OFF-PEAK ELECTRIC HEAT STORAGE SYSTEM HAVING EXTENDED HEATWITHDRAWAL

TO ALL WHOM IT MAY CONCERN:

Be it known that I, James L. McKenney, a citizen of 5 the United States of America, residing at 35 Norwell Avenue, Norwell, MA., have invented a certain new and useful hot water heater having extended heat withdrawal of which the following is a specification.

CROSS REFERENCE TO RELATED APPLICATIONS 0 In my co-pending application S/N 174,204, titled "THERMO STORAGE HEATING SYSTEM" a hot water heater employing horizontal heat storage tanks and dual immersed heat exchangers for heat extraction has been disclosed. The disclosure and all amendments thereto 5 are^"incorporated herein By reference.

Also incorporated by reference are U.S. Patents 3,422,248, titled "HYDRONIC ELECTRIC HEATING SYSTEMS", and ϋ. S. Patent 4,243,871, titled "FLUID HEATING SYSTEM WITH STORAGE OF ELECTRIC HEAT".

0 BACKGROUND OF THE INVENTION

This invention relates generally to stored energy liquid heaters, employing thermal storage. Heaters of this type have proven advantageous in supplying contin¬ uous heat at controlled temperatures to space heating 5 and process 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 0 electrical utility system through load management (Ref. Fig. 5). . The particular configuration disclosed employs water heated above its atmospheric pressure and temper¬ ature, allowing increased energy storage. Although those skilled in the art will recognize that other storage materials utilizing an intermediate liquid for transfer¬ ring heat can be substituted for water storage.

Units disclosed in the above mentioned patents function satisfactorily 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 of its diameter, in conjunction with a novel orifice/standpipe flow control, provides increased utilization of the stored energy heat through improved internal storage temperature distribution.

Therefore, the invention disclosed here provides increased heater reliability 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 elimi¬ nation of a thermal mixing valve. An- additional object of this invention is to provide a standpipe/orifice combination which apportions liquid storage media so as to maintain storage outlet temper¬ ature by minimizing mixing with return liquid.

SUMMARY OF THE INVENTION

In a preferred embodiment of the invention disclsoed a plurality of storage tanks consisting of a single master and one or more slave storage tanks is utilized to store periodically available heat, and supply contin- uous heat to a connected system, at a predetermined temperature substantially lower than that of the storage medium. An external dual concentric tube heat exchanger is utilized wherein the higher temperature storage or transfer liquid is circulated through an inner tube, 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 combinati^'on 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. Flow of high temperature storage liquid in this mode, is controlled by the stand pipe orifice. The orifice- /standpipe combination therefore control heat extrac¬ tion, and storage container internal liquid flow patterns so as to essentially confine withdrawal to pre¬ determined portions of the storage. On increased heat demand or long time heat extrac¬ tion from, the lower portion of heat storage, a temper¬ ature 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

OMFI extracted 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, establishes a thermocline, or teiϊroerature interface between return 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 horizontal 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 below 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 a 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

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. Figure 4 is a partial section of the master unit shown on Figure 1, particularly showing the heat exchanger location and its interconnections to the master storage container. Flow directions are schemat- ically shown.

Figure 5 is a sectional view of the orifice/stand¬ pipe combination.

Figure 6 is a sectional view of an alternate orifice- /standpoint embodiment.

Figure 7 (an appendix to the application) is an article "Electric Heat; The Right Price at the Right Time"; Technology Review, Volume 82, No. 3., Dec/Jan 1981.

O FI DETAILED DESCRIPTION OF THE INVENTION

The- following 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 modifications 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 claims is also intended 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 2 and 3, a master module 1 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. Electrically immersion heating elements 60 and 61 are located adjacent to the bottom of the tanks 6 and 7, as shown. Standpipes 53 amd 54 are contained in each tank having am 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, corresponding elements are dis¬ closed. However, except when the slave connection 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 storage. Those skilled in the art will readily understand that ϊ

OMFI heat withdrawal from the parallel connection of slave and 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 extremity of the tank 6. A pump 25 provides circulation of the storage water via exit 40 and inlet 35 of the tank. The concen- trie tube heat exchanger provides a flow passage or con¬ duit 22 internal of an outer conduit 21. This arrange¬ ment provides an annular flow space 23. As piped, (ref. Figure 2), the pump 25 circulates heated water drawn from the tank 6 via the standpipe 52 through both the upper end 50 and the orifice 41 as will be further dis¬ cussed.

As shown in Figures 5 (a), (b) , and Figure 6 (a), (b), two forms of outflow orifice 41 can be utilized. In the preferred embodiment shown on Figure ^'5a short length of conduit, or pipe "spud" 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 Figure 6), an orifice 41a is shown. As disclosed, the intersection of the 41a orifice, and standpipe 53 defines inlet and out¬ let control apertures 41c and 4Id. 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

OMFI location, which essentially divides the storage tank into a mix portion 65, and a stratified portion 70. Other control elements such as a master storage heat exchanger outlet temperature control 31, a storage pres- sure relief valve 30, and a drain valve 11 provide required control and access of the heating fluid/storage 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 to the outer shell 16_. No details are provided as the panel is not a part of the invention, providing electrical energy to heating elements 60 during desig¬ nated "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 of 280°F is attained. Additinal 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 entering the annular flow space 23 of the concentric tube exchanger 20 enters at^'5, passes through the annular space 25, and exits at heat exchange outlet 55. When system water reaches a predetermined temperature, thus reducing the temperature of the aquastat or temperature sensitive switch 56 and initiating 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, .supplying heated system water. At this point flow through the tank 6 is predominently limited

OMFI to the- lower or mix area 65, entering the standpipe 52 via the.orifice 41 and the upper end 50 in a ratio typi¬ cally 4/1.

When the heat storage capacity contained in the tank portion 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 stratified water 70 above the prior 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 at a^' high pumping rate, cold water return- ing via inlet 35, due to its higher density, essentially drops to the bottom of the tank 6, establishing a verti¬ cally moving wall of water having a ther oclinic separ¬ ation or interface. The configuration disclosed essen¬ tially minimizes thermal interaction at the thermocline with the vertically moving interface providing exit temperature at standpipe outlet 50, which are substan¬ tially higher due to the absence of mixing, then 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 vertically moving interface. Extended with¬ drawal at a higher temperature results in improved

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 exit and high temperature storage water from storage via tank exit 40 have a minimum temperature difference, is 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 above. it should be noted that prior art systems require the use of a substantially unreliable, and relatively 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

OM and simplify the performance of a periodically charged stored energy heater. Therefore, I claim:

OMFI