WO1996004499A1

WO1996004499A1 - Control arrangement for the temperature of the water drawn from a water pipe

Info

Publication number: WO1996004499A1
Application number: PCT/DK1995/000292
Authority: WO
Inventors: Erik Andresen
Original assignee: Danfoss A/S
Priority date: 1994-08-05
Filing date: 1995-07-07
Publication date: 1996-02-15
Also published as: SE9700225D0; DE4427846C2; PL318102A1; PL176277B1; SE9700225L; DE4427846A1; AU2976495A; SE507228C2

Abstract

A control arrangement for the temperature of the water drawn from a water pipe (5) contains a heat exchanger (3) lying with its primary side in series with a flow-adjusting valve (4) in a heated water circuit (2), and with its secondary side in the water pipe (5), a temperature sensor (6) lying in the water pipe (5) downstream of the heat exchanger (3), which temperature sensor converts the measured temperature into a pressure acting on a closure member of the flow-adjusting valve (4) against the force of a spring bearing against the housing (16) of the flow-adjusting valve (4), and a measuring orifice (7) in the water pipe (5). The flow-adjusting valve (4) contains a diaphragm between two chambers (10, 11), of which one (10) is connected to the high pressure side of the measuring orifice (7) and the other (11) is connected to the low pressure side of the measuring orifice (7). The deflection of the diaphragm (9) caused by the differential pressure at the measuring orifice (7) acts against the pressure of the temperature sensor (6) on the closure member of the flow-adjusting valve (4). To provide an energy-saving control arrangement, the diaphragm is rigidly connected to the closure member of the flow-adjusting valve (4) in the closing direction thereof, and its deflection in the opening direction of the flow-adjusting valve (4) is continually correlated with the pressure difference at the measuring orifice (7) and the difference between the spring force and the pressure force of the temperature sensor.

Description

DANFOSS A/S, DK-6430 NORDBORG

Control arrangement for the temperature of the water drawn from a water pipe.

The invention relates to a control arrangement for the temperature of the water drawn from a water pipe, having a heat exchanger, the primary side of which lies in series with a flow-adjusting valve in a heated water circuit, and the secondary side of which has the water pipe passing through it, having a temperature sensor, which measures the temperature of the water in the water pipe downstream of the heat exchanger and converts it into a pressure acting on a closure member of the flow-adjusting valve against the force of a spring bearing against the housing of the flow- adjusting valve, and having a measuring orifice lying in the water pipe, the flow-adjusting valve comprising a diaphragm between two chambers, of which one is connected to the high pressure side of the measuring orifice and the other is connected to the low pressure side of the measuring orifice, and the deflection of the diaphragm caused by the differential pressure at the measuring orifice acting against the pressure of the temperature sensor on the closure member of the flow-adjusting valve.

In a known commercially available control arrangement of that kind, the deflection of the diaphragm caused by the pressure difference at the measuring orifice is transferred by way of a second spring to the closure member of the flow-adjusting valve in the closing direction thereof. The deflection of the diaphragm is so narrowly limited in the opening direction by a stop member that even slight opening of a hot water draw-off valve in the water pipe downstream of the heat exchanger, for drawing off of hot water for use, leads at the measuring orifice to a pressure difference which is sufficient to deflect the diaphragm as far as its stop member, without the flow-adjusting valve opening fully. The flow-adjusting valve continues to open further only when the flow or the drawing-off of water through the hot water draw-off valve has increased sufficiently for the temperature of the water drawn off for use to have dropped further and the temperature change to have been detected by the temperature sensor. This can lead to the water drawn off for use cooling too much, when the amount drawn off is relatively high, before the temperature rises again by correspondingly further opening of the flow-adjusting valve by the temperature sensor; the temperature may rise beyond the desired value before the immoderate increase in temperature is detected by the temperature sensor. The temperature sensor then throttles the flow through the flow-adjusting valve again, wherein finally, when a lower limit value is reached, the differential pressure at the measuring orifice detecting the flow-through drops so low that the flow-adjusting valve is again fully closed by the opposing deflection of the diaphragm, with the result that if drawing off of water continues, the temperature of the water drawn off for use is again considerably below the desired value until the flow-adjusting valve is again opened jointly by the differential pressure-dependent deflection of the diaphragm and the action of the temperature sensor on the closure member of the flow-adjusting valve. In particular, exceeding the desired temperature value requires excessive heating energy on the primary side of the heat-exchanger.

The invention is based on the problem of providing a control arrangement of the kind mentioned in the introduction, which enables the temperature of the water drawn off for use to be maintained with relatively little heating energy, regardless of the amount of water drawn off per unit of time.

According to the invention, this problem is solved in that the diaphragm is rigidly connected to the closure member of the flow-adjusting valve in the closing direction thereof, and its deflection in the opening direction of the flow-adjusting valve is continually correlated with the pressure difference at the measuring orifice and the difference between the spring force and the pressure force of the temperature sensor.

In this solution, a change in the pressure difference detected by the measuring orifice, which corresponds to the flow of the water drawn off for use, immediately causes an approximately proportional change in the diaphragm deflection, corresponding to that flow, in the opening direction of the flow-adjusting valve determining the flow of heated water, even before the temperature sensor has established a temperature change. In this manner, too great a fluctuation in the temperature of the water for use over and above the desired value, and therefore excessive consumption of energy, is prevented.

The measuring orifice is preferably arranged upstream of the temperature sensor in the water pipe. It therefore detects a change in the flow of hot water for use especially quickly, even before the temperature of the water has markedly changed.

The opening of the measuring orifice can be bounded by a valve seat which co-operates with a closure member biassed in the closing direction by a spring having an adjustable spring force against the direction in which the water flows through the measuring orifice. In this manner, the desired value of the temperature of the water for use can be adjusted especially simply, for example, the higher it is to be set, the higher is the spring force, and conversely.

The measuring orifice can have a by-pass channel, the opening width of which is dimensioned so that, when drawing off of hot water is interrupted, a minimum opening of the flow-adjusting valve is maintained. This ensures that the measuring orifice exerts no differential pressure on the diaphragm and this remains in equilibrium in order to keep the flow-adjusting valve largely closed, when no hot water for use is being drawn off, but the water for use still has a lower limit temperature prior to drawing off.

Provision can then be made for the closure member of the flow-adjusting valve, immediately before it reaches its closed position, to be biassed in the opening direction by an additional spring force. Even in extreme load situations, such as high heated water temperature and high differential pressure at the measuring orifice and small amounts of hot water being drawn off per unit of time, a stable control is therefore achieved, since the opening characteristic of the flow-adjusting valve in this case should be exponential. The additional spring force considerably increases the force required to close the flow- adjusting valve immediately before it closes, so that even small amounts of hot water being drawn off at high heated water temperature result in a stable control. The invention is described in greater detail hereinafter with reference to the drawings of a preferred embodiment, in which Fig. 1 is a block circuit diagram of a control arrangement according to the invention, Fig. 2 shows main components of the control arrangement, partly in section, and Fig. 3 is a fragmentary view from Fig. 2 showing a modified component.

As shown in Fig. 1, a heating system 1 feeds a heated water circuit 2, in which a heat exchanger 3 lies with its primary side in series with a flow-adjusting valve 4. The secondary side of the heat exchanger 3 has passing through it a water pipe 5 which is connected to a cold water supply system. In the water pipe 5 a temperature sensor 6 is located downstream of the heat exchanger 3 and measures the temperature of the water in the water pipe 5. The temperature sensor 6 is a so- called "vapour pressure thermometer" which converts the measured temperature into a corresponding vapour pressure. Upstream of the secondary side of the heat exchanger 3 the water pipe 5 also contains a measuring orifice 7 and downstream of the heat-exchanger 3 a hot water draw-off valve 8.

As shown in Fig. 2, the flow-adjusting valve 4 determining the flow of heated water through the primary side of the heat-exchanger 3 has a diaphragm 9, the edge of which is hermetically clamped between the edges of two connected chambers 10 and 11. The diaphragm 9 is also clamped between two diaphragm plates 12 and 13 which, like the diaphragm 9, have a hole in the middle, at the edge of which the diaphragm plates 12, 13 and the diaphragm 9 are held together hermetically by the flange of a portion 14a of a multi- part valve plunger 14. Hermetically secured in an opening in the wall of the chamber 10 is a multi-part housing 15, the end part 16 of which forms a valve housing in which there is constructed a valve seat 17 on which a valve closure member 18 sits in the closed state of the flow-adjusting valve 4. The closure member 18 is secured to one end of a further portion 14b of the valve plunger 14. The portion 14b passes, sealed, through an opening in a cover 19 of the valve housing 16 and has its other end screwed into a threaded bore of a nut 20. A spring 21 bears against the nut 20 at one end and indirectly on the covering 19. A ring 22 is then firmly locked on the portion 14b of the valve plunger 14 by means of at least one locking screw 23 passing through a threaded bore of the ring 22. Between the cover 19 and the ring 22 the portion 14b is surrounded by a further spring 24.

The closure member 18 has a central axial bore in which one end of the portion 14b of the valve plunger 14 is secured. The portion 14b, lying firmly against the upper side of the closure piece 18, is furthermore surrounded by a chamber 26, the interior of which is in connection by way of a radial bore 27, and an axial bore 28 in the portion 14b connected thereto, and by way of the bore 25 to the input side of the valve housing 16. The other end of the portion 14b of the valve plunger 14 bears against one end of a pin forming a further portion 14c of the valve plunger 14, the other end of which pin projects into an axial blind bore at the lower end of the portion 14a of the valve plunger 14, the pin being sealed against an end wall of the housing 15.

A further housing 29 is secured, sealed, in a hole in the wall of the chamber 11; in the housing 29 there is arranged a bellows 30, the top part 31 of which through the intermediary of a further portion 14d is supported by way of a further portion 14e, formed by a pin, in an axial bore of the other end of the portion 14a, the portion 14e passing, sealed, through a base 32 of the housing 29. The lower end of the bellows 30 is supported on the housing 29.

The space between the housing 29 and the bellows 30 is connected by way of a pipeline 33 to the temperature sensor 6.

The interior of the chamber 10 is connected by way of a pipeline 34 to the high pressure side of the measuring orifice 7 and the interior of the chamber 11 is connected by way of a pipeline 36 to the low pressure side of the measuring orifice 7.

The opening in the measuring orifice 7 is bounded by a valve seat 36 which co-operates with a closure member 38 biassed in the closing direction by a spring 37 of adjustable spring force against the direction in which water flows through the measuring orifice. The force of the spring 37 is set by means of a cap 39 which can be turned manually; the cap has an internal thread and is screwed over a housing attachment 40 of the measuring orifice 7, through the end face of which a pin 41 joined to the inside of the cap 39 passes, sealed, and presses on the spring 37 by way of a supporting plate 42. The spring 37 in its turn transfers the pressure to the valve closure member 38. The desired value of the temperature of the water flowing through the heat exchanger 3 on the secondary side through the water pipe is adjustable by means of this cap 39. The measuring orifice 7 is furthermore provided with a by-pass channel, not illustrated, the opening width of which is dimensioned so that when drawing off of hot water through the draw-off valve 8 is interrupted, that is, when the draw-off valve 8 closes, a minimum opening of the flow-adjusting valve 4 is maintained.

Fig. 3 shows, in the form of an enlarged fragment of the flow-adjusting valve 4, a modification which comprises the provision of a resilient rubber spring in the form of an 0-ring 43 in place of the helical spring 24 shown in Fig. 2.

The mode of operation of the control arrangement illustrated is as follows:

As long as the draw-off valve 8 is closed, no water flows through the water pipe 5, so that because of the by-pass channel no pressure difference forms at the measuring orifice 7. The pressures in the chambers 10 and 11 are therefore equal, so that the force of the bellows 30, corresponding to the vapour pressure exerted by the temperature sensor 6 in the space between the housing 29 and the bellows 30, is transferred by way of the valve plunger 14, against the force of the spring 21, to the closure member 18 of the flow-adjusting valve 4 in the closing direction thereof. The force of the spring 21 is set so that the valve closure member 18 maintains a flow of heated water which corresponds to a hot water temperature on the secondary side of the heat exchanger 3 in the water pipe 5 of about 35°C.

When the draw-off valve 8 is opened, the cold water supplied from the water supply system by way of the water pipe 5 flows through the measuring orifice 7 and the secondary side of the heat-exchanger 3 past the temperature sensor 6. Even before the temperature sensor 6 detects a corresponding decrease in the hot water temperature, a differential pressure occurs at the measuring orifice 7; this pressure moves the diaphragm 9, assisted by the force of the spring 21, in the opening direction of the closure member 18 against the force of the vapour pressure generated by the temperature sensor 6. The flow-adjusting valve 4 is thus opened further, corresponding to the differential pressure at the measuring orifice 7, so that the flow of heated water through the primary side of the heat- exchanger 3 increases. The effect is an increase in the temperature in the water pipe 5 and a corresponding increase in the vapour pressure generated by the temperature sensor 6. The differential pressure at the measuring orifice 7, however, rises only to a desired temperature value set by the cap 39, which can be set, for example at 50°C. In the state of equilibrium of the forces acting on the closure member 18 of the flow- adjusting valve 4, the flow through the flow-adjusting valve 4 is such that the temperature measured by the temperature sensor 6 corresponds to the desired value.

The ring 22 does not bear on the spring 24 or 43 until just before the closure member 18 has reached its closed position, so that the spring 24 or 43 does not become effective until just before closure of the flow- adjusting valve. A stable control in extreme load situations is therefore achieved. An extreme load situation can comprise a very high heated water temperature on the primary side of the heat exchanger 3 and a very high differential pressure at the measuring orifice 7, as small amounts of water for use per unit of time are being drawn off. The characteristic of the flow-adjusting valve 4, that is to say, the dependency of its opening width on the travel of the valve closure member 18, would, if need be, have to be exponential. The realization of such a characteristic is difficult and expensive. The use of the additional spring 24 or 43 avoids such a realization in that the force required for closure of the flow-adjusting valve rises sharply just before the closed position is reached. This increase in the closing force causes a stable control to be achieved in the extreme load situations mentioned.

The pressure of the heated water acting on the closure member 18 in the opening direction acts at the same time by way of the bores 25, 28 and 27 also on the side of the closure member 18 remote from the valve seat 17, so that it has no influence on the forces actuating the closure member 18.

The interior of the bellows 30 is in connection with the atmosphere by way of a venting bore, not illustrated, in the base 32. The interior of the housing 15 is similarly in connection with the atmosphere by way of a bore 44.

In the illustrated and described control arrangement, the influence of the flow of water through the water pipe 5 on the temperature in the secondary side of the heat-exchanger 3 is accordingly continually compensated in accordance with the magnitude of the through-flow.

Claims

Patent Claims

1. A control arrangement for the temperature of the water drawn from a water pipe (5) , having a heat exchanger (3) , the primary side of which lies in series with a flow-adjusting valve (4) in a heated water circuit (2) , and the secondary side of which has the water pipe (5) passing through it, having a temperature sensor (6) , which measures the temperature of the water in the water pipe (5) downstream of the heat exchanger (3) and converts it into a pressure acting on a closure member (18) of the flow-adjusting valve (4) against the force of a spring (21) bearing against the housing (16) of the flow-adjusting valve (4) , and having a measuring orifice (7) lying in the water pipe (5) , the flow- adjusting valve (4) comprising a diaphragm (9) between two chambers (10, 11) , of which one (10) is connected to the high pressure side of the measuring orifice (7) and the other (11) is connected to the low pressure side of the measuring orifice (7) , and the deflection of the diaphragm (9) caused by the differential pressure at the measuring orifice (7) acting against the pressure of the temperature sensor (6) on the closure member (18) of the flow-adjusting valve (4) , characterized in that the diaphragm (9) is rigidly connected to the closure member (18) of the flow- adjusting valve (4) in the closing direction thereof, and its deflection in the opening direction of the flow-adjusting valve (4) is continually correlated with the pressure difference at the measuring orifice (7) and the difference between the spring force and the pressure force of the temperature sensor (6) .

2. A control arrangement according to claim 1, characterized in that the measuring orifice (7) is arranged upstream of the temperature sensor (6) in the water pipe (5) .

3. A control arrangement according to claim 1 or 2, characterized in that the opening of the measuring orifice (7) is bounded by a valve seat which co¬ operates with a closure member (38) biassed in the closing direction by a spring (37) having an adjustable spring force against the direction in which the water flows through the measuring orifice (7) .

4. A control arrangement according to claim 3, characterized in that the measuring orifice (7) has a by-pass channel, the opening width of which is dimensioned so that, when drawing off of hot water is interrupted, a minimum opening of the flow-adjusting valve (4) is maintained.

5. A control arrangement according to one of claims 1 to 4, characterized in that, immediately before it reaches its closed position, the closure member (18) of the flow-adjusting valve (4) is biassed in the opening direction by an additional spring force (24; 43).