Compact high flow rate electric instantaneous water heater

A compact instantaneous-type electric water heater for household and commercial use provides hot water at a rate of at least five gallons per minute and includes a plurality of individual heating chambers connected in series flow relationship between a cold water inlet and a hot water outlet. A metallic mixing coil is disposed in series between each adjacent pair of chambers to promote even heating. The chambers are provided with electric heating elements having a combined wattage of at least thirty-thousand (30,000) watts. The heating elements are energized by a flow switch only at the time hot water is demanded and are controlled by an adjustable thermostat which sets the outlet water temperature and by a high temperature safety switch limiting outlet water temperature should the thermostat fail. The heating elements are connected to the electrical utility system by contactor-type relays so that some of the heating elements are connected to the service side of the utility system while the others are connected to the building side of the system. An adjustable regulator is provided to assure that the water flow rate will not exceed the capacity of the heater to heat the water to a minimum acceptable level. The heater is enclosed in a sheet metal casing capable of being accomodated inside a standard wood wall between a pair of adjacent studs thereof.

FIELD OF THE INVENTION 
The present invention relates generally to the field of water heating 
apparatus, and, more particularly, to instanteous-type water heaters 
wherein water is heated immediately prior to the time it is used. 
DESCRIPTION OF THE PRIOR ART 
The conventional method of heating water for domestic use is to slowly heat 
water in a large holding tank having sufficient capacity to supply all of 
the hot water that a consumer would reasonably demand over a relatively 
long period of time. Representative dimensions of the tank are 21 inches 
in diameter and 66 inches in height. Not only does the standard water 
heater require a substantial amount of space, it also wastes energy since 
the water is kept hot at all times. 
Since the conventional water heater is especially inefficient for 
intermittent use, instantaneous-type water heaters have been developed 
which heat the water immediately prior to its use. Typically known as "in 
line heaters", they supply hot water at a rather limited flow rate. 
SUMMARY OF THE INVENTION 
It is a principal object of the present invention to replace the 
conventional bulky storage-tank water heater with a compact, space saving 
unit which also provides an unlimited supply of hot water at a high flow 
rate in sufficient volume to service an entire house. 
It is another object of the present invention to provide an 
instantaneous-type water heater which can supply heat energy at a rate of 
at least 30 kilowatts. 
A further object of the invention is to provide an instantaneous-type water 
heater which has precise temperature regulation and insures that the water 
delivered is at an even temperature. 
It is a further object to provide an instantaneous-type water heater which 
may be easily wired to accept either single or multiple sources of 
electrical power. 
A further object of the invention is to provide an instantaneous-type water 
heater having means for regulating against excessive hot water demand, 
means for limiting the water temperature in the event of thermostat 
malfunction, and means for activating the water heater only when hot water 
is desired by the consumer. 
Other objects and advantages of the invention will become apparent from the 
following detailed description and the accompanying drawings. 
In accordance with the present invention, an instantaneous water heater 
provides hot water at a high flow rate and even temperature by passing the 
water to be heated through a series of water heating chambers and means 
between the heating chambers for mixing the water so that the water tends 
to be evenly heated. In order that the instantaneous water heater consumes 
power only when the consumer demands hot water, the instantaneous water 
heater has means responsive to the flow of water to turn on electrical 
heating elements in the heating chambers. The heating elements are also 
controlled by an adjustable thermostat which sets the final temperature of 
the hot water. A high temperature sensing switch is also used as a safety 
device to turn off the heating elements if a high temperature limit is 
exceeded. To further insure that the hot water is delivered at a desired 
temperature, the instantaneous water heater includes an adjustable means 
for limiting the rate of flow of water from the heater so that the heating 
elements can always raise the water temperature to an acceptable minimum 
temperature. But this maximum flow rate is indeed quite high since 
according to an important aspect of the invention the combined power 
dissipation of the heating elements is at least thirty-thousand (30,000) 
watts, thereby providing a flow rate of at least five gallons per minute. 
The instantaneous water heater, however, may be built into a generally 
rectangular sheet metal case approximately four inches deep and fourteen 
and one-half inches wide so that it may be mounted inside a standard wood 
wall between the studs, thereby saving space. The electrical connection 
between the utility system and the heating elements is provided by 
contactor-type relays so that the heating elements may be wired to the 
electrical utility system to accommodate various sourcing configurations, 
including dual sourcing wherein some of the heating elements are connected 
to the service side of the utility system, and the other heating elements 
are connected to the building side of the utility system.

While the invention is susceptible to various modifications and alternative 
forms, a specific embodiment thereof has been shown by way of example in 
the drawings and will be described in detail herein. It should be 
understood, however, that it is not intended to limit the invention to the 
particular form disclosed, but, on the contrary, the intention is to cover 
all modifications, equivalents, and alternatives falling within the spirit 
and scope of the invention as defined by the appended claims. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawing and referring first to FIGS. 1 and 2, there is 
shown an instantaneous hot water heater generally designated 10 having a 
cold water input pipe 21, a hot water output pipe 22, and a pair of 
electrical lines 23, 24 supplying 240 volts from the service lines of the 
electrical utility system. Generally speaking, the instantaneous water 
heater 10 senses the flow of water in the cold water pipe 21 and out the 
hot water pipe 22, and when a substantial flow is present the water heater 
transfers electrical energy from the service lines 23, 24 to heat energy 
in the water flowing out the hot water pipe 22. In fact, the electrical 
power consumed at any given time is approximately that amount of power 
required to heat the quantity of water flowing out the hot water pipe 22. 
The actual heating of the water takes place in five series-connected water 
heating chambers designated 11-15. As shown, the cold water flows into the 
cold water pipe 21 after passing through a back-flow prevention valve 21a 
(which might be required by some local utility codes). The cold water then 
passes through a copper mixing pipe 31 to the top of the first heating 
chamber 11. The water flows out the bottom of the heating chamber 11 
through a second copper mixing pipe 32 to the top of the second heating 
chamber 12. Similarly, a third copper mixing pipe 33 interconnects the 
second and third heating chambers 12, 13. A short copper pipe 34 
interconnects the bottoms of the third and fourth heating chambers 13 and 
14. The top of the fourth heating chamber 14 is connected to the top of 
the last heating chamber 15 by a short length of copper pipe 35. 
The first heating chamber 11 is shown in greater detail in FIG. 3. The 
outer wall of the heating chamber is a cylindrical copper pipe 25 having 
an inlet pipe 26 brazed at its top end portion and having a funnel 27 
brazed on its bottom end. Above the inlet pipe 26 is a bleeder valve 26a 
for permitting the release of air out of the heating chamber 11 when the 
instantaneous water heater 10 is installed. The bleeder valve 26a is 
merely a machine screw and sealing washer, the machine screw being 
received by a nut brazed over a hole in the cylindrical pipe 25. The top 
end of the cylindrical pipe 25 is screwed or otherwise attached to a 
collar 28 having a bore 29 receiving a heating element generally 
designated 40. The heating element 40 is known in the trade as a Calrod 
and in the embodiment shown each of the heating elements has a six 
kilowatt rating, or 25 amperes at 240 volts (APCOM Part No. D3025H). The 
heating element 40 has electrical leads 11a, 11b which internally connect 
to an electrical heater inside a tubular rod 41. Thus, water entering the 
inlet pipe 26 flows through the cylindrical pipe 25 and passes down and 
around the heated rod 41 to the bottom funnel 27 and exits from an elbow 
pipe 42. 
The mixing coils 31-33 which precede and interconnect the first heating 
three chambers 11-13 perform a number of functions which promote even 
heating of the water. The mixing coils 31-33 serve as a temporary 
reservoir of water at room temperature so that the water delivered to the 
consumer when he first turns on his hot water faucet becomes heated to a 
hot temperature almost instantaneously. This is especially important 
during winter when the water flowing in the cold water input pipe 21 could 
be at a very low temperature, for example, about 40.degree. F. By 
temporarily storing water at room temperature in the mixing coils 31-33, 
an approximately 30.degree. F. temperature rise to room temperature is 
performed even before the consumer turns on his hot water tap. Short pipes 
34, 35 rather than mixing coils are placed between the last three heating 
chambers 13-15. If mixing coils were used in lieu of these short pipes 34, 
35, the water stored in these mixing coils would not be heated to the 
desired high temperature merely by passing through the last two heating 
chambers 14-15. In particularly severe cold weather environments, the 
mixing coils 31-33 could be kept at room temperature by wrapping them in 
electrically heated "heat tape". 
A second function performed by the mixing coils 31-33, as well as the short 
pipes 34-35, is to interconnect the heating chambers 11-15 so that the 
flow of water is disrupted as it passes by one heating element 40 to the 
next so that the water is more evenly heated. 
A third function performed by the metal mixing coils 31-33 is to 
temporarily store and exchange heat so that the water flowing out of each 
mixing coil is at a more uniform temperature than when it flowed into the 
mixing coil. In other words, a temporary surge of hot water flowing into a 
mixing coil tends to give up its heat to the metal walls of the pipe 
making up the coil so that the heat may later be absorbed by cooler water 
flowing through the coil. 
In order to assure that the water is heated to a desired high temperature, 
a thermostat switch 45 is activated by the temperature of the water 
flowing out of the last heating chamber 15 as sensed by a temperature 
sensing bulb 46' inside an enlargement 46 of the pipe from the heating 
chamber 15. The thermostat 45 has a user-adjustable control 47 calibrated 
over a range of temperature, for example 60.degree.-170.degree. F. 
(Honeywell Part No. T675A). The precise temperature control provided is 
especially desirable when the instantaneous water heater is used in 
nursing homes. Children as well as the elderly are protected from 
scalding. 
Under some conditions of extremely high flow rate, the thermostat 45 may be 
ineffective to regulate the desired water temperature if the combined 
heating capacity of the heating elements 40 is insufficient to raise the 
temperature of the cold water on the input pipe 21 to the desired 
temperature. For the embodiment shown, this is an unlikely event since the 
combined electrical dissipation of the heating elements 40 is 
thirty-thousand (30,000) watts, which is sufficient to heat at least five 
gallons of water per minute. But the possibility exists that more than one 
consumer will demand hot water at the same time which could exceed the 
five gallon per minute rate. If the flow rate is not limited, for example, 
two users could open their hot water taps expecting to receive more hot 
water, but instead they would receive more cool water. Under these 
circumstances it is usually better to receive a proportionate but smaller 
share of hot water than to receive a large share of cool water. 
So that the instantaneous water heater will always deliver hot water, a 
flow regulating valve 49 is placed in the series water connection between 
the cold water input pipe 21 and the hot water output pipe 22 as a means 
for limiting the maximum flow of water from the input pipe to the output 
pipe. Preferably an adjustable valve such as a 3/8 inch "gate valve" is 
used so that the maximum flow may be limited to a rate at which the 
heating elements can raise the water temperature to an acceptable minimum 
hot temperature, depending on the user's desired minimum hot temperature 
and the local water pressure. If 3/8 inch diameter copper pipe is used for 
the coils 31-33 and the other pipes 21, 22, 34, 35, a flow rate of up to 5 
gallons per minute may be obtained. This may be increased to 8 gallons per 
minute by using 1/2 inch diameter pipe, although in this case the total 
power dissipation of the heating elements should be 48,000 watts to heat 
the increased flow of water. 
As a safety precaution (and as might be required by some local utility 
codes) a pressure relief valve 50 is connected to vent the last heating 
chamber 15 in case of an abnormal pressure build-up. Although a pressure 
relief valve could be connected at the hot water output pipe 22, it is 
safer to locate the pressure relief valve at the bottom of the last 
heating chamber 15 since the highest temperatures and pressures are 
generated there. 
The heating elements 40 are further controlled so that they are turned off 
completely when the consumer does not require hot water. In a conventional 
tank-type water heater, the heating element may be on even though the 
consumer does not need hot water since the temperature of the water in the 
tank is always set at a hot temperature. Thus for the tank-type water 
heater there is always a heat loss through the walls of the tank to the 
outside environment, and this heat loss wastes energy. The energy loss 
ranges from about 17 to 21% for conventional electric water heaters. For 
motels, vacation homes and other locations that are infrequently occupied 
this heat loss is indeed excessive and for this reason the tank heater may 
be shut off when the premises are not occupied. Not only does this require 
intervention on the part of the consumer, but it may take considerable 
time for the water in the tank to reach a desired high temperature when 
the heater is turned back on. 
In contrast to the tank-type water heater, the instantaneous water heater 
does not use electricity during idle periods and automatically turns 
itself on when hot water is desired by the consumer and turns itself off 
after the consumer's needs have been satisfied. Thus the instantaneous 
water heater is especially suited for locations that are temporarily 
occupied. In order to sense the actual consumer demand for hot water, 
means responsive to the flow of the water activates a flow switch which 
must be on in order for the heating elements 40 to receive power from the 
power lines 23, 24. Preferrably, the flow sensing means is active when the 
flow exceeds a predetermined threshold, so that a drip or slight leak of 
water from a hot water faucet does not activate the instantaneous water 
heater. For the embodiment shown in FIG. 1, the flow is sensed by a 
pressure-sensitive switch 51 shunting the water path through the heating 
chambers 11-15 and the series-connecting pipes 31-35. Since the heating 
chambers and interconnecting pipe present a resistance to the flow of 
water, a pressure proportional to the rate of flow is generated across the 
pressure-sensing switch 51. Note that the flow regulating valve 49 is not 
part of the flow resistance, so that the flow resistance is generally 
constant. The flow switch 51 is normally open and closes when a pressure 
is generated by a flow rate exceeding the desired threshold flow. A 
representative pressure-sensing switch is the Delaval EPDISAA3 (Barksdale 
Controls Div.). 
For safety, the instantaneous water heater also has a normally-closed high 
temperature switch 52 for shutting off the heating elements 40 in the 
event that there is a malfunction of the thermostat 45. The 
high-temperature switch 52 has a factory-set threshold temperature which 
should be above the upper range of the thermostat control 47. The 
high-temperature switch 52 is placed in the last water heating chamber 15. 
The electrical components for controlling the flow of power from the power 
lines 23, 24 to the heating elements 40 are enclosed in a separate section 
generally designated 53 in the upper right-hand corner of the 
instantaneous water heater 10. The power lines 23, 24 are anchored at a 
contact block 54 which splits each main line 23, 24 into three separate 
lines leading to individual 60 amp fuses 55. For the embodiment shown, the 
power lines 23, 24 are 240 volt lines, and thus each line is 120 volts 
above ground and is separately fused. The fuses off the right-hand power 
line 24 are wired directly to terminals 11a-15a of the heating elements. 
The fuses off the left-hand power line 23 are wired to normally-open relay 
contacts which are series-connected to the other terminals 11b-15b of the 
heating element. Two relays 56 are used, each having three independent 
pairs of contacts so that each heating element is series connected to an 
individual contact. The relays 56 shown in FIG. 1 are three pole 
"contactors" rated at 30 amps per pole (48 amps resistive load) (Sylvania 
Part No. A77-309044A-2 having a 240 V coil). The coils of the contactors 
56 are wired in parallel and then series connected between a right and 
left-hand side fuse with the pressure-sensing switch 51, the thermostat 
switch 45, and the high-temperature sensitive switch 52 being wired in 
series with the contactor coils. Thus the contactors 56 are active to 
connect the heating elements 40 to the power lines 23, 24 only when the 
pressure switch 51 is closed indicating that the consumer is drawing 
water, the thermostat switch is closed indicating that the water in the 
last heating chamber 15 is colder than desired, and the high-temperature 
switch 52 is closed indicating the absence of an abnormal high temperature 
condition. 
The embodiment shown in FIG. 1 uses conventional electro-mechanical 
controls. Although solid-state controls could be substituted to provide 
more even temperature regulation, the rather high total current of 125 
amperes and the relatively high voltage of 240 volts suggest that the 
contactors 56 are more economical than triacs for controlling the 
connection of the heating elements to the electrical power source. The 
mechanical design of the water heating chambers 11-15 interconnected by 
the mixing coils 31-33 ensures that the hot water temperature is 
relatively constant despite the fact that the mechanical control system 
repetitively switches the heating elements on and off rather than 
continuously regulating the flow of power to the heating elements 40, as 
could be done with solid-state controls. 
An important advantage of the instantaneous water heater according to the 
present invention is that it may be mounted between the studs 57 inside a 
conventional wood wall. As shown in FIGS. 4 and 5, the water heater 
components all fit inside a generally rectangular sheet metal enclosure 58 
approximately 141/2 inches wide and 4 inches deep. Preferably the sheet 
metal case has generally planar mounting brackets 59 to allow either 
external or internal wall mounting for both commercial and domestic 
environments. The sheet metal cover 58a provides user access for 
adjustment and maintenance. To limit the temperature rise of the encosure 
58 when water is being heated, the heating chambers 11-15 and mixing coils 
31-33 are encased in polyurethane foam insulation (not shown) filling the 
bottom half of the enclosure 58. 
Another important feature of the present invention is that the electrical 
circuits 53 may be wired to accommodate a number of electrical source 
configurations. As shown in FIG. 6, the electrical circuits 53' are wired 
in an alternative configuration for dual sourcing wherein one source is 
the service lines 23, 24 and the second source is the building lines 61, 
62. The service lines are conventionally the lines just after the electric 
power meter while the building lines are the lines just after the main 
fuse and terminal block inside the building. Local electric codes 
sometimes specify and restrict the maximum amperage per pair of 
independent lines. The instantaneous water heater, however, may be wired 
by the electrician familiar with the local codes to accommodate the 
minimum number of independent lines required to supply the power to the 
heating elements 40. The fuses 55 and contactors 56 accept up to three 
pairs of independent lines and hence they may be wired by an electrician 
in a fashion that will satisfy practically any local electric code. The 
wiring in FIG. 6, for example, connects the building lines 61, 62 to the 
heating element terminals 13a and 13b independent of the service lines 23, 
24. It will become apparent to persons skilled in the electrical arts that 
if a sixth heating chamber is added, the six independent fuses and six 
independent pairs of relay contacts facilitates the wiring of the 
instantaneous water heater to three-phase industrial power lines by 
pairing the fuses, pairs of relay contacts, and heating elements and 
associating each pair with a respective one of the electrical phases. 
Another alternative for connecting the instantaneous water heater to the 
electrical utility system is shown in FIG. 7. Brackets 59' are spot-welded 
at the back of the case 58' for wall mounting of the unit. An aperture 65 
is provided in the back of the case 58' and is aligned with the electrical 
section 53 so that a male electrical connector 66 may plug into a female 
connector installed in the wall (not shown). This method of wall mounting 
facilitates installation and makes the instantaneous water heater a 
portable applicance, to be installed by the user at his option and 
convenience. 
As can be seen from the foregoing detailed description, the present 
invention provides an instantaneous-type water heater which is an enery 
saving improvement over the conventional tank-type water heater without 
subjecting the consumer to an unduely limited flow of hot water. The 
instantaneous water heater provides a virtually endless supply of hot 
water at a precisely controlled temperature. The electrical heating 
elements are on only when the consumer desires hot water. The 
instantaneous water heater is space saving since it may be built into the 
conventional wall of a house. The small size does not limit the flow 
capacity or power dissipation, and in fact, thirty-thousand watts of heat 
are available when the consumer turns on his hot water tap. The 
instantaneous water heater also has means for regulating against excessive 
hot water demand and has a high-temperature switch for guarding against 
thermostat malfunction.