GB2482685A - Transferring heat from air around a stove to water - Google Patents

Transferring heat from air around a stove to water Download PDF

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Publication number
GB2482685A
GB2482685A GB1013371.8A GB201013371A GB2482685A GB 2482685 A GB2482685 A GB 2482685A GB 201013371 A GB201013371 A GB 201013371A GB 2482685 A GB2482685 A GB 2482685A
Authority
GB
United Kingdom
Prior art keywords
air
stove
firebox
heat exchanger
duct
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1013371.8A
Other versions
GB201013371D0 (en
Inventor
Simon J Redford
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
KINXERG Ltd
Original Assignee
KINXERG Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by KINXERG Ltd filed Critical KINXERG Ltd
Priority to GB1013371.8A priority Critical patent/GB2482685A/en
Publication of GB201013371D0 publication Critical patent/GB201013371D0/en
Priority to GB1303800.5A priority patent/GB2497029B/en
Priority to PCT/GB2011/051449 priority patent/WO2012020240A1/en
Publication of GB2482685A publication Critical patent/GB2482685A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24B—DOMESTIC STOVES OR RANGES FOR SOLID FUELS; IMPLEMENTS FOR USE IN CONNECTION WITH STOVES OR RANGES
    • F24B1/00—Stoves or ranges
    • F24B1/18—Stoves with open fires, e.g. fireplaces
    • F24B1/185—Stoves with open fires, e.g. fireplaces with air-handling means, heat exchange means, or additional provisions for convection heating ; Controlling combustion
    • F24B1/188—Stoves with open fires, e.g. fireplaces with air-handling means, heat exchange means, or additional provisions for convection heating ; Controlling combustion characterised by use of heat exchange means , e.g. using a particular heat exchange medium, e.g. oil, gas  
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24B—DOMESTIC STOVES OR RANGES FOR SOLID FUELS; IMPLEMENTS FOR USE IN CONNECTION WITH STOVES OR RANGES
    • F24B1/00—Stoves or ranges
    • F24B1/18—Stoves with open fires, e.g. fireplaces
    • F24B1/185—Stoves with open fires, e.g. fireplaces with air-handling means, heat exchange means, or additional provisions for convection heating ; Controlling combustion
    • F24B1/188—Stoves with open fires, e.g. fireplaces with air-handling means, heat exchange means, or additional provisions for convection heating ; Controlling combustion characterised by use of heat exchange means , e.g. using a particular heat exchange medium, e.g. oil, gas  
    • F24B1/1881—Stoves with open fires, e.g. fireplaces with air-handling means, heat exchange means, or additional provisions for convection heating ; Controlling combustion characterised by use of heat exchange means , e.g. using a particular heat exchange medium, e.g. oil, gas   the heat exchange medium being either water or air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24B—DOMESTIC STOVES OR RANGES FOR SOLID FUELS; IMPLEMENTS FOR USE IN CONNECTION WITH STOVES OR RANGES
    • F24B7/00—Stoves, ranges or flue-gas ducts, with additional provisions for convection heating 
    • F24B7/007—Stoves or ranges with additional provisions for heating both air and water
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24B—DOMESTIC STOVES OR RANGES FOR SOLID FUELS; IMPLEMENTS FOR USE IN CONNECTION WITH STOVES OR RANGES
    • F24B7/00—Stoves, ranges or flue-gas ducts, with additional provisions for convection heating 
    • F24B7/02—Stoves, ranges or flue-gas ducts, with additional provisions for convection heating  with external air ducts
    • F24B7/025—Stoves, ranges or flue-gas ducts, with additional provisions for convection heating  with external air ducts with forced circulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
    • F24H1/0063—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters using solid fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H3/00—Air heaters
    • F24H3/008—Air heaters using solid fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H3/00—Air heaters
    • F24H3/02—Air heaters with forced circulation
    • F24H3/06—Air heaters with forced circulation the air being kept separate from the heating medium, e.g. using forced circulation of air over radiators
    • F24H3/067—Air heaters with forced circulation the air being kept separate from the heating medium, e.g. using forced circulation of air over radiators using solid fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H3/00—Air heaters
    • F24H3/02—Air heaters with forced circulation
    • F24H3/06—Air heaters with forced circulation the air being kept separate from the heating medium, e.g. using forced circulation of air over radiators
    • F24H3/10—Air heaters with forced circulation the air being kept separate from the heating medium, e.g. using forced circulation of air over radiators by plates
    • F24H3/107—Air heaters with forced circulation the air being kept separate from the heating medium, e.g. using forced circulation of air over radiators by plates using solid fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H6/00—Combined water and air heaters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H9/00—Details
    • F24H9/0052—Details for air heaters
    • F24H9/0057—Guiding means
    • F24H9/0063—Guiding means in air channels

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Air Supply (AREA)

Abstract

Apparatus for capturing heat from a stove has an enclosure 12 around a firebox 10 of the stove; an air duct 20 connected to a convection space 18 within the enclosure and having an opening 22 to a space surrounding the stove; and an air-water heat exchanger 24 and a fan or impeller 26 within the duct 20 that can cause air to flow towards the opening 22, so that in a first mode (fig 4) air flows from the duct 20 to the space surrounding the stove at least partly by natural convection, while in a second mode the impeller 26 induces air flow from the convection space 18 to the heat exchanger. Air flows in opposite directions within the duct 20 in first and second modes, the first mode cooling the heat exchanger 24, and the second mode heating it. The stove can be inserted within a hearth, with the opening 22, impeller 26 and heat exchanger 24 beneath the firebox 10. The heated water can be used in a central heating system.

Description

Transferring heat from solid-fuel stoves This invention relates to an arrangement for transferring heat from solid-fuel stoves.
Enclosed burning of solid fuels in modern stoves and inset fires with controlled combustion can result in considerable improvements in efficiency and reductions in smoke, particulates and unburned gas emissions, compared to combustion of fuels in open grates. Further benefit can be gained through transferring part of the fire heat to a water circuit, for example that of a central heating system. This allows heat to be distributed to other parts of the property and thus helps avoid overheating in the vicinity of the stove or fire. When fire heat is dispersed to other parts of the property, the customer saves money on fuel burned in other heating systems and, when wood is burned in the stove, carbon savings can be achieved through displacing burning of fossil fuel in the other heating systems.
In GB-A-2 459 348 the present applicant has disclosed a practical system for transferring heat from convector type stoves. In these systems, the natural convection of heat from the sides, back and top of a stove is reversed by the use of a low power fan to take heated air from outer surfaces of the firebox to a heat exchanger connected to a hydronic heating system.
The present applicant has also disclosed further systems for transferring heat from the outer surfaces of the firebox of a stove to a heat exchanger connected to a hydronic system in patent GB-A-2 466 925. One of the various systems described in that application includes recovering hot air from outer surfaces of a firebox by drawing heated air from the top of a convective space to a heat exchanger. This system is shown in Figure 1 of this application.
The amount of heat that can be recovered at the heat exchanger is limited by the difference in temperature between the water entering the heat exchanger and the hot air entering the heat exchanger. Therefore, maintaining a high inlet air temperature is important for practical heat recovery. However, in the system of GB-A-2 466 925, air that is drawn into the heat exchanger is likely to entrain unheated air from the environment (arrow A) around the stove in addition to heated air from the convective space. Although some of the heat from the stove sides can be recovered by the heat exchanger, dilution with cool air leads to a higher mass flow rate of air at a lower temperature than would be attained if no cool air were entrained (as is achieved in the system disclosed in GB2459348) and a consequential reduction in the amount of heat that can be captured.
An aim of this invention is to improve upon the performance of the system disclosed in GB-A-2 466 925.
At its most general, the invention provides a system in which hot air that is delivered to a heat exchanger has, to as great as possible an extent, passed over hot surfaces of the stove rather than being drawn directly from air surrounding the stove. This means that the air is as hot as is practical when it reaches the heat exchanger, so maximising the temperature difference between it and the water, and thereby maximising heat transfer.
To this end, from a first aspect, the invention provides apparatus for capturing heat from a stove, the apparatus comprising an enclosure for surrounding a firebox of a stove; an air duct connected to a convection space within the enclosure and having an opening to a space surrounding the stove; an air-water heat exchanger within the air duct, the heat exchanger having an air side and a water side and being operative to transfer heat between air on the air side and water flowing in channels in the water side; and an impeller within the duct that can operate to cause air to flow within the duct towards the opening; wherein in a first mode of operation air is allowed to flow from the air duct to a space surrounding the stove at least partly by natural convection and in a second mode, the impeller induces air to flow from the convection space duct to the air side of the heat exchanger.
Since the air that arrives at the heat exchanger is drawn from the convection space, it is largely undiluted by air at ambient temperature, so maximising the heat that can be transferred to the water by the heat exchanger. When in the first mode, the air moving by natural convention ensures that the water within the heat exchanger does not become excessively hot.
Air may enter the duct in the second mode, having entered the convection space and then passing over a side wall, a rear wall or a top hot surface of the firebox.
Typically, the impeller operates only in the second mode.
From a second aspect, this invention provides a stove comprising a firebox surrounded by apparatus for capturing heat from a stove embodying the first aspect of the invention.
In such embodiments, the convection space is located between walls of the firebox that become hot in use and the enclosure. These include side and top walls of the firebox.
The opening may be disposed below the firebox, as may the heat exchanger and the impeller.
Embodiments of the invention may be stand-alone stoves or may take the form of an insert to replace an open fire within a hearth. The small size of heat exchanger that can be used with this invention provides a compact arrangement that is advantageous or even essential for such an insert.
An embodiment of the invention will now be described in detail, by way of example, and with reference to the accompanying drawings, in which: Figure 1 shows a stove including known system for capturing heat from a stove, and has already been discussed; Figures 2 and 3 are side and front diagrammatic views of natural convection occurring within an enclosed firebox of a stove incorporating a system for extracting heat being an embodiment of the invention; Figure 4 shows the embodiment of Figures 2 and 3 operating in a first mode; and Figure 5 shows the embodiment of Figures 2 and 3 operating in a second mode.
With reference to Figures 2 and 3, a stove embodying the invention has a firebox 10 surrounded on its sides and its top, by an enclosure 12. The firebox 10 has side walls and an upper wall that are heated by a fire 14 within the firebox 10. A convection space is defined between the walls of the firebox 10 and the enclosure 12. Air within the convection space is heated by the walls of the firebox 10. This causes the air within the convention space to rise by natural convection to exit through several air openings 16 above the upper wall of the firebox 10, SO extracting heat from the stove and delivering it to the surroundings of the stove. Air from the surroundings of the stove can enter the lower part of the convection space, at 18, between the enclosure and the side and rear walls of the firebox. The firebox also has a flue, but this has not been shown in the interest of clarity. There is no direct connection between flue gasses and heated air in the convection space.
Further components of the embodiment are shown in Figures 4 and 5.
An air duct 20 is connected to the convention space through a wall of the enclosure 12 close to an upper surface of the firebox 10 positioned to be as far away from the air openings 16 as feasible. The air duct 20 extends downwardly from its connection with the convection space to the rear of the firebox 10 and extends under the firebox 10, to a lower opening 22 to surrounding air towards the front of the stove.
Within the air duct 20, in a position below the firebox 10, there is an air-water heat exchanger 24 and an air impeller, which, in this embodiment, is an axial flow fan 26, the fan 26 being between the heat exchanger 24 and the lower opening 22. Other fan types such as crossflow or centrifugal fans could also be deployed in this application, and the fan and heat exchanger could be locates elsewhere, for example, to the back or sides of the stove.
The stove can operate in two modes.
In a first mode, illustrated in Figure 4, the fan 26 does not operate. Most of the air that passes hot surfaces of the firebox 10 enters the convective space formed around the sides and back of the firebox 10 from the bottom of the stove, atlB, moving by natural convection. A small airflow is induced through the heat exchanger 24, entering the duct through the lower opening 22. This ensures that any radiative heat passed to the heat exchanger due to its location near hot surfaces of the firebox 10 is dispersed by the cool incoming air, so ensuring that water within the heat exchanger 24 does not reach dangerously high temperatures. The induced airflow is assisted by the profile of the upper convective space In a second mode, illustrated in Figure 5, the fan 26 operates. The effect of the fan 26 in operation is to drive a stream of air from within the duct 20 out of the lower opening 22. In doing so, it draws air from within the duct 20 through the heat exchanger 24.
Some of the total airstream passing through the duct 20 is drawn from air that is below the firebox 10 of the stove, at 18, through the convective space around the sides and back of the firebox 10. The remainder of the airstream is drawn in through the air openings 16 at the upper front of the stove. This means that all of the air in the airstream passes across hot surfaces of the firebox 10. Careful dimensioning of the convective spaces, and the size of the air openings 16 and the lower opening 18, ensures a balance of air flowing across each hot surface of the firebox 10. Note that some of the hot air from the sides of the stove also passes across the top surface.
It is important to note that the arrangement shown in Figures 4 and 5 overcomes the impracticalities of the arrangements previously discussed by ensuring that substantially all air drawn into the duct in the second mode first passes over hot surfaces of the stove without entraining cool air from the environment. This means that a lower air mass flow rate is required in the second mode which helps to reduce the power that must be supplied to the fan 26 (thus reducing fan noise as well as energy consumption) and obtaining improved operation of the heat exchanger 24. Experimental evaluation shows that air drawn towards the heat exchanger 24 is expected to be heated to around 200°C, which is significantly greater than the temperature of the water in the heat exchanger, which benefits heat transfer.
As only a small airflow passes through the heat exchanger when the fan is off, there is no need to either produce a bypass route for air around the heat exchanger or to arrange for a low pressure drop across the heat exchanger. This allows a compact, multi-tube heat exchanger to be used.
The arrangement described may be particularly appropriate for inset fires, in which only the front surface of the fire is visible, the majority of the fire being located within a fireplace opening. In such an arrangement, when operating in the first mode, hot air from the convective space enters the room from the air openings 16, and air is drawn into the convective space from the underside of the firebox, at 18, and through the fan 26 and the heat exchanger 24. In the second mode, air exhausting from the heat exchanger 24 is blown under the firebox to exit near floor level. Air is drawn into the convective space from both the underside of the firebox, at 18, and the air openings 16.
In such circumstances, the ability to use a compact heat exchanger is a benefit as space is restricted by the size of the fireplace opening.
Although this invention is described with reference to a firebox that is rectangular in shape when viewed from above, it may also be applied to other shapes of firebox, provided the air duct 20 is located relative to the convective air opening 16 such that when operated in the second mode, air must pass across heated surfaces of the firebox before entering the duct 20.
Optimal performance may be obtained when the hot surfaces of the firebox 10 are finned to maximise heat transfer at low mass flow rates of air.

Claims (12)

  1. Claims 1. Apparatus for capturing heat from a stove, the apparatus comprising an enclosure for surrounding a firebox of a stove; an air duct connected to a convection space within the enclosure and having an opening to a space surrounding the stove; an air-water heat exchanger within the air duct, the heat exchanger having an air side and a water side and being operative to transfer r-10 heat between air on the air side and water flowing in channels in the water side; and an impeller within the duct that can operate to cause air to flow within the Q duct towards the opening; wherein in a first mode of operation air is allowed to (\J flow from the air duct to a space surrounding the stove at least partly by natural C\I convection and in a second mode, the impeller induces air to flow from the convection space duct to the air side of the heat exchanger.
  2. 2. Apparatus according to claim 1 in which air may enter the duct in the second mode, having entered the convection space and then passing over a side wall, a rear wall or a top hot surface of the firebox.
  3. 3. Apparatus according to claim 1 or claim 2 in which the impeller operates only in the second mode.
  4. 4. Apparatus for capturing heat from a stove substantially as described herein with reference to the accompanying drawings.
  5. 5. A stove comprising a firebox surrounded by apparatus for capturing heat from a stove according to any preceding claim.
  6. 6. A stove according to claim 5 in which the convection space is located between walls of the firebox that become hot in use and the enclosure.
  7. 7. A stove according to claim 6 in which the walls of the firebox include side and top walls of the firebox.
  8. 8. A stove according to any one of claims 5 to 7 in which the opening is disposed below the firebox, as may the heat exchanger and the impeller.
  9. 9. A stove according to any one of claims 5 to 8 being in the form of a stand-alone stove.
  10. 10. A stove according to any one of claims S to 8 being in the form of an insert to Q replace an open fire within a hearth. (\J
    C\J
  11. 11.A stove according to any one of claims 5 to lOin which, in the second mode, air exhausting from the heat exchanger 24 is blown under the firebox to exit near floor level.
  12. 12.A stove substantially as described herein with reference to the accompanying drawings.
GB1013371.8A 2010-08-09 2010-08-09 Transferring heat from air around a stove to water Withdrawn GB2482685A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB1013371.8A GB2482685A (en) 2010-08-09 2010-08-09 Transferring heat from air around a stove to water
GB1303800.5A GB2497029B (en) 2010-08-09 2011-08-01 Transferring heat from solid-fuel stoves
PCT/GB2011/051449 WO2012020240A1 (en) 2010-08-09 2011-08-01 Transferring heat from solid-fuel stoves

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB1013371.8A GB2482685A (en) 2010-08-09 2010-08-09 Transferring heat from air around a stove to water

Publications (2)

Publication Number Publication Date
GB201013371D0 GB201013371D0 (en) 2010-09-22
GB2482685A true GB2482685A (en) 2012-02-15

Family

ID=42931397

Family Applications (2)

Application Number Title Priority Date Filing Date
GB1013371.8A Withdrawn GB2482685A (en) 2010-08-09 2010-08-09 Transferring heat from air around a stove to water
GB1303800.5A Expired - Fee Related GB2497029B (en) 2010-08-09 2011-08-01 Transferring heat from solid-fuel stoves

Family Applications After (1)

Application Number Title Priority Date Filing Date
GB1303800.5A Expired - Fee Related GB2497029B (en) 2010-08-09 2011-08-01 Transferring heat from solid-fuel stoves

Country Status (2)

Country Link
GB (2) GB2482685A (en)
WO (1) WO2012020240A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102013005970A1 (en) * 2012-06-10 2013-12-12 novaTec Elektronik GmbH Heat system for heating building with e.g. domestic hot water, has hot gas channel conveying hot gas heated from hot gas generator to heat exchanger, and hot water channel conveying liquid secondary medium from heat exchanger

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2044441A (en) * 1979-02-16 1980-10-15 Skaenninge Ventilations Ab Water heating arrangements in stoves
US4424934A (en) * 1981-04-06 1984-01-10 Wilhoite Murray O Hot water heating system
JPS6023728A (en) * 1983-07-18 1985-02-06 Matsushita Electric Ind Co Ltd Hot-water floor heating apparatus
GB2459348A (en) * 2009-01-09 2009-10-28 Kinxerg Ltd Apparatus for capturing heat from a stove to selectively heat room air and/or water for central heating with failsafe operation

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2044441A (en) * 1979-02-16 1980-10-15 Skaenninge Ventilations Ab Water heating arrangements in stoves
US4424934A (en) * 1981-04-06 1984-01-10 Wilhoite Murray O Hot water heating system
JPS6023728A (en) * 1983-07-18 1985-02-06 Matsushita Electric Ind Co Ltd Hot-water floor heating apparatus
GB2459348A (en) * 2009-01-09 2009-10-28 Kinxerg Ltd Apparatus for capturing heat from a stove to selectively heat room air and/or water for central heating with failsafe operation

Also Published As

Publication number Publication date
GB2497029A (en) 2013-05-29
GB201013371D0 (en) 2010-09-22
GB201303800D0 (en) 2013-04-17
WO2012020240A1 (en) 2012-02-16
GB2497029B (en) 2015-02-11

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