Heating system control

United States Patent

[] 3,608,818

<td> [72]</td><td> Inventor</td><td> Jost Eduard Von Fellenberg Bahnkobstrasse 49,9320, Arbon, Thurgau, Switzerland</td>

<td> [21]</td><td> Appl. No.</td><td> 830,993</td>

<td> [22]</td><td> Filed</td><td> June 6,1969</td>

<td> [45]</td><td> Patented</td><td> Sept. 28,1971</td>

<td> [32]</td><td> Priority</td><td> June 15,1968, May 22,1969</td>

<td> [33]</td><td></td><td> Switzerland</td>

<td> [31]</td><td></td><td> 8906/68 and 7785/69</td>

[54] HEATING SYSTEM CONTROL 6 Claims, 9 Drawing Figs.

[52] U.S. Cl........................................................ 237/8,

237/62, 237/63

[51] Int.Cl......................................................... F24d3/02

[50] Field of Search............................................ 237/8,8 H,

62,63; 165/22

[56] References Cited

UNITED STATES PATENTS

2,344,555 3/1944 McGrath....................... 237/63UX

2,490,932 12/1949 Thuney 237/8

3,236,292 2/1966 Smith............................ 165/11

Primary Examiner—Edward J. Michael Attorney—Kurt Kelman

ABSTRACT: A variable-speed pump is provided in a liquid feed line between a boiler and a heat exchanger, while a bypass line extends from a return line between the heat exchanger and boiler to a three-way valve in the feed line upstream from the pump. The pump speed is varied as a function of temperature changes and liquid pressure variations in the feed line under varying pump speeds actuate a control for the three-way valve. In a modified embodiment the pump speed is constant and liquid pressure variations in the feed line are produced by a temperature-responsive throttle valve.

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PATENTED SEP28 B7I 3,608,818

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PATENTED SEP281971

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PATENTED SEP28I97I

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INVENTOR.

Jost Eduard vw by . '

3,608,818

HEATING SYSTEM CONTROL

This invention relates to a control of heating systems working with liquid heat medium and having at least one circulating pump in the heat medium circulation system and further having a device for the admixture of returning cooled liquid to the forward flow, with the object of attaining and maintaining a control quantity, in particular the forward-line or room temperature, wherein the adjustment of the return admixture device is effected with the aid of a pressure difference developed by the circulating pump.

Central heating systems with liquid heat media and constant temperature in the heat reservoir (e.g. a boiler, heat converter or the like) are normally provided with a bypass line which bypasses the heat reservoir or heat source and which passes into the forward line through a three-way mixing element. This three-way mixing element may be operated by a setting motor, for instance, controlled by a controller. The controller in its turn receives its signals from temperature probes arranged in the heat medium forward line and in a room, for instance. The controller ensures that by suitable setting of the mixing element the heat medium flows from the forward-line to the radiators with the appropriate mixing temperature, so that the heat emission of the radiators has a stationary pattern at the planned or preset temperature or the target temperatures. When the outside temperature changes, the forward line temperature is regulated by means of the controller. This control is termed atmospheric control, wherein the outside temperature constitutes the reference quantity, and the forwardline temperature the control quantity.

Temperature control systems could be based on room temperature or constant forward-line temperature alone. Instead of the motor drive of the three-way mixing element, it is conceivable to employ a thermal drive, such as one operated by a bimetallic element, bringing the mixing element into the position required by the controller.

Also known are very simple temperature control systems in central heating systems in which the forward-line is opened or closed by a throttle-valve controlled by a thermostate and operated by a setting motor.

The drawback of these known control systems consists in their complicated construction and, accordingly, their high price, or in the intermittent feed of hot boiler water to the radiators, causing great variations in room temperature and a very uncomfortable climate, in that rooms controlled in this manner always feel either chilly or too hot.

Likewise, the obvious idea of continuously controlling the delivery rate of the circulating pump by a controller according to the thermal requirements of the heating system tends to fail because in the case of low thermal requirements, i.e. low delivery rate, the heat distribution in the heating system becomes very unsatisfactory.

The object of the present invention is to provide a system which avoids the aforesaid drawbacks and permits the construction of a heating system which keeps the rooms to be heated at practically constant temperatures.

The said system is characterized in that at least part of the pressure difference is varied by way of control action.

The heating system in which a pressure-differential-controlled flow control element each is arranged between the heat source and the junction of the bypass line with the forward line and also in the bypass line itself for the purpose of developing a preset forward-line mixing temperature, is characterized in that it has a controller controlling the means for varying the pressure difference.

Embodiments of the said invention are now illustrated by way of example in the drawings, in which

FIG. 1 shows a diagram of a central heating system according to the invention;

FIGS. 2 and 3 show diagrams of control elements in the forward-line and in the bypass line of the heating system, with a circulating pump diagrammatically indicated

FIG. 4 shows a circuit diagram of an automatic control device for a mixed water pump heating system;

FIG. 5 shows a circuit diagram of a heating system representing one embodiment of the invention;

FIG. 6 shows a variant circuit of a heating system analogous to that in FIG. 5;

FIG. 7 shows a set of characteristics with operating point of the circulating pump according to FIG. 4;

FIG. 8 shows a set of pump characteristics for fixed total resistance of the system and variable speed of the circulating pump, and

FIG. 9 shows a set of pump characteristics for variable pump speed and variable system resistance.

From a heat source, such as boiler 1, a boiler forward-line 3 leads through a pump forward-line 5 to a circulating pump 7. From this, a supply line 9 conducts the heat medium to a radiator 11. After dissipating part of its heat, the heat medium returns through a return line 13 to boiler 1. A bypass line 15 permits the boiler 1 to be bypassed and cooler return water to be admixed to the hot heat medium in the boiler forward-line 3. For the purpose of controlling the temperature of the heat medium passing into the pump forward-line 5, there is fitted into the boiler forward-line 3 and the bypass line 15 a pressure-differential control 16 of known type with a setting motor 17 and a valve 19, whose construction is described more closely below. The valve 19 is provided on its stem 22 with a valve disk 20 which, when closed, rests either on the seat of a valve seat plate 18 or on the end of the bypass pipe 15 designed as a valve seat. The connection of the pump intake line 5 with one side of the diaphragm 27 is by a line 24, while that of the pump delivery line or supply line 9, with the other side of the diaphragm 27 is by a line 26. An outside temperature probe 21 and a forward water temperature probe 23 act on a controller 25, which in its turn influences the speed of the circulating pump 7, so that the flow of heat medium circulating in the heating system can be increased and the delivery rate of the circulating pump also rises according to the pump characteristics as a result of the rising resistances in the system. The diaphragm 27 is fixed around its periphery, and its resetting power is based on its elasticity and can, if necessary, be assisted by an adjustable recovery spring (not shown).

The system is so designed that when the outside temperature falls and, accordingly, the temperature near the radiator 11 falls, the target value of the temperature of the forward water rises and the required forward water temperature is reached by variation of the pump speed. Thus when the outside temperature falls, i.e. when the water forward temperature target value rises, the controller 25 increases the speed of the circulating pump 7, thus increasing the pressure difference developed by the pump, the delivery rate, between intake and delivery sides and also increasing the throughput. This increase in the differential pressure affects the control 16 in such a way that the forward line 3 opens to a corresponding degree and the bypass line 15 closes to a corresponding degree, in other words, is adjusted towards the closing position. The valve disk 20 moves towards the junction of the bypass line 15. The forward-line temperature rises, as does the heat emission of the radiator 11, so that the fall in the outside temperature is compensated by appropriate control of the heating system and the temperature of the room with the radiator 11 keeps within the preset temperature range. Instead of the outside thermometer, it is of course also possible to install a room thermometer, which acts on the controller 25 accordingly.

As regards its output signal or control command, the controller 25 is adapted to the requirements of the circulating pump 7 and the drive motor of the pump 7. The control 16 is so arranged that in extreme operating conditions it fully opens the forward-line 3 and fully closes the bypass line 15, or vice versa.

FIG. 2 shows a diagram of a section of the heating system in the range of the circulating pump 7 and the forward-line 3 as well as the bypass line 15. The forward-line 3 and the bypass line 15 are connected to the side of the valve housing 50. The outflow is through the circulating pump intake line 5 which is followed by the circulating pump 7. Arranged in the valve housing 50 are two cages 52 and 54. A valve stem 56 is provided with valve disks 59 and 60 for the forward-line 3 and for

3,608,818 the bypass line 15, respectively. A spring 63 supported on the cage 54 develops the particular resetting power for the valve stem 56. Arranged at one end of the valve stem 56 and facing the pump 7 is a floating plunger 65. Owing to the arrangement of the valve disks 59 and 60 shown, a pressure equalization arises at the slidable part of the valve. The forces on the valve disks 59 and 60 caused by the liquid pressure are equalized. In this embodiment, therefore, the setting force is varied in correlation with the pump speed and the pump delivery rate and the delivery pressure by means of the floating plunger 65. When the throughput increases, the floating plunger 65, owing to the greater drag on it, moves towards the pump 7 and thus opens the valve disk 59 for the boiler forward-line 3 and moves the valve disk 60 towards the seat of the cage 54, i.e. with closing effect. The forward-line mixing temperature increases, as was intended by the increase of the speed of the circulating pump 7. The spring 63 provides the counterforce to the drag on the floating plunger 65. This spring 63 acts as a recovery spring.

The embodiment shown in FIG. 3 again comprises two cages 71 and 72 in a valve housing 70, and also a valve stem 74 with the valve disks 77 and 78. The free end of the valve stem 74 is attached to a diaphragm 81, representing the setting motor. In conjunction with the circulating pump 7, it divides the valve housing 70 into an intake chamber and a delivery chamber. Here, because the pressure forces on the valve disks 77 and 78 equalize, the valve stem 74 and the disks 77 and 78 are moved by the difference, acting on the diaphragm 81, of the pressure-produced forces. This movement also produces the necessary resetting power. According to the variation of the delivery rate of the pump, the diaphragm is pushed to the left when the pressure differential rises. The orifice of the mixing valve for the boiler forward-line is opened by the valve disk 77 moving away from its seat in the cage 71. The orifice of the mixing valve for the bypass line 15 is closed by the valve disk 78 moving towards the seat of its cage 72. When the speed of the circulating pump is reduced, the pressure difference between the right and the left side of the diaphragm 81, which is adjustable preferably in respect of hardness, falls, and the diaphragm moves from its leftward-bulging position towards its stretched rest position, so that the valve disk 77 of the boiler forward-line 3 closes, and the valve disk 78 of the bypass line 15 opens, accordingly.

The circulating pump may be a displacement pump, an impeller pump or a centrifugal pump. It is preferably driven by a speed-controllable electric motor, possibly fed by the controller as a power source.

For the resetting of the valves, it is also possible to use means other than springs, such as pneumatic elements, which can be set by suitable means, such as vanes, etc. If necessary, central operation may be provided for the resetting elements. It is also possible to interconnect several quantity control elements rigidly, as described, or elastically, as by a spring.

By setting the spring forces and their interrelation, it is possible to set the heating characteristics of the heating system in relation to the object to be heated (building, building section, room, etc.). Likewise, it is possible by the choice of the spring forces to determine the capacity range, in other words, the working range, within which the circulating pump is controlled.

The correlation of outside temperature and forward-line temperature, i.e. the quotient thereof, is termed gradient. For the purpose of simplifying the apparatus, its installation, its operation and also its electric assembly, the controller together with all its setting and operating means and, where required, with a clock for the time program, can be designed to form a unit with circulating pump and control elements.

In order to adapt the circulating pump to the heating system into which it is to be fitted, the simplest practice is to provide the pump with an adjustable throttle-valve which can be fixed and set when the system is installed and which can be used to adjust the resistance parabola of the whole system for a particular pump type to the target parabola. For this purpose, the throttle-valve is closed to a greater or lesser degree. This permits the pump with its predetermined variable speed range to be supplied irrespective of the particular system, as it always runs on the same curve section of the resistance parabola.

Another solution, which, while more complicated, is possible cheaper in operation, consists in tuning the variable speed range by setting the corresponding pump speed for the purpose of obtaining a preset normal throughput per radiator. This speed-setting can be achieved by the connecting of electric resistances. However, owing to the changed target value of the control pressure difference for the mixing element, this solution also requires tuning of this mixing element. A basic idea, as was described with reference to the embodiments, consists in having an arrangement wherein a primary control function mainly influences the admixing ratio, while a secondary control function, derived therefrom, mainly influences the circulating quantity. This thus involves two mutually supporting setting actions on the control assembly.

FIG. 4 shows the diagram of a known system, comprising a boiler 85, one or several radiators 87, an admixing valve 89 and a circulating pump 90 with a pump motor 91. A boiler forward-line 93 leads from the boiler 85 to the admixing valve 89, while a supply line 95 from the circulating pump 90 supplies the radiator or radiators 87 with forward-line hot water. A return line 97 passes the cooled water from the radiator 87 either to the boiler 85 or through a bypass line 98 to the admixing valve 89.

The admixing valve 89 is controlled by a room thermostat 103, which controls a solenoid valve 101 in a pressure line 100 in such a way that the solenoid valve, when open, permits the full pressure from the delivery side of the pump 90 to act on the admixing valve 89 or, when closed, keeps the admixing valve 89 pressureless. This ensures that the admixing valve 89 takes up one of two positions: In the one position, the hot water passes from the boiler 85 through the forward-line 93 and the mixing valve 89 to the circulating pump 90 and thence through the supply line 95 to the radiators 87, whence it returns through the return line 97 to the boiler 85. In the other position of the admixing valve 89, the boiler forward-line 93 is closed, and the water returning through the return line 97 passes through the bypass line 98 to the admixing valve 89.

In this known arrangement, the radiators 87 are supplied either with water circulating through the boiler 85 or with the water through the bypass line 98, in which case the boiler 85 is completely bypassed. This arrangement basically keeps the temperature and the throughput of the heat medium in the system constant, as the resistance relations in the system in bypassing as well as in passing through the boiler are approximately equal, i.e. equalized.

As this known arrangement involves an open-close control for the bypass and the normal forward flow, and as the resistances in the system are matched up accordingly, the working point P of the pump in the associated pump characteristics shown in FIG. 7 for a fixed system resistance W and a nonvariable speed n appears as an invariable, which does not even change when the system switches from forward line to bypass. Thus, there is no control involving variation of the working point, and the pressure difference developed by the circulating pump 90 plays no part at all in respect of the quantity for the control of this system, For the rest, it cannot be varied.

FIG. 5 shows part of the circuit of the system according to FIG. 1. Here, the forward water temperature probe 23 acts on the controller 25, which in its turn controls the drive motor SM of the circulating pump 7 in this variant and varies its speed. This varies, according to the pump characteristics (FIG. 8), 82 the pressure difference deltap which exists in the lines 24 and 26 and which adjusts the control 16 accordingly. The latter controls the quotas of the hot water coming from the boiler forward-line 3 and the quotas of the colder return water coming from the return line 13 through the bypass line 15. The control process can be easily seen from the pump characteristics in FIG. 8. The system resistance W_o is constant. Varying the normal speed n₀ to n, or n ₂ varies the working

3,608,818 point 0 to 0, or β₂ as according to the resistance parabola W_oof the whole heating system a greater throughput Q, implies a correspondingly greater pressure drop delta p,. Analogous considerations apply to the operating point 0₂.

The object of this control is to vary the control quantity of the mixing valve 16, and with it, the ratio between the quantity of hot water and that of returned water by varying the value of delta p. This results in a variation of the total throughput Q according to the pump characteristics, as may be seen from FIG. 8. This throughput variation has the positive effect of assisting the control process started. Thus, if it is intended, with temperature falling, to increase the forward water quantity in conjunction with a corresponding throttling of the admixed return water quantity and the speed n₀ is therefore increased to n_t the variation of the mixing ratio for the purpose of increasing the temperature of the forward water will be accompanied by a variation of the total throughput Q, which will rise from Q„ to Qp An analogous action will occur if the temperature in the heating system is to be reduced. Here, the process is assisted in terms of control technology, as not only the mixing temperature falls, but also the throughput drops from Q_o to Q₂.

It is basically also possible, however, to achieve a control function as shown by the dash-dotted lines in Fig. 5, at constant speed (n„=constant), by means of a bypass line 110 bypassing the pump 7, and a control valve 111 operated by the controller 25, for instance. In this, as a result of the parallel connection, the total resistance W falls and, accordingly, the total throughput Q rises along the curve for n„, while delta p drops. Despite the increased total delivery rate of the pump, the quantity of water flowing through the heating system is smaller, as part of it is continually extracted after the pump and returned through the bypass line 110 to the pump intake side, so that this control can achieve the same effect as regards the heating aspect as can the speed control towards lower speeds n₂. However, the bypass control is achieved at the price of lower efficiency, as the total circulation quantity is increased and the power input of the pump rises accordingly, despite the smaller water quantity put through the heating system.

FIG. 6 shows a circuit according to the invention in which the speed of the circulating pump 7 is constant. Fitted into the supply line 9 is a throttle-valve 114 in the form of a flap or a control valve, whose position is influenced by the forward water temperature probe 23 through the controller 25. Such a throttle-valve 114 permits the total resistance W of the heating system to be varied, which shows in the position of the resistance parabolas given in Fig. 9 for instance, where the parabola W„ represents a mean value, W, the total resistance with throttle-valve 114 open, and W₂ the total resistance of the system under heavy throttling. By suitable control of the throttle-valve 114, the differential pressure delta p developed by the pump 7 and used to control the mixing valve 16 is varied. The whole circuit can be so arranged that the varying total throughput varies in accordance with the intended variation, i.e. so that with increasing heat supply to the consumer the total throughput rises by the throttle-valve 114 opening, in which process the mixing valve 16 influences the boiler forward-line 3 with opening effect and the return water line 15 with closing effect.

It follows that the adaption of a heating system to the total through-flow system is preferably achieved by speed control of the pump or then with the aid of a throttle device as shown in Figs. 5 and 6. The idea of the invention can also be implemented by an arrangement in which the pressure difference developed by the circulating pump and acting on the return admixture device is controlled by a throttle-valve 118 in a connecting line 119 between the pressure extraction lines 24 and 26, in a continuously controllable manner, for instance. Thus, part of the pressure difference developed by the circu. lating pump running at constant speed is used for control. The dimensioning of the lines 24, 26 and 119 is important in this case. Fitted between the valve 118 and the line 9 is a throttlevalve 120, and the line 119 is given a large flow section as compared with lines 24 and 26. When the valve 118 is closed, the full differential pressure acts on the control 16 (but without any flow in the two lines 24 and 26). When the valve 118 is opened, the two lines 24 and 26) are short circuited through the line 119, so that only a small pressure difference, in extreme cases none at all, can build up at the pressure difference receiver, such as the diaphragm 27, and in any case the pressure difference will be considerably smaller than that produced by the pump 7. Even with the valve 118 fully open, the water quantity flowing through the line 119 is so small that the delivery rate and the pressure difference at the pump 7 are practically not changed.

The subject matter of the invention involves a further simplification of the electric installation: The usual practice of also switching off the circulating pump when the heating is turned off necessitates, in an automatic system, an additional switch or a contact in the program selection device and its electric connecting line to the circulating pump. In the control system described, the circulating pump is turned off in order to turn off the heating. The pump pressure becomes zero, the valve in the boiler forward-line closes, and that in the bypass line opens.