Note: Descriptions are shown in the official language in which they were submitted.
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DEMAND MANAGEMENT FOR WATER HEATERS
BACKGROUND
The present disclosure relates generally to managing water heater systems.
More
particularly, it relates to managing and controlling water heater systems in a
manner
responsive to varying energy demand periods.
Water heater storage tanks are used for storing and supplying hot water to
households. A
typical residential water heater holds about fifty gallons (190 liters) of
water inside a steel
reservoir tank. A thermostat is used to control the temperature of the water
inside the
tank. Many water heaters permit a consumer to set the thermostat to a
temperature
between 90 and 150 degrees Fahrenheit (F) (32 to 65 degrees Celsius (C)). To
prevent
scalding and to save energy, most consumers set the thermostat to heat the
reservoir water
to a temperature in a range between 120.0 degrees F to 140.0 degrees F (about
forty-nine
degrees C to sixty degrees C).
A water heater typically delivers hot water according to the thermostat
temperature
setting. As a consumer draws water from the water heater, the water
temperature in the
water heater usually drops. Any time the thermostat senses that the
temperature of the
water inside the tank drops too far below thermostat's set point, power is
sent to the
electric resistance heating element (or a burner in a gas water heater). The
electric
elements then draw energy to heat the water inside the tank to a preset
temperature level.
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In some locations of the United States and globally, the cost for electrical
energy can vary
as a function of the time of day, day of the week and season of the year. In
areas of the
United States where energy is at a premium, utility companies often divide
their time of
use rates into off-peak and on-peak energy demand periods with a significant
rate
difference between the periods. For example, energy used during off-peak hours
may
cost the consumer in United States dollars around 5 cents to 6 cents per
kilowatt hour
(kWh), while on-peak period energy may cost anywhere from 20 cents per kWh to
$1.20
or more per kWh.
A water heater that heats based on the water demand of a typical household is
likely to
heat at the same time as when energy demand on a utility company is at its
highest. As a
result, drawing energy to heat a water heater during these on-peak energy
periods
increases a consumer's monthly energy bill. The disclosure seeks to provide a
means to
avoid on peak energy use, saving the consumer operating expense, while
supplying a
continuous supply of domestic hot water utilizing conventional and possibly
existing
electric water heating systems.
One approach to negotiate the utility companies' time of use energy rates
would be to use
a programmable timer to turn off the entire water heater or the lower element.
For
example, a clock timer could be used to provide planned heating periods during
known
off peak periods of the day. While this approach is possible, adapting to
period variation
in the rate schedule and emergency load shedding request signals from the
utility are not
accommodated.
Simply increasing the storage size of the tank and/or increasing the set
temperature of the
tank in combination with use of a thermostatic mixing valve at the hot water
outlet,
serves to increase the hot water capacity, but it does not alter the energy
consumption
pattern of the water heating system. The lower heating element will also need
to be
disengaged in order to avoid consumption during "on peak" energy rate hot
water usage.
Set point alteration is another means to reduce heating events during on peak
water usage.
While this will produce a similar outcome as disengagement of the heating
elements, it
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requires a substantially different control mechanism for regulation and
limiting of the
tank temperature and cannot be easily retrofit to an existing water heating
system.
Another approach is simply shutting the entire water heater off during on peak
energy
periods. This could result in the consumer running out of hot water during
peak hours
and left to wait until off peak hours to resume heating the entire stored
water volume of
the tank, meeting demand. This approach requires consumer behavior change or
purchase and installation of a larger storage tank size to bridge the peak
hour water usage.
This results in an investment requirement from the consumer and presumes the
availability of space to install a larger tank. Commonly, space limitation
prevents
installation of a water heater large enough to meet the storage meets to
bridge the peak
hours.
A non-replenishing tank could be used to maintain heated temperatures during
"on peak"
hours and be refilled and heated only during off peak hours. However, this
approach
requires an open tank or a means to compensate for pressure and volume
changes.
Copending U.S. Application Serial No. 12/623,753 describes a system which
provides a
continuous supply of domestic hot water to meet the needs of a consumer, while
utilizing
off peak hours for heating of the stored water. Such a system also provides a
valuable
mechanism for a utility to shed load during peak and critical power demand
periods.
Another aspect of said application is that the upper and lower heating
elements can be
enabled/disabled independently based on the demand response signal level.
Still another
aspect of the disclosure is the heating operation corresponding to the demand
response
level is consumer selectable for multiple tier signals (which may be greater
than four
levels). During low energy rate conditions, the lower element is engaged to
heat the
contents of the full tank for future use during high energy rate periods. The
lower
element is then disengaged during high energy rate periods according to the
programmed
schedule, or an external or consumer input, reducing energy consumption during
high
energy rate periods. A limitation of this system is that the stored energy can
only be used
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for hot water. If the consumer is away, or not using water that stored, energy
is
essentially wasted.
Thus there is a need for a system that can remove excess energy from the hot
water heater
when energy rates are high and store additional energy when electric rates are
low.
SUMMARY
A water heating and storage system includes an insulated tank with an upper
and lower
heating element which may be resistive heating or a heat pump, each with
independent
temperature regulating and limiting capability and a control device for
operating each
element independently. The water heater could also be fired by natural gas or
propane if
in the future the cost of those varied over time. The control is configured to
provide
heating input during low energy rate or usage conditions to minimize operating
cost. The
signal for the control indicative of the energy rate or usage condition can be
either
generated in accordance with a programmed time schedule, or an external input
signal
from the utility or energy provider indicating a change in energy cost rate or
from the
consumer/owner. The water heater is provided with a thermostatic control valve
to
provide consistent output temperatures.
A plumbing connection is also provided to allow hot water from the tank to be
diverted to
a heat exchanger before going through the thermostatic valve. This may be
accomplished
by removing the water from the hot water tank and sending it to the heat
exchanger and
returning it to the tank, or providing plumbing connections to remove the
water from the
tank and storing it in a new tank, and using a mixing valve to fill the new
tank to a
desired temperature. This allows heat transfer from the tank without mixing
the fluids.
The water is heated up to the maximum temperature allowed by the tank
construction.
Typically 170 ¨ 180F for a standard water heater, but the methods for
operating at higher
temperatures and pressure are well documented in the boiler industry. A
thermostatic
mixing valve is used at the hot discharge of the storage tank to reduce the
temperature of
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the water delivered to the user, reducing scalding risk and effectively
increasing the
thermal energy storage capacity of the system.
In one embodiment, a water heating control and storage system comprises a
first
insulated tank for holding water to be heated and a second insulated tank for
holding
water to be heated. A first plumbing connection is coupled to the first and
the second
tank, and configured to enable a first flow of water heated to a storage
temperature
greater than approximately 150 degrees F from the first tank towards the
second tank. A
heat exchanger operatively selectively coupled in a parallel in heat exchange
relationship
with the water in connection to the first and the second insulated tank for
transferring heat
from a first flow of water that is heated to another medium. The system also
comprises
an operation control device configured to receive and process a demand
response signal
and operate the first tank in at least one of a plurality of operating modes,
including at
least a water heating mode and a heat exchange mode.
These and other aspects of the present disclosure will become apparent upon a
reading of
the detail description and a review of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a water heater system in accordance with an
illustrative
embodiment of the present disclosure;
FIG. 2 is an isometric view of a water heater system in accordance with an
illustrative
embodiment of the present disclosure;
FIG. 3 is an isometric view of a water heater system in accordance with an
illustrative
embodiment of the present disclosure;
FIG. 4 illustrates a utility time of use rates for a summer season;
FIG. 5 illustrates a utility time of use rates for a winter season;
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DETAILED DESCRIPTION
Referring to FIG. 1, a water heating control and storage system 10 in
accordance with an
exemplary embodiment of the present disclosure is illustrated. The water
heater system
includes a water heater 12, a control panel 14, a mixing valve 16, and a
cutoff valve
18.
The water heater has a heater and a tank to store heated water. The water
heater includes
a shell 20, a "cold in" pipe 22, a "hot out" pipe 24, and a cover 26. The
casing surrounds
a tank 30 that acts as an interior reservoir for water. Insulation is provided
around the
exterior of the tank to reduce heat transfer. For typical domestic household
use, the tank
is preferably 80-gallon capacity or more. The cold in pipe delivers water to
the water
heater at a temperature typically 40 to 80 degrees F (4 to 27 degrees C). The
hot out pipe
conventionally delivers water away from the water heater at a temperature of
about 120
degrees F (about 49 degrees C). The cover and base seals the shell providing
an
enclosure for the tank, insulation and wiring system.
The water heater control and storage system 10 of FIG. 1 further comprises a
heat
exchanger 70 that is operatively selectively coupled in heat exchange
relationship with
the water in tank 30. In the embodiment of Figure 1, heat exchanger 70 is
connected to
the water heater 12 via a closed loop 76. The close loop 76 includes the
storage tank 30
connected to the heat exchanger 70 with a first plumbing connection 72 and a
second
plumbing connection 74. The heat exchanger 70 is provided for extracting
energy from
the water in tank 30 in accordance with an exemplary embodiment of the
disclosure.
The heat exchanger 70 is configured for efficient heat transfer from a first
medium
comprising water to another medium, which can be water, another different
fluid, air, or
metal, for example. The media may be separated by a wall (not shown) or in
direct
physical contact in some cases. The heat exchanger 70 is used in any setting
(e.g.,
industry, home use, etc.) both for cooling and/or heating. The type and size
of the heat
exchanger used can be tailored to suit a process depending on the type of
fluid, its phase,
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temperature, density, viscosity, pressures, chemical composition and various
other
thermodynamic properties.
To take advantage of low cost electricity during an off peak operating state
of an energy
provider, the water heating system 10 heats the water in the storage tank to
an above
normal temperature, e.g., above a temperature of about 150 degrees F. Thus
electric
energy provided during the off peak lower rate period is stored in the form of
heat
energy in water heated above normal storage temperature (e.g., water above 150
degrees
F). During periods of time when electricity is more expensive, the water
heating system
can be operated in an energy saving mode which would include the heat exchange
mode to transfer energy in the stored water heated above normal storage
temperature to
another medium to provide energy for the other device or function served by
the heat
exchanger at a lower cost, which is provided by the DR signals or TOU rates
sent by the
utility and received at the system further discussed below. For example, if
the heat
exchanger 70 is configured to function as source of heat for a radiator or a
forced air unit,
heat in the form of water heated above normal storage temperature is
transferred from
tank 30 to the air for heating a dwelling or building. In another example, the
heat is used
in HVAC coils for air conditioning. Liquid-to-air or air-to-liquid HVAC coils
are of a
modified cross flow arrangement. On the liquid side of these types of heat
exchangers,
the fluids are water, a water-glycol solution, steam or a refrigerant, for
example. The
present disclosure is not limited to any one type of medium, nor is the
disclosure limited
to any one type of heat exchanger for making use of energy stored in the
system 10.
In another embodiment, the heat exchanger 70 is a thermoelectric generator or
a turbine,
for example, for converting heat stored in the water heated above normal
storage
temperature to electricity. Thermoelectric generators are devices which
convert heat
differentials (e.g., heat gradients) directly into electrical energy. A
principal of operation
is based on the thermoelectric effect, which is the direct conversion of
temperature
differences to electric voltage and vice versa. A thermoelectric device
creates a voltage
when there is a different temperature on each side of junction within a close
loop, for
example. Conversely when a voltage is applied to it, a temperature difference
is created
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(known as the Peltier effect). At atomic scale (specifically, charge
carriers), an applied
temperature gradient causes charged carriers in the material, whether they are
electrons or
electron holes, to diffuse from the hot side to the cold side, similar to a
classical gas that
expands when heated; hence, the thermally-induced current. This effect can be
used to
generate electricity, to measure temperature, to cool objects, or to heat them
or cook
them. Because the direction of heating and cooling is determined by the sign
of the
applied voltage, thermoelectric devices can make good temperature controllers.
Referring again to Fig. 1, the first plumbing connection 72 comprises a hot
water
connection for providing a first flow 78 of water heated above normal storage
temperature to to heat exchanger 70 to transfer heat from the water to another
medium
within the heat exchanger. Pressure within the system 10 is substantially
constant.
Therefore, the system 10 includes a pump 80 to selectively create the first
flow 78 into
the heat exchanger 70 and a second flow 82 that returns water back to the tank
30. When
the system is operating in the normal water heating mode, pump 80 is not
energized and
the water is simply maintained at the prevailing set point temperature. For
example,
during low rate off peak states, the set point temperature may be set for the
heat storage
mode during which the water is heated to the higher than normal temperature
set point,
preferably a temperature set point greater than 150 degrees F. When operating
in the
energy saving mode, such as during a peak or high rate utility state, the
water heater set
point may be adjusted to heat the water to a more typical or normal
temperature on the
order of 120 degrees F. When in the energy saving mode, the system may also
operate in
the heat exchange mode by energizing pump 80 to circulate hot water from the
storage
tank through the heat exchanger 70. During circulation in the heat exchange
mode,
cooler water in the second flow 82 returns to the bottom of the tank in order
to keep the
water temperature stratified with the hot water at the top and cooler water at
the bottom
of the tank 30. Thus, the first flow 78 of water comprises water of a higher
temperature
than the second flow 82 of water returning to the tank 30. This difference in
temperature
results from the heat from the stored water being extracted as it moves
through the heat
exchanger and transferred to the the other medium, which flows through the
heat
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exchanger via connections 71 and 73. For example, connections 71 and 73 may be
conducting air to be heated for a forced air heating system, in which case,
air is heated by
the water heated above normal storage temperature and used as hot air to heat
the system.
In another exemplary embodiment illustrated in Fig. 2, water is not diverted
from the
water tank to the heat exchanger, but rather kept within the water tank (FIG.
2). In this
example, a low pressure loop 110 is provided with a pressure sensor 120 for
determining
a change in pressure in the case of any leakage occurring. The loop 110
comprises the
heat exchanger 70 and the pump 80, as discussed supra. The loop 110 is a
closed loop
that could comprise a glycol fluid or other fluid that is not harmful if
leaked out. The
fluid is in heat exchange relationship with the water in the tank and with
heat exchanger
70. Hot water (e.g., water heated above normal storage temperature) in the
tank is
therefore used to heat the fluid in the loop 110 for the heat exchanger 70. An
air chamber
or plenum 87 encloses heat exchanger 70. Air enters the plenum through filter
85 and
flows over the heat exchanger absorbing heat from the fluid flowing in loop
110. The
heated air exits at 81 into the environment being heated.
Hot water service is typically provided at 120 degrees F, therefore the
thermostatic
mixing valve setting is about 120 degrees F. Typical element settings are in a
range from
120 degrees F to 140 degrees F for a conventional water heater. When a water
heater is
being configured to perform under a demand response approach as described in
this
disclosure, the energy storage capacity of a water heater can be maximized by
elevating
the element setting to a maximum level greater than the normal setting, and
preferably
greater than about 150 degrees F for heating water in the tank in a heat
storing mode of
operation.
Referring back to FIG. 1, when the water heater is supplied power directly, a
thermostat
36 can provide sole control over the flow of energy to the heating elements to
maintain a
predetermined substantially stable temperature in the tank. If the thermostat
provides the
only control over the flow of energy to the water heater, then the water
heater may
operate during on-peak energy periods. To provide more control over the
operation of
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the heating elements, the water heater system includes the demand response
control panel
which is configured to disable or prevent or otherwise control energization of
the water
heater elements in response to the rate or energy usage condition information.
The water heater system further includes mixing valve 16 connected to a cold
in pipe 22
and the hot out pipe 24. The temperature of the water in the cold in pipe is
about 40
degrees F to 80 degrees F (about four degrees C to twenty-seven degrees C).
On receiving cold water from the cold in pipe and hot water from the hot out
pipe 24, the
mixing valve 16 is configured to combine the two different temperature waters
into
mixed water having a temperature selected by the user by adjusting the
temperature set
point for the mixing valve. For example, the user typically selects a set
point in the 110 ¨
120 degrees F range and in response water from the mixing valve outputs into a
service
pipe 60 at approximately the set point temperature.
The cutoff valve 18 is provided as a safety backup to the mixing valve. In
other words,
the cutoff valve is a thermostat-controlled safety device that automatically
closes if the
water in the service pipe 60 reaches a predetermined high temperature, such as
about
160.0 degrees F (about seventy-one degrees C.).
Through an interface of the control panel 14, a consumer inputs the preferred
response to
the tiered signal levels from the energy provider and/or the programmed daily
off-
pealdon-peak demand periods scheduled into a timer. The signal line also
delivers this
information into the control panel from, for example, utility companies.
The control panel 14 includes a demand response (DR) control 48 which in turn
is
connected to a transceiver 54, which is connected directly or indirectly to a
source of
utility rate information such as for example, a "smart" utility meter 42. A
power
connection is provided to the water heater system. The water tank, as well as
the control
panel is provided power from this connection. The control panel serves to
enable control
of power to the water heater and pump 80 to operate the system in the normal
mode and
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the energy saving mode, including the heat exchange mode, based on a
communication
signal to an interfaced port.
The demand response control 48 communicates via a signal line 50 from an
energy
provider, via a transceiver or hard line connection. The signal line
communicates status
information such as the response level regarding off-peak and on-peak
information from
energy generating facilities. The demand response control can be configured to
receive
and process a signal indicative of a current state of a utility or energy
provider. The
utility state has an associated energy cost.
The demand response control is configured to override the normal operating
mode of the
water heater based on the operating state of the utility to reduce energy
consumption
during peak usage states thereby lowering the energy cost for the user. A
manual override
for a user can be provided to override the demand response signal if desired.
As one
example, the control may be configured to operate the water heater system in
an energy
savings mode when the utility is operating in a peak state. Alternatively, the
user may
select a target or threshold energy cost. If a current energy cost indicated
by the utility
state signal, exceeds the user selected cost, the water heater system is
operated in an
energy saving mode. If the utility is operating in an off-peak mode, or
current energy
cost is less than the user selected cost, the operation control device
operates the water
heater system in a normal operating mode. When operating in the normal
operating
mode, the water heater is enabled operate in a heat storing mode to heat the
water to a
higher than normal temperature, e.g., a predetermined temperature in excess of
150
degrees F, taking advantage of low cost energy being provided by heating the
water
above normal storage temperature in the tank. This energy is then used during
operation
in the heat exchange mode for reducing energy cost during peak times when
energy cost
is higher.
The DR control acts as a radio receiver or has a remote transceiver, which
could receive
a multiple tiered response level signal, directly or indirectly from the
utility for example.
A multi leveled response is operable for triggering an "on peak" response. For
example,
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the control has a cost control that processes at least one signal having an
associated
energy cost. The control enables operation of the heat exchanger 70 in the
heat exchange
mode when the energy cost associated with the signal is high. Thus, the heat
exchanger
70 operates to save cost when costs are high. Likewise, when the energy cost
is lower,
then the tank operates in a heat storing mode to heat water above normal
storage
temperature for storing.
Referring now to FIG. 3, a water heating control and storage system 310 in
accordance
with another exemplary embodiment of the present disclosure is illustrated.
The water
heater system 310 includes a first water heater 302, a second water heater
304, an
operation control 314, a mixing valve 316, and a heat exchanger 370.
The first water heater 302 has a "cold in" pipe 322, a "hot out" pipe 324, and
a cover 326.
The casing surrounds a tank 330 that acts as an interior reservoir for water.
Insulation is
provided around the exterior of the tank to reduce heat transfer. The cold in
pipe 322
delivers water to the first water heater 302 at a temperature typically in the
range of 40 to
80 degrees F (4 to 27 degrees C). The hot out pipe conventionally in a water
heating
mode delivers water away from the water heater at a temperature of about 120
degrees F
(about 49 degrees C). However, since the first water heater 302 is used as a
means for
storing water heated above normal storage temperature, the "hot out" pipe 324
delivers
water heated above normal storage temperature at a temperature above about 150
degrees
F to the second water tank 304. The mixing valve 316 intercepts the water
heated above
normal storage temperature flow and mixes cooler water directed to it from the
heat
exchanger 370 via a second plumbing connection 374. Consequently, water
entering the
second water heater 304 is cooler at a more standard temperature of about 120
degrees F.
The water heater control and storage system 310 of FIG. 3 further comprises a
first
plumbing connection 372 connecting the heat exchanger 370 to the "hot out"
pipe 324.
Water heated above normal storage temperature is supplied to the heat
exchanger 370 via
the first plumbing connection 372.
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The first water heater 302 in conjunction with the second water heater 304
increases the
water storage capacity of the system. The second water heater 304 is
maintained at a
standard water temperature, while the first water heater 302 maintains the
water stored at
a heat storing mode level for providing energy with the heat exchanger 370.
The water in the first tank 302 is heated when energy is provided at a
relatively reduced
cost with respect to different cost levels. The operation control 314 is
configured as a
demand response control that acts as a radio receiver or has a remote
transceiver, which
could receive a multiple tiered response level signal, for example. As
discussed above, a
multi leveled response is operable for triggering an "on peak" response. The
control 314
operates the heat exchanger 370 in the heat exchange mode to transfer the
energy stored
in the hot water to another medium to supplement the energy needed by another
device
when the energy cost associated with the signal is relatively high.
FIGS. 4 and 5 illustrate examples of a utility's time of use rates for a
summer season and
winter season, respectively. The peaks mostly follow residential heating and
cooling load
and appliance (including water heating) consumer usage patterns. For example,
rates
peak between 1:00 p.m. and 5:00 p.m. in the summer and between 6:00 p.m. and
9:00
p.m. in the winter. Of particular importance is a winter peak of 6-9pm. These
are
examples of a specific utility, and they can vary significantly. Especially in
the
southeastern United States, on winter mornings there is high electrical demand
from hot
water for bathing, cooking, and heating the home, which can lead to peak rates
in the
early AM, or even two peak rate periods a day.
The disclosure has been described with reference to the preferred embodiments.
Obviously, modifications and alterations will occur to others upon reading and
understanding the preceding detailed description. It is intended that the
invention be
construed as including all such modifications and alterations.
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