Transcritical vapor compression cycle device with a variable high side volume element.

(74) Agent

Sinvent AS, Strindveien 2, 7034 Trondheim, NO

Gustav Lorentzen, Trondheim, NO

Jostein Pettersen, Ranheim, NO

Ivan Ricanek, Norsk Hydro AS, Oslo (54) Name Device for controlling the pressure in the high pressure side of a transcritical compression debt system and method for carrying out the same (56) Published publications None (57) Summary A device and method for varying the pressure in the high pressure side in a transcritical compression debt system is based on one or more variable volume elements associated with the flow circuit. The device consists of a variable volume member (5) consisting of a chamber connected and communicating with the high pressure side, so that the flow of refrigerant into the chamber is possible, and a movable dividing device defining at least one side of the chamber and which is displaceable between a first and a second chamber. a second position corresponding to a first and a second volume of refrigerant in the chamber, respectively.

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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to compression refrigeration devices, such as refrigeration machines, air conditioning systems and heat pumps, which use a refrigerant operating in a closed system under transcritical conditions, and more specifically to devices and a method for variable control of the high pressure side pressure in these devices.

The invention relates to transcritical vapor compression systems, as described in WO-A-90/07683.

Current subcritical compression technology requires an operating pressure and an operating temperature below the critical point for a particular refrigerant. A transcritical vapor compression process operates at a pressure higher than critical pressure on the high pressure side of the flow circuit. Since the main object of the invention is to provide equipment and methods which give rise to the use of alternatives to environmentally unacceptable refrigerants, the background of the invention is best explained on the basis of standard cold vapor compression technology.

The main components of a one-stage steam system consist of a compressor, a capacitor, a throttle valve or an expansion valve and an evaporator. These basic components can further be supplemented with a countercurrent heat exchanger.

The basic subcritical process is as follows. The refrigerant liquid is partially evaporated and cooled by pressure reduction in the throttle valve. In the evaporator, 20 and the refrigerant liquid boil completely by absorbing heat from the fluid flowing through the evaporator, i.e., the fluid flowing through the evaporator is cooled. The low pressure steam is then sucked into the compressor, where the pressure is increased to a point where the superheated gas can be condensed by the available cooling fluid. The compressed gas flows into the condenser, where the gas 5 is cooled and condensed by heat being transported to air, water or another cooling medium. The condensed liquid then flows to the throttle valve.

The term transcritical process refers to a cooling process that operates partly below and partly above the critical pressure of the refrigerant. In the supercritical range, the pressure is more or less independent of temperature since no saturation state exists anymore. The pressure can therefore be freely chosen as a design variable. Downstream from the compressor outlet, the refrigerant is cooled at approximately constant pressure by heat exchange with a cooling medium. The cooling gradually increases the density of the refrigerant which is in a single phase state.

A change in volume and / or instantaneous refrigerant filling on the high pressure side will affect the pressure, which is determined by the ratio of filling to volume.

Unlike this, subcritical processes will operate below the critical point of the refrigerant with a two-phase state of liquid and vapor in the condenser. A change in the volume on the high pressure side will not directly affect the equilibrium of the saturation pressure.

In a transcritical process, the pressure on the high pressure side can be regulated to achieve capacity change or optimization of the power factor, and the change is effected by regulating the refrigerant filling and / or controlling the total internal volume of the high pressure side.

WO-A-90/07683 discloses one of these possibilities for controlling the pressure on the high pressure side in the supercritical range by means of variation of instantaneous refrigerant filling in the high pressure side.

From DE-C-898 751 it is known to use a high pressure liquid accumulator for the purpose of maintaining the cold performance and smoothing out temperature variations on the low pressure side during standstill. This is a system operating with a subcritical pressure on the high pressure side, 5 and the invention has other purposes and mechanisms than with the regulation of supercritical pressure in accordance with the present invention.

An object of the present invention is to provide an apparatus and method for varying the volume in the high pressure side of a transcritical compression cooling system for the purpose of controlling the pressure on the high pressure side.

Another object of the invention is to provide an apparatus and method for compensating refrigerant leakage effects.

A further object is to provide a variable volume element which can be operatively linked to a conventional hydraulic system, for example in a motor vehicle, so that the volume can be varied on the high pressure side of a transcritical steam process system.

Another object of the invention is to provide a variable volume element integrated into any control system for optimizing high pressure side pressure or capacity regulation in a transcritical vapor processing system.

Another object of the invention is to provide equipment for reducing pressure when the transcritical plant is not in operation, thereby achieving a weight reduction and a reduction in material cost since the low pressure side of the circuit can be designed for a lower maximum pressure.

A further object of the invention is to provide devices and a method of air conditioning of a car, without using environmentally unacceptable refrigerants.

These and other objects of the present invention have been achieved by providing a system and method operating in accordance with claims 1-9.

Several system embodiments of the concept of the invention are illustrated in the accompanying Figures 1-4, 5 wherein:

<td>Fig. 1</td><td>is a schematic presentation of a transcritical compression cooling system with a pressure vessel containing an inner flexible membrane which can be displaced by variation of the pressure in a fluid which fills the shaded portion of the pressure vessel.</td>

<td>Fig. 2</td><td>is a schematic representation of another variable volume element performed as a movable piston cylinder.</td>

<td>Fig. 3</td><td>is a schematic representation of a third embodiment of a variable volume element with the element designed as a flexible hose surrounded by hydraulic oil.</td>

<td>Fig. 4a, b</td><td>illustrates schematically yet another embodiment of the variable volume element to which a bellows is attached or integrated in the flow circuit.</td>

Fig. 1 shows the main components of a transcritical compression cooling system comprising the device of the invention and operating in accordance with the method of the invention. In the flow circuit, the refrigerant stream flows from compressor 1 to gas cooler or heat exchanger 2. The variable volume element 5 of the invention is connected to the high pressure side of the flow circuit, in particular between the outlet of the compressor 1 and the inlet of the throttle valve 3 which is of a conventional type, for example a thermostatic expansion valve. The refrigerant flows on to the evaporator 4 and then back to the compressor inlet.

The variable volume element 5 is located between the compressor 1 and the throttle valve 3, but need not be placed as schematically shown in FIG. 1.1 the preferred embodiment shown in FIG. 1, the variable volume element 5 will have a construction as a conventional pressure vessel.

The variable volume element 5 contains an inner flexible membrane or partition 6 of a conventional type. The diaphragm 6 moves contiguously or flush with internal surfaces of the variable volume element 5 so that the interior is divided into two non-communicating chambers 7,8, the relative volume being determined by the position 10 of the diaphragm 6.

In the preferred embodiment of the invention, the diaphragm or divider 6 is continuously displaceable within the variable volume element 5, so that the relative volume of chambers 7 and 8. can be continuously altered, although the concept of invention also includes non-continuous displacement of diaphragm 6, stepless or continuous adjustment of the position of the diaphragm 6 provides a more flexible and effective control than stepwise adjustment.

Chamber 8 communicates with a valve 9 connected to a hydraulic system (not shown). The valve 9 can control the amount of any fluid, preferably hydraulic fluid, in chamber 8. It is convenient, but not necessary, that hydraulic oil or a hydraulic system be used to move the flexible diaphragm.

6. Mechanical devices connected to the diaphragm 6 or pressure-carrying devices connected to the variable volume element 5, for example compressed gas filling chamber 8, or even spring pressure for displacing the diaphragm or partition 6, are encompassed by the concept of the invention.

When the valve 9 releases a controlled amount of hydraulic oil into chamber 8, the oil will push against the flexible membrane 6 and push it away from the valve 9 so that the volume in chambers 7 is reduced and thereby regulated.

Chamber 7 is connected to the high pressure side of the flow circuit of the transcritical compression cooling system. When hydraulic oil flows into chamber 8 so that the volume in chamber 7 is reduced, the refrigerant in chamber 7 will be forced out of chamber 7 in accordance 5 with the reduction of the volume.

This extortion of the refrigerant from chamber 7 increases the pressure in the high pressure side of the plant. As the hydraulic oil is forced out through the valve 9 from chamber 8, the oil pressure in chamber 8 becomes lower so that the oil can no longer push the diaphragm 6 as far from the valve 9 as before.

The refrigerant flows from the flow circuit into chamber 7 as the diaphragm 6 moves to an inner circular extent in a position closer to the valve 9. The volume in chamber 7 is then increased while the volume in chamber 8 is reduced. Meanwhile, the pressure on the high pressure side of the flow circuit will be reduced.

2, 3 and 4 show alternative embodiments of the variable volume element 5. The above detailed description of the variable volume element 5 and its function as shown in FIG. 1 is equally applicable to the embodiments shown in FIG. 2-4 modified with respect to the various embodiments.

Fig. 2 shows a variable volume control element 5 designed as a cylinder 10 having a top 13. A piston rod 12 is connected at one end to a control mechanism 20 (not shown) and at the other end to a piston 11 which is well adapted the cylinder 10 and which is movable back and forth or up and down according to the position of the control mechanism. A chamber 14 is defined in the interior of the cylinder 10 at the distance between the cylinder top 13 and the top of the piston 11, the piston top being the surface facing the cylinder top 13.

Chamber 14 is connected to the high pressure side of the flow circuit of the compression cooling system so that the volume of the chamber is filled with refrigerant.

The depicted embodiments of the variable volume element 5 are shown in FIG. 1 and 2 related to a saw branch from the main flow circuit between compressor 1 and throttle valve 3.

This positioning of these embodiments on the side or outside of the flow circuit is appropriate in operation for the shape and function of these embodiments. As depicted, these designs will allow for volume control without directly changing the volume of the tubes in the main flow circuit. However, it is within the concept of the invention to place the designs of FIG. 1 and 3 directly in the main flow circuit between the compressor 1 and the throttle valve 3.

The embodiment depicted in FIG. 3 suggests the possibility of placing a variable volume element 5 directly in the main flow circuit, although element 5 according to the invention concept can also be placed in a position on the side of the flow circuit. Fig. 3 shows a variable volume element 5 formed as a flexible hose 15 connected and in communication with parts of the main flow circuit, the hose being enclosed by a sealed chamber 16 containing hydraulic oil or other compressed fluid. The sealed chamber 16 does not prevent connection between hose 15 and the main flow circuit, and has no connection with chamber 17 in the hose 15. Chamber 16 20 is preferably not flexible. The hose 15 can be expanded or narrowed according to the pressure of the hydraulic oil flowing through the valve 18 so that the volume is varied. This design is likely to provide the best opportunity to counteract the accumulation of lubricating oil.

Other variable volume elements, such as bellows, may also be used, as schematically illustrated in FIG. 4a and 4b. The variable volume element 5 is shown as bellows where the internal volume (chamber) 17 will vary as it is subjected to a mechanical control mechanism / displacement device or a variable pressure from an external medium (not shown in the figure). The bellows can either be connected to a connection to the flow circuit (fig. 4a) or placed in series as an integral part of the flow circuit (Fig. 4b).

The concept of the invention is also expressed in the form of a procedure for varying the volume of the high pressure side of a transcritical compression cooling system, where the flow circuit conducts a refrigerant downstream from a compressor 1 through a heat exchanger 2 to a throttle valve 3. The method comprises connecting a volume control element 5 to the flow circuit at a point between the compressor 1 and the throttle valve 3, and arranging the chambers 7, 14,17 within element 5 so that the chambers 7,14,17 are connected 10 to the flow circuit at the connection site, mobile sharing

6,11,15 within element 5 to define at least one side of the chambers 7,14,17 in the element, so that the division 6,11,15 may be displaced between a first position characterized by a first volume of the chambers 7,14; 17 and a second position characterized by a second volume greater than the first volume, and attachment of displacements 9,12,18 15 so as to be in contact or engagement with the divider 6,11,15 and move the divider

6,11,15 between the first and second positions by operating the displacement device 9,12,18. In a preferred embodiment of the method of the invention, the displacement is performed continuously.

By controlling the internal volume of the variable volume element 5, the pressure in the high pressure side of the transcritical compression cooling system is controlled. This control is achieved by varying the mechanical displacement of the partition 6,11,15 or the amount of pressurized fluid outside the flow circuit (i.e. fluid which does not undergo compression in the cooling system) which serves to compress the refrigerant out of the variable volume element 5. Installed in a car, the car's hydraulic system can be connected via a valve arrangement. This volume control system can be integrated into any control strategy for optimizing pressure in the high pressure side, for capacity control and for capacity increase.

The ability to reduce pressure out of operation or downtime is a particular advantage of the concept of the invention. For example, in an air conditioning system for a car, the variable volume element of the invention (with different designs as shown in the figures) 5 may reduce the pressure by increasing the volume when the system is turned off. This is desirable because the high temperature in the engine compartment will be transferred to the non-active air conditioning system as the pressure increases. Using the variable volume element of the invention, the low pressure side can be designed for lower maximum pressure, thus reducing material consumption, cost and weight.