US2387179A - Water heater control system - Google Patents

Description

Patented Oct. 16, 1945 WATER HEATER CONTROL SYSTEM Clark M. Osterheld, Stoughton, Wis., asslgnor to McGraw Electric Company, Elgin, Ill., a corporation of Delaware Application July 17, 1944, Serial No. 545,354

3 Claims. (01. 219-39) My invention relates to electric heating, and particularly to systems for controlling the energization of an electric heater for a domestic hot water tank.

Among the objects of my invention are: to pro vide a control system for the electric heater of a domestic hot water storage tank that shall cause immediate energization of the heater in case a relatively large quantity of hot water has been withdrawn from the tank and to cause deenergization of the heater when substantially onehalf of the tank is full of hot water; to cause energization of the heater with a predetermined time delay period after closure of a time-controlled switch in case the tank contains only a relatively small amount of cold water and to cause deenergization of said heater when substantially all of the water in the tank is hot, independent of the position of a time-controlled switch.

In the drawing,

Figure 1 is a view in vertical section through a usual domestic hot water tank, with which is associated the system embodying my invention, and,

Fig. 2 is a diagram of connections embodying my invention.

Referring first to Fig. 1 of the drawing, I have there shown a domestic hot water tank I I, having a lower cold water inlet pipe I3, an upper hot water outlet pipe I5, surrounded by a mass ll of heat-insulating material, which is held in place by an outer casing I9. I provide also an electric heater 2|, which, if only a single electric heater is provided, is located adjacent to the lower end portion of the tank and may be of a clamp-on typ located in a tunnel 23. While I have illu trated a specific embodiment of a domestic hot water tank and of an electric heater, I do not desire to be limited thereto, since any equivalent or similar element may be used in place thereof.

I provide a lower thermally-actuable heater control switch, designated by numeral 25, which is positioned adjacent to the lower end of the tank The switch 25 comprises a tube 21, having a closed inner end and having its open outer end secured in a fluid-tight manner in an opening in tank adjacent the lower end thereof. An expansion rod 29 is positioned in the tube 21 and is adapted to engage with and be disengaged from a small lug 3| of electric-insulating material secured to the free end of a resilient contact arm 33, which latter is adapted to engage with and be disengaged from a substantially rigid contact arm 35. The two contact arms 33 and 35 may be supported by blocks 31 of electric-insulating material. The design, construction, and adjustment of the switch 25 is such that when tube 21 is subject to cold water'in the tank, the length of expansion rod 29 will be such that the contact arm 33 will be in engagement with contact arm 35, while if tube 21 is subject to hot water, the length of expansion rod 29 will be such that contact arm 33 will be out of engagement with contact arm 35. When I speak of cold water, I refer to water, the temperature of which is on the order of 60 to 70 F., while when I speak of hot water, I refer towater, the temperature of which is on the order of 150 F. or even slightly higher.

I provide a thermal retarder switch, designated generally by numeral 39, which is a modification, as will be hereinafter explained, of the device disclosed and claimed in my co-pending application, S. N. 537,941, filed May 29, 1944, and assigned to the same assignee as is the present application.

The thermal retarder heater control switch unit 39 comprises a first thermal switch having a first bimetal bar 4| and a second bimetal bar-43. The two bimetal bars 4| and 43 are adapted to be positioned in abutting engagement relatively to each other, the bimetal bar 4| being provided with a plurality of pivot plates 45 secured to its outer end, while the bar 43 is provided with sharpened ends adapted to pivotally engage the pivot plates 45. The two bars 4| and 43 are each provided with a central longitudinally-extending slot in the adjacent abutting end portions, and an over center spring 41 is positioned in the slots, the ends of spring 41 being secured to the bars 4| and 43 adjacent the ends of the respective slots, so that the free end of bimetal bar 43 will move with a snap action upon change of temperature.

I provide a contact bridging member 49 insulatedly mounted on the outer end of bimetal bar 43, which is adapted to engage with and be disengaged from a pair of fixed contact members 5| and 53. When the bimetal bar 4| is subject to cold water in the tank, the position of the bimetal bars 4| and 43 will be that shown in Fi 2 of the drawing, and contact bridging member 49 will be in contacting engagement with the contacts 5| and 53. When the first thermal switch is subject to hot water in the tank, the bimetal bars 4| and 43 will have moved into the opposite position, where bimetal bar 43 will be in engagement with a stop member 55, such movements occurring with a snap action.

I provide a second snap-acting thermal switch in the thermal retarder 39, comprising a first blmetal bar 51, a second bimetal bar 59, positioned in pivotally abutting end-to-end relation, sharpened end portions at the inner end of bimetal bar 59 engaging pivot plates 6| on the outer end of bimetal bar 51. An over center spring 63 is positioned in two aligned slots provided in the two bimetal bars 51 and 59, the ends of spring 53 being secured to the intermediate portions of the bimetal bars 51 and 59. I provide a contact bridging member 55 insulatedly mounted on the outer free end of bimetal bar 59, and the design and-construction of the second thermal switch is such' that contact bridging member 65 will be out of engagement with two fixed contact members 61 and I59 when the thermal retarder is subject to cold water and-also subject to hot water in the tank, but will be"in such position that the contact bridging member 65will be in engagement with the contacts 61 and 69 when the bimetal bars have been heated to an appreciably higher temperature on the order of 200 to 250 F. To obtain this increased temperature, I provide a heating coil 1| on bimetal bar 51, the

energy translatable into heat in heating coil 1| being only very small and requiring some four to six hours to cause temperature rise of bimetal bar 51 to a temperature on the order of 200 to 250 F.

I provide a third thermal switch in the thermal retarder switch unit 39, which third switch is not disclosed in the hereinbefore mentioned co-pending application but is substantially the same as is the second thermal switch. The third thermal switch comprises a first bimetal bar 13, a second bimetal bar 15 held in abutting end-to-end relation by an over center spring 11. The sharpened inner ends of bimetal bar 15 are adapted to fit into pivot plates 19 on the outer end of bimetal bar 13, the two bars 13 and 15 being provided with aligned central longitudinally-extending slots, within which spring 11 is located. A contact bridging member 8| is insulatedly positioned on the outer end of bimetal bar 15, and as long as the temperature of bimetal bar 13 is not to exceed 150 F., bimetal bar 15 will be in engagement with a stop member 83. However, when the temperature of bimetal bar 13 has been raised to a value on the order of 200 to 250 F. or thereabouts, the contact bridging member 8| will be moved into engagement with a, snap action with a pair of fixed contacts 85 and 81. I provide also a heating coil 89 for the bimetal bar 13, and this heating coil is so designed and constructed as to be traversed by the current traversing the electric heater 2 I. ,The amount of energy translated into heat in heating coil 89 is relatively very small but is of such value as to cause a temperature rise in bimetal bar 13' to a value on the order of 250 F. within say fifteen to thirty minutes.

I provide further a time-controlled .switch, shown generally only in Fig. 2 of the drawing as comprising a first contact arm 9| and a. second contact arm 93, which are adapted to be out of engagement with each other during on-peak periods of a twenty-four hour day, but are adapted to be in engagement with each other during oii peak periods. The design and construction of the rest of the timer mechanism is not shown, since I may use any one of the several devices of this general kind now on the market.-

I provide a, first-supply circuit conductorl95 35 of the lower thermally-actuable switch 25. Contact arm 33 is connected by a conductor I to the second supply circuit conductor 91.

A conductor I91 connects contact 53 to one terminal of heating coil 89 on the bimetal bar 13 of the third thermal switch of the thermal retarder switch unit. The other terminal of heating coil 89 is connected to a conductor I99, which connects contacts 81 and 69. Contact 61 is connected by a conductor III with the second contact arm 93 of the time-controlled switch. Another conductor I |3 connects contact 61 to one terminal of heating coil 1|, the other terminal of which is connected by a conductor II5 with contact arm 35 of the switch 25.

In the usual domestic hot water tank installation, pressure is on the water in the tank at all times, and upon withdrawal of hot water from the tank through the upper hot water outlet pipe I 5, a corresponding amount of cold water will enter the tank through the lower cold water inlet pipe I 3, the cold water remaining in the lower part ofthe tank and the hot water remaining in the upper part of the tank.

Let it now be assumed that a relatively large quantity of hot water has been withdrawn from the tank during on-peak hours of the day, usually the daylight hours, so that the thermal retarder unit 39 is subject to cold water, which will cause a snap-acting movement of the first thermal switch of the thermal retarder, comprising bimetal bars 4| and 43, into the position shown in full lines in Fig. 2 of the drawing, thereby closing an energizing circuit for the heater 2|,

traceable as follows: from supply circuit conductor 95 through conductor 99, through the engaged contact bridging member 49 and contacts 5| and 53, through conductor |9|, heater 2|, conductor I93, through the engaged contact arms 35 and 33, and through conductor I95 to the second supply circui-t conductor 91.

As soon as enough water has been heated in the tank to cause the hot water to fall below the thermal retarder 39, which may, for illustrative purposes, be said to be positioned at substantially half of the height of the tank, the first thermal switch of the thermal retarder unit will be subject to hot water, with the result that the contact bridging member 49 will be moved out of engagement with the contacts 5| and 53 with a snap action, whereby deenergization of the heater 2| is effected. It is therefore evident that in case of use of a relatively large quantity of hot water, the control system disclosed herein and discussed thus far is efiectlve to cause heating o1 enough water to fill one-half of the tank, that is the upper half, with hot water, whereby a relatively large amount of hot water is available for ordinary household uses, irrespective of the position of the time-controlled switch.

Let it now be assumed that only a relatively small amount of hot water has been withdrawn from the tank during on-peak hours, so that only the lower thermally-actuable switch 25 is subject to cold water, while the thermal retarder switch unit is still subject to hot water. The heater 2| will not be energized and no circuit of my improved control system will be closed and energized until closure of the time-controlled switch at the start of an off-peak period. This starting time may be 10 p. m. or 11 p. 111. When the two contact arms 9| and 93 are engaged, an energization circuit is closed through heating coil 1|, traceable as follows: from the first supply circuit conductor 95 through the engaged contact arms 9| and 93, through conductors III and H3 to heating coil ll, conductor II5, through engaged contact arms 35 and 33, and from there through conductor I to the second supply circuit conductor 91-. If it be assumed that the timecontrolled switch was closed at say o'clock, and if it be further assumed that the length of ,time necessary for coil 'II cause temperature ductor I09, heating coil 89 of the third thermal switch, through conductors I01 and IOI, heater 2 I, conductor I03, through engaged contact arms 35 and 33, and through conductor I05 to the second supply circuit conductor 91. As has hereinbefore been stated, the length of time necessary -for the energized heating coil 09 to cause temperature rise of bimetal bar I3 to a value sufficient to cause closing movement of contact bridging member BI is on the order offifteen minutes to thirty minutes, so that this action will occur after said predetermined relatively short delay period. This will close a new circuit through the heating coil 2|, traceable as follows: from supply circuit conductor 95 through conductor 99, engaged contacts 85 and 81 with contact bridging member 8|, through conductor I09, heating coil 89, through conductors I01 and NI, through heater 2|, conductor I03, engaged contact arms 35 and 33, and from there through conductor I05 to the second supply circuit conductor 91, This latter circuit is independent of the time-controlled clock, so that should it happen that a relatively large quantity of hot water is withdrawn from the tank during the very late night hours, energization of the heater 2| will be continued, even the time-controlled switch, including the arms 9| and 93, is opened. The lower thermally-actuable switch 25 will ultimately be subject to hot water in the tank, and it will then move into open or heater-deenergizingposition, which will cause return of the various parts of the system to their normal imoperative positions, where the first thermal switch will be open, as will also the second and third thermal switches, as well as the lower thermally-actuable switch.

The system embodying my invention is thus effective to cause maintenance of at least onehalf tankful of hot water in the tank during onpeak periods of a twentyfour hour day and is further efiective to ensure that the heater 2| will not be deenergizecl during the early morning hours until substantially all of the water in the tank is hot.

Various modifications may be made in the system embodying my invention without departing from the spirit and scope thereof, and all such modifications coming clearly within the scope of the appended claims shall be considered as covered thereby.

I claim as my invention:

1. A control system for a domestic hot water 'tank having an electric heater, subject to withdrawals of hot water throughout a twenty-four hour day, comprising a lower thermally-actuable heater control switch mounted inheat-recelving relation on the tank adjacent the lower end thereof, a, time-controlled switch adapted to be in closed position during off-peak periods only, a thermal retarder unit mounted in heat-receiving relation on the tank intermediate the ends thereof, comprising a first thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when its temperature has been raised to a predetermined appreciably higher value, a heating coil for said second switch for raising its temperature to said predetermined higher value, the energization of said coil being controlled jointly by said time-controlled switch and said lower thermally-actuable switch, a third thermal switch adapted to be in open position when subject to cold and to hot water in the tank and adapted to be in closed position when heated to a predetermined appreciably higher temperature and other electric connections between said heater and said switches to cause selective energization of said heater immediately when said thermal retarder is subject to cold water, irrespective of the position of said time-controlled switch, said energization continuing until the thermal retarder is subject to hot water and with a predetermined time period of delay after closure of said time-controlled switch in case said lower thermally-actuable switch only is subject to cold water, said energization continuing until substantially all of the water in the tank is hot, irrespective of the position of the time-controlled switch.

2. A control system for a domestic hot water tank havin an electric heater, subject to withdrawals of hot water throughout a twenty-four hour day, compising a lower thermally-actuable heater control switch mounted in heat-receiving relation on the tank adjacent the lower end thereof, a time-controlled switch adapted to be in closed position during oil-peak periods only, a thermal retarder unit mounted in heat-receiving relation on the tank intermediate the ends thereof, comprising a first thermal switch adapted to be in closed position when subject to cold water in the tank and in open position when subject to hot water in the tank, a second thermal switch adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when its temperature has been raised to a predetermined appreciably higher value, a heating coil for said second switch for raising its temperature to said predetermined higher value, the energization of said coil being controlled jointly by said time-controlled switch and said lower thermally-actuable switch, a third thermal switch adapted to be in open position when subject to cold and to hot water in the tank and adapted to be in closed position when heated to a predetermined appreciably higher temperature and other electric connections between said heater and said switches to cause selective energization of said heater through said lower thermally-actuable switch and said first thermal switch as soon as said first thermal switch is subject to cold water, irrespective of the position of said time-controlled switch, said energization continuing until the first thermal switch is subject to hot water and with a predetermined time delay period after closure of said time-controlled switch in case said lower thermally-actuable switch only is subject to cold water at that time, said energization being initially efiected through said lower thermally-actuable switch, the heating coil of said third switch, said second thermal switch and said time-controlled switch and then continued through said lower thermally-actuable respective of the position, of the time-controlled switch.

3 A control system as set forth in claim 2,'in which deenergization of the heater is effected by switch, the heating coil of said third thermal a said lower thermally-actuable switc when 11-, is

switch and said third thermal switch until substantially all of the water in the tank is hot, ir-

subject to hot water.

CLARK M. OS'IERI IELD.

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