EP2122272A2

EP2122272A2 - Refrigerating plant.

Info

Publication number: EP2122272A2
Application number: EP07859138A
Authority: EP
Inventors: Mauro Barbieri; Ezio Fornasieri
Original assignee: Teklab Sas Di Barbieri Mauro E C
Current assignee: Teklab Sas Di Barbieri Mauro E C
Priority date: 2006-12-21
Filing date: 2007-12-21
Publication date: 2009-11-25
Also published as: WO2008081273A3; ITMO20060418A1; WO2008081273A2; US20100132395A1

Abstract

Refrigerating plant comprising a coolant fluid, a compressor (1), A condenser (3), an expansion valve (5), an evaporator (6), a collecting receptacle (s) for collecting said coolant fluid, and controlling means (14, 15) for piloting said expansion valve (5), said collecting receptacle (8) is interposed between an outlet of said evaporator (6) and an inlet of said compressor (l).

Description

Refrigerating plant.

The invention relates to a refrigerating plant, in particular a plant in which the heat exchange in the evaporator is optimised and the quantity of coolant required by the plant per refrigerating power unit is optimised.

From the prior art so-called dry-expansion refrigeration plants are known that consist of a compressor_/ a first heat exchanger acting as a condenser of the refrigerating fluid and a second heat exchanger acting as an evaporator o£ the coolant fluid. The coolant fluid, in overheated steam state, is compressed at high pressure by the compressor and sent to the condenser, where it surrenders heat to the external environment, condensing in the form of high-pressure liquid. Between the condenser and the evaporator there is interposed an expansion valve, through which the coolant liquid passing through coming from the condenser, expands adiabatically, cooling before entering the evaporator. In the evaporator, the low-pressure coolant absorbs heat from the environment and is transformed into steam that is returned, via the suction line, to the inlet of the compressor.

In many traditional refrigerating plants, the expansion valve is represented by a so-called thermostatic expansion valve. Different types of thermostatic expansion valves are in use; the most common ones are the mechanical and the electronic valves and the operating principle is common to both. A common mechanical thermostatic expansion valve has inside an expansion chamber with a limiting orifice and a shutter for regulating the flow of the coolant through said orifice, A spring pushes the shutter inside the orifice to the closing position thereof. The valve is also provided with an actuating diaphragm, A face of the diaphragm is in direct communication with the coolant fluid delivered into the valve, whilst the other face is in communication, through a capillary pipe, with a thermostatic bulb that detects through contact .the temperature of the fluid in overheated steam state at the outlet of the evaporator. The bulb is loaded with a suitable volatile fluid (for example the same coolant fluid that circulates in the refrigerating plant or another suitable fluid) and is thus able to exert pressure on the shutter of the valve by means of the actuating diaphragm, contrasting both the force of the spring and the pressure of the coolant fluid inside the valve. If the thermostatic valve detects an increase in the outlet temperature of the coolant at the outlet of the evaporator, the force exerted on the actuating diaphragm increases proportionally, determining a greater opening of the valve and a consequent increase in the flow of coolant through the evaporator and this causes a decrease in the temperature of the coolant at the outlet of the evaporator. If, on the other hand, the thermostatic bulb detects a decrease in the coolant temperature the force exerted on the actuating diaphragm decreases proportionally, enabling the spring to close partially and thus reducing the flow of coolant through the evaporator and this produces an increase in the temperature of the coolant fluid leaving the evaporator. In this sense, the expansion valve adjusts overheating of the coolant fluid at the outlet of the evaporator, i.e. the difference between the temperature of the coolant fluid and a saturated fluid of the coolant fluid at the same pressure . Alternatively to the mechanical expansion valves, electronically controlled expansion valves are used that are piloted by an electronic drive by means of an electronic control unit that is connected, for example, to temperature and pressure sensors located at the outlet of the evaporator. The degree of opening of the valve and, therefore, the flow of coolant fluid sent to the evaporator are adjusted in function of the overheating of the coolant, which is calculated on the basis of pressure and temperature values read by the sensors located at the outlet of the evaporator. The electronically controlled valves generally permit more precise adjustment of the flow of the coolant sent to the evaporator, but above all eliminate the proportional behaviour, which, is the main drawback in mechanical thermostatic valves.

The dry-expansion, refrigerating plants mentioned above have the drawback that the coolant fluid at the outlet of the evaporator has to be in overheated steam state in order to enable the coolant flow to be adjusted. This means that the heat-exchange potential of the evaporator is not exploited fully because in the end part of the evaporator the coolant fluid is in the condition of overheated steam, which has a heat exchange coefficient that is much less than that of a saturated steam, and because, in said, end part, the temperature difference between the coolant fluid and the environment to be cooled diminishes , In order to overcome this drawback liquid circulation refrigeration plants, also known as '"flooded" plants are used, in which between the expansion valve and the evaporator there is interposed a collecting receptacle, said "liquid separator" being provided with a first inlet through which it receives the coolant fluid coming from the expansion valve, with a first outlet through which the coolant fluid is sent to the evaporator, with a second inlet through which the collecting receptacle receives the coolant fluid exiting the evaporator and a second outlet through which the coolant fluid is sucked from the compressor of the refrigerating system.

The refrigerating coolant fluid leaving the evaporator and delivered to said collecting receptacle is in a saturated condition (liquid and steam balanced) . Inside the receptacle the liquid phase and the gas phase of the saturated fluid separate, with the liquid phase remaining inside the collecting receptacle and being pumped or recirculated in the evaporator, whilst the gas phase is sucked by the compressor, through said second outlet, In these types of systems the potential of the evaporator is fully exploited because the coolant fluid leaves the evaporator in humid saturated steam state and so all the exchange surface, being wet by the liquid, is active for evaporation purposes.

Nevertheless, these systems have the drawback of requiring a great dose of coolant fluid, because the vacuum level inside the evaporator is rather great, the titre of the humid saturated steam at the outlet of the evaporator being significantly less than 1. The quantity of liquid in the separator is added to the greater retention of evaporator liquid, AS a result the load of coolant fluid required in a plant with a flooded evaporator is noticeably greater than that which would be strictly necessary on the basis of the refrigerating power of the plant. The expansion valve is adjusted in two ways: a) by controlling the low pressure level and b) by controlling the high pressure level.

In the low-pressure level control system the level of liquid in the separator is kept constant, increasing the degree of opening of the valve if the level decreases and decreasing the degree of opening of the valve if the level increases. The level of liquid in the collecting receptacle is detected by a level sensor.

In the system with a high pressure level control the level is kept constant at the bottom of the condenser or on a capacity located on the outlet thereof. The level is kept constant by opening the valve if the level rises and closing the valve if the level falls. Also in this case, the level of the liquid is detected by a level sensor. The object of the present invention is to remedy the drawbacks indicated above.

According to the present invention a refrigerating plant is provided comprising a coolant fluid, a compressor, a condenser, an expansion valve, an evaporator, a collecting receptacle for collecting said coolant fluid, and means for piloting said expansion valve, characterised in that said collecting receptacle is interposed between an outlet of said evaporator and an inlet of said compressor. Owing to the invention the liquid, fraction of the saturated steam leaving the evaporator can be minimised compared with a system with a flooded evaporator, but maintaining the advantage of exploiting to the full the potential of the evaporator, to which the advantage of substantially reducing the quantity of coolant fluid loaded in the system is added. In fact, the liquid that is collected in the collecting receptacle is not used to supply the evaporator, but is used to provide a reference for the level sensor, for adjusting the degree of opening of the expansion valve. The quantity of liquid in the collecting receptacle can thus be reduced to the minimum indispensable for ensuring correct operation of the level sensor, As a result, the titre of the humid saturated steam leaving the evaporator can be very near to 1 , for example can be equal to about 0.9.

The invention will now be disclosed below, purely by way of non-limiting example, with reference to the attached drawings, in which:

Figure 1 is a general diagram of a refrigerating plant according to the invention;

Figure 2 is a detail of the refrigerating plant of Figure 1; Figure 3 is a first version of the detail in Figure 2; Figure 4 is a second version of the detail in Figure 2;

Figure 5 is a further version that can be applied to the drawings of Figure 2, Figure 3 and Figure 4;

Figure 6 is a general diagram of a plant with heat pump according to the invention. With reference to Figure 1, a refrigerating plant according to the invention comprises a compressor 1 that comprises a coolant fluid entering the compressor 1 in overheated steam state and sends the coolant fluid, via a first conduit 2, to a condenser 3 in which the coolant fluid condenses, yielding heat to the external environment. The coolant fluid, exiting the condenser 3, passes into a second conduit 4 in which there is placed an expansion valve 5, passing through, which the coolant fluid reduces pressure and cools. The second conduit 4 delivers the coolant fluid to an evaporator 6, in which the coolant fluid evaporates, removing heat from an environment to be cooled. The coolant fluid, which leaves the evaporator 6 in humid saturated steam state, with titre just below 1, for example with titre equal to 0.9, is sent, through a third conduit 7, to a collecting receptacle S in which the liquid fraction of the coolant fluid is separated from the gas fraction, gathering on the bottom of the collecting receptacle 8, whilst the gas fraction gathers in the upper part of the collecting receptacle 8. The collecting receptacle S communicates, above, with a first outlet conduit 9, through which the gas phase of the coolant fluid exits, and, below, with a second outlet conduit 10 through which the liquid phase of the coolant fluid exits. The first outlet conduit 9 and the second outlet conduit 10 flow together into a fourth conduit 11 in which the gas phase and the liquid phase of the coolant fluid are mixed together. The fourth conduit 11 sends the coolant fluid to a heat exchanger 12 in which the liquid fraction of the coolant fluid is evaporated so that the coolant fluid leaves the exchanger 12 in the form of overheated steam. The coolant fluid exiting the heat exchanger 12 is sent through a fifth conduit 2.3 to the compressor 1, to restart the refrigerating cycle.

The heat for evaporating the liquid fraction of the coolant fluid in the heat exchanger 12 is supplied by the coolant fluid coming from the condenser 3 via the second conduit 4, which passes through the heat exchanger 12.

The flow of coolant fluid in the evaporator 6 is regulated by the expansion valve 5, the degree of opening of which determines the flow of coolant fluid that is sent to the evaporator 6. The degree of opening of the expansion valve 5 is adjusted by an electronic control device 14 in function of the level of liquid in the collecting receptacle 8 , The level L of liquid in. the collecting receptacle 8 is detected by a level sensor 15, preferably an infrared-ray sensor associated with the collecting- receptacle 8. The signal generated by the level sensor 15 is sent to the control device 14 which, in response to said signal, adjusts the degree of opening of the expansion valve 5, increasing the degree of opening if the level L of liquid in the collecting receptacle S decreases and decreasing the degree of opening if the level L of liquid increases, In Figure 2 there is illustrated a first embodiment of the collecting receptacle S.

Xn this first embodiment, the collecting receptacle 8 has a substantially cylindrical shape, with an inlet 16 into which the third conduit 7 coming from the evaporator 6 leads . The inlet 16 is preferably arranged so that the coolant fluid coming from the evaporator 16 enters the collecting receptacle 8 in a noticeably tangential direction, &o that a turbulent motion of the coolant fluid in .the collecting receptacle 8 is generated, so as to promote the separation of the liquid phase from the gas phase.

Inside the collecting receptacle 8 first separating_, means 17 and second separating means 18 are arranged, arranged respectively in the upper part and in the lower part of the receptacle. Said separating means has the following functions: the means 17 promotes the separation of the liquid phase of the coolant fluid from the gas phase, ensuring in the conduit 9 a sole flow of steam_/ the means 18 prevents the underlying level of liquid being disturbed by the turbulence of the steam. Said separating means 17, 18 can be constituted, for example, by net means, or by radial protrusions of the internal wall of the receptacle. The collecting receptacle 8 is provided, above, with a first outlet 19, through which the gas fraction of the coolant fluid enters the first outlet conduit 9, and, below, with a second outlet 20 through which the liquid fraction of the coolant fluid, which has collected on the bottom of the collecting receptacle 8, enters the second outlet conduit 10. The first and the second outlet conduit 10 flow, as said, into the fourth conduit 11 that conveys the coolant fluid to the heat exchanger 12.

In the second outlet conduit 10 flow adjusting means 10a is provided, for example a diaphragm with a calibrated hole_/ for adjusting the flow of liquid that is supplied to the fourth conduit 11, in function of the potential of the heat exchanger 12, so as to guarantee that all the liquid delivered to the fourth conduit 11 evaporates in the evaporator 12 before then reaching the compressor 1. Alternatively to the calibrated orifice, a valve can if necessary be used that modulates the fluid in function of the overheating of the steam measured at the outlet of the exchanger 12, so as to ensure, together with the safety of the computer against the shocks from liquid, an effective use of the exchange surface of the exchanger 12. In the lower part of the collecting receptacle S, at the receptacle zone in which the liquid phase of the coolant fluid is collected, the level sensor 15 is arranged, preferably an infrared-ray sensor, which detects if the level L of the liquid is lower or higher than a preset level, sending a corresponding signal to the control device 14, which adjusts the expansion valve 5,

In Figure 3 there is illustrated a second embodiment of the collecting receptacle Sa, In this second embodiment, about half way up the height of the second embodiment there is a narrowing 21, the object of which is to reduce the influence of the free surface of the liquid of the turbulences generated by the coolant fluid, which enters the collecting receptacle S. Said turbulences, may in fact cause oscillations of the free surface of the liquid that may negatively influence the readings of the level sensor 15 , In Figure 4 there is illustrated a third embodiment of a collecting receptacle Sb. In this third embodiment the collecting receptacle 8b has a first further opening 22, located in the upper part of the receptacle and a second further opening 23 , located in the lower part of the receptacle at the zone in which the coolant fluid is collected in liquid state. The first further opening 22 and the second further opening 23 make the collecting receptacle 8b communicate with an auxiliary receptacle 24, so that in the auxiliary receptacle 24 there is, through the effect of the communicating vessels principle, a level L of liquid equal to that of the receptacle Sa, without the free surface of the liquid in the auxiliary receptacle 24 being disturbed by the turbulences that are generated in the collecting receptacle Sb at the inlet of the coolant fluid coming from the evaporator 6. The level sensor 15 is associated with the auxiliary receptacle 24. The auxiliary receptacle can also have the shape of a level pipe. in Figure 5 there is illustrated a further version of the system in Figure 3, that is applicable also to the diagrams of Figure 2 and of Figure 4, that differs by the methods with which the liquid collected in the receptacle 8a is evaporated: in this case, in addition to, or instead of the exchanger 12, an exchanger 25 is used inside which a coil 27 is located that is condensed fluid coming from the condenser 3, located below the level of liquid fixed in the receptacle 8a. Through the law of communicating vessels the coil is submerged in the liquid supplied through gravity by the receptacle 8a, so that the liquid is restored automatically by the quantity that evaporates, without any need for calibrated orifices or adjusting valves; the steam that is formed through the effect of the heat exchange returns to the receptacle Sa through the conduit 22 to be subsequently aspirated by the compressor 1 through the conduit 9. The return to the compressor of the oil that may accumulate in the exchanger 25 can be obtained by a controlled injection of liquid in the sucking conduit of the compressor. In Figure 6 there is illustrated an embodiment of the invention in a plant with a reversible heat pump that can operate both for cooling and for heating an environment.

The plant comprises a compressor 101 in which the coolant fluid is compressed that, via a first conduit 102, is sent to a v inversion valve, for example a four-way valve, that reverses the flow direction of the coolant fluid in the plant, when switching from operation as a refrigerator to operation as a heat pump. The V valve is connected, via a second conduit 103 with a first heat exchanger 104 that, in the operation as a refrigerator, acts as a condenser, whilst, in operation as a heat pump, it acts as an evaporator. The first heat exchanger 104 is associated with a first receptacle 108 that, when the exchanger acts as an evaporator, performs the same function as the collecting receptacle 8, 8a, 8b disclosed previously and which is provided with a respective level sensor (which is not shown) . The coolant fluid exiting the first heat exchanger 104 is sent to a third conduit 105 in which a two- directional expansion valve 106 is arranged. The third conduit 105 leads into a second heat exchanger 107 that in operation as a refrigerator acts as an evaporator, whilst in operation as a heat pump acts as a condenser. The second heat exchanger 107 is associated with a second receptacle 108a that is completely similar to the first receptacle 108 associated with the first heat exchanger 104. Also the second receptacle 108a is provided with a respective level sensor (which is not shown) . The level sensors associated with the collecting receptacles 108 and 108a are operationally associated with a control device 109, for example an electronic control device that pilots the expansion valve 106, increasing the degree of opening thereof when the level of liquid in the collecting receptacle 108, or 108a, associated with the heat exchanger 104, or 107, that acts as an evaporator, decreases and the level of opening of the expansion valve 106 decreases when the level of liquid in the collecting receptacle 108, or 108a, increases.

A fourth conduit 110 connects the second heat exchanger 107 to the inversion valve V and a fifth conduit 111 connects the inversion valve V to the suction of the compressor 101, possibly through a suction accumulator 112.

The receptacles 108 and 108a are any way connected to an exchanger, which is not shown in Figure 6, having the function of evaporating the liquid contained in the bottom of the aforesaid receptacles for cooling the liquid condensate directed to the lamination valve. Said exchanger is shown as a component 12 in Figure l_r or 25 in Figure 5. In operation of the plant as a refrigerator, the coolant fluid compressed by the compressor 101 is sent, for example, by the valve v to the first heat exchanger 104 in which it condenses, releasing heat to the exterior. The coolant fluid, before entering the first heat exchanger 104, passes through the first receptacle 108, which, in this case, does not perform any function, the level sensor associated thereto being disabled. The coolant fluid that has condensed in the first heat exchanger 104 is sent, passing through the expansion valve 106, to the second exchanger 107 in which it evaporates, absorbing heat from the exterior, passing to saturate steam state, with titre near 1, By exiting the second heat exchanger, the coolant fluid passes through the second receptacle 108a in which the liquid phase separates from the steam phase, becoming deposited at the bottom of the receptacle 108a, as already disclosed with reference to the refrigerating plant illustrated in Figures l to 5. The level sensor associated with the second receptacle 108a is active and sends to the control device 109 a signal indicating the level of the liquid in the receptacle 108a, on the basis of _,which the control device adjusts the degree of opening of the expansion valve 106. The liquid phase and the gas phase of the coolant fluid separated in the second receptacle 108a are mixed together, as already disclosed, at the outlet of the receptacle and the coolant fluid is sent to the compressor to restart the cycle .

During operation of the plant as a heat pump the direction of. the flow of the coolant fluid into the exchangers 104 and 107 is reversed by the inversion valve V, so that the second heat exchanger 107 acts as a condenser and the first exchanger 104 acts as an evaporator. In this way, the second receptacle 108a associated with the second exchanger 107 does not perform any function and the level sensor associated therewith is disabled, whilst the first receptacle 108 acts as a collecting receptacle, in which the gas phase and the liquid phase of the coolant fluid exiting the first exchanger 104 separate. The level sensor associated with the first receptacle 108 is, in this case, active.

It should be noted that the invention is applicable to refrigerating plants that are provided with a single compressor/condenser unit, or with a plurality of compressor/condenser groups operating in parallel that supply a plurality of evaporators that are parallel to one another, In this case, each evaporator will be associated with a respective collecting receptacle 8. In the practical embodiment the material, dimensions and constructional details may be different from those indicated but be technically equivalent thereto without thereby falling outside the legal domain of the present invention.

Claims

1. Refrigerating plant comprising a coolant fluid, a compressor (1) , a condenser (3) , an expansion valve (5) , at least an evaporator (6) , a collecting receptacle (8) for collecting said coolant fluid, and controlling means (14, 15) for piloting said expansion valve (5) , characterised in that said collecting receptacle (8) is interposed between an outlet of said evaporator (6) and an inlet of said compressor (1) .

2. Plant according to claim 1, wherein said coolant fluid exits said evaporator (6) in humid saturated steam state.

3. Plant according to claim 2, wherein said humid saturated steam has a titre not less than approximately 0,9.

4. Plant according to any preceding claim, wherein said collecting receptacle (8; 8a; 8b) is provided with an inlet (16) , connected to a conduit (7) that connects said outlet of said evaporator (6) to said inlet (16) , with a first outlet (19) placed in an upper part of the collecting receptacle (8; 8a; 8b) and with a second outlet (20) located in a lower part of the receptacle (8; 8a; 8b) .

5. Plant according to claim 4, wherein said conduit (7) and said inlet (16) are arranged so that said coolant fluid enters said collecting receptacle (8; 8a; 8b) in a noticeably tangential direction.

6. , Plant according to claim 4, or 5, wherein said first outlet (19) is connected to a first outlet conduit (9) and said second outlet (20) is connected to a second outlet conduit (10) , said first outlet conduit (9) and said second outlet conduit (10) flowing into a conduit (11) connected to a suction conduit of said compressor (1) .

7. Plant according to claim 6, wherein said second outlet conduit is provided with flow adjusting means (10a) .

8. Plant according to claim 7, wherein said flow adjusting means comprises a diaphragm (10a) with calibrated passage hole.

9. Plant according to claim 7, wherein said flow adjusting means comprises a valve, the control signal of which is the overheating of the steam at the outlet of the exchanger (12) , or another signal suitable for assuring the protecting of the compressor against the risk of taking in liquid.

10. Plant according to any one of claims 4 to 9, wherein said collecting receptacle (8; 8a; 8b) is provided with first separating means (17) and with second separating means (18) , arranged respectively in said upper part and in said lower part of the receptacle (8; 8a; 8b), said first separating means (17) and said second separating means (18) being suitable for promoting a separation of the liquid phase of said coolant fluid from the gas phase.

11. Plant according to claim 10, wherein said first separating means (17) and said second separating means (18) comprise net means.

12. Plant according to claim 10, wherein said first separating means (17) and said second separating means (18) comprises radial deflectors associated with the internal surface of said collecting receptacle (8; 8a; 8b) .

12. Plant according to any preceding claim, wherein said collecting receptacle (8; 8a; 8b) is associated with level detecting means (15) .

14. Plant according to claim 13, wherein said level detecting means comprises a level sensor (15) arranged at the lower part of the receptacle (8; 8a/ Sb) .

15. Plant according to claim 14, wherein said level sensor (15) is an infrared-ray sensor, or a float sensor, or a capacitive sensor.

16. Plant according to claim 14, or l≤, wherein said level sensor (15) is operationally associated with a control device (14) suitable for driving said expansion valve (5) .

17. Plant according to any one of claims 4 to 16, wherein said collecting receptacle (Sa) is provided with a narrowing (21) arranged between said upper part and said lower part.

18. Plant according to any one of claims 4 to 16, wherein said collecting receptacle (Sb) is associated with an auxiliary receptacle (24) having an upper part that communicates with the upper part of the collecting receptacle (8b) and a lower part that communicates with the lower part of the collecting receptacle (Sb) .

19. Plant according to any one of claims S to 18, wherein between said collecting receptacle (S; 8a_/ 8b) and said compressor (1) there is interposed a heat exchanger (12) through which the coolant fluid coming from said receptacle through said conduit (11) (8; 8a; Bb) passes and the coolant fluid coming from the outlet of the condenser (3) through a further conduit (4) passes.

20. Plant according to any one of claims 6 to 18, wherein the liquid coolant fluid collected in the receptacle (S; 8a; 8b) supplies an exchanger (25) by gravity inside which pipes (27) traversed by the liquid condensate coming from said condenser (3) are submerged by the liquid coming from said receptacle {8; 8a; 8b) that evaporates to cool said condensate .

21. Plant according to claim 20, wherein the fluid evaporated in said exchanger (25) returns to said receptacle

(8_/ 8a; Bb) by a conduit (26) ,

22. Refrigerating and heat pump plant comprising a coolant fluid, a compressor (101) , a first heat exchanger (104) , a two-way expansion valve (106) , a second heat exchanger (107), an inversion valve (V) of the flow of said coolant, and controlling means (109) suitable for piloting said expansion valve (106) , characterised in that said first heat exchanger (104) and second heat exchanger (107) are associated with respective collecting receptacles (108; 108a) that, when the respective heat exchanger (104; 107) acts as an evaporator, receive said coolant fluid leaving the respective heat exchanger (104; 107) in the form of humid saturated steam.

23. Plant according to claim 22, whei-ein each of said collecting receptacles (108; 108a) is associated with a respective level sensor.

24. Plant according to claim 23, wherein each of said level sensors is operationally associated with said controlling means (109) .

25. Plant according to any one of claims 22 to 24, wherein each of said collecting receptacles (108,- 108a) is a collecting receptacle according to any one of claims 4 to 12, or according to any one of claims 17, 18, 19, 20, 21.