Note: Descriptions are shown in the official language in which they were submitted.
CA 02354242 2001-06-15
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CANADA
APPLICANTS: NAZIR DOSANI and NIZAR LADHA
TITLE: HVAC controller
CA 02354242 2001-06-15
-1-
POWER CONTROLLER DEVICE
Field of the Invention
This invention relates to a power controller device for controlling electrical
power
consumed by resistive load devices, such as electric water heaters, electric
baseboard
heaters, brick heaters and the like.
Background of the Invention
Large electrical utilities use several different kinds of generating means to
generate
electrical power.
These include hydro electric and nuclear, as well as coal and oil fired
generators.
Generally, hydro electric and nuclear power generators provide the base energy
required
and coal and oil fired generators are operated only during "on-peak" load
periods when
larger amounts of electricity are required to meet additional demand. The
additional
energy generated during the on-peak periods by oil and coal fired generators
tends to be
more expensive for the utility companies to generate. Therefore, the utility
companies
greatly benefit to the extent that power consumption can be shifted from "on-
peak"
periods to "off peak" periods when demand for electrical power is lower.
In addition, hydro electric and nuclear generators must operate continuously
and cannot
be turned off even when the power generated by these generators is not needed.
This
condition, when the general power consumption drops below the power which is
capable
of being produced by the continuous generating means, is generally called
"free
wheeling". Any energy not used during these periods is wasted. In addition, it
is not
always possible to predict when "free wheeling" conditions will exist.
Power controller devices have previously been developed in attempts to shift
the power
demands from onpeak periods to off peak periods. Such prior art power
controller
devices have essentially comprised timers which turned electrical resistive
load devices
on and off, so that the load devices were off during on-peak periods when
electrical
power demands are high and on during oil peak periods when power demands are
lower.
There are a number of difficulties inherent in such prior art devices. First,
by only being
able to turn the load devices on and off, the prior art power control devices
did not
adequately control the resistive load devices. Secondly, because the timers
were preset,
and because the prior art power controller devices could not independently
sense free
wheeling conditions, the prior art devices could not take advantage of extra
power
available when electrical demand unexpectedly dropped.
Furthermore, because the prior art devices could only turn load devices on or
off, and
because many of these devices were synchronized with expected off peak periods
and
thus would turn their respective loads on simultaneously, sudden large demands
for
power resulted when all of the resistive load devices equipped with the prior
art timer
devices were turned on simultaneously. A similar problem, known as "fly-back",
occurs
generally when power resumes after brownouts and blackouts.
CA 02354242 2001-06-15
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Brownout, generally defined as a condition where the supply voltage drops 10%
or more,
is itself a problem due to the increase in current which accompanies a voltage
drop. In
extreme conditions the current increase, particularly if it is sudden, can
damage hydro
electric distribution stations and power-sensitive devices such as air
conditioner
compressors.
The'present invention overcomes these disadvantages by providing a power
controller
device which provides greater versatility and higher efficiency in the control
and
utilization of resistive electrical devices. The present invention in a
preferred embodiment
includes voltage sensing means for detecting a voltage drop in the power
supply and
comparator means for deactivating the load when the voltage drop exceeds a
preselected
value, such as 10% of nominal voltage. This avoids damage to hydroelectric
equipment
and household appliances due to current overload during such conditions. The
present
invention further provides a "soft-start" function which increases power to
the load in
controlled increments, and the controller of the present invention thus offers
"fly-back"
protection after blackout and brownout conditions.
The present invention further provides a power controller which can detect and
take
advantage of "free wheeling" conditions, delivering power to the load so as to
make use
of excess electrical power which would otherwise be wasted during these time
periods.
In an embodiment of the invention for controlling the power delivered to a
water heater,
the present invention further provides means for maintaining consistency in
the
temperature of hot water delivered by the water heater through means for
bypassing a
heat exchanger, in which heat is exchanged between the cold water supply and
the hot
water output of the water heater, or through a mixing valve, by detecting when
thermal
dropoff occurs in the hot water output and closing off the flow of cold water
to
compensate.
Summary of the Invention
The present invention thus provides a power controller device comprising a
power input
means for receiving input power from an electrical power source, a power
output means
for delivering output power to a load at a predetermined power level, a power
reduction
means electrically associated with the power input means and the power output
means
operable to reduce the maximum output power level by discreet intervals,
control means
for controlling the power reduction means, and memory means for recording a
desired
output power level or temperature level or both for each of a plurality of
predetermined
periods of time.
Further more the controller reduces standby loses by heating fluid over a
period of time.
To reduce the heat loss in a gas or an alternate fuel boiler the heating is
delayed for a
period of time.
The controller also sets internal or fluid temperature in sync or pre-set
ratio to external
temperature.
CA 02354242 2001-06-15
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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;
Figure 2 is a diagrammatic view of an embodiment of the power controller of
the present
invention controlling a water heater;
Figure 3 is a schematic diagram of the power supply, voltage detection and
reset circuitry
for the power controller of Figure 1;
Figure 4 is a schematic diagram of the load switching circuitry for the power
controller of
Figure 1;
Figure 5 is a schematic diagram of the temperature sensor and stepper motor
driver
circuitry for the power controller of Figure l;
Figure 6 is a schematic diagram of the microprocessor for the power controller
of Figure
1; ;
Figure 7 is a graphic representation showing temperature as a function of
water output in
the water heater of Figure 1; and
Figure 8 is a schematic view of a utility controlled system controlling power
controller
devices within a power grid.
Detailed Description of the Invention
As shown in Figure 1, in one embodiment the present invention comprises a
power
controller device, shown generally as 10, for controlling the power consumed
by a
resistive load device, in the embodiment shown a water heater 2 such as that
described in
U. S. Patent No.
5,115,491. The power controller device 10 comprises an input power means 12,
an output
power means 14, a power reduction means 16 and a control means 18.
The input power means 12, illustrated schematically in Figure 3, is capable of
receiving
input power from an alternating current power source (not shown). This could
be any
alternating current power source, including a standard wall plug as found in
any
residential building and which derives power from the local electrical
utility.
The output power means 14 is capable of providing output power from the device
10 to a
resistive load device such as a water heater, baseboard heater, brick heater
or the like. It
will be appreciated that the resistive load device could be any electrical
device which
exhibits power consumption characteristics similar to that of a resistor. The
controller can
also be used in similar fashion to control a reactive load, such as an air
conditioner
compressor.
As shown in Figure 1, the device further comprises power reduction means 16
electrically
associated with both the pawer input means 12 and the power output means 14.
The
power reduction means 16 is operable to reduce the output power going to the
load
CA 02354242 2001-06-15
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device by discreet intervals.
Figure 3 illustrates the power input means comprising a power supply circuit
including a
bridge rectifier 50. The microprocessor 18 is stimulated to energize the power
output
means 14 by a zero crossing firing circuit 52, also shown in Figure 3, which
serves two
functions. First, firing the TRIACs at the zero crossing point of the input
signal
eliminates the effects of radio interference and surge currents, and
eliminates frequency
dependence because the firing circuit resets with each cycle of the input
signal. Second,
electrical utilities in many parts of North America are required to ensure
that at a specific
time of day (e.g. 7:00 a.m.) the average cycles per second over the previous
24 hours is
exactly 60. The zero crossing detector 52 can therefore be associated with a
counter (not
shown) which counts the number of zero crossings and resets the microprocessor
clock
circuitry 18a every 24 hours. This ensures that the controller 18, which
cannot feasibly
have a perfect clock but must be able to operate for years without servicing,
exhibits only
negligible deviation from true time because any deviation is automatically
corrected on a
daily basis.
Figure 3 also illustrates the voltage detection circuit 22, which detects
changes in the
supply voltage and signals the microprocessor 18 when the voltage drops below
a preset
level, preferably 10% of the nominal supply voltage, to interrupt the output
power during
brownout conditions; and signals the microprocessor to increase the output
power level
when the voltage rises above a preset limit, in the case of a 240V supply for
example
257V (an increase of 7% over nominal voltage), which would indicate free
wheeling
conditions. Figure 3 further illustrates a reset circuit 54 which signals the
microprocessor
18 when the supply voltage returns to within the selected limit.
Figure 4 illustrates the output power means 14 for the controller illustrated
in Figure 1,
comprising switching circuits 14a, 14b for each of the upper and lower
resistance heating
elements 3, 4 in the water heater 2. A low current (100 mA) opto-isolator 56
signalled by
the microprocessor 18 switches a heavy duty
TRIAC 58 which controls the output power to the load 2.
Figure 6 illustrates the microprocessor 18 and its associated clock circuitry
18a and
E2PROM memory 20.
As noted above, the clock 18a is associated with the zero-crossing detector 52
to maintain
accurate count of time by resetting every 24 hours when the exact number of
cycles for
that 24 hour period have been counted. The vacation and override switches SWl,
SW2
enable the user to deviate from the preset power output configuration for any
given time
period to account for absence from the household, unusually large hot water
requirements
and the like. Preferably the override function is limited to a single interval
of specified
length during any 24 hour period, to prevent constant circumvention of the
controller. An
LED indicator 60 may be provided to indicate that override is in effect.
During normal operation, the AC power used by an electrical resistive load
device is
governed by the following equation: (1) P = Irms x Vrms
CA 02354242 2001-06-15
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Furthermore, from Ohm's law, the current and voltage are dependent on the
resistance of
the resistive load device such that: (2) V = I x R and therefore (3) P =
(Vrms)2 / R or P =
{Irms)2 x R
Therefore, during normal operation, for a constant resistance and a constant
voltage, the
power consumed will also stay constant. The power consumed during normal
conditions
as shown in equation (3) will be referred to as the maximum output level to
the resistive
load device.
Most local utility companies can usually predict when the on-peak and oil peak
periods
will occur.
Therefore, the desired power output levels for predetermined time intervals
can be
recorded in the memory means 20. In this way, the desired output level could
be set close
to or at the maximum output level during traditionally ofd peak periods, such
as late night
and early morning, and at lower levels, or off, during traditionally on-peak
periods such
as daytime.
The power controller device 10 comprises memory means 20 upon which or in
which the
desired output power levels or temperature settings for a plurality of
predetermined time
intervals can be recorded. The duration of the intervals can vary, such as
from 10 seconds
to several hours, and different intervals can be selected for different times
of the day,
weekends, holidays etc. In this way, the device 10 can be programmed to output
different
power levels to the load device during specified periods of time so that power
can be
conserved during on-peak periods and the resistive load device can operate for
longer
intervals, and at higher power levels, during off peak periods.
For instance, the memory means 20 can have recorded thereon relatively higher
desired
power output levels for daytime periods during Sundays and holidays than for
normal
weekdays, since most industries are closed on Sundays and holidays and power
consumption is traditionally lower than during daytime periods during weekdays
when
energy consumption is higher. In one embodiment, the memory means 20 may be
programmed for up to 5 years in advance to provide for all anticipated onpeak
and oil
peak conditions during that period.
Therefore, device 10 can balance the needs of the consumer {delivery of power
demanded) and the needs of the utility (conservation of power at on-peak
periods) by
varying the power output level to the load device depending on traditional
power
demands.
The following are recorded in the memory means 20: 1. The date and duration of
each
time interval for the various settings of power and temperature levels,
including week
days, weekends, public holidays and desired vacation days, including four days
per year
selected by the user for deviation from normal activity; 2. The upper voltage
limit at
which free wheeling conditions are deemed to be in effect; 3. The time
intervals during
which free wheeling conditions are deemed to be in effect; 4. The lower
voltage limit at
which brownout conditions are deemed to be in effect; 5. The output power
levels for
CA 02354242 2001-06-15
each time interval, for each load controlled by the device (for example for
each of upper
and lower heating elements in a water heater 2); 6. Temperature levels for
each time
interval, for each load being controlled; 7. The by-pass valve 74 (or mixing
valve)
opening for each time interval; 8. The steps or increments of power level
increase/reduction; 9. An address for remote addressing; 10. In the case of a
water heater,
the desired temperature of hot water output to the user, responsive to
temperature sensor
T2; and 11. The time delay following which power will resume after a
brownout/blackout.
The power controller device may be remately programmable, for example through
a main
frame computer operated by the electrical utility communicating with a number
of local
area networks 72. The utility could thus remotely disable, enable or adjust
power to
appliances controlled by the power controller device 10. The utility can
communicate
with the power control devices 10 via spread spectrum utilizing power supply
lines at the
end user location, as illustrated schematically in Figure 8. Essentially, a
main frame
computer 70 controlled by the utility will be in communication with each LAN
72
through a modem, and each LAN 72 would in turn communicate with power
controller
devices 10 in the various households 74 via spread spectrum across the
twophase AC
power mains. In this fashion, the utility would effectively control power
usage in the
most power consumptive home appliances over an entire grid or neighbourhood of
electrical users. Spread spectrum is preferred, but other communication
protocols rnay be
used if desired. Power controller devices 10 could be addressed individually
or in groups,
giving the utility extremely versatile control over power consumption in any
particular
locale.
Alternatively, the memory means 20 could store, in addition to the previously
listed data,
information concerning power usage, the numbers of brownout and free wheeling
cycles,
temperature settings and on/oi~times over any specified interval. This
information can be
used to apply "fuzzy logic" to the limits recorded in the memory means 20, and
these
limits can then be changed automatically by the power controller device 10 in
accordance
with an average value taken over a preset period of time. In this situation,
it would be the
actual power usage requirements of the user which would determine the recorded
data for
upper and lower voltage limits, output power levels and temperature levels,
etc.;
essentially the power controller device would "adapt", over time, to the
particular power
usage requirements of a specific subscriber. At the same time, certain values
stored in the
memory means 20, which would be programmed either at the factory or at a depot
prior
to delivery of the device 10 to the user or power company, could be set to
remain
unaffected by power consumption at the user premises, or to stay within limits
preset by
the power company.
The power reduction means 16 reduces the power to any resistive load device
from the
maximum output level to lower output levels through conventional means such as
"cycle
stealing", which entails periodically eliminating half cycles or full cycles
from the
alternating current being supplied to the resistive load device. In this way,
both the power
consumed by the load and the power supplied by the alternating current source
are
reduced, thereby resulting in a net reduction and savings in power
consumption.
CA 02354242 2001-06-15
_ 7
Control means 18 controls the power reduction means 16. In a preferred
embodiment, the
control means 18 comprises a microprocessor running in real time. In this way,
the
control means 18 selectively directs the power reduction means 16 to deliver
power at
different power output levels for dii~erent time intervals programmed into the
device 10.
The power reduction means 16 reduces the output power level delivered to a
resistive
load device 2 by discreet intervals. For instance, in a preferred embodiment
the intervals
are equal to 10% of the maximum output level. Therefore, in this embodiment,
the power
output level will be preset at 10%, 20%,...80%, 90% or 100t of the maximum
output level
for any given interval.
As an example, power output might be set at 100% for the interval 2:00 a.m. to
5:00 a.m.,
and at 10% for the interval 8:00 a.m. to 5:00 p.m., depending upon anticipated
demand.
Other discreet intervals, such as 5% or 1% of the maximum output level, could
also be
used.
Most power utilities generate electrical power using means which operate
continuously.
Such energy generating means include hydro electric power and nuclear power.
During
some oil peak periods, the power generated by many of these continuous
generation
means exceeds that which is generally required. During these periods, turbines
located in
hydro electric facilities are allowed to turn without generating any power. As
a result,
power is wasted during these periods.
As stated above, conditions such as these, when the general energy consumption
drops
below the power which is capable of being produced by the continuous
generating means,
are generally called "free wheeling" conditions. When this occurs, it is
common for the
voltage supplied by the utility to increase marginally.
For example, in countries such as Canada and the United
States where the voltage supplied by the utility is approximately 120/240
volts, the line
voltage could increase significantly in free wheeling conditions.
In a preferred embodiment of the present invention, the device 10 comprises an
over-
voltage sensor means 22 coupled to the supply voltage detection circuit 15,
which
continuously monitors the voltage of the power entering the input power means
12. This
voltage corresponds to the voltage of the power source. The over-voltage
sensor means
22 sends a first signal S 1 to the controller means 18 when the voltage sensed
by the
detection circuit 15 exceeds a preset upper voltage. In the case of countries
where the
voltage is 120/240 volts, this preset upper voltage may be up to 132/264
volts.
When the signal S 1 is received by the control means 18, the control means 18
can
override the predetermined output level which has been recorded in the memory
means
20 for that period of time and signal the power reduction means 16 to increase
the output
power to a level above the preset output level. In this situation the output
level would
generally be increased to equal the maximum output power level and the
temperature of
CA 02354242 2001-06-15
- g
the elements 3,4 would similarly be set to the maximum. In this way, the
device 10
permits the resistive load device to use and store power (as heat) which would
be
normally lost during free wheeling conditions.
In the case of reactive devices such as air conditioners, the power controller
device 10
could activate the air conditioner during free wheeling conditions and
supercool the room
or environment, thus reducing the amount of power required to run the air
conditioner
when demand is high, because the temperature of the supercooled environment
can be
allowed to rise over time while still being within tolerable levels.
Since the temperature to which the room may be cooled can be selected by the
power
controller device 10, rather than preset at a specific level, the utility can
take advantage of
free wheeling conditions in this manner.
Similarly the "cold" could be stored as ice or otherwise, to absorb heat when
the demand
for power is high. It should be noted that the device 10 could also be
programmed to
disregard the over-voltage sensor signal Sl during some periods of the day or
night.
Once the over-voltage sensor 22 senses that the voltage of the power inputted
from the
input power means 12 has fallen below the upper voltage limit, the overvoltage
sensor 22
sends a second signal S2 to the control means 18 so that the control means 18
may
resume the predetermined power output level and temperature which was recorded
in the
memory means 20 for that time interval.
In the preferred embodiment, the device 10 further comprises a brownout and
blackout
sensor means 24 which is also responsive to the supply voltage. The brownout
and
blackout sensor means 24 could be combined as one sensor means, as shown in
Figure l,
or could be two separate sensors. The brownout and blackout sensor means 24
includes
the supply voltage detection circuit 15, which as noted above continuously
senses the
power being delivered to the input power means 12 from the alternating power
source.
The brownout and blackout sensor means 24 detects the commencement of a
brownout or
blackout as a voltage drop to the preset minimum, which may be 10% of nominal
supply
voltage, and turns the load ofl until the voltage detection circuit 15 senses
that the
brownout or blackout has ended. This assists utilities by decreasing the
general power
demand during brownouts.
When the voltage detection circuit 15 senses a resumption of supply power
above the
preset minimum after a brownout or blackout, the brownout and blackout sensor
means
24 sends a signal S3 to the control means 18. In response to the signal S3,
the control
means 18 will deliver power to a resistive load in gradually increasing
increments (of
10% in the preferred embodiment) rather than immediately increasing the output
power
to the preset output level, a so-called "soft-start". This helps to prevent
"fly-back", which
is a condition that occurs after a blackout or brownout when the power supply
resumes
and electrical devices switched on at the time of the blackout or brownout all
begin to
draw power simultaneously, creating a power surge which overloads the system
and can
cause another brownout or blackout.
CA 02354242 2001-06-15
-9-
Preferably the control means 18 further selects a short random time delay, for
example
between 1 to 30 minutes, following which it resumes delivering power to the
load after a
brownout or blackout. Alternatively, control means 18 in power controller
devices 10
controlling loads in different households in the same area can be programmed
to resume
delivering power to their respective loads after difFerent preset delay
intervals; for
example, after a brownout or blackout the power controller 10 in each
successive
household may be programmed to resume power output one minute after that of
the
previous household, until a 30 minute delay interval is reached (in the 30th
household) at
which point a 1 minute delay interval is preset for the next (31 st)
household, and so on. In
this fashion, not all of the devices 10 will resume delivering power to their
respective
load devices at the same time, which also helps to avoid fly-back.
The over-voltage sensor means 22 and the brownout and blackout sensor means 24
can
also be used to control inductive loads, such as electric motors. For example,
if the
voltage detection circuit 15 senses the voltage exceeding an upper limit, the
over-voltage
means 22 could send a signal causing a control means to turn the induction
device off.
Likewise, if the voltage detection circuit 15 senses that power has decreased
significantly,
the brownout or blackout sensor 24 could send another signal causing the
control means
to turn off the device. In this way, the inductive load would never operate
during
conditions of excess or deficient voltage, and damage to the inductive load
could be
avoided.
In a further preferred embodiment, the device 10 is connected to an electric
hot water
heater 36, as shown in Figure 2. The water heater shown is that described in
U. S. Patent No. 5,115,491, and utilizes a heat exchanger through which the
cold water
supply to the tank is heated by the hot water output from the tank. In this
embodiment,
the device 10 further comprises a temperature sensor means 30 connected to
temperature
sensors Tl, T2,
T3, T4 and T5, placement of which is illustrated in
Figure 2. Temperature sensor T 1 measures the temperature of the water leaving
the hot
water tank 40. Temperature sensor T5 measures the temperature of the cold
water
entering the hot water tank 40. The temperature of the cold water entering the
heat
exchanger 72 will vary seasonally as the temperature of the ground and/or
ground water
changes.
Accordingly, in this embodiment of the invention, to further conserve energy,
the device
will not heat the water in the tank 40 to a fixed temperature.
Rather, the water in the tank 40 will be heated to a temperature which is
greater by a
predetermined amount than the temperature of the water entering the hot water
tank 40.
For example, the difference between the target temperature for the water
leaving the hot
water tank 40 and the cold water supply entering the hot water tank 40 could
be
programmed to be 50 degrees Celsius. The temperature of the water leaving the
hot water
tank 40 will thus be slightly colder during the winter months than in the
summer months
because the cold water supply entering the hot water tank 40 is also colder
during the
CA 02354242 2001-06-15
-10-
winter months. The net result is that no further energy will be required
during the winter
season than during the summer season to heat water in the hot water tank 40.
The desired temperature difference between the water in the hot water tank 40
and the
cold water supply entering the hot water tank 40 can be predetermined at the
time of
installation of the device 10. To accommodate slight variations in ground
water
temperatures due to daily changes, the temperature of the water in the hot
water tank 40
may be determined as a function of an average of the temperatures of the water
entering
the hot water tank 40 over previous days or weeks as measured by sensor 34.
In most hot water tanks, there are two heating elements; an upper heating
element 3 and
lower heating element 4. In a preferred embodiment, the lower element 4 is not
turned on
during on-peak hours and the device 10 sends power only to the upper element
3. The
upper element 3 and the lower element 4 will both operate only at times when
maximum
power is being sent to the water heater 2, or when free wheeling conditions
are sensed by
the over-voltage sensor means 22. In these circumstances, the temperature of
the water in
the hot water tank 2 may be allowed to rise above the target temperature
determined by
the temperature of the water entering the hot water tank 2. In this way,
excess energy
created during free wheeling conditions may be stored in the form of heat
energy by
overheating the water in the hot water tank 2. The device 10 will of course be
programmed not to overheat the water beyond an upper maximum, such as 90
degrees
Celsius, to avoid scalding and damage to the tank 2.
As can be seen in Figure 7, a phenomenon associated with water heaters of this
type is
the invariable temperature drop which occurs in the hot water output
commencing after
usage of about 250 litres of water from the tank 2, which is referred to
herein as "thermal
dropoff'. Thus, in the embodiment of the invention used to control the power
consumption of the electric water heater of Figure 2, a bypass valve 70 is
provided to
route the cold water supply around the heat exchanger 72 in response to the
temperature
sensor means
TS detecting thermal dropoff in the hot water output, thus eliminating cooling
of the hot
water output and retaining a consistent output temperature. In order to
achieve a
consistent output temperature with minimal variation, the bypass valve 70 is
actuated by
a stepper motor 74 which controls the flow of cold water through the valve 70,
ie. diverts
the cold water supply from the heat exchanger 72, in precise amounts. The
stepper motor
74 is controlled by the stepper motor circuit 76 illustrated in Figure 5. In a
water heater
that does not use a heat exchanger 72, the stepper motor could be used to
control a
mixing valve (not shown) which would thus adjust a flow of cold water mixing
with the
hot water output to regulate the temperature of the output. It will be
recognized that this
aspect of the invention can be used to control fluid flow of other types as
well, for
example in gas furnaces, oil burners etc., where the desired flow rate is
dependant on the
temperature of either the device or its environment.
Figure 5 also illustrates the temperature sensor means for the controller 10
illustrated in
Figure 2.
CA 02354242 2001-06-15
-11-
Each sensor comprises a thermistor 78 with an associated voltage detector. The
microprocessor 18 is programmed with known voltage values corresponding to
temperatures within the range of the thermistors 78. Changes in temperature
are thus
detected, and if the temperature of heated water drops the soft-start process
is activated
for one or both heating elements 3,4 {in response to signals from T 1, T3 and
T4) in
accordance with the preset output requirements for that time period, or the
stepper motor
driver circuit 76, also illustrated in Figure 5, is activated (in response to
signals from T1,
T2 and TS) to effect any necessary change in the bypass valve 70 to divert
cold water
from the heat exchanger 72 and compensate for thermal dropoff. An additional
safety
function is provided by feedback signals from both temperature sensor and
motor driver
circuits 30, 76 to the microprocessor 18, which is thus alerted to any
tampering {e.g. the
motor or a sensor is shorted out or removed) and can shut down the load 2 in
response.
In a preferred embodiment, the microprocessor 18 is capable of controlling not
only the
power output to the heating elements 3, 4, but also the temperature of each
heating
element. The power control device 10 may thus be programmed to supply a
certain level
of power to each heating element, or to maintain each heating element at a
specified
temperature, or both, until hot water in the water heater reaches a specified
maximum
temperature.
In fact, the temperature to which each element will rise is independent of the
power level
output to the heating element, but the time taken by the element to reach the
preset
temperature is directly related to the output power level. It is believed that
ultimately the
most energy-efficient control will involve balancing the power output level
and the
maximum temperature of the element to achieve optimum power usage.
The slow heating process reduces the standby losses of the equipment such as
hot water
tank. Following the DOE test method for hot water tank, a slow heating process
saves
0.968KWh per 60 gal tank per day.
For tanks that use alternate fuels such as natural gas, which cannot be
controlled (When
the gas flow to the burner is slowed, the flame becomes less eWcient and
increases the
harm-full emissions.) a delay in starting the heating process reduces the
standby losses
also. Over a period of time this saving can be significant.
In wood burner the amount of air that can enter the main burner section can be
delayed or
slowed down to start the flames properly. Again, a temperature to sense the
temperature
of emissions can be used to regulate the amount of air entering the burner
section.
The controller has the further capability to set the temperature in proportion
to external or
outside temperature. The amount of hot water usage changes with the season
that is in
winter months more hot water is required while in summer months less hot water
is
required. This concept can be applied to coolers also where by the internal
temperature of
the cooler is set in proportion to external temperature. By reducing the
diiTerence in
temperature between the external enviroment and internal setting the standby
losses are
reduced, again saving energy.
CA 02354242 2001-06-15
-12-
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 with other
features and embodiments of the invention 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.
