NO801257L - HEATER FOR AIR OR WATER. - Google Patents

Description

In most forced air or water heaters currently in use, a fuel is burned, usually either gas or No. 2 fuel oil, and the products of combustion are passed through one side of a heat exchanger before being released into the atmosphere. When air is used under forced circulation, the air from the building or other room to be heated is led from the cold air return line through the other side of the heat exchanger and back through the building. In the case where hot water is used for heating, the cold water that flows back from the radiators in the building will similarly be led through the other side of the heat exchanger and back to the building's radiators. Due to the high temperature of the exhaust gas emitted

to the atmosphere, a significant amount of heat is lost. Typically, conventional gas-fired heaters or boilers have an efficiency of 70 - 75% during periods of stable conditions, while conventional oil-fired heaters or boilers have an efficiency of 65 - 70%. As a result of additional heat loss during both off and on cycles, during cold starts and from the ignition flame, the total fanning rate is in typical cases only 40 - 60%, and thus 40 - 60% of the fuel's potential heating value is lost. The heating device according to the invention will provide total efficiencies which both during stable operation and overall are generally above 90%, usually higher than 95% and can reach up to 98%, which enables a significant reduction in the amount of fuel consumed during the heating of the building or the location to be heated.

Briefly, the invention relates to an improved, highly efficient heating device for air or water under forced circulation. Although any fuel can be used in the heating device, it is preferred to use gas or fuel oil No. 2, which is usually used for such purposes. The combustion products from the burning fuel and a certain excess of air are blown or passed under the influence of drafts through a contact device where water circulates, to cool the combustion gases and transfer heat to water. The construction and operation of the contact device is such that almost all the heat recovered from the combustion products is transferred to the water, that the exhaust gases from the contact device are released into the atmosphere, and that the heated water is then passed through one side of a heat exchanger to heat a fluid on the other side of the heat exchanger. The fluid to be heated can be air for heating a building or the like. A typical example is air in an air heating system with forced circulation. The fluid to be heated can also be a liquid, such as water, for a hot-water-based heating system for a house or other building, or for use in a laundry or for other household use. The fluid to be heated can also be the fluid used in a solar heating system for storing solar energy, such as e.g. glycol or a mixture of glycol and water,

e.g. ethyleriglycol and water in the mixing ratio 1:1.

More specifically, the invention provides a heating device or a boiler system comprising a burner for the formation of hot combustion products, a contact device adapted to bring said combustion products into countercurrent contact with water, which device is capable of providing at least 1.2 theoretical steps,

a fan adapted for conveying the combustion products from the burner through the contact device and for conveying the exhaust gases of these combustion products to an exhaust direction, and a heat exchanger adapted for absorbing the water heated by the combustion products and for transferring the heat content of the water to a fluid, the product of the heat transfer surface in the heat exchanger and the heat transfer coefficient of the fluid for which the heater is adapted being in the range from 1.5 to 38 per- 1000kcal/h fuel burned.

According to the invention, there is also provided a method for heating a fluid, in which method one (a) burns a fuel to form combustion products, (b) with an output corresponding to at least 1.2 theoretical steps brings said combustion products into countercurrent contact with water to raise the temperature of the water to between 48.9° and 85°C, and (c) passing the water through a heat exchanger to heat said fluid.

Fig. 1 is an elevation, which is not to the correct scale,

of an embodiment of the heating device according to the invention. Fig. 2 is an elevation, partly in section and not to the correct scale, of an embodiment of the contact device in the heating apparatus according to fig. 1.

Fig. 3 is an elevation, which is not to the correct scale,

of a part of another heating device according to the invention.

Fig. 4 schematically shows a typical flow pattern inside the heat exchanger belonging to the heating device according to fig. 1. Fig. 5 is a perspective sketch of a part of a heat exchanger which is made of a thermoplastic, and which is suitable for use in the heating device according to the invention. Fig. 6 shows a section through one of the elements in the heat exchanger shown in fig. 5. Fig. 7 is a perspective sketch which, enlarged and partially in section, shows part of an element of the one in fig. 5 showed heat exchanger.

The example shown in fig. 1 is an embodiment of the invention which is suitable for use as a heating device or a central heating unit for an apartment, a house or other building. In a contact device 10, a fuel is burned to form hot combustion products which are brought into countercurrent contact with water to produce hot water and form cooled exhaust gases. In a conventional burner unit (not shown)

at the lower end of the contact device 10, a fuel is burned which is introduced through pipeline 11. The fuel can e.g. be natural gas, water gas, propane, liquefied natural gas (LNG), fuel oil no. 2, kerosene, diesel oil, etc. The burner unit used is selected with regard to the fuel to be used. Cold water which is introduced through pipeline 12 into the contact device 10 is heated in it by the hot combustion products in a manner that will be described in more detail with reference to fig. 2, and hot water is taken out through pipe line 21. The cooled exhaust gases are blown out through exhaust gas channels 24 and 26 by means of fan 25, and are led to the atmosphere via devices not shown, such as a chimney, pipe or other channel. The transport energy provided by the fan 25 replaces the heat draft in the chimney used in connection with a conventional oven. The fan 25 also serves to draw the hot combustion products up through the contact

the facility 10.

The housing 13 has several sections, one of which contains a heat exchanger 14. A cold air chamber 15 receives cold air from the house or other building through return duct 16, and main fan 17 leads the cold air through chamber 18 to the heat exchanger 14, from which heated air flows into hot -air chamber 19 and from there through hot air supply duct 20 to the house or other location to be heated.

Hot water from the contact device 10 is led via pipeline 21 to the heat exchanger 14, and after removing its heat content in the heat exchanger 14, the water flows as cold

water through pipeline 20 to container 23. A pump 28 re-circulates the water through pipeline 12 to the contact device 10. The pump 28 can be of any suitable type

itself for pumping water, e.g. a submersible centrifugal pump. Usually the hot water will flow through the pipeline 21 by its own weight, but in other arrangements a pump can be used.

One of the combustion products from a fuel is

water, and although smaller amounts of water vapor will be carried along in the exhaust gas, excess water will normally accumulate in the circulating water system, because the cold water which. introduced into the contact device 10 through the pipeline 12, will condense it. Accordingly, in the upper part of the container 23, a pipeline 27 is arranged to enable the drainage of collected excess water to any suitable drainage system. The container 23, the pump 28 and the pipeline 27 are preferably placed at a level which ensures that the side of the heat exchanger 14 which receives hot water from the contact device 10 remains

filled with water at all times, so that no gas or air bubbles form which could accumulate in the heat exchanger and reduce its efficiency. However, the container can be placed higher or lower, if desired.

The fan or blower 25 can e.g. be a little

fan capable of providing a pressure differential of as little as 50.8 mm water column.

In a similar, but slightly modified system, the contact device can be placed under the container 23, towards the lower end of the housing 13. In this case, the pump 28 will be placed in the pipeline 12 to pump hot water that is taken out of the contact device 10, up to the heat exchanger 14 intake. Cold water from the heat exchanger 14 will flow by its own weight through the container 23 and the connected pipelines to the contact device 10. The container 23 will in this case have two overflow pipes, namely a first overflow pipe through which water will be able to flow to the contact device 10,

and another overflow pipe, placed above the first, for the removal of accumulated excess water. However, it is preferable to use a pump in the return system for the cold water instead of in the hot water line, as a pump will usually function more smoothly when the water being pumped is cold.

The contact device 10, which is shown in more detail in the section shown in fig. 2, comprises a cylindrical outer wall 40, a top plate 41, a bottom plate 42 and a cylindrical inner wall 43. The parts 40, 41, 42 and 43 are suitably made of stainless steel. The inner wall 43 comprises a lower part 43a of relatively large diameter, an inclined part 43b and an upper part 43c of relatively small diameter.

In the embodiment shown, a gaseous fuel supplied through pipeline 11 and air introduced through sleeve 44 are mixed and burned in a burner 45. The burner 45 is a conventional type of burner with a perforated metal plate or screen, which is closed at the top with a close plate 46 to prevent loss of unburnt fuel. Hot combustion products accumulate in a combustion chamber 47

and moves upwards through a space 48 to a contact section 49, in which the hot combustion products are brought into intimate . and direct contact with cold water. The section 49 is filled with filler elements 50, which in typical cases may have the form of saddles, spirals, short cylinders or rings, or may have another appropriate form, made of ceramic material, glass or other suitable material. For example, the filling elements can be Raschig rings or berl saddles. The filling material 50 rests in the device 10 on plate 51, which in typical cases is a shower plate comprising an unperforated central part 51a and a peripheral, perforated part 51b containing perforations 52.

Cold water is introduced into the upper part of the contact device 10 through the pipeline 12, is collected in a vessel 53, flows by overflow onto the filling material, then flows down over and through the filling material 50 and through the perforations 52 and is collected in a cylindrical well 54 which is located between the outer wall 40 and the inner wall 43. The central part 51a of the plate 51 has a slightly larger diameter than the upper part 43c of the inner wall 43 to prevent downward flowing water from falling into the combustion chamber 47 and thereby coming into contact with burner elements 45 and 46. The fan 25 (shown in Fig. 1) the hot products of combustion collected in combustion chamber 47 pass up through space 48, perforations 52, section 49 where they are brought into intimate contact with the downwardly flowing water, and out. through exhaust duct 24. The fan 25 also serves to draw the fuel emitted from pipeline 11, and air through the sleeve 44 to the burner 45.

Hot water collected in the well 54 flows through a pipeline 55, an aerated overflow 56 and a pipeline 21 to the heat exchanger .14. The upper end of the pipeline 55 terminates inside the aerated overflow 56 at a level which ensures that the well 54 remains filled with water up to the same level. This is done to reduce the heat losses by radiation or conduction through the contact device 10 walls in the area near the burner 45.

Alternatively, instead of the tub 53, a shower head or other device can be used to distribute the water above. the filling material's 50 peak. Instead of a filler material 50

it is also possible to use plates, such as perforated shower plates, bell plates, strainer plates or other suitable plates to ensure intimate contact between the water and the combustion products. Alternatively, the fan 25 can also be moved and connected via a connection part to the sleeve 44 so as to

blow air into the combustion chamber and thereby blow the combustion products through the contact device 10 instead of drawing them out through the exhaust ducts.

It will be understood that the indicated burner elements 45 and

4 6 can be replaced by other suitable conventional burner elements, which may be necessary when choosing another fuel, such as one of those listed above.

The control and regulation devices used

for ignition, for flame detection, for switching on and off the fuel supply, for starting and switching off the exhaust fan, the house air fan and the water pump, for preventing overheating, etc., are not shown, because they are conventional.

For this liquid-gas heat exchange, the heat transfer surface in the heat exchanger 14 is in the range from 11.1 to 111 m 2 per 10,000 kcal/h. For a typical residential heat exchanger with an output of 15,000 kcal/h, the total heat transfer surface in the heat exchanger 14 can be approx. 46.5 m<2>.

The contact section 49 should be filled with a sufficient amount of filler material 50 or alternatively with a sufficient number of plates as mentioned above, so that at least 1.2 and preferably from 3 to 5 theoretical heat exchange stages are achieved. Usually, there is no need for more than 6 theoretical heat exchange stages, as practically all of the recycled

only amount of heat can be transferred to the liquid with 6 theoretical steps. In one theoretical heat exchange step, both thermal equilibrium and thermodynamic equilibrium are reached between the gas and the liquid which are brought into contact with each other.

The number of theoretical heat exchange stages can be calculated

based on the initial temperature and weight of the water introduced into the contact device, the final temperature and weight of the water taken out of the contact device, the temperature, weight and composition of • the combustion products introduced into the contact device and the temperature, weight and composition of the exhaust gas taken out from the contact device. Although a fairly accurate estimate of the number of theoretical stages can also be made if the composition of the combustion gases is estimated from the composition of the fuel and the air mixture used, it is more accurate to

use the composition of the combustion gases determined by analysis. The calculation can be carried out as a calculation in several steps, using psychrometric charts and the material balance and the heat balance. An estimate can also be made from scrimetric charts using the same data determined as above.

With regard to theoretical heat exchange steps and the calculation of the number of steps by repetition, reference is made to the following literature: Unit Operations of Chemical Engineering, McCabe and Smith, 3rd ed., McGraw-Hill Book'Co., N.Y. 1976, especially dei (Section) 18, Equilibrium.Stage Operations, pg part 24, Humidification Operations; and Mass Transfer Process Calculations, Sawitoski and Smith, Interscience Publishers,

NEW. 1963, especially Chapter 5, Humidification and Water Cooling. For air and water, psychrometric charts will be found in the Chemical Engineer's Handbook, Textbook Edition, Perry, 3rd ed., McGraw-Hill Book Co., N.Y. 1950, pages 763-765.

During operation, cold water of a temperature between 21° and 40°C is introduced into the contact device 10 in an amount of from 127 to 907 kg per 10,000 kcal/h. heat generated in the burner. When the water velocity is within these limits and when the contact device 10 is operated as indicated, with countercurrent contact between the water and the combustion gases, and has at least 1.2 theoretical stages, the water can be heated in the contact device to a temperature in the range from 49° to 85°C, preferably from 65.5° to 75.7°c. At the same time, most of the usable amount of heat is removed from the hot combustion gases, and the exhaust gas is taken out at a temperature between 24° and 49°C, preferably between 24° and 38°C. When operation is set up in this way, at least 90%, and up to 98%, of the available heat will be extracted from the hot combustion products. As most of the water vapor in the hot combustion gases is condensed by the cold water introduced into the contact device, the heat content associated with the water's latent heat of vaporization will be recovered from the water that is condensed, and the exhaust gas differs from the hot combustion products in that the exhaust gas is free of most of the water in the combustion products and have a lower temperature.

The contact device 10 can be very compact. For a heating device with a calculated output of 15,000 kcal/h, which

is a typical size for an average-sized residential building, suitable overall dimensions for the contact core 10 may be 152.4 mm and 660.4 mm, for the diameter and height, respectively.

If more than 907 kg of water per 10,000 kcal/h is used, the water's temperature will not increase by more than approx. 11°C, but the required heat transfer surface in the heat exchanger will be excessively large and the air circulation speed high. If less than 127 kg of water per 10,000 kcal/h is used, so much water will evaporate and be lost as steam together with the exhaust gas

'that the heat loss "associated with the latent heat of vaporization of the water will be significant. With decreasing water velocity within the specified range, the number of theoretical heat exchange stages required in the contact device increases, while the size of the gas-liquid contact surface required in the heat exchanger decreases. For a heater for heating of forced-circulated air is the amount of water that is circulated, preferably in the range from 181.4 to 271 kg per 10,000 kcal/h. For heating water for radiators, laundry or other household use, the amount of water that is circulated through contact device 10, preferably in the range from 145.1 to 217.7 kg per 10,000 kcal/h.

For example, the typical operating conditions for a heating device with an output of 15,000 kcal/h can be as follows:

contact device:.

heat exchanger:

In a heating device operated under these conditions, the contact device will provide 4-5 theoretical heat exchange steps.

The heating device and the method according to the invention are adapted to the heating fluid of any kind, including gases and liquids. The specific embodiment described above with reference to Figures 1 and 2 represents an example of heating a gas, in this case air for space heating. Other gases can be heated in the same way, whenever this is desired.

The fluid to be heated can also be a "liquid, such as water. One such example is heating water for home heating, where heat is transferred to radiators in the house or the home using hot water. In this case, both sides of the heat exchanger will lead water, i.e. hot water from the contact device 10 will be cooled in the heat exchanger 14 while heating water which is then circulated to hot water radiators.

In such a system, the elements 13 - 20 shown in fig... 1 will be eliminated, and as a replacement for these, the elements shown in fig. 3 be used. Fig. 3 shows a housing or capsule 68 which comprises a cold water chamber 71, a hot water chamber 72 and a middle section 69 adapted to hold the heat exchanger 14. Hot water from the contact device 10 flows by its own weight through pipe line 21 to the first side of the heat exchanger 14, emits its heat content here and flows out as cold water through pipeline 22. Water to be heated for radiators, a laundry or for other uses flows as cold water from pipeline 70 to the chamber. 71, which serves to distribute the water to be heated, on all passages in the heat exchanger 14 on the other side. After being heated in these, the hot water from the heat exchanger 14 is collected in the chamber 72. A pump 74 pumps the water up through the chambers 71 and 72, the heat exchanger 14 and the pipelines 73 and 75 to the places where the hot water is desired. The pump 74 is preferably positioned so that it pumps the water in the pipeline that receives the water from the heat exchanger 14, to avoid excessively high pressures occurring in the thermoplastic heat exchanger which could cause damage to the heat exchanger. Such damage could occur if the pump were placed in the intake pipeline 70.

For a liquid-liquid heat exchange of this type, it is sufficient that the heat transfer surface in the heat exchanger 14 is in the range from 0.74 to 37.1 m<3>per. 10,000 kcal/h. For a-

typical home heating device designed for a performance of

15,000 kcal/h, the total heat transfer surface in the heat exchanger 14 can thus be approx. 9.3 m. It is also possible to heat water in the same way for other household uses, e.g. for laundries, wash basins, showers, etc. The invention can also be adapted to further increase the temperature of fluids heated in solar heating systems. Such a fluid can e.g. be a mixture of ethylene glycol and water. Other liquids can also be heated in the same way, if desired, e.g. dye bath, chemical treatment bath, etc.

Another possibility is a double system for heating both a gas and a liquid. For example, for a house with a heating system based on forced air circulation, both the heat for the forcibly circulated air and the heat for the hot water for wash basins and laundry can be supplied by means of a heating device equipped with a contact device 10

of sufficiently large capacity to operate two heat exchangers for respectively heating forced-circulated air and water for wash basins and laundry.

It will also be understood that the housing 13 can have small dimensions and e.g. not have a larger cross-section than typical ducts 16 and 20 which are used as a return line for cold air and a supply line for hot air. This can be adapted when installing a heating device according to the invention in new houses or buildings. When it concerns an existing heating device in an older house or an older building, it is possible to refurbish the existing heating device by replacing only the elements that are no longer needed, e.g. the burner and an existing metal heat exchanger, while the heater's container, air fan and duct system are retained. In such a case, the thermoplastic heat exchanger 14 will be installed in the existing container, and likewise the contact device and all other connected elements will be installed and the necessary connection to the existing container made.

As indicated above, the heat transfer surface in the heat exchanger 14 will vary, depending on whether the fluid to be heated in it is a gas or a liquid. If it is a gas, the required area will be from 11.1 to 111 m 2 per

10 0.00 kcal/h, and if it is a liquid, one will be required

2

area of between 0.74 and 37.1 m per 10,000 kcal/h. The flat

which is used in any given case, will lie within the specified ranges and will vary with the amount of water (in kg per

10,000 kcal/h) which is introduced into the contact device 10 to remove the heat from the combustion products, and, to a lesser extent, with the gas or liquid to be heated in the heat exchanger. That the areas for the heat exchanger surface are different when heating gas and heating liquid is due to the difference between the heat transfer coefficient for. gases and the heat transfer coefficient for liquids. When e.g. if the fluid to be heated is air, the heat transfer coefficient U will be in the range from 17.1 to 34.2 kcal/h.m^.°C, while when the fluid to be heated is water, it will be in the range from 342. to 1284 kcal/h.m .°C. The heat transfer coefficients vary within the specified ranges according to the fluid to be heated, the system's spatial dimensions and the flow rate. Because the heat transfer to a liquid occurs faster than to a gas, the heat transfer surface in the heat exchanger can be smaller in liquid-liquid heat transfer than in liquid-gas heat transfer. However, for any heating device according to the invention, the product of U and the heat transfer area A in the heat exchanger will be the same, regardless of whether the fluid to be heated is a gas or liquid. The product U x A must be at least 1.5

per 1000 kcal/h of fuel burned and need not exceed 38 per 1000 kcal/h fuel burned, although the upper limit is not particularly critical. A preferred area for. U x A is 2.3 - 7.6 per 1000 kcal/h fuel burned.

In the heat exchanger 14, a number of first passages are provided which are adapted to guide the water supplied from the contact device 10. and, adjacent to these, a number of other passages which are adapted to carry the fluid to be heated. The first and second passages can be arranged in different types of geometric and spatial relationships to each other,

as long as the flow patterns of the two streams are suitable for transferring most of the recoverable heat from the aqueous fluid to the fluid being heated.

Preferably, the heat exchanger is constructed with several

step, the direction of flow of the water being mainly perpendicular to the direction of flow of the fluid to be heated. As an example, fig. 4 schematically shows the flow pattern for a heat exchanger with 6 stages. A heat exchanger element 80

is divided into several first passages 81, 82, 83, 84, 85 and 86 by means of partitions 87, so that a curved path is delimited, as indicated by the arrows, for the water which is introduced through pipeline 21 and taken out through pipeline 22, which path is oriented essentially perpendicular to the direction of flow of the fluid to be heated in contact with the element 80.

In this case, the passages shown define several heat exchange stages. There can of course be a greater or lesser number of passages and steps. There will usually be several heat exchange elements in a heat exchanger, and in such cases pipelines 21 and 22 for the supply of water to and withdrawal of water from the heat exchanger can terminate in the chamber that serves all the elements 80.

A suitable and preferred embodiment of a heat exchanger for use in the heating device according to the invention is shown in figures 5, 6 and 7.

Referring first to the specific heat exchanger element shown in fig. 7, plates 151 and 152, which are made of a thermoplastic film and serve as heat exchange surfaces, are arranged at a distance from each other. The facing surfaces of the two plates are attached to each other near the edges of the plates, in this embodiment by means of edge partitions, of which only one, namely edge partition 153, is shown

in this subsection. Distributed over the space delimited by the two plates and by the edge partitions, a number of elevations 168 are arranged which extend from plate 152 towards plate 151. The elevations 168 serve to keep the plates 151 and 152 at a distance from each other, so that the plates are prevented from collapsing, which would limit or stop the flow of fluid between the plates. A channel partition wall 165 extends between and is attached to opposite surfaces of the plates 151 and 152 and serves as a partition wall between channels to direct the flow of a first fluid into a defined

path between the two plates.

As shown by the connection 171 between edge partition

153 and plate 152, at the connection 172 between channel partition wall 165 and plate 152 and at the connection 173 between elevation 168 and plate 152, the edge partitions, the elevations and the channel partition walls are preferably designed in one piece with plate 152. Plate 152 with elevations 168 can conveniently be produced by extrusion of a thermoplastic from a suitable die to a patterned drum according to the method described in all three US patents 3,509,005, 3,515,778 and 3,635,631. The plate 151 is then attached to the edges of the plate 152, e.g. by heat sealing or with a suitable adhesive, preferably by heat sealing, either directly as indicated above or by sealing to the upper side 174 of the edge partition 153 and to the upper side of other edge partitions not shown, to the upper side 175 of the channel partition 165 and to the upper side of all other channel partitions . A suitable method for sealing the plate 152 to the upper side of the edge partitions and channel partitions is described in US Patent No. 3,821,051.

It is preferred that the elevations 168 extend to and are attached to the plate 151. When the elevations 168 are attached to the plate 151, this can also conveniently be carried out by attaching the upper side 176 of each individual elevation 168 to the plate 151

by heat sealing or by means of a suitable adhesive, preferably by heat sealing. It is preferred to connect the elevations 168 to both plates 151 and 152, as this prevents bulging of the plates 151 and 152 when the pressure of the first fluid in the heat transfer element exceeds the pressure of the second fluid in contact with the outer surfaces of the element. If such bulging was not prevented, the flow of the second fluid in contact with the outer surfaces of the element could be limited or stopped.

Fig. 6 shows a cross section through a heat exchanger element.

The plate 152, which consists of a thermoplastic film, carries edge partitions 153, 154, 155 and 156 attached to the plate's (edges. The space inside the element is divided into channels 157, 158, 159, 160, 161 and 162 by means of channel partitions 163 , 164, 165, 166 and 167, which are attached to the plate 152 as described above. Elevations 168, of which only three groups are shown in Fig. 6, project from the plate 152 in all of the channels. , namely a first opening 169, through which the first fluid is introduced into the interior of the element, and a second opening 170 through which the first fluid is withdrawn from the element. The first fluid flows through the channels in the direction shown by the arrows.

The number of channels 157 etc. can vary from one channel up to any number that may be desirable or necessary for a given heat exchange.

The six-channel element shown in FIG. 6, is just a typical example and is suitable for many applications where six heat exchange stages are desired. The heat exchanger elements can have either an equal or an unequal number of channels, and the location of opening 170 through which the first fluid is taken out will vary. It will be located at the downstream end of the last channel through which the first fluid flows.

In fig. 5, a section of a typical heat exchanger according to the invention is shown in perspective. The arrows in connection with the reference numbers 6, 6 indicate the orientation of the section shown in fig. 6. Five individual heat exchanger elements' 101, 102, 103 , . 104 and 105 are shown. This figure shows plates 151 and 152 and edge partitions 153 and 154. Each of the plates 151 and 152 and the corresponding plates in all the other elements 102 etc. with the exception of the last element (not shown) have both a first and a second opening which is not seen in this figure, such as first opening 169 and second opening 170 which is seen in fig. 6. All the first openings are aligned and all the other openings are aligned. The last element (not shown) has a first and second opening only in the first plate, i.e. the plate facing the neighboring element. There is no opening in the second plate, i.e. the plate in the last element which is furthest from the penultimate element. A first row of coaxial lines 106, 107, 108, 109 and 110 are arranged so that each ring lies between and is attached to neighboring elements. The rings are arranged so that they surround the first openings in the plates they are in contact with. For example, ring 106 is attached to the plate 152", so that it surrounds the first opening 169, and it is attached to the plate 150 so that it surrounds the corresponding first opening in this plate. In a similar way, a second series of coaxial rings 111,

112, 113, 114 and 115 arranged so that each ring lies between

and is attached to neighboring elements, as the rings are arranged in this way

that they surround the other openings in the plates they are in contact with. For example, ring 111 is attached to plate 152 so that it

surrounds the second opening 170 and likewise attached to the plate 150 so that it surrounds the corresponding second opening in this plate. Spacer strips 116, 117, 118, 119 and 120 are placed between neighboring pairs of heat exchanger elements to help keep the elements at a distance from each other. The distance lists should be

fixed to prevent them from coming out of position. This can be done e.g. by attaching them to the heat exchanger elements by heat sealing or with a suitable adhesive. It is not necessary to attach the spacer strips to the elements over their entire length, as it is sufficient to attach them at each end of the strip. Passages 131, 132, 133, 134, etc., and corresponding passages (not indicated by reference number) on the opposite side of the distance strips, are used for the second fluid which is to be heat-exchanged with the first fluid. The spacer strips are arranged substantially perpendicular to the direction in which the first fluid flows through the channels in the elements, whereby they serve to direct the flow of the second fluid in a direction substantially perpendicular to the direction of flow of the first fluid. Two hollow, cylindrical pipe connections are attached to the plate 151, with a first pipe connection 121 surrounding the first opening in the plate 151 and a second pipe connection 122 surrounding the second opening in the plate 151. The pipe connections serve as devices for connecting pipes, hoses or other guides to the heat exchanger for supplying the first fluid to the heat exchanger element and removing it therefrom.

Together, pipe connection 121 and rings 106, 107, 108, etc. form a discontinuous channel, which serves to distribute the first fluid to the inside of the heat exchanger elements 101, 102, 103, etc. In a similar way, pipe connection 122 forms

and rings 111, 112, 113, etc. a discontinuous channel which serves to collect the first fluid from the inside of all heat exchanger elements 101, 102, 103, etc.

It will be understood that a heat exchanger can have a number of heat exchanger elements that vary from a single element to as many elements as would be desirable for a given

application. This number can reach several hundreds.

It is appropriate that the rings 106 - 110 and 111 -115 are circular. They can be attached to the plates 152 and 150 and other similar plates by heat sealing or by means of a suitable adhesive, preferably by heat sealing. A preferred method for joining the parts together is a method known as electromagnetic bonding or magnetic heat sealing, and where a material comprising a suitable thermoplastic, such as polyethylene, and a magnetic material, such as iron, steel, iron oxide or a ferrite, in the form of particles in the micron size range or below is applied to all the places where a seal is to be formed, after which the whole is placed in a high-frequency magnetic field in an electric induction generator, whereby the material is heated and forms a secure bond to the thermo-plastic parts with which it is in contact . Such sealing materials are known in the art and are available on the market in many forms, including as molded and extruded articles, such as films and gaskets, liquid or paste materials in aqueous or solvent-based binder systems, and hot melts. Information regarding the method will be found in Modern Plastics, Encyclopedia, 1977-78 ed. McGraw-Hill, N.Y., October 1977, pages 420-21, "Electromagnetic Bonding", and pages 424-25, "Magnetic Heat-Sealing". Further information regarding the technique and typical materials suitable for such seals can be found, e.g. in US Patent Nos. 3,620,875, 3,620,876, 3,461,014 and 3,779,564.

One method, which is the preferred method, of designing the distribution and collection systems for the first fluid to and from the interior of the heat exchanger elements is to attach the rings 106, 107, etc. and 111, 112, etc. to plates 152, 150 etc. before the first and second openings, exemplified by openings 169 and 170, have been formed. This means that each individual heat exchanger element is first produced without any first or second opening. Rings 106 etc. and 111 etc. are then fixed at the places where openings 169 and 170 and corresponding openings in the other plates are to be formed. Pipe connections 121 and 122 are also attached to the plate 151 at the places where the openings in the plate 151 are to be formed. The openings are then cut out by inserting a tubular cutting device through the assembled unit, on the inside of each row of coaxial rings. The openings can be cut through all the plates, except for the second plate in the last heat exchanger element. Alternatively, the openings can be cut out through both plates in all elements including the last element, after which the two openings in the second plate in the last element are closed with a thermoplastic film, a disc or a bowl-like part. If bowl-like parts are used, these can be fixed in place before the openings are cut out, i.e. at the same time as the rings and pipe connections are fixed in place.

The elevations 168 can expediently have a circular cross-section, or they can have any other desired shape, the cross-section e.g. can be triangular, oval, streamlined, rectangular, etc., as desired.

The elevations may be arranged offset relative to each other or in a rectangular pattern, triangular pattern or any other fixed or random pattern.

The size of the heat exchange surface in such a heat exchanger and the overall dimensions of the heat exchanger will vary greatly, depending on the type and the added quantities of the fluids between which the heat exchange is to take place, the heat transfer coefficient of the given system and the amount of heat to be transferred. The active heat transfer surface can vary from a few tenths of a square meter to thousands of square meters. The two longest dimensions of the individual heat exchanger elements can vary from a few centimeters to several metres. The length can be 30 m or more. When spacing strips are used, these will usually be placed at a distance of from 50.8 mm to 152.4 mm from each other. The heat exchanger can have anything from a few heat exchanger elements to hundreds of elements.

An example of such a heat exchanger is a heat exchanger made of high-density polyethylene. This heat exchanger is suitable for an air-water heat exchanger task where heat from water of 48.9 - 85°C is transferred to air in an amount of up to 15 1000 kcal/h. The elements are 0.61 m long and -0.305 m high and are arranged as shown in fig. 6. Plates 151 and 152 are 0.0762 mm thick. The distance between the plates is 0.863 mm. The edge partitions are 0.863 mm thick and 2.54 mm wide. The channel partitions are 0.863 mm thick and 0.203 mm wide and extend over the plates for a length of 559 ram, starting alternatively from opposite sides of the plates, so that the channels are connected to each other at the plate ends forming a meandering flow path for the first fluid, which is water. The elevations 168 have a circular cross-section of diameter

0.889 mm, are 0.863 mm thick and are attached to plates 151 and 152. They have been formed during the extrusion of one plate and are then heat sealed to the other plate. They are arranged in a triangular pattern with a center distance of 3.18 mm. The element's total thickness is 1.016 mm. Each of the six channels is approx. 50.8 mm wide.

The heat exchanger has 125 such heat exchanger elements. The elements are fastened together using two rows of polyethylene rings 106, 107, etc. and 111, 112, etc., each ring being 2.54 mm thick and having an outside diameter of 19.05 mm and an inside diameter of 12.7 mm. The two rows are placed at neighboring corners. of the elements, one coaxial row at the entrance to the first flow channel and the other coaxial row at the end of the last flow channel. Two pipe fittings 121 and 122, each 38.1 mm long and having an outside diameter of 19.05 mm and an inside diameter of 12.7 mm, are attached to the first plate of the first member, being a pipe connection is placed coaxially with each of the rows of rings. The rings and pipe connections are attached to the elements by sealing using an inductively heated material comprising polyethylene and magnetic iron oxide. The first openings, exemplified by opening 169, and the second openings, exemplified by opening 170, have then been cut out by inserting a tubular cutting device of diameter 12.7 mm through the entire assembled unit, once through the first row of coaxial rings and once through the second row of coaxial rings. The first and second openings which have been cut in the second plate in the last (125th) heat exchanger element have then been closed by placing over each opening one polyethylene disc of thickness 2.54 mm and diametdr 19.05 mm, using the sealing technique described above. Spacer strips of length 304.8 mm, thickness 2.54 mm and width 2.54 mm are then inserted between adjacent elements and arranged parallel to edge partitions 153 and 155, i.e. in a direction mainly perpendicular to the channel partitions and the direction of fluid flow through the channels. They are attached to both ends. both the two adjacent elements, using the sealing technique described above. Five spacer strips are placed between each adjacent pair of boards, on center lines at a distance of approx. 121.9 mm apart, a strip being placed near the edges of the elements at the edge partition 155 and the corresponding edge partitions in the other elements. Thus, passages are formed between neighboring elements for the other fluid, which is air. This flows in the passages in a direction that is parallel to the distance strips. As indicated above, the dimensions of the elements in the plane are 0.305 m x 0.61 m. The thickness of the heat exchanger/through the 125 elements and 124 passages that separate the elements from each other is approx. 442 m.

In use, the heat exchanger will be mounted in a housing (13) which closes tightly around four sides of the heat exchanger and provides chambers for distributing cold air to the passages between the elements and for collecting hot air when it flows

out of the passages. The four sides around which the housing closes are (1) the side at the edge partition 153 and the corresponding edge partitions in the other elements, (2) the side at the edge partition 155 and the corresponding edge partitions in the other elements, (3) the side at the first plate in the first element, i.e. plate 151, and (4) the side by the second plate in the last element, the second plate being the plate facing away from the penultimate element.

The heat exchanger will function efficiently when the direction of flow in the elements is such that the channel which is first supplied with the first fluid, which in the example above is water, is adjacent to the downstream end of the passages which carry the second fluid, as in this example is air.

Further information about such heat exchangers and modifications of such heat exchangers can be found in Norwegian patent application no. 801 256.

Another type of thermoplastic heat exchanger which can be used in the heating device according to the invention, and which has narrow channels through which the first fluid, water, flows, is described in US patent document no. 4 069 807.

The thermoplastic resin used for the manufacture of such heat exchangers should have a softening point of at least 104.4°C and should have a reasonable stiffness. A modulus of elasticity

when bending higher than 703 kg/cm 2 provides suitable stiffness. The preferred thermoplastic resins are high density polyethylene, isotactic polypropylene, acrylonitrile-butadiene-styrene resins, styrene-acrylonitrile copolymers and fluorocarbon resins such as fluorinated ethylene/propylene copolymers and polytetrafluoroethylene. High density polyethylene and isotactic polypropylene are particularly preferred because they are cheap. However, the invention is not limited with regard to the construction materials. For example, if desired, heat exchangers of known construction, made of anodized aluminum foil or copper-plated steel, can be used.

The heating device and the method according to the invention offer many advantages, primarily the advantage of efficiencies of up to 98%. With the help of the invention, the heat losses up through the chimney are significantly reduced, because the exhaust gas is discharged at a temperature between 24° and 38°C, usually at a temperature of approx. 32°C, while the exhaust gas temperature in a conventional heating device is

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between 205 and 315 C, and because the heat content is recovered from the gaseous combustion water by condensation of the water vapour. As a result of this more efficient and almost complete recovery of heat from the combustion products, the fuel requirement is reduced to between 50 and 60% of the fuel requirement in a conventional heating device. Conversion of existing heating devices to heating devices according to the invention will result in very significant amounts of oil and natural gas being saved. In addition, the operation of conventional gas-fired heating devices is such that a certain amount of carbon monoxide and/or soot is formed. Carbon monoxide is very toxic, and incomplete combustion involves a certain loss of calorific value. In contrast, the present invention is very effective, even when using excess air, e.g. an excess of from 10 to 200% over the stoichiometric amount for complete combustion. Under such conditions

the formation of toxic carbon monoxide can practically be avoided, and the fuel's calorific value is fully utilized. Furthermore

would it be possible to eliminate the chimney and the costs associated with it in the case of new construction.. To replace the chimney, a simple duct to an outer wall or to the roof or a connection to the ventilation duct for the building's pipework would be fully sufficient. A further advantage lies in the possibility of converting conventional heating devices in existing houses and buildings as described above.

Claims (18)

1. heater, characterized in that it comprises a burner for the formation of hot combustion products, a contact device adapted to bring the combustion products. in counter-flow contact with water, which device is capable of providing at least 1.2 theoretical steps, a fan adapted for conveying the products of combustion from the burner through the contact device and for conveying the exhaust gases produced by these combustion products to an exhaust device, and a heat exchanger which is adapted for taking in the water which has been heated by means of the combustion products, and for transferring the heat content of the water to a fluid, the product of the heat transfer surface in the heat exchanger and the heat transfer coefficient of the fluid for which the heater is adapted being in the range from 1.5 to 38 per 1000 kcal/h fuel burned. 2. Heating device according to claim 1, characterized in that it comprises a pump which is adapted to pump said water flowing out from one of the heat exchanger's outlets to the upper end of the contact device. 3. Heating device according to claim 1, characterized in that it comprises a pump adapted to pump said water flowing from the contact device to the heat exchanger, and a device to recycle said water flowing from the heat exchanger to the upper end of the contact device. 4. Heating device according to claim 2, characterized in that the contact device is adapted for operation at 3-5 theoretical steps, in . , 5. Heating device according to claim 4, characterized in that it. is adapted for upward flow of the combustion products and downward flow of said water through the contact device. 6. Heating device according to claim 5, characterized in that the contact device and the heat exchanger are adapted to transport said water in an amount of from 127 to 907 kg of water per 10,000 kcal/h burner capacity. 7. Heating device according to claim 6, characterized in that the heat exchanger is made from a thermos plastic resin and has a heat transfer surface of between 0.74 and 111.3 m 2 per 10,000 kcal/h burner capacity and that the heat exchanger is provided with a first passage adapted to lead said water and, adjacent to these, second passages adapted to lead said fluid in a direction which is mainly perpendicular to the direction of flow of said water. 8. Heating device according to claim 7, characterized in that the first passages are arranged in several stages, the stage which is first supplied with said water being in a neighboring position to the downstream end of said second passage. 9. Heating device according to claim 8, for use when said fluid is a gas, characterized in that the heat exchanger has a heat transfer surface of between 11.1 and 111 m 2 per 10,000, kcal/h burner capacity. 10. Heating device according to claim 9, characterized in that the heat exchanger has a heat transfer surface of between 37 and 93 m , and that the gas is air. 11. Heating device according to claim 8, for use when said fluid is a liquid, characterized in that the heat exchanger has a heat transfer surface of between 0.74 and 37.1 m <2> per 10,000 kcal/h burner capacity. 12. Heating device according to claim 11, characterized in that the heat exchanger has a heat transfer surface of between 4.6 and 18.6 m 2 , and that the second liquid is water or a mixture of water and glycol. 13. Method for heating a fluid, characterized by (a) burning a fuel to form combustion products, (b) using at least 1.2 theoretical steps these combustion products are brought into countercurrent contact with water to increase the water's temperature from approx. 49°C to approx. 85°C, and (c) passes the water through a heat exchanger to heat the fluid. 14. Method according to claim 13, characterized in that the water is used in step (b) in 3 - 5 theoretical steps, in an amount of from 127 to 907 kg of water per 10,000 kcal/h heat to be removed from the combustion products, and recycled from step (c) to step (b). 15. Method according to claim 14, characterized in that the water is introduced in step (b) at a temperature of from 21° to 46°C, and that the exhaust gas of the combustion products is discharged from step (b) at a temperature of from 24° to 38°C. 16. Method according to claim 15, characterized in that a heat exchanger is used which is made of a thermoplastic resin, and which comprises several stages, with the flow of said fluid mainly perpendicular to the direction of flow of the water. 17. Method according to claim 16, characterized in that the water in step (b) is used in an amount of from 181.4 to 271 kg per 10,000 kcal/h, and that forcibly circulated air is used as the aforementioned fluid. 18. Method according to claim 16, characterized in that the water in step (b) is used in one quantity of from 145.1 to 217.7 kg per 10,000 kcal/h, and that water or a mixture of water and glycol is used as said fluid.