SE2050001A1 - A liquid heating system and a method for heating liquid - Google Patents

Abstract

The invention relates to a heating system for heating a substance, preferably a liquid, comprising a heat storage vessel (2) with a heat storage medium (HM1) to be heated by means of a heat source (5) and a sealed tubing (4) arranged to transfer heat to a heat transfer unit (7), said sealed tubing (4) having a partial filling of a substrate partially in liquid state (W) and partially gas state (G) and comprising a return tube (41) arranged to return substrate in liquid state (L) from said heat transfer unit (7) and a supply Lube (40) arranged to supply heat in gas state (G) to said heat transfer unit (7), wherein a part of said sealed tubing includes a condensing tubing (77) that is included in said heat transfer unit (7) and positioned above a third system level (L3) and the upper liquid level of said heat storage medium (HM1) is positioned below said third system level (L3), characterized in that an outlet tube (77B) of said condensing tubing (77) is connected to a control member (410) at a second system level (L2), which control member (410) includes a movable connector part (413), wherein said movable connector part (413) is controllably, movably arranged between a first position (415) and a second position (416) a vertical distance (L) apart, wherein said first position (415) coincides with said third system level (L3) or is at a second system level (L2) above said third system level (L3) and said second position (416) is in level with a first system level (L1), wherein a substantial portion of said condensing tubing (77) corresponding to a contained condensing volume (VM) is positioned below said first system level (L1). It also relates to a method for heating a substance.

Description

A LIQUID HEATING SYSTEM AND A METHOD FOR HEATING LIQUID TECHNICAL FIELD This invention relates to a system for heating liquid, comprising a heat storage vesselthat acts as a heat storage, a first sealed duct having a partial filling of water under sub-atmospheric pressure, having an upper part arranged to supply heat from the heatstorage vessel to a heat exchanger device acting as a heat transfer unit, and in somecases a second sealed duct of the same kind arranged to supply heat to the heat storagevessel from, e.g. a solar heat-collecting panel.

BACKGROUND It is known to use different types of technologies and methods for cooking and heatingof liquids, e. g. water. For instance, one can use solid fuel, gas, electric resistance heatersor induction, the latter being a relatively new technology that is efficient and allows forfast heating. It is also known to use solar heat for the heating of water, both for domestichot water and for cooking, which could help make life easier for many people,especially in poor areas of the world. In that regard it is known to use phase changes of different media, e. g. water, for heat transportation.

From GB 2032613 there is known a system for water heating in domestic hot watersystems, wherein the water heating system utilizes the principle of heat transfer byvapour generated at low pressure, to convey heat from a solar heat-collecting panel to avessel in which water is to be heated. It comprises a vapour transfer heating with asealed duct partially filled with a liquid under sub atmospheric pressure. The duct has afirst part arranged in heat exchange relation with the water and a second part locatedwithin the solar heat collecting panel, the arrangement of the duct being such that in useof the system vapour produced by heating of the second part of the duct passes into thefirst part of the duct where it condenses, giving up heat to the water in the vessel.Thereafter the condensed liquid is conveyed back to in a closed cycle. This knownsystem has its advantages in regard to using solar energy to warm water for use withinbuildings, e. g. to be used as warm tap water. However, there is disadvantage with the known system in that it may only provide moderately heated water.

From WO20l6l8503l there is known a system that is an improvement over the priorart, such that boiling water may be provided, in a cost-efficient and flexible manner. It discloses a system for heating liquid, comprising a heat storage vessel that acts as a heat storage, a first sealed duct having a partial filling of water under sub-atmosphericpressure, having an upper part arranged to supply heat from the heat storage vessel to aheat exchanger device acting as a heat transfer unit, and a second sealed duct of thesame kind arranged to supply heat to the heat storage vessel from, e. g. a solar heat-collecting panel. This system fulfils its purpose but presents some disadvantages from adesign perspective.

SUMMARY OF THE INVENTION It is an object of the invention to provide an improved liquid heating system that mayprovide for boiling water, by transferring heat from a heat source or a heat storage to theheat transfer unit as defined in claim 1.

Thanks to the invention many applications can draw benefit from rapid heating ofchosen materia, e. g. water, to boiling temperature, e. g. kitchen appliances for cookingand hot water for cleaning purposes, etc, wherein quickly different modes can be chosento either use the heat source to directly heat the heat transfer unit or to store heat in the heat storage.

Thanks to the invention according to one embodiment according to the invention a solarheating system makes it possible for many people to make easy use of solar energy toheat water or other liquids that may be used for cooking food and/or preparation of hotdrinks and also for other purposes.

In transferring heat from the heat storage vessel to the heat transfer unit the systemmakes use of the phase change between liquid and gas. Water can be used as well asrefrigerants with no or little temperature glide. Water is an easily available liquid andthe temperature at which water boils is reduced as the pressure on the water is reduced,likewise the boiling temperature is higher if the pressure is higher. Thanks to the factthat the heat transfer in the heat storage vessel and in the heat transfer unit takes placeessentially through the evaporation and the condensation of the water in sealed ducts,the operation of the system is potentially highly efficient since there will be a negligibletemperature gradient between the two heat exchanger devices.

In the example of water, to a part filling the ducts/tubes in lower section and the higherbeing filled with water vapour, will boil and condensate at the same temperature set bythe balance between the two parts. This process will continue as long as there is a driving force, e. g. a temperature difference between the lower part of the tube and the higher. A possible preferable combination of temperature and pressure when the energy storage vessel is loaded with energy can be 160 C and 6 bar(A).

In one exemplary use of the system of the invention, with the tubes half filled withwater in liquid state that are connected to an associated solar heat collecting device thatis exposed to the sun may cause water within the tube to boil at 160 C, producingvapour which is heated further before leaving the solar heat collecting device and thenpasses through the tubing either directly to the heat transfer unit or to the heat storagevessel, where the water vapour condenses, giving up its latent and sensible heat. If tothe heat medium in the storage vessel, the condensed water will return to the solar-heat-collecting device. If directly to the heat transfer unit, the condensed water will alsoreturn to the solar-heat-collecting device. The hot heat medium in the heat storagevessel in a similar manner may, when the heat source is off, cause water to boil at 160C, producing vapour which passes to the cooking device, where it quickly can causewater to boil by condensation and the condensed water therefrom will return to the heatstorage vessel in a similar manner may, when the heat source is off, cause water to boilat 160 C.

The system preferably relies upon gravity to maintain the circulation of water in thesealed ducts, by arranging that the heat/vapour producing parts at a lower level than the heat emitting condensation parts.

BRIEF DESCRIPTION OF THE FIGURESThe invention will now be further described, by way of example, with reference to the accompanying schematic figures, in which: Figure l is a schematic view of an embodiment of the invention, in a one stage ofoperation,Figure 2 is a schematic view of the same embodiment of the invention as Fig 1, in a first different stage of operation.

Figure 3 is a schematic view of the same embodiment of the invention as Fig 1, in asecond different stage of operation.

Figure 4 is a schematic view of the same embodiment of the invention as Fig 1, in athird different stage of operation.

Figure 5 is a cross-sectional schematic view of an alternate embodiment of acooking vessel within the heat transfer unit, and In Fig 6 and 7 it is shown that in altemate embodiments of the invention the basic principles thereof may also be used in connection with two separate closed systems.

DETAILED DESCRIPTION The principle of the invention is to primarily use the latent heat in the phase changesbetween liquid and vapour of a transfer medium in order to transport heat to a coldermedium, wherein a sealed tubing 4 is used having a partial filling of a liquid, wherein water is the preferred medium.

The transfer medium and pressure within the sealed tubing 4 including it is chosen tohave appropriate vaporisation/condensation levels. When using water, it is preferred toarrange a slight over pressure, within the sealed tubing 4, e. g. a pressure of about 1,4 to- 1,6 bar, to obtain a vaporisation temperature in the range of 150 - 200 °. The systempreferably relies upon gravity to maintain the circulation of liquid in the sealed tubing,by arranging the heat absorbing vaporization parts of a heat transfer tubing 4 to passthrough heat importing members 2, 5 at a lower level than the level of the heatdelivering condensation parts of the heat transfer tubing 4, hereinafter referred to as a heat transfer unit 7.

As shown in figures 1-4, the invention comprises a heat storage container 2 arrangedbelow the heat transfer device unit 7. The heat storage container 2 serves as a heatstorage and a heat exchanger device that may provide heat to the heat transfer unit 7,which in tum may transfers heat to a cooking vessel 70 containing a liquid W to beheated, e. g. water, positioned in the heat transfer unit 7. The space V of the heat storagecontainer 2 containing a volume V" of a heat medium HM1 that should not boil at theoperating temperatures, preferably filled with oil, e. g. 500 - 2000 litres.

The invention also includes a sealed tubing 4 that comprises a supply tube 40 that maytransfer heat from the heat storage container 2 to the heat transfer unit 7. The supplytube 40 leades to a condensation space 73A within the heat transfer unit 7. In a returntube 41 fluid from the heat transfer unit 7 may be returned to the heat storage container2. The tubes 40, 41 may be made of solid or flexible material, but must regardless becompletely sealed. In the preferred embodiment metal is used in the sealed tubing 4, forgood heat conduction, e.g. cupper tubes having a diameter of 15- 30 mm.

The condensation space 73A is preferably contained in a storage vessel 73 that is filledwith a heat transfer fluid HM2, e. g. frying oil, in an amount V" substantially smallerthan V, e. g. about 1 - 5% of the volume V" of oil in the heat storage container 2. The cooking vessel 70 may be withdrawable from an opening 701 at the top that matches the outer diameter of the Cooking vessel. Preferably there is arranged some kind of Collarand sealing means 70C at the outer surface of the Cooking vessel 70 that both supportsthe Cooking vessel 70 in the heat transfer unit 7 and seals, e. g. a labyrinth seal, whereinthe seal enables vapor/steam to escape from the inner but hinders water from enteringinto the opening 710. The collar and sealing means 70C, is positioned at level such thata desired portion 70A of a lower part of the Cooking vessel 70 is Contained within the oilin the Condensation space 72A, i.e. in direct heat conducting Contact with the Cookingvessel 70.

The heat transfer unit 7 has a housing 71 that has an isolating layer 71A to minimizeheat leakage out from the inner of the heat transfer unit 7. The storage vessel 73 ispositioned inside the housing 71. Within the inner of the heat transfer device 7, thesealed tubing 40,41 includes a central condensing tubing part 77C, e. g. in the form of aback and forth running tubing part 77C. A substantial portion of said central condensingtubing part 77C is positioned within the Condensation space 73A. The Centralcondensing tubing part 77C preferably provides a relatively long path, e.g. 15 - 30 m.

Partly to provide a large surface exposure, partly to contain a desired volume VH.

Preferably, a maj or portion of the Central condensing tubing part 77C that is arrangedwithin the Condensation space 73A is in the form of a spirally wound tubing part 77A,that is arranged outside of /enclosing a desired portion 70A of the lower part of theCooking vessel 70, in a preferred version of the invention a major portion of the spirallywound tubing part 77A is positioned under the Cooking vessel 70. The Condensationspace 73A need not be sealed. An inlet tube 77A leads from above into the heat transferunit 7 and there Connects to the Central condensing tubing part 77C and an outlet tube77B leads away from and downwards from the heat transfer unit 7. Hereinafter these tube parts 77A-C will be referred to as the condensing tubing 77.

A Control member 410, preferably pivotable, e. g. in the form of a U-shaped tube part410 is connected in between the heat transfer unit 7 and the return tube 41, which U-shaped tube part 410 Comprises a first leg 411, a second leg 412 and a Connector part413. The pivoting axis 415 is positioned at a second system level L2 that may Coincidewith a lowest point of the outlet tube 77B from the heat transfer unit 7. When the U-shaped tube part 410 is positioned vertically (see Fig. 1) the Connector part 413 will beat a position Corresponding to a first system level L1 that determines the maximumvolume VM of liquid that may be Contained in the condensing tubing 77. In the shown example the first system level L1 is above a highest possible water level Wl, e. g. above the highest point of an inlet tube 77A to the heat transfer unit 7, connecting to thesupply tube 40. The highest point of the inlet tube 77A connects to an uppermost part ofthe supply tube 40 and from that point gravity will arrange for flow into the condensingtubing 77. Accordingly, this position 416 of the connector part 413 Will cause a hinderincreasing the level of pressure needed in the supply tube 40 for fluid to circulate in thetubes 40, 41 and due to the fact that the pressure is constant within the sealed tubing 4 no circulation will then occur.

In the figures it is shown an exemplary embodiment where the highest point of the inlettube 77A is positioned at a distance away from the housing 71. However, the highestpoint may also be positioned near housing 71 or at the outer wall of the housing 71 or even inside the housing 71.

The heat storage container 2 is positioned below a third system level L3. This thirdsystem level L3 is positioned below the condensing tubes 77 of the heat transfer device7, i.e. between the heat storage container 2 and the active parts of heat transfer device 7.Preferably the heat storage container 2 is substantially filled with the heat storagemedium HMl, preferably at least above 90%. Within the inner of the heat storagecontainer 2 there is an exchange tubing 42, which may include back and forth runningtubing parts, or a plurality of parallel arranged tubes (not shown), e.g. of a smallerdiameter than that of the condensing tubing 77. In total the tubing must contain adesired volume VS that is substantially equal to the volume VH of the condensingtubing 77. For both tubing 42, 77 the surface exposure may be enlarged by arrangingfins/flanges (not shown).

The basic heat importing member of the system is a solar collector 5, having a concavereflecting collector surface 500 that reflects the collected sun beams into an axis where a tfollectcßr tube 430 of a solar supply tube member 43 is positioned.

As mentioned above the system preferably relies upon gravity to maintain thecirculation of liquid in the sealed tubing 4, wherein different parts of the system aremounted at positions related different horizontal levels Ll, L2, L3 and L4 of the system.The collector tube 430 is therefore preferably positioned below a fourth system levelL4, wherein the fourth system level extends below the heat storage container 2. Thesolar supply tube member 43 connects to the supply tube 40 at a position 43A that isabove the heat storage container 2.

The design of the concave reflecting collector surface 500 is preferably such that atemperature of above 400° C is obtained in the collector tube 430 of the solar supplytube member 43. Accordingly, the solar energy impinging upon the solar collector 5heats the water within the ttolltzcttvr tube 430 and causes the latter to boil at atemperature which will be determined by the pressure and kind of liquid within thesealed tubing 4, wherein water is preferred, and a pressure is chosen to typically obtainvaporisation at between 150 C and 180 C.

The common heat transfer process as shown in figures 1-4 operates according to thefollowing principle.

To start with it is assumed that the system is totally empty of stored energy, which hasbeen achieved by first positioning the pivotable control member 410 in its low position415, (see Fig. 2) whereby stored heat is taken out and thereafter (due to no sun duringnight) all parts assume the same temperature of the surroundings. This implies that thetemperature within the heat transfer unit 7, the heat storage container 2 and the sealedtubing 4 is more or less the same and all liquid W is collected in a lower part of thesealed tubing 4 (see Fig. 2).

During start of the process the pivotable control member 410 is preferably set in itsblocking position (see Fig. 3), i.e. having the connecting member 413 at a position 416at or above the first system level L1, to start storing heat in the heat storage container 2.Now, when sun impinges upon the solar collector 5 and vapor starts to produce in thecollector tube 430, vario:- will iriovt: up into the solar supply tube 43, due to theexistence of liquid W within the lower part 41B of the return tube 41, below thecollector tiibe 41%). Vapor will reach the connection point 43A to the supply tube 40 andthen, at least partly, rnove into the cortflensiiig tubing 77, vvhere it will condense andstart filling the condensing tubing 77 (see Fig. 4) and eventually' fill the condensingvolunie. VM 'with liquid Wl (see Fig. 1). At this latter stage no further circulationthrough the heat transfer unit 7 will be possible.

However, circulation may then occur between the solar collector 5 and the heat storagecontainer 2. Vapor produced in the collecttor tube 430 Will ttontinutf to ngitive up into the.solar supply tube 43, due to the liquid W2 within the lower part 41B of the retum tube41 below the tfollectoi' tube 430. The vapor will come to the connection point 43A to thesupply tube 40 and thereafter be moved down into the exchange tubing 42 within theheat storage container 2. The heat exchange tubing 42 will be, at least partly, in gasstate, due to the fact that a first amount of liquid W1 is trapped within the condensing tubing 77 (see Fig 1), which in this state corresponds to a maximum volume possible contained volume VM. A second amount of liquid W2 is then contained in the lowerpart 41B of the return tubing 41.

Within the heat storage container 2 the vapor will condense and thereby supply heat tothe storage media HM1 within the storage container 2. Thereafter the condensed liquidwill flow out of the storage container 2 at branch 41A connecting the exchange tubing42 with the return tubing 41 at a position above the lower part 41B of the return tubing41. Via the lower supply part 41B the solar collecting tube part 430 of the solarcollector 5 will again be replenished. This process will continue until there is reached alevel of saturation, e.g. when the temperature Tmax of the storage medium HM withinthe heat storage container 2 has reached a high enough temperature wherein the leakageof heat out from the heat storage container 2 is equal to the heat input from the solarcollector 5. According to the preferred design concept the saturation temperature will bebetween 200 - 280°C. At this stage the system is loaded with a large amount of storedheat energy within the heat storage container 2. The stored heat energy may be freelyused at desired times, simply by pivoting the pivotable control member 410 into thesecond system level L2, i.e. having the connecting member 413 at its lower position 415whereby heat will start to be transferred from the heat storage container 2 to the heattransfer unit 7.

The process will then be that liquid W1 from the condensing tubing flows down throughthe return pipe 41 and fills the exchange tubing 42. In turn vapor will be producedwithin the exchange tubing 42 in the heat storage container 2 and move into the heattransfer unit 7 where it condenses and transfers heat to the cooking vessel 70. As isevident the process may continue until a saturation level is achieved, e.g. when thetemperature of the oil HM in the storage container 2 is at a level where it coincides withthe vaporization temperature of the water in the sealed tubing 4. However, thanks to thecontrol member 410 the process may be controlled, such that heat supply to the heattransfer unit 7 may be immediately stopped, by again moving the connecting member413 to its upper position 416. Hence also during build up of heat in the heat storagecontainer 2 cooking may be provided by means of the heat transfer unit 7 in a flexibleand simple manner.

As can be noted in figure Fig. 1 the first phase of the above described heating transferprocess will result in a build-up of an upper water buffer Wl within the part of the heattransfer device 7, at the same time as the amount of water in the heat storage container 2is diminished. When the upper water buffer W1 is totally filled and the connectingmember 413 at its lower position 415 there will be continuous refill of the water into theheat storage container 2 thanks to the circulation wherein a continuous addition of condensed water will flow back through the return pipe 41 into the exchange tubing 42of the heat storage container 2.

As mentioned above if the solar collector 5 is active it may be realised that the vaporproduced within the tubing 43 of the solar collector 5 will nonnally be hotter (e. g. 460°C) than the temperature (e. g. 270° C) of the heat storage media HM in the heat storagecontainer 2. As a consequence, the refill of heat energy to the heat transfer unit 7 willnormally be provided directly from the active solar collector 5, once the connectingmember 413 is set at its lower position 415. Consequently, the heat storage container 2will be more or less inactive / bypassed, in this situation. Hence the condensed watersupplied through the return tubing 41 from the heat transfer unit 7 will then directlyreturn to the solar collector 5 and circulation will occur more or less without anyinfluence from the heat storage container 2.

As is evident this system aspect may advantageously be used if there is spontaneousneed of cooking during a heat up-phase of the heat storage container 2. Hence, if there isa spontaneous need to intenupt the heat storage build-up it is feasible to quickly arrangefor heat delivery at the heat transfer unit 7, by simply pivoting the pivotal controlmember 410 from its locking, vertical position to its horizontal position. Once thespontaneous need of cooking has been fulfilled, the pivotal control member 410 mayagain be put into its locking position and the process of building up heat in the heatstorage container 2 may continue.

Regarding Figs. 5, 6 and 7 it is referred to WO2016185031, which is herewithintroduced by way of reference, In Fig 5 there is shown an alternate cooking vessel 70that also may be used in connection with the basic principles of the invention, whereinthe condensing tubing 77 includes a cylindrical condensation space 77 of a cookingvessel 70 that is fixed within the heat transfer unit 7. In Fig 6 and 7 it is shown that inalternate embodiments of the invention the basic principles thereof may also be used inconnection with two separate closed systems, one 5 for the input of heat and one for theheat transfer to the cooking vessel 70. Briefly describing the principle as shown in Fig6, there is shown a space G connected to the supply tube 40 above a line P that is filledwith vapour G. The supply tube 40 transfers moving vapour to the sealed condensationspace 77 of the heat transfer unit 7, that has a heating vessel 70 providing a space filledwith a cold liquid (e. g. water), being colder than the vapour. The vapour in thecondensation space 77 will then condense against the inner wall and thereby transferheat to the cold liquid. The condensation results in a high output of heat transfer and thecold liquid is heated in a rapid manner. The condensate flows down and back to the heatstorage 2 through the return pipe 41, and then recirculated, i.e. eventually again heated up to vapour.

Furthermore, it is evident that also the basic principles according to the invention may be of such dimensions that it is easily moved.

In a test that was performed with a solar heating system 5 according to the invention thefollowing applied; The invention is not limited to what is exemplified above but may be varied within thescope of the claims. For instance, it is evident for the skilled person that another liquidthan oil may be used with the heat storage vessel 2, e. g. water, but from a safety point ofview oil is preferred, and especially a non-toxic oil, such as vegetable oil. Further it isevident for the skilled person that another liquid than water may be used within thesealed tubing 4, e. g. alcohol, but from an availability view point water is preferred.Moreover, it is evident for the skilled person that the principles of the invention may beused for a variety of heat transfer units/cooking vessels 70, of a different design thanthat shown in the figures, e.g. instead an oven like space for heating of different items,e. g. non liquid food, or a plate like interface for indirect heating stuff in a pan, or similarcooking vessel. Further, it is evident for the skilled person within the field that the firstsystem level Ll must not be positioned above the upper point of the inflow tube 70A.An essential aspect in regard to this feature is that the amount of volume contained inthe condensing tubing 77 between the upper and lower positions 416, 415 containssufficient amounts of liquid to provide for the essential effect according to theinvention, i.e. arrange for possibility to relatively quickly change from a mode where amaj or amount of the supplied heat energy (via ref. 5) is stored in the storage container 2to a mode where a major amount of the supplied heat energy is directly supplied to theheat transfer unit 7 and there quickly may heat the cooking vessel 70. In a similarmanner also the lowest point 415 must not be positioned below all parts of the condensing unit 77.

Claims (1)

1. CLAIMS A heating systern for heating a suhstance, preferalnly' a liquid, eomprising a heatstorage iaesset (2) with a heat storage inediurn (litt/l 1) to be heated by means iaf aheat source(5) anda stfalerl tubing (_ 4) arranged to transfer heat to a heat transferunit (7), said sealetl tuhing (4) having a partial filling of a substrate partially inliquid state (KN) and partially' gas state (G) and comprising a return tube (41)arranged to return substrate in liquid state (_ _11.) frorn said heat transfer unit (7) and asupply tube (46) arranged to supply heat in state (G) to said heat transfer unit(7), vvhereiii a part of said sealtäd tuhing includes a eondeiisiiig tubing (77) that isinciutiecl in said heat transfer unit (7) and pcasitiorteti above a third systern level (lsß)aiid the upper liquid level of said heat strirage ineditini (i-iMl) is positionetl belowsaid third systern level (13), charaeterizeci in that an outlet tube, ( '77 B) of saidconderisitig tuhing (77) is connected to a control member (410) at a second systemlevel (L2), Which control member (410) includes a movable connector part (413),Wherein said movable connector part (413) is controllably, movably arrangedbetween a first position (415) and a second position (416) a vertical distance (L)apart, Wherein said first position (415) coincides With said third systern level (Lš) oris at a second system level (L2) above said third system level (1..-3) and said secondposition (416) is in level With a first system level (Ll), Wherein a substantial portionof said etindtfnsing tubing (_) eorresponclitng to a etantttintazl tfondtænsing volurntt: (Vit/l) is gitasitiririeti below said first systern ievel (1,1)Heat. transfer systern according to elairn l, v/hertæin the highest point of an inlet tube (77A) rn' said condenslng tttbing (77) is positioned below' said second position (416)l-leat transfer' system according to claini 1 or 2, characterizetl i n that said heat sourceis in the form of a solar Collector (S) and that a ctillectrir tttbe (430) is arrangecl toabsorb solar energy saved from tfoneeifttrattäti solar energy Within said solar tftilleettii'(5) arranged to provide a ternperature of at least .ÉÛÛPC tvithin said Collector tube (430), preferably least 350%, more preferred at least 400°Clfieat transfer systern according to claim 3, characteri zed in that there is a solarsupply tube member (43) connecting the coileetor tube (43%) With said supply' tube(40) at a titisititiii ( 431~X) dcmfiistreairt oi an exchange tubing (42) of the heat storage 's/'essel (2)Heat transfer systern according to claim 3, characterized in that said heat storagetfessel (2) is rnounted alwotfe a ftiurth s jysterii level (1,4) and that said Collector tube ( 431)) is niounted below said fonrth system level (1,4)Heat transfer sytiteiii aceordirlg to claint arty of clainis l-S, cliaracterizetl in ttiat saidtfondensiiig woluine (VB/l) tfoiitainetl *within said substantial portion of saideonrlensiiig tuhing (7 "/') is stihstantialtly equal to the total volurnt: (VS) tfoiitainetlwithin the exchange tubing (42), trvhereiri the volume ditferenee is less than lllïíø, preferably less than 5970, more preferred less than 2%Heat transfer system according to any of claini 1-6, tfiharacterized in that said heattransfer unit (7) includes a ttondentsin g space(7 3A) and that a stibstantietl part of a central condensing tubirig (77C) is arranged vvithiri said ccindensittg space (7šft)Heat transfer systern aceordiïng to elainit 7 , tfharacttfrizefl in that said txinflensingspace (73A) is limited by a tfessel (73) and that said vessei (73) ccintaiiis a heat transfer nieditiin (liltlll)Heat transfer systemaccording to claiin 8, characterized in that the voltnne(X/Hh/ll) :if the heattrntfdittintt (Hit/ll) in the heat storage, tlessel (2) i suhstaiitiallyflarger than the volurne (Vill/EZ) of heat transfer rnetliurn (lik/iQ) in said condensin gvessel (73), tfalierein preferably' 'wflflMl > lt) Vlfilwill., Heat transfer system aecrirdirig to any tireceding claints, characterized in that saidcontrol rneinhei' (41) is in the form of tubes in a li--shaifie liaving ttvo ltfgs (4l l, 412),'ovherein said connector' ntetnlver ti4l 3) connects said the tvvf) legs (4l l, 412) at theirends, and ttIhereiri said ll-shaped member (4l l, 412, 413) is arranged to he inoved'iaettvtaen said two positions (415, 416) either hy rneans of a pifvtat arrangtænient or bythe use of lvendahle legs (41l, 4l2)A niethtid for heating a stibstanetä, prtfftäralnly' a liquid, with a heating systeatnaccording to any of clailns l~l(), cornprising the steps of extracting heat iloin a heatsotirtfe (5) and hy means of a sealed ttihing (4) transferriiig said heat to a heatstorage ntediutri tilfllvll) in a heat storage tfessel (2) anti/or to a heat transfer unit (7),charaeterized by providing a control member (410) including a movable connectorpart (413) and controllably moving said movable connector part (413) between a first position (415) and a second position (416) a vertical distance (L) apart, to control if a major part of said extraft Etta-rat is to be transferrtfd to the heat storage xfassei (2) or to the heat transfer unit (7).