WO2015048973A1

WO2015048973A1 - Cooling system with thermosiphon, use and method of operating such a system

Info

Publication number: WO2015048973A1
Application number: PCT/DK2014/050307
Authority: WO
Inventors: Morten Espersen
Original assignee: Dantherm Cooling A/S
Priority date: 2013-10-02
Filing date: 2014-10-01
Publication date: 2015-04-09

Abstract

A cooling system (2) comprising at least one thermosiphon (3) which thermsiphon (3) comprises a valve (18) is disclosed. It is the object of the invention to achieve a limited flow of liquid refrigerant from the condenser (10) back to the evaporator (4) in situations where the valve (18) is forced to open by high pressure of liquid refrigerant above the valve (18). This can be achieved by a second tubing (16) of the cooling system (2) comprising at least one liquid storage volume (20) for storing liquid refrigerant, which liquid storage volume (20) is placed between the valve (18) and the evaporator (4), which liquid storage volume (20) comprises an inlet (22) connected to the valve (18) and an outlet (24) connected to the evaporator (4), which outlet (24) comprises at least one flow restriction (26), which liquid storage volume (20) reduces any effect of rapid opening of the valve (18) to prevent flooding of the evaporator (4). Hereby can thermo shock in the evaporator (4) be prevented because the storage volume will in critical situations fill up the storage with cold liquid refrigerant and reduce the flow back to the evaporator (4) so that only small amount of liquid refrigerant is flowing to the evaporator (4) where normal operation therefore can be performed because flooding of the evaporator (4) is avoided. In a normal situation for the operation of the thermosiphon (3) the extra volume has a very limited effect on the function.

Description

COOLING SYSTEM WITH THERMOSIPHON, USE AND METHOD OF

OPERATING SUCH A SYSTEM

Field of the Invention

The present invention concerns a cooling system comprising at least one thermosi- phon, which thermosiphon comprises at least one indoor evaporator which indoor evaporator is heat conductive connected to indoor cooling fins, in which indoor evaporator liquid refrigerant is evaporated, which indoor evaporator is by first tubing connected to at least one outdoor condenser which first tubing conduct evaporated refrigerant from the evaporator to the outdoor condenser, which outdoor condenser is heat conductive connected to outdoor cooling fins for cooling the condenser, which condenser is placed in a defined vertical distance to use the gravity to generate a flow of liquid refrigerant from the condenser through a second tubing back to the evaporator, which second tubing comprises a valve, which valve comprises a valve seat and a moveable valve piston, which valve piston is moved by a valve actuator, which valve piston is by decreasing temperature by the actuator moving towards the valve seat for closing the valve.

Background of the Invention

US 2011048676 A discloses a cooling system applying a thermosiphon therein, being superior in energy saving and/or ecology, with an effective cooling, and also an elec- tronic apparatus applying that therein, in particular, for cooling a CPU mounted on a printed circuit board within a housing thereof, comprises a heat-receiving jacket, being thermally connected with a surface of the CPU generating heats therein, and for evaporating liquid refrigerant stored in a pressure-reduced inner space with heat generation thereof, a condenser for receiving refrigerant vapour from the heat-receiving jacket within a pressure-reduced inner space thereof and for condensing the refrigerant vapour into a liquid by transferring the heats into an outside of the apparatus, a vapour tube, and a liquid return tube, with applying the thermosiphon for circulating the refrigerant due to phase change thereof, wherein the condenser forms fine grooves on an inner wall surface thereof along a direction of flow of the refrigerant, and is also formed flat in a cross-section thereof, for cooling the refrigerant vapour from the heat- receiving jacket on the inner wall surface thereof, efficiently. Object of the Invention

It is the object of the invention to achieve a limited flow of liquid refrigerant from the condenser back to the evaporator in situations where the valve is forced to open by high pressure of liquid refrigerant above the valve.

Description of the Invention

The object of the invention can be fulfilled by a system as disclosed in the opening paragraph and further modified by a second tubing of the cooling system comprising at least one liquid storage volume for storing liquid refrigerant, which liquid storage volume is placed between the valve and the evaporator, which liquid storage volume comprises an inlet connected to the valve and an outlet connected to the evaporator, which outlet comprises at least one flow restriction, which liquid storage volume reduces any effect of rapid opening of the valve to prevent flooding of the evaporator.

The cooling system may comprise at least one thermosiphon comprising at least one evaporator in which a liquid refrigerant can be evaporated and which evaporator is connected to at least one condenser by a first tubing that conducts evaporated refrigerant from the evaporator to the at least one condenser, placed in a defined vertical distance from the least one evaporator to use gravity to generate a flow of liquid refrigerant from the condenser back to the evaporator through a second tubing with a valve where the second tubing comprises at least one volume for storing liquid refrigerant and placed between the valve and the evaporator, which volume comprises at least one flow obstacle and is configured to reduce the effect of a rapid opening of the valve to prevent flooding of the evaporator. Thus, the volume is understood as a volume beyond the volume of the tubing itself. The volume may be a storage volume for storing a liquid. Likewise the obstacle may be imposing a restriction in the direct flow, but with limited reduction of flow capacity. As such the obstacle may be a breaker such as a wave breaker or a flush breaker. The volume and the obstacle are arranged according to each other to reduce the effect of a flush of fluids. In an embodiment the volume and the obstacle are arranged to allow the passing of the essentially the same quantity of fluid as the tubing would otherwise have allowed, but as a more constant flow.

In an embodiment, the volume is an expansion of the tubing. The obstacle may be a plate located in the volume with an opening. There may be an apparent opening from an inlet to an outlet, which opening is similar in size to the cross section of the tubing.

The evaporator may be configured to be located indoor or inside. The condenser may be configured to be located outdoor or outside.

The volume may be configured as a storage volume for storing of liquid refrigerant.

Hereby can be achieved that in situations where low outdoor temperatures occur and a large amount of refrigerant of the thermosiphon is evaporated and therefore stored as liquid refrigerant in the condenser and the actual liquid pressure is so high, that the valve that is preventing flow is forced to open. In that situation a large amount of liquid very cold refrigerant will flow directly to the evaporator. This can perform a rapid cooling and it takes a long time to get the large amount of liquid very cold refrigerant evaporated. In order to avoid thermo shock the storage volume will in this critical sit- uation fill up the storage with cold liquid refrigerant and reduce the flow back to the evaporator so that only small amount of liquid refrigerant is flowing to the evaporator where normal operation therefore can be performed because over flooding of the evaporator is avoided. In a normal situation for the operation of the thermosiphon the extra volume has a very limited effect on the function. The volume will automatically be filled up and the flow restriction will then be very limited so that the flow from condenser to evaporator is performed nearly without influence of the flow restriction. In order to have perfect operation of the thermosiphon the amount of refrigerant has to be adjusted so that in normal operation there is sufficient refrigerant in the storage volume to achieve a traditional operation. It is possible in one invention to place the storage volume indoor and in relation to the evaporator. In that situation the storage volume will in low degree also in warm situations perform evaporation and therefore also reduce the temperature of the refrigerant entering the evaporator. In a preferred embodiment for the invention the liquid storage volume can be formed as an outer volume connected to the valve and an inner tube connected to the tubing towards the evaporator, which inner tube comprises at least one opening for flow of liquid refrigerant. Hereby can be achieved that a very simple storage volume can be performed in the outer tubing. The inner tubing can in fact just be opened in the top and liquid re- frigerant will flow to the opening as soon as the volume is filled up. In that way a relative primitive liquid storage can be performed and the effective size of the storage volume simply can be adjusted in the placement of the inner tube.

In a further preferred embodiment for the invention the liquid storage volume can be formed as an outer volume connected to the valve and an inner tube connected to the tubing towards the evaporator, which inner tube comprises a plurality of opening for flow of liquid refrigerant. By placing a number of openings in the inner tube it is possible that the volume has a limited effect in the normal operation of the thermosiphon because some lower openings will perform the flow of the refrigerant. In that way most of the refrigerant of the system can be active in situations of normal operation. By increasing flow the outer volume will fill up with liquid refrigerant and more of the openings will be active. Probably a kind of equilibrium will be achieved where the liquid level in the outer volume will stabilise independent of the actual cooling demand. But the effect of the storage volume is that any rapid change in the flow from condenser to evaporator is avoided. Increasing flow will in the beginning just lead to increasing amount of refrigerant stored in the storage. The different openings in the inner tube will automatically start a reduced flow of refrigerant towards the evaporator.

In a further preferred embodiment for the invention the liquid storage volume can be formed as an upright placed outer volume connected to the valve and an inner tube connected to the tubing towards the evaporator, which inner tube comprises at least some lower openings of a first diameter and a plurality of higher placed openings of a larger opening diameter. It is possible to have a number of different openings in the inner tube and in that way an active flow adjustment can be achieved. Use of a system as disclosed previously for cooling electronic systems, by the electronic systems are placed inside a housing, which electronic systems generate heat, whereby the inner of the housing needs cooling, which cooling is performed with at least one thermosiphon, which evaporator of the thermosiphon is placed inside the housing for the electronic system, which condenser of the thermosiphon is placed outside the housing. Hereby effective cooling can be achieved, especially for electronic devices such as transmitter receiving system for mobile communication placed in small housings in relation to the communication or transformer housings placed near consumers. In all of these housings there is a climatic shield that protects the electro- or electronic devices inside but the devices inside the housing are producing heat which has to be re- moved. A plurality of thermosiphons can therefore be used because these perform the cooling of the housings rather efficiently but with very low energy consumption. The number of thermosiphons can be relatively high because when the thermosiphons have been installed there will be almost no service or operation costs. Therefore, the evaporator can be placed inside the housing and the condenser can be placed outside the housing. In some situations circulating air will be used inside the housing so that air blowing means will blow air around the evaporators inside the housing and air blowing means could also be used for circulating outdoor air through the condensers.

By the present invention it is achieved that if a situation occurs in which the outside temperature is decreasing, for example during winter, cooling of the condensers can take place and the temperature of the condenser is lower than the temperature of the evaporator inside the housing. In such a situation a rather unrestricted flow will occur from the condenser down to the evaporator, and the evaporator will be cooled near to the outdoor temperature. To avoid such a situation when the outdoor temperature is low, the valve is placed in the liquid line between the condenser and evaporator. As soon as the temperature decreases to a certain level, this valve will close fully or partly and the thermosiphon as such will stop or reduce its operation until the temperature is increasing in the condenser, thereby increasing the temperature and pressure in the entire thermosiphon. Method for operating a cooling system as disclosed previously is disclosed in at least the following sequence of steps: a. perform evaporation of refrigerant in an evaporator for generating a refrigerant gas, b. let the gas flow in a piping towards a condenser placed a gravity level higher than the evaporator, c. perform condensation in the condenser for generating liquid refrigerant, d. let the liquid refrigerant flow in a tubing towards a normal closed valve, e. open the valve depending of a pressure of liquid refrigerant above the valve, f. force by gravity the liquid refrigerant to flow in a piping back towards the evapora- tor, g. liquid refrigerant is forced by gravity to flow into at least one storage volume, which storage volume is placed in relation to the piping, which storage volume reduces the flow of liquid refrigerant by at least one flow restriction. Similarly an object is achieved by a method for operating a cooling system as disclosed and comprising actions of: evaporating a refrigerant in an evaporator thereby generating a refrigerant gas, guiding the refrigerant gas flow in a tubing towards a condenser laced a gravity level higher than the evaporator, condensing the refrigerant gas in the condenser and thereby generating a liquid refrigerant, guiding the liquid refrigerant flow in a tubing (15) towards a valve, opening the valve depending on a pressure of the liquid refrigerant above the valve, forcing by gravity the liquid refrigerant to flow in a tubing back towards the evaporator, breaking the flow of liquid refrigerant forced by gravity to flow to the evaporator by passing the flow into at least one volume placed in relation to the tubing, which volume has an obstacle and is con- figured to reduce the effect of a rapid opening of the valve.

By such method a thermosiphon system can be achieved which automatically stops or reduces the flow of refrigerant in a situation where the temperature is so low that less cooling capacity in Watt/Kelvin is needed. In such a situation, there will probably be decreased or no cooling demand. Therefore, the closing of the valve will give as result that no or reduced further refrigerant is delivered to the evaporator. Thereby it is avoided that the evaporator is further cooled by sending very cold refrigerant down to the evaporator. In an indoor environment, for example a housing for electronic cir- cuits, it will be possible to reduce the air flow for short periods of time thereby letting the temperature in the housing increase. The increasing temperature will relatively quickly lead to a low degree of evaporation in the evaporator. Evaporated gas will continue flowing in the piping towards the condenser. If the temperature around the condenser is very low, condensation takes place immediately. However, only if there is a certain pressure of refrigerant placed above the valve, there will be circulation back to the evaporator. If the valve is adjusted correctly, a defined temperature and thereby the pressure must be achieved to start a very limited circulation, and therefore an automatic adjustment of the amount of circulating refrigerant can be achieved. The storage volume will reduce the flow because some of the liquid refrigerant will fill up the storage volume and a reduced flow of refrigerant back to the evaporator is achieved. Increasing temperature at the evaporator will lead to a higher degree of evaporation which then automatically increases the pressure in the condenser and an increasing pressure in the liquid refrigerant will be achieved above the valve, which valve will then open more to increase the flow of liquid refrigerant through the valve. This will probably relate to situations in the winter period. In the summer period, with high indoor and outdoor temperatures, the valve will probably be open most of the time so that full circulation can take place.

The fill ratio for a thermosiphon system is of paramount importance in order to oper- ate the thermosiphon with high efficiency. For the purpose of this text we define the fill ratio as the liquid volume of the operation fluid divided by the total internal hydraulic volume available to the liquid fluid at the maximum operation temperature of the thermosiphon system. If the fill ratio is continuously increased, the heat transfer capability of the thermosiphon is reduced until it eventually ceases. Under normal conditions this happens when the condenser is shocked with liquid leaving no room for heat transfer. Therefore, in practical applications there is a maximum limit constraint on the fill ratio. In the text of 87305154.4 (BT) where the thermosiphon system comprises a standard commercially available suction pressure valve from an evaporator in a HVAC system, it is claimed that the internal pressure of the system is defined by whichever of the heat exchangers that has the highest temperature. If practice, that has a significant implication namely the fact that a minimum fill ratio is required. If a minimum refrigerant fill ratio is not present in the system, the internal operating pressure is dictated by the condenser temperature in the temperature range where you would want to close the valve and halt the fluid circulation by means of the valve. In this situation the condenser probably operates at a significantly lower temperature than the evaporator and the partial pressure in the condenser is the lowest pressure in the entire system facilitating that all the liquid fluid collects in the condenser element provided enough fluid exists to fill the condenser completely in the liquid state at the given temperature. In this situation the pressure dominated by the condenser state. However, as known from 87305154.4 if enough liquid is present to completely fill the condenser leaving a small amount of excess liquid trapped in the hot zone, for instance in the evaporator, then the system will increase its internal pressure provided the evaporator temperature increases. However, this approach is completely useless as the maximum fill ratio is heavily exceeded and the performance of the entire thermosiphon system is dramatically reduced useless provided the internal volume ratio is evenly or at least balanced. By this we mean the following. Provided the internal condenser volume is considerably smaller than the internal evaporator volume, the condenser could possibly be flooded when needed. However, such a system would probably be metastable i.e. unsteady and therefore not desirable. Also such a system would probably not be designed out of a practical application.

This application describes a thermosiphon system that does not have the limitations and implications of the above. This system comprises a valve and a hot liquid reservoir which is specifically designed for a given thermosiphon system. The hot reservoir operates in combination with the safeguard valve. The combination of the safeguard and the hot liquid reservoir allows the system to effectively alter the amount of the liquid fluid present in the coils and further explicitly control exactly where the refrigerant is present in the thermosiphon system. This combination allows the system to operate with a much higher fill ratio than a normal system allowing condenser flood- ing when needed combined with the ability to drain the condenser into the hot reservoir when needed. In other words it enables controlling the fill ratio of the coils allowing them to be operated at maximum efficiency rather than to try and control the fill ratio of the entire system.

In a scenario with low outside temperatures and low heat input into the evaporator, the safeguard valve is programmed to close at a certain low temperature. This allows the liquid to collect in the condenser which is eventually flooded and seizes to operate. When this happens, excess liquid is still present in the hot reservoir or in the evapora- tor securing pressure causality in order to open the safeguard valve when needed. This will happen when the condenser temperature exceeds the safeguard valves' set point, but it will also happen when the evaporator temperature increases up to the set point value of the safeguard because this arrangement facilitates that liquid is present in the evaporator forcing saturation state. This is critically important as this secures the nec- essary system causality which means that the valve can open in case the evaporator is getting hotter which means the heat input will probably increase which again demands the valve to open in order to facilitate the needed cooling. When this happens, the valve opens and dumps excess fluid into the hot reservoir, which traps a certain amount of the liquid refrigerant before it is feed to the evaporator. This device allows the system to operate with maximum efficiency when the valve is open, and reduces its efficiency when needed. When the valve is fully closed and the condenser is fully flooded, the system efficiency is literally zero which means that no cooling takes place. This system state is maintained until the safeguard valve opens. When the safeguard valve opens, cold liquid quickly enters the hot liquid reservoir which is eventually flooded. When this happens, cold liquid is attitudinally fed into the evaporator. If this change is too violent and facilitates a violent temperature drop, the hot liquid reservoir can be designed to limit the flow into the evaporator. One way to do this is to insert a raiser tube into the hot liquid reservoir. The raiser tube could preferably have a calibrated bore or a number of calibrated bores in order to lead the cold liquid refrigerant slowly into the evaporator. When the temperature outside is low enough and there is low heat input into the evaporator and the saturation pressure of the system decreases below the set point temperature of the valve, the valve will close fully. Following this the liquid will collect into the condenser until the internal condenser volume is totally filled with liquid refrigerant which is eventually cooled to the external temperature. If the power input into the evaporator is increased with amplitude high enough to increase the temperature to a level where the internal saturation pressure is high enough to exceed the valve set point, the valve will open and cold liquid refrigerant is drained very quickly into the hot reservoir. When the reservoir is totally filled the refrigerant flows into the evaporator filling the evaporator with a high amount of very cold refrigerant which might facilitate a large temperature undershoot before the pressure eventually is low enough on order for the valve to close. In order to avoid this, the raiser with calibrated bores will prevent this from occurring because the cold liquid refrigerant is leaked slowly into the evaporator which means that the cooling starts slowly enough so that the pressure drops slovenly enough in order for the valve to close fast enough for the temperature not to undershoot. The object of the invention may be achieved by a method of operating a cooling system as disclosed. Such method may comprise actions or steps of: evaporating a refrigerant in an evaporator generating a refrigerant gas, guiding the refrigerant gas flow in a tubing towards a condenser placed a gravity level higher than the evaporator, condensing the refrigerant gas in the condenser generating a liquid refrigerant, guiding the liquid refrigerant flow in a tubing towards a valve, opening the valve depending on a pressure of the liquid refrigerant above the valve, forcing by gravity the liquid refrigerant to flow in a tubing back towards the evaporator, and breaking the flow of liquid refrigerant forced by gravity to flow to the evaporator by passing the flow into at least one volume placed in relation to the tubing, which volume has an obstacle and is con- figured to reduce the effect of a rapid opening of the valve.

By breaking the flow is understood to reduce or diminish one or more effects of a flush of a fluid.

Description of the Drawing

Fig. 1 shows a possible embodiment for the invention.

Fig. 2 shows a sectional enlarged view of the storage volume.

Fig. 3 shows a sectional view of a second preferred embodiment for the invention. Detailed Description of the Invention

Fig. 1 shows a system 2 comprising a thermosiphon 3. This thermosiphon comprises an evaporator 4 which evaporator by tubing 8 is connected to a condenser 10. This condenser 10 is further by tubing 16 connected to a valve 18. This valve 18 is further by tubing 19 connected to a storage volume 20 by an inlet 22. The storage volume 20 has an outlet 24. The storage volume has a flow restriction 26 as a wall dividing the storage volume for refrigerant into two sections. The sectional view does not indicate the length of the storage volume 20 but typically the volume 20 will be formed in a branch tube, may be placed parallel to the evaporator 4. In operation the liquid refrig- erant generated in the condenser 10 will flow through the tubing 16, the valve 18 and the tubing 19 towards the storage volume 20. Filling up the storage volume the refrigerant will flow through the outlet 24 to the evaporator where the process is repeated.

In situations where very low temperatures occur around the condenser 10, most of the refrigerant will be liquefied in the condenser and generate a relative high pressure at the valve 18. In situations where the evaporator 4 is totally dried out by evaporation there is a very limited cooling effect of the system and in that situation the pressure can reach a level that opens the valve 18. In that situation the storage volume 20 will be flooded by cold liquid refrigerant. Because of the flow restriction 26 the flow to- wards the evaporator 4 is restricted in a way where a thermal shock of the evaporator is avoided.

Fig. 2 shows an enlarged view of the sectional view of the storage volume 20 as seen on fig. 1. The storage volume 20 is connected by an inlet 22 for filling up the storage volume. Further is an outlet 24 indicated. The inlet and the outlet are connected to different parts of the storage volume 20 by the flow restriction 26. This flow restriction comprises openings 28 in the lower part and bigger openings 30 in the upper part. Further the flow restriction 26 is open in the top so the largest opening occurs in situations where the volume 20 is totally filled.

By the flow through the small openings 28, 30 can be achieved in normal operation that only a small amount of refrigerant is stored in the storage 20. In a situation where the valve 18 as seen on fig. 1 is opened because of too high liquid pressure the volume 28 will simply fill up and the flow restrictions 26 with the openings 28, 30 will avoid any flooding of the evaporator 4.

Fig. 3 shows an alternative embodiment to the invention indicating tubing 116, it is the tube leading to the condenser which tubing is connected to the valve 118 which is further connected to an outer volume 122 which outer volume comprises a tube 124 connected towards the evaporator 4. Inside the volume 120 is placed a tube 126. This inner tube comprises a number of small openings 128. A plurality of larger openings 130 and some very large openings 132 are disclosed.

In operation the valve 118 will be open and liquid refrigerant will partly fill the volume 122. Probably most of the openings 128 will be sufficient during normal operations to achieve sufficient flow towards the evaporator 4. In situations where larger amount of liquid refrigerant increases the pressure in a tube 116 and forces the valve 118 to open, the volume 122 is sufficient large to prevent any flooding of the evaporator 4 with very cold refrigerant. The volume 122 will instead be filled up and the different openings 128, 130, 132 will reduce the flow towards the evaporator. Therefore, the flow to the evaporator will reduce into a partly filling of the evaporator so that traditional evaporation can be performed.

Reference is made to the content of Danish Patent Application PA 2013 70550, which content and figures hereby is incorporated by reference.

Claims

1. Cooling system (2) comprising at least one thermosiphon (3) comprising at least one evaporator (4) in which a liquid refrigerant can be evaporated and which evaporator (4) is connected to at least one condenser (10) by a first tubing (8) that conducts evaporated refrigerant from the evaporator (4) to at least one condenser (10) placed in a defined vertical distance from least one evaporator (4) to use gravity to generate a flow of liquid refrigerant from the condenser (10) back to the evaporator (4) through a second tubing (16, 116) with a valve (18) characterized in, that the second tubing (16) comprises at least one volume (20, 120) placed between the valve (18, 118) and the evaporator (4), which volume (20, 120) comprises at least one flow obstacle (26, 126) and is configured to reduce the effect of a rapid opening of the valve (18, 118) to prevent flooding of the evaporator (4).

2. Cooling system according to claim 1, characterized in that the volume (20, 120) is formed as an outer volume connected to the valve (18, 118) and an inner tube (124) connected to the tubing towards the evaporator (4), which inner tube (124) comprises at least one opening (128, 130, 132) for flow of a liquid.

3. Cooling system according to claim 1 or 2, characterized in that the volume (20, 120) is formed as an outer volume (122) connected to the valve (18, 118) and an inner tube (126) connected to the tubing towards the evaporator (4), which inner tube comprises a plurality of openings (128, 130, 132) for flow of liquid refrigerant.

4. Cooling system according to any of claim 1 to 3, characterized in that volume (120) is formed as an upright placed outer volume (122) connected to the valve (118) and an inner tube (126) connected to the tubing towards the evaporator (4), which inner tube (126) comprises at least some lower openings (128) of a first flow area and a plurality of higher placed openings (130, 132) of a larger flow area.

5. Cooling system according to any of claim 1 to 4, characterized in that the volume (20,120) is configured as a storage volume (20, 120) for storing of liquid refrigerant.

6. Use of a system as disclosed in any of claim 1 to 5 for cooling electronic systems, characterized in that electronic systems are placed inside a housing, which electronic systems generate heat, whereby the inner of the housing needs cooling, which cooling is performed with at least one thermosiphon (3), which evaporator (4) of the thermosi- phon (3) is placed inside the housing for the electronic system, which condenser (10) of the thermosiphon (3) is placed outside the housing.

7. Method for operating a cooling system (2) as disclosed in any of claim 1-5 comprising actions of: a. evaporating a refrigerant in an evaporator (4) thereby generating a refrigerant gas, b. guiding the refrigerant gas flow in a tubing (8) towards a condenser (10) placed a gravity level (14) higher than the evaporator (4), c. condensing the refrigerant gas in the condenser (10) thereby generating a liquid refrigerant, d. guiding the liquid refrigerant flow in a tubing (15) towards a valve (18), e. opening the valve (18) depending on a pressure of the liquid refrigerant above the valve (18), f. forcing by gravity the liquid refrigerant to flow in a tubing (16) back towards the evaporator (4), g. breaking the flow of liquid refrigerant forced by gravity to flow to the evaporator (4) by passing the flow into at least one volume placed in relation to the tubing (16), which volume has an obstacle and is configured to reduce the effect of a rapid opening of the valve (18).