US3766974A

US3766974A - Water heating and supply system

Info

Publication number: US3766974A
Application number: US00174090A
Authority: US
Inventors: R Kirschner
Original assignee: PATTERSON KELLEY CO
Current assignee: HARSCH Corp (HARSCO)
Priority date: 1971-08-23
Filing date: 1971-08-23
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23
Also published as: CA965670A

Abstract

A water heating and storage system accommodating occasional peak demands for hot water, characterized by the utilization of a relatively small sized heated water storage tank and means to maximize efficiencies of the heat exchanger associated therewith and to insure delivery of properly heated water during both peak and normal demand periods.

Description

United States Patent 1191 Kirschner 1 Oct.- 23, 1973 [54] WATER HEATING AND SUPPLY SYSTEM 3,666,003 5/1972 Clark, Jr. et a1 165/39 3,447,560 6/1969 Dodson et al 126/362 [75] Robe" Lakevme 2,756,739 7 1956 Schaub 126 362 Mass- 3,276,517 10 1966 Lowe 165/108 x 3,383,040 S/1968 Darm 126/362 X [73] Asslgnee' g lgfi gf i 3,195,555 7 1965 Schaub 137 114 2,308,583 1 1943 Berges 137 526 1 Notice; The portion of [he term of this patent 2,481,018 9/1949 Johnson 137/526 subsequent to Dec. 21, 1988, has been disclaimed, Primary ExaminerManuel A. Antonakas [22] Filed: 23, 1971 Attorney John B. Bean et a1. 21 App1. No.2 174,090 A [57] ABSTRACT [52] [1.5. CI 165/39, 126/362, 165/108 A water heating and Storage system accommodating [221;] i ntiiCl.t F24h 01/16 occasional peak demands for hot water, characterized 1e 0 Searc 126/361, 362, by the utilization of a relatively Small sized heated 236/245 137/114 165/39 108 water storage tank and means to maximize efficiencies of the heat exchanger associated therewith and to in- [56] References C'ted sure delivery of properly heated water during both UNITED STATES PATENTS peak and normal demand periods.

3,688,839 9/1972 Kirschner 165/108 3,666,918 5 1972 Clark, Jr. et al 219 314 14 Clams 2 Draw F'gures PAIENIEMma ma 3; 766L974 sum 10F 2 INVENTOR ROBERT E KIRSCHNEP ATTORNEYS PAIENIEBucraa ms 3; 766974 SHEET 2 [If 2 [NVENTOR ROBERT E KIRSCHNEP BY 65%; gm

A T TORNEYS WATER HEATING AND SUPPLY SYSTEM SUMMARY OF THE INVENTION The present invention relates to water heating and storage systems, and more particularly to improvements in systems adapted for installation in office, school or apartment buildings or the like, wherein space saving is an important consideration, and wherein peak demands for hot water are interspersed by pluralities of normal demands, which require water flow rates through the system substantially below that required by the peak demands.

Specifically, the system of the present' invention features a relatively small heated water storage tank. The tank is provided with a cold water supply inlet for replenishing water withdrawn from the tank through a shrouded heat exchanger with heating capacity sufficient to increase the temperature of water passing therethrough during a peak demand up to a desired delivery temperature. A pump is also connected into the discharge end of the heat exchanger and employed to normally circulate water through the heat exchanger between different levels of the tank with a view to bring up and/or maintain water within the tank at the desired delivery temperature; the heat exchanger being regulatable by a suitable sensor arranged to sense the temperature of water passing from the heat exchanger.

In that heat exchangers must be designed to at least substantially accommodate peak hot water demands, they necessarily possess reduced heat exchange efficiencies during normal demand periods, which may require flow rates which are typically less than 50 percent of the flow rate experiencedduring a peak demand. Further, time delays are necessarily experienced between the sensing of the temperature of water passing from the heat exchanger and regulation of the heat exchanger in accordance therewith, as by adjustably controlling a flow control valve through which a suitable heating medium is admitted to the heat exchanger. As a result, a heat exchanger is ofttimes subject to wildly cycling or fluctuating operating conditions, thereby resulting in inefficient power consumption and substantial variances from the desired temperature of the delivery water.

The above problems are particularly acute when the heating medium is steam, but may be encountered in varying degrees when other heating mediums including boiler water are employed. In this respect, it has been recognized that when conventional flow control valves are operated from between about and 50 percent capacity (which accommodates for normal hot water demands on the system) such valves are'very inefficient and promote cycling of the temperature control system. However, as the control valve is operated from between about 50 and 100 percent capacity, the problem of cycling of the system is progressively reduced, because both the flow control valve and the heat exchanger approach their rnost efficient ranges of operation.

In accordance with the present invention, the problems heretofore described are substantially reduced by providing the heat exchanger with 'a pair of water inlets; a first of such inlets accommodating for system recov cry and normal demand or withdrawal periods, and the second inlet accommodating for additional water intake requirements occasioned by peak demands.

For example, as shown in the drawing herewith the first water intake to the heat exchanger is in the form of a vertically extending manifold arranged to take in water from different levels of the tank at which levels water at varying temperatures will exist, due to pump circulation or turbulence conditions occasioned by the introduction of cold supply water into the tank during a withdrawal. The manifold, in effect, serves to pass water to the heat exchanger at some integrated or averaged value, which increases or decreases in a relatively smooth or consistent manner. By thus dampening the variations in temperature of water passing to the heat exchanger, the magnitude and period of temperature variations in the water passing from the heat exchanger into association with the temperature sensor is of course reduced, thereby permitting the control valve to be smoothly operated to achieve optimum efficiency of the temperature control system during both recovery and withdrawal periods.

The manifold is designed to accommodate only recovery circulation and withdrawals at normal rates; thereafter effectively limiting the rate at which water may be withdrawn therethrough by creating an effective pressure drop, thereby establishing a pressure differential between the interiors of the tank and the heat exchanger. In accordance with the present invention this pressure differential is employed to control operation of the second inlet means, which is in the form of a valve automatically operable to permit appropriate amounts of water to be added to that taken in through the manifold whenever required by larger than normal withdrawal demands. Preferably, the valve when opened, would initially permit hot water from within the upper level of the tank to enter the heat exchanger;

thereby dampening the temperature transition.

As will be appreciated, the admission of water through the second inlet means will not by itself, produce undesirable cycling of the control system, since the system design will be such that the heat exchanger and control valve will be operable in their most efficient operational ranges during above normal draws.

DRAWINGS I The nature and mode of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein:

FIG. 1 is a schematic sectional view illustrating one form of the water heating and storage system of the present invention; and

FIG. 2 is a schematic sectional view illustrating a modified form of the present invention.

DETAILED DESCRIPTION Now referring more particularly to FIG. 1, the water heating and storage system of the present invention is generally designated as 10 and shown as including a generally horizontally disposed water storage tank 12 having a cold water supply inlet connection 14 for replenishing water withdrawn from the tank.

A heat exchange unit, generally designated at 16, includes a tubular shroud 18 housing a bundle of return bent heat-exchange tubes 20. Tubes 20 extend through a tube sheet 22, which closes the outer end of shroud 18, and into a heating medium supply bonnet 24. Alternately disposed baffle plates 26 are preferably arranged within shroud 18 to guide the flow of water therethrough along an undulating or zig-zag path relative to tubes to insure maximum heat exchange efficiency.

Bonnet 24 is provided with an internal partition or rib 28, which divides the fluid chamber portion thereof into multiple sections into which in turn are connected heating medium inlet and

outlet conduits

30 and 32, respectively. The heating medium may be steam, boiler water, etc. The admission of the heating medium through inlet conduit 30 may be varied by a flow control valve 34 whose operation is adjustably controlled by a suitable water temperature sensing device 36 arranged adjacent the outlet or delivery end portion of shroud 18.

By referring to FIG. 1, it will be apparent that heated water may be 'withdrawn from the delivery or outlet end portion of shroud 18 either for delivery to a point of use through a heated water delivery conduit 38 and- /or for reintroduction into a lower level of tank 12 by a conduit 40 including a pump 42, which preferably runs continuously.

At this point, it will be understood that heat exchange unit 16 is preferably designed to raise the temperature of water passing therethrough up to a desired withdrawal or delivery temperature, when such water is flowing at a given maximum rate determined by a peak demand required by fixtures, not shown, to which delivery conduit 38 is connected. However, for many installations, including multiple tenant dwellings, normal demands occurring periodically throughout any given 24 hour period are normally satisfied by the operations of the heat exchange unit at less than about 50 percent capacity.

The inlet end portion of shroud 18 is disposed interiorly of tank 12 and receives tank water to be heated from anovel selective flow source/rate feed system generally designated as 44. System 44 includes a first water intake device in the form of a substantially vertically extending manifold 46, which is arranged to take in water from throughout a relatively lower region of the tank, and a second water intake device in the form of a pressure-differential responsive valve 48, which is arranged adjacent the upper end of manifold 46 in order to take in water from a relatively upper region of the tank.

Manifold 46 is shown as being provided with a plurality of water intake openings 50, which are spaced vertically along the manifold and an outlet opening 52.arranged in flow communication with 'the inlet end portion of shroud 18. As will be apparent from viewing FIG. 1, intake openings 50 are arranged in flow communication with different levels within tank 12 at which levels water at different or varying temperatures may exist, due to pump circulation or turbulance occasioned by the introduction of cold supply water into the tank during a draw period.

Manifold 46 may be fabricated in any suitable manner, as from standard tubular stock, and inlet openings 50 may be suitably formed, as by a series of saw cuts or drilled or punched holes through the side wall of the tubular stock. Alternatively, manifold 46 may be inclined relative to its position shown in FIG. 1, and/or the plural inlet openings may be replaced by a single elongated inlet opening arranged to take in water from desired levels within the tank.

Further, the inlet openings of manifold 46 are sized so as to permit up to about a normal rate of flow of water into shroud 18, which is an amount equivalent to a selected rate of circulation determined by operation of pump 42 plus withdrawals from the system at normal" rates through delivery conduit 38. Thus, the operation of pump 42 and the initiation of a draw will cause water to be sucked into manifold 46 through openings 50 from all levels within the tank that are within the elevational reaches of the manifold, such water being mixed or integrated within the manifold for passage into heat exchange association with tubes 20. The amounts of water withdrawn from each of the several levels within the tank may be equal or varied, depending upon the relative sizes and placements of the openings 50. It will be understood that the term lower region is meant to include a substantial portion of the vertical extent of tank 10, in that it is desirable to permit manifold 46 to take in water from levels at which widely differing water temperatures may exist. On the other hand, the term upper region is meant to include only a relatively small portion of the vertical extent of the tank in which is normally formed a reservoir of hot water, as a result of stratification phenomena.

Thus, it will be appreciated that the provision of manifold 46 serves to increase the recovery efficiencies of the system. In this respect, the mixing or integrating of water from the different temperature levels within the tank serves at least for a substantial portion of the recovery period to decrease the temperature of water supplied to shroud 18, whose elevated position would otherwise result in only relatively hot water from the relatively upper region of tank 12 to be drawn thereinto; thereby forcing the heat exchange unit to initially operate in a more efficient range in order to quickly bring the circulated water up to the prescribed withdrawal temperature. The required output of the heat exchanger would of course be progressively reduced as all the water within the tank is brought up to the substantially desired withdrawal temperature.

When a normal draw is initiated and cold supply water enters the tank, manifold 46 serves to minimize sudden turbulence induced variations in the temperature of water passing into shroud 18 with the result that the integrated" or averaged temperature of such water is progressively reduced. As a result, temperature sensor 36 serves to smoothly and progressively open the control valve 34 to permit heating of the water to be more efficiently accomplished.

Valve 48 is adjusted so as to remain closed when operating under pressure differentials such as are encountered under normal operations of the system. Thus, as indicated above, when operating under recovery and normal withdrawal conditions, pump 42 gently circulates water at a selected rate through manifold 46, shroud l8, and then into the lower level of the tank; thereby maintaining and/or gradually bringing the entire tank contents up to the desired withdrawal temper ature However, when withdrawals of hot water through conduit 38 increase above the normal withdrawal rate, the pressure drop across manifold 46 becomes sufficient to initiate opening of valve 48 so as to allow appropriate amounts of hot water to be drawn from the uppermost region or level of the tank and to be mixed with the relatively cool water being drawn in through manifold 46. The withdrawal of relatively hot water from the upper level of the tank serves to initially meet the excess demand for water at the desired withdrawal temperatures without requiring an immediate surge of heater operation such as would otherwise be occasioned if valve 48 were to remain closed and cause the inflow of relatively cold supply water through the lower portion of the manifold in an amount sufficient to accommodate for the increased demand. The amount of hot water present in the upper level of tank 12 is sufficient to afford the heat exchanger time to obtain its most efficient operating condition. Also, the ad-' mission of water through valve 48 reduces the problem of undesirable control system cycling. As illustrated at FIG. 1, the opening and closing of valve 48 may be controlled by a suitable spring device 54; which is made accessible for purposes of adjustment and/or replacement by providing tank 12 with an access opening 56.

FIG. 2 illustrates a modified form of the heating system of the present invention, wherein similar components are designated by similar prime numerals. In this form, tank 12' is of the stand up type in order to minimize the floor space required for installation; and inlet connection'l4', conduit 40' and manhole 56" are arranged to permit tank 12' to be installed within a room or room recess with minimum spacing between the room walls and three sides of the tank.

Thus, it will be appreciated that the present invention provides a novel water heating and storage system embodying various important features and advantages as set forth hereinabove. While the invention has been illustrated and described with reference to a heating system by steam or hot fluid energized type immersion heater, it will be understood that the invention maybe embodied in other forms of heating systems' We claim:

1. A system for supplying water within a desired temperature range to an installation characterized as having peak demands for such water at up to a given maximum rate of flow and normal demands for such water.

at normal rates of flow substantially less than said maximum rate of flow, said system comprising in combination:

a hot water storage tank having a capacity sufficient to accommodate for only relatively short demands of water within said temperature range at said maximum rate;

inlet means for delivering relatively cold supply water into a relatively lower region of said tank to replenish water withdrawn therefrom, whereby said tank tends to become filled with relatively cold water progressively upwardly throughout said lower region as water is withdrawn from said tank;

water temperature sensing means;- E

a conduit system including (1) heater means, having means responsive to said sensing means for regulating the heating output thereof, (2) intake means for delivering tank water to said heater means and (3) means downstream of said heater means for normally circulating water heated by said heater means into said tank at a selected rate thereby tending to add heat to the water contents of said tank and to establish a reservoir of tank water heated up to within said temperature range at least within a relatively upper region of said tank; and

outlet means connected into said conduit system downstream of said heater means for withdrawing water from said tank for delivery to said installation upon demand at rates up to said maximum rate;"

said intake means including (1) first means fordelivering tank water to said heater means from said lower region at flow rates accommodating for said selected flow rate and said normal flow rates and (2) normally-closed second means for delivering tank water to said heater means from said upper region whenever the rate of withdrawal of water through said outlet means is at a rate in excess of said normal flow rates.

2. A system according to claim 1, wherein said heater means is characterized as having relatively maximum heating efficiency when operating at a heating output rate needed to heat the water to within said temperature range at said maximum withdrawal rate and being relatively inefficient when operating at a heating output rate needed to heat water to within said temperature range at flow rates below said normal rates.

3. A system according to claim 2, wherein said heater means includes a steam powered heat exchanger and a steam flow control valve operable in response to said temperature sensing means.

4. A system according to claim 1, wherein said first intake means includes means for inducing a pressure differential in said conduit system upstream of said heater means relative to said tank whenever the withdrawal demand exceeds said normal flow rates, and said second intake means includes normally-closed valve means operable in response to said pressure differential.

5. A system according to claim 1, wherein said first intake means is arranged in flow communication with vertically different levels within said tank at which levels different water temperatures may exist, whereby the temperature of water passing through said first intake means into heat exchange relationship with said heater means is an integral of the temperatures of water withdrawn from said levels.

6. A system according to claim 5, wherein said first intake means includes means for inducing a pressure differential in said conduit system upstream of said heater means relative to said tank whenever the withdrawal demand exceeds said normal flow rates, and said second intake means includes normally-closed valve means operable by said pressure differential to admit the additional flow of water to said heater means.

7. A system according to claim 6, wherein said heater means includes a steam powered heat exchanger and a steam flow control valve operable in response to said temperature sensing means, and said control valve is characterized as having an efficiency of less than about 50 percent for heating tank water to within said temperature range when withdrawal flow rates are less than about said normal flow rates and as having progressively increasing efficiency as withdrawal flow rates increase above said normal flow rates towards said relatively maximum flow rate.

8. A system according to claim 1, wherein said water circulating means includes a continuously driven pump.

9. A system according to claim 1, wherein said conduitsystem includes a shroud having an inlet end portion disposed within said tank in flow communication with said intake means and an outlet end portion disposed exteriorly of said tank in flow communication with said outlet means and said water circulating means, said water circulating means includes a continuously driven pump and delivers circulated water into said lower region of said tank, said heater means is an immersion heater to which heating medium is supplied under the control of a heating medium flow control valve, said sensing means is arranged within said outlet end portion, said first intake means is open to vertically spaced levels within said tank at which levels significantly different water temperatures may be expected to exist during operation, said first intake means includes means for inducing a pressure differential in said shroud inlet end portion relative to said tank whenever the withdrawal demand exceeds said normal flow rates, and said second intake means includes a normallyclosed spring-biased valve operable by said pressure differential to admit additional water flow to said r d. nlasnyextismt a 10. A system according to claim 1, wherein said water temperature sensing means senses the temperature of the heated water downstream of the heater means. 11. A system for supplying water within a desired temperature range to an installation characterized as having peak demands for such water at up to a given maximum rate of flow and normal demands for such water at normal rates of flow substatially less than said maximum rate of flow, said system comprising in combing tignz i f,. a a hot waterstorage tank having a capacity sufficient to accommodate for only relatively short demands of water within said temperature range at said maximum rate; inlet means for delivering relatively cold'supply water into a relatively lower region of said tank to replenish water withdrawn therefrom, whereby said tank tends to become filled with relatively cold water progressively upwardly from said lower region as water is'withdrawn from said tank; water temperature sensing means; water heating means including (1) a heater having means responsive to said sensing means for regulating the heating output thereof to maintain the temperature of water passing downstream therefrom within said temperature range, (2) intake means for delivering tank water to said heater and (3) means for increasing the temperature of the tank water at least within an upper region of the tank to within said temperature range during periods of less than normal demands; and outlet means for withdrawing water from said tank successively through said intake means and said heater for delivery to said installation at flow rates up to said maximum rate; said intake means including (1) first means for concurrently delivering tank water to said heater from vertically different levels within said tank, at which said control valve is characterized as having an efficiency of less than about 50 percent for heating tank water to within said temperature range when withdrawal flow rates are less than said normal flow rates and as having progressively increasing efficiency as withdrawal flow rates increase above said normal rates towards said relatively maximum flow rate.

13. A system according to claim 12, wherein:

said first intake means includes means'for inducing a pressure differential in said intake means relative to said tank whenever the withdrawal demand on said outlet means exceeds said normal flow rates; and

said second intake means includes normally-closed valve means operable in response to said pressure differential to provide additional flow of water to said intake means. k

14. A system for supplying water within a desired temperature range to an installation characterized as having peak demands for such water at up to a given maximum rate of flow and normal demands for such water at normal rates of flow substantially less than said maximum rate of flow, said system comprising in combination:

a hot water storage tank having a capacity sufficient to accommodate only relatively short demands for water within said temperature range at said maximum rate;

inlet means for supplying replacement water into the lower region of said tank upon withdrawals therefrom, whereby said tank remains filled with water at different temperatures, the water in the upper region of the tank being normally considerably hotter than that in the lower region of the tank;

a conduit system including (1) a regulatable heater for heating water passing therethrough, (2) a first water intake means disposed within the lower region of said tank and (3) a second water'intake means in communication with the upper region of said tank;

outlet means for withdrawing water from said tank for delivery to said installation upon demand at rates up to said maximum rate, said outlet means being coupled into said conduit system downstream of said heater; and

water temperature sensor means in association with said conduit system for regulating the operation of said heater in response to changes in temperature of the water flowing through said conduit system; said first water intake means including means for accommodating normal rate flow demands upon said system without substantial pressure drop between the interior'of the tank and the interior of said conduit system, and said second water intake means having a pressure responsive control means operable to maintain said second water intake means closed under said normal rate flow conditions and to open said second water intake means in response to a flow demand above said normal flow rates.

3 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,766,974 Dated October 23, 1973 lnventofl Robert F. Kirschner It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 27, after "ferential" insert -to provide additional flow of water to said heater means--.

Signed and sealed this 2nd day of April 197 4.

(SEAL) Attest:

EDWARD I' LFLETQEERJR. C MARSHALL DANN [attesting Officer Commissioner of Patents

Claims

1. A system for supplying water within a desired temperature range to an installation characterized as having peak demands for such water at up to a given maximum rate of flow and normal demands for such water at normal rates of flow substantially less than said maximum rate of flow, said system comprising in combination: a hot water storage tank having a capacity sufficient to accommodate for only relatively short demands of water within said temperature range at said maximum rate; inlet means for delivering relatively cold supply water into a relatively lower region of said tank to replenish water withdrawn therefrom, whereby said tank tends to become filled with relatively cold water progressively upwardly throughout said lower region as water is withdrawn from said tank; water temperature sensing means; a conduit system including (1) heater means, having means responsive to said sensing means for regulating the heating output thereof, (2) intake means for delivering tank water to said heater means and (3) means downstream of said heater means for normally circulating water heated by said heater means into said tank at a selected rate thereby tending to add heat to the water contents of said tank and to establish a reservoir of tank water heated up to within said temperature range at least within a relatively upper region of said tank; and outlet means connected into said conduit system downstream of said heater means for withdrawing water from said tank for delivery to said installation upon demand at rates up to said maximum rate; said intake means including (1) first means for delivering tank water to said heater means from said lower region at flow rates accommodating for said selected flow rate and said normal flow rates and (2) normally-closed second means for delivering tank water to said heater means from said upper region whenever the rate of withdrawal of water through said outlet means is at a rate in excess of said normal flow rates.

9. A system according to claim 1, wherein said conduit system includes a shroud having an inlet end portion disposed within said tank in flow communication with said intake means and an outlet end portion disposed exteriorly of said tank in flow communication with said outlet means and said water circulating means, said water circulating means includes a continuously driven pump and delivers circulated water into said lower region of said tank, said heater means is an immersion heater to which heating medium is supplied under the control of a heating medium flow control valve, said sensing means is arranged within said outlet end portion, said first intake means is open to vertically spaced levels within said tank at which levels significantly different water temperatures may be expected to exist during operation, said first intake means includes means for inducing a pressure differential in said shroud inlet end portion relative to said tank whenever the withdrawal demand exceeds said normal flow rates, and said second intake means includes a normally-closed spring-biased valve operable by said pressure differential to admit additional water flow to said shroud inlet end portion. 10 A system according to claim 1, wherein said water temperature sensing means senses the temperature of the heated water downstream of the heater means.

11. A system for supplying water within a desired temperature range to an installation characterized as having peak demands for such water at up to a given maximum rate of flow and normal demands for such water at normal rates of flow substantially less than said maximum rate of flow, said system comprising in combination: a hot water storage tank having a capacity sufficient to accommodate for only relatively short demands of water within said temperature range at said maximum rate; inlet means for delivering relatively cold supply water into a relatively lower region of said tank to replenish water withdrawn therefrom, whereby said tank tends to become filled with relatively cold water progressively upwardly from said lower region as water is withdrawn from said tank; water temperature sensing means; water heating means including (1) a heater having means responsive to said sensing means for regulating the heating output thereof to maintain the temperature of water passing downstream therefrom within said temperature range, (2) intake means for delivering tank water to said heater and (3) means for increasing the temperature of the tank water at least within an upper region of the tank to within said temperature range during periods of less than normal demands; and outlet means for withdrawing water from said tank successively through said intake means and said heater for delivery to said installation at flow rates up to said maximum rate; said intake means including (1) first means for concurrently delivering tank water to said heater from vertically different levels within said tank, at which levels significantly different water temperatures may be expected to exist during operation, at rates accommodating for said nOrmal flow rates and (2) normally-closed second means for delivering additional tank water to said heater from said upper region of said tank to accommodate for withdrawal at rates in excess of said normal flow rates.

12. A system according to claim 11, wherein: said heater means includes a steam powered heat exchanger and a steam flow control valve operable in response to said temperature sensing means; and said control valve is characterized as having an efficiency of less than about 50 percent for heating tank water to within said temperature range when withdrawal flow rates are less than said normal flow rates and as having progressively increasing efficiency as withdrawal flow rates increase above said normal rates towards said relatively maximum flow rate.

13. A system according to claim 12, wherein: said first intake means includes means for inducing a pressure differential in said intake means relative to said tank whenever the withdrawal demand on said outlet means exceeds said normal flow rates; and said second intake means includes normally-closed valve means operable in response to said pressure differential to provide additional flow of water to said intake means.

14. A system for supplying water within a desired temperature range to an installation characterized as having peak demands for such water at up to a given maximum rate of flow and normal demands for such water at normal rates of flow substantially less than said maximum rate of flow, said system comprising in combination: a hot water storage tank having a capacity sufficient to accommodate only relatively short demands for water within said temperature range at said maximum rate; inlet means for supplying replacement water into the lower region of said tank upon withdrawals therefrom, whereby said tank remains filled with water at different temperatures, the water in the upper region of the tank being normally considerably hotter than that in the lower region of the tank; a conduit system including (1) a regulatable heater for heating water passing therethrough, (2) a first water intake means disposed within the lower region of said tank and (3) a second water intake means in communication with the upper region of said tank; outlet means for withdrawing water from said tank for delivery to said installation upon demand at rates up to said maximum rate, said outlet means being coupled into said conduit system downstream of said heater; and water temperature sensor means in association with said conduit system for regulating the operation of said heater in response to changes in temperature of the water flowing through said conduit system; said first water intake means including means for accommodating normal rate flow demands upon said system without substantial pressure drop between the interior of the tank and the interior of said conduit system, and said second water intake means having a pressure responsive control means operable to maintain said second water intake means closed under said normal rate flow conditions and to open said second water intake means in response to a flow demand above said normal flow rates.