US2889116A

US2889116A - Hot water heating systems

Info

Publication number: US2889116A
Application number: US355602A
Authority: US
Inventors: Calvin D Maccracken; George N Miles
Original assignee: JET HEET Inc
Current assignee: JET HEET Inc
Priority date: 1953-05-18
Filing date: 1953-05-18
Publication date: 1959-06-02
Anticipated expiration: 1976-06-02

Description

"vm inlizi June 2, 1959 c, acc c T- 2,889,116

HOT WATER HEATING SYSTEMS 2 Sheets-Sheet l FLOW sPAcE CONTROL HEATERS Filed May 18, 1953 BOILER BURNER um Tn aw I 20 WA 'O/VOLUME; .3

LOWHEAT 24 STORAGE g cAPAuTY) sERwcE WATER 5O HEATER 28 5 19.].

M, IHIHIHHI. 9 44 NORMALLY I OPEN 2 2o S INVENTOR.

2 BY GEORGE N. MILE$ m Maw ATTORNEY CALVIN D. MAcCKAcKEN June 2, 1959 c, MaccRACKEN ET AL 2,889,116

HOT WATER HEATING SYSTEMS I Filed May 18, 1953 2 Sheets-Sheet 2 v PRIMARY J r common.

I/BOILER I IE QE IEJ NORMALLY 6 CLQSED I sPAc ITHERMOSTAT' I002 r-- *1 ,sERvIcE INVENTOR. CALVIN D. MACCRACKEN. GEORGE N. MILES W #4: ATTORNEY.

Patented June 2, 1959 HOT WATER HEATING SYSTEMS Calvin D. MacCracken and George, N. Miles, Tenafly, NJ., assignors to Jet-Heat, Inc., Englewo'od, N.J., a corporation of New York Application May 18, 1953, SerialNo. 355,602

13 Claims. ('01. 237- 8) This invention relates toimprovements in heating systems, and particularly toan improved heating system of the hot water type forboth space heating and service water heating.

At one time, it was common practice tocirculate the heating medium through the various components of a hot water heating system solely by thermogravitational action. However, with the advent of intermittently fired burners both for warm air and for hot water heating systems, the hot water system with thermogravitational circulation was at a competitive disadvantage because of its slower pickup or response toa demand for heat. This led" to the adoption of circulating pumps in hot water systems. for speeding up the distribution of heated water to the space heating elements (e.g., radiators, convectors, etc.), although it is still common practice to supply hot liquid by thermogravitation to the service water heater in systems supplying both space and service water heat.

Forced circulationalone, however, does not give an entirely satisfactory solution to the problem. In the usual case, a demand. for space heat will come after the heating system hasbeen quiescent for a time, so that the temperature of the water in the space heating elements will be at or near room temperature. Therefore, in order to have fast pickup, there should be somewhere in the system a reserve supply of hot water that can be circulated promptly to the space heaters, because the conventional boiler will not pass heat to the liquid rapidly enough to raise the system liquid temperature instantaneously.

In a majority of hotwater heating, systems, the boiler cqmprises one or more thick-walled cast iron or steel sections of considerable water capacity and considerable heat storage capacity. In such systems, it is the water in the boiler that is relied; on as the hot reserve supply that; will be available for quick pickup when there is a demand for space heat. However, as is Well known, draftinduced air flow through the combustion space andflue vention to provide an improved hot Water heating system which will respond rapidly to a demand for space heat, and yet which will have very low stand-by losses and consequent economy of operation.

Another object of the invention is to provide a hot water system, both for space heating and; for service water heating, that will insure an adequate supply of hot service gas passages of a-boiler when the burner is not operating has a definite cooling. effect on the boiler and the water containedtherein. This so-called stand&by loss isquite substantial, audit. the intervals between. firings of the boiler are of any appreciable duration, practically all" of the reserye heatin the boiler water and the boiler walls will be dissipated between callsfor heat. This, of course, will result in a marked lag in the space heating pickup, regardless of the factthat forced: circulation is used, be-

cause the boiler walls and the water in the boiler both must be reheated before any heat will be delivered to the space heaters.

In short, the only reliable method of avoiding pickup ag n ys em f e o e ng yp s o arrange system controls so that the burner will operate as often as neededto maintain the boiler water at the required temperature, This is a, wasteful expedient, since the boi er m st be r d r y o ake p c s y f the stand;by losses, even though there is little demand for space heat.

It is, accordingly, among the objects of the present in- Water at all times, that will have minimum response time when space heat is called for, that will have negligible stand-by losses, and in which the space heaters are bypassed by means of simple, inexpensivev elements when no. space heat is required.

In accordance with a preferred embodiment of the invention, the foregoing and other related objects and advantages are attained in a system wherein heated water is force-circulated from a boiler of very small water capacity and negligible heat storage capacity through serially connected space heating and service Water heating elements. By having a boiler of very low water-andheat storage capacity, the stand-by losses are kept at a minimum. A valving and bypass arrangement paralleling the space heating element or elements allows. the system to force-circulate hot water solely through: the service water heater when space heat is not needed, to maintain the service water temperature. Then, when space heat is called for, quick pickup is assured by the reserve supply of heated water that is maintained in the service water heater. Since the service water heater can be insulated readily to store heat much more efiiciently than a boiler subject to stand-by draft cooling, it is seen that the quick pickup requirement is simply satisfied and at a minimum of operational expense.

A more complete understanding of the invention, and of furtherobjects and features thereof, can be had by reference to the following description of illustrative embodiments thereof, when considered in connection with the accompanying drawing, wherein:

Figure 1 is a block diagram showing the general arrangement of the elements in a system embodying the invention,

Figure 2 illustrates a three-way valve suitable for use in the system of Figure 1,

Figures 3 and 3a are schematic diagrams, showing in more specific detail the arrangement of elements in a system embodying the invention.

Figure 4 is a circuit diagram, showing an electric control circuit forthe system of Figure 3, and

Figure 5. is a schematic diagram showing an alternative arrangement of elements in a system embodying the invention.

Referring to Figure l of the drawing, the elements of a hot water heating system embodying the present invention include a boiler-burner unit 10, preferably having a boiler of small water-containing volume and relatively low heat storage capacity. A particularly suitable boilerburner unit for a system of the type being described is disclosed and claimed in Patent No. 2,773,488. of Mac- Cracken et 211., issued December 11', 1956 and assigned to the assignee of the present application. Briefly, the boiler element inthe unit described in detail in, the foregoing patent comprises a quilted surface shell formed of thin superposed metalsheets. The superposed sheetsare sealed together along the edges and at spaced points therebetween, and separated except where sealed to. provide a water jacket of relatively small water-containing volume and low heat storage capacity. It will, of course, be understood that the present invention is not limited to this specific type of boiler element, and that the system described herein can be used to. advantage with many .water heater.

hereinafter. One line 16 from the flow control 14 leads to one or more space heating elements 18, such as radiators, convectors, radiant panels, or the like. A second line 20 from the control 14 by-passes the space heaters 18 and connects on the down-stream side of the heaters to a connecting line 22 which leads to a service water heater 24. As is explained more fully hereinafter, the heater 24 may be either of the storage type, where in boiler water is circulated through a coil in a hot water storage tank, or of the tankless type, wherein the boiler water circulates through a tank which contains a coil for conducting service water. In either event, the service water will comprise two water-conducting elements in heat exchanging relation, and one of these elements preferably will comprise a tank having a substantial water storage capacity, say, of the order of 20 gallons or more. From the service water heater 24, a line 26 leads to a circulating pump 28 which is connected to a boiler inlet line 30.

It will be seen from the foregoing that the space heaters 18, the service water heater 24, and the pump 28 all are connected in a series liquid circuit between the boiler outlet and

inlet lines

12 and 30, with a by-pass line 20 paralleling the space heater 18. The control 14 and

coupling lines

16, 20 are so arranged that the boiler water can be circulated either through or around the space heaters 18, as required. However, the service water heater 24 will always be in the circuit.

In operation, if heat is required either by the space being heated or by the service water heater, a suitable electric circuit will function to energize the boiler-burner unit for heating the boiler water. Simultaneously, the pump 28 will be energized to force circulation through the circuit. If the space to be heated is calling for heat, the control 14 can be arranged to direct the boiler water to circluate through the line 16, through the space heaters 18, through the line 22 and thence through the service .water heater 24. If, on the other hand, heat is required only for the service water heater 24, then the control 14 can be set to divert the entire flow through the service In either case, however, it is seen that the water is force-circulated through the service water heater. The advantage of this is two-fold. First, a supply of hot service water is assured at all times, with quick recovery after a prolonged draw. Second, the heater 24 serves as a reservoir of heated liquid which is always available for quick pickup when the system is being asked to supply space heat. Therefore, even though the space heating portion of the system may have been quiescent for a considerable period of time, there will always be a reserve supply of hot liquid to give a quick space heat response when space heat is called for. At the same time, the stand-by losses from the storage heater and from the low heat-and-water storing boiler will be quite negligible.

The flow control 14 may take any one of a number of different forms. For example, a three-way valve 32, may be used at the junction of the outlet line 12 and the

distribution lines

16, 20, as shown in Figure 2. Such a. valve can be operated either manually or by a system of automatic controls to direct the system circulation either through the line 16 to the space heaters, or through the line 20 around the space heaters, depending on the heating requirements at any given time. However, a manual control ordinarily will be objectionable, as it will require recurrent attention, while an automatic control system for a valve of the type shown in Figure 2 will be relatively complex. Examples of very simple (and, hence,

preferable) automatic flow control means, wherein the fiow is primarily controlled by temperature responsive elements, are described in connection with other system details given hereinafter.

In hot water heating systems heretofore proposed wherein the boiler water is force-circulated either through the space heaters or the service water heaters, it has been customary, and, in fact, rather essential, to give the 4 service water heater priority of demand on the system output in order to insure an adequate supply of hot service water at all times. Otherwise, during a prolonged space heat demand, the hot service water supply might be completely exhausted and could not be replenished until the space heat demand was satisfied. On the other hand, this can well entail a substantial delay in supplying space heat, where calls for both space and service water heat occur simultaneously. This is particularly true where there is a prolnoged demand for hot service water. In the system of the present invention, there is no such limitation on the choice of demand priority. By circulating the boiler water through the space heaters and the service water heater in series, either space heat demands or service water heat can be given nominal priority without seriously effecting the supply of the secondary demand.

With the so-called tankless type service water heater, there is a theoretical advantage in giving the service water heater demand priority, which simply means arranging the controls so that the temperature of the service heater tank must be above a preset minimum before any space heat will be delivered. With the storage tank type of heater, there is no reason to prefer the service heater, and space heat can be given priority. In either case, however, within a comparatively short time after space heating begins, the temperature of the system liquid will priority vs. space heat priority in the system of the present invention is not nearly as critical as it is in a system where only one demand can be handled at any given time.

Consider, for example, the system shown in Figure 3. This system is seen to include a boiler-burner unit 10, comprising a boiler 34 carrying a top-mounted burner 36 as described in the above-mentioned patent of Mac- Cracken et a1. At a T 37, the boiler outlet line 12 is connected to an expansion tank 38 and to the inlet port 39 of a Venturi fitting 40. The Venturi fitting 40 is cooperable with a solenoid actuated valve 42 in a by-pass line 20 to control the direction of flow of the boiler water.

The Venturi fitting 40 comprises a hollow casting having an inlet port 39, a first outlet port 44 opposite the inlet port 39, and a side outlet port 46. A tapered nozzle 48 extends from the inlet port 39 to a point somewhat beyond the second or side outlet port 46. The by-pass line 20 is connected to the first outlet port 44, while a line 16 extends from the second outlet port 46 through a check valve 50 to a space heater 18, schematically represented as a radiator. The by-pass line 20 extends through the valve 42 to a T 52 in the radiator outlet line 22.

the water temperature in the boiler.

'In the Figure 3 system, the valve 42 is arranged to be actuated by a solenoid 66 that is connected in the electrical control circuit for the system, which circuit will now be described.

Referring to Figure 4, there is shown an electrical circuit comprising power supply lines 68 leading in from the usual alternating voltage supply source (not shown).

.Con'nected across the lines 68 is the primary winding 70 of a step-down transformer 72. The transformer secondary 74 is connected through the operating winding 76 of a relay 78 to the

contacts

80, 82 of athermostat element 84.

The thermostat 84 will 'belocated. at-a suitable point inthe space stozbe -heated,. and .may compriserany one ofaa;,variety of. temperature-responsive switching devices wellknownin the art. For simplicity,- one ofthe thermostat contacts. 80-is shown as a bimetallic member that will bend in responseto variationsin the temperature of the space in whichathe; thermostatis located tomake orbreakt a circuit through the other contact 82.

The relay 78 has two sets of contacts, 86, 88, and 90, 92; One set of'contacts, 90, 92, is connected to the supply :lines 68in serieswiththe solenoid 66 that actuates the .valve 42. The other set of relay contacts 86, 88is connected in .series'with the

contacts

96, 98 of therboiler Aquastat 64 to make or. break acircuit from the/lines. 681' through a -so-called primary control element? 94- A second set of contacts for completing a similar circuit through the primary control 94 and the Aquastat 64 comprises thecontacts 100, 102 of the servicewater heater Aquastat 62. Both aquastats are shown schematically as, having a temperature sensitive bimetal contact element (96 and 100').

Forsimplicity, the details of the. primary control 94 are not shown, as such controls are well known inthe art. Suffice it .to say that whenta circuit from the power supply 68 is completed. through the primary control, the burner 36 and the pump 28 in the Figure 3 system will be energized. Since the

boiler Aquastat contacts

96, 98 normallywill be closed, and will open onlyif the boiler water temperature goes above a safe upper limit, the supply of powerto the primarycontrol 94 will depend mainly on the position of the relay contacts 86, 88V or the service water Aquastat contacts 100, 102.

Thesystem operation can be seen to depend on the heat requirementsof the space to beheated and of the service water heater; If, forexample, heat is required by the service water heater but not by the space to be heated, the contacts-100,- 102 will close, completing the circuit to theprimary control 94 and thereby energizing theburner 36 and the pump-9.8. Under these conditions, the

thermostat contacts

80, 82 will be open, leaving the relay. 78 de-energized- Hence, the valveactuatirig: solenoid 66 will receive no. energizing current, and the.valve 42 will. remain open. This will allow the liquidiflowing throughithe Venturi fitting 40-to pass through the. by-pass line 20,. and all ofthe system. heat will ,go..to-.the tank 56 through the medium of the heat exchangecoil54. As long as the valve42 *is open, the action-of the Venturi element 40 will prevent any of the system liquid. from circulating through the space heater line 16. In fact, there will be a slight suction or pressure drop. at the. side outlet'port 46uas the water flows. through the nozzle- 48. and out of'the port 44. Undervthese conditions, it would. be possible for small amounts ofhot liquid to..fiow backward through the space heater 18 from theT 52 to the Venturi port 46. To. preclude the possibility ofthis reverse flow when no spaceheat is required, it is preferable to include the check valve 50in the.space-.heaterline.16, as shown.

When space heat is required, the thermostat contacts 80, 82.willclose,. completing a circuit through the relay winding-76. andthereby closing the

contacts

86, 88 and 90,92.

This. .will. complete the. circuit of. :the. primary control to..energize:the .pump and. burner, and.a1so will energize the. solenoid 66. to close the, valve/42. Now the hot water-from. the boil'erwill .be diverted through the side 1 port 46 or" .the Venturi40' to How through the. space heaters.18.. However,- the system liquid will continue to flow through theservice heater coil. 54in series with the. space heater 18. Since the.tank 56 normally will be filled .with .hot.water at all times, rapid pickup in space heatiwill be. insured. by the .heatexchange between the I hot service-water-and the. circulating system liquid. During -a given firing cycle, the temperature drop across-the .space heaters will increasewhilethetemperature rise.

across the "boiler :remains .constant .and the boiler outlet temperature rises. Initially, of course, theserviceheater tank temperaturev will drop. somewhat when the room temperature radiator .water begins circulating through the heater tank coil and picksup. heat fromthe hot service water. However, until thewater temperature at the boiler outlet reaches a maximum, the temperature drop across the space heaterswill: be lessthan the temperature rise across the boiler, so that the circulating liquid. temperature at the inlet to the service water heater will rise fairly quickly to a value at which the waterin-the. tank 56 will no longer belosing heat. Meanwhile, .a. fairly limited demand forv hot service water ordinarily can be met, if required, because there will'be a..temperatur e drop across the service tank from topto bottom, rather than a uniform decrease in the entire. tank liquidtemperature. This willleave a. supply of .hot. water near the top of the service tank for filling a reasonabledemand. Within a fairly short time, the temperature of the water leaving the radiators will be high enough -to reverse the direction of heat exchange in .the heater tank 56,- and the temperature in the latter.,will begin to riseagain. Thereafter, the system will rapidly regain balance through! out. When the system has been operating long enough for the boiler outlet temperature to be at. or near maxi: mum, enough heat can .be supplied to the service heater tank. to maintain. the .temperature of the service water fairly well, even though service water is being. drawn at the time.

For example, in a typical case, the system. might be designed for a 20 temperaturerise across the boiler, a 20 drop across the space heaters at a maximum boiler outlet temperature of 200, and a minimum service .water tanktemperature of 14.0". With such an arrangement it is seen. that. for any boiler outlet temperature above, say, 158-l60 F., theserviceheater tank temperature will begin to go above the design minimum. 0f-,140 F., and may even goas high as 180 F.

Obviously, there are a great manypossible combinations: of demand conditions that can. occur in atypical system installation, each. of which will cause av slightly diiferent system reaction. At one extreme, thereis the possibility that. a. demand for space heat will occurduring or just after a prolonged draw of .service water, in which case the temperature of the liquid in the tank. 56v may be toolow to obtain the desired spaceheat boosting action. However, this is not considered. a comparative disadvantage, since it detracts no. more from the desired operating characteristics of the present system than does asimilar coincidence. of demands in other; comparable types of heating systems. In. fact, it is believed that the present system will satisfy both demands, even under the severely adverse conditions suggested above, more promptly and effectively than any comparable prior art system. Furthermore, as has justbeen explained, a condition, will soon be reached in which both demands can be met on a continuing basis, which is not the case with any system of the type, for-example, in which either space heat or service water heat can be supplied at any. given time by .forced circulation, but not both.

While the system shown in .Figure. 3 .will.function in an entirely satisfactory manner, it can be simplifiedsomewhat as shown in Figure. 3a to eliminate the check, valve 50.from the Figure3 arrangement. To simplify the drawing, only'part of the complete system is shown in Figure 16 that; extends from thesideVenturi outlet 46., Withthis arrangement, as long as there is no demand for space heat, the valve 43 will divert the liquid flow through the by-pass line 16. When space heat is called for, the control circuit of Figure 4 will function to open the valve 43, allowing the heated boiler water to pass through the space heater 18. If there should be some reverse flow through the line 16 under these conditions due to the action of the Venturi 40, it will be of little consequence.

In Figure 5 there is shown an alternative embodiment of the invention, wherein both the expansion tank 38 and the check valve 50 in the space heater line 16 in the Figure 3 system have been eliminated.

Referring to Figure 5, there is shown a boiler-burner unit 10, corresponding to the unit shown in Figure 3, with an outlet line 12 leading to the inlet 39 of a Venturi fitting 40. The first outlet port 44 of the fitting 40 is coupled to a line 20 leading to a space heater 18 through a valve 104, while the second Venturi outlet port 46 is coupled to a by-pass line 16 leading to a T 52 on the downstream side of the space heater 18. From the T 52, the line 22 opens into the tank 56 of a service water heater 24. Inside the tank 56, a coil 106 is provided through which to circulate service water to be heated. Inlet and

outlet lines

58, 60 are provided for the coil 106, to connect to the usual service water supply and faucets (not shown). With this so-called tankless type heater, there may also be included a tempering or mixing valve (not shown) on the outlet line 60 for mixing the heated service water with cooler water to maintain a more uniform supply temperature.

Extending into the tank 56 is a temperature responsive element 57 for mechanically actuating the valve 104. The mechanical details of the element 57 and the linkage to the valve 104 can take any one of a number of well known forms. A typical arrangement of such a valve control is shown, for example, in US. Patent No. 2,322,- 872 to Moore.

From the tank 56, a line 26 leads through a circulating pump 28 back to the boiler inlet line 30.

It will be understood that the system of Figure 5 also will include an electrical control circuit generally similar to that shown in Figure 4, connecting the

Aquastats

62, 64 and a thermostat (not shown) located in the space to be heated, to control the operation of the burner and the pump, although, of course, such circuit will not include the solenoid 66 of Figure 4. In the Figure 5 system, when either the service water temperature or the temperature in the space to be heated falls below a preselected minimum value, the burner 36 and pump 28 will be energized to heat and circulate the water in the system. If the boiler water temperature exceeds a safe maximum value, the Aquastat 64 will act to shut ofi the burner and pump.

One of the diiferences between the systems shown in Figures 3 and 5 is that in the service water heater 24 in Figure 5 service water is circulated through a stored body of heated liquid, rather than storing any appreciable quantity of heated service Water. While the heater 24 in Figure 5 is similar to the usual tankless type heater, the tank 56 has a considerably greater liquid capacity than is conventional in this type of heater. The reason for this is to provide suflicient reserve stored heat to insure quick pickup when space heat is called for.

An advantage in using the tankless type of service water heater is that the storage tank can be utilized both for heating the service water and as an expansion tank. That is, when the system is filled, the tank 56 is only partly filled, say to the level indicated by the broken line 59. A small amount of air is trapped in the upper part of the tank to serve as a cushion to absorb the changes in system pressure that accompany changes in the temperature of the liquid in the system. This, of course, eliminates the necessity for the separate expansion tank 38 shown in the Figure 3 system.

While the Figure 5 system can be arranged either for space heating or service water heating priority, it is preferably with the tankless type heater to give the service heater first priority. With a storage type heater, as explained in connection with the Figure 3 system, an appreciable time will elapse after space heat is called for before the temperature of water at the hot water faucet will change noticeably. With the tankless heater, on the other hand, a change in the temperature of the boiler water circulating through the heater will be reflected rather quickly at the hot water faucet. Hence, if hot water is being drawn for a shower bath, for example, and the hot-cold mixture has been adjusted as desired, any appreciable change in the temperature of the water in the heater tank, such as could be expected to accompany a demand for space heat, no doubt would produce an undesirable change in the shower water temperature; Therefore, service heater demand priority is deemed preferable with the tankless type heater, simply to insure a uniform service tank temperature. On the other hand, even if the service heater is given first demand, it is still advantageous to have the space heater and service heater in series when space heat is being supplied because once the space heaters begin to warm up, as already explained, the residual heat in the water leaving the space heaters often will be suiiicient to maintain the temperature in the service heater tank even though service water is being drawn at the time.

The direction of flow in the Venturi fitting 40 will depend on the setting of the valve 104 in Figure 5. This, in turn, will depend on the temperature of the liquid in the service heater tank 56. If the temperature in the service water heater is below the pre-set minimum, the valve 104 will remain closed until the service tank temperature is high enough to actuate the thermally responsive element 57. Thereupon, the valve 104 will be opened by the element 57. If space heat then is called for, the flow will be through the line 20 and the space heater 18. Since there will be an assured supply of hot liquid in the tank 56 at all times, it is seen that only hot liquid normally will flow through the space heater 18. If the liquid in the space heater 18 is at a relatively low temperature when the system comes on, after a short interval the temperature in the service water tank 56 will drop sufliciently to close the valve 104 and divert the flow from the space heater 18 until the service tank temperature has returned to normal. Thereupon, the valve 104 again will open, allowing the heated liquid to flow through the space heater 18. Even under the most adverse conditions, as where space heat is called for at the end of a prolonged draw of service water, heated liquid will begin to flow through the space heater at the earliest possible time that there is liquid of suificiently high temperature available to do any appreciable heating. On the other hand, if the space heat demand comes when the tank 56 is fully heated, then the space heat demand will be met promptly, and the series flow of liquid through the space heater and the service heater soon will reach the balanced condition of heat transfer previously described.

What is claimed is:

1. In a space heating and service water heating system, a boiler for heating water to be circulated through said system and having a relatively small water containing volume and relatively low heat storage capacity, a service water heater comprising means defining first and second water heater passages through which to circulate water, said passages being arranged in said heater in heat exchanging relations to each other, a space heating element through which to circulate heated water from said boiler for space heating, water inlet and outlet lines leading to and from said boiler, a Venturi fitting having an inlet port and two outlet ports,'said outlet line being connected to said inlet port, a line connecting one of said 'outlet ports to said space heating element, a circulating pump, a liquid circuit connecting one of said water heater passag'esand said pump in series between the other of said asssgri e butletpjorts'aiidsaid'inlet line; aline connectin'gathe downstream side of, said 'space heating element to said circuit on-the upstreamside-ofsaid one water heater passage; and avalve in said system cooperable'with said fitting to direct water flow in said system either through said space-"heating element-or'throughthe portion of said circuit-connecting saidother outlet=port to said onewater heaterpassage;

2; In a space heating and service waterheatingsystem, a'boiler for heating water tobecirculated through said system and having a relatively small water containing volumeand relatively low heat-storage'capacity, a service water heater comprising means defining first and second water 'heater passages through a which to circulate water, said passages being arranged in said heater'in heat ex oh'angingrelation'toeach other, a space heating'element through which to circulate heated water for space heating, water inlet and outletalinesaleading to and from said boiler, a Venturi fitting having an inlt=portand two outlet ports, said outletline being connected to said inlet port, a line connecting one of saidoutletports to said space heating element, a circulating pump, a liquid circuit connecting oneof' said water heaterpassages and said pump inseries .b'etweentthe other of said outlet ports andlsaid inlet line, a line connecting thedownstreamside ofsaidspace heating element to saidtcir cuit on the upstream side. of said one Water heater passage, a valve in saidsystem cooperable with said fitting to direct water flow in said system either through-said space heating element or. through the POItlOIl'Of saidcircuit connecting said fitting to said one water heater passage, and a tem perature-responsive control element connected to said valve to control the actuation of said valve.

3. In a space heating and service water heating system, a boiler for heating water to be circulated through said system and having a relatively small water containing volume and relatively low heat storage capacity, water inlet and outlet lines leading to and from said boiler, a space heating element through which to circulate heated water for space heating, a service water heater comprising means defining a first water heater passage through which to circulate water to be heated and a second water heater passage through which to circulate heated water from said boiler, said Water heater passages being arranged in said heater in heat exchanging relation to each other, a circulating pump, a liquid circuit connecting said space heating element, said second service water heater passage and said pump in series between said outlet and inlet lines, a by-pass line connected in parallel with said space heating element, and flow control means including a valve in series with said space heating element for directing Water flow in said system either through said space heater or through said by-pass line.

4. In a space heating and service water heating system, a boiler for heating water to be circulated through said system and having a relatively small water containing volume and relatively low heat storage capacity, water inlet and outlet lines leading to and from said boiler, an element through which to circulate heated water for space heating, a tank through which to circulate service water to be heated and containing a coil through which to circulate heated boiler water, a circulating pump, a liquid circuit connecting said space heating element, said coil and said pump in series between said outlet and inlet lines, a by-pass line connected in parallel with said space heating element, flow control means including a normally-open solenoid-actuated valve in series with said space heating element to direct water from said boiler either through said element or through said by-pass line, and an electrical control circuit for said system including a temperature-responsive switch element responsive to the temperature of the space to be heated by said space heating element and connected in said electrical circuit to control the actuation of said valve solenoid.

5. In a space heating and service Water heating systern, aboilrfor heatingwater toi be circulated through said system and having a relatively'fsmallzwater con-1 taining *volume'and relatively low heat: storage capacity; a tank through: which to circulate water to be: heatedga coil in' said tank--through "which to circulate heated water from said boiler, an element through which to'circulate heated'water from said-boiler for space heating, water inlet and outlet-lines leading to and from-said boiler,'.a Venturi fitting having an inlet port and two outlet ports, said outletline beingconnected 'to saidinlet porn-a line connecting one of said outletports to: said space heating element, acirculating pump, a liquidcircuit connecting saidcoiland said pump in series" between the otheri'of said outlet ports "and said inlet 1 line, a line connecting the downstream side of'said space' heatingelement to said circuit on the -upstream'-side ofsaid coil,-and fiow control means-including avalve in series with said space heating element for directing water flow insaid system either through" said space" heating element or through the portion of said circuit connecting said coil to -said other: outlet port; I v

6'. In :a space heating and service water heating-system; axboiler for: heating water to be circulated through said system-and having a relatively small water containing volume: and .1 relatively lowheat storage' capacity, a: tank through which to-circulate heated water-from said boiler for heating servicewater andcontaining a-coil through which to 2circulatefsaid"service water, an element through which to circulateheated water from said: boiler for space heating, water inlet and outlet lines leading: to and from said boiler, a Venturi fitting having an inlet port and two outlet ports, said outlet line being connected to said inlet port, a line connecting one of said outlet ports to said space heating element, a circulating pump, a liquid circuit connecting said tank and said pump in series between the other of said outlet ports and said inlet line, a line connecting the downstream side of said space heating element to said circuit on the upstream side of said tank, and flow control means including a valve in series with said space heating element for directing water flow in said system either through said space heating element or through the portion of said circuit connecting said other outlet port to said tank.

7. In a space heating and service water heating system, a boiler for heating water to be circulated through said system and having a relatively small Water containing volume and relatively low heat storage capacity, a tank through which to circulate Water to be heated and a coil in said tank through which to circulate heated Water from said boiler, an element through which to circulate heated water from said boiler for space heating, water inlet and outlet lines leading to and from said boiler, a Venturi fitting having an inlet port and two outlet ports, said outlet line being connected to said inlet port, a line connecting one of said outlet ports to said space heating element, a circulating pump, a liquid circuit connecting said coil and said pump in series between the other of said outlet ports and said inlet line, a line connecting the downstream side of said space heating element to said circuit on the upstream side of said coil, flow control means including a normally-open solenoid-actuated valve in series with said space heating element to direct water flow from said boiler either through said element or through the portion of said circuit connecting said coil to said other outlet port, and an electrical control circuit for said system including a temperature sensitive switching element responsive to the temperature of the space to be heated by said space heating element and connected to control the actuation of said valve solenoid.

8. In a space heating and service water heating system, a boiler for heating water to be circulated through said system and having a relatively small water containing volume and relatively low heat storage capacity, a tank through which to circulate heated water from said boiler for heating service water and containing a coil through which to circulate said service water, an element through which to circulate heated water from said boiler for space heating, water inlet and outlet lines leading to and from said boiler, a Venturi fitting having an inlet port and two outlet ports, said outlet line beingconnected to said inlet port, a line connecting one of said outlet ports to said space heating element, a circulating pump, a liquid circuit connecting said tank and said pump in series between the other of said outlet ports and said inlet line, a line connecting the downstream side of said space heating element to said circuit on the upstream side of said tank, flow control means including a normally-open valve in series with said space heating element to direct water flow from said boiler either through said element or through the portion of said circuit connecting said tank to said other outlet port, and a temperature-responsive control element responsive to the temperature of the water in said tank and connected to said valve to ontrol the actuation of said valve.

9. In a space heating and service water heating system, a boiler for heating water to be circulated through .said system, a service water heater comprising means defining a first passage through which to circulate water to be heated and a second passage through which to circulate heated water from said boiler, said passages being arranged in said heater in heat exchanging relation to each other, a circulating pump, a space heater through which to circulate heated water from said boiler, circuit means connecting said boiler, said second passage, said pump 12 and said space heater in series, a by-pass circuit connected in parallel with said space heater, and flow control'means in said system for directing water flow in said system either through said space heater or through said by-pass circuit. I

10. The invention defined in claim 9, wherein said control means includes a valve and a temperature-responsive control element for said valve, said temperatureresponsive element being disposed in said first water heater passage to respond to the temperature of the water in said first water heater passage.

,11. The invention defined in claim 9, wherein said first water heater passage comprises a tank and wherein said second water heater passage comprises a coil contained within said tank.

, 12. Ihe invention defined in claim 9, wherein said second water heater passage comprises a tank, and wherein said first water heater passage comprises a coil contained within said tank.

13. A system as defined in claim 9 wherein said flow control means comprises a valve in said by-pass circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,081,831 Moore May 25, 1937 2,290,347 Moore July 21, 1942 2,322,872 Moore June 29, 1943 FOREIGN PATENTS 411,333 Great Britain June 7, 1934