CA1235615A - Furnace heat exchanger - Google Patents
Furnace heat exchangerInfo
- Publication number
- CA1235615A CA1235615A CA000463521A CA463521A CA1235615A CA 1235615 A CA1235615 A CA 1235615A CA 000463521 A CA000463521 A CA 000463521A CA 463521 A CA463521 A CA 463521A CA 1235615 A CA1235615 A CA 1235615A
- Authority
- CA
- Canada
- Prior art keywords
- heat
- water
- duct
- heat exchange
- flue gases
- 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.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
- F24D12/00—Other central heating systems
- F24D12/02—Other central heating systems having more than one heat source
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
- F24D2200/00—Heat sources or energy sources
- F24D2200/16—Waste heat
- F24D2200/18—Flue gas recuperation
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
Abstract
INVENTOR: ROGER MICHAUD
TITLE: FURNACE HEAT EXCHANGER
ABSTRACT OF THE DISCLOSURE
A heat recovery system recovers heat from flue gases from a furnace or the like and a hot water cylinder. Flue gases are passed through series of chambers in which coils are located. Water is passed through the coils in a direction opposite to flue gas flow to maximise heat transfer and the heated water is passed to either a heat radiating system or into preheater tank for the hot water supply. The coils for the heat radiation and water heating are in separate circuits and the flue gases from the hot water is passed only over the coil used for water heating. Pumps are used for water recirculation in both the heat radiating circuit and the water heating circuit. The system has application to domestic and industrial furnaces which provide gaseous combustion products with recoverable thermal energy and permits the use of a small diameter exhaust vent without adversely affecting the ignition and combustion system of conventional furnaces.
TITLE: FURNACE HEAT EXCHANGER
ABSTRACT OF THE DISCLOSURE
A heat recovery system recovers heat from flue gases from a furnace or the like and a hot water cylinder. Flue gases are passed through series of chambers in which coils are located. Water is passed through the coils in a direction opposite to flue gas flow to maximise heat transfer and the heated water is passed to either a heat radiating system or into preheater tank for the hot water supply. The coils for the heat radiation and water heating are in separate circuits and the flue gases from the hot water is passed only over the coil used for water heating. Pumps are used for water recirculation in both the heat radiating circuit and the water heating circuit. The system has application to domestic and industrial furnaces which provide gaseous combustion products with recoverable thermal energy and permits the use of a small diameter exhaust vent without adversely affecting the ignition and combustion system of conventional furnaces.
Description
~' 123516~S
I~E~ RE~OVERY SYST~M
. . _ The preserlt invention relates to ~ heat recovery svstem, oarticularlv hllt not exc~usivelY ~or use with domestic furnaces fuelLed wlth gas, oil or propane.
With conventional qas, oil or ~ropane furnaces, combustion of the energy supDly usually results in the production of flue qases which retain relatively larqe amounts of heat but which are, because of their toxic nature, exhausted dieectly to atmosphere throuqh chimneys or "B" vents. This results in a considerahle wastaqe of energv and reduction in the efEiciency of the system.
A heat recovery svstem is discLosed in U.S. Patent No.
4,210,102 in which fLue gases contact a heat exchanger with a .set of water heatinq coils. The flue gases pass around the 15 coils and the water within the coils is used to heat water within a hot water heater. The heat transfer bv this areangement is relativelv inefficient because the-furnace operates independently of the water temperature so that if hot water is not being drawn from the heater much of the usable ~0 thermal enerqy in the flue gases is not recovered. Moreover, because the heat recoverv unit may~be bypassed, the outlet to atmos~here must be sized to take hot flue gases so that when reduced temperature gases are exhausted there is considerahle condensation in the chimney. Thi~s is highly undesirable and in order to reduce this effect the amount of heat extracte~ from the flue gas must be limited.
An object of the present invention is to obviate or *
~' 1235615 mitigate ~he above said disadvantages.
~ ccording to the present invention there i.s providec1 a heat recovery system comprising input means for receiving the flue gases from a furnace, convoluted passage means for directing the flow of said flue gases to an outlet, heat exchange means located in proximity to said convoluted passage means, said heat exchange means containing a heat exchange medium adaptea to receive heat energy fron, said flue gases as they flow through said heat exchange conduit.
Preferably, the heat exchange medium is water.
~ n embodiment of the present invention is presented, by way of example with reference to the accompanying drawing which is a schematic diagranm showing the general layout of a heat recovery system including the flow paths of the flue gases and the heat exchange medium.
Referring now to the drawing a heating system comprises a furnace 10 which is an atmospheric gas fired ~ot water furnace whose combustion products are exhausted into a 6 inch flue 14.
The furnace 10 supplies heat to a conventional recirculating water system 11 including a bank of radiators 13 and a pump 15 to maintain water circulation. The flue 14 is connected to an inlet duct 16 of a heat exchange unit 18 which is located in an insulated cabinet 20. The unit 18 has an outlet 21 which is connected to a 6 inch exhaust conduit 22 through which flue gases are passed to the atmosphere via a 2 inch ABS vent 23.
Connected between the inlet duct 16 and outlet is an inlet chamber 23 connected to a first generally vertical heat 123~15 exchanger chamber 2q. The lower end of chamber 24 is connected by a transverse chamber 26 to a second vertical heat exchange chanlber 28 which in turn is connecte~ by a transversc- chamt)er 2 to a third vertical heat exchange charnber 30. 'Ihe third vertical chamber 30 is connected to the outlet 20 through an exit chamber 31. Each of the vertical chambers 24, 28 and 30 are hollow cylindrical tubes of 8 inches internal diameter in which heat exchange coils are mounted.
~`he flue 51 of a conventional gas fired water heater 50 is fed through an outlet pipe 52 into the transverse chamber 29 between the vertical chambers 26, 28 so that the exhaust gases of the water heater 50 only pass through the chamber 30. ~`he water cylinder 50 receives water from the main supply 96 through a preheater tank 58 and heats and stores the water to supply it on demand to the domestic outlets.
Heat is recovered fror,l the flue gases in two separate circuits, a first heat exchange circuit 40 which includes two coil assemblies 42 and 44 located within the chambers 24, 28 respectively and~a second heat exchange circuit 46 in which a coil assembly 48 is located in the chamber 30. Each of the coil assemblies 42, 44, 48 comprises a pair of helically wound denoted by suffixes a and b respectively, which are connected in parallel and mounted one within the other.
In the first heat exchange circuit 40 the coil assemblies 42, 44 are connected in series and the circuit 40 is arranged in parallel with the system 11 such that water from the circuit 11 is pumped by a pump lS through the coil assemblies ~2~S6~5 42, 44 an~ returne~ to the low pressure side of the pump l5.
~rhe direction of flow o~ the water in the coils is from top to hottom o~ the coil a~ssembly 44 and vice versa fof coil a~sembly 42 so that the water in the coils ~lows counter the direction oF
flow of the ~lue furnace qases indicated by arrows 70. Thus in the vertical chambers 26, 28 heat from the flue gases is transferred to the water in the coil assemblies so that water enterinq the jacket oE the furnace for circulation to the radiators 13 is preheated. The counter flow circulation maximises the heat transfer to improve the efficiency of the system.
The second heat exchange circuit 46 serves to preheat the water supplied to the tank 58 from the main supply 46. A
coil 60 is located in the tank 58 and is connected by conduits 62 to opposite ends of the coil 48. A pump 52 is provided in one of the conduits 62 to provlde water~ circulation. ~lue gases passin4 through the chamber 30 transfer heat to t~e water within the coil assembly 48 and transfers heat from the flue gases to water in the tank 58. As water ls~taken from the heater S0, water heated by the circuit 46 is drawn from the heater tank 58 into the heater S0 and thus there is less enerqy required to heat the water in the heater S0 to the required temperature. A
make up valve 46b is provided between the main supply ~6 and the conduit 62 to ensure the conduits remain full at all times and to accommodate exoansion of the water as it is heated.
The transverse chamber 26, the outlet chamber 3l the exhaust conduit 22 each have drain valves 61 so that any _5_ -.
~23~6~L5 condensed water vapour can be extracted. 'I`he valves are connected by one and one-half inch diameter pioe ~2 to an open drain 66 such as is normally found in the hasernent of a house.
To ensure exhaust of the combustion products a two speed fan 67 is located in a chamber 68 of the exhaust conduit 22 to augment extraction of the Elue gases and to make the recirculation process more efficient. The fan is operated at low speed, typically 20 c.f.m. while the furnace is at idle and upon iqnition of the furnace is operated at high spped, typicallv 60c.f.m., to accommodate the increased volume of combustion products. The flow of combustion products is also regulated by a balancing damper 72 located between the chamber 30 and outlet chamber 31 and by damper 74 located in the flue 22 and a danger 78 located in the heater flue 51. With this arrangement of dangecs it has been found possible to pcovide a discharge pressure of O.S inches of water gauge in the vent pipe 23 whilst maintaininq a pressure of - 0.005 inch~s of water qauge at the combustion chamber of the furnace 10. Thus, it is possible to utilise atmospheric fired furnace.
Various modifications may be made to the embodiment described without departinq from the scope of the invention.
For example the number of coils used and the sizes and types of materials used could be varied and if desired mixing valves could be used on the heat exchangers to control the termperature at which the water is recirculated.
The opposite flow of coolant and exhaust qas ensures maximum heat recovery and hence efficiency of the heat exchange 1235~S
system and the col~ection of condensation and water vapour avoids condellsation in chimnQys and damage such as rnortar erosion. Moreover since the exhaust products flow throu~h the heat exchangers, the flue 23 may be dimensioned to provide the correet dischacge coefficient for the Elue for eorreet operation.
It will be noted that the provision of a separate heat exchanqe chamber ~oc each of the cireuits ensures that a heat sink is available whenever one of the applianees is activated.
Thus if the water heater is aetivated the heat of the exhaust gas is used to supplement the heat being supplied by the heater and similarly upon heat being required in the radiator eireuit II the furnace flue qases are used to supplement this funetion.
In tests eonducted on a prototype installation the flue gases had an initial temperature of 390F. A temperature drop of 150F was observed aeross the ehamber 28 and a further temperature drop of 100F observed aeross the ehamber 28 representing a eonsiderable energy reeovery. This was aehieved with chamber 24,28,30 of nominal diameter eiqht inches and the coil assemblies 42,44,48 having eoils of nominal 7 ineh and 5 ~0 inch diameter would from l/2 ineh diameter eopper pipe.
I~E~ RE~OVERY SYST~M
. . _ The preserlt invention relates to ~ heat recovery svstem, oarticularlv hllt not exc~usivelY ~or use with domestic furnaces fuelLed wlth gas, oil or propane.
With conventional qas, oil or ~ropane furnaces, combustion of the energy supDly usually results in the production of flue qases which retain relatively larqe amounts of heat but which are, because of their toxic nature, exhausted dieectly to atmosphere throuqh chimneys or "B" vents. This results in a considerahle wastaqe of energv and reduction in the efEiciency of the system.
A heat recovery svstem is discLosed in U.S. Patent No.
4,210,102 in which fLue gases contact a heat exchanger with a .set of water heatinq coils. The flue gases pass around the 15 coils and the water within the coils is used to heat water within a hot water heater. The heat transfer bv this areangement is relativelv inefficient because the-furnace operates independently of the water temperature so that if hot water is not being drawn from the heater much of the usable ~0 thermal enerqy in the flue gases is not recovered. Moreover, because the heat recoverv unit may~be bypassed, the outlet to atmos~here must be sized to take hot flue gases so that when reduced temperature gases are exhausted there is considerahle condensation in the chimney. Thi~s is highly undesirable and in order to reduce this effect the amount of heat extracte~ from the flue gas must be limited.
An object of the present invention is to obviate or *
~' 1235615 mitigate ~he above said disadvantages.
~ ccording to the present invention there i.s providec1 a heat recovery system comprising input means for receiving the flue gases from a furnace, convoluted passage means for directing the flow of said flue gases to an outlet, heat exchange means located in proximity to said convoluted passage means, said heat exchange means containing a heat exchange medium adaptea to receive heat energy fron, said flue gases as they flow through said heat exchange conduit.
Preferably, the heat exchange medium is water.
~ n embodiment of the present invention is presented, by way of example with reference to the accompanying drawing which is a schematic diagranm showing the general layout of a heat recovery system including the flow paths of the flue gases and the heat exchange medium.
Referring now to the drawing a heating system comprises a furnace 10 which is an atmospheric gas fired ~ot water furnace whose combustion products are exhausted into a 6 inch flue 14.
The furnace 10 supplies heat to a conventional recirculating water system 11 including a bank of radiators 13 and a pump 15 to maintain water circulation. The flue 14 is connected to an inlet duct 16 of a heat exchange unit 18 which is located in an insulated cabinet 20. The unit 18 has an outlet 21 which is connected to a 6 inch exhaust conduit 22 through which flue gases are passed to the atmosphere via a 2 inch ABS vent 23.
Connected between the inlet duct 16 and outlet is an inlet chamber 23 connected to a first generally vertical heat 123~15 exchanger chamber 2q. The lower end of chamber 24 is connected by a transverse chamber 26 to a second vertical heat exchange chanlber 28 which in turn is connecte~ by a transversc- chamt)er 2 to a third vertical heat exchange charnber 30. 'Ihe third vertical chamber 30 is connected to the outlet 20 through an exit chamber 31. Each of the vertical chambers 24, 28 and 30 are hollow cylindrical tubes of 8 inches internal diameter in which heat exchange coils are mounted.
~`he flue 51 of a conventional gas fired water heater 50 is fed through an outlet pipe 52 into the transverse chamber 29 between the vertical chambers 26, 28 so that the exhaust gases of the water heater 50 only pass through the chamber 30. ~`he water cylinder 50 receives water from the main supply 96 through a preheater tank 58 and heats and stores the water to supply it on demand to the domestic outlets.
Heat is recovered fror,l the flue gases in two separate circuits, a first heat exchange circuit 40 which includes two coil assemblies 42 and 44 located within the chambers 24, 28 respectively and~a second heat exchange circuit 46 in which a coil assembly 48 is located in the chamber 30. Each of the coil assemblies 42, 44, 48 comprises a pair of helically wound denoted by suffixes a and b respectively, which are connected in parallel and mounted one within the other.
In the first heat exchange circuit 40 the coil assemblies 42, 44 are connected in series and the circuit 40 is arranged in parallel with the system 11 such that water from the circuit 11 is pumped by a pump lS through the coil assemblies ~2~S6~5 42, 44 an~ returne~ to the low pressure side of the pump l5.
~rhe direction of flow o~ the water in the coils is from top to hottom o~ the coil a~ssembly 44 and vice versa fof coil a~sembly 42 so that the water in the coils ~lows counter the direction oF
flow of the ~lue furnace qases indicated by arrows 70. Thus in the vertical chambers 26, 28 heat from the flue gases is transferred to the water in the coil assemblies so that water enterinq the jacket oE the furnace for circulation to the radiators 13 is preheated. The counter flow circulation maximises the heat transfer to improve the efficiency of the system.
The second heat exchange circuit 46 serves to preheat the water supplied to the tank 58 from the main supply 46. A
coil 60 is located in the tank 58 and is connected by conduits 62 to opposite ends of the coil 48. A pump 52 is provided in one of the conduits 62 to provlde water~ circulation. ~lue gases passin4 through the chamber 30 transfer heat to t~e water within the coil assembly 48 and transfers heat from the flue gases to water in the tank 58. As water ls~taken from the heater S0, water heated by the circuit 46 is drawn from the heater tank 58 into the heater S0 and thus there is less enerqy required to heat the water in the heater S0 to the required temperature. A
make up valve 46b is provided between the main supply ~6 and the conduit 62 to ensure the conduits remain full at all times and to accommodate exoansion of the water as it is heated.
The transverse chamber 26, the outlet chamber 3l the exhaust conduit 22 each have drain valves 61 so that any _5_ -.
~23~6~L5 condensed water vapour can be extracted. 'I`he valves are connected by one and one-half inch diameter pioe ~2 to an open drain 66 such as is normally found in the hasernent of a house.
To ensure exhaust of the combustion products a two speed fan 67 is located in a chamber 68 of the exhaust conduit 22 to augment extraction of the Elue gases and to make the recirculation process more efficient. The fan is operated at low speed, typically 20 c.f.m. while the furnace is at idle and upon iqnition of the furnace is operated at high spped, typicallv 60c.f.m., to accommodate the increased volume of combustion products. The flow of combustion products is also regulated by a balancing damper 72 located between the chamber 30 and outlet chamber 31 and by damper 74 located in the flue 22 and a danger 78 located in the heater flue 51. With this arrangement of dangecs it has been found possible to pcovide a discharge pressure of O.S inches of water gauge in the vent pipe 23 whilst maintaininq a pressure of - 0.005 inch~s of water qauge at the combustion chamber of the furnace 10. Thus, it is possible to utilise atmospheric fired furnace.
Various modifications may be made to the embodiment described without departinq from the scope of the invention.
For example the number of coils used and the sizes and types of materials used could be varied and if desired mixing valves could be used on the heat exchangers to control the termperature at which the water is recirculated.
The opposite flow of coolant and exhaust qas ensures maximum heat recovery and hence efficiency of the heat exchange 1235~S
system and the col~ection of condensation and water vapour avoids condellsation in chimnQys and damage such as rnortar erosion. Moreover since the exhaust products flow throu~h the heat exchangers, the flue 23 may be dimensioned to provide the correet dischacge coefficient for the Elue for eorreet operation.
It will be noted that the provision of a separate heat exchanqe chamber ~oc each of the cireuits ensures that a heat sink is available whenever one of the applianees is activated.
Thus if the water heater is aetivated the heat of the exhaust gas is used to supplement the heat being supplied by the heater and similarly upon heat being required in the radiator eireuit II the furnace flue qases are used to supplement this funetion.
In tests eonducted on a prototype installation the flue gases had an initial temperature of 390F. A temperature drop of 150F was observed aeross the ehamber 28 and a further temperature drop of 100F observed aeross the ehamber 28 representing a eonsiderable energy reeovery. This was aehieved with chamber 24,28,30 of nominal diameter eiqht inches and the coil assemblies 42,44,48 having eoils of nominal 7 ineh and 5 ~0 inch diameter would from l/2 ineh diameter eopper pipe.
Claims (16)
1. A heat recovery system for recovering heat from the flue gases of a plurality of heating appliances each supplying heat to a respective heat transfer medium, said system comprising first and second interconnected duct means to receive the flue gases of respective ones of said appliances and convey the gases to a common outlet, a first heat recovery circuit operatively connected to said heat transfer medium of said first appliance and including a first heat exchange means located in said first duct and a second heat recovery circuit operatively connected to said heat transfer medium of said second appliance and including a second heat exchange means in said second duct said ducts being arranged such that one of said heat exchange means is supplied with flue gases from only one of said appliances.
2. A heat recovery system according to claim 1 wherein said first and second ducts are arranged in series so that flue gases from said first appliance pass over said second heat exchange medium.
3. A heat recovery system as according to claim 2 wherein said first duct includes a pair of discrete chambers connected in series and each having a heat exchanger located therein.
4. A heat recovery system as according to claim 3 wherein said heat exchangers in said chambers are connected in series.
5. A heat recovery system as according to claim 4 wherein each of said heat exchangers includes a pair of coolant conveying coils connected in parallel.
6. A heat recovery system according to claim 4 wherein coolant in said first circuit flows counter to the flow direction of said flue gases.
7. A heat recovery system as claimed in claim 6 wherein the heat exchange medium in said distribution system is water.
8. A heating installation comprising a first appliance to supply heat to a heat transfer medium for space heating, a second appliance to supply heat to elevate the temperature of water in a disbribution system, and a heat recovery unit for recovering heat from the combustion products of said first and second applicance, said heat recovery unit including first duct means for receiving combustion products from said first applicance, first heat exchange means located in said first duct and connected in a first heat circulation system to transfer heat from said first heat exchange means to said space heating heat transfer medium, second duct means for receiving combustion products from said second applicance and second_heat exchange means located in said second duct and connected in a second heat circulation system to transfer heat from said second heat exchange means to water in said distribution sytem.
9. A heating installation according to claim 8 wherein said space heating transfer means is water circulated in a closed loop by a pump and said first heat circulation system is connected in parallel to said closed loop and an opposite sides of said pump.
10. A heating installation according to claim 8 wherein said second heat circulation system includes a heat exchanger located in a holding tank to preheat water prior to supply to said second appliance.
11. A heating installation according to claim 8 wherein said first and second ducts are connected in series.
12. A heating installation according to claim 11 including a vent pipe downstream of said second duct and a two speed fan is connected to remove gas from said vent pipe.
13. A heating installation according to claim 12 wherein said first duct includes a pair of interconnected chambers, each of which has a heat exchange assembly located therein.
14. A heating installation according to claim 13 wherein said chambers are connected in series.
15. A heating installation according to claim 14 wherein said second duct includes a third chamber connected in series with said first and second chambers.
16. A heating installation according to claim 15 wherein flue gas from said second appliance is introduced between said second and third chambers.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000463521A CA1235615A (en) | 1984-09-18 | 1984-09-18 | Furnace heat exchanger |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000463521A CA1235615A (en) | 1984-09-18 | 1984-09-18 | Furnace heat exchanger |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1235615A true CA1235615A (en) | 1988-04-26 |
Family
ID=4128741
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000463521A Expired CA1235615A (en) | 1984-09-18 | 1984-09-18 | Furnace heat exchanger |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1235615A (en) |
-
1984
- 1984-09-18 CA CA000463521A patent/CA1235615A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |