Description

The present invention concerns a kitchen extractor hood , wh ich allows to recover thermal energy from the flow of a gaseous mixtu re sucked by the hood itself, a gaseous mixtu re which is formed as a consequence of the operation of a cook- top underneath .

It is known that the trad itional kitchen hoods are provided with a suction device and can operate in two d ifferent modes as follow:

a suction operation , wherein the flow of a gaseous mixtu re sucked from the environment in wh ich the hood is located (internal environment), is completely exhausted to the external world (external environ ment) via an exhaust duct;

filtering operation , wherein the flow of a gaseous mixtu re sucked from the internal environ ment is conveyed , via a filtering duct, toward a nu mber of filters (for instance, activated carbon filters) at the output from which it is subsequently re-injected into the internal environment.

It is also known that energy saving became more and more important in the last years, consequently it becomes important to recover the energy that previously was lost, in th is specific case part of the energy lost during the preparation of meals and/or the change of air. It is worth saying that the hoods featuring a filtering operation are already hoods of th is type, considering that they don 't d isperse heat in the external environ ment, even though they don't allow a change of air. Therefore, the problem of recovering thermal energy only exists for the hoods featuring a suction operation , wh ich will be referred to as extractor hoods here below.

I n the Italian patent application MI2008A661 a kitchen extractor hood is described wh ich allows to recover the thermal energy contained in the gaseous mixtu re sucked by it. The hood comprises a first heat exchanger wh ich allows to subtract a first amount of heat from the sucked gaseous mixture. The first heat exchanger is connected to compression means, wh ich are in turn connected to a second heat exchanger wh ich allows to subtract a second amount of heat from the gaseous mixtu re, proportional to that recovered in the first heat exchanger. The second heat exchanger is connected to the first heat exchanger via a lamination device. In the two heat exchangers, a vector flu id flows in the lamination device and in the compression means, wh ich realizes a thermodynamic cycle whereby the satu rated vapors of the vector flu id are compressed .

The first heat exchanger can also be connected to a partialization circuit wh ich allows to use a portion only of the first heat exchanger. The partialization circuit possibly comprises valve partialization means to adjust the amount of the vector flu id that flows in the first heat exchanger.

Even though the extractor hood whose basic featu res have been described above proved to be very efficient, it presents the non-negligible d rawbacks of being rather complex, of being provided with an external lamination/condensation unit, besides being expensive and having sign ificant overall d imensions.

Extractor hoods provided with a thermal energy recovery device consisting of a crossflow heat exchanger are already present on the market. Hoods of th is type are for instance the model LE 1 55/250 by Johnson and Starley Ltd and the model Sentinel Kinetic CS L by Vent-Axia Ltd . However, these hoods too featu re sign ificant overall d imensions, especially in height and width , wh ich is possibly a non negligible d rawback condition ing the choice concerning the furn ish ing of a kitchen , especially when the space available is small, so as to lead to renouncing the installation of a heat recovery extractor hood .

A pu rpose of the present invention is to provide a kitchen extractor hood that allows to recover part of the thermal energy contained in the sucked gaseous mixtu re, but featu res overall d imensions definitely smaller than those of the extractor hoods provided with a recovery device known so far, besides not having any external un it (contrary to the hood accord ing to MI2008A661 ).

Before describing how is said purpose ach ieved by the present invention and is its respective techn ical problem solved , let's remember that a type of heat ex- changer known under the name of heat pipe or Perking pipe and better known today as heat pipe (see its respective description in Wikiped ia) is already known since at least 200 years. It is a matter of a highly efficient thermal exchange device, wh ich is capable of transporting big amounts of thermal energy in the presence of an even very small difference in temperature between the hot and cold interfaces (as small as 1 degree on ly).

Such device usually comprises a pipe hermetically closed at its two ends, made of a metal featuring a good thermal conductivity (for instance copper or alumin iu m). A small quantity of a refrigerating flu id in satu ration conditions, for instance water, ethanol, ammon ia, mercu ry, a hydrofluorocarbon (H FC) or a hyd roch loro- fluorocarbon (HCFC) has been inserted into the pipe. In practice, a small quantity of refrigerating liqu id is present in the pipe, whereas the rest of the pipe is filled with the vapor of the same refrigerant.

If the pipe is held vertical or tilted with respect to the horizontal line and its end featuring the lower elevation is heated (hot end or evaporation section ) so as to make the refrigerating liqu id vaporize, an increase in the internal pressu re of the pipe results. Simu ltaneously the latent vaporization heat absorbed by the liqu id makes the temperatu re of the hot end decrease. The vapor pressu re in correspondence with the hot end is h igher than that in correspondence with the other end (cold end or condensation section), consequently a very fast transfer of vapor takes place toward the cold end . It has been found that the movement of the vapor molecules takes place approximately at the velocity of sound (300 m/s ca .) and in practice depends on the velocity of condensation of the vapor at the cold end . Because of gravity, the liqu id that condensates in correspondence with the cold end (condensation section ) goes back toward the hot end (evaporation section). Therefore, it is a matter of a device very efficient in transferring heat (a kind of superconductor), with the further advantage of not having moving parts, hence it does not requ ire any maintenance due to wear nor does it consu me energy, losses of gas because of d iffusion through the walls of the pipe only possibly occu rring in the long term. The thermal exchange capacity can be estimated to equal 7,000 W/m3K and is rough ly proportional to the square of the diameter. Un like a thermal conductor, the heat transfer capacity is, with in certain limits, almost independent of the length of the pipe, in the sense that a 1 m long pipe features the same heat rate as a 2 m long pipe of the same type. However, the latter puts a greater surface of thermal exchange available, consequently it makes it easier to reach the limit of internal heat transportation capacity.

It is worth noting that varying the tilt of the pipe results in varying the amount of the thermal exchange. Equ ipping a simple device that allows to vary the tilt of the pipe makes it possible to adjust the thermal exchange.

According to a variant, the retu rn of the liqu id toward the evaporating section can also be obtained by capillarity, by using, for instance, a material featuring a capillary structu re coated inside the pipe. I n th is event, the pipe can be arranged horizontally and even be lightly countersloped .

The temperatu re at which a heat pipe exchanger is efficient depends on the refrigerating liqu id used and on its boiling temperatu re, wh ich is in turn depend ing on the pressu re inside the pipe.

It is possible to implement a heat exchanger formed of several parallel heat pipes, arranged in battery to each other, possibly finned to foster thermal exchange, and an intermediate diaph ragm that does not interrupt the pipes and is perpendicular thereto, whose function is that of separating the gaseous flow from wh ich to recover thermal energy from the gaseous flow that thermal energy is to be transferred to. The d iaph ragm is located in correspondence with the center line of the heat exchanger if the two flows feature the same rate. Otherwise, the diaph ragm can be located in a position ranging from 25% to 75% of the length of the pipes, depend ing on their respective air flow rates. The separator d iaph ragm isolates the two air flow rates very effectively, to such an extent that it is possible to thin k having no contamination between the two flows up to pressure d ifferentials between them of up to 12 kPa. If necessary, a dual-wall d iaphragm with a gap venting to the external world cou ld be used .

All of this results in an extremely compact and h igh ly efficient heat exchanger.

Heat pipe exchangers have been used so far for cooling electron ic components (in particu lar for cooling portable PCs) and in the field of the thermal solar plants, but also in big air cond ition ing systems for offices, hospitals, theaters, restau rants, shopping centers, and centralized systems of residential bu ildings, as well as in industrial dehumidification, drying, and coffee roasting systems, foundries, textile and food factories, and spray booths.

Coming back to the (previously mentioned) purpose of the present invention, it is achieved and its technical problem solved thanks to an extractor hood according to attached claim 1. Other features of said hood are set in the remaining claims.

As a matter of fact, the inventor of the present invention realized that using a heat pipe exchanger as a thermal energy recovery device made it possible to obtain an extractor hood featuring overall dimensions definitely smaller than those of the known extractor hoods provided with a recovery device as described before, which represents a very significant advantage, besides achieving a high efficiency in thermal energy recovery.

The invention will be more easily understandable upon reading the following description of an illustrative embodiment thereof. In such description, reference will be made to the attached drawings, in which: figure 1 is a perspective view of an extractor hood with thermal energy recovery, according to the present invention;

figure 2 is an elevation view thereof according to the arrow 2 of figure 1 ; figures 3-5 are three different perspective views of the thermal energy recovery device only being part of the hood according to figures 1 and 2;

figure 6 is a perspective view of half of the same device, obtained by sectioning it according to a median vertical plane; figure 7 is a perspective view of the heat pipe exchanger only being part of said recovery device;

figure 8 is a top view thereof;

figure 9 is an elevation view thereof according to the arrow 9 in figure 7; figures are sketches which very schematically illustrate how could a hood according to the present invention be structured and what its operating modes might be.

The extractor hood 110 visible in figures 1 and 2 comprises a true extractor hood 11, of a conventional type (a so called overturned-T one), and means 10 for recovering thermal energy. In the part 12, which substantially has a shape of a squeezed parallelepiped, of the recovery means 10 a recovery device 14 is enclosed, consisting of a heat exchanger 14, of a heat pipe type, which is shown isolated from the rest in figures 7-9. In the specific case here illustrated the heat exchanger 14 comprises a battery of forty-five heat pipes, referred to by the reference numeral 16, arranged in three superimposed ranks, each composed of fifteen hot pipes 16. The latter are so spaced from each other as to enable a gaseous flow to pass through them. Unlike the case here illustrated, the intermediate pipes 16 might also be arranged staggered with respect to those of the remaining two ranks.

In this specific case the pipes 16 are made of cupper, with an inner diameter of 9.52 mm, a wall thickness of 0.43 mm, and a length of approximately 300 mm and sealed at both of their ends. Conveniently, inside the pipes 16 are ruled to increase the surface of thermal exchange with the refrigerating fluid flowing internally thereto. The two ends of the pipes 16 are fixed to their respective support elements 18 and 20 perpendicular to the pipes 16 and made of a galvanized and bent iron sheet. A diaphragm 22, also made of a galvanized and bent sheet and also perpendicular to the pipes 16, is used to separate (without interrupting the continuity of the pipes 16) the two sections that make up the heat exchanger 14, i.e. the condensation section, referred to with the reference 14C in figure 5, and the evaporation section, identified by the reference 14E. Consequently the diaphragm 22 separates the respective flows. It is also worth noting that the diaphragm 22 is arranged at a distance from the support element 20 that is approximately 1/3 of the length of the pipes 16, this in order to take account of the ratio between the rates of the two gaseous flows concerning the evaporation section 14E and the condensation section 14C respectively, as well as the thermal exchange surface of the heat exchanger 14 and the tilt of the pipes 16.

The pipes 16 contain a refrigerating fluid, in this specific case that indicated in the ANSI/ASHRAE Standard 34-2004 by the abbreviation R134a, its quantity being 10 g per pipe. This fluid is a hydrofluorocarbon (HFC) as commonly used in refrigerators. In order to foster the thermal exchange between the pipes 16 and the two gas flows concerning them, a sequence of equally spaced fins 24 has been provided (for instance fins made of aluminium, with a thickness of 0.1 mm and arranged at a distance between their axis of 2.1 mm) which allow to substantially increase the thermal exchange surface. In this specific case the fins 24 are perpendicular to the pipes 16, obviously without interrupting their continuity.

Preferably, in order to optimize the yield of the heat exchanger 14, the pipes 16 are tilted by 5° to 10° with respect to the horizontal line, however it has been proved that the operation is satisfactory even with the pipes 16 arranged horizontally (zero tilt).

A heat pipe exchanger like that represented and indicated by the reference numeral 14, whose dimensions don't exceed 30 x 30 x 7 cm, proved to be particularly suitable for recovering thermal energy in a kitchen extractor hood like that indicated by the reference numeral 110 in figures 1 and 2, which consequently can have very small dimensions and anyway definitely smaller than those of the known extractor hoods equipped with a thermal energy recovery device, which represents an important advantage.

As figures 3-6 also show, the energy recovery device 10 also comprises a suction aperture 26, through which the gaseous mixture sucked by the true hood 11, installed above a respective cooktop (not shown in the figures), passes through.

It is worth pointing out that even though in the case of the hood 110 the conventional filters used to filter out the dust and the fats that are normally carried by the gaseous mixture sucked by the true hood 11 and which goes through the suction aperture 26 of the heat recovery means 10 are not visible, however such filters are anyway provided in the true hood 11, to prevent the internal parts of the hood 110, and in particular the pipes 16 of the heat exchanger 14, from getting dirty in short time, thus jeopardizing the efficiency of the heat exchanger and more in general of the hood 110, and even causing sanitary problems. Such filters will in particular be provided upstream (with reference to the sucked flow) with respect to the suction aperture 26 of the heat recovery means 10. It is also worth pointing out that the flow of gaseous mixture sucked through the suction apertu re 26 (the flow indicated by the arrow A in figu re 6 and wh ich will be shortly referred to as first flow here below) is created either by natural d raught whenever the section apertu re 26 is in particu lar in communication with a ch imney which d rains outwards, on usually via a first suction device (not visible in the figu res, but of the conventional type) arranged in the specific illustrated case internally to the true hood 1 1 , just downstream with respect to said filters (with reference to the direction of the first flow A), but wh ich might even be provided even more downstream.

Going on in the description of the heat recovery means 1 0 (with reference above all to figu re 6), immed iately downstream with respect to the suction apertu re 26 the first flow A, consisting of a hot gaseous mixtu re, encounters the evaporation section 14E of the heat exchanger 14 , whereby in the pipes 1 6 the refrigerating liqu id contained therein evaporates wh ich resu lts in a thermal energy being transferred to such liqu id , wh ich just evaporates. Therefore the first flow, downstream with respect to the evaporation section 14E, goes on as a flow B featu ring a temperatu re lower than that of the flow A and is outlet into the external environment (exhaust flow).

The condensation section 14C of the heat exchanger 14 is in turn concerned , whenever the hood 1 1 0 is in operation , by a second air flow, represented by arrow C in figu re 4, wh ich is generated by a second suction device included in its respective canalization 36. Th is second suction device is in this specific case formed of th ree fans, arranged on one and the same horizontal plane, which operate in parallel with each other, one of which , identified by the reference numeral 28, is visible in figu re 4. The second flow C is obtained by picking up air from the internal environment via (in the specific case here illustrated) two symmetrical located inlets 30 (one inlet only might be alternatively provided , indeed), or from the external environ ment, if there is provided that both in lets 30 are connected to the latter via a respective duct (not shown in the figu re). Anyway, the second flow C, after passing th rough the condensation section 14C of the heat exchanger 14, which transfers thermal energy thereto because of the condensation of the refrigerating liqu id , becomes a flow D which obviously featu res a temperatu re greater than that of the flow C and is injected into the internal environment via the inlet aperture 32. As a result, a sign ificant part of the thermal energy contained in the flow A is re-injected into the internal environment via the flow D.

Take into account that in correspondence with the compensation section 14C a condensation might form. In the absence of the fins 24, if the pipes 1 6 feature a tilt of even few degrees, such a condensation streams down along the pipes by gravity and can be collected in correspondence with end featuring the lower elevation by a small basin underneath , to be period ically emptied or wh ich communicates with a d rain . If the fins 24 are present, in order to ach ieve the same pu rpose, it might be conven ient to tilt the heat exchanger 14 in such a way that the pipes 1 6 are laid horizontal (wh ich , as already said , resu lts in slightly reducing the efficiency of the heat exchanger 14) but the fins 24 are tilted , in such a way that the condensation streams down along the lower edge of said fins by gravity, in order to be collected in correspondence with the lower elevation end of the fins, still by using a small basin underneath .

I n the specific case of the hood 1 1 0 the thermal energy recovery means comprise, besides the heat exchanger 14 , a second recovery device (second thermal energy recovery stage) of a crossflow type. As a matter of fact, the air sucked through the in lets 30 forms the flow C, passes th rough a properly shaped duct 36 wh ich laterally encloses the exhaust duct 34. Therefore, the flow C externally laps the exhaust duct 34. If the latter is made of a good heat conductor material, part of the thermal energy still contained in the flow B that flows therein is transferred to the flow C via the side wall of the duct 34. Let's ind icate said second thermal recovery device as a whole with the reference nu meral 1 5.

I n the hood 1 1 0 there might also be provided that the heat exchanger 14 (wh ich is an independent element, with no connections to any other elements) is removable to make it possible to inspect, clean , and , if necessary, replace it. Considering the d imensions of the heat exchanger 14, it might even be specified that it be period ically washed in a normal d ish-washer.

The hood 1 1 0 can be equ ipped with a microprocessor-type control unit wh ich detects, by means of appropriate thermocouples, the temperature of the air outlet to the external world (flow B) and of the incoming air upstream and downstream the condensation section 14C, and regu lates the speed of the first and second suction devices accordingly, in order to maximize the efficiency of thermal energy recovery.

Let's now consider, with reference to the diagrams in figures 8-11, the different possible locations of the individual elements that make up the extractor hood according to the present invention, as well as its respective operating modes.

A first type of extractor hood according to the present invention, identified by the reference numeral 110.1, is very schematically represented in figure 10, which basically represents a vertical cross sectional view thereof made with a plane perpendicular to the wall, indicated by the reference numeral 50, which separates the internal environment 51 in which the hood 110.1 is located from the external environment indicated by the reference numeral 52.

The hood 110.1 is similar to the hood 110 in that it is provided with an exhaust duct toward the external world similar to the exhaust duct 34 of the hood 10, therefore we will give the same reference numeral thereto. The suction of the gaseous mixture above the cooktop (not shown here neither for the sake of simplicity, but obviously located below the hood 110.1) takes place because of the activation of that which formerly called first suction device (of a conventional type) and referred to here by the reference numeral 38, which generate a first flow (flow A) which lets in the hood 110.1 via an usual aperture provided with filters, generically indicated by the same reference numeral as the suction aperture 26 of the hood 110. The first suction device 38 is in this specific case located downstream (with reference to the direction of the flow A) with respect to the heat pipe exchanger visible in figure 10, equivalent to the heat exchanger 14 of the hood 10 and consequently identified by the same reference numeral.

The sucked flow A concerns the evaporation section 14E of the heat exchanger 14, therefore the flow B expelled into the external environment 52 features a temperature lower than that of the flow A. Obviously the function of the first suction device 38 can be replaced by putting the exhaust channel 34 in direct communication to a chimney provided with an appropriate natural draught.

Conversely, the condensation section 14C of the heat exchanger 14 is concerned by a second flow (flow C) which is picked-up directly from the internal environment 51 via an aperture equivalent to the two inlets 30 of the hood 10, and consequently this aperture is identified by the same reference numeral.

The flow C is generated because of the operation of that which we called second suction device, which performs a function equivalent to that of the three recovery fans 28 of the hood 110, whereby we will identify it with the same reference numeral. The flow C collide with the condensation section 14C of the heat exchanger 14 thus acquiring thermal energy and originating a flow D (which is still part of said second flow) which is injected into the internal environment and features a temperature higher than that of the flow C.

It is worth noting that the heat pipe exchanger 14 is represented in figure 10 (as well as in the remaining figures) very much tilted with respect to the horizontal line. However, take into account that such a tilt is purely indicative. As a matter of fact, as already pointed out with reference to the hood 10, such tilt might even be of few degrees or even nil without jeopardizing the operation of the heat pipe exchanger.

The hood 110.1 in figure 10 is preset to a winter operation (temperature of the air sucked from the external environment lower with heat recovery from the inside). However, note that in the specific case here illustrated, downstream (with reference to the second flow C, D) of the condensation section 14C there is provided a shutter 40 which is represented in its open position in figure 10. Closing such shutter and activating the first suction device 38 only (second suction device 28 deactivated) sets the hood 110.1 to the summer operating situation, wherein it would in any case be meaningless to recover heat to be injected into the internal environment.

A variant, indicated by the reference numeral 110.2, of the hood 110.1 is represented in the diagram of figure 11 in which elements equal or similar to those of the hood 110.1 have been identified by the same reference numerals. The only differences consist in that in the hood 110.2 the suction device 38 is mounted upstream with respect to the evaporation section 14E, and likewise also upstream with respect to the condensation section 14C is arranged the second suction device 28. We think it is not necessary to add anything for that which concerns the hood 110.2. A different solution 1 1 0.3 of an extractor hood accord ing to the present invention is depicted by the d iagram in figu re 12.

That which makes the hood 1 1 0.3 d ifferent from hood 1 1 0.1 is in that the former picks-up air from the external environment 52 th rough an aperture 42 present in the wall 50, whereby the incoming flow C is in th is case made up of external air. The remain ing components of the hood 1 1 0.3 are similar or equal to those of the hood 1 1 0.1 and consequently the same reference numerals have been used to identify them .

The hood 1 1 0.3 in figu re 12 is also preset to winter operation , but with heat recovery from the external world . I n this case too, downstream (with reference to the second flow C, D) of the condensation section 14C there is provided a shutter 40, closing which and on ly activating the first suction device 38 (second suction device 28 switched-off) sets the hood 1 0.1 to a summer operating condition (no heat recovered from the external world).

It is evident that it is possible to implement a hood accord ing to the present invention wherein , by means of a two-way valve, located in the incoming air duct 34, upstream with respect to the condensation section 14E, it is possible to suck air (flow C) selectively from the external environment 52 or from the internal one 51 .

A variant 1 1 0.4 of the hood 1 1 0.3 is depicted in the diagram in figure 1 3, in which elements equal or similar to those of the hood 1 1 0.3 have been identified by the same reference numerals. The only d ifferences consist in that in the hood 1 1 0.4 the first suction device 38 is mounted upstream with respect to the evaporation section 14E, and likewise also upstream with respect to the condensation section 14C is mounted the second suction device 28.

Obviously, in all cases described above, if the second suction device 28 is not activated , then the hood operates as a traditional extractor hood without thermal energy recovery. It is also worth noting that in all hoods depicted in figures 10-13, unlike the hood 110, there is no provided a second thermal energy recovery stage. However, it is evident that, if one so requires, there are no particular difficulties in transforming such hoods into hoods provided with a second thermal energy recovery stage.