ADIABATIC COOLING UNIT FOR REFRIGERATION SYSTEMS, REFRIGERATION MACHINE AND METHOD OF OPERATION THEREOF

Abstract

 A method for treating a refrigerant fluid that performs a refrigeration cycle in a refrigeration machine (100), comprising the consecutive steps of
a. compressing the refrigerant fluid in a compressor (101) of the refrigeration machine (100),
b. cooling the refrigerant fluid in a main cooling unit (102) of the refrigeration machine (100),
c. expanding the refrigerant fluid in an expander (103) of the refrigeration machine (100),
d. placing the refrigerant fluid in a heat exchange with a fluid to be cooled, in a main heat exchanger (104) of the refrigeration machine (100).
The method further comprises the steps of
e. cooling adiabatically an air flow
f. placing in a heat exchange the adiabatically cooled air flow with the refrigerant fluid,
at least step f. being performed between steps b. and c..

Description

[0001] The present invention relates to an adiabatic cooling unit for a refrigeration machine (refrigeration system), to a refrigeration machine provided with said cooling unit and to a method for the treatment of a refrigerant fluid which performs a refrigeration cycle in a refrigeration machine.

[0002] Refrigeration systems typically comprise a compressor, a cooling unit and/or a sub-cooling unit, an expander, and an evaporator, arranged consecutively on the path followed by the refrigerant fluid that circulates in the refrigeration machine.

[0003] The refrigeration systems to which the present invention relates mainly but not exclusively are the ones in which the refrigeration cycle occurs in subcritical or transcritical conditions.

[0004] In the case of refrigeration systems in which the refrigerant follows a subcritical cycle, typically the cooling unit is a condenser and the expander is a throttling valve. It is known in the literature that in these machines the energy efficiency and the useful effect are inversely proportional to the condensation temperature: the lower the latter, the higher the former; hence the need to have low condensation temperatures, which however often clashes with the technical solutions required to obtain them, which in some cases can lead to a lower limit beyond which it is not convenient/appropriate to push.

[0005] As regards instead the refrigeration systems in which the refrigerant follows a transcritical cycle, the cooling unit is appropriately a so-called gas cooler. In these machines the increase in the useful effect is linked to a reduction of the temperature of the refrigerant in the gas cooler itself; this temperature is of course linked to the temperature of the ambient air (with which the refrigerant exchanges heat in the gas cooler), with the consequence that in hot climates (for example southern Europe) current machines have operating limitations.

[0006] In order to try to obviate at least partly some of these limitations, various technical solutions have arisen over time, for example adiabatic condensers and evaporative condensers.

[0007] In evaporative condensers, the refrigerant to be condensed is introduced in a bank of tubes on which recirculated water is sprayed continuously, its evaporation removing the heat to be dissipated by means of the exchange surface of the bank.

[0008] In adiabatic condensers, the refrigerant to be condensed is introduced in a bank of tubes that is struck by air pre-cooled by means of the adiabatic saturation process; the air thus treated removes the heat to be dissipated by means of the exchange surface.

[0009] Although the use of the methods cited above (instead of traditional "dry" condensers) has partly improved the current situation, however they have some technical limitations: these systems in fact must be sized so as to dissipate all of the condensation heat, and this, with respect to the proposed solution, entails a high air flow-rate, with a consequent greater energy expenditure for the fans due to load losses; moreover, water consumption is also high, since it is proportional to the air flow-rate.

[0010] The aim of the present invention is to provide an adiabatic cooling unit for refrigeration systems and/or a refrigeration machine and/or a method for its operation that solve the technical problem described above, obviate the drawbacks and overcome the limitations of the background art, allowing to provide high-efficiency refrigeration systems despite the temperature of the ambient air in which the machine operates.

[0011] Within this aim, an object of the invention is to provide a cooling unit for refrigeration systems and/or a refrigeration machine and/or a method of operation thereof that are capable of giving the greatest assurances of reliability and safety in use.

[0012] Last but not least, another object of the invention is to provide an adiabatic cooling unit for refrigeration systems and/or a refrigeration machine and/or a method of operation thereof that are relatively easy to provide and economically competitive if compared with the background art.

[0013] This aim, these objects and others which will become better apparent hereinafter are achieved by a method for treating a refrigerant fluid that performs a refrigeration cycle in a refrigeration machine, comprising the consecutive steps of

a. compressing the refrigerant fluid in a compressor of said refrigeration machine,

b. cooling the refrigerant fluid in a cooling unit of the refrigeration machine,

c. expanding the refrigerant fluid in an expander of the refrigeration machine,

d. placing the refrigerant fluid in a heat exchange with a fluid to be cooled, in a heat exchanger of the refrigeration machine,

characterized in that it comprises steps that consist in

e. cooling adiabatically an air flow

f. placing in a heat exchange the adiabatically cooled air flow with the refrigerant fluid,

at least step f. being performed between steps b. and c..

[0014] In particular, the following is used in the refrigeration system:

• in the case of subcritical systems, an adiabatic sub-cooling unit in series to the condenser
• in the case of transcritical systems, an adiabatic cooling unit in series to a gas cooler which further reduces the temperature of the gas in output from said gas cooler.

[0015] In other words, in this manner a sub-cooling of the refrigerant fluid is performed in the case of subcritical systems and a further cooling of the gas is performed in the case of transcritical systems.

[0016] The effect is to utilize otherwise unused enthalpy gaps, providing benefits to the refrigeration system.

[0017] Usually step b. is provided by means of a dry cooling unit, so as to obtain (by observing the cycle of the refrigerant fluid as a whole) a step for cooling the refrigerant fluid of the combined type, in which two different methods, i.e., dry cooling (provided for example in so-called dry-coolers) and an adiabatic cooling step, are used in mutual combination.

[0018] In particular, as regards the dry cooling unit:

• if one operates in a subcritical condition, it is a heat exchanger of the air-liquid/gas type, whereas,
• if one operates in a transcritical condition, it is an air-gas exchanger;

in both cases the air is ambient air, at ambient temperature and humidity conditions.

[0019] The adiabatic sub-cooling/cooling unit comprises a dedicated air-gas (in the transcritical condition) or air-liquid/gas or air-liquid (in the subcritical condition) heat exchanger, in which the air is ambient air which is indeed cooled adiabatically.

[0020] Furthermore, by using in combination an adiabatic sub-cooling/cooling unit downstream of a condenser/gas cooler, additional advantages are achieved; for example, the Applicant has noticed that since adiabatic cooling is used to generate so-called sub-cooling (i.e., an additional cooling of the refrigerant fluid with respect to the one that can be obtained with dry cooling alone), since the dimensions of the adiabatic cooling unit are reduced with respect to the technical systems cited above (evaporative condenser/adiabatic condenser), the power of the fans is reduced, since the treated air flow-rate decreases, the water consumption is distinctly lower than with normal evaporative condensers or adiabatic condensers, and the system can be adapted to any refrigeration machine, even an existing one, as a retrofit that is relatively simple to install and has a modest cost.

[0021] Analyzing first of all the advantageous effects of the method according to the invention applied to the case of a subcritical cycle, a displacement of the refrigeration cycle to the left (in a pressure-enthalpy diagram) is obtained, increasing the useful effect and leaving substantially unchanged the work of the compressor.

[0022] If one wishes to make a comparison among some operating parameters of a traditional refrigeration machine or unit with subcritical operation ("basic"), one with "adiabatic condensation" and one operating according to the invention, one obtains the following situation (in which the data related to the method according to the invention appear in the last row "refrigeration unit with adiabatic SR"):

	T air = 35°C			T air = 30°C			T air = 25°C
	Power [kW]	COP	Water consumption [l/h]	Power [kW]	COP	Water consumption [l/h]	Power [kW]	COP	Water consumption [l/h]
Basic refrigeration unit	100	2.71		106.8	3.13		115	3.62
Refrigeration unit with adiabatic condensation	111,7	3.25	140	118.2	3.65	125.7	122.8	3.99	114.3
	11.7%	11.7%		10.7%	16.4%		6.8%	10.2%
Refrigeration unit with adiabatic SR	123.4	3.60	21.7	129.7	4.05	19.4	135.8	4.52	17.2
	23.4%	33.0%		21.5%	29.3%		18.1%	25.0%

[0023] Furthermore, with respect to the machine with adiabatic condensation, it is also possible to use, for the cooling of the refrigerant fluid, a smaller mass of air, reducing the energy expenditure for air flow generators (typically fans), and to reduce water consumption (since it is proportional to the air flow-rate).

[0024] This occurs because by virtue of the invention the overall gap differential is increased, ultimately utilizing enthalpy levels that otherwise would be unused.

[0025] It is therefore possible to reduce the size of the refrigeration system and together with the increase in COP reduce the energy allocation required by the electric meter (which can be estimated at around €30 per year for each kW of power saved), reducing the annual operating expense by virtue of the increase in energy efficiency.

[0026] Moving on now to analyzing the advantages of the invention when it is applied in the case of a transcritical cycle, it is noted that the temperature of the air flow cooled by adiabatic cooling is lower than that of the ambient air with which the refrigerant exchanges heat in the gas cooler.

[0027] The advantages are immediately visible in the table below, which shows the typical results of a refrigerated preservation system as the temperature of the external air varies, in a comparison between a traditional unit or machine ("basic") and one provided according to the invention (the data related to the method according to the invention appear in the last row "refrigeration unit with adiabatic SR").

	T air = 40°C			T air = 30°C			T air = 20°C
	Power [kW]	COP	Water consumption [l/h]	Power [kW]	COP	Water consumption [l/h]	Power [kW]	COP	Water consumption [l/h]
Basic refrigeration unit	100	1.59		100	2.35		100	3.43
Refrigeration unit with adiabatic SR	126.8	1.99	44.1	120.9	2.80	35.9	112.3	3.79	27.7
	26.8%	25.7%		20.9%	19.2%		12.3%	10.4%

[0028] The higher power yielded leads to savings, since it is possible to limit the number of compressors.

[0029] A further object of the invention is an adiabatic cooling unit for refrigeration systems, comprising
a generator of an air flow which is functionally connected to a channel for said air flow

• an evaporating pack arranged in the channel
• a humidification assembly for the evaporating pack
• a heat exchanger connected to said channel downstream of the evaporating pack, with reference to a direction of travel of the air flow in the channel, in order to allow heat exchange between the said air flow and a refrigerant fluid that circulates in the exchanger.

[0030] Another object of the invention is a refrigeration machine, comprising: a compressor, a main cooling unit, an expander, a main heat exchanger, which are designed to be crossed by a refrigerant fluid which performs a refrigeration cycle and which further comprises an adiabatic cooling unit according to the invention, which is arranged downstream of the main cooling unit with reference to a direction of travel of the refrigerant fluid in the machine.

[0031] Further characteristics and advantages of the invention will become better apparent from the description related to the refrigeration machine and to two embodiments of an adiabatic cooling unit according to the invention, illustrated by way of nonlimiting example with the aid of the accompanying drawings, wherein:

Figure 1 is a simplified schematic view of a refrigeration machine according to the invention;

Figure 2 is a sectional side view of a first embodiment of an adiabatic cooling unit according to the invention;

Figure 3 is a sectional side view of a first embodiment of an adiabatic cooling unit according to the invention.

[0032] With reference to Figure 1, such figure shows schematically a refrigeration machine 100 according to the invention.

[0033] In its general outline, the refrigeration machine 100 comprises a compressor 101, a main cooling unit 102, an expander 103, a main heat exchanger 104, which are designed to be crossed by a refrigerant fluid that performs a refrigeration cycle.

[0034] The refrigerant fluid can vary depending on the chosen embodiments, being for example R134A or R410A or CO₂: the first two are particularly used in the case of subcritical cycles while the latter is used in the case of transcritical cycles.

[0035] In this regard, it is useful to specify right now that in the case of a refrigerating fluid that performs a subcritical cycle the main cooling unit 102 is a condenser (in which the refrigerant fluid changes state and condenses), while in the case in which the cycle is transcritical then the main cooling unit is a so-called gas-cooler (in which the refrigerant fluid does not change state and remains gaseous).

[0036] The expander 103 can be a thermostat-controlled valve or a turbine, as needed.

[0037] The heat exchanger 104, in the case of subcritical conditions, is an evaporator, in which the refrigerant changes state.

[0038] Characteristically, the machine 100 according to the invention comprises an adiabatic sub-cooling/cooling unit 1, which is arranged downstream of the main cooling unit 102 with reference to a direction of travel of the refrigerant fluid in the machine 100.

[0039] One shall return hereafter to the details of the adiabatic sub-cooling/cooling unit 1, during the descriptions of Figures 2 and 3; for the time being, it is sufficient to note that the refrigerant fluid flows through the circuit that has just been defined, passing through the adiabatic cooling unit 1 after passing through the main cooling unit 102.

[0040] As regards the latter, it is usually a dry cooling unit (also known as dry-cooler) - in the case of both subcritical and transcritical cycles - in which the refrigerant fluid (which is hot and at high pressure) that arrives from the compressor 101 is placed in heat exchange contact with a second fluid - usually ambient air.

[0041] The dry cooling units are of the air-liquid/gas or air-gas type and comprise for example a finned tube bundle in which the refrigerant flows, thus exchanging heat with the ambient air that flows over the fins; optionally, the air can be appropriately forced onto the fins by virtue of fans 108 appropriately provided for this purpose; the ambient air is conveyed onto the fins in the ambient temperature and humidity conditions, without a pretreatment to modify them.

[0042] In a refrigeration machine 100 thus provided, regardless of the refrigerant fluid and of the cycle - subcritical or transcritical - that it follows, in a fully general way the treatment of the refrigerant fluid that performs a refrigeration cycle is provided, comprising the consecutive steps of:

a. compressing the refrigerant fluid in the compressor 101,

b. cooling the refrigerant fluid in the main cooling unit 102,

c. expanding the refrigerant fluid in the expander 103,

d. placing the refrigerant fluid in a heat exchange with a fluid to be cooled, in the main heat exchanger 104.

[0043] Typically, the fluid to be cooled is air, which is present or directed in an environment that one wishes to cool.

[0044] The method according to the invention further comprises the steps of

e. cooling adiabatically an air flow

f. placing in heat exchange contact the adiabatically cooled air flow with the refrigerant fluid,

at least step f. being performed between steps b. and c., in accordance with the machine 100 that has just been described.

[0045] Although one shall return later to this matter, it is useful to note that step f. is performed in an air-gas or air-liquid/gas heat exchanger of the adiabatic cooling unit according to the invention.

[0046] In practice, by observing the path followed by the refrigerant fluid in the machine 100, it (downstream of the compressor 101) first passes through the main cooling unit 102 and then through the adiabatic cooling unit 1 (or, more precisely, the air-gas or air-liquid/gas or air-liquid exchanger of the latter).

[0047] The main cooling unit 102 is usually of the dry type (air-gas/liquid or air-gas) as detailed earlier and therein the refrigerant fluid cools by heat exchange with air, typically ambient air at the ambient humidity and temperature conditions.

[0048] Advantageously, therefore, the refrigerant fluid arrives at the adiabatic cooling unit 1 with a temperature that is lower than that with which it is fed to the main cooling unit 102 and optionally it is already (at least partly) condensed, if one operates in a subcritical condition.

[0049] The temperature of the refrigerant is further decreased in the adiabatic cooling unit 1, by virtue of the heat exchange that is provided therein between the refrigerant fluid and an adiabatically cooled air flow.

[0050] The adiabatic cooling of the air is performed by drawing an air flow-rate from the environment, which is made to transit through (or in any case at) a humidified evaporating pack 5: the temperature of the air decreases and simultaneously its humidity increases, by virtue of the fact that the air that is present in the pack 5 evaporates partially, removing heat from the air flow and transferring water in the form of an increase in humidity which can almost reach saturation (over 95%).

[0051] The advantageous effects have been described and shown above with the aid of the tables, both in the case of a subcritical cycle and in the case of a transcritical cycle, and will not be dwelt upon further.

[0052] Moving on to the detailed description of some examples of the adiabatic cooling unit 1 of Figure 2 for refrigeration systems 100 as described above, in a fully general manner it comprises a generator of an air flow 11 which is functionally connected to an air flow channel 12.

[0053] The generator 11 is provided with an intake 111 which is open toward an external environment and is optionally provided with filters or cleaning meshes, of a per se known type which will not be dwelt upon further.

[0054] Preferably, in order to optimize the fluid dynamics conditions of the air flow, directly downstream of the generator 11 the channel 12 is provided with a diverging portion.

[0055] The air flow generator 11, in the nonlimiting example shown in Figures 2 and 3, is a centrifugal fan.

[0056] In the channel 12, preferably in an intermediate portion with constant cross-section thereof, arranged directly downstream (with reference to the air flow path) of the diverging portion, there is an evaporating pack 13 which is crossed by the air flow moved by the generator 11.

[0057] The evaporating pack 13 comprises evaporating panels 131.

[0058] The adiabatic cooling unit 1 further comprises a humidification assembly 14 for the evaporating pack 13, which is adapted to keep the evaporating pack impregnated with water (during use).

[0059] Downstream of the evaporating pack (again with reference to the path of the air flow) there is a heat exchanger 15 which is connected to the channel 12.

[0060] The heat exchanger 15 is adapted to allow heat exchange between the adiabatically cooled air flow and the refrigerant fluid that circulates inside the exchanger 15.

[0061] The heat exchanger 15 of the adiabatic cooling unit 1 is an air-gas or air-liquid/gas or air-liquid exchanger, in which the air is cooled adiabatically.

[0062] By briefly viewing the diagram of Figure 1 again, one clearly understands that the exchanger 15 is crossed by the refrigerant fluid downstream of the main exchanger 102.

[0063] The exchanger 15 is preferably in the form of a finned tube bundle, in which the finned ducts convey said refrigerant fluid and are skimmed by the air flow that is cooled adiabatically by the cooling unit 1, as just described.

[0064] The channel 12 then ends with an outlet 112 downstream of the exchanger 15, by means of which the air is expelled.

[0065] It should be noted that in the embodiment that has just been described, in the installation condition the intake 111 and the outlet 112 are arranged at the same height from the ground, so that in the installed condition the channel 12 is substantially horizontal.

[0066] As regards the humidification assembly 14, it comprises a water tank 141, a pump 142, and water dispensing nozzles 143 directed toward the pack 13.

[0067] Preferably, in order to reduce the number of parts, the tank 141 is arranged below the evaporating pack 13 and the pump 142 is functionally connected to the tank 141 and to the nozzles 143 in order to dispense water drawn from the tank 141 onto the evaporating pack 13.

[0068] The excess water, after wetting the panels 131 of the pack 13, is collected in the tank 141 to be then reused and reduce consumption; for this purpose, the tank 141 is preferably provided like a tub.

[0069] In the embodiment of Figure 3, the adiabatic cooling unit is designated generally by the reference numeral 10.

[0070] It comprises substantially the same parts, designated by the same reference numeral and with the same function, as the cooling unit 1 that has just been described and on which one dwells no further, referencing the description made above.

[0071] The main difference between the cooling unit 1 and the cooling unit 10 resides in that in the former the channel 12 was horizontal, while in this example the channel 120 has a vertically extended portion, so that the intake 1110 and the outlet 1120 are arranged, when installed, at different heights, the latter being higher than the former.

[0072] A further difference that is observed is related to the cross-section of the channel 12 and 120: whereas in the channel 12 the pack 13 is located between a diverging portion and a converging portion of the channel, the channel 120 has a substantially constant passage section.

[0073] The two variations allow advantageously to have adiabatic cooling units with reduced vertical space occupation (such as the cooling unit 1) or with a reduced horizontal space occupation (such as the cooling unit 10), which can be used at will as a function of the installation conditions and of the available spaces.

[0074] In practice it has been found that the method, the machine, and the colling unit according to the present invention achieve the intended aim and objects, since it allows to reduce the temperature of the refrigerant fluid in output from the main exchanger so as to optimize the operation of the machine, both when it operates subcritically and when it operates transcritically, as clearly highlighted above from the experimental results listed in the tables.

[0075] The method, the machine or the cooling unit thus conceived are susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

[0076] All the details may further be replaced with other technically equivalent elements.

[0077] In practice, the materials used, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to the requirements.

[0078] The disclosures in Italian Patent Application No. 102016000099080 (UA2016A007039) from which this application claims priority are incorporated herein by reference.

[0079] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A method for treating a refrigerant fluid that performs a refrigeration cycle in a refrigeration machine (100), comprising the consecutive steps of

a. compressing the refrigerant fluid in a compressor (101) of said refrigeration machine (100),

b. cooling the refrigerant fluid in a main cooling unit (102) of the refrigeration machine (100),

c. expanding the refrigerant fluid in an expander (103) of the refrigeration machine (100),

d. placing the refrigerant fluid in a heat exchange with a fluid to be cooled, in a main heat exchanger (104) of the refrigeration machine (100),

characterized in that it further comprises the steps of

e. cooling adiabatically an air flow

f. placing in a heat exchange the adiabatically cooled air flow with the refrigerant fluid,

at least step f. being performed between steps b. and c..

2. The method according to claim 1, characterized in that step b. is performed by means of a main dry cooling unit (102).

3. The method according to claim 1 or 2, characterized in that step e. is performed at least by means of a crossing, by the air flow, of a humidified evaporating pack (103) in an adiabatic cooling unit (1, 10).

4. An adiabatic sub-cooling/cooling unit (1, 10) for refrigeration systems (100), comprising
a generator of an air flow (11) that is functionally connected to a channel (12, 120) for said air flow,
characterized in that it further comprises
an evaporating pack (13) arranged in the channel (12, 120)
a humidification assembly (14) for the evaporating pack (13)
a heat exchanger (15) connected to said channel (12, 120) downstream of the evaporating pack (13), with reference to a direction of travel of the air flow in the channel (12), in order to allow heat exchange between said air flow and a refrigerant fluid.

5. The sub-cooling/cooling unit (1, 10) according to claim 4, characterized in that the evaporating pack (13) comprises one or more evaporating panels (131).

6. The sub-cooling/cooling unit (1, 10) according to claim 4 or 5, characterized in that the humidification assembly (14) comprises a water tank (141), a pump (142), dispensing nozzles (143), wherein the tank (141) is arranged below said evaporating pack (13), the pump (142) has a functional connection to the tank (141) and to the nozzles (143) in order to dispense water taken from the tank (141) on said evaporating pack (13).

7. A refrigeration machine (100), comprising: a compressor (101), a main cooling unit (102), an expander (103), a main heat exchanger (104), which are intended to be crossed by a refrigerant fluid that performs a refrigeration cycle,
characterized in that it further comprises a sub-cooling/cooling unit (1, 10) according to one or more of claims 4 to 6, arranged downstream of the main cooling unit (102) with reference to a direction of travel of the refrigerant fluid in the machine (100).

8. The refrigeration machine (100) according to claim 6, wherein the main cooling unit (102) is a dry cooling unit in which the refrigerant fluid exchanges heat with ambient air.

9. The refrigeration machine (100) according to claim 7 or 8, wherein the heat exchanger (15) of the sub-cooling/cooling unit (1, 10) is an air-gas or air-liquid/gas or air-liquid exchanger arranged downstream of the main cooling unit (102).

10. The refrigeration machine (100) according to claim 8 or 9, characterized in that it provides the method according to one or more of claims 1 to 3.

Drawing