Boiler and combustion unit

Field of the Invention

[0001] The present invention relates to the field of heating systems, more specifically the invention relates to a combustion unit, a boiler, and a system comprising a combustion unit and a boiler.

Background to the Invention

[0002] The burning of fuel, such as heating oils, for example kerosene, diesel fuels, or other similar fuels can be performed in a combustion unit. A combustion unit may be attached to a boiler to heat water. The water heated in this manner may be used, for example, in heating systems for buildings.

[0003] It is desirable that combustion units and boilers are efficient so as to provide the maximum heat per amount of oil burned. A conventional combustion unit such as a kerosene combustion unit may not be efficient in the combustion of fuel. This means that some energy is wasted during combustion.

[0004] Burning fuels creates emissions. Emissions may contribute to global warming, for example carbon dioxide emission may contribute to global warming. Emissions may be detrimental to the health of animals exposed to these emissions, for example carbon monoxide. It is desirable to reduce emissions caused by burning fuels.

[0005] There is a need for more efficient combustion units and boilers. There is a need for combustion units and boilers which have fewer emissions.

Summary of the Invention

[0006] In one aspect, the present invention provides a combustion unit for a boiler comprising:

(a) a burner box forming a burn chamber in which fuel may be burned, the burner box comprising a base plate,

(b) a spray nozzle which is connectable to a fuel source for providing fuel to the spray nozzle and an oxygen source for providing oxygen to the spray nozzle,

(c) an antechamber projecting from the burner box on the opposite side to the base plate,

(d) the spray nozzle being arranged in the antechamber, the tip of the spray nozzle extending into the burner box, the tip of the nozzle comprising an orifice, and wherein the orifice is positioned at a distance H from the base plate, the distance H being 90 to 540 times the diameter of the orifice.

[0007] The combustion unit of the invention is suitable for use with a boiler. The boiler may be a boiler for heating water, for example for heating water for a central heating system and / or a water system in a house. Beneficially the combustion unit may be suitable to be retrofitted to existing boilers which may be installed in buildings, for example in homes.

[0008] The combustion unit comprises a burner box forming a burn chamber in which fuel may be burned. Beneficially the burner box is made from materials which will not deform or melt when exposed to the heat generated by burning fuel in the burn chamber. For example, the burner box may be made from metal, such as steel, for example a stainless steel. The inner walls of the burner box may form the burn chamber in which fuel may be burned.

[0009] The burner box comprises a base plate. The base plate may be a wall of the burner box. The base plate may be a separate plate which is attached to a wall of the burner box. The base plate may be formed of metal, such as steel. The base plate provides an extra layer of protection for the burner box as, when the fuel is burning, the flame may extend from the spray nozzle toward the base plate. Beneficially the base plate prevents heat damage to the burner box while the combustion unit is in operation.

[0010] The combustion unit comprises a spray nozzle which is connectable to a fuel source for providing fuel to the spray nozzle and an oxygen source for providing oxygen to the spray nozzle. The fuel may be a fluid, for example a gas or a liquid. The oxygen supply may be air, for example ambient air outside the combustion unit. Fuel from the fuel source and oxygen from the oxygen source combine to form a combustible fluid prior to exiting the spray nozzle. The spray nozzle acts to break the combustible fluid apart into a spray pattern. The spray nozzle may be a single fluid nozzle, in which case the fuel and oxygen are mixed prior to entering the spray nozzle. The spray nozzle may be a two-fluid nozzle, in which case the fuel and oxygen enter the spray nozzle separately and are mixed in the spray nozzle.

[0011] The combustion unit comprises an antechamber projecting from the burner box on the opposite side to the base plate. Beneficially the antechamber may act as an oxygen reservoir to aid combustion of the fuel.

[0012] The spray nozzle is arranged in the antechamber and the tip of the spray nozzle extends into the burner box. Beneficially the spray nozzle extending from the antechamber into the burner box allows sufficient space in the antechamber such that it can act as an oxygen reservoir.

[0013] The tip of the spray nozzle comprises an orifice. The orifice may be substantially round. The combustible fluid formed from the fuel from the fuel source and oxygen from the oxygen source pass through the orifice of the spray nozzle where the combustible fluid breaks apart to form a spray. The orifice may be from about 0.2 mm to about 6 mm in diameter, for example from about 0.5 mm to about 5 mm, for example from about 0.75 mm to about 4 mm for example from about 1 mm to about 3 mm. When the orifice has a diameter of below 0.2 mm not enough fuel will be delivered for the system to become hot enough to heat the boiler. When the orifice has a diameter above 6 mm too much fuel will be delivered and not all the fuel will burn/ combust which reduces the efficiency of the combustion unit.

[0014] The orifice is positioned at a distance H from the base plate. The orifice faces the base plate such that when combustion fluid comprising fuel and oxygen is sprayed from the orifice the combustion fluid is aimed directly toward the base plate. The distance H is 90 to 540 times the diameter of the orifice, for example 100 to 500 times the diameter of the orifice, for example 150 to 450 times the diameter of the orifice, for example 200 to 400 times the diameter of the orifice, for example 250 to 350 times the diameter of the orifice. Beneficially when the distance H is 90 to 540 times the diameter of the orifice the spray of the combustion fluid, which comprises fuel and oxygen, is reflected back from the base plate. The reflection of the combustion fluid is beneficial to the fuel burning in a clean manner. The reflection of the combustion fluid minimises any harmful emissions generated in the combustion unit. When the distance H is too small in comparison to the diameter of the orifice the amount of combustion fluid reflected may be too great. When the distance H is too great in comparison to the diameter of the orifice the amount of combustion fluid reflected is too little.

[0015] The spray nozzle may be an atomizing nozzle. Beneficially an atomising nozzle will break the combustible fluid comprising fuel and oxygen into small droplets. Small droplets may aid in efficient burning / combustion of the fuel. In a spray nozzle the oxygen may be provided separately to the spray nozzle than the fuel. The oxygen is provided at a higher velocity to the fuel. The stream of fuel will disintegrate into droplets due to the relative difference in velocities. Beneficially the velocity or pressure of the oxygen and / or the fuel may be adjusted to control the droplet size.

[0016] The fuel source may contain kerosene, paraffin, petroleum, diesel including clean diesel and dirty diesel, cooking oil, for example vegetable oil, waste cooking oil, for example waste vegetable oil, or natural gas such as methane. The fuel should be a fluid, for example a gas or a liquid. Beneficially the combustion unit of the invention provides clean combustion of fuels which are dirty, for example oil waste from cars/ used motor oil or oil waste from industry. When fuels are burned/ combusted in the combustion unit the emissions, for example of carbon dioxide (CO2), carbon monoxide (CO), may be reduced. The reduction in emissions may be achieved while burning fuels which are dirty.

[0017] The antechamber projects outward from the burner box on the opposite side to the base plate. The antechamber is in fluid connection with the burner chamber, for example gas such as oxygen can move between the antechamber and the burner chamber. The burner chamber defines a volume and the antechamber defines a separate volume. The volume defined by the burner chamber may be from 8 to 15 times greater than the volume defined by the antechamber, for example 9 to 14 times greater, for example 10 to 13 times greater than the volume defined by the antechamber. The antechamber defines a smaller volume than the volume defined by the burner chamber. Beneficially the antechamber projecting from the burner box and defining a large enough volume acts as a sufficient reservoir of oxygen for the volume of the burner chamber. The skilled person will appreciate that at a certain volume that the antechamber provides a sufficiently sized reservoir for the volume of the burner chamber and that there is a reduced benefit of increasing the size further.

[0018] A jacket containing a working fluid may envelope the burner box and optionally the antechamber. The working fluid may be a gas or a liquid. For example, the working fluid may be water. Beneficially the working fluid absorbs heat generated when the fuel is burned/ combusted. The working fluid will be heated by burning / combustion of the fuel in the combustion unit. Beneficially the working fluid absorbing generated heat means that the combustion unit will not overheat, overheating may damage the combustion unit. Beneficially the heated working fluid can be transported to and / or used in separate systems where heated working fluid is required, for example central heating systems or hot water systems.

[0019] The combustion unit may comprise a secondary fan unit for providing oxygen to the burn chamber. The secondary fan unit may provide additional oxygen which is not mixed with fuel. Beneficially the additional oxygen may help the combustion unit burn/ combust fuel while minimising emissions, for example minimising CO2 and / or CO emissions. The combustion unit may comprise a door, for example a rear door. The door may allow access to the interior of the combustion unit, for example for repairs or maintenance. Beneficially the secondary fan unit may be positioned close to door, which would allow the oxygen provided by the secondary fan unit to cool the door.

[0020] The oxygen source may be connectable to the antechamber. The oxygen source may be connectable to the antechamber and provide oxygen to the antechamber. Beneficially the oxygen source being connectable to the antechamber allows oxygen reservoir in the antechamber to be replenished such that an adequate oxygen reservoir is maintained in the antechamber.

[0021 ] The combustion unit may comprise a means for adjusting the amount of fuel and / or oxygen provided to the spray nozzle. The same means for adjusting may be used for adjusting the amount of fuel and oxygen provided to the spray nozzle. For example when the fuel and oxygen are mixed to form a combustible fluid a single means for adjusting may be used to adjust the amount of fuel and oxygen. Separate means for adjusting may be used to adjust the amount fuel and oxygen before the fuel and oxygen are combined to form a combustible fluid. The skilled person will appreciate that a combination of means for adjusting may be provided such that the amounts of fuel and oxygen can be adjusted prior to being mixed to form a combustible fluid and another means for adjusting can be subsequently used to adjust the amount of combustible fluid.

[0022] The combustion unit of the invention may produce CO emissions of less than 300 ppm, for example less than 200 ppm. It is beneficial to reduce emissions from burning fuels. [0023] In another aspect the invention relates to a boiler comprising at least one heat transfer box comprising at least one heat transfer chamber. Beneficially the boiler comprising at least one heat transfer box and at least one heat transfer chamber allows for the efficient use of heat generated by a combustion unit.

[0024] The boiler may comprise a jacket enveloping the heat transfer box, the jacket containing a working fluid. The heat transfer box may be used to efficiently transfer heat from a heat source, for example a combustion unit, to a working fluid contained in the jacket. The jacket envelopes the heat transfer box so as to maximise the surface area available for heat transfer. Beneficially the jacket may be formed from a material which is insulated which aids retention of heat in the working fluid. The working fluid in the jacket may be transported away from the boiler to a separate system, for example a home heating system, or hot water system.

[0025] The boiler may comprise two or more heat transfer boxes, wherein the heat transfer chambers of the heat transfer boxes are in fluid connection to each other. Beneficially two or more heat transfer boxes being in fluid connection with each other means that the heat transfer boxes can be connected in a manner which saves space, for example by allowing the heat transfer boxes to be arranged on top of one another, for example by allowing the heat transfer boxes to be arranged beside one and other. Beneficially two or more heat transfer boxes being in fluid connection to one another allows the surface area over which heat transfer can take place to be maximised.

[0026] The heat transfer box may comprise two, three, or four heat transfer chambers. The heat transfer box may comprise from 2 to 10 heat transfer chambers, for example 4 to 8, for example 4 to 6 heat transfer chambers. Beneficially it may be possible to increase the surface area available for heat transfer by increasing the number of heat transfer chambers.

[0027] In another aspect the invention relates to a system comprising the combustion unit according to the invention and a boiler according to the invention. Beneficially the system comprising the combustion unit according to the invention and a boiler according to the invention may provide the benefits of both the combustion unit and the boiler simultaneously.

Brief Description of the Drawings

[0028] Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

[0029] Figure 1 is a combustion unit according to an embodiment of the invention. The combustion unit is shown in fluid connection with a boiler;

[0030] Figure 2 is a nozzle suitable for use with the combustion unit of the invention;

[0031] Figure 3 is a boiler according to an embodiment of the invention. The boiler is shown in fluid connection with a combustion unit. [0032] Figure 4 shows an embodiment of a heat transfer box of the boiler of the invention. The heat transfer box is shown comprising four heat transfer chambers.

Detailed Description of the Drawings

[0033] An embodiment of the combustion unit 100 is shown in Figure 1. The combustion unit 100 comprises a burner box 102. The burner box 102 forms a burn chamber

103 in which fuel 104 is burned. The fuel 104 may be a hydrocarbon, for example a C1 to a C20 hydrocarbon, for example kerosene, paraffin, petroleum, diesel including clean diesel and dirty diesel, cooking oil, for example vegetable oil, or natural gas such as methane. Beneficially the fuel can also be waste oil, for example waste oil from motor vehicles, for example waste cooking oil or waste vegetable oil. Waste oil contains contaminants which make it difficult to burn these oils cleanly. Beneficially the combustion unit of the invention burns waste oils cleanly, for example the combustion unit burns waste oil with CO emissions of less than 300 ppm, for example less than 200 ppm.

[0034] The burner box 102 comprises a base plate 106. Beneficially the base plate 106 prevent the burner box 102 from being damaged by the heat generated from burning fuel 104 in burn chamber 103.

[0035] The combustion unit 100 comprises a spray nozzle 108 which is connectable to a fuel 104 source and an oxygen source 110 and is shown connected to a fuel

104 source and an oxygen source 110 in Figure 1. The fuel 104 may be fed to the spray nozzle 108 under pressure, for example the fuel may be pumped or may be provided under hydrostatic pressure. The amount of fuel 104 which is provided to the spray nozzle 108 may be controlled by control means such as valves. The oxygen source 110 may be a conduit which extends from the spray nozzle 108 to a source of oxygen, for example ambient air, outside the combustion unit 100. The oxygen may be pumped to the spray nozzle 108 by a pump 112. Beneficially the fuel 104 can be provided to the spray nozzle 108 at a constant pressure. Beneficially using a fan 112 allows the flow of oxygen to be controlled, for example the speed or amount of oxygen may be controlled. Beneficially the fan 112 drives oxygen into the antechamber 114 which helps keep the antechamber 114 cool. Cooling may be beneficial to cool any electrical components which may be attached to the antechamber. The fan 112 may also drive oxygen into the burner box 102 which helps combustion or burning of the fuel 104 by ensuring adequate oxygen is available for burning the fuel 104. A mixture of hydrogen and oxygen may be added to oxygen as it travels through the oxygen source 110 to the spray nozzle 108. For example a mixture of hydrogen and oxygen may be injected into the oxygen source 110 before oxygen is provided to the spray nozzle 108. The mixture of hydrogen and oxygen may be added from about 250 ml per hour of burn time to about 2 litres per hour of burn time. Per hour of burn time means per hour while the combustion unit 100 is burning fuel. The mixture of additional hydrogen to oxygen may be at a ratio of from about 3 parts hydrogen to about 1 part oxygen by volume to a ratio of about 1 part hydrogen to about 1 part oxygen by volume, for example about 2 parts hydrogen to about 1 part oxygen by volume. Beneficially this additional hydrogen and oxygen provides additional fuel efficiency.

[0036] The spray nozzle 108 is for spraying fuel 104 which is to be burned in the combustion unit 100. It will be appreciated that the fuel 104 may be mixed with oxygen prior to being sprayed from the spray nozzle 108. The oxygen source 110 may provide oxygen which may be mixed with the fuel 104 prior to burning in the combustion unit 100. The fan 112 may compress the oxygen which is mixed with the fuel 104 prior to being sprayed from the spray nozzle 108. A schematic of a spray nozzle 108 is shown in Figure 2. The spray nozzle 108 has a tip 202 with an orifice 204 through which the fuel 104 is sprayed. The spray nozzle 108 may have a body 206. The spray nozzle 108 may be an atomizing nozzle. The spray nozzle 108 may be of any suitable dimension. The orifice 204 at the tip 202 of the spray nozzle 108 through which fuel 104 is sprayed may be from 0.2 mm to 6 mm in diameter, for example 0.5 mm to 5 mm, for example 0.75 mm to 4 mm, for example 1 mm to 3 mm. The diameter of the orifice 204 may be chosen so as to use as little fuel as possible while still providing sufficient fuel to the burn chamber 103 to burn with sufficient heat. Beneficially using little fuel 104 may help the combustion chamber 100 be more fuel efficient.

[0037] The combustion unit 100 comprises an antechamber 114 projecting from the burner box 102 on the opposite side to the base plate 106. The antechamber 114 is a raised chamber which extends outward from the burner box 102. The antechamber 114 is in fluid connection with the burner box 102 so that fluids such as oxygen can travel between the antechamber 114 and the burner box 102. The antechamber 114 acts as a reservoir of oxygen which allows for burning the fuel. The antechamber 114 may receive enough oxygen from the burner box 102 to act as a reservoir. If the antechamber 114 is not present the fuel 104 in the combustion unit 100 will not burn as there may not be enough oxygen, for example air present to allow combustion or burning to occur.

[0038] The combustion unit 100 as shown in Figure 1 also comprises starter 116 which is used to start the fuel 104 burning as it exits the spray nozzle 108. The starter 116 may be a gas pilot light and a pair of spark electrodes. The starter 116 turns off shortly after the combustion unit 100 begins to burn fuel, for example the starter 116 may run for less than 30 seconds, for example less than 15 seconds after the combustion unit 100 begins to burn fuel. Once the combustion unit 100 is burning fuel for a period of time, for example 15 seconds or less, for example 30 seconds or less, then the starter 116 can be turned off as the fuel 104 will remain burning as it exits the spray nozzle 108. The burning of the fuel 104 is self-sustaining after a short time, for example 15 seconds or less, for example 30 seconds or less.

[0039] The spray nozzle 108 is positioned in the antechamber 114 and the tip of the spray nozzle 108 extends into the burner box 102. That is the body 206 of the spray nozzle 108 may be wholly or partly positioned in the antechamber 114 while the tip 202 of the spray nozzle 202 is positioned in the burn chamber 103 formed by the burner box 102. Beneficially the body of the spray nozzle 108 being positioned in the antechamber 114 while the tip of the spray nozzle 108 extends into the burner box 102 means that when the fuel 104 is ignited that the flame will extend from the tip of the spray nozzle 108 and the antechamber 114 acts as an additional reservoir of oxygen which aid combustion or burning of the fuel 104.

[0040] The tip of the spray nozzle 108 may be positioned at a distance H which is proportional to the size of the orifice 204 in the spray nozzle 108 through which the fuel 104 being burned passes. Distance H may be from about 90 to 540 times the diameter of the orifice 204 in the spray nozzle 108, for example the distance H may be from 100 to 500 times the diameter of the orifice, for example 150 to 450 times the diameter of the orifice, for example 200 to 400 times the diameter of the orifice, for example 250 to 350 times the diameter of the orifice. For example when the orifice 204 in the spray nozzle 108 is 0.75 mm in diameter the distance H may be from about 67.5 mm to 405 mm. Beneficially the tip of the spray nozzle being positioned at a distance H from about 90 to 540 times the diameter of the orifice 204 in the spray nozzle means that some fuel is reflected from the base plate 106 to form an ideal mixture of fuel 104 and oxygen for efficient burning of fuel 104 which maximises the heat output from the combustion unit 100.

[0041] The antechamber 114 projects from the burner box 102 and is in fluid connection to the burner box 102 so that gases such as oxygen can move between the antechamber 114 and the burner box 102. The antechamber 114 defines a volume. The burner chamber 103 defines a separate volume to the volume defined by the antechamber 114. The volume of the burner chamber 103 may be 8 to 15 times greater than the volume of the antechamber, for example 9 to 14 times greater, for example 10 to 13 times greater. The antechamber 114 having this volume in comparison to the volume of the burner chamber 103 provides an adequate store of oxygen in the antechamber 114 relative to the size of the burn chamber 103 to efficiently burn the fuel 104.

[0042] When in use the spray nozzle 108 is ideally positioned as shown in Figure 1 wherein the tip of the spray nozzle 108 faces downward toward the ground. The fuel will be sprayed downward toward the base plate 106 which is positioned at the bottom of the burner box 102. The fuel 104 may reflect back from the base plate 106 while it is burning.

[0043] Beneficially the positioning of the spray nozzle 108 and the base plate 106 means that once the fuel 104 is ignited, for example by the starter 116, some fuel 104 is reflected back from the base plate 106 which brings down the ignition temperature of the fuel 104. This allows the starter 116 to be switched off and the fuel 104 will burn as it is sprayed from the spray nozzle 108 into the burn chamber 103. The starter 116 does not need to be employed again until the combustion unit 100 has been switched off and it is required to be switched on again.

[0044] The embodiment shown in Figure 1 comprises a secondary fan unit 118. The secondary fan unit 118 supplies oxygen to the burn chamber 103. Beneficially the oxygen supplied by the secondary fan unit 118 reduces the down draft from the oxygen supply 110 by supplying a constant supply of oxygen in the burn chamber 103.

[0045] The embodiment shown in Figure 1 comprises a rear door 120. Beneficially the rear door 120 is positioned close the secondary fan unit 118 so that the flow of oxygen from the secondary fan unit 118 cools the rear door 120 allowing the rear door 120 for access to the components within the burner box 102 for maintenance and repair.

[0046] The combustion unit 100 shown in Figure 1 comprises a jacket 122 which surrounds the burner box 102. The jacket 122 may be formed between the burner box 102 and an outer box 124. The jacket 122 contains a working fluid, for example water. The working fluid may absorb heat generated within the burn chamber 103 while the fuel 104 is being burned. By absorbing heat generated in the burn chamber 103 the working fluid prevents the burner box 102 from overheating which may cause the burner box 102 to melt.

[0047] The working fluid may be cold, for example below 30 °C when initially introduced through inlet pipe 126 into the jacket 122. The working fluid will travel through the jacket 122. The working fluid will be in thermal connection with the burner box 102 so that it can absorb heat from the burner box. The temperature of the working fluid will increase as it absorbs heat from the burner box 102. The working fluid now has a higher temperature than at the inlet pipe 126. The higher temperature working fluid can be sent from the jacket 122, through transfer pipe 128, to a boiler 130.

[0048] The combustion unit 100 may comprise an exhaust system 132. The exhaust system 132 may be connected to the boiler 130. The exhaust system 132 is in thermal connection with both the burner box 102 of the combustion unit 100 and the boiler 130. Beneficially the exhaust system 132 may transfer heat from the combustion unit 100 to the boiler 130.

[0049] An embodiment of the boiler 130 is shown in Figure 3. The boiler 130 comprises heat transfer boxes 400 as shown in Figure 4. The heat from the combustion unit 100 is transferred by means of the exhaust system 132 to a first heat transfer box 400a. The heat travels through the first heat transfer box 400a until reaching the end of far end of the boiler 130. At this point a gap 302 is provided which allow the heat to transfer from the first heat transfer box 400a to an intermediate heat transfer box 400b. At the end of intermediate heat transfer box 400b which is furthest from gap 302 a second gap 304 is provided. The heat travels through intermediate transfer box 400b, moving from gap 302 to second gap 304 where the heat can pass through gap 304 to another heat transfer box 400.

[0050] In the embodiment shown in Figure 3 the heat travels through the second gap 304 and into a final heat transfer box 400c. It will be appreciated that there may more than one intermediate heat transfer boxes 400b between the first heat transfer box 400a and the final heat transfer box 400c. Additional intermediate heat transfer boxes 400b will be in thermal connection with one another and with the first and final heat transfer boxes 400a, 400c so that the heat can transfer from the first heat transfer box 400a to the final heat transfer box 400c. The final heat transfer box 400c may comprise an exhaust 306 for release of emissions and any other by products.

[0051] It will be appreciated that a single heat transfer box 400 may be provided in which case the exhaust 306 will be positioned at the far end of the heat transfer box 400 from the exhaust system 132.

[0052] Figure 4 shows a view of a heat transfer box 400 when viewed along dashed line A. Each heat transfer box 400 comprises heat transfer chambers 402. In the embodiment shown in Figure 4 four heat transfer chambers 402 are provided. Beneficially having four heat transfer chambers 402 provides a good balance between reducing manufacturing costs and providing a large surface area for heat transfer.

[0053] Each heat transfer chamber may be covered in a jacket 404. The jacket is filled with a working fluid, for example water. Heat is provided from the combustion unit 100 into the heat transfer chambers 402 of the heat transfer boxes 400. Heat transfers from the heat transfer chambers 402 into the working fluid. It will be appreciated that the transfer of heat is dependent on the surface area of the heat transfer chambers 402. While the embodiment shown in Figure 3 has three heat transfer boxes 400a, 400b, 400c which may provide an adequate surface area to maximise heat transfer to the working fluid it will be appreciated that the surface area of the heat transfer boxes 400 can be altered by adjusting, for example, the length of the heat transfer boxes 400, or, for example, by providing additional intermediate heat transfer boxes 400b in the boiler 130.

[0054] It will be appreciated that the working fluid in the jacket 122 of the combustion unit 100 may be in fluid connection with the working fluid in the jacket 404 of the heat transfer boxes 400, for example in fluid connection via transfer pipe 128. It will be appreciated that the jackets 404 covering each of the first, intermediate, and final heat transfer boxes 400a, 400b, 400c are in fluid connection with each other. The working fluid may move between the jacket 404 of each of the first, intermediate, and final heat transfer boxes 400a, 400b, 400c.

[0055] The boiler 130 converts the heat generated by the combustion unit 100 burning fuel 104 into heat stored by a working fluid. The working fluid may exit the boiler through outlet pipe 308. The working fluid which stores heat can be transported to, for example, a heating system, a home heating system, a central heating system, or a hot water system, for example a domestic hot water system.

[0056] The boiler 130 may be configured so at to rest on an oil store 310. This has the benefit of reducing the space required for the boiler 130.

[0057] When a fuel is burned in the combustion unit 100 the CO emissions may be less than 300 ppm, for example less than 200 ppm.

Examples

[0058] A system comprising the combustion unit and the boiler of the invention was tested to determine the fuel usage and emissions. Fuel usage was determined by measuring in millilitres the amount of fuel used. Emissions were measured using a Testo-310 Flue Gas Analyser. The flue gas probe was zeroed in ambient air and was subsequently positioned at the outlet pipe of the boiler. Carbon dioxide, carbon monoxide, and oxygen emissions were measured during combustion.

[0059] The fuel burned was kerosene (paraffin). The orifice of the spray nozzle had a diameter of 0.75 mm. The orifice of the spray nozzle was positioned at a distance H of about 267 times the diameter of the orifice from the base plate (approximately 200 mm).

[0060] The starter (a gas pilot light and pair of spark electrodes) was used to ignite a mixture of fuel and oxygen which were sprayed from the orifice of the nozzle. The oxygen flow pressure was adjusted to approximately 70 KPa. Once the mixture of fuel and oxygen was ignited and burning the starter was turned off (approximately 30 seconds after ignition) and the amount of fuel was adjusted to minimise fuel usage which maintaining combustion.

[0061] The system was tested from cold which means that the system was at room temperature prior to the boiler being turned on. The system was also tested from hot which means that the boiler was previously run and turned off so that the temperature of the system was above room temperature prior to testing. Testing was performed for one hour.

[0062] The system was controlled by a thermostat which measured the temperature of the working fluid (water) at the outlet pipe of the boiler. The outlet pipe was connected to a domestic central heating system. The thermostat was set so the combustion unit was turned on to combust fuel when the temperature of the working fluid was from 35 ° C to 45 ° C. From initial start-up of the system the combustion unit burned fuel until the working fluid was heated to 45 ° C. Once the working fluid reached 45 ° C to combustion unit was switched off allowing the working fluid to cool. When the temperature of the working fluid fell to 35 ° C the combustion unit restarted and burned fuel until the working fluid was again heated to 45 ° C at which point the combustion unit switched off. This combustion cycle was repeated for the one hour of testing.

[0063] The combustion unit turns on and off as the working fluid heats and cools. The fuel usage over the one hour testing period was measured in millilitres (mis).

[0064] Emissions were tested using a Testo-310 Flue Gas Analyser while the combustion unit was active during the testing period. The temperature of the emissions were also measured using a T esto-310 Flue Gas Analyser.

[0065] The results of testing are shown in table 1.

Table 1 : results

[0066] As can be seen in table 1 the system comprising the combustion unit of the invention uses a minimal amount of fuel. After the initial heating of the system the CO emissions were very low at 154 parts per million.

[0067] The amount of time the combustion unit was active during the hour test was measured. The results are shown in table 2.

Table 2: cycle times

[0068] The system took 12 minutes to heat the working fluid to 45 ° C from room temperature during the from cold testing. Once the working fluid was initially heated the combustion unit was switched off for the majority of the subsequent time. Once the system is operating between 35 ° C and 45 ° C the combustion unit is on for approximately one quarter of a combustion cycle and a combustion cycle lasts approximately 20 minutes. Prior art boilers are also thermostatically controlled. However they have much shorted combustion cycle times and the combustion unit is active for a longer period of time over any given period of time. Beneficially the system allows the combustion unit to be switched off for the majority of the heating time.

[0069] The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0070] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.