This invention relates to liquid heat systems and in particular to those employing thermal storage at ^' tempera¬ tures substantially above that of the heated system. It is well known that heating equipment utilizing thermal storage is highly desirable in that infrequent or a periodic heat source can be utilized in addition to providing a means to defer or reduce peaks on energy supplied by utility systems. Examples of a periodic heat which is made usable through a storage system include waste heat from inciner¬ ators, prime movers, and heat pump outputs.

Systems of this type are disclosed in the following U.S. Patents; 3,422,248, 3,630,275, 3,298,431, 3,411,571, 2,911,513, and 2,461,774. The above systems; in particular, the '431 and '571 patents employ thermal storage at sub¬ stantially higher temperatures than the systems which are supplied with the stored thermal energy. Use of a high temperature storage is highly advantageous as it reduces the physical size of the storage unit, and provides a large temperature difference which improves heat transfer and response to demands for heat. However, due to the fact that most heated systems utilize liquids such as water which undergo phase changes through boiling at temperatures near those required to satisfy system needs, and resultant pressure increases of the vapors produced by boiling, which in addition to being dangerous, result in unsteady flow of the liquid and substantial forces and noise due to pressure pulsations in the heated system, approaches disclosed in the above patents employ elaborate, expensive, and in many cases unreliable techniques in transferring heat.

The major technical problem involved in heating vola¬ tile liquids from high thermal potentials or temperatures is well known in the art as thermal "matching". In order to accomplish heat transfer without phase change it is necessary either to provide increased surface area, flow rates, or other methods which effectively adjust the

hydro-dynamic films between the liquid and heated surfaces to provide sufficient thermal gradiant, preventing the highly undesirable boiling. It is also necessary to accomplish this in a thermally efficient manner varying the heat transfer conditions with load, since ordinary cooling of the films would result in substantial heat losses.

A practical solution to this problem has been provide by the systems disclosed in the above United States 3,422,248, and 3,630,275 patents in which the applicant was a co-inventor and are hereby incorporated by reference to this application. The schemes disclosed in these patent are off peak stored energy heating systems which utilize a proprietary condensing system which essentially "matches" the energy contained in the higher temperature stored with that required in the reserved water system. However, a characteristic of this system requires that an initial heat demand results in a certain amount, although controlled, of liquid flashing into vapor within the storage tank heat exchanger. An additional difficulty encountered in prior art systems involves pressure differential between thermal storage and heat utilizing systems. For example, in a water heating system employing storage at 280°F (137.5°C) to provide 160° delivered hot water, heated or system water the "system" pressure cannot be reduced below saturation values for water at its highest temperature at any point in the system. Due to variation in film coefficients in various parts of the heat exchange system, it is necessary to maintain a substantially higher pressure than that corresponding to saturation at the delivered water tempera¬ ture if flashing is to be avoided. However, in many applications such as high rise building "system" pressure is relatively high and construction of condensing and/or equalizing chambers becomes difficult and expensive. Here- tofore, although high pressure heat exchanges were economically attractive and available, the flashing or thermal matching problem precluded their use. However, application of the novel concepts of the invention allows

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use of conventional heat exchanges over a wide range of liquid temperatures and pressures without flashing or phase change.

Generally speaking, therefore, the attendant diffi- culties resulting from utilizing high temperature storage to supply heat for medium or low temperature systems, at reasonable cost and providing necessary reliability is still a substantial problem in the industry. As indicated above, the present state of the art has produced only partial solutions to the problem.

OBJECTS OF THE INVENTION

It is, therefore, the object of this invention to provide a liquid heater employing high temperature heat storage and providing matching of the thermal loads and stored heat over a wide range of heat requirements and he storage temperatures.

It is a further object of this invention to provide liquid heater having heat storage and providing modulatio of the thermal output and/or temperature of the heated liquid over a wide range of heat output requirements. It is a still further object of this invention to provide a liquid heater employing heat energy storage tha is highly responsive to load changes in the heated system. It is a still further object of this invention to provide a liquid heater employing thermal storage wherein the pressures of the liquid storage medium are isolated and not affected by the operating pressure of the heated system.

An additional object of this invention is to provide a thermal storage liquid heater wherein heat exchanger between the heat storage and heat demand systems is con¬ trolled to eliminate flashing when heat is withdrawn from storage.

An additional object of this invention is to provide a unit which cools an external system by supplying heat from that system to a thermal storage mass operating at a substantially lower temperature without phase change in the external system.

SUMMARY OF THE INVENTION

A heating system is provided which utilizes thermal storage and provide closely controlled ^' or modulated output over a wide range of loads. The unit disclosed in a pre- ferred embodiment employs water in a closed circulation loop consisting of a heat exchanger shell, the liquid storage tank, a circulating pump, and contains a tempera¬ ture sensitive diverting valve. Although water is used, those skilled in the art will recognize that many other methods of storage could be employed including compounds which liquify at pre-set temperatures and are solid at others. Use of storage which undergoes a phase change or fusion would of course require auxiliary heat transfer components to equalize liquid and solid state areas and transfer rates. In the preferred embodiment, a conventional aquastat is utilized to maintain the shell temperature at a preset value. In operation, the storage tank containing water is heated, preferably by electric emersion heaters, to a value of approximately 280° (138°C) . Changes in the supplied system demand are detected as a temperature change by the aquastat sensing bulb which is located in the heat exchanger shell at its outlet side. Under these conditions should the temperature fall, the aquastat initiates pump operation providing flow of the load cooled liquid through the temperature sensing diverter valve which adjust the flow proportions to match the heat loss. These flows in the form of high temperature stored liquid and recirculated liquid, remix and enter the exchanger shell at a temperature required to maintain system load conditions. it will be appreciated by those skilled in the art that the location of the aquastat and the utilization of counter flow between shell and .Ihe tubes of the ^' heat exchanger allows the heat exchanger to supply initial demand from the water contained in the shell while at the same time supply- ing long term demand by actuating the temperature sensitive valve to increase the proportion of flow from the high temperature storage resulting in a highly responsive system. It will also be appreciated by those skilled in

the art that the establishment of flow through the heat exchanger and the storage reserve prior to any change .in state or temperature of either the stored liquid or heated liquid provides a novel method for extracting heat from the higher temperature liquid heat storage, thus a novel "thermal matching" concept is disclosed.

On a reduction in system load, the rise in system water temperature is sensed, somewhat delayed, relative to the rapid sensing of the drop in temperature since the higher temperature water first enters the heat exchanger shell at a location opposite to that of the aquastat temperature sensor. Therefore, under these conditions, pump operation is delayed, providing retention of the established flow conditions until a proper position of the mixing valve is establsihed resulting in a closed loop circulation pattern between periods of heat withdrawal, which utilizes minimum energy from the high temperature storage. This results in minimizing flashing and greatly reduced losses from the storage since the external heat exchanger pump and attendant piping operates at or very near the minimum or preset temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent upon reading the following descriptions and upon reference to the drawings in which; Figure 1 is a somewhat schematic diagram showing inter¬ connection of major components along with fluid and energy flows.

Figure 2 is a pictorial view of the preferred embodiment of the heater as viewed from one end showing typical locations of the major components, including the heat storage tank, circulating pump, tube/shell heat exchange, diverter valve and associated piping.

Figure 3 is an additional view of the heater of Figure 1 as viewed from one side.

DETAILED DESCRIPTION OF THE INVENTION

While the invention will be described in connection with the preferred embodiment utilizing water as the stora means and generally speaking utilizing water as the trans- fer medium in the system to be heated, it will be under¬ stood that this preferred embodiment does not limit the invention to that embodiment. On the contrary, a water system is disclosed since the applicant has most experienc with water systems and generally speaking feels ^' that a bes disclosure will be made available in this way. However, this disclosure is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention which will be define by the hereafter appended claims. As best indicated in Figure 1, returning system water W at temperature TW in, is circulated through the tube side 40 of the tube/shell heat exchanger 30, this flow, as indicated, transfers heat through the heat transfer path "Q" from the shell side 35. Shell side flow of the exchang (designated as W shell) is circulated through the loop con¬ sisting of the exchanger shell 35, the storage circulating pump 50 and the diverter valve 45. ^' It should be noted that the shell loop contains that portion of the liquid which the diverter valve apportions for recirculation based on the shell exit temperature. An additional loop containing the remainder of the flow from the diverter valve 45 consists of the shell 35, circulating pump 50, diverter valve 45, and the heat storage container 10.

The storage container or tank 10 utilizes conventional pressure and temperature control and relief equipment plus service accessories, not a part of the invention, but included to complete the disclosure. These include, a pressure relief valve 112 and tank pressure control 108, a tank fill valve 106, fill relief port 111, and tank temperature control 108. It will be appreciated by those skilled in the art that many other approaches to con¬ trolling pressure and temperature in a storage tank are possible.

In operation, depending on the shell exit temperature (designaed as T shell) , the diverter valve 45 apportions flow either through the storage tank 10 and then to the shell 35 or directly from the valve through the shell side. Aquastat 55 senses the temperature T shell at the heat exchanger shell exit as indicated above and initiates operation of the storage circulating pump when the shell temperature falls below a predesignaged value. The tempera¬ ture of the storage liquid contained in the tank 10 main- tains an additional pre-set temperature by the aquastat ^' 33 which senses temperature of the storage medium contained in the tank, and adds additional heat "Q" as needed. In the preferred embodiment, electric energy is utilized, however, other sources of "Q" would be suitable. In operation, the system heat requirements are detected by the aquastat 55 due to a drop in temperature of the system water returning to the tube side of the heat exchanger 40. Initially, the required heat is furnished by the volume of fluid contained in the shell side 35 of the exchanger, however, as this is limited, a sizable demand for heat will reduce the shell temperature and initiate the operation of circulating pump 50. At this point, as will be discussed later, the diverter valve 45 is essentailly adjusted for zero flow through the storage tank. Therefore, pump operation will be initiated prior to operation of the temperature sensitive diverter valve since the pumped liquid at reduced temperature is required to adjust the heat extraction from the storage tank to the demand value. This initial or "lead" pump operation is extremely important in establishing flow conditions through both the storage tank, and, in particular, estab¬ lishing heat transfer films of sufficient magnitude around the tubes 40 of the heat exchanger. This flow and film establishment provides the essential heat transfer mechanism which allows successful heat transfer from the high temperature fluid contained in storage to the relatively low temperature heated system without allowing the intermediate fluid films to reach saturation

temperature. As indicated above, entering the saturation region results in undesirable flashing of the lower tempera ture fluid.

Additional assistance in establishing the proper heat transfer mechanism during a period of load reduction is provided by the counter-flow connection of the tube/shell heat exchanger. When a reduction in the heating load occur the system return flow designated W sr begins to rise, thereby reducing the heat transfer between the tubes 40 and shell 35 and ultimately increasing the shell tempera¬ ture. At this time, the operation of the circulating pump 50 and the setting of the diverter valve 45 are such that excessive heat is being extracted from the tank 10. As the diverter valve is sensitive to liquid temperature in its loop, the rise due to load reduction will result in fast valve action to reduce the amount of liquid circulated through the high temperature storage. However, the aqua¬ stat sensor location is such that shell temperature will continue operation for an additional period of time insuring that the diverter valve reaches a position of minimum flow through the storage, a situation highly desirable from the standpoint of reducing storage losses. Additionally, the minimum storage flow position is important in readying the system for a subsequent heating cycle.

Returning now to Figures 2 and 3, showing front and side views of a preferred embodiment of the invention. The major components numbers correspond to those in Figure 1 discussed above. Figure 2 is the front view of a configu- ration embodying the invention of this disclosure utilizing a tank 10 containing water typically heated to 320°F (160°C) mounted on a suitable base 12 and having an outlet 20 internal to the tank and located at a point substantially above the tank center line. A tank inlet 15 is located near the lower surface of the tank. The relative locations of the inlet outlet are important in order to most properly utilize the heat contained in the stored liquid as will be described later. Heat sources 25 consisting of electrical

emersion heaters in this embodiment, but which those skilled in the art will readily see could be other sources of heat such as a heat exchanger tube or steam condensor. These heat sources are strategically located near the bottom center line of the tank in order to improve the heat trans¬ fer efficiency to the heat storage liquid contained in the tank. A tube and shell exchanger generally designated as 30 having a shell 35 and internal tube bundles terminated in the fittings 40 is located alongside and parallel to the tank 10. Associated piping 75, 65, and 60 connects the heat exchanger shell and the tank inlet and outlet with the circulating pump 50. Also contained in a loop as shown on Figure 1 is the diverter valve 45. An aquastat 55 is located with its sensing element internal to the heat exchanger shell.

Operation essentially is as indicated above. Water flows are indicated by arrows generally located on piping connecting the system components.

The invention disclosed also contemplates a mode of operation wherein the heat storage is operated at tempera¬ tures substantially below the system operating temperatures. In this ^■ situation, heat is withdrawn from the demand system to effect cooling. While temperature differences in cool¬ ing are substantially less than those of heating, and saturation difficulties are absent, fusion, or freezing of the cooled system liquid occurs and again heat exchange must be controlled. Therefore, the novel concepts of "thermal matching" contained in the invention of this application apply equally well to a cooling system. Thus it is apparent that there has been provided, in accordance with the invention, a stored energy water heater that fully satisfies the objects, aims and advan¬ tages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to t ose skilled in the art in light of the foregoing description. Accordingly, it

is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims. ^' *