Note: Descriptions are shown in the official language in which they were submitted.
CA 02324669 2000-10-30
APPI,1(''ANT~~_ NAZIR DOSANI and NIZAR LADHA
T1T1,F~v Element Control Within A Hot Water Tank
CA 02324669 2000-10-30
APP1.TC'.ANT~: NAZIR DOSANI and NIZAR LADHA
TTTT,F: Element Control Within A Hot Water Tank
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Field of Invention
This invention relates to standard electric water
heaters. In particular, this invention relates to a
method and apparatus for controlling the lower
immersion (electric) element.
Background of the Invention
Maintaining a balance between a customer's needs
for hot water and a electric utility's power
1o generation capability is a major problem.
Various methods have been proposed to control the
energy used by electric hot water tanks.
Typically the hot water usage is highest during the
morning and evening, at other times, the
requirement for hot water is low.
Dosani et al. (Patent number EP0647365) shows a
2o method of controlling both elements within a tank.
The controller is made complex as both the
temperature and power to the element is controlled.
Described herein is a simpler method which is to
insert a power switch between input power and lower
immersion element to control the lower immersion
element, leaving the top immersion element to work
normally.
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This simple method, according to Ontario Hydro
report of 1995-2005 Ontario Hydro Generation Mix
Forecast" saves 1754 Kg/yr of Co2, averaged for
60ga1 and 80ga1 tanks.
Reference:
17. Incremental Energy Production - April, 1995
Forecast; ref. Banty Tezazu, Electricity
Exchange, OH.
l0 18. Fossil Emissions, Ash production and Used
Fuel Production: 1995 Fossil Business Report.
19. TSP: 1990 ratio of particulate emission to
coal ash production - 8202 Mg/836000 Mg -
0.009811.
Summarv of the Invention
The present invention thus provides a programmable
thermostat for controlling lower immersion
2o element(s~ within a electric hot water tank having
a power supply for activating upper and lower
elements according to pre-stored time schedule.
The present invention further provides a
programmable thermostat for controlling a water
heater having a power supply for activating upper
and lower elements coupled to a temperature sensor
associated with each element, the thermostat
including a voltage monitoring circuit connected to
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the power supply and being capable of being
programmed to switch from a consumption mode, in
which the thermostat deactivates the water heater
when water in the heater reaches a consumption
temperature, and a shift mode, in which the
thermostat deactivates the lower immersed element
within the water heater in response to an increase
or decrease in the power supply voltage beyond a
pre-selected level.
The present invention further provides means for
storing data within the programmable thermostat,
which sets the consumption temperature, 'shift'
mode time, input power level and the number of
elements to control. The stored data can be active
for a period of time (minutes, hours or any other
time unit), and different stored data can be active
for each time period. The length of each time
period can also be programmed.
The present invention further provides means for
communication to re-program the data stored within
the programmable thermostat.
The present invention further provides means of
controlling a mixing valve to deliver pre-mixed hot
and cold water, at required temperature, to the
dispensing fixture.
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The present invention further provides a
programmable thermostat for a water heater having
at least two heating elements for heating water in
the water tank, and switching means for activating
each heating element independently, fault detection
means for determining whether an activated heating
element is functional, and means for activating an
alternate heating element if the activated heating
element is not functional.
to
Brief Description of the Drawings
In drawings which illustrate by way of example only
a preferred embodiment of the present invention,
Figure 1 is a block diagram of one embodiment of
the present invention; and
Detailed Description of the Invention
Figure 1 illustrates the block diagram of the
programmable thermostat system including the wiring
diagram.
The water heater 10 is provided with upper and
lower heating elements 35, 45 respectively,
detachably connected to sealed receptacles (not
shown) built into the wall of tank 10. A
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temperature sensor 30, 40, such as a thermistor,
are located immediately adjacent to each of the
upper and lower heating elements 35, 45.
In a conventional water heater the upper and lower
elements 35, 45 are controlled by a thermostat
through a conventional flip-flop circuit which
alternately activates one or the other of the
elements 35, 45 according to the temperature sensed
1o by the temperature sensors 30, 40 associated with
each element. Typically the upper element 35 is
activated first, to heat water in the upper portion
of the tank 10, and during other periods the lower
element 45 is activated to bring the remaining
water in the tank 10 up to the preset consumption
temperature desired by the user, which is generally
between 50 and 60 degree C.
The upper element 35 is activated first, as it
2o heats a smaller portion (1/3) of tank 10 and thus
provides the user with hot water in shorter time.
The present invention in a preferred embodiment
utilizes a programmable thermostat 25, illustrated
in Figure 1, to control the activation of the
heating elements 35 and 45. The thermostat 25 is
connected to the temperature sensors 30 and 40
through a flip-flop circuit in micro-controller 70,
and most of the time operates in a consumption
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mode, activating and deactivating the heating
elements 35 and 45 in the conventional fashion.
According to the invention the thermostat 25
includes means for switching from consumption mode
to a shift mode. In one preferred embodiment a
timer circuit regularly switches the thermostat 25
to the shift mode at predetermined intervals.
According to another preferred embodiment of the
invention, the thermostat 25 is provided with a
voltage sensor circuit 50 which continually
monitors the supply voltage. The thermostat 25 is
programmed to detect an increase or decrease in the
supply voltage beyond a preset level, which may be
about 7o beyond the nominal supply voltage, and to
respond to such a voltage swing by switching to the
shift mode. The shift mode is active only when the
voltage is beyond the preset value.
According to another preferred embodiment of the
invention, the thermostat 25 is provided with a
voltage sensor circuit 50 which continually
monitors the supply voltage. The thermostat 25 is
programmed to detect an increase or decrease in the
supply voltage beyond a preset level, which may be
about 7o beyond the nominal supply voltage, and to
respond to such a voltage swing by switching to the
shift mode. The length of the shift mode is
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controlled by the timer circuit.
During the shift mode:
The flip-flop circuit in micro-controller 70 is
circumvented. The thermostat 25 deactivates
the lower element 45
to To prevent water at higher then consumption
temperature, if pre-set, during consumption cycle,
from reaching a dispensing fixture, a mixing valve
65, within the distribution system, is controlled
by stepper motor 67 to pre-mix cold water and hot
water from outlet 75, to reduce the temperature of
water within the distribution system.
Temperature sensor 85, as shown in figure 1, is
used to set the ratio of cold water mixed with hot
water from outlet 75 to reduce the temperature of
water within the distribution system.
In another embodiment the invention may be designed
to allow for selectively activating the shift mode
when a brownout condition detected by voltage
sensing circuit 50. Brownout condition occurs when
the line voltage drops due over demand from
electric customers. Shift mode active for the
duration of the brownout condition.
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In another embodiment the invention, timer circuit
within thermostat 25 can be activated to time the
shift cycle if required. When the timer signals
that the shift cycle is complete, the thermostat 25
automatically switches back to the consumption
mode.
Use of lower consumption temperature during peak
electrical demand time, can help the electrical
utility by lowering the demand and by setting
higher consumption or normal consumption
temperature during other times can ensure the user
does not run out of hot water.
To meet the demands of the electrical utility and
the user the following parameters have to be set
for each time period which may be minutes, hours or
any other time period:
1. Consumption temperature:
Temperature of hot water supplied to the
user at outlet 85.
2. Shift interval:
If using timer to activate shift cycle
then specify the time between the shift
cycle.
3. Voltage swings:
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Over voltage or under voltage to
start/stop the shift cycle.
4. Voltage swing duration:
Length of time that the voltage must
change for the programmable thermostat to
recognize the change.
6. Duration of each cycle:
to Different consumption cycles and shift
cycles can be programmed into the
programmable thermostat, each cycle can
have different control parameters (e. g.
consumption temperature can be different
in each consumption cycle). The time of
the cycle is entered here, the time can be
in minutes, hours or any other time unit.
The time periods and the parameters can be
2o programmed into the programmable thermostat
remotely or by a keypad (not shown) either by the
user or the electrical utility company.
In a first embodiment, in the event that the
micro-controller 70 activates a heating element 35
or 45, and after a short delay the temperature
sensed by its associated sensor 30 or 40 does not
rise, the micro-controller 70 will automatically
switch the flip-flop circuit to deactivate that
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element and activate the other of the heating
elements 35, 45 as backup. For example, if the
temperature sensor 30 senses a temperature below
the set temperature, the micro-controller 70 will
activate the heating element 35 to raise the
temperature of water in the upper portion of the
tank 10 to set the temperature. If the element 35
does not respond, a fault condition is assumed and
the micro-controller 70 will activate the element
45 automatically. A warning light may be provided
to notify the user of the faulty element 35, and
also the electrical utility company can be notified
of the fault via the remote communication means.
For this monitoring function the micro-controller
70 includes a temperature monitoring circuit, not
shown, which monitors the status of the heating
element 35 or 45 at all times when an element is
activated. In one preferred embodiment this is
2o accomplished by monitoring the temperature of the
heating elements 35, 45 through the temperature
sensor 30, 40 as described above. This monitoring
circuit is subject to a time delay of 10 to 20
seconds after activation of the element, to prevent
a "failed element" reading immediately after the
power to element is switched on, while the element
is still cool. Following this delay the
micro-controller 70 reads the temperature sensors
or 40 as an analog to digital convertor (ADC)
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count from the associated heating element 35 or 45.
The ADC output changes proportionately with the
thermistor output, so that at any time when the
element 35 or 45 is activated, after the initial
delay, if the temperature detected by the
associated sensor 30 or 40 does not increase then
the micro-controller 70 will switch the flip-flop
circuit to activate the other of the heating
elements 35, 45 (or an auxiliary element, if
provided). The micro-controller 70 can time stamp
the failed element and record the information for a
technician, and also display an alarm for the user
and also call the local electrical utility company
with fault indication.
To further enhance the thermostat 25, the heating
elements are deactivated when ever the temperature
sensors are shorted or opened by the user in an
attempt to get more hot water or water at a higher
2o temperature.
It is advantageous to provide a programmable
thermostat 25, which can be programmed locally or
by remote means to lower the maximum temperature
setting during periods when local utility
anticipates peak power demand, to promote load
shifting. This allows the elements 35, 45 to off
for a longer periods of time. The programming can
include alternate settings for weekends, vacations
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and intermittent uses (such as summer cottage),
with an optional override switch accessible to the
power utility company or the user.
It will be understood that, although various
features of the invention have been described with
respect to one or another of the embodiments of the
invention, the features and embodiments of the
invention may be combined or used in conjunction
to with other features and embodiments of the
inventions as described and illustrated herein.
Although this disclosure has described and
illustrated certain preferred embodiments of the
invention, it is to be understood that the
invention is not restricted to these particular
embodiments. Rather, the invention includes all
embodiments which are functional or mechanical
equivalents of the specific embodiments and
features that have been described and illustrated
herein.
A preferred embodiment of the invention having thus
been described by way of example only, it will be
apparent to those skilled in the art that
modifications and adaptations may be made without
departing from the scope of invention, as set out
in the appended claims.
