US20130074786A1

US20130074786A1 - Gas water heater with increased thermal efficiency and safety

Info

Publication number: US20130074786A1
Application number: US13/245,184
Authority: US
Inventors: Claude Lesage; Jean-Claude Lesage
Original assignee: Miclau SRI Inc
Current assignee: Miclau SRI Inc
Priority date: 2011-09-26
Filing date: 2011-09-26
Publication date: 2013-03-28

Abstract

A gas water heater having increased thermal efficiency comprises a water tank having a sealed combustion chamber thereunder. An atmospheric burner is located in the combustion chamber. A flue pipe extends from the sealed combustion chamber and through the water tank for heat exchange of hot atmospheric gas therein with water in the water tank. A heat exchanger is in communication with the combustion gases exiting the water tank to extract residual heat from the combustion gas in the flue pipe for mixture with ambient air to produce pre-heated combustion air. An air convection or draft inducing device directs the hot combustion air from the heat exchanger through a sealed conduit to direct the pre-heated combustion air to the combustion chamber.

Description

TECHNICAL FIELD

The present invention relates to a gas water heater having increased thermal efficiency and wherein pre-heated combustion air is drawn from above the water heater housing.

BACKGROUND OF THE ART

It is known from our pending application Ser. No. 12/886,910 filed Sep. 21, 2010 to provide heat exchangers with hot water heaters whereby to extract residual heat from the flue gases exiting the water heater to heat ambient air in the surrounding space and/or to feed the recovered heat into the ducting system of the building.
It is also known in the prior art to integrate heat pumps with domestic hot water heaters wherein the hot gases are used in heat exchange with water circulated from the hot water heater to provide an added heat source to heat water and this usually results in complex devices integrated together in a single unit. A disadvantage of these integrated systems is that they are expensive to fabricate and require additional maintenance. Also, after the life cycle of the water tank it is necessary to also discard the integrated heat exchange devices. Accordingly, such hot water heaters are expensive to fabricate and maintain and the economical advantages of such systems are therefore not realizable due to added costs.
Explosion proof water heaters are also known wherein combustion air is drawn through a pipe which is elevated from the floor and wherein the combustion chamber is sealed whereby explosive gases, which are denser than air, will not enter the combustion chamber through the bottom end of the water heater and cause an explosion. However, these combustion air conduits have been known to block due to debris such as lint entering the conduit or blocking a screen at the entrance. Children may also find it convenient to introduce objects in the screen opening. It is also known to provide gas detectors on the exterior wall of the water heater and close to the bottom end thereof whereby to detect able vapors and upon detection to shut off the gas supply to the water heater.

SUMMARY OF THE INVENTION

It is a feature of the present invention to provide a gas water heater having increased thermal efficiency and which substantially overcomes the above disadvantages of the prior art.
According to a further feature of the present invention there is provided a gas water heater having increased thermal efficiency and wherein the combustion air is pre-heated prior to being introduced in the combustion chamber by heat extracted from the residual gases exiting the water heater through the flue pipe.
Another feature of the present invention is to draw the combustion air above the water heater and feed it to the bottom combustion chamber in a protected duct and with the combustion air being heated by residual heat from the flue pipe above the water heater.
Another feature of the present invention is to provide a gas water heater having increased thermal efficiency and having a sealed combustion chamber with a gas detector located externally of the water heater to detect explosive gases in the vicinity of the water heater to shut off the water heater thereby preventing explosion.
According to the above features, from a broad aspect, the present invention provides a gas water heater having increased thermal efficiency and which is comprised of a water tank having a sealed combustion chamber thereunder. An atmospheric burner is provided in the sealed combustion chamber. A flue pipe extends from the sealed combustion chamber and through the water tank for heat exchange of hot combustion gas therein with water in the water tank. A heat exchanger is in communication with the combustion gases exiting the water tank to extract residual heat from the combustion gas for mixture with ambient air to produce heated combustion air. A draft inducing means is provided to pull the hot combustion gases from the combustion chamber through the flue pipe. Conduit means is also provided to direct the pre-heated combustion air to the combustion chamber.

DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a gas water heater constructed in accordance with the present invention and provided with a heat exchanger in a top of the hot water heater and a conduit extending from the heat exchanger to the sealed combustion chamber at the bottom of the gas water heater to supply pre-heated combustion air to the combustion chamber; and

FIG. 2 is a fragmented view showing the construction of the gas water heater of the present invention as shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, there is shown generally at 10 a gas water heater constructed in accordance with the present invention. As better seen in FIG. 2 the gas water heater has a water tank which is a glass lined steel tank 11 for containing water to be heated. Cold water is admitted inside the water tank through a diptube 12 connected to a cold water inlet, herein the pressurized domestic cold water supply 13. Such supplies are equipped with a shut-off valve 14. Hot water is extracted from the tank 11 from the top end thereof through a hot water line 15, also provided with a shut-off valve 16.
In the particular embodiment of the gas water heater of the present invention a sealed combustion chamber 17 is provided under the inner tank 11 and is provided with an atmospheric gas burner 18. An outer casing 19 is provided secured spaced around the inner tank 11 and a thermal insulation, not shown, is introduced in the gap 24 between the outer casing 19 and the inner tank 11. The gas supply to the burner 18 is provided through a gas control device 20. The gas conduit 21 as well as the temperature sensor 22 and ignition unit 23 are introduced into the combustion chamber and hot water tank through sealed gaskets, not shown therein, but obvious to a person skilled in the art.
As shown in FIG. 2 hot combustion gases from the atmospheric burner exit the combustion chamber through a flue pipe 25. A baffle plate assembly 26 is mounted within the flue pipe to slow down the hot flue gases for better heat exchange of the hot flue gases with the water surrounding it contained within the water tank 11. A blower unit 27 draws the hot combustion gases through the flue pipe 25. A draft inducing means such as a small fan can replace the blower 27.
As herein shown the hot water heater of the present invention is provided with a heat exchanger 30 mounted at a top end thereof and in communication with the exit end 31 of the flue pipe exiting the top wall 32 of the outer casing 19 surrounding the inner hot water tank 11. The heat exchanger 30 is provided with a plurality of spaced-apart conduits 33 mounted in a heat exchange assembly comprised of a plurality of heat sink plates 34 for extracting heat rising in the conduits 33 from a bottom chamber 35 of the heat exchanger and exiting into an upper chamber 36 which is connected to the venting conduit 37 leading to the outside of a building containing the hot water heater whereby to release the cooled flue gases into the atmosphere. The heat exchanger 30 is herein contained within a heat exchanger housing 40 which has a portion of its sidewall 41 perforated, such as shown at 42, to provide for the admission of ambient air therein. The ambient air inside the heat exchanger housing 40 is heated by the heat exchanger 30 and drawn or pushed into a sealed conduit 45, which is better illustrated in FIG. 1, and which is in sealing contact about the outer surface 19′ of the outer casing 19.
The sealed conduit 45 draws air above the water heater and its inlet 48 is protected by the housing 40. The heated air is drawn into the sealed conduit 45 which at its lower end is secured to an air inlet port 47 of the sealed combustion chamber 17. The hot air from the heat exchanger housing 40 is drawn in to the sealed conduit 45 by the draft created by the blower unit 27 which draws air from the flue pipe and from the sealed combustion chamber thereby causing a suction in the sealed conduit 45 to create a combustion air flow. Optionally, a combustion air fan 47 may be secured at the inlet 48 of the sealed combustion conduit to create a stronger air flow through the heat exchanger housing 40. Accordingly, the air displacement means through the sealed conduit can be realised by the blower unit 27 assisted by an air combustion fan 47. The blower unit 27 may also not be necessary and the fan 47 may be sufficient to create the draft in the flue pipe together with the hot rising combustion gases. One advantage of this unit is that it can use a draft inducer instead of the blower 27 so that the pressure in the vent system could remain non-positive thus fall into Category II appliance and be vented with Category II chimney (non-positive vent static pressure—condensing). One could also use a blower and fall into Category IV appliance and be vented with Category IV chimney (positive vent static pressure—condensing).
As herein shown and described, the heat exchanger 30 an air-to-air heat exchanger fabricated from a plurality of conduits and heat sink plates, but other form of heat exchangers may be used to extract the residual heat from the flue gases and used for heating combustion air for feeding the sealed combustion chamber through the conduit 45. As also herein shown a condensate drain pipe 49 is secured to the heat exchanger 30 to evacuate condensate therefrom as the hot flue gases are cooled by the extraction of heat therefrom. Further, because the flue gases have been considerably cooled by the combination of the baffle 26 and the heat exchanger 30 the flue gases exiting the heat exchanger 30 are cooled enough to use venting conduits 37 constructed from plastic materials, such as PVC plastic piping.
Because the gas water heater of the present invention uses a sealed combustion chamber with increased thermal efficiency due to the pre-heating of combustion air and further seeing because the combustion air is taken from above the hot water heater in a protective heat exchanger housing, the combustion air flow path is from the top of the water heater down into a sealed conduit extending vertically along the sidewall of the outer casing of the water heater and into the sealed combustion chamber at the bottom thereof. Accordingly, the hot water heater is substantially sealed all along its height leading to the top heat exchanger housing 40. Therefore, any explosive gas that may leak on the floor in the lower end of the hot water heater will not enter into the combustion chamber to cause an explosion. However, to provide added security there may be provided a gas detector 50 mounted exteriorly at a lower end of the outer casing 19 to detect explosive gases close to the bottom end of the hot water heater and provide an alarm condition causing the gas control device 20 to shut off the gas supply to the burner and provide an alarm indicating that such gases have been detected and that remedial action is necessary. An added safety feature is provided by having the combustion air inlet located higher from the floor above the water heater tank in a protective housing to prevent easy access thereto.
It is within the ambit of the present invention to cover any obvious modifications of the preferred embodiment described herein provided such modifications fall within the scope of the appended claims,

Claims

1. A gas water heater having increased thermal efficiency comprising a water tank having a sealed combustion chamber thereunder, an atmospheric burner in said sealed combustion chamber, a flue pipe extending from said sealed combustion chamber and through said water tank for heat exchange of hot combustion gas therein with water in said water tank, a heat exchanger in communication with said combustion gases exiting said water tank to extract residual heat from said combustion gas for mixture with ambient air to produce pre-heated combustion air, draft inducing means to pull said hot combustion gases from said combustion chamber through said flue pipe, and conduit means to direct said pre-heated combustion air to said combustion chamber.

2. A gas water heater as claimed in claim I, wherein said conduit means is a sealed conduit, and air displacement means to displace said pre-heated combustion air into a top end of said sealed conduit and therethrough; said sealed conduit communicating, at a lower end thereof, with a combustion air inlet port of said sealed combustion chamber.

3. A gas water heater as claimed in claim 2, wherein said displacement means is a fan.

4. A gas water heater as claimed in claim 1, wherein said flue pipe is provided h baffles therein to slow said hot flue gases therein for heating said flue pipe in heat exchange with water in said water tank.

5. A gas water heater as claimed in claim wherein said heat exchanger is an air-to-air heat exchanger.

6. A gas water heater as claimed in claim 1, wherein there is further provided condensate evacuation means to evacuate condensate from said heat exchanger.

7. A gas water heater as claimed in claim 1, wherein said flue pipe above said heat exchanger is a plastic vent pipe adequate to exhaust cooled combustion gases from an outlet of said heat exchanger.

8. A gas water heater as claimed in claim 1, wherein said draft inducing means creates a combustion air flow path from a top end of said gas water heater. where combustion air is extracted and pre-heated, to be sealingly directed to said sealed combustion chamber and exhausted to atmosphere after heat extraction therefrom, said gas water heater having a gas detector exteriorly mounted at a lower end thereof to detect explosive gases to provide for an explosion proof gas water heater.

9. A gas water heater as claimed in claim 2, wherein said conduit means is a combustion air conduit sealingly secured to an outer casing of said hot water heater, said water tank being a glass lined steel tank, thermal insulation between said steel tank and said outer casing, said heat exchanger being secured in a heat exchanger housing secured above a top end of said outer casing, said heat exchanger housing having air inlet means, and a fan in said heat exchanger housing constituting said air displacement means to draw in ambient air into said heat exchanger and direct it in a top end of said combustion air conduit where it is connected to said combustion chamber for admixture with combustible fuel fed to said atmospheric burner.

10. A gas water heater as claimed in claim 2, wherein said top end of said sealed conduit is surrounded by a protective housing secured above said gas water heater water tank.

A gas water heater as claimed in claim 10, wherein said protective housing is a housing surrounding said heat exchanger.