Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLOW-THROUGH TANKLESS WATER HEATER WITH FLOW SWITCH AND HEATER
CONTROL SYSTEM
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates to an electrically powered,
tankless, demand responsive water heater.
2- DESCRIPTION OF THE PRIOR ART
Electrically operated water heaters generally are known in
the prior art, and include many common features. Many of these
are directed to tankless, or instantaneous, type heaters for
heating water only when hot water is demanded. Energy saving
benefits of such an arrangement are sufficiently discussed in the
prior art, and will not be repeated herein. Examples of these
patents which illustrate features relevant to the present
invention include in U.S. Pat. Nos. 3,351,739, issued to Hanford
L. Eckman on November 7, 1967; 3, 795, 789, issued to Tulio Malzoni
et al. on March 5, 1974; 4,459,465, issued on July 10, 1984 to
Earl J. Knight; 4,567,350, issued on January 28, 1986 to Alvin
E. Todd, Jr. ; 4, 604, 515, issued to Mel Davidson on August 5,
1986; 4,638,147, issued to Anthony Dytch et al. on January 20,
1987; 5,020,127, issued on May 28, 1991, to Harry Eddas et al.;
5,129,034, issued to Leonard Sydenstricker on July 7, 1992; and
U.K. Pat. No. 471,730, issued on September 3, 1937, to Alfred
Reginald Shepherd.
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Eckman '739 illustrates staged energization of electrical
electrical heating elements, a step-down control circuit
transformer, and a high temperature cutout switch.
Control of electrical power by a flow switch, and water
heaters sufficiently compact to be built into a building wall or
interior partition are taught in Malzoni et al. '789, Todd, Jr.
'350 and the U.K. reference '730. The flow switch disclosed in
the U.K. reference includes a plunger displaced by water flow.
It is known to employ solid state switches to control
electrical current to the heating elements. Examples are seen
in Davidson '515 and Dytch et al. '147. The latter reference
teaches mounting solid state switches on a wall of the heating
chamber, thereby recovering heat generated by these switches.
This reference also teaches locating a temperature sensor at the
outlet of the heater.
Further location of electrical components on a flat heating
chamber wall is shown in Knight '465, wherein disc type switches
are featured.
The use of triacs as switches, and control of the triacs by
optotriacs is shown in Davidson '515 and Eddas '127.
Sydenstricker ' 034 discloses a pressure control valve, a one
way check valve, a pressure relief valve, and pressure initiated
heating control.
None of the above inventions an patents, taken either singly
or in combination, is seen to describe the instant invention as
claimed.
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SUMMARY OF THE INVENTION
An electrically operated tankless water heater is disclosed
for connection to AC electric power. The tankless water heater
includes a pressure vessel having a flat front wall for
receiving, heating, and discharging water to be heated. An inlet
conduit conducts unheated water into the pressure vessel. An
outlet conduit discharges heated water from the pressure vessel.
A plurality of electric heating elements is axially disposed
within the pressure vessel. A flow switch is attached to the
inlet conduit exteriorly of the pressure vessel. The flow switch
has a plunger displaced by water flowing into the tankless water
heater, and means completing an electrical circuit to a control
system. Power is thereby provided to and activates the control
system.
The tankless water heater also includes a control system
responsive to power being supplied thereto through the flow
switch. The control system includes a source of DC power for
supplying control power. First and second voltage divider
circuits are each connected to the DC power source and to a
ground. A thermally responsive variable resistor is connected
in series in the first voltage divider circuit and disposed to
monitor and respond to temperature within the pressure vessel.
The control system has at least one power switching subcircuit
which includes a comparator for monitoring the two voltage
divider circuits and controlling a driver in response thereto.
The driver responds to the comparator and drives an optotriac.
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The optotriac is driven by the driver for controlling a power
triac. The power triac is controlled by the optotriac for
switching AC electric power to the plurality of electric heating
elements.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a front elevational view of the novel water
heater, as assembled.
Fig. 2 is an isometric view of the pressure vessel and major
electrical control components, shown partially exploded.
Fig. 3 is a cross sectional detail view of the flow switch,
drawn to enlarged scale.
Fig. 4 is an electrical schematic of the novel water heater.
Fig. 5 is a diagrammatic, cross sectional detail view of a
water diverting baffle within the pressure vessel of the novel
water heater.
Fig. 6 is a perspective detail view of the flow switch
plunger, drawn to enlarged scale.
Similar reference characters denote corresponding features
consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A tankless water heater is provided which is extremely
compact, applies and discontinues electrical power in close
proportion to demand for heat, eliminates voltage drop when
energizing the heating elements, and which provides safety and
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control features which enable virtually all of the power and
control circuitry to be deenergized when the heater is not
actively heating water.
The particular combination of features employed herein has
enabled design of a practical preferred embodiment to be
realized. This preferred embodiment provides a compact package,
with respect to exterior dimensions, as yet not achieved in prior
art heaters of the same general heat output. A preferred
embodiment provides up to 22 kilowatts of heat in four equal
incremental steps of heating, yet measures only 24 inches in
height, 5.5 inches in width, and 4 inches in depth (61 cm in
height, 14 cm in width, and 10 cm in depth).
The design is long lived, and a model of the preferred
embodiment has surpassed rigorous testing conducted by
Underwriters Laboratories, Inc. (UL), and is now listed under
File E142552.
The maj or components of the novel water heater include a box
like pressure vessel having flat sides, a water inlet at the
bottom, and water outlet at the top thereof; four heating
elements and a uncomplicated yet effective electronic control
system incorporating a temperature sensor and two overtemperature
switches. The temperature sensor enables electrical power to be
applied to the heating elements in proportion to heat
requirements. The overtemperature switches are safety devices,
breaking electrical connection to all downstream components in
the event of excessive heating.
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Switching of the heating elements is performed by triacs
which are controlled by optotriacs. Thus, electrical connection
of an AC power source is performed at the moment when the AC sine
wave is at zero electrical potential. Momentary voltage drop,
which manifests itself in flickering of household lights, and
which stresses utility power transformers, is avoided.
The layout of the components is crucial in realizing the
advantages of the instant water heater. The pressure vessel is
tall and thin, and, due to its flat sides, many electrical
components are mounted on a front wall thereof. These include
the aforementioned sensor and switches, which are mounted high
on the pressure vessel, so as to sense the highest temperatures
attained. This layout is important since the sensor must monitor
the final temperature of water exiting the heater, and since the
switches must monitor the highest attained water temperature.
Located low on the pressure vessel, near the coolest portion
thereof, are four triacs controlling the four heating elements.
This serves the dual purpose of transferring heat from the triacs
to water, thus cooling the triacs, and prolonging the life
thereof, and of recapturing heat which would otherwise be lost.
A control board having a step-down control transformer and
many electronic control components is also mounted on the vessel
front wall. Since so many components are mounted on the front
wall of the pressure vessel, overall height and width dimensions
of the water heater are not increased by electrical components.
Moreover, the actual control system selected results in
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sufficiently few and small components that the overall depth of
the heater is so limited that the novel heater can be mounted
inside a typical building internal wall or partition.
An important feature augmenting the layout is a water
diverting baffle located in the pressure vessel. This baffle
directs incoming cool water to flow directly against that portion
of the vessel wall on which are mounted the triacs. Thus, the
triacs are subjected to the greatest possible temperature
difference, which maximizes heat transfer therefrom.
Another important feature is a pressure responsive flow
switch which responds to even a very small volume of water flow.
This flow switch connects power to the electrical control system.
By this arrangement, two important benefits are realized. The
first benefit is that when heating is not being demanded,
virtually the entire control system has no voltage present . This
prevents injury from electrical shocks, as by contact with
exposed components, and prevents damage to sensitive components,
as by inadvertent shorts to ground. A second benefit is that the
initiating control device consumes no power when no heating is
demanded, unlike those systems requiring the initiating control
device to be constantly energized in order to accomplish its
monitoring function.
The tankless water heater 10 of the present invention is
seen assembled in Fig. 1, although not including an outer
enclosure or housing (not shown), and includes pressure vessel
12, inlet conduit 14, flow switch 16, and outlet conduit 18. A
conventional valve V is shown connected to outlet conduit 18.
Major electrical components, which will be explained in detail
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hereinafter, are seen mounted on the flat front wall 20 of
pressure vessel 12.
With reference to Fig. 2, when being used, water is heated
by four heating elements 21 which extend vertically through
pressure valve 12. Heating elements 21, which are electrically
powered resistive elements of known type, are installed from the
bottom of pressure vessel 12, and are formed integral with flange
23.
When not in use, no water f lows through water heater 10 , and
no electrical power is consumed. Operation of the tankless water
heater 10 is dependent upon a user opening a hot water tap (not
shown), whereupon water pressure within the plumbing system (not
shown) operates flow switch 16. Turning now to Fig. 3, flow
switch 16 is seen to have inlet and outlet fittings 22 and 24,
respectively. Fittings 22 and 24 are preferably threaded to
enable ready conventional assembly. A plunger 26 is constrained
by sleeve 28 to move only vertically, as seen in this view. A
yoke 30 formed in plunger 26 retains an arm 32 in contact
therewith. Arm 32 is pivotally mounted at 34, and, when it
pivots, trips a limit switch 36 to complete a power circuit to
the control system (described hereinafter).
Even slight displacement of plunger 26 by water flow enables
water to flow into a chamber 38 formed in flow switch 16, and
then on towards outlet fitting 24. This is enabled by
construction of plunger 26, seen in greater detail in Fig. 6.
Vertical travel of arm 32, and therefore, vertical travel
of plunger 26, are limited by interference at points 40 and 42
of the body of flow switch 16.
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Referring to Fig. 6 plunger 26 has a head 44 which prevents
flow of water past plunger 26. Below head 44 are walls 46 which
maintain plunger 26, centered and true within sleeve 28 (see Fig.
3?, but which allow water to flow into chamber 38 (see Fig. 3)
Operation of the control system will now be discussed, with
reference to Fig. 4. When limit switch 36 closes, AC power from
one of the main power circuits completes a circuit, fused at 48,
to the primary side 50 of a step-down transformer 52. The
secondary side 54 of transformer 52 feeds AC power at reduced
voltage to a bridge 56. Bridge 56 rectifies the reduced voltage
AC power to DC power, which DC power is then conditioned by
smoothing capacitor 58 and voltage regulator 60 to provide
steady, limited voltage DC power to the rest of the control
system. Thus the AC source, transformer 52, bridge 56, smoothing
capacitor 58, and voltage regulator 60 combine to provide a
source of DC power for control purposes from the AC power circuit
provided for heating. It will be appreciated that the electrical
components employed herein are well known within the art, and
need not be explained in detail herein. Accordingly, overall
function of the control system will be summarized, and specific
functions will not explained in detail.
DC power then feeds two voltage divider circuits 62 and 64.
First voltage divider circuit 62 includes a thermistor 66 in
series therein, and the second voltage divider circuit includes
a manually adjustable potentiometer 68 in series therein.
Voltage divider circuit 62 includes a resistor 70 and divider
circuit 64 includes four resistors 72. Both voltage divider
circuits 62,64 are grounded at 74.
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Four comparators 76 are connected to voltage divider
circuits 62 and 64. Each comparator 76 monitors voltage divider
circuit 64 at a different segment thereof, due to location of its
respective connection to voltage divider circuit 64 relative to
resistors 72. Each comparator 76 provides.input controlling a
driver 78, which in turn drives an optotriac 80, which in turn
controls a power triac 82. Power triac 82 switches AC power to
an associated heating element 21. Each electrically connected
combination of one comparator 76, one driver 78, one optotriac
10 80, and one power triac 82 defines a power switching subcircuit
84.
In the illustrated embodiment, there are four power
switching subcircuits 84 controlling four heating elements 21.
In a preferred embodiment, heating elements 21 consume 5500 watts
each, for a total heat output of 22 kilowatts . They are fed from
two AC circuits having a potential of 240 volts, nominal, line
to line. One AC circuit is connected to power terminals 86 and
88, and the other AC circuit is connected to power terminals 90
and 92. Power connected to flow switch l6 is arbitrarily taken
from one AC circuit, in the present case connection being to
terminals 86 and 88.
In the event of a problem leading to overheating of water
within pressure vessel 12, overtemperature switches 94 provide
two pole breaking of the 240 volt power circuits. In the
preferred embodiment, snap action switches, in which a metallic
element flexes when heated above a predetermined temperature, and
separates appropriate contacts, serve well in this capacity.
Either switch 94 will deenergize all downstream electrical
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components in the circuit being switched thereby. If both
switches 94 trip, all power is removed from all downstream
components.
Returning to Fig. 1, the location of major electrical
components will be discussed. Terminal blocks 96 of various
types are illustrated in their actual location, but serve merely
for convenience in making necessary electrical connections in
order to practice the present invention, and are not inherently
important. Therefore, such terminal blocks are shown, but will
not be discussed. Thermistor 66 is mounted at the tap of
pressure vessel flat front wall 20. Below are snap action
switches 94 and a control board 98 supporting step-down
transformer 52 and some electronic components. Power triacs 82
are seen to be among those components located at the lowest
portion of pressure vessel front wall 20.
Controlling such a level of power imposes a significant
cooling burden on power triacs 82. In the preferred embodiment,
a triac manufactured by Teccor Company, Irving, Texas, model
Q4040J9, which is rated by the manufacturer at 40 amperes, 240
volts, has proved satisfactory. Using this component, the
cooling burden is the heat equivalent of 15 watts . Since the
novel tankless water heater 10 is intended for mounting within
a building wall or partition, convective cooling is unreliable
at best.
Mounting power triacs 82 on pressure vessel 12 solves this
problem by providing a heat sink. To optimize the value of this
heat sink, power triacs 82 are mounted at a point proximate inlet
conduit 14, so that unheated water will hasten heat transfer.
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And, as seen in Fig. 5 a water diverting baffle 100 is mounted
within pressure vessel 12 to direct water to flow directly
against flat front wall 20, near power triacs 82.
It will thus be seen that a tankless water heater is
provided which heats water responsive only to actual flow of
water. Power is controlled by selectively and sequentially
energizing heating elements 21 in four discrete steps, according
to demand. If the control system should fail, and excessive
heating occurs, thermally responsive switches 94 will shut off
all power to both heating elements 21 and to the control system.
The present invention thus provides and extremely compact
source of limitless heated water which utilizes no power when
dormant, which responds quickly to demand, which provides maximum
safety when exposed by removal of its cover, which prolongs the
life of heat generating components, which avoids objectionable
voltage spikes when energizing heating elements, which responds
to any quantity of water flow, and which consumes power in
proportion to demand.
It is to be understood that the present invention is not
limited to the sole embodiment described above, but encompasses
any and all embodiments within the scope of the following claims .
