US3536048A

US3536048A - Instantaneous hot water heater and hot air supply

Info

Publication number: US3536048A
Application number: US765042A
Authority: US
Inventors: Dean T Morgan
Original assignee: Thermo Electron Corp
Current assignee: Thermo Fisher Scientific Inc
Priority date: 1968-10-04
Filing date: 1968-10-04
Publication date: 1970-10-27
Anticipated expiration: 1987-10-27
Also published as: DE1926882A1; SE348279B; NL6909320A; BE734064A; FR2019874A1; GB1261367A

Description

United States Patent 122/(AHI) 122/(AH1) m m m m m W W .m lJ m T ,7 a mm mm d5 L m mamwmmw m m m m M m v uma w.

.m AFPA H. UDHU a corporation of Delaware [54] INSTANTANEOUS HOT WATER HEATER AND HOT AIR SUPPLY 5 ABSTRACT: A water heater f0 7 Claims, 4 Drawing figs.

r supplying hot water continu- 101; l22/33(AH1) 51 Int.Cl.................. [so

water charge is heated by a two-stage surface heater comprising a surface burner stage followed by a jet impingement stage. The apparatus includes means for producing a supply of 122/33 hot air.

[5 6] References Cited UNITED STATES PATENTS ,775 6/1908 Dupuis etal.

in as 3% ew m n Patented Oct. 27, 1970 O 0 O 0.0 O O O a -a o o o o o o 9 P 0 I 4 dVMWMhE v -4 9-\M u i M Z:

M c 23 7 A c, nor 5 &

H s5 1 8| 33 tm VALVE CONTROL MEANS 'FIG. 2

INVENTOK DEAN TMORGAN BYMWAQMIMB\WM I ATTORNEYS Patented Ot. 19 70 a Sheet FIG. 4

ATTORNEYS INSTANT ANEOUS HOT WATER HEATER AND HOT AIR SUPPLY My invention relates to heat exchangers, and particularly to a novel hot water heater that may be associated with an auxiliary air heater for supplying hot air and water at varying demand rates.

Particularly for modern residential and small commercial requirements, it is highly desirable that a hot water supply be highly compact and inexpensive as well as a reliable source of water that does not vary widely in temperature over a reasonably wide range of demand rates from a zero demand rate. The principal objects of my invention are to decrease the size and cost of hot water heaters, while increasing their efficiency and reducing the dependence ofhot water temperature on demand rate. Another object is to facilitate the provision of a supply of hot air as a byproduct of the water heating process without interfering with the temperature of the hot water supply.

The above and other objects of my invention are attained by a novel water heater construction in which a sealed tank of water is used as a thermal storage intermediate and serves directly to heat water from the cold water supply through a thin coil of copper tubing disposed in the tank and adapted to be connected to the supply. The tank is preferably a thin. flat rectangular metal box, over the wide sides of which are disposed surface heaters. Outside of the surface heaters is an insulated housing defining, with the tank walls, a gas space through which burning fuel can pass to heat the water tank. Preferably, the surface heaters are gas-fired and comprise an inlet stage consisting of a radiating surface burner followed by an outlet stage of jet impingement heating. A blower is disposed to draw gas and air through the heater, and a conventional pilot control is provided for disconnecting the fuel supply unless the pilot is lit. The temperature of the water in the 'tank is used as a control medium for regulating the flow rate of fuel to the burner. By that arrangement, the charge of water serving as a thermal storage intermediate can be maintained in a desired temperature range while the heat taken out in the water coil fluctuates with demand. And, when the water temperature is reduced by a large demand, a higher temperature is available almost immediately by simply reducing the demand.

An accessory to the water heater of my invention is an air heater comprising a heat exchanger having a vapor connection to the water tank and a condensate return line to the tank. Since the water temperature is used as the control variable, it is inmaterial whether heat is removed from the water in the tank by the hot water coil or by the air heater. Because of the heat capacity of the thermal storage intermediate, the demand rates of either can be varied over a relatively wide range without materially affecting either the hot air supply or the temperature of the hot water produced.

The water and air heating apparatus of my invention will best be understood in the light of the following detailed description, together with the accompanying drawings, of a preferred embodiment thereof.

In the drawings,

FIG. 1 is a front elevational view, with parts shown in cross section and parts broken away, of a hot water heater in accordance with my invention that is adapted to be connected to an auxiliary hot air heater;

FIG. 2 is a side view of the apparatus of FIG. 1, with parts shown in cross section and parts broken away;

FIG. 3 is a cross-sectional view in plan of the apparatus of FIG. 1, taken substantially on the lines 3-3 in FIG. 1; and

FIG. 4 is a schematic orthogonal sketch of the apparatus of FIGS. 1 through 3 shown associated with an accessory air heater in accordance with my invention, with parts broken away.

Referring to FIGS. 1 through 4, the novel air and water heater of my invention comprises a rectangular outer housing 1 of sheet metal or the like, such as carbon steel of approximately 0.035 inches in thickness. The outer dimensions of this rectangular sheet metal housing may be selected to suit the maximum hot water flow rate and temperature as desired, but for a unit suitable for supplying from 0 to 3 gallons per minute of '160F. hot water produced by heating 60F. incoming cold water, the overall outside dimensions may be 14 inches by 25 /2 by 4 /8 inches deep. Such a size is convenient for installation in space normally wasted in a house, for example, between the studs of a partition.

Within the outer metal housing 1 is a layer of insulation 3 with the illustrative dimensions cited above, the insulation is preferably a 1% inch layer of glass fiber insulating material. As best shown in FIGS. 2 and 3, on the wide sides of the insulating housing just described are

fire walls

5 and 7 of sheet metal, such as low alloy steel of 0.035 inches in thickness.

A thin flat rectangular tank generally indicated at 9 is disposed within the insulated housing described above. The tank 9 may be made from carbon steel with a wall thickness of about one-sixteenth of an inch, and, in the illustrative example given, may be 13 inches wide by 24 inches high and 2% inches deep.

The cold water supply line I1 is connected to the inlet side of a heat exchanger generally designated at 13, that may comprise inch copper tubing 15 formed into a flat open coil and sinously disposed to make eight passes in the tank 9 as shown. Preferably, the tubing 15 is provided with vertical fins l7 schematically indicated in FIGS. 1 and 2 but shown more clearly in FIG. 3 as preferably comprising 12 fins. The outer diameter of the finned portion of the tubing may be approximately 1% inches.

The output end of the tubing 15 is connected to a hot water supply line 19 leading to distributing valves schematically indicated at 21, such as the sink and tub faucets of a house, which serve to determine the demand rate for hot water at any time. The connections to the heat exchanger 13 of course pass through sealed fittings in the tank 9, for example, the lines leading into the tank may be brazed to it.

As indicated in FIGS. 1 through 3, the end walls 23 and'25 of the tank 9 are essentially in contact with the insulation 3. The bottom wall 27 rests on the insulation 3 at the bottom of the outer housing, and the top wall 29 is spaced from the insulation 3 at the top of the outer housing. The

wide side walls

31 and 33 of the tank are spaced from the fire walls 7 and '5, respectively, to provide gas passages between each

wall

31 and 33 of the tank and its adjacent fire wall.

As best shown in FIGS. 1 and 2,

openings

35 and 37 at the bottom of the outer housing admit air to the entrance end of the gas passages just described. A gas impeller having an inlet housing schematically indicated at 39 is connected to a suitable opening in the upper part of the

housing

1, 3, and an outlet port 41 suitably vented to a flue is arranged to provide a draft of gas upwardly in the passages between the tank 9 and the

fire walls

5 and 7. As schematically indicated, the gas impeller may be provided with a rotor 43 driven by a conventional electric motor 45.

Sealed within the tank 9 is a fixed charge of thermal energy storage fluid, preferably a charge 47 sufiicient to cover the heat exchanger coils, but leaving a vapor space 49 at the top of the tank. In practice, it is preferred to use purified water to which a rust inhibitor has been added as the thermal storage fluid.

As best shown in FIGS. 1 and 4, heat for an accessory source of hot air may be supplied by a closed system including a vapor line 51 connected to the tank and extending through outer insulation 53 to a heat exchanger coil schematically indicated at 55 and located in an air duct 57. An air blower generally indicated at 59 may be provided in the duct 57 to force cold air over the coils 55 and produce a stream of warm air for such purposes as hair and hand drying or for space heating. Condensate formed in the heat exchanger 55 is returned to the tank by gravity through a return line 61 provided with outer insulation 63. These fittings can be omitted if a hot air source is not desired.

A two-stage surface heater is mounted in each of the passages formed between the

fire walls

5 and 7 and the tank 9. Each such heater includes as a first stage adjacent the entrance end of each passage 5 sheet 65 of porous material. The material 65 may be ametal screen, but is preferably of relatively thick porous ceramic material such as that described in U.S. Pat. Nos. 3,l79,156 and 3,l9l,659 to Weiss et al. In operation, combustible gas flowing through the sheets 65 is ignited at the inner surface, and, by heating that surface, promotes heat transfei' by radiation as well as by conduction and convection. The incoming gas through the relatively thick porous ceramic wall is heated, reducing the temperature of the outer wall of the material.

The sheets 65 are secured at the .bottom to the lower wall of the outer housing, and at the top to brackets 67 that are in turn secured to the

fire walls

5 and 7. It will be apparent that by this arrangement gas flowing upwardly through the passages around the water tank will enter through the

openings

35 and 37 on the outsides of the porous ceramic sheets 65 and will pass through the sheets into contact with the walls of the tank 9. Then, around the baffles 67, gas will be directed to the outside of the second stage of each heater. This second stage adjacent the exit end of the passage formed adjacent the wide walls of the tank comprises a jet impingement heater section, best shown in FIGS. 2 and 3, and formed by two sheets of metal 69 provided with perforations as at 71. The sheets 69 are connected at their lower ends to flanges 73 secured to the

walls

31 and 33 of the water tank. At their upper ends, the plates 69 are secured to flanges 75 formed by bending over the upper edges of the

fire walls

5 and 7. The jet impingement heater sections function in the manner shown and described in US. application for Letters Pat. Ser. No. 446,476, filed on Mar. 29, [965 now US. Pat. No. 3,416,01 l issued Dec. 10, 1968 for Heat Exchangers by Felix .l. Lyczko, and assigned to the assignee of my application, and US. application for Letters Pat. Ser. No. 694,744, filed on Dec. 29, 1967, by Pierre J. Brosens and Dov. Z. Glucksman for Radiant and Convective Burner, and assigned to the assignee of our application.

Essentially, the second stage heater plates 69 function to direct burning gases entering from the first stage section around the battle 67 and outside of the plate 69 into jets of hot gases through the apertures 71 impinging on the walls of the tank 9. Basically, the heating jets formed by the apertures in the plates 69 serve to increase the heat transfer coefficient considerably more than the effective heat transfer surface is reduced by their introduction without materially affecting the effective temperature drop across the heat transfer surface, thus materially improving efficiency.

Fuel, and preferably natural gas, is supplied from a supply line 77, shown in FIGS. 2 and 4, through a conventional set of one or more valves schematically indicated at 79 and a pair of

supply lines

81 and 83 to two

manifolds

85 and 87 located in the entrance ends of the passages outside of the surface burner sheets 65. Fuel control may be essentially conventional in that it comprises valve control means schematically indicated at 89 for controlling the valve set 79, when a pilot 9] is lit as sensed by a temperature responsive element, and at a rate needed to maintain the temperature of the water charge 47 in the tank 9 within a predetermined range of, for example, between 190 and 200F., as sensed by a temperature sensing element 95 mounted in the tank and connected to the valve control means. Alternatively, if desired, the pressure of the water in the tank 9 may be used as the control variable.

Preferably, a relief valve 97 schematically indicated at the upper end of the water tank 9 is provided to prevent destructive bursting of the tank in the event of a malfunction involving overheating. The relief valve 97 may be connected to a vent line 99 leading outside of the building in which the heating unit is located.

A connecting slot 101 is formed in the insulation adjacent the side wall 23 of the tank 9 to form a gas passage by means of which gas admitted from the manifold 87 will be ignited when the pilot 91 is lit and gas admitted from the manifold is ignited by the pilot. The slot 101 forms a channel through which the pressure drop experienced when the gas from the manifold 85 is ignited propogates flame around through the slot 101 to the gas-air mixture on the other side of the tank.

In operation, when the valve set 79 is opened to admit gas to the

manifolds

85 and 87 and the pilot is lit, a mixture of air and gas drawn into the passages between the tank 9 and the

walls

5 and 7 will be ignited on the sides of the surface heater elements 65 adjacent the tank wall, heating the tank 9 and causing local boiling of the charge 47. Approximately 60 percent of the total fuel thermal rate is transferred to the tank 9 in this first stage, primarily by radiant heat transfer but also with some forced convection. The hot combustion gases leaving the first stages of the burners heat the tank 9 through the jet impingement stages 69, in which about 20 to 25 percent of the total fuel and thermal energy is transferred from the combustion gases to the charge 47. The location of the blower 44 downstream of the heater provides a pressure below atmosphere in the heater, thus effectively protecting against gas leakage out of the unit when it is in operation.

With the apparatus shown in FIGS. 1 and 4, including the air heater 55, heat may be drawn from the charge 47 in the tank 9 either by the air heater 55, by the heat exchanger 13 to heat the water supplied from the line 1 l, or by both. The rate of heat extracted in this manner will determine the demand for fuel made by the charge 47, as determined by its temperature sensed by the responsive element 95, and communicated to the valve control means 89. It will be apparent that the heat demands made by the hot water supply and the air heating supply can thus fluctuate fairly widely without materially effecting the temperature of the hot water supply to the line 19. i

For example, the water temperature may drop to approximately l60F. at the maximum 3 gallons per minute rate, or somewhat lower if the demand rate exceeds 3 gallons per minute, but still sufiiciently high to be useful, and rise to F. or so at a zero demand rate. Should hotter water be desired at any time when demand has lowered the temperature, merely reducing the demand will quickly supply it. In order to further smooth the operation of the system, a mixing valve may be provided in a conventional manner well understood in the art for mixing the output hot water in the line 19 with such proportions of cold water as necessary to maintain a constant temperature regardless of demand rate.

if a low demand, high temperature water source is desired, such as a F. source for coffee making or the like, an extension of the heat exchanger 13 may be provided. For example, a tee connected to the line 15, inside the tank 9 and upstream of the outlet 19, may be connected to an extra length of finned tubing leading to a second outlet line. The additional heat exchanger thus provided will inherently provide a higher water temperature at any demand rate.

While I have described my invention with respect to the details of a preferred embodiment thereof, many changes and variations will occur to those skilled in the art upon reading my description, and such can obviously be made without departing from the scope of my invention.

I claim:

1. A hot water heater, comprising a sealed rectangular metal tank, a heat exchanger mounted in said tank and adapted to be connected to a source of water to be heated, a charge of water sealed in said tank outside of and covering said heat exchanger, a vapor space in said tank over said charge of water, insulating wall means surrounding said tank and spaced at least from first and second parallel side walls of said tankto form gas passages along said first and second walls from an entrance end forming an air inlet adjacent one end of said tank to an exit end adjacent the opposite end of said tank,

surface heaters comprising flat gas permeable sheets in said passages and spaced from and parallel to said first and second walls, and means for supplying combustible gas to said entrance end.

2. The apparatus of claim 1, in which each of said heaters comprises a sheet of porous ceramic material adjacent the entrance end of each passage and a sheet of perforated metal forming a jet impingement heater section adjacent said porous ceramic sheet and said entrance end.

3. The apparatus of claim 2, further comprising an air heater, means for supplying vapor from said tank to said heater, and means for returning condensate from said heater to said tank.

4. The apparatus of claim 2, further comprising means responsive to a thermodynamic property of the water in said tank for controlling the supply of gas to said burners to maintain the value of said property within a predetermined range.

5. The apparatus of claim 1, in which said first and second walls have dimensions large with respect to the distance between them, and in which said heat exchanger comprises a flat open coil of finned metal tubing sinuously disposed in said tank.

6. A hot water heater, comprising an enclosed metal water tank, a heat exchanger in said tank, means for connecting a water supply line to said heat exchanger, a charge of water in said tank outside of and covering said heat exchanger and less in volume than the volume inside said tank and outside said heat exchanger, an insulated housing surrounding said tank and forming a bifurcated gas passage with said tank extending from an open entrance end adjacent a first end of said tank along at least first and second opposite sides of said tank to an exit end adjacent a second end of said tank opposite said first end, a two-stage surface heater mounted adjacent said first side, a two-stage surface heater mounted adjacent said second side, each of said two-stage heaters comprising as the first stage a surface burner including a sheet of porous material adjacent said entrance end and spaced from and parallel to said side to which it is adjacent, and as the second stage a sheet of metal perforated to form a jet impingement heater located between said porous sheet and said exit end and spaced from and parallel to said side to which it is adjacent, the sheets comprising each two-staged heater having approximately equal areas which together approximate the area of the side to which they are adjacent, means for admitting gas in said passage of each surface burner adjacent said entrance end, baffle means formed between each first and second stage to direct gas from said first stage outside of the sheet forming said second stage, and blower means connected to said passage at said exit end to draw air and gas through said passage.

7. In a hot water heater, a heat exchanger, means for supplying water to be heated to said heat exchanger, first wall means forming a sealed rectangular metal tank containing a charge of heat transfer fluid and enclosing said heat exchanger, said tank having two spaced opposite parallel walls having dimensions large with respect to the distance between them, second wall means forming a gas passage with said first wall means and a surface burner mounted between said first and second wall means, said burner comprising a sheet of gas-permeable ceramic material spaced from and parallel to at least one of said parallel walls.