STANDBY HEATING ELEMENT FOR A WATER HEATER

ELEMENT CHAUFFANT DE SECOURS POUR CHAUFFE-EAU

English Abstract

Abstract of the Disclosure
A water heater has a standby heating element that eliminates or greatly
reduces the cyclical energization and de-energization of the high capacity heating
elements during standby periods. The standby heating element is constantly
energized, and it is sized to compensate for the water heater heat losses during the
standby periods. The service lives of the high capacity heating elements and their
controls are thus greatly increased, and the possibility of withdrawing undesirably cool
or hot water from the water heater is eliminated.

Claims

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We claim:
1. An electric circuit for maintaining a fluid in a tank at a
substantially constant temperature between a first calibrated temperature and second
calibrated temperature lower than the first calibrated temperature comprising:
a. a source of electric power;
b. at least one heating element connected to the source of
electric power and immersed in the fluid;
c. control means for actuating the heating element between
an energized state in which the heating element transfers heat to the fluid to raise
the fluid temperature to the first calibrated temperature and a de-energized state in
which no heat is transferred to the fluid by the heating element and the fluid loses
heat such that the temperature thereof tends to fall to the second calibrated
temperature; and
d. a standby heating element connected to the source of
electric power and immersed in the fluid, the standby heating element being
continuously energized to transfer an amount of heat to the fluid substantially equal
to the heat lost by the fluid while the heating element is de-energized and the fluid
temperature tends to fall from the first to the second calibrated temperatures,
so that the standby heating element can maintain the fluid at the
constant temperature without the control means actuating the heating element.
2. In a water heater subject to heat losses during standby periods
when no hot water is withdrawn from the water heater and having at least one
heating element immersed in the water in the heater, and thermostat means for
cyclically energizing and de-energizing the heating element to transfer heat therefrom
to the water and thereby control the water temperature through a differential of the
thermostat means between predetermined high and low temperatures,
the improvement comprising a standby heating element immersed in
the water and continuously energized to compensate for the heater heat losses and
to maintain the water between the predetermined high and low temperatures during

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the standby periods and thereby substantially eliminate cyclical energizing and de-
energizing of the heating element during standby periods.
3. The improvement of claim 2 wherein the standby heating
element has a power rating of between approximately 50 and 150 watts.
4. Apparatus for heating a fluid comprising:
a. a tank for holding the fluid, the fluid losing heat during
standby periods when no fluid is withdrawn from the tank;
b. at least one first heating element immersed in the fluid;
c. control means for cyclically energizing and de-energizing
the first heating element to transfer heat to the fluid during a heating portion of the
cycle when the first heating element is energized to raise the fluid temperature to a
first calibrated temperature, the fluid temperature tending to fall to a second
calibrated temperature lower than the first calibrated temperature during a cooling
portion of the cycle when the first heating element is de-energized; and
d. a standby heating element immersed in the fluid and
continuously energized to transfer heat to the fluid in an amount substantially equal
to the fluid heat losses during the cooling portion of the cycle,
so that the fluid remains at a constant temperature during standby
periods without cyclically energizing and de-energizing the first heating element by
the control means.
5. In combination with a tank for supplying a heated fluid, and first
heating means for cyclically raising the temperature of the fluid during a standby
period when no fluid is supplied by the tank from a second calibrated temperature
to a first calibrated temperature higher than the second calibrated temperature
during a heating portion of the cycle and for allowing heat losses of the fluid during
the standby period to lower the fluid temperature from the first to the second
calibrated temperatures during a cooling portion of the cycle,

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a standby heating element immersed in the fluid, the standby heating
element continuously transferring heat therefrom to the fluid to compensate for the
heat losses of the fluid during the cooling portion of the first heating means cycle
during the standby period and thereby eliminating the cyclical raising of the fluid
temperature by the first heating means.
6. A water heater comprising:
a. a tank for holding water and having inlet and outlet ports,
the tank and water being subject heat losses during standby periods when no water
enters and leaves the tank through the inlet and outlet ports; and
b. a standby heating element immersed in the water in the
tank, the standby heating element being continuously energized and having a rating
that substantially equals the tank and water heat losses during standby periods to
thereby maintain the water temperature at a constant temperature during the standby
periods.
7. A method of heating a fluid in a tank comprising the steps of:
a. immersing at least one heating element in the fluid;
b. energizing the heating element to raise the fluid tempera-
ture from a second calibrated temperature to a first calibrated temperature higher
than the second calibrated temperature in response to the fluid temperature falling
to the second calibrated temperature because of withdrawal of fluid from the tank;
c. de-energizing the heating element when the fluid
temperature reaches the first calibrated temperature;
d. immersing a standby heating element in the fluid; and
e. continuously energizing the standby heating element to
maintain the fluid at a constant temperature between the first and second calibrated
temperatures during standby periods when no fluid is withdrawn from the tank.
8. A method of supplying a fluid at a predetermined temperature
comprising the steps of:

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a. providing a tank filled with the fluid at the predetermined
temperature;
b. determining the heat losses of the fluid during standby
periods when no fluid is supplied by the tank; and
c. continuously heating the fluid with an amount of heat
equal to the fluid heat losses,
so that the fluid remains at the predetermined temperature.

Description

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Patent
Docket 13026/9Oæ
Back~nd of the Invention
1. Field of the invention. This invention pertains to temperature
control, and more particnlarly to apparatus for contro31irlg the temperature of a fluid.
2. Description of the prior art. Yarious equipment hæ been
developed to colltrol the temperature of a fluid inside a closed vessel. For example,
domestic and commercial water heaters are well known.
Fig 1 illustrates in schematic ~orm a typic~l circuit 1 employed in aI~
electric water heater 2. The circuit 1 includes an upper heating e]ement 4 that is
controlled by a thermostat and temperature limit control combination 3. Ihe upper
heating element 4 typically has a power rating of between appro~matel~ 2500 and
5500 watts. A. similar lower heating element S and lower thermostat control 7 are
also instaUed in the water heater 2 as part of the circuit 1.
During periods when no hot water is withdrawn from the water heater
2, the standby periods, the water heater undergoes heating-cooling cycles. The
thermostat controls 3 and 7 energize thç heating elements 4 and 5, respectively, until
the- temperature of the water in the heater 2 reaches the callbrated switch-off point
of the thermostats.~ From that time, the water loses heat until the water reaches the
callbrated switch-on point of the thermostats. At that point, the heating process
starts again, and another cycle begins. The difference between the calibrated switch-
off and switch-on temperatures of the thennostats is referred to in the industry as the
difl~erential of the thermostat. The di~erential of the thermostat is an inherent
characteristic of electro-mechanical thennostats because of the very l~igh electric
currents they are required to switch. Typical ~ifferentials of the thermostat incornmercia31y availab3e water heaters range ~om approximately 8~ to 25~ F.
,

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A typical prior domestic 52 gal. electric water heater 2 undergoes a
heating-cooling cycle on the average of six times during a 24 hour standby period.
Each cycle has a small but cumu]ative adverse effect on the lives of the theImostat
controls 3 and 7 and on the heating elements 4 and 5.
Another disadvantage of the prior contro] circuits 1 is that a person
may withdraw water at the end of the cooling portion of the heating-cooling cycle.
At that point, the water may be coo]er than the person desires. A solution to that
problem is to raise the callbrated switch-off and switch-on settings of the thermostat
controLs 3 and 5 to higher temperatures. However, that solution is unsatisfactory
because of the increase risk of scalding if the person withdraws water at the end of
the heating portion of the heating-cooling cycle. In fact, the water heater industry,
in conjunction with certification agencies, has recently revised the temperature switch-
off and switch-on temperatures of eleetric water heaters from 140 F. to 120 F. in
order to reduse the potential Iisk of scalding accidents.
New temperature contro]s have been designed that reduce the
differential of the thermostat from previous ranges to approximately 6 F. to 10 F.
Nevertheless, a need rernains for improvements in water heater heating circuits.
Surnmar of the Invenbon
In accordance with the present invention, an electric water heater is
~0 provided that has greatly improved performance and safety characteristics compared
with prior water heaters. This is accomplished by designing the water heater electric
circuit with a standby heating element that compensates for heat losses during
standby periods.
The standby heating elernent is installed in the water heater elec~ric
circuit together with the conventional high capacity heating elements and their
thermostat controls. The standby heating element is constantly energized, and it has
a relatively low power output. It is sized to match the heat loss of the water in the
heater during standby periods. A typical rating for a standby heating element used
in a 52 gal. water heater is between approximately 50 and lS0 watls

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With the standby heating element, the number of heating-cooling cycles
of the heating circuit during standby periods is ~eatly reduced and eYen e~i~ated.
Consequently, the service lives of the high capacity thermostat controls and heating
elements are extended. Moreover, the elimination of the heating-cooli~g cycles
S results in a supply of hot water at a constant tempera~ure. As a consequence, the
iikelihood of a person withdrawing undesirably cool or hot water, as is coramon with
prior water heaters, is eliminated.
Other advantages, benefits, and features of the invention will become
apparent to those sl~lled in the art upon reading the detailed description of the
invention.
Brief Description of the Drawings
Fig. 1 is a schematic view of a heating circuit of a typical prior art
water heater.
Fig. 2 is a schematic view of the heating circuit of a water heater
according to the present invention.
Detailed Description of the Invention
Referring to Fig. 2, an electric circuit 11 is schematically illustrated that
includes the present invention. The electric circuit 11 is particu]arly useful when used
in conjunction with a closed vessel or tank 9 for supplying hot water for residential
and commercial uses. However, it will be understood that the invention is not limited
to liquid storage applications.
The tank 9 typically has inlet and outlet ports and a drain faucet, which
are well known and thus are not shown. The water heater tank is typically wrapped
with insulation, also not shown.
~5 To heat the water in the tank 9, the electric circuit 11 comprises an
upper heating element 4' and a lower heating element 5'. The upper heating element
4' is controlled by a known upper therrnostat and limit control combination 3'. The

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upper heating element 4' typically has a power rating of between approximatelty 2500
and 5500 watts. The electric circmt 11 further comprises a lower thermostat control
7 that controls the lower heating element 5'. The lower heating element 5' is
generally sized with a power rating of betwee~ approximately 2sno and 5500 watts.
The thermostat controls 3' arld T operate to maintain the water in the
tank 9 within a predetermined range of temperatures. When the temperature falls
to a callbrated rninimurn temperature, the controls actuate to energize the respective
heating elements, and heat is transferred from the heating elements to the water.
When the water reaches a calibrated ma~mum temperature, the controls operate to
de-energize the heating elements. From that temperature, the water eventually cools
down to the calibrated mil~imum temperature. Water cooling occurs continuously,
including during standby periods when no water is withdrawn, through conduction,convection and radiant losses. As a consequence, the controls 3' and 7' operate over
relatively long heating-cooling cycles to repeatedly reheat the water through a
differential of the thermostats between the call~rated ma~num and minimum
temperatures.
In accordance with the present invention, the electric circuit 11 is
designed with a standby heating element 13 that greatly reduces and even eliminates
cyclical operation of the thermostat controls 3' and 5' during standby penods. The
standby heating elernent 13 is irnmersed in the water in the tank 9 like the
conventional heating element. 4' and S'. The standby heating elemPnt is preferably
connected by wires 15 directly to the main switch from the power lines L1 and L2and in parallel with the heating elements 4' and 5'. In that manner, the standbyheating element is continuously energized to transfer heat therefrom to the water
~3 regardless of the state of ener~zation of the heating elements 4' and 5'.
The standby heating element 13 is sized to compensate as closely as
possible for the various heat losses from the tank 9 during standby periods. Typical
power ratings for the standby heating element are between appro~amately 50 and 150
watts. When the standby heating element is in operation, the therrnostat controls 3'
and 7' need not energize the heating elements 4' and 5', respectively, in on-offfashion during standby periods. (:onsequently, the service lives of the thermostat
.

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controls and heating elements are greatly extçnded. In additio~, water withdrawnfrom the tank 9 is always at a temperature within a much narrower range than is the
case with prior water heaters, in which the thermostat contro]s and hçating e]ements
continuously cycle through the differential of the thermostats. As a resu]t, the5 posslbility of withdrawing undesirably cool water at the end of the cooling portion of
a heating-cooling cycle and the potential danger of scalds from water withdrawn at
the end of the heating portion of a heating-cooling cycle are eliminated.
Thus, it is apparent that there has been provided, in accordance with
the invention, a standby heating element ~or a water heater that fully satis~;es the
~ims and advantages set forth above. Wh~e the invention has been descnbed in
conjunction with specific embodiments thereof, it is evident that many altematives,
modifications, a~d variations wil~ be apparent to those skilled in the art in light of the
foregoing descIiption. Accordingly, it is intended to embrace all such a~ternatives,
modifications, and var~ations as fall withiII the spirit and broad scope of the appended
15 claims.
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Representative Drawing