condensed (the temperature of the second condenser 23) is variable to an external temperature, which is typically 20 to 60 ° C, more particularly 20 to 45 ° C. This can be, for example, +10 < 0 > C for an external temperature.

The condensation temperature of the first heat-exchanger fluid in the cascaded heat exchanger 30 is variable to the evaporation temperature of the second heat-exchange fluid in this same exchanger. This may be, for example, +5 [deg.] C for the evaporation temperature.

The present invention also provides an evaporation temperature regulating means 42 in the cascaded heat exchanger 30 as a function of the device 41 for measuring the temperature of the external medium and also the temperature of the external medium to be measured.

The overall performance of the plant is optimized when the temperature of the second heat-exchange fluid in the cascaded heat exchanger 30 is adjusted as a function of the external temperature (i. E., For the given cooling temperature of the fluid or body to be cooled, Is the minimum). For better efficiency, the higher the outside temperature, the higher the temperature of the second heat-exchange fluid in the cascaded heat exchanger 30, and vice versa.

According to a preferred embodiment, in the cascaded heat exchanger 30 the evaporation temperature is adjusted to the optimum evaporation temperature, which is measured by the calculation module as a function of the external medium temperature being measured.

The optimum evaporation temperature may be selected from the group consisting of: (for a given cooling capacity of the cooled fluid or body and / or for a given cooling temperature) a cascaded heat exchanger 30 in which the total coefficient of plant performance is the maximum and the total energy consumption of the plant is minimal Is the evaporation temperature of < / RTI >

For a given installation, the optimum evaporation temperature is directly determined using the data provided in Example 1 below with respect to FIG. 3 ; Or for the facility being discussed, the same calculations as those given in Example 1 below are performed; Or can also be measured empirically or empirically by measuring the energy consumption of the plant to different evaporation temperatures of the hot circuit and establishing a correction to the external temperature.

Means for measuring the optimum evaporation temperature may be included in the installation. Alternatively and preferably, the function relating the optimal evaporation temperature to the external temperature is measured in advance, and then only such function is included in the above-mentioned calculation module.

In the cascaded heat exchanger 30, the evaporation temperature can also be adjusted to a temperature different from the optimum evaporation temperature, to account for other limitations. For example, it may be appropriate to limit the possible change in evaporation temperature in the cascaded heat exchanger 30 to a specific temperature range T ₁ -T ₂ . In this case, the evaporation temperature of the cascade heat exchanger 30 is adjusted to the optimum evaporation temperature, or if the latter belong to a range of T ₁ -T _2, else it is optimal evaporation temperature to a temperature T ₁ is less than the T ₁ and it adjusted, and finally adjusted to a temperature T ₂ which case the optimum evaporation temperature of more than T _2.

Many other variations are possible. In particular, it is possible to provide a hysteresis control or a delay adjustment of the evaporation temperature in the cascaded heat exchanger 30 as a function of the external medium temperature, in order to prevent overly frequent or excessive abrupt control.

In general, the optimum evaporation temperature is an increasing function of the external medium temperature. Thus, it is desirable that the evaporation temperature of the cascaded heat exchanger 30 is increased when a temperature increase of the external medium is detected, and that the temperature of the cascaded heat exchanger 30 It is preferred that the evaporation temperature is reduced. Alternatively, according to another embodiment, the control is such that for all given temperatures T ₁ and T ₂ of the external medium T ₂ > T ₁ , the evaporation temperatures of the cascaded heat exchangers 30 are respectively T ₂ ' ₁ is about "and equal to or greater than the temperature T _1, which is adjusted to and T ₂ '.

Adjustment of the evaporation temperature in the cascaded heat exchanger 30 can be obtained by controlling the second compressors 22a, 22b, and 22c. For example, in the cascaded heat exchanger 30, the means for adjusting the evaporation temperature 42 may comprise means for adjusting the rotational speed of the second compressors 22a, 22b, 22c, 22a), (22b), (22c).

Adjustment of the evaporation temperature in the cascaded heat exchanger 30 can be performed continuously or at a separate instant and at regular intervals of time (e.g., every minute, every 15, 30, 45 or 60 minutes). Temperature control can also be performed by taking an average of the temperature of the external medium measured over a specific period of time, e.g., 10 minutes, 30 minutes, or 1 hour, by reference.

Example

The following examples illustrate the invention without limitation.

Example 1 - Evidence of Optimum Evaporation Temperature

Figure 2 shows a typical example of a change in temperature (ambient temperature) of the external medium for one day, and also a typical example of the cooling capacity requirement for the day to cool a compartment containing frozen or high frozen product in supermarket type stores to provide.

Cooling is a type diagrammatically shown in Figure 1. The low temperature circuit includes carbon dioxide, and the high temperature circuit includes HFO-1234yf or HFO-1234ze.

For low temperature circuits, the evaporation temperature is -40 ° C, the overheating is 25 ° C and the overheating is 5 ° C. The compressor is an axial compressor with isentropic efficiency according to: η _iso = 0.00476ι ² - 0.09238 ι + 0.8981 (where ι is the ratio of pressure) (Thermodynamic analysis of optimal condensing temperature of cascade -condenser in CO ₂ / NH ₃ cascade refrigeration systems, Tzong-Shring et al., International Journal of Refrigeration, vol. 29, No. 7, 2006, pp. 100-1108).

The condensation temperature exceeds the evaporation temperature in the high temperature circuit by 5 ° C.

With respect to the high temperature circuit, the evaporation temperature may be fixed at a constant value (-10 DEG C or -18 DEG C) or may vary as a function of the external temperature. The overheating is 25 ° C, and the overheating is 5 ° C. The compressor is an axial compressor with isothermal efficiency according to the following equation: η _iso = 0.00060079ι ² - 0.03002352 ι + 0.90880781 (Reference: ASHRAE 2008 Handbook, HVAC system and equipments, Chapter 37, 34). The condensation temperature exceeds the external temperature by 10 ° C.

Depending on the evaporation temperature (the evaporation temperature in the high temperature stage) as a parameter, the coefficient of performance (COP) is optimized as a function of the ambient temperature. The value of COP for the entire plant corresponds to the following equation:

(Where COP ₁ and COP ₂ are coefficients of low temperature and high temperature circuit performance).

The correlation between the ambient temperature (T _ext) and the optimum evaporation temperature in the high-temperature circuit (T _opt) is shown in Fig.

The tendency equation is very similar for the two refrigerants tested:

- HFO-1234yf, T _opt = 0.4411 XT _ext - 26.549 (C).

- HFO-1234ze, T _opt = 0.4208 XT _ext - 26.107 (C).

Example 2 - Benefits Provided by the Invention

In this embodiment, the optimum evaporation temperature proved in Example 1 is used to achieve energy savings.

The graph of Figure 4 therefore illustrates a comparison between: (1) according to the present invention, i.e. to adjustment to the evaporation temperature of the high temperature circuit (measured in Figure 3 ) with respect to its optimum value as a function of ambient temperature It is assumed that the total energy consumption (gray) of the equipment being operated on, the temperature is changed over the day according to the curve of FIG. 2 ; And (2) the total energy consumption (black) of the same equipment normally operating, depending on the constant evaporation temperature in the high temperature circuit at -10 ° C, which is the most commonly selected value.

The graph of Figure 5 illustrates a comparison between the same two conditions for the TEWI (Total Equivalent Warming Impact) index as defined in Annex B to the standard EN 378-1: 2008 + A1: 2010 . In the graph, the exponent is for a reference value of 100 for equipment normally operating with HFO-1234yf in a high temperature circuit.

The graphs of FIGS. 6 and 7 are similar to those of FIGS. 4 and 5 , except that the equipment that is normally operated operates at a constant evaporation temperature in a high temperature circuit at -18 ° C instead of -10 ° C.

It has also been verified that the present invention allows accurate estimation (especially based on the graph of Figure 3 ) of daily energy consumption in the case of warmer or cooler ambient temperatures than that of the representative blade of Figure 2 .

Claims (24)

A method of cooling a fluid or a body by at least one first vapor compression circuit (10) comprising a first heat-exchange fluid and at least one second vapor compression circuit (20) comprising a second heat- Comprising:
- in the first vapor compression circuit (10):
Partial evaporation of a portion of the first heat-exchange fluid by heat exchange with the fluid or body;
■ First heat - compression of the exchange fluid;
A second heat - a portion of the first heat-exchange fluid is condensed by heat exchange with the exchange fluid;
■ First heat - pressure reduction of the exchange fluid;
- in the second vapor compression circuit (20):
■ first heat - partial evaporation of the second heat-exchange fluid by heat exchange with the exchange fluid;
■ second heat - compression of the exchange fluid;
■ second heat by heat exchange with the external medium - condensation of at least some of the exchange fluid;
■ second heat - pressure reduction of the exchange fluid;
Also included is a method comprising:
- measuring the temperature of the external medium; And
- regulation of the second heat exchange fluid temperature during evaporation, as a function of the external medium temperature. The method of claim 1 wherein the control of the second heat-exchange fluid temperature during evaporation is performed continuously or more than once per hour. The method of claim 1 or 2, further comprising detecting a change in temperature of the external medium, wherein the temperature control of the second heat-exchange fluid upon evaporation is such that when the temperature increase of the external medium is detected, A temperature increase of the exchange fluid, and a temperature decrease of the second heat exchange fluid upon evaporation when a temperature decrease of the external medium is detected. 4. The method according to any one of claims 1 to 3, comprising calculating the optimum evaporation temperature as a function of the temperature measurement of the external medium. 5. The method of claim 4, wherein the temperature of the second heat-exchange fluid during evaporation is adjusted to the optimum evaporation temperature. The method according to claim 4 or 5, wherein the optimum evaporation temperature corresponds to a vaporization temperature at which the total coefficient of performance of the first vapor compression circuit and the second vapor compression circuit is at a maximum. 7. A method according to any one of claims 4 to 6, characterized in that the optimum evaporation temperature is given by the equation T _opt = A x T _ext + B, where T _ext is the external medium temperature to C, A is a dimensionless constant, B Is a constant to < RTI ID = 0.0 > 0 C. < / RTI > The process according to claim 7, wherein the constant A has a value of 0.3 to 0.6, preferably 0.4 to 0.45, and the constant B has a value of -50 ° C to 0 ° C, preferably -30 ° C to -20 ° C. 9. A process according to any one of claims 1 to 8, wherein the fluid or body is cooled to a temperature of -50 to -15 占 폚, preferably -40 to -25 占 폚. 10. The method according to any one of claims 1 to 9,
The first heat exchange fluid is selected from carbon dioxide, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably carbon dioxide; And / or
The second heat exchange fluid is selected from ammonia, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably tetrafluoropropene, more particularly preferably 2, 3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene. 11. The method according to any one of the preceding claims, wherein the compression of the second heat-exchange fluid is performed by one or more compressors (22a, 22b, 22c) and the temperature of the second heat- Is performed by control of said compressors (22a, 22b, 22c). The method of claim 11, wherein control of the compressors (22a, 22b, 22c) comprises adjusting the rotational speed of the compressors (22a, 22b, 22c) or by continuous start and shutdown of the compressors How to do it. 13. A method according to any one of claims 1 to 12 for cooling a compartment containing a high-frozen or frozen product, preferably a food product. A cooling system for a fluid or body, comprising at least:
- a first vapor compression circuit (10) comprising a first column-exchange fluid;
- a second vapor compression circuit (20) comprising a second column-exchange fluid;
A cascaded heat exchanger (30) suitable for heat exchange between the first heat exchange fluid and the second heat exchange fluid;
The first vapor compression circuit (10) comprises:
A first evaporator (11) suitable for heat exchange between the first heat exchange fluid and the fluid or body;
At least one first compressor (12);
- a first expansion device (14);
The second vapor compression circuit (20) comprises:
At least one second compressor (22a, 22b, 22c);
- a second condenser (23) suitable for heat exchange between the second heat exchange medium and the external medium;
- a second expansion device (24);
The facility also includes:
A device for measuring the temperature of the external medium 41; And
Means for adjusting the evaporation temperature (42) in the cascaded heat exchanger (30) as a function of the temperature measurement of the external medium. 15. The installation according to claim 14, further comprising a module for calculating the optimum evaporation temperature as a function of the temperature measurement of the external medium. 16. Apparatus according to claim 15, wherein the evaporation temperature regulating means (42) in the cascaded heat exchanger (30) is adapted to control the evaporation temperature of the cascaded heat exchanger (30) to the optimum evaporating temperature. 17. The installation according to claim 15 or 16, wherein the optimum evaporation temperature corresponds to a vaporization temperature at which the total coefficient of performance of the first vapor compression circuit and the second vapor compression circuit is at a maximum. 18. The process according to any one of claims 15 to 17, wherein the optimum evaporation temperature is calculated by the equation T _opt = A x T _ext + B, where T _ext is the temperature of the external medium at C, A is a dimensionless constant, And B is a constant in 占 폚. 19. The method of claim 18, wherein the constant A has a value of 0.3 to 0.6, preferably 0.4 to 0.45; And the constant B has a value of -50 ° C to 0 ° C, preferably -30 ° C to -20 ° C. 20. Apparatus according to any one of claims 14 to 19, wherein the body or fluid is cooled to a temperature of -50 to -15 占 폚, preferably -40 to -25 占 폚. 21. The apparatus according to any one of claims 14 to 20, wherein:
The first heat exchange fluid is selected from carbon dioxide, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably carbon dioxide; And / or
The second heat exchange fluid is selected from ammonia, hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, fluoroolefins and mixtures thereof, preferably tetrafluoropropene, more particularly preferably 2 , 3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene. 22. Apparatus according to any one of claims 14 to 21, wherein the evaporative temperature control means (42) in the cascaded heat exchanger (30) comprises control means of the second compressors (22a, 22b, 22c). The compressor of claim 22, wherein the control means of the second compressors (22a, 22b, 22c) is adapted to adjust the rotational speed of the second compressors (22a, 22b, 22c) Appropriate for start-up and shutdown. 24. An installation according to any one of claims 14 to 23, comprising a compartment suitable for receiving a highly refrigerated or frozen product, preferably a food product.

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