Note: Descriptions are shown in the official language in which they were submitted.
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THERMO STORAGE WATER HEATER
HAVING EXTEN~ED HEAT WIT~DRAWAL
A hot water heater employing horizontal heat
storage tanks and dual immersed heat exchangers for
heat extraction has been disclosed.
Reference may be made to U.S. patents 3,422,248,
S titled "HYDRONIC ELECTRIC HEATING SYSTEMS", and U.S.
patent 4,243,871, titled "FLUID HEATING SYSTEM WITH
STORAGE OF ELECTRIC HEAT".
BACKGROUND OF THE INVENTION
This invention relates generally to stored energy
liquid heaters, employing thermal storage. Heaters of
this type have proven advantag~ous in supplying continuous
heat at controlled temperatures to space heating and pro-
cess application, from heat sources which are aperiodic
in nature. A particular application involves the use of
electrical energy during "off-peak" periods for "equalizing"
utility electric generating capacity, thereby improving
overall efficiency of the supplying electrical utility
system through load management. The particular configura-
tion of the invention disclosed employs water heated to a
2~ temperature above its atmospheric saturation or boiling
value thereby providing increased energy storage. Although
those skilled in the art will recognize that other storage
materials utilizing an intermediate liquid for transferring
heat can be substituted for water storage.
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Units disclosed in the above mentioned patents
function satis~actorily and are in substantial use.
However, it has been found that the control systems
utilized require at least one thermal mixing valve to
achieve controlled heat withdrawal from storage. Also,
the above discussed units utilize horizontal storage
tanks containing the heat storage medium, typically a
liquid such as water.
It has been discovered that a storage tank or
container having essentially a vertical orientation or
aspect ratio, i.e., wherein its vertical dimension is
some multiple greater than one of its diameter, in
conjunction with a novel orifice/standpipe flow control,
provides increased ultilization of the stored energy
heat through improved internal storage temperature dis-
tribution.
Therefore, the invention disclosed here provides
increased heater reliahility through elimination of the
above mentioned mixing valve, and essentially extends
the capability of the heater to supply energy at a pre-
determined temperature through better utilization of the
storage medium.
It is, therefore, an object of this invention to
provide a stored energy heater having extended supply
capabilities through control of internal mixing and tem-
perature distribution of the storage medium.
It is a further object of this invention to provide
automatic adjustment of heat withdrawal through storage
medium flow control.
It is a further object of this invention to provide
a stored energy heater featuring reduced storage heat
losses through improved tank design.
It is a still further object of this invention to
provide a stored energy heater which is more economic in
construction through reduced piping, weight, and elimination of a thermal mixing valve
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An additional object of this invention is to provide
a standpipe/orifice combination which apportions liquid
storage media so as to maintain storage outlet ternper-
ature by minimizing mixing with return liquid.
SUMMARY OF THE INVENTION
In a preferred embodiment of the invention disclosed
a plurality of storage tanks consisting of a single
master and one or more slave storage tanks i5 utilized
to store periodically available heat, and supply contin-
uous heat to fluid in a connected system, at a predeterminedtemperature substantially lower than that of the storage
medium. An external dual concentric tube heat exchanger
is utilized wherein the higher temperature storage or
transf~r liquid is circulated through an inner ~ube,
while the system liquid or water flows through an
annular space between the inner tube and a concen-
trically disposed outer tube or conduit. Heat with-
drawal from the above mentioned storage tanks is accom-
plished through the use of a unique stand pipe~orifice
combination contained in each tank.
System demand controls the operation of a liquid
pump, which on initial reduced flow operation circulates
the storage fluid through a lower portion of the tank.
F1QW of high temperature storage liquid in this mode, is
controlled by the stand pipe orifice. The orifice/
standpipe combination therefore controls heat extrac-
tion, and storage container internal liquid flow
patterns so as to essentially confine withdrawal to pre-
determined portions of the storage tank~
On increased heat demand or ~ong time heat extrac-
tion from the lower portion of the heat storage tank, a
temperature signal increases the pumping capacity thereby
modifying the flow patterns through the standpipe and
orifice combination to readjust storage fluid flow so
that a major portion of the circulated storage fluid is
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extracte~ from the extreme upper end of the storage
tank.
At this point flow internal of said thermal storage,
dictated by the essentially vertical orientation of the
tank or container, establishes a virtual "wall of low
temperature water" which ascends vertically as heat as
extracted, and establishes a thermocline, or tempera-ture
interface, betweenreturn water and remaining higher
temperature water remaining in the storage tank. It has
been discovered that liquid mixing, and diffusion under
these operating conditions is minimal, resulting in
negligible dilution ~i.e., temperature reduction) of the
remaining storage fluid above the before mentioned verti-
cally ascending wall of water. In this manner heat can
be supplied to the system water at a consistently higher
temperature than would be available with horiæontal tank
configurations disclosed by the prior art.
A standpipe/orifice combination is utilized wherein
total stored liquid outflow exits a tank at its lower
extremity. Storage liquid or water is drawn from a stor-
age tank through the standpipe upper end and an orifice
in combination flow. The particular orifice utilized
provides preferential withdrawal, particularly at lower
withdrawal flow rates, from storage liquid located ~elow
the tank return. In this way mixing of higher temper-
ature storage water and lower temperature return water
is minimized providing extended storage water outflow
over a broader demand range.
Thus the disclosed heater provides extended output at
predetermined temperature, through the use of a stand
pipe/orifice combination providing load-adjusting flow
and temperature control of the storage medium. This
discovery further allows operation of the disclosed
heater without the use of a temperature sensitive mixing
valve utilized in the prior art systems.
In addition,.as indicated, slave tanks can be oper-
ated in flow parallel, having flow and temperature
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patterns essentially identical to those of the master
unit. Assuming pump capacity is adjusted correspond-
ingly, additional "slave" units provide multiples of
capacity while maintaining the above essentially
improved output characteristics and reliability.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a semi-pictorial elevation/front view of
a two unit (one master, one slave) with a portion of the
master outer shell removed, showing essential locations
of the control panel, external piping, heat exchanger,
and the insulation-housing envelope.
Figure 2 is a pictorial semi-schematic of the above
mentioned master slave combination showing in
pictorial/symbolic/circuit notation essential flow
paths, and associated control components.
Figure 3 is a perspective, semi cut-away view of the
lower or control portion of a master unit. Particularly
disclosed is termination of the concentric tube heat
exchanger, system and slave unit connections, and loca-
tion of a "typical" tank temperature control element.Elements familiar to those skilled in the art and non-
essential to the disclosed invention have been omitted
in the interest of clarifying the disclosed invention.
Figure 4 is a partial section of the master unit
shown on line 4-4 of Figure 1, particularly showing the
heat exchanger location and its interconnections to the
master storage container. Flow directions are schemat-
ically shown.
Figures 5a and 5b are sectional views of the orifice/
standpipe combination.
Figures 6a and 6b are sectional views of an alternate
orifice/standpipe embodiment.
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DETAILED DESCRIPTION OF THE IMVENTION
The ~ollowing description will describe the inven-
tion in connection with a preferred embodiment wherein
system or process water is heated by heat initially
stored in a tank or container utilizing water as an
isolated storage medium. In the disclosed embodiment
storage water is heated electrically by immersion
elements. However, it is not the intention of this dis-
closure to limit the invention to this embodiment. On
the contrary, it is the intent of this application to
contemplate all alternatives and modlfications such as
utilizing heat from external high temperature liquids
transferred to the storage medium through immersion heat
exchangers, from other heat sources such as high temper-
ature gases. The disclosure and cl~ims is alsoint~nded to cover other alternatives, modifications and
equivalences may be included within the spirit and scope
of the invention, and defined by the appended claims.
Turning first to Figures 1, 2 and 3, a master module 1
2~ and slave module 2 are shown piped so as to provide
essentially parallel flow of an isolated liquid storage
medium hereinafter described as storage water contained
in master tank 6 and slave tank 7 through said tanks.
Electrical immersion heating elements 60 and 61 are
located adjacent to the bottom of the tanks 6 and 7, as
shown. Standpipes 53 and 54 are contained in the respective
tanks and each has an open end 50, 51 and lower orifice 41
and 42, respectively arranged to be below the upper level of
tank storage water at all times.
It should be noted that as the slave module 2 is
from the storage point of view essentially identical to
the master module 1, corrcsponding elements are dis-
closed. However, except when the slave module
departs from operation of the master, the following dis-
cussion will be essentially concerned with a single unit,
i.e., that employing only the master module storage.
Those skilled in the art will readily understand that
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heat wi-thdrawal from the parallel connection of slave
an~ master as disclosed through opening connecting
valves 69, will proceed in a manner identical to that of
the master alone.
As further disclosed in Figures 3 and 4, an essen-
tially circular concentric tube heat exchanger assembly
20 is disposed coaxial to the lower extremit~ of the
tank 6. A pump 25 provides circulation of the storage
water via exit 40 and inlet 35 of the tank. The concen-
tric tube heat exchanger provides a flow passage or con-
duit 22 internal of an outer conduit 21A This arrange-
ment provides an annular flow space 23~ As piped, (ref.
~igure 2 ) ~ the pump 25 circulates heated water drawn
from the tank 6 via the standpipe 52 through both the
upper end SO and the orifice ~1 as will be further dis-
cussed.
As shown in Figures 5a, 5b, and Figure 6a and 6b, two
forms of outflow orifice 41 or 41a can be utilized. In
the preferred embodiment shown on Figure 5a short length
20 Of conduit, or pipe "spud" 41b is shown intersecting
-the standpipe 53. The intersection angle of the conduit
41b is arranged to preferentially supply heated storage
water from the lower portion 65 of the storage tank 6.
In the alternate embodiment (reference 6a, 6b), an
orifice 41a is shown. As disclosed, the intersection of
the ~la orifice and standpipe 53 defines inlet and out-
let control apertures 41c and 41d. In operation, these
act to direct inflow so as to withdraw water from the
lower tank portion for an initial pump volume.
The high temperature heat source fluid, in this case
water, exits the tank at 40, passes through the inner
heat exchange conduit 22, the pump 25 and is returned to
the tank via inlet 35. System water enters the annular
flow space 23 (ref. Figure 4~ via inlet 5, and exits at
the outlet 55, returning to the system via flow path 15.
A temperature sensitive element 52 has its sensing
portion immersed in the storage water at a predetermined
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location, which essentially divides the storage tank
into a mix portion 65, and a stratifi.ed portion 70.
Other control elemen-ts such as a master storage heat
exchanger outlet temperature control 31, a storage pres-
sure relief valve 30, and a drain valve 11 providerequired control and access of the heating fluid/sto~age
in master module 1. As indicated in Figure 2, a two
unit embodiment employing a master module 1 and slave
module 2 is arranged to have parallel flow from the pump
25 via interconnecting conduits 32 and 10, allowing
extraction of heated storage liquid contained in the
slave tank 7 via the standpipe/orifice combination 51,
54 and 42 as discussed above.
An electrical control panel assembly 75 is shown
attached ~o the outer shell 16. No details are provided
as the panel is not a part of the invention. The panel
supplies electrical energy to hearing elements 60 during
designated."off peaks" periods through the use of conven-
tional electrical contactors. Maximum heat input is
controlled by tank temperature controls 52 and 52a, pro-
viding power cutoff when a storage temperature o~ 280F
is attained~ Additional over temperature protection is
provided by master and slave storage pressure relief
valves 30 and 29 respectively. A pressure/temperature
gage 8 is provided for monitoring tank storage condi~
tions.
In operation, system water initially enter.ing the
annular ~low space 23 o~ the concentric tube exchanger
20 enters at 5, passes through the annular space 23, and
exits at heat exchange outlet 55. When system wa~er
reaches a predetermined temperature, thus reducing the
temperature of the aquastat or temperature sensitive
switch 56 operation of the pump 25 is initiated.
Heated storage water is then circulated via the inner
heat exchanger tube 22, hot water exit 40, and tank
return 35 to heat system water. At this point
flow through the tank 5 is predominently limited
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to the lower or mix area 65, entering the standpipe 52
via the ori~ice 41 and the upper end 50 in a ratio typi-
cally 4~1.
When the heat storage capacity contained in the tank
por~ion 65 is exhausted, exiting system water will
further reduce the temperature detected by the aquastat
56, thereby increasing the pump 25 output to a substan-
tially greater value. Due to the characteristics of the
orifice 41, additional storage water will enter the
standpipe 52, via the upper end 50. As distinguished
over the prior art systems, the particular aspect ratio
of the storage tank 6 provides a reservoir of strati-
fied water 70 above the mix section 65 at a substan-
tially higher temperature. This action arises from the
discovery that during initial-heat extraction or draw
via inlet 35 and orifice 41 very little diffusion or
mixing occurrs between tank storage liquid portions 65
and 70. Thus, it has been discovered that with the pump
25 operating a~ a high pumping rate, cold water return-
ing via inlet 35, due to its higher density, essentiallydrops to the bottom of the tank 6, establishing a verti-
cally moving wall of water having a thermoclinic separ-
ation or interface. The configuration disclosed essen-
tially minimizes thermal interaction at the thermocline
~5 with the vertically moving interface providing exit
temperatures at standpipe outlet 50, which are substan-
tially higher due to the absence of mixing, than would
be encountered with a tank having identical withdrawal
means in essentially a horizontal plane.
This discovery has resulted in utilizing what has
normally been considered a disadvantage, i.e., stratifi-
cation due to differences in density between cold and
hot storage water, to extend or sustain the delivered
temperature of the storage water. This extension is
primarily due to the piston like action of the above
mentioned verti~ally moving interface. ~xtended with-
drawal at a higher temperature results in improved
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utilizatlon of remaining stored heat due to its
increased energy or ~vailable heat. As shown on
Figure 2, a slave module 2 incorporating identical
elements o~ the master module 1 and the utilizing a
pump heat exchanger in common, results in combination
having essentially doubled heat capacity. Obviously,
those skilled in the art will realize that allowing for
increased pumping requirements, a plurality of slave
tanks could be utilized. Thus, the disclosed heater is
also modular in nature, allowing economical capacity
adjustment to particular load requirements.
The particular aspect ratio of the storage tank dis~
closed also provides a solution to the "flashing" phe-
nomena disclosed in the earlier mentioned prior art. It
has been discovered that the disclosed location of tank
inlet 35, storage water orifice 41, and immersion ele-
ments 61, result in initial withdrawal of the heated
storage water at a temperature and flow rate, substan-
tially below that of the stratified tank. Therefore,
difficulties due to flashing of the external system water
in the area internal of heat exchanger 20 at location 55,
where heated system water exits and high temperatures stor-
age water from storage via tank exit 40 enters the heat
exchanger 20 have a minimum temperature difference, are
prevented. Continued flow through orifice 41 results in
moderating storage water temperature through mixing in the
low zone 65, further eliminating flashing of the heated
system water, which would most likely occur at exit 55 of
the heat exchanger 20 as described abov~.
It should be noted that prior art systems require
the use of a substantially unreliable, and relati~ely
expensive mixing valve to eliminate flashing when stor-
age tank orientation was essentially horizontal.
Thus, it is once again apparent that the invention
disclosed here has utilized a heretofore considered
undesirable condition, i.e., storage tank temperature
stratification, in a novel and unobvious way to enhance
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and simplify the performance of a periodically charged
stored energy heater.
