NL2009854C2 - COOLING AND FREEZING UNIT AND THE COOLING AND FREEZING EQUIPMENT PROVIDED FOR THE COOLING AND FREEZING UNIT, IN PARTICULAR FOR A COOLING OR FREEZING CELL OF A BAKERY. - Google Patents

Abstract

A refrigeration and freezer unit Al comprises a compressor 1 for circulating a refrigerant, as well as an oil separator 2 connected to the pressure pipe of the compressor, via which oil separator the refrigerant flows to a compressed gas heat exchanger 4 which forms part of the refrigeration and freezer unit, which compressed gas heat exchanger 4 is connected via a vapour return pipe LI to a cascade heat exchanger 28 from which a condensate pipe L2 carries the liquid to an evaporator 11 which forms part of the refrigeration and freezer unit, which evaporator leads the refrigerant to a suction pipe of the compressor 1. The refrigerant is C02 and between the oil separator, the compressed gas heat exchanger, the evaporator and the compressor is located a reversing valve 3 which in a first operation state connects the oil separator to the compressed gas heat exchanger and the evaporator to the compressor, and in a second operation state connects the oil separator to the evaporator and the compressed gas heat exchanger to the compressor.

Description

Cooling and freezing unit as well as cooling and freezing installation provided with the cooling and freezing unit, in particular for a cold store or freezer cell of a bakery 5 DESCRIPTION:

FIELD OF THE INVENTION

The invention relates to a cooling and freezing unit, in particular for a cooling or freezing cell of a bakery, comprising a compressor for circulating a refrigerant, and an oil separator connected to the pressure line of the compressor, via which the refrigerant passes to a compressed gas heat exchanger forming part of the cooling and freezing unit, which is connected via a vapor return line to a cascade heat exchanger, a condensate line of which carries the liquid to an evaporator forming part of the cooling and freezing unit, which refrigerant flows to a suction line of the cooling unit compressor leads.

State of the art Such a cooling and freezing unit is generally known. Commercial refrigeration mainly uses synthetic refrigerants that have a negative impact on the greenhouse effect in two different ways, directly in the event of leakage or indirectly due to their higher energy consumption. Natural refrigerants have no influence on the greenhouse effect in the event of a leak. The refrigerant CO2 itself does not 25 either because it is extracted from the ambient air and therefore comes back in the event of a leak. If applied correctly, natural refrigerants have a significantly higher efficiency and their CO2 emissions related to energy generation are therefore significantly lower.

The pursuit of sustainability by governments makes synthetic refrigerants expensive (punishment taxes) and installations with natural refrigerants become more attractive (subsidies). Nevertheless, few commercial refrigeration and freezing installations are built with natural refrigerants, which is mainly related to their safety aspects: • fire hazard and / or explosion hazard such as with hydrocarbons (propane), 2 • toxic as with ammonia, • suffocating as with CO2 but actually like any gas that is heavier than air, so also the synthetic cooling gases.

These safety aspects: • work against general application, certainly when it comes to public spaces (a bit double, if we realize that most refrigerators and freezers are filled with propane refrigerant), • require a higher professional competence of the installer and the operating staff, 10 · increases costs due to fire and explosion proof components such as propane, or components that can withstand much higher pressures such as CO2, or components that can withstand aggressive media such as ammonia, • increase the cost of the total installation is significant because the decades-old and trusted concept of industrial installations is being copied.

15 In commercial cooling, prices are mainly purchased and hardly taken into account the influence of energy costs on total operational management. Public opinion with regard to safety aspects associated with natural refrigerants makes it difficult to sell substantially more expensive installations based on payback times. If the natural refrigerant solution, whether or not supported by investment incentives, is price equal to the normal (synthetic) installation, then the sustainable conscious entrepreneur will switch.

If the natural refrigerants are to be used on a large scale within commercial cooling technology, installation concepts will have to be developed that can compete in cost terms with the current synthetic cooling installations. CO2 is non-toxic and / or flammable, only oxygen-displacing, just like the synthetic refrigerants. The much better thermodynamic properties of CO2 and its high density make it ideally suited to use as an alternative, where public opinion is opposed to any other natural alternative.

Summary of the invention 3

An object of the invention is to provide a cooling and freezing unit of the type described in the preamble in which a natural refrigerant is used and which can compete in terms of cost price with the current synthetic cooling installations while retaining the characteristic energetic advantages.

To this end, the cooling and freezing unit according to the invention is characterized in that the refrigerant is CO2 and a reversing valve is present between the oil separator, the compressed gas heat exchanger, the evaporator and the compressor, and in a first position the oil separator with the compressed gas heat exchanger and connects the evaporator with the compressor, and in a second position brings the oil separator with the evaporator and the compressed gas heat exchanger with the compressor.

A large cost item in cooling installations concerns the pipework. By applying the natural refrigerant CO2 instead of synthetic refrigerants such as R507 and 404A, the pipe diameters can be halved, while the wall thickness of conventional pipe is still sufficient at these diameters. This piping generally relates to the connection between the cooling unit in the engine room or outside on the roof, to the air cooler (s). These are the vapor return and condensate lines.

By being able to switch to "heat pump" function, you can effectively defrost with compressed gas. The use of a switch from cooling 20 to "heating" (in this case defrosting) is well known with air conditioning units, but is hardly or not used with cooling units. With CO2 as a refrigerant, this is certainly not because the required reversing valve is not available.

In commercial refrigeration technology, the air coolers are electrically defrosted, where large electrical connection capacities are required for the cold store or freezer room. 25 The much more effective hot gas defrosting is usually not an option, because there are usually too few parallel coolers to generate sufficient defrosting capacity, but also because of the complexity and the high costs (an extra compressed gas pipe must be installed). By choosing one unit in the immediate vicinity of the cell, switching to "heat pump" function makes it easy to defrost with hot gas at a maximum of 30 power. This eliminates high connection costs for electrical defrosting. Hot gas defrosting is twice as fast, the electrical power required is that of the compressor 3 times as low as with electric defrost. In addition to saving on installation and energy costs, the much shorter defrosting time will lead to less product drying.

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Furthermore, by applying the refrigerant CO2, thanks to the stroke volume that is 6 times smaller, a smaller and therefore cheaper compressor can be used (the compressor is the most expensive part of a cooling installation) and smaller diameter evaporator tubes will suffice, making the filling smaller . Furthermore, a better heat transfer is hereby obtained, whereby either the heat exchanger can be smaller and therefore cheaper and / or a better efficiency can be achieved.

An embodiment of the cooling and freezing unit according to the invention is characterized in that the reversing valve comprises an upper and a lower control valve and a valve housing provided with an upper opening communicating with the upper control valve and a lower opening communicating with the lower control valve, which control valves can connect the openings to the compressor press line and the compressor suction line, and which valve housing is furthermore provided with four further openings on which the compressor press line, the compressor suction line, the line to and from the evaporator, and the line to and from 15, the vapor return line is connected, in which valve housing an upper and lower valve slidable along a hollow valve stem are present, as well as an upper and lower control head which are present between the valve stem and the lower and upper openings, and an upper compression spring arranged between the two valves is present and a lower compression spring that t between the valve housing and the lower control head, the upper valve being movable between an upper position in which it connects the compressor pressure line to the line to the vapor return line and a lower position in which it connects the line of the vapor return line to the compressor suction line, and wherein the lower valve is movable between an upper position in which it connects the evaporator line to the compressor suction line and a lower position in which it connects the compressor press line to the line to the evaporator.

The two control valves can for instance be formed by two three-way valves or a combined multi-way valve.

This reversing valve is force neutral, so independent of the pressure differences prevailing thereon. The reversing valve is equipped with self-adjusting valves. By using a compression spring, the valve that is not yet abutting the seat can be pushed to the correct position by the compression spring. The compression spring then deposits against a chest or the other valve, which is already seated. This allows for greater tolerance differences between the housing and the check valve.

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A further embodiment of the cooling and freezing unit according to the invention is characterized in that the valves are provided with two opposite closing faces, each of which is provided with a groove in which an elastic sealing ring is present which is softer than the closing faces. The valves have a soft sealing surface formed on each side by the sealing ring, followed by a hard sealing surface formed by the sealing surface. Regardless of the pressure difference across the valves, this combination of a soft and hard seat ensures that no leakage can occur. The sealing ring is provided to close properly with small pressure differences. If the pressure difference increases, the, preferably metallic, sealing surfaces take over, thereby protecting the sealing ring against too high a surface pressure, resulting in permanent deformation. The sealing ring continues to cooperate so that leakage and therefore loss of compressor stroke volume is excluded. The control head diameters and springs are dimensioned in such a way that a minimum surface pressure on the soft sealing ring seat is achieved, so that leakage is excluded.

A still further embodiment of the cooling and freezing unit according to the invention is characterized in that a heat-pipe heat exchanger is present between the condensate line and the evaporator and the condensation line and the vapor return line, which breaks the connection between compressor and evaporator. A heat pipe or thermo-siphon makes it possible to operate outside the scope of the compressor when using the same refrigerant. This solution can be used for any refrigerant.

A still further embodiment of the cooling and freezing unit according to the invention is characterized in that a non-return valve combination is present in the drop line between the condensation line and the evaporator, and in the injection line between the heat pipe heat exchanger and the evaporator comprises a valve, which float is present as a diving bell around the connection of the down pipe, and which valve can close the connection of the injection pipe with an upper part and with a lower part the connection of the down pipe.

30 There is not yet a 4-way return valve for CO2. The much higher workload would only mean a heavier home implementation, but that is not the problem. With CO2, the cooking pressure per degree rises 6x as fast as with the synthetic refrigerants. The reversing valves designed for these synthetic refrigerants can therefore not be used, since the internal pressure losses occurring would mean a large part of the compressor stroke volume. The design to be claimed has a soft followed by a hard sealing surface. The seal ring (O-ring) is used to close well with small pressure differences. If the pressure difference increases, the metallic sealing surfaces take over, thereby protecting the O-ring against excessive surface pressure, resulting in permanent deformation.

5 The O-ring continues to cooperate so that leakage and therefore loss of compressor stroke volume is excluded. To exclude the influence of the operating pressure and occurring pressure differences, a balanced valve design has been used, as is also customary with multi-way valves from pneumatics and hydraulics. The reversing valve must never remain in an intermediate position, because otherwise the pressure difference necessary for controlling and sealing cannot be built up by the compressor. For this reason, a rest position spring is built in and the steering heads are matched to this in diameter.

This new type of valve combines two non-return valve functions with negligible opening pressure difference and maximum passage. The solution has been found in the use of a float that is provided on the top and bottom with the same soft and hard seat as used in the reversing valve. The floater is based on the diving bell principle, because a ball or other pressure-resistant body would become too heavy due to the very high working pressure. The flash gas flowing in at the bottom of the float provides the buoyancy.

For the heat pipe system to function properly, there must be a non-return valve in both the thermosiphon trap line and the injection line. The trap line has a large passage so that any vapor bubbles can rise against the liquid flow. addition to pressure losses in the cooler, the condenser placed above it and the intermediate pipework, must be compensated for by the weight of the liquid column in the down pipe. Due to the small differences in height, a spring-loaded non-return valve is not an option. The solution is found in a floating valve body.

The invention also relates to a cooling and freezing installation comprising a cooling or freezing cell for a bakery, as well as a cooling and freezing unit according to the invention. With regard to the cooling and freezing installation, the invention is characterized in that the cooling and freezing unit is mounted directly on or on the cooling or freezing cell. A large cost item in cooling installations concerns the pipework. By mounting the CO2 cooling unit directly on or to the cell, the length of the suction line can be reduced to a minimum. The distance from the cold room or freezer room to the engine room or outside is now taken over by the 1 to 2 diameters of smaller, therefore cheaper, pressure line 7. The energy loss due to pipe pressure losses decreases by 50%. The mounting of cooling units on or against (i.e. in the immediate vicinity of) the cooling or freezing cell is already very old, not for CO2 as a refrigerant.

An embodiment of the cooling and freezing installation according to the invention is characterized in that the cooling and freezing installation also comprises a cascade heat exchanger to which on one side the condensate line and the vapor return line for the refrigerant are connected and on the other side a further condensate line and a further vapor return line is connected for a further refrigerant, which further vapor return line is connected to a further compressor which via a further oil separator carries the further refrigerant to a further heat exchanger, a discharge of which carries the condensate to the cascade heat exchanger, the further refrigerant being propane .

By using propane as a refrigerant in the (upper) part of the cascade, the following advantages are achieved: I. the use of a natural instead of a synthetic refrigerant, II. obtaining a leak-proof installation (no shaft seal), III. reducing installation costs, IV. improving efficiency, V. reducing refrigerant charge, and VI. reducing noise production to the environment.

The closer you work to the critical temperature of a refrigerant (CO2 = + 31 ° C), the poorer the efficiency. That is why CO2 is only used as a refrigerant if cooling below -10 ° C is required, above that CO2 is only used as a coolant. To transport the heat absorbed by the CO2 to the environment, we therefore need a cascade cooling system (see Fig. 7). In the upper cooling system, where the heat absorbed by the CO2 is going to be discharged to the environment, ammonia has the best efficiency. But this was not chosen for two reasons. First of all, there are no small hermetic compressors, so one has to deal with a leak-sensitive shaft seal. Secondly, at the usual pressure ratios in the summer or at part load, piston compressors are not an option because of too high compressed gas temperatures and screw compressors must be chosen, which are a lot more expensive because of the many additional components required for oil management. That is why we opt for another highly suitable natural refrigerant and propane R290. The decades used for 8 R22 and therefore inexpensive components can also be used here without any problems. The pressure of propane is much lower than with the synthetic refrigerants, thus the noise production in the external condensers drops significantly. Due to the much lower specific mass of propane, the installation filling halves compared to.

5 synthetic refrigerants. The less refrigerant is required for operating the cooling installation, the better it is for the environment and people. Propane has a better efficiency than the best synthetic refrigerant R22 so far, but is approximately 10 to 15% worse in the same system version than when using ammonia. Another disadvantage of propane is the strong dissolving power in the lubricating oil, which greatly reduces the viscosity (lubricating power). After all, the used lubricating oil and propane are made from the same raw material, i.e. petroleum refined. By using a suction gas heat exchanger, the suction gas and therefore also the lubricating oil contained therein is heated. As a result, less propane can be absorbed into the oil and the viscosity, so lubrication properties, remains good. By extracting the heat from the condensate, the efficiency of the cooling installation also increases to that which is achievable with ammonia.

A further embodiment of the cooling and freezing installation according to the invention is characterized in that the cooling and freezing installation also comprises an internal heat exchanger which is present between the further vapor return line and the further compressor and between the discharge of the further heat exchanger and the cascade heat exchanger. By using an internal heat exchanger in the propane aggregate, the efficiency increases by 10 to 15% and is therefore equal or better than that of an aggregate working with the refrigerant ammonia. Furthermore, the propane dissolved in the lubricating oil largely evaporates, whereby the viscosity of the lubricating oil increases such that correct lubrication of the compressor is guaranteed.

A still further embodiment of the cooling and freezing installation according to the invention is characterized in that the further heat exchanger is an air-cooled microchannel condenser with split heat transfer functions, namely de-heating, followed by condensing, followed by subcooling. In contrast to the usual placement of the liquid vessel after the heat exchanger, it is now placed between condenser and subcooler. This creates the required fluid lock necessary for maintaining the undercooling achieved.

Yet another embodiment of the cooling and freezing installation according to the invention is characterized in that a liquid vessel is present between the cascade heat exchanger and the condensate line, the cascade heat exchanger, the further compressor, the further oil separator, and the further heat exchanger in a housing present. In the event of a fire, the heat radiation will cause the pressure in the vessel to rise above the maximum and the spring safety device placed on the vessel to blow off CO2 and to choke / extinguish the fire.

Yet another embodiment of the cooling and freezing installation according to the invention is characterized in that the cooling and freezing installation comprises a further cooling freezing unit which is also connected to the vapor return line and the condensate line. Both the compressed gas from the aggregates and the vapor from the pump circulation coolers are fed to the cascade heat exchanger via 1 joint pipe. In this cascade heat exchanger the CO2 vapor condenses, because propane evaporates on the other side. The CO2 condensate then flows into a liquid collection vessel. The condensate flows from the liquid vessel to the aggregates. If cooling is also required above -10 ° C, a pump will be mounted under this liquid vessel, which pumps the CO2 liquid to the coolers. The evaporated CO2 is returned via the central vapor line to the cascade heat exchanger. Connecting the compressed gas from the aggregates as well as the vapor from the pump circulation coolers to one common pipe ensures that the temperature of this pipe is so high that it does not have to be insulated.

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Brief description of the drawings

The invention will be explained in more detail below with reference to an exemplary embodiment of the cooling and freezing installation according to the invention shown in the drawings. Hereby shows:

Figure 1 the cooling and freezing unit of the cooling and freezing installation in cooling / freezing position;

Figure 2 the cooling and freezing unit in the defrosting position;

Figure 3a shows the reversing valve of the cooling and freezing installation in rest position 30 (cooling position);

Figure 3b shows the reversing valve in defrosting position;

Figure 4 shows the cooling and freezing unit in a high evaporating temperature position; 10

Figure 5a and Figure 5b show the check valve combination of the cooling and freezing installation during normal cooling;

6a, 6b and 6c show the evaporator of the cooling and freezing installation, in the normal version and designed as suitable for a heat pipe; and Figure 7 the cascade system of the cooling and freezing installation with propane aggregate.

Detailed description of the drawings Figure 1 shows the cooling and freezing unit A1 of the cooling-freezing installation according to the invention in the cooling / freezing position. The gaseous refrigerant compressed by a compressor 1 flows through a high-efficiency oil separator 2, which ensures that the lubricating oil emitted by the compressor 1 is separated and returned to the compressor 1. From the oil separator 2, 15, the gas flows through a compressor pressure line Cp a reversing valve 3 standing in a cool / freeze (= rest) position, and from there via a line K to a compressed gas heat exchanger 4, and then via a non-return valve 5 to a central vapor return line L1, which returns the vapor to the cascade heat exchanger. The refrigerant condensed in the cascade heat exchanger flows via a condensate line L2 and via a filter 20 and / or dryer 15 and sight glass 16 to a liquid valve 7. This electric valve 7 is opened when there is a demand for cooling, at that moment a electrical or mechanical expansion valve 8 supplying metered refrigerant to an evaporator 11 present in a cooling / freezing cell B. The evaporated refrigerant will then, with controlled 8, overheat via line V to the reversing valve 3 which is in the cool (= rest) position and then flow back to the compressor via a compressor suction line Cz, where the process starts again.

Figure 2 shows the cooling and freezing unit A1 in the defrosting position. The hot compressed gas now flows via the reversed reversing valve 3 to the outlet of the evaporator 11. The entrance of the evaporator 11 is closed in the direction of the expansion valve 8 by a non-return valve 9 and in the direction of the central condensate line L2 there is a non-return valve 12 with a passage adapted to the desired defrosting pressure (45 bara corresponds to a saturation temperature of + 10 ° C). The pressure behind non-return valve 12 is the cascade pressure (for example, 30 bara). The mass flow rate of the compressor is initially higher than that of non-return valve 12, 11, as a result of which the pressure in the evaporator 11 will rise. Because the external surface of the evaporator is covered with frost (ice), when the saturation temperature of 0 ° C in the evaporator 11 is exceeded, the gas supplied by the compressor will condense. This condensation process continues until the last ice has melted and the cooler continues to heat up. If non-return valve 11 no longer allows liquid through but gas, the difference in mass flow rate between compressor and non-return valve increases sharply and the pressure will rise rapidly. The defrosting process is finished, a pressure or temperature switch now switches the reversing valve 3 to cooling mode. Part of the gas that the compressor brings to the defrost cooler comes via 10 throttle valve 6, from the central vapor return line. This gas, braked to an acceptable compressor suction pressure, is then mixed with expanding cold agent coming from expansion valve 8 and then collectively enters the hot gas cooler 4. The latter is a length and diameter tube adapted to the aggregate and its working condition, in which the gas cools against the cold tube wall. The tube wall is wet with the evaporating liquid refrigerant. With an overheating controlled by expansion valve 8, the gas is then sucked in by the compressor.

Figure 3 shows the reversing valve 3 of the cooling and freezing installation in the rest position (cooling position). 3-way solenoid valve 47, is de-energized in such a position that the pressure above control head 42 is equal to the compressor suction pressure. 3-20 way solenoid valve 48, is de-energized in such a position that the pressure under control head 43 is equal to the compressor discharge pressure. Even if there is no pressure difference between compressor press and suction, the reversing valve will be in the upper position, and this by rest position spring 49. In this position, the upper breast 51 of the valve stem 52 is free from the valve 45, but presses the lower breast 53 of the valve stem valve 46 against its seat 54. In this position, the compressor pressure line Cp is connected to the central vapor return line L1 and the evaporator 11 to the compressor suction line Cz. Because the valve stem 52 of the reversing valve 3 is hollow and connects the space under control head 42 and the compressor suction line Cz, the pressure under control head 42 will always be the compressor suction pressure. The complete pressure difference now stands between both valves 45 and 46 between compressor press pipe Cp and compressor suction pipe Cz. Valve 45 is thereby pressed against its seat 55, while the contact pressure of valve 46 is precisely reduced thereby. The sum of the spring force and that exerted by the pressure difference over control head 43, however, must push the reversing valve up so hard that the lower valve stem breast 53, valve 46, presses against its seat 54 with sufficient contact pressure. The play between valve stem breast and valve is absorbed by the spring 50 placed between valves 45 and 46. The rest position spring ensures that the valve (s) are always in one closed position, the rest position.

In figure 3b the reversing valve is shown in defrosting position. 3-5 way solenoid valve coil 47, is activated in such a position that the pressure above control head 42 is equal to the compressor discharge pressure. 3-way solenoid valve 48, is activated and is in such a position that the pressure under control head 43 is equal to the compressor suction pressure. The resulting force due to the pressure difference over the control heads 42 and 43, as well as determined by their diameter difference, is sufficient to provide sufficient contact pressure against the rest position spring in valve 45 to close it leak-tight. Valve 46 is pressed against its seat 54 due to its pressure difference. In this position, the compressor pressure line Cp is connected to the evaporator 11 and compressor suction line Cz with the central vapor return line. The play between valve stem breast 53 and valve 46 is absorbed by the spring 50 placed between valves 45 and 46.

Figure 4 shows the cooling and freezing unit in a high evaporating temperature (to) position. A number of additional components are included in the normal aggregate circuit; heat exchanger 17, non-return valve combination 18, non-return valve 21, solenoid valve 20, and non-return valve 12 has been replaced by a solenoid valve 19. The non-return valve 3 is in defrosting position. The refrigerant evaporates in evaporator 11, rises via fall line 31 to heat exchanger 17, where it condenses and falls down via injection line 32 to the combination check valve 18. On the other side of heat exchanger 17, refrigerant evaporated is supplied and metered in by expansion valve 8. heat exchanger 17 evaporated refrigerant now flows through the hot gas cooler 4, reversing valve 3 and is sucked in by the compressor 1. The pressure in the heat-pipe circuit can assume any pressure, for safety reasons limited by a spring safety (not shown). Which pressure arises, or in other words which desired boiling temperature arises, depends on how the components are selected. Until the heat pipe is flush with the cascade system pressure (= compressor press pressure), 30 refrigerant from the compressor will be pressed into the heat pipe system. This excess of refrigerant in the heat pipe system is needed for it to work efficiently. If the heat pipe pressure has risen above the cascade pressure, the compressor will press its gas through the solenoid valve 20 into the cascade system. To prevent the heat pipe pressure from flowing away, the non-return valve 12 has been changed into a solenoid valve 19.

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Figures 5a and 5b show the check valve combination of the cooling and freezing installation during normal cooling, ie the compressor extracts the evaporated refrigerant from cooler 11. Expansion valve injects the liquid / vapor mixture (flash gas) via connection 33. The vapor fills the "diver's clock" space of the floater 34. Liquid and excess of vapor then escapes into the housing 35. There is now liquid around the float 34, the float rises and the valve 36 on the float closes connection 37. The injected liquid and vapor now flows via connection 38 to the evaporator 11. The pressure difference across the evaporator 11 is also across the valve 36 against connection 37, so that no undesired short-circuit current can arise. During defrosting, the condensate flowing out of the cooler will fill the space under the float 34, causing it to sink down and close the lower part of the valve 36, connection 33. The function of the non-return valve combination works in the same way when cooling on heat-pipe as when defrosting.

Figures 6a, 6b and 6c show the evaporator of the cooling and freezing installation, normal and suitable for heat pipe. If we look at Figure 7, we see a dotted pump 30 in the central condensate supply line L2. If we only have aggregates A1, A2, this is not necessary. However, if we also have coolers operating at the cascade temperature or above, without aggregate, we need a circulation pump 30. How an air cooler is normally connected Fig. 6a, 20 requires no explanation. If we also want to evaporate much higher here than is possible with the cascade temperature, this would only be possible if the pump can achieve an enormous head in combination with a throttle valve at the outlet of the evaporator. The pump must then realize the minimum pressure difference required for the expansion valve and also be able to press against the higher evaporating pressure. The current refrigerant pumps available on the market reach a maximum of 5 bar, which is just enough to make the expansion valve work. By making use of the reversing valve 3 described above in combination with heat-pipe heat exchanger 17, such a process can be realized. The refrigerant evaporated in 11 during normal cooling (Fig. 6b) flows back into the central vapor return line via the non-operating heat exchanger 17 and the reversing valve. The refrigerant to be injected passes through the heat exchanger 17 and reversing valve 3 in the reverse direction to the entrance of 11. With heat pipe cooling, the refrigerant is injected directly into the heat exchanger 17 and evaporates therein against the refrigerant condensing on the other side the evaporator 11. The evaporated refrigerant then flows back via the reversing valve in the other position 14 to the central vapor return line. The condensate then enters the evaporator 11 via the reversing valve in the other position, and then evaporates in 11 and ascends to the heat exchanger 17.

For evaporation temperatures above the CO2 cascade temperature, where one comes outside the operating range of the compressors, a "heat pipe" or thermosiphon system has been implemented (see figure 4). The connection between compressor and cooler is hereby broken. The refrigerant evaporated in the cooler condenses in the heat exchanger located above, where on the other hand refrigerant evaporates at a pressure acceptable to the compressor.

Figure 7 shows the cascade system of the cooling and freezing installation C with propane aggregate. The propane evaporated in the cascade heat exchanger 28 is sucked in by the compressor via an internal heat exchanger 27. The suction gas increases therein in temperature, due to the cooling of condensate on the other side. The gaseous refrigerant 15 compressed by the compressor 22 flows through the high-efficiency oil separator 23, which ensures that the lubricating oil emitted by the compressor is separated and returned to the compressor. The gas flows from the oil separator to the air-cooled microchannel heat exchanger 24. This is split into 3 parts. The condensate cooled in 26 flows to the internal heat exchanger 27, where it is further cooled. From 27 it is then dosed through an injection combination to the cascade heat exchanger 28. The vapor from the central vapor return line condenses on the other side of heat exchanger 28. The condensate then falls into liquid vessel 29, from which it flows via the central condensate line L2 with or without pump is supplied to the aggregates or evaporators.

The propane unit (Figure 7) is placed on the roof and provided with a microchannel condenser 24 and 25. Since the condenser in this application is dominating in the refrigerant charge, the 5x so small refrigerant content will ensure that the total propane charge is acceptable. Together with the other installation components, the prop filling is then 0.1 kg per kW cooling capacity. The condenser is split into 3 parts, i.e. heater followed by the condenser. The condenser is connected to a liquid container, which forms a liquid lock with the 3rd part, i.e. the subcooler. By splitting these three heat transfer functions in this way, the maximum attainable heat transfer is achieved with the lowest refrigerant charge.

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In commercial refrigeration technology, the air coolers are electrically defrosted, where large electrical connection capacities are required for the cold store or freezer room. The much more effective hot gas defrosting is usually not an option, because there are usually too few parallel coolers to generate sufficient defrosting capacity, but also because of the complexity and the high costs (an extra compressed gas line must be installed). By choosing one unit in the immediate vicinity of the cell, switching to "heat pump" function makes it easy to defrost with hot gas at maximum power. The "defrosting power" is taken from the central gas line to the cascade heat exchanger. The amount of gas required for defrosting is choked and cooled from the central gas line to an overheat acceptable to the compressor. The compressor then compresses the gas to defrost pressure and transports the gas to the cooler (s) to be defrosted. This eliminates high connection costs for electrical defrosting. Hot gas defrosting is twice as fast, the electrical power required is therefore that of the compressor 3x as low as with electrical defrosting. In addition to saving on installation and energy costs, the much shorter defrosting time will lead to less product drying.

A CO2 compressor has a stroke volume that is 6 times smaller than an R507 or 404A compressor, but a much thicker house due to the much higher operating pressure. The latter, however, has a much smaller influence on the cost price than the stroke volume. The actual (slightly different from the market price) cost price of a CO2 compressor should be significantly lower than that of an R507 / 404a compressor. The compressor is the most expensive part of a cooling installation.

Evaporators (in this case, air coolers) work best when the evaporating refrigerant consumes the entire pipe circumference. The heavier the gas and the smaller the pipe diameter, the better this goes (CO2 is 3.5 times heavier than R507 / 404A). The much better heat transfer can be translated into less heat-exchanging surface and therefore cheaper, or to a better efficiency. The smaller diameter tube means less refrigerant charge.

By making use of the density difference between propane and air 30, with a well-considered casing it can be ensured as follows that normal (so not cost-increasing) electrical switching equipment can be used: I. placing a drip tray at the bottom of the casing and 16 II . ensure an underpressure throughout the enclosure, by having an explosion-proof auxiliary fan extracting the mixture at the lowest point, or running the explosion-proof condenser fan at low speed.

TTT - to place the control cabinet far away from the unit, i.e. in the building, or 5 IV. by mounting a gas-tight switch box V. by placing a gas sensor at the bottom of the unit, which when the 20% of the LFL is reached (lowest ignition limit) releases the voltage from the unit, but allows auxiliary fan (for the underpressure) to run , or VI. the condenser fan switches to a higher speed.

VII. place the CO2 liquid container inside the housing. In the event of a fire, the heat in the vessel will cause the pressure in the vessel to rise above the maximum and the spring safety device placed on the vessel will blow off CO2 and choke / extinguish the fire.

Although in the foregoing the invention has been elucidated with reference to the drawings, it should be noted that the invention is by no means limited to the embodiment shown in the drawings. The invention also extends to all embodiments deviating from the embodiment shown in the drawings within the scope defined by the claims.

Claims (11)

Cooling and freezing unit (A1), in particular for a cold store or freezer cell (B) of a bakery, comprising a compressor (1) for circulating a refrigerant, as well as an oil oil connected to the pressure line of the compressor separator (2), via which the refrigerant passes to a compressed gas heat exchanger (4) forming part of the cooling and freezing unit, which is connected via a vapor return line (L1) to a cascade heat exchanger (28) of which a condensate line (L2) transports the liquid to conducts an evaporator (11) forming part of the cooling and freezing unit which leads the refrigerant to a suction line of the compressor (1), characterized in that the refrigerant is CO2 and between the oil separator (2), the compressed gas heat exchanger (4), the evaporator (11) and the compressor (1) a reversing valve (3) is present which in a first position brings the oil separator into contact with the compressed gas heat exchanger and the evaporator with the compressor, and in a second position the oil sc connects the heater with the evaporator and the compressed gas heat exchanger 15 with the compressor. Cooling and freezing unit (A1) according to claim 1, characterized in that the reversing valve (3) comprises an upper and a lower control valve (47.48) and a valve housing (41) provided with an upper opening in communication with the upper control valve (47) and a lower opening communicating with the lower control valve (48), which control valves can connect the openings to the compressor pressure line (Cp) and the compressor suction line (Cz), and which valve housing is furthermore provided with four further openings to which the compressor pressure line (Cp), the compressor suction line (Cz), the line (V) from and to the evaporator (11), and the line (K) from and to the vapor return line (LI) are connected, in said valve housing having an upper and lower valve (45, 46) slidable along a hollow valve stem (44), as well as an upper and lower control head (42, 43) which are present between the valve stem and the lower and upper openings, and upper compression spring (50) ie e is present between the two valves and a lower compression spring (49) which is present between the valve housing and the lower control head (43), the upper valve (45) being movable between an upper position in which it enters the compressor pressure line (Cp) connects the line (K) to the vapor return line (L1) and a lower position in which it connects the line (K) of the vapor return line (L1) to the compressor suction line (Cz), and where the lower valve (46) is movable is between an upper position in which it connects the line (V) of the evaporator (11) to the compressor suction line (Cz) and a lower position in which it connects the compressor pressure line (Cp) with the line (V) to the evaporator (11). 3. Cooling and freezing unit (A1) according to claim 2, characterized in that the valves (45, 46) are provided with two opposite closing faces, each of which is provided with a groove in which an elastic sealing ring is present which is softer is then the closing faces. Cooling and freezing unit (A1) according to claim 1, 2 or 3, characterized in that between the condensate line (L2) and the evaporator (11) and the condensation line (L2) and the vapor return line (L1) pipe heat exchanger (17) is present, which breaks the connection between compressor (1) and evaporator (11). Cooling and freezing unit (A1) according to claim 4, characterized in that in a fall pipe (31) between the condensation pipe (L2) and the evaporator (11), and in an injection pipe (32) between the heat pipe heat exchanger (17) and the evaporator (11), a non-return valve combination (18) is present, which comprises a float (34) provided with a valve (36), which float acts as a diving bell around the connection (33) of the fall line (31) ), and which valve (36) can close the connection (37) of the injection line (32) with an upper part and the connection (33) of the drop line (31) with a lower part. Cooling and freezing installation (C) comprising a cooling or freezing cell for a bakery, as well as a cooling and freezing unit (A1) according to one of the preceding claims, characterized in that the cooling and freezing unit (A1) directly on or is mounted on the cold store or freezer (B). 7. Cooling and freezing installation (C) according to claim 6, characterized in that the cooling and freezing installation also comprises a cascade heat exchanger (28) on which on one side the condensate line (L2) and the vapor return line (L1) for the refrigerant is connected and on the other side a further condensate line and a further vapor return line is connected for a further refrigerant, which further vapor return line is connected to a further compressor (22) which via a further oil separator (23) transports the further refrigerant to a further conducts heat exchanger (24), a drain of which carries the condensate to the cascade heat exchanger (28), the further refrigerant being propane. Cooling and freezing installation (C) according to claim 7, characterized in that the cooling and freezing installation also comprises an internal heat exchanger (27) present between the further vapor return line and the further compressor (22) and between the discharge of the further heat exchanger (24) and the cascade heat exchanger (28). Cooling and freezing installation (C) according to claim 7 or 8, characterized in that the further heat exchanger (24) is an air-cooled microchannel condenser with 5 split heat transfer functions, namely de-heating, followed by condensation, followed by subcooling. Cooling and freezing installation (C) according to one of the preceding claims 6 to 9, characterized in that a liquid vessel (29) is present between the cascade heat exchanger (28) and the condensate line (L2), the cascade heat exchanger (29) 28), the further compressor (22), the further oil separator (23), and the further heat exchanger (24) are present in a housing. Cooling and freezing installation (C) according to one of the preceding claims 6 to 10, characterized in that the cooling and freezing installation (C) comprises a further cooling and freezing unit (A2) which is also on the vapor return line (L1 ) and the condensate line (L2) is connected.