GB2316474A

GB2316474A - Waterheaters

Info

Publication number: GB2316474A
Application number: GB9717043A
Authority: GB
Inventors: Richard Martyn Griffiths
Original assignee: IMI WATERHEATING Ltd
Current assignee: IMI WATERHEATING Ltd
Priority date: 1996-08-16
Filing date: 1997-08-12
Publication date: 1998-02-25
Also published as: GB9717043D0; GB9617273D0

Abstract

The bubble top (17, Fig 1) of a mains-fed unvented storage waterheater is continually replenished with air which, during a demand for hot water (2), is drawn in from the atmosphere by a venturi device 19 incorporated into the mains cold water feed pipe (4). The amount of air drawn in is controlled so as, in particular, not to be excessive at high cold water feed rates by providing a variable cross-section venturi orifice 24 or a combination of a fixed cross-section venturi orifice and a variable air-intake throttle 35. The venturi can be of elastomeric material and is preferably of conical shape.

Description

WATERHEATERS This invention relates to waterheaters, and more particularly, to mains-fed unvented storage waterheaters.

In our prior UK patent No. 2271835, the disclosure of which is incorporated herein by way of reference thereto, we describe and claim, inter alia, means comprising an air intake venturi arrangement located in the mains cold water feed to an unvented storage waterheater whereby an internal bubble top, which serves to accommodate thermal expansion of the stored secondary hot water, will continually be replenished with air. Whilst such an arrangement generally functions satisfactorily, we have discovered that an excessive amount of air might, especially at sustained high cold water feed rates (i.e. when there is a heavy demand for hot water), be admitted into the bubble top. It is an object of the present invention to provide means to solve or at least mitigate that problem.

According to the present invention, therefore, there is provided a mains-fed unvented storage waterheater including an internal bubble top for accommodating thermal expansion of stored secondary hot water and a mains cold water feed pipe including a venturi device adapted to draw air into the cold water, via a non-return valve, from the atmosphere in response, during a demand for hot water, to the flow of cold water through the pipe above a predetermined lower flow rate, whence the air discharges into the bubble top, characterised in that means are provided to limit the rate (ie. the amount per unit time) that air is drawn into the cold water to a predetermined maximum value notwithstanding an increase in the rate of flow of cold water through the feed pipe above that at which said value is initially attained.

Preferably, the arrangement is such that some air will be drawn in regardless of the rate of flow of cold water in the feed pipe although, as will be appreciated, there may be insufficient pressure drop across the venturi device at very low cold water flow rates to cause inflow of air. Advantageously, between normal water flow rates that would prevail when, for example, filling a wash hand basin on the one hand and, on the other hand, filling a bath, the rate at which air is drawn in lies within a fairly narrow range of values and optimally may be more or less constant. However, at high cold water flow rates it may equally be expedient for substantially no air to be drawn in.

The arrangement may be such that the cross-sectional area of the venturi orifice (i.e. the orifice across which a pressure drop is established thereby causing air to be drawn in by the venturi device) progressively and reversibly increases in cross-sectional area in response to increasing water flow rates above a lower limit. This may be achieved by, for example, providing an orifice defined by elastic material such as a synthetic rubber which tends to expand resiliently and progressively with increasing water flow rate, whereby the crosssectional area of the orifice progressively increases. Alternatively, the venturi orifice may be fixed, an air inlet duct through which the air is drawn from the atmosphere including a variable throttle device, for example incorporated in the non-return valve, that provides a progressively increasing throttling effect as the water flow rate increases.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic view of a mains-fed unvented storage waterheater constructed in accordance with the invention; Fig. 2 is a detail at II of Fig. 1 showing one form of venturi device; Fig. 3 is a similar detail as that of Fig. 2 but showing an alternative form of venturi device; and Fig. 4 is a similar detail as that of Fig. 2 but showing a further alternative form of venturi device.

Referring firstly to Fig. 1, the unvented waterheater depicted comprises a lagged cylinder 1, for example of copper or steel, for storing secondary hot water 2 typically at about 60 - 65" C. In a domestic context the capacity of the cylinder 1 is usually between 80 and 210 litres, depending on the likely demand for hot water. The secondary hot water 2 is conveyed to points of use via an outlet pipe 3 connected to the top of the cylinder 1, by means of pressurised cold water connected to the mains supply by a pipe 4. The pipe 4 includes a strainer 5, a pressure reducing valve 6, usually set at around 2 bar gauge (i.e. 3 bar absolute), a non-return valve 7 and an expansion relief valve 8. The system further comprises a temperature relief valve 9 whose outlet, together with the outlet of the expansion relief valve, leads to a tundish 10. The secondary water 2 may be heated directly, for example by an electric immersion heater 11, and/or indirectly by a remote boiler via a coiled heat exchanger 12 located in the cylinder 1.

In addition, the system includes an energy cut out device 13 that, in the event of the secondary hot water 2 attaining too high a temperature, prevents further heating of the secondary water 2 by closing a motorised valve 14 located in the primary circuit 15 of a boiler-heated system. The valve 15 is also actuable by a cylinder thermostat 16, typically set at 60 to 650 C. Where the water 2 is heated by an immersion heater, a cut out device 13' is incorporated in the heater 11. During service, when there is a demand for secondary hot water 2, cold water in the pipe 4 drives hot water, at high pressure, from the cylinder 1 through supply pipe 3 to the point of demand.

A bubble top 17 containing air is defined at the top of the cylinder 1 by an inverted cup-shaped member 18 and the surface of the secondary hot water 2 as described in Fig. 2 of our aforesaid patent.

The bubble top 17 serves to accommodate thermal expansion of the secondary water 2. Under certain conditions, the air comprised in the bubble top 17 may be absorbed by the water 2 to such an extent that, unless replenished, the bubble top ceases to function correctly.

In accordance with the present invention, a variable venturi device 19 is provided automatically to effect replenishment of air in the bubble top 17.

Fig. 2 shows, in detail, one form of variable venturi device 19.

The device 19 comprises a tubular body comprising two like parts 20, 21, secured together by a flanged coupling 22. The body has such an internal diameter that it may be coupled into the pipe 4, where shown in Fig. 1, which typically will be of 22mm copper. The flanged coupling 22 serves to retain the annular periphery 23 of a one-piece member 24 moulded in a synthetic elastomer. The member 24 also comprises a frusto-conical wall portion 25 which defines a central circular orifice 26. The venturi device 19 further comprises an openended air inlet tube 27. The open end 27' of the tube 27 located within the bore of the tubular body terminates more or less at the plane of the orifice 26 whereas the other open end 27", opens to atmosphere via a non-return valve 28. The drawing shows the member 24 in its static, as-moulded condition, i.e. when there is no flow of water in the pipe 4. When there is a demand for hot water 2, mains cold water flows (in the direction of the arrows A) at a corresponding rate through the pipe 4 and a pressure drop occurs within the frusto-conical portion 25, reaching a maximum at the orifice 26, in accordance with Bernouilli's theorem upon which the operation of a venturi device relies. At low flow rates of the cold water, the pressure drop will be insignificant but as the rate increases to a critical value, the pressure drop will increase to produce a sub-atmospheric pressure zone adjacent to the orifice 26 whereupon air will be drawn into the cold water stream via the open end 27" of the tube 27 and the non-return valve 28. The air drawn in rises in the form of bubbles through the mass of hot water 2 into the bubble top 17, thus replenishing same.

With a fixed orifice 26, the pressure drop would progressively increase with increasing flow rate of the cold water through the pipe 4 and so, at very high flow rates, an excessive amount of air might be drawn in. However, because the member 24 is elastic, its wall portion 25 will tend to be forced progressively and resiliently outwards, as indicated by the arrows B, as the water flow rate in pipe 4 increases, thereby increasing the size of the orifice 26. The pressure drop is therefore confined to a fairly narrow, acceptable range of values.

Accordingly, the rate of inflow of air will remain within a fairly narrow range of values, regardless of the rate of flow of water, above a particular lower value, through the pipe 4. Needless to say, in order to achieve that result, the moulded member 4 needs to have the appropriate mechanical properties but these may be ascertained by simple experiment as may the overall geometry of the venturi device 19 in order to achieve the desired air intake. By way of example, the as-moulded diameter of the orifice may be about 6mm, increasing to about 1 5mm at the maximum cold water flow rate, typically about 30 litres per minute, likely to be encountered in practice.

Fig. 3 of the drawings, in which parts identical or similar to those in the Fig. 2 bear the same reference numerals used in Fig. 2, shows an alternative design of venturi device 19.

Fig. 4 of the drawings shows a somewhat different form of venturi device 19, which is in the form of a modified, known check valve. The check valve comprises a body 29 having an internal, radially extending annular wall 30 defining a central, circular port 31.

The periphery of the port 31 defines a valve seat against which is urged, by a compression spring 32, a conical valve closure 33 mounted on a stem 34. The check valve is modified for the purposes of the present invention by forming a small diameter radial bore 35 in the body 29/wall 30 and this communicates, via a short tube 36 and a non-return valve 37, with the atmosphere. In this arrangement, the annular gap 38 between the wall of the port 31 and the external surface of the closure 33 acts as a venturi orifice, thus drawing in air through the tube 36 when the flow rate of water exceeds a critical value. At the same time, of course, the closure 33 is axially displaced away from the valve seat by an amount proportional to the water flow rate. The width ofthe gap 38 thus increases with increasing water flow rate whereby the rate that air is drawn in through the tube 36 is confined to a fairly narrow range of acceptable values.

As noted above, in all the embodiments illustrated, the size of the venturi orifice may be arranged to increase sufficiently at high cold water flow rates through the pipe 4 that a sub-atmospheric pressure zone will not be produced adjacent to the orifice so that no air will be drawn in at such rates.

Because the venturi device shown in Fig. 4 has a check (nonreturn) valve function with respect to the flow of cold water in the pipe 4, the non-return valve 7 of the waterheater may be dispensed with.

Claims

1. A mains-fed unvented storage waterheater including an internal bubble top for accommodating thermal expansion of stored secondary hot water and a mains cold water feed pipe including a venturi device adapted to draw air into the cold water, via a non-return valve, from the atmosphere in response, during a demand for hot water, to the flow of cold water through the pipe above a predetermined lower flow rate, whence the air discharges into the bubble top, characterised in that means are provided to limit the rate (ie. the amount per unit time) that air is drawn into the cold water to a predetermined maximum value notwithstanding an increase in the rate of flow of cold water through the feed pipe above that at which said value is initially attained.

2. A waterheater according to claim 1 wherein said means is arranged such that the rate at which air is drawn into the cold water is, between pre-determined lower and upper cold water flow rates, substantially constant.

3. A waterheater according to claim 2 wherein said means is arranged such that, at cold water flow rates in excess of said predetermined upper rate, substantially no air is drawn in.

4. A waterheater according to any one of claims 1 to 3 wherein said means is afforded by providing said venturi device with a venturi orifice that progressively and reversibly increases in cross-sectional area in response to an increasing mains cold water flow rate through the orifice.

5. A waterheater according to claim 4 wherein said venturi orifice is defined by a hollow, substantially conical member that is radially and resiliently expansible.

6. A waterheater according to claim 5 wherein said member comprises an elastomer.

7. A waterheater according to claim 4 wherein said venturi orifice is defined by a member having an orifice therein of fixed size and, located in said fixed-size orifice, a substantially conical member axially moveable relative to the fixed-size orifice in response to the flow of mains cold water so as to vary, in dependance upon the flow rate of the mains cold water, the cross-sectional area of the orifice available to the flow of mains cold water therethrough.

8. A waterheater according to claim 7 wherein said substantially conical member is spring-biased into a position in which, when there is no cold water flow, it completely closes the fixed-size orifice.

9. A waterheater according to any one of claims 1 to 3 wherein said means is afforded by the combination of a venturi device having a fixed-size venturi orifice and a variable throttle device that provides a progressively increasing throttling effect on the air flow from the atmosphere into the venturi device as the mains cold water flow rate increases.

10. A waterheater according to claim 9 wherein the variable throttle device is incorporated in said non-return valve.

11. A waterheater substantially as hereinbefore described with reference to, and as illustrated in, Figs 1 and 2, Figs 1 and 3 or Figs 1 and 4 of the accompanying drawings.