Note: Descriptions are shown in the official language in which they were submitted.
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HIGH EFFICIENCY, PEAK-POWER REDUCING,
DOMESTIC HOT WATER HEATER
TECHNICAL FIELD
[0001] The present invention relates to a high
efficiency, peak-power reducing, domestic hot water heater
provided with three resistive heating elements.
BACKGROUND ART
(0002] In U.S.
Patent 4,948,948, there is described a
water heater with multiple heating elements having different
power factors and wherein these elements are controlled by a
control circuit so that the elements are switched on at
different periods of a day, outside peak hours, in order to
reduce the power loads on an electrical distribution network
during peak electrical power demand periods.
[0003] During
peak hours when hot water is used, normally
between 6:00 a.m. and 9:00 a.m. and 6:00 p.m. to 9:00 p.m.,
there is an excessive demand of power on the electrical
distribution network. Electrical
utilities have been
searching for adequate solutions to this problem and one
such solution is to increase the cost of electricity during
peak periods of time thereby forcing consumers to use hot
water at different periods of time whereby to try and reduce
the demand during peak power periods. Another solution is
for utilities to control the domestic circuits branched to
high power rated appliances during this peak period of time
and such controls have to be done remotely or with timers.
These solutions are, however, costly to the utilities and
are not popular with consumers. They also cause very high
instantaneous demand at re-activation if too many units are
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turned back on at the same time. The U.S. Patent 4,948,948
referred to hereinabove also discusses other attempts by
utilities to control power consumption during peak demand
periods. These other attempts are however limited and are
the cause of various other problems.
[0004] As described in U.S. Patent 4,948,948 the
resistive elements are of different power ratings, with the
top one of the elements being the highest power rated for
heating a small volume of water in the top portion of the
reservoir where water is drawn out of the tank to maintain
the water in top portion at the set hot water temperature.
However, during periods of peak demand, the amount of water
in the top portion of the reservoir is quickly exhausted as
it has been found that many consumers will draw hot water
during a single peak period of the day rather than two
separate periods, which therefore requires a much larger hot
water volume.
SUMMARY
[0005] It is therefore a feature of the present
application to provide a high efficiency, peak-power
reducing, domestic hot water heater which addresses issues
associated with the prior art.
[0006] Accordingly, there is provided a high efficiency,
peak-power reducing, domestic hot water heater having three
spaced-apart resistive heating elements which is an
improvement of the hot water heater described in the afore-
mentioned U.S. Patent.
[0007] According to an embodiment, there is further
provided a high efficiency, peak-power reducing, domestic
hot water heater having three spaced-apart resistive heating
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elements mounted in a tank having a capacity of 270 liters
and 20 inch or less diameter and wherein a low watt density
resistive heating element is mounted at the bottom of the
tank.
Mos] According
to another embodiment, there is further
provided a high efficiency, peak-power reducing, domestic
hot water heater and wherein the middle resistive heating
element is disposed at a level exceeding an average maximum
water consumption volume of water drawn during a peak-power
demand time period.
[0009] According
to yet another embodiment, a high
efficiency, peak-power reducing, domestic hot water heater
is described. It
comprises a closed tank having a
predetermined water holding capacity. A hot water outlet is
provided in a top end wall of the tank. A cold water inlet
is provided in a side wall of the tank adjacent a bottom
wall thereof. Three spaced apart resistive heating elements
project substantially horizontally in the tank. A bottom
one of the resistive heating elements extends in the tank
spaced slightly above the bottom wall. A middle one of the
resistive heating elements extends in the tank at a level
calculated at approximately an average maximum water
consumption volume of water drawn during a peak power demand
time period. A top one of the resistive heating elements
extends between the middle element and the top end wall of
the tank. The bottom element has a low watt density in the
range of from about 15 to 30 Win2.
[00010] According
to still another embodiment, there is
provided a method of reducing the kilowatt demand of a
domestic hot water heater during peak hour periods without
reducing the amount of hot water requested by a user using a
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large volume of hot water between 90 to 220 liters from a
hot water tank having a predetermined water holding capacity
of 180 or 270 liters. The method comprises the steps of
providing a hot water tank with three spaced-apart
electrical resistive heating elements extending therein in a
spaced-apart manner. The bottom
one of the resistive
heating elements has a low watt density rating in the range
of from about 15 to 30 Win2. A middle one of the resistive
heating elements is positioned at a level calculated at
approximately an average maximum water consumption of
between about 90 to 130 liters dependent on the tank size of
about 180 or 270 liters.
[00011] According
to yet another embodiment, the above
method further comprises operating the middle resistive
heating element to maintain a water temperature at its level
to approximately 140 F to form a barrier in the hot water
tank to reduce the propagation of harmful bacteria from the
bottom of the tank towards a top portion of the tank where
hot water is drawn.
[00012] In
accordance with still another embodiment of the
present application, there is provided a peak-power reducing
domestic hot water heater comprising: a closed tank having a
predetermined water holding capacity, a hot water outlet in
a top end wall of the tank, a cold water inlet in a side
wall of the tank adjacent a bottom wall thereof, three
spaced apart resistive heating elements projecting
substantially horizontally in the tank, each of the
resistive heating elements having a temperature sensing
element to enable a control of their respective activation;
a bottom one of the resistive heating elements extending in
the tank spaced slightly above the bottom wall and having a
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lowest power rating, the bottom resistive heating element
being turned on when water is flowing into the cold water
inlet and drawn out of the hot water outlet during one of
the daily peak-power demand time periods; a middle one of
the resistive heating elements extending in the tank at a
level which is calculated to be equal or above an average
maximum daily water consumption volume drawn out during the
peak power demand time periods; and a top one of the
resistive heating elements extending between the middle
element and the top end wall of the tank and having a
highest power rating; the middle and the bottom resistive
heating elements being activated simultaneously only when
the top resistive heating element is inactive.
000131 Yet
another embodiment provides a method of
reducing the kilowatt demand of a domestic hot water heater
during peak hour periods without reducing the amount of hot
water requested by a user from a hot water tank having a
predetermined water holding capacity, the method comprising
the steps of: providing a hot water tank with three spaced-
apart electrical resistive heating elements extending
therein in a spaced-apart manner and each having a
thermostat to enable a control of their respective
activation; positioning a middle one of the resistive
heating elements at a level exceeding an average maximum
daily water consumption volume drawn during one of the peak
hour periods, and activating the bottom one of the resistive
heating elements when water is flowing into the cold water
inlet and drawn out of the hot water outlet during the peak
hour periods, and simultaneously activating the middle and
the bottom one of the resistive heating elements only when
the top resistive heating element is inactive.
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[00014] Further details of these and other embodiment will
be apparent from the detailed description and accompanying
figures.
BRIEF DESCRIPTION OF DRAWINGS
[00016] Reference is now made to the Figures, in which:
[00017] FIG. I is a graph from the Florida Solar Energy
Center which shows a comparison between different fractional
daily hot water draw profiles as compiled by various
organizations.
[00018] Fig. 2 is a schematic sectional view showing a hot
water tank constructed in accordance with the prior art; and
[00019] FIG. 3 is a comparable schematic sectional view of
a high efficiency, peak-power reducing, domestic hot water
tank in accordance with an embodiment;
[00020] FIG. 4 is another schematic sectional view of a
high efficiency, peak-power reducing, domestic hot water
tank in accordance with another embodiment;
[00021] FIG. 5 is a graph showing typical diversified
electrical power demand for typical resistance water heaters
and heat pump water heaters;
[00022] FIG. 6 is a block diagram showing a switching
apparatus used in a testing of the tank of Fig. 3 or 4, and
a testing of a typical design of a two-element hot water
heating tank;
[00023] FIG. 7 is a graph showing a bin destitution of
daily hot water consumption for the tank of Fig. 3 or 4,
where about 5,000 data points are measured and averaged over
all the customers involved in the testing;
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[00024] FIG. 8 is a graph of an average cumulated daily
hot water usage per customer involved in the testing;
[00025] Fig. 9 is a graph illustrating all of the
collected hot daily water usage profiles for all the
customers involved in the testing of the typical two-
elements design;
[00026] Fig. 10 is a graph illustrating all of the
collected hot daily water usage profiles for all the
customers involved in the testing of the tank of Fig. 3 or
4;
[00027] Fig. 11 is a graph of the diversified power demand
for the tank of Fig. 3 or 4 compared to the diversified
power demand for a two-element resistive water heater tank;
[00028] Fig. 12a is a graph showing the mean, maximum and
minimum during the daily peak power demand period between
7h-11h in the morning, for to a two-element resistive water
heater tank;
[00029] Fig. 12b is a graph showing the mean, maximum and
minimum during the daily peak power demand period between
7h-11h in the morning, for the tank of Fig. 3 or 4;
[00030] Fig. 13a is a graph showing the mean, maximum and
minimum during the daily peak power demand period between
19h-21h in the evening, for to a two-element resistive water
heater tank; and
[00031] Fig. 13b is a graph showing the mean, maximum and
minimum during the daily peak power demand period between
19h-21h in the evening, for the tank of Fig. 3 or 4.
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DESCRIPTION OF PREFERRED EMBODIMENTS
[00032] Although it is stated in the above referred-to
U.S. Patent that any size of tank can be used, one must be
careful in the actual position of the elements in order to
insure that end users do not run out of hot water and that
the intermediate element does not activate unless absolutely
necessary. Furthermore, it is not recommendable that the
actual size of the tank be less than 270 liters in cold
climate geographical areas due to the fact that a smaller
tank will not provide the appropriate amount of hot water
requested by a user during peak periods. Warmer climates
where tank inlet water temperatures are higher than in
northern areas of North-America, could most likely allow
smaller volume tanks such as 180 liters. Nonetheless, hot
water drawing trends must be looked at. As such,
the
following table exposes figures of the average hot water
consumption. These were taken from ASHRAE Standard.
Average Hot Water Use, L
Hourly Daily Weekly fvfonthtv
Gmup OVL Peak OVL Peak OVI, Peak OVL Prat¨
All families 98 17.3 236 254 1652 1873 7178 7700
'Typical" families 9.9 21.9 239 252 1673 1981 7270 7866
[00033] One can easily see that the peak water consumption
must be taken into account as to eliminate the possibility
of lacking hot water. Thus, the amount for typical daily hot
water consumption can be set at a minimum amount of 254
liters per day.
[00034] Another study realized by the Florida Solar Energy
Center clearly indicates that the consumption is slightly
more. The graph of Fig. 1 compares different fractional
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daily hot water draw profiles compiled by various
organizations.
(00035] Knowing that the graph of Fig. 1 indicates
fractional draws, one must take into consideration the size
of the tank in use. Assuming that the water heater in use
is a 270 liter tank, by extrapolating the values in the
graph to the volume of the tank, we obtain the following
table.
Hour ASHRAE Becker
Fraction of Volume Fraction of Volume
daily hot according to daily hot
according to
water draw tank size water draw tank size
1 0.009 2.430 0.006 1.620
2 0.009 2.430 0.003 0.810
_
3 0.009 2.430 0.001 0.270
4 0.009 2.430 0.001 0.270
0.009 2.430 0.003 0.810
6 0.010 2.700 0.022 5.940
7 0.075 20.250 0.075 20.250
8 0.075 20.256 0.080 21.600
9 0.065 17.550 0.077 20.790
0.065 17.550 0.067 18.090
11 0.065 17.550 0.061 16.470
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12 0.047 12.690 0.049 13.230
13 0.047 12.690 0.042 11.340
14 0.038 10.260 0.038 10.125
15 0.038 10.260 0.034 9.180
16 0.038 10.260 0.038 10.260
17 0.038 10.260 0.044 11.880
18 0.063 17.010 0.058 15.660
19 0.063 17.010 0.069 18.630
20 0.063 17.010 0.065 17.550
21 0.063 17.010 0.059 15.930
22 0.051 13.770 0.049 13.230
23 0.051 13.770 0.043 11.610
24 0.009 2.430 0.024 6.480
Total 1.009 272.430 1.008 272.025
[00036] From this table, we can clearly see that an entire
tank is usually used up in one day by an average family.
However, care must be taken in interpreting this as this
profile may not cover exceptions. One must keep in mind
that it is crucial to avoid lack of hot water particularly
where people tend to concentrate their consumption in one
peak period of a day rather than two, i.e. morning and
nighttime. As such the hot water drawn can be as high as
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130 to 150 liters. Therefore, in order to always satisfy
demand and to avoid increasing peak power demand from the
utilities the volume of water to be heated by the bottom
element should be set between 130 and 150 liters, for
instance at 130 liters.
00037] Other hot water consumption studies have been
done. For example, a study by the Canadian Building Data and
Analysis Centre titled "Domestic Water Heating and Water
Heating Energy Consumption in Canada" (C.Aguilar, D.J. White
and David L. Ryan, Domestic Water Heating and Water Heater
Energy Consumption in Canada, CBEEDAC 2005-RP-02, April
2005) found relevant studies on household energy demand for
Hot Water. According to Wiehagen and Sikora (2002a), a 1985
study that monitored hot water use for 59 residences in
Canada found average hot water use per household to be 236
liters per-capita consumption values ranging from 47 to 86
liters per day ... .
Source Location Per Household
measure
Liters/day
Wiehagen and Sikora Canada 236
(2002a)
[Perlman and Mills -
Henze (2002) US 227.4
DeOreo (2000) US 246.8
Since there does not appear to be any information on
energy consumption for water heating purposes by
Canadian households, it is necessary to utilize
U.S. values.... Household Values Underlying US DOE
(Department of Energy) calculations for year 2000 in the
following Table.
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Water Heater Average Average Hot
Fuel Type Household Water Use
Size (Liters/day)
Electricity 2.45 171.5
Natural Gas 2.82 188.9
LPG 2.58 173.0
Oil 2.68 178.1
U.S. Average 178.1
[00038] The
present water heater is therefore developed to
raise the utilization factor of a load and reduce the peak
demand of the water heater, which is designed as a three
elements water heater.
[00039] Referring
now to Figures 2 and 3, there is shown
an example of a 20 inch diameter 270 liters water heater
tank with Figure 2 representing the tank of the prior patent
referred to.
[00040] Fig.3
represents the high efficiency, peak-power
reducing, domestic hot water tank in accordance with an
embodiment.
[00041] Although
different sizes of tanks can be used, the
tank is usually chosen to be as high as possible in order to
take full advantage of the stratification effect of hot and
cold water in the tank in order to reduce water temperature
diffusion. In other
words, a shorter, stubbier tank of
equal volume may have more difficulty to deliver as much hot
water as a taller, slimmer one.
Furthermore, the water
heater is adapted to be capable of meeting the required
specifications of the CSA delivery test stated in C191
Standards.
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[00042] Although the previous design is made to meet the
demand of a typical consumer, variations of this can be made
for people who consume more or less water. The actual
positions of the elements are all related proportionally to
the volumes of water to be heated as per the extrapolations
and statistics demonstrated herein. For example, one could
design a smaller tank for people that consume very little
hot water, such as about 175 liters, (38.5 US gallons).
When extrapolating the values from the graph of Fig. 1, we
obtain the following table.
Hour ASHRAE Becker
õ .
Fraction of Volume- . - - -
Fraction of Volume
daily hot according to daily hot
according to
water draw tank size water draw tank size
',4-',".4" d
1 0.009 1.575 0.006 1.050
2 0.009 1.575 0.003 0.525
3 0.009 1.575 0.001 0.175
4 0.009 1.575 0.001 0.175
0.009 1.575 0.003 0.525
6 0.010 1.750 0.022 3.850
7 0.075 13.125 0.075 13.125
8 0.075 13.125 0.080 14.000
9 0.065 11.375 0.077 13.475
0.065 11.375 0.067 11.725
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11 0.065 11.375 0.061 10.675
12 0.047 8.225 0.049 8.575
13 0.047 8.225 0.042 7.350
14 0.038 6.650 0.038 6.563
15 0.038 6.650 0.034 5.950
16 0.038 6.650 0.038 6.650
17 0.038 6.650 0.044 7.700
18 0.063 11.025 0.058 10.150
19 0.063 11.025 0.069 12.075
20 0.063 11.025 0.065 11.375
21 0.063 11.025 0.059 10.325
22 0.051 8.925 0.049 8.575
23 0.051 8.925 0.043 7.525
24 0.009 1.575 0.024 4.200
Total 1.009 176.575 1.008 176.313
[00043] We can see once again that peak period consumption
is relatively high. Using the same reasoning as before, we
can assume that a below average user that concentrates his
use of hot water during one period rather than two could use
about 90 liters. Thus, the intermediate element would have
to be positioned as to never be activated before
approximately 90 or more liters of water are consumed.
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(00044) From the above study one can therefore conclude that a consumer who
draws hot water during a single peak demand period will draw from anywhere
between
90 to 130 liters or more.
(00045) Thus, with reference to Figure 2, it can be seen that with the 270
liter prior
art tank 10, the central resistive heating element 11 would be rendered
operative as it is
disposed at a level 11' of about 130 liters. Accordingly, as soon as the
consumption
approaches 130 liters the central element is switched on therefore increasing
power
demand on the power distribution network.
(00046) Alco, the top resistive element 12 is located at a level 12' in the
uppermost
portion of the tank and heats approximately 12 gallons of water, but that
element has a
large power rating of 3800 watts to 4500 watts or more. However, this element
is only
turned on when the heater is plugged in for the first time, or if the consumer
uses up
most of the hot water in the tank.
(00047) The lowermost resistive element 13 is located at a lower level 13',
and has
a power rating of 800 watts or less, but that element is on most of the time
and because
of this, the lifespan of that element is much longer than the other elements
and
therefore must be designed accordingly to increase its lifespan.
(00048) As previously mentioned, the purpose of the three resistive
elements at
their respective locations inside the tank and their control circuit, is to
heat the water in
priority during very low power demand periods.
(00049) For example, between 8:00 p.m. and 7:00 a.m., the water is slowly
heated
to a usable hot water temperature. Therefore, during morning and early evening
peak
power
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demand periods, there should be ample hot water to be drawn
from the tank. However, if, as described hereinabove, many
consumers only demand hot water during only one peak period
of time during a day, thereby demanding much larger volumes
at a time, the supply of hot water from a hot water heater
may not be adequate and the top resistive heating element is
switched on, thereby increasing the load on the network of
the utility. Thermostat
accuracy must also be considered
because if they are not precise from one to the other, the
resistive heating elements will not be activated at the
right time, thus not meeting delivery tests.
[00050] Figure 3
shows the improved design of the domestic
hot water heater of the present invention. A tank 20 similar
to the one as described in the prior art is used, namely a
tank of 270 liters, having a diameter of about 20 inches. In
this case however, the middle resistive heating element 21
is disposed as near as possible or slightly above the
average maximum water consumption volume drawn during a
single peak hour demand time period. This
maximum water
volume is identified by the level 22. Level 22 may vary
depending on a cumulated daily water consumption volume
taken only during both of the peak power demand time periods
which is also referred to as an averaged maximum daily water
consumption volume taken during the peak power demand time
periods. Accordingly, the middle resistive heating element
21 will not be activated by a consumer drawing a volume of
hot water during a single peak demand time period which is
lower or corresponding to the averaged maximum daily water
consumption volume described above.
[00051] Another
feature of the high efficiency, peak-power
reducing, domestic hot water heater 20 of the present
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invention is that the bottom heating element 24 optionally
has a low watt density rating in the range of from about 15
to 30 Win2. It is also disposed close to the bottom wall
25 of the tank, similar to that as shown in Figure 2.
[00052] It is to be noted here that a cold water inlet 26
is connected to the side wall 27 and adjacent the bottom
wall 25 whereby not to create too much turbulence at the
bottom of the tank, as is the case with top entry tanks
where the feed tube extends in the tank vertically downwards
from the top wall 28 of the tank. Turbulence causes water
to mix in large volume taking more time to supply hot water,
thus reducing the amount of hot water available, at the top
of the tank and entraining bacteria in the top region of the
tank where hot water is drawn.
[00053] In both tanks 10 and 20, the hot water outlet 29
is connected to the top wall to draw the hot water in the
top portion 30 of the tank. Also, the top resistive heating
element 25 extends substantially at the same height as with
the prior art tank 10 and, as herein shown, is at a level
wherein there are approximately 46.21 liters of water
thereabove for a 270 liter tank or within 30-50 liters.
[00054] It is further pointed out that the positions of
the resistive heating elements 21, 23 and 24 also provide
for efficient water temperature stratification within the
tank thereby reducing diffusion of the cold water introduced
at the bottom of the tank in a non-turbulent manner. This
ensures that the top portion 30 of the tank has an adequate
supply of hot water.
[00055] Further, the middle heating element produces a
heat barrier in the water within the tank, and the
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temperature in the vicinity of the middle resistive heating
element is in the range of about 140 F. This reduces the
propagation of harmful bacteria such as legionnela to the
hot water top portion 30 of the tank.
[00056] The tank
as shown in Figure 3 is a 270 liter tank
and the bottom heating element extends at a water level of
about 20 liters from the bottom. The middle
resistive
heating element 21 extends at a water level of about 130
liters from the bottom wall 25 whereas the top heating
element extends at a water level of about 220 liters from
the bottom wall 25. As
previously described this top
resistive heating element 23 is at a distance of about 46 or
less liters from the top wall 28.
[00057] The bottom
resistive heating element is of a low
watt density rating to have an extended lifespan, as this
element will operate almost all of the time to maintain the
set hot water temperature of the tank.
[00058] This
bottom resistive heating element 24 has a
metal sheath which can be made of copper, incoloy or
stainless steel or other suitable materials. The resistance
is typically made of a nickel-chromium alloy coil surrounded
by magnesium oxide powder or other suitable materials. It
is also important that the surface watts load of the coil be
kept at a minimum to increase its life. Although many means
can be used to accomplish this, one means is to increase the
gauge of the resistance wire.
[00059] It is
noted that the resistive heating elements
may also have a polymer core in accordance with other
suitable heating element design configurations.
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(00060] Typical
domestic water heaters are equipped with
screw-type elements that have a watt output value ranging
anywhere from 1500 to 5500 watts. The surface load density,
expressed in watts per square inch of tube surface, usually
ranges from 80 to 130 Wiin2. This
surface load is also
present on the resistance inside of the element and ranges
usually from 2 to 4 times the surface load of the tube. It
is known that the higher the surface load of the coil as
well as the tube, the shorter is the expected life of the
element.
[00061] Furthermore, these elements are designed to
operate in cycles. They heat the water on demand for the
period of time required for it to heat the water to the
desired temperature. The higher the output rating of the
element (Watts), the shorter it will take for it to heat a
definite volume of water. Inversely, the lower the output,
the longer it will take to heat the water.
[00062] Since it
is desirable that the bottom element 24
lasts just as long as the tank itself, it must be built for
that purpose. The most important factor that must be taken
into consideration is that the lower resistive heating
element 24, which is rated at 800 watt, will operate
continuously for a very long period of time until the water
in the tank reaches the set thermostat temperature. As such
the following criteria are respected: the bottom resistive
element 24 has an increased life and therefore has a very
low watt surface load of 15-30 Win2), a heavy resistance
gauge (1 - 2 wire gauge oversize), is of premium quality
material for the resistance (High grade Nickel-Chromium
Alloy), is of resistor style design, bolt-on instead of
screw-in attachment, and has a premium quality grade MgO
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(magnesium oxide powder), and fusion welds on pin-coil
assemblies and electrical contacts.
[00063] One can therefore appreciate that the high
efficiency, peak-power reducing, domestic hot water heater
tank 20 as described herein has features which produce
beneficial results and one of these features is the position
of the middle resistive heating element which creates a
second tempered zone in a predetermined area of the tank
which lies around or above the average maximum water
consumption volume drawn during the two peak power demand
time periods, on a daily basis per typical household usage.
That middle element also provides a temperature barrier of
about 140 F thereby preventing bacteria from migrating to
the top hot water portion of the tank. Further, the bottom
resistive heating element is rated to outlast the life of
the tank as it operates most of the time to maintain the set
hot water temperature of the tank.
[00064] The above described hot water tank can have, for
example and as illustrated in Fig. 4, three resistive
heating elements (23, 21 and 24) each controlled through
their dedicated thermostat (32, 33 and 34 respectively), and
spaced apart so as to accommodate for various peak demand
hot water consumption profiles.
[00065] The bottom resistive element has a lowest power
rating set at about 800 Watts or lower. This bottom heating
element is activated as soon as there is an admission of
cold water into the cold water inlet 26 and that hot water
is drawn out of the tank through the hot water outlet 29.
Such an activation permits a heating of the water inside the
tank using a low power demand over a long period of time.
Considering a 270 L tank and an average household hot water
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daily demand determined to be about 194 to 220 L, the bottom
heating element functions almost continuously.
[00066] The middle heating element has a power rating set
at about 3000 Watts or lower and is located at and or above
the average maximum water consumption volume drawn during
the peak power demand time periods, which can be calculated
from the average maximum household daily consumption of hot
water as detailed hereinabove. The top heating element has
the highest power rating and the highest priority compared
to the other two heating elements. The power rating of the
top element is set at about 3800 Watts or lower.
[00067] For a 270 L tank capacity and an average daily hot
water consumption around 200 L per day, the lowest element
is positioned such that the 800 Watts is activated during
the utility peak demand time periods, thereby reducing the
power demand below the typical diversified power demand of 1
to 1.4 kW.
[00068] In addition, the bottom resistive element and the
middle resistive element are activated simultaneously only
when the top resistive heating element is inactive or not
heating.
[00069] The following describes tests which were performed
on the above described embodiment of the high-efficiency,
peak-power reducing, domestic hot water tank.
[00070] On a daily basis, diversified residential water
heater loads generally have two peaks, one in the morning
and one in the afternoon, as illustrated in the graph of
Fig. 5. Although the installed resistive elements of
standard water heaters typically reaches between 3.8 kW
to about 5.5kW, the diversified demand in the peaks
CA 02621819 2008-02-20
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tends to coincide approximately with those of electric
utilities and typically varies from 1.0 to 1.4 kW.
Figure 5 shows the diversified demand for typical resistive
water heater from Northeast Utilities in a year 2002
study. The highest curve being for the Resistance Water
Heater type (resistive) and the lowest one with heat pump
water heater (taken from NYLE Heat-pump water heater
evaluation - Final report - January 2002, Submitted to
Northeast Utilities, AIL Research, Inc.). By taking
advantage of the thermal storage of water heaters, the
control strategies are to smooth out the demand curves to
eliminate short-term extremes. This reduces the average
cost of electricity by improving the load factor, reducing
the need for generation capacity by shifting electricity
use from peak demand to off-peak demand time periods.
Since it is now becoming more difficult to justify the
construction of new power generation stations as well as
transport and distribution lines, load management is
being considered by electric utilities.
[00071.] The tests
were conducted on hot water tanks
especially designed for the purpose of testing and comparing
the above-described design with the conventional two
resistive elements hot water heaters. The
especially
designed hot water tanks have five resistive elements to
incorporate both the standard two elements heater with the
herein described three elements peak power reducing water
heater into one and only tank. The two elements design has
two resistive heating elements each having a power rating of
about 3800 Watts, and never operating simultaneously such
that the maximum peak power demand on this water heater
design never exceeds 3.8 kW.
CA 02621819 2008-02-20
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[00072] The testing was done over 4 months, in 75
households all selected to best represent typical families.
The hot water consumption and the electrical demand for two
tank modes: the traditional two elements design and the
proposed three elements design were measured.
[00073] For the purpose of the experiment, a timer was
used to switch between operation modes, that is, from the
operation of one design to the operation of the other
design. The switching between the two operation modes was
done late in the evening on a daily basis to allow a testing
of both concepts for a same customer. The switching
apparatus used is illustrated in Fig. 6. In addition, the
thermostats in both operation modes were all set to 60
degrees Celsius or 140 degrees Fahrenheit.
[00074] The study was conducted during the winter time for
approximately four months switching day to day around ten
o'clock in the evening, from one type of element
configuration to the other.
[00075] A survey done by Multi-Res group shows how hot
water was used amongst the families involved:
1) 3 persons in average per family;
2) 67 % full time workers; 11 % part time; 14 % retired
et 8 % at home;
3) Average use of Dishwasher : 3.7 per week;
4) Clothes Washing Machine: 6.5 per week. 66 % cold
water only; 32 % warm and 5 % hot water only;
5) On average, 17 showers per week and 4 baths per week;
61 % of customer having a low flow shower head.
CA 02621819 2008-02-20
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[00076] Each site
had two data logger Smart readerTM that
monitored the following parameters: Electrical power to
water heater and hot water flow rate. A Watt -
nodeTm
accumulates the power and a given number of pulses are
generated per kWh. Pulses are also output by the hot water
flowmeter (1 pulse per liter). Data of pulses were stored
every five minutes. A 30 amps CT was used to measure the
input power at the water heater while a 5 amps CT only
for the lower 800 Watts element. Indeed, the current
can be as low as 3.3 amps when the water heater operates
on its 800 Watts element (800 Watts divided by 240 Vac) and
a low range CT must then be used to achieve accuracy.
[00077] The graph
of Fig. 7 shows the bin destitution of
daily hot water consumption for the three elements operation
mode wherein roughly 5,000 data points were taken and
averaged over all the customers involved in the testing. As
stated hereinabove, seventy-five (75) residents participated
in the study during roughly 4 months. Since the two tank
modes were alternated on daily basis, each tank mode was
tested for about 5,000 days, hence the 5,000 data points
(one data point per day). Fig. 8 shows the cumulated daily
hot water usage for each of the customers involved.
[00078] The graphs
in Fig. 9 and Fig. 10 illustrate that a
wide range of hot water usage profile exists for either one
of the three elements operation mode and the two elements
operation mode. The horizontal line in the two graphs shows
the general trend for the average hot water usage in
contrast with all the data points. Each data point indicates
the daily use of hot water for one household. Overall, near
5,000 data points are plotted for each operation mode. An
CA 02621819 2008-02-20
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average of about 194 liters per day of hot water consumption
is reached per household, in any operation mode.
[00079] These values are seen to fit well with other
studies made relating to hot water consumption rates. For
example, a survey of study done in 1998 by, Abrams, D. W.
"Field Test Results From Residential Electric Resistance
Water-Heating Systems," ASHRAE Trans., 1998, Vol. 104,
Part 1B, No. SF-98-31-1, 1843-1851, estimated average daily
hot water consumption on 14 sites to 218,8 liters per day
per household. A previous study by Perlman et Mills in
1985 (refer to Perlman, M. wt B.E. Mills (1984),
"Development of Hot Water syue Patterns", ASHRAE
Transactions 91(2): 657-679), a study done in Canada
estimated the average daily hot water to be 236 liters.
[00080] By using data from previous studies of Hydro-
Quebec and the survey done by Multi Reso-Senergis in January
2007 to estimate the habits of hot water usage per
household, weekly hot water consumption was found to be of
1491 liters, or 213 liters daily, as shown in the following
table from the Multi-Res group.
Approximate calculation of daily use of hot water based on
typical usage and habits of customer based on the survey of
Multi Reso among the households of the pilot project
Usage Liters of kWh per Number of Hot
water
Hot water usage use liters
at 60 C per from 8 C to per week per week
6
usage 0 C*
(B) (A x B)
Bathing 57,5 liters 3,4 kWh 4 230
Shower 37,1 liters 2,2 kWh 17 631
CA 02621819 2008-02-20
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Dishwashers 28,3 liters 1,7 kWh 3,7 105
Clothes 32,3 liters 1,9 kWh 6,5 210
Washing
Machine
Other uses 15 liters 0,9 kWh 7 315
per day
per
TOTAL per week: 1491 liters
per day 213 liters
* : Does not take into account the standby losses
** : Le Chauffage electrique residentiel de
l'eau: Canadian Electrical Association (CEA),
1990
CA 02621819 2008-02-20
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Approximate calculation of energy consumption to heat water
to 60 C based on Hydro-Quebec's report LTE-RT-2006-0114
Daily hot water consumption at 60 C in liter per
day
1 2 3 4 ou + Average
household
Bathing 20 33 59 79 53
Shower 8 liters/min 25 43 60 74 56
Dishwashers 8 11 15 21 16
Other uses 15 30 45 60 42
Clothes Washing
13 20 32 45 30
Machine
Total per day 81 138 213 279 197
Daily hot water energy consumption (kWh)*
1 2 3 4 ou + Average
household
Bathing 1,22,0 3,6 4,7 3,2
Shower 8 liters/min 1,52,6 3,6 4,5 3,4
Dishwashers 0,50,7 0,9 1,3 1,0
Other uses 0,91,8 2,7 3,6 2,5
Clothes Washing 0,81,2 1,9 2,7 1,8
Machine
Total per day 4,98,3 12,7 16,8 11,8
* : Energy requires to heat water from 8 C to 60 C
without standby losses
[0080] As seen in the previous table, the 213 liters per
day is quite close to the value of 194 liters per day
measured in the field by the actual study. In an other study
by De Oreo et Mayer (taken from De Oreo, W.B. et P.W. Mayer
(2000), "The End Uses of Hot Water in Single Family Homes
from Flow Trace Analysis", Aquacraft Inc. Report, undated.)
(10 houses from Seattle) in year 2000, 235 liters per day
were measured. The Canadian study from Perlman and Mills in
CA 02621819 2008-02-20
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1985 showed a daily hot water consumption of 236 liters per
day(taken from Perlman, M. et B.E. Mills (1984), "Development
of Hot Water use Patterns", ASHRAE Transactions 91 (2) : 657-679).
Comparison of the study from DeOreo et Mayer in year 2000
with the actual test pilot
Usage Hydro-Quebec Hydro-Quebec
DeOreo et DeOreo
pilot project Mayer pilot and
(year 2006- (year project (year Mayer (year
2007) liters 2000) 2006- 2000)
per day liters 2007) % of % of daily usage
per day daily
usage
Bathing 33 liters 41 liters 15 % 18 %
Shower 90 liters 62 liters 42 % 26 %
Dishwashers 15 liters 9 liters 7 % 4 %
Clothes Washing 30 liters 38 liters 14 % 16 %
Machine
Other uses 45 liters 85 liters 21 % 36 %
Total per day 213 liters 235 liters
(from Table
1)
[0081] Comparison of previous studies shows the average
hot water consumption of this actual study to fit well
within the range of previous studies. Since the Pearlman's
study was done in 1984, one should now expect a reduction
of the hot water consumption due to energy efficiency having
been improved over the last decades. Furthermore, the use of
low flow shower heads and faucets as well as the promotion
of cold water for clothes washing also contribute to the
CA 02621819 2008-02-20
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reduction of hot water consumption when compared to earlier
studies.
[0082] The graphs
shown in Fig. 11 to Fig. 13b illustrate
that the diversified power demand for the herein proposed
three element hot water tank exhibits a flatter behavior
compared to the diversified power demand for a conventional
two element hot water tank. A flatter
diversified power
demand is advantageous since the generation capacity demand
and the electrical load are better managed.
[0083] As can be
seen in the graph of Fig. 11, the three
elements water heater exhibits a reduction in its
diversified peak power demand of about 200 Watts, down to a
value lower than 800 Watts. This reduction translates to
about a 20% reduction in peak demand when compared to
conventional hot water tanks having two resistive heating
elements. This information was provided through the field
study mentioned hereinabove which was conducted in 2007 by
Hydro-Quebec.
[0084] The mean,
the maximum and the minimum values of
the diversified power demand for each average daily hot
water usage of a specific customer household, in both the
morning and the afternoon peak power demand periods (7h-11h
and 17h-21h), was calculated for the two elements operation
mode (graphs of Figures 12a and 13a) and the three elements
operation mode (graphs Figures 12b and 13b).
[0085] As the
mean daily hot water usage increase, the
demand rises. A curve fit is provided for the maximum, the
mean and the minimum values. The following table summarizes
the mean and maximum values for each peak power demand
CA 02621819 2008-02-20
- 30 -
period, along with the power reductions seen for the three
elements water heater design.
Period Mean Power (kW) Reduction
Two (2) Three (3)
elements elements
7h - 11h 0,72 0,56 22 ,
17h - 21h 0,83 0,70 16%
Period Maximum Power (kW)
Two (2) Three (3)
elements elements
7h- 11h 0,85 0,64 25%
17h - 21h 0,94 0,78 17%
[0 0 8 6 ] The proposed three element water heater therefore
addresses the issues related to the prior art and offers
efficient, simple and less costly solution to peak demand
management without the drawbacks of unwanted peaks occurring
when turning water heaters back on after long periods of
inactivation.
[ 0 0 8 7 ] It is within the ambit of the present invention to
cover any obvious modifications of the preferred embodiment
described herein, provided such modifications fall within
the scope of the appended claims'.
