GB2333145A - Storage waterheater with cold water overflow - Google Patents

Abstract

A cisternless, vented storage waterheater comprises means 13 for inhibiting admixture of incoming mains water with hot water stored in the vessel 1, thus establishing a zone of relatively cool water in the lower region of the vessel 1. The overflow pipe 15 has its inlet 16 located within the cool water zone, so that in the event that the control 11 on the cold water inlet 9 remains open due to a fault, the water which discharges from the vessel 1 is relatively cold water from the cool zone. The overflow 15 is preferably in the shape of an inverted U and further may comprise a vent pipe 18 which also acts as an anti-siphon valve.

Description

Storage Waterheater This invention relates to storage waterheaters and more particularly to storage waterheaters of the so-called cisternless, vented type which are hereinafter referred to as "of the type described".

A storage waterheater of the type described essentially comprises a water storage vessel having a lower mains cold water inlet and an upper hot water outlet, level-sensing means located in the vessel at a level therein corresponding to a pre-determined, normal maximum water level, an expansion air space, vented to atmosphere, above said level, valve means for controlling the flow of mains cold water through said inlet and responsive to the level- sensing means, means to heat most of the water in the vessel to a pre-determined storage temperature, and an overflow pipe.

The construction and operation of a waterheater of the type described will be well-known to those skilled in the art. Briefly, however, when there is a demand for hot water at a point of use, such as a sink or basin, (and assuming that the hot water level in the vessel is at its normal, maximum level with the valve means closed), hot water is conveyed from the storage vessel, under gravity action of a small head of water in the vessel, via the hot water outlet and pipework to the point of use. This results in an initial drop in the water level in the vessel, which is sensed by the level-sensing means. In response thereto, the level-sensing means causes the valve means to open whereupon mains cold water flows through the inlet into a lower region of the vessel and displaces the mass of hot water in the vessel upwards. For so long as hot water is drawn-off, the valve means will remain open. When drawoff ceases, the hot water level in the vessel will rise back to the predetermined maximum level and, in sensing this, the level-sensing means causes the valve means to close. This cycle is repeated during each hot water demand. Most of the water in the vessel is continually heated by the heating means, under the control of a thermostat, to a pre-determined elevated storage temperature. As will be appreciated, therefore, operation of a waterheater of the type described is analagous to a cistern-fed, vented waterheater but the former has the advantage that it is unnecessary to provide a feed cistern.

The level-sensing means may comprise, for example, a float switch in which case the valve means would comprise an electricallyoperated valve such as a solenoid valve. Alternatively, for example, the level-sensing means and the valve means could comprise purely mechanical means such as a float ("ball") valve.

One common problem associated with known designs of waterheaters of the type described is that, should the level-sensing means and/or valve means develop certain fault conditions, the valve means remains open and so, under static conditions, the vessel overfills until water discharges from the overflow pipe. Because, in known designs, the inlet to the overflow pipe is located slightly above the normal maximum water level, the discharged overflow water comprises hot water typically between 45 and 60"C in temperature. Discharge will continue for so long as the fault condition prevails. This, of course, is potentially hazardous especially where, as may be the case, the hot overflow water is discharged at an elevated external location. It is also wasteful of hot water and energy.

It is an object of the present invention to mitigate the aforesaid problem.

According to the present invention, there is provided a storage waterheater of the type described, characterised in that means are provided to inhibit admixture of incoming mains cold water, as it enters the vessel, with hot water stored in the vessel whereby a zone of relatively cool water is established in the lower region of the vessel, and in that the overflow pipe includes a portion that extends generally upwardly from said zone to an overflow level slightly above said normal maximum water level, the inlet to the overflow pipe being located in said zone, whereby, in the event that the valve means remains open because of a fault condition in said level sensing means and/or in the valve means, the level of water in the vessel will rise to said overflow level whereupon relatively cool water in said zone discharges through the overflow pipe via its inlet for so long as the fault condition prevails.

Accordingly, in a waterheater of the invention, most of the overflow water will be at a relatively low, "safe" temperature, typically between 10 and 20"C. This should be contrasted with prior waterheaters of the type described wherein, as noted earlier, overflow water consists of stored hot water displaced out of the overflow outlet by incoming mains cold water.

In a preferred embodiment, the means to inhibit admixture of incoming cold water and the stored hot water comprises an enclosure, for example in the form of a cuboid chamber, located adjacent to the base of the storage vessel, into which the mains cold water inlet and the inlet end of the overflow pipe extend and which is formed with an opening through which, normally, incoming mains cold water flows into the vessel. The walls of the enclosure serve, in particular, to baffle, ie. reduce the velocity of, the incoming mains cold water thereby inhibiting mixing thereof with the bulk of the hot water stored in the vessel.

The overflow pipe may, at the upper end of the generally upwardly extending portion, terminate in, for example, a substantially horizontal portion. Preferably, however, the overflow pipe is generally U-shaped and comprises, in addition to said upwardly extending portion, a downwardly extending portion. In that arrangement, the uppermost part of the overflow pipe is provided with an anti-siphon vent to atmosphere, as is described in more detail later.

The overflow pipe is preferably located within the vessel but it may be located externally thereof.

One embodiment of 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 schematic side elevation of a waterheater constructed in accordance with the invention; and Fig 2 is an underplan view of the waterheater shown in Fig 1.

Referring to the drawings, the storage waterheater comprises an enclosed hot water storage vessel 1 which is of"slimline" cuboid form, although it may equally be, say, cylindrical. The vessel may be made of stainless steel or other corrosion-resistant material, such as copper. An electric immersion heater 2 is sealingly mounted, by means of a boss 3, in the base 4 of the vessel 1. The heater 2 serves to heat and maintain water stored in the vessel 1 to and at a pre-determined temperature of, say, about 65"C under the control of a thermostat which includes a temperature probe 5 sealingly mounted in the base 4 of the vessel 1.

Alternatively, of course, the water could be heated indirectly by, for example, a coiled heat exchanger through which hot primary water is circulated to and from a boiler.

Also sealingly mounted in the base 4 is a hot water outlet pipe 6, typically of 22mm O.D., which extends vertically within the vessel 1 almost to its top 7. The lower end of the pipe 6 is, externally of the vessel 1, connected to the hot water inlet of an adjustable thermostatic mixing valve 8. A mains cold water feed pipe 9 is, via a pressure regulator 10, connected to the cold water inlet of the mixing valve 8.

The outlet of the mixing valve 8 is, in the installed waterheater, connected to pipework (not shown) for conveying domestic hot water to points of use, such as sinks, basins etc as is indicated by the arrow in Fig 1 marked "DHW OUT".

In the pipe 9, upstream of the pressure regulator 10, there is a Tconnector to which is connected, via a solenoid valve 11, an inlet pipe 12, typically of 1 Smm O.D., for conveying mains cold water into the vessel 1. The solenoid valve 11 incorporates a flow controller of known type for maintaining the cold water flow rate substantially constant, for example about 8 lr/minute, regardless of fluctuations in the mains pressure. The inlet pipe 12 sealingly penetrates the base 4 of the vessel 1 and terminates inside an enclosed compartment 13 located within the lower region of the vessel 1. The compartment 13, which is of cuboid form, is defined by top and side walls and the base 4 of the vessel 1.

One of the side walls has a slotted aperture 14 formed in it through which mains cold water issues into the vessel 1.

The vessel 1 has vertically mounted in it an inverted U-shaped overflow pipe, for example of 22mm O.D., designated generally 15 and comprising two vertical limbs 15' and 15" joined at their respective upper ends by an inverted U-bend 15"' positioned slightly above the normal maximum water level in the vessel 1. The lower end of the limb 15' sealingly penetrates the top wall of the compartment 13 where it terminates in an inlet 16, whereas the lower end of the limb 15" sealingly penetrates the base 4 of the vessel 1 and terminates in an overflow outlet 17. The inverted U-bend 15"' is provided with a vent pipe 18 that penetrates the top 7 of the vessel 1 and opens to atmosphere; the pipe 18 is formed, internally of the vessel 1, with a lateral opening 19 which serves as a vent for the expansion air space in the vessel 1 above the water level. Of course, the latter could be achieved by providing a separate vent in, say, the top 7 of the vessel 1.

A float switch 20 is located in the vessel 1 slightly below the level of the U-bend 15"' but above the upper, open end of the hot water outlet pipe 6. The solenoid valve 11 is connected, via the float switch 20, to an electrical power source (not shown).

The waterheater also comprises a decorative outer casing 21 which, in particular, envelops a layer of thermal insulation around the vessel 1.

The waterheater specifically described above operates as follows.

Assume that the vessel contains its normal complement of stored hot water 22 at, say, about 65"C i.e. up to the level indicated by the dashed line 22' which corresponds to the level at which the float switch 20 is located. The switch 20 will therefore be open and the valve 11 will be de-energised and closed. Then, when there is a demand for hot water at a point of use, hot water 22 will flow out of the vessel via the upper open end of the outlet pipe 6 (as indicated by an arrow in Fig 1) and will be conveyed to the point of use via the pipe 6 and the mixing valve 8 where it mixes with cold water to provide domestic hot water at a suitable, pre-determined temperature, say around 40 to 500C, as determined by the setting of the mixing valve 8.

Thus, there will be an initial small drop in the level 22' in response to which the float switch 20 closes and energises the solenoid valve 11 whereupon cold main water flows into the vessel l via the mains cold water feed pipe 9, the pressure regulator 10, the valve 11, the inlet pipe 12, the compartment 13 and the aperture 14, as indicated by arrows in Fig 1. As the mains cold water enters the compartment 13, it is deflected off its walls thereby changing its flow direction a number of times. This serves to reduce the velocity of the water issuing from the aperture 14. Thus, the stored hot water and the incoming cold water tend to remain stratified and the cold water dispaces the mass of stored hot water 22 generally upwards without a significant degree of mixing.

Accordingly, water adjacent to the base 4 of the vessel 1, and particularly in the compartment 13, remains at a relatively low temperature.

For so long as the demand for domestic hot water continues, the level 22' will fluctuate slightly depending on the relative hot water outflow and cold water inflow rates. When the demand ceases, the valve 11 remains open until the level 22 again attains its normal maximum level, as sensed by the float switch 20 which then opens, thereby causing the valve 11 to become de-energised and closed. The above-described cycle will be repeated each time there is a demand for domestic hot water and the heater 2 will continually operate, in response to its thermostat, to maintain most of the water 22 stored in the vessel 1 at a pre-determined elevated temperature. As will be appreciated, the limb 15' of the overflow pipe 15 will contain water up to the same level as the level of hot water 22 in the vessel 1.

In waterheaters of the type described, a common problem is that of failure of the float switch 20 and/or of the solenoid valve II and in certain failure modes the valve 11 may remain partially or fully open even when there is no demand for hot water. For example, the float switch 20 could stick in its closed position or the valve 11 itself could stick in a partially or fully open position. In known designs, this results in displacement of the stored hot water 22 up to the level of an overflow outlet whence hot water is discharged, for example to an external location. As noted earlier, this is potentially hazardous and is wasteful of hot water and energy especially as the heater 2 will continuously operate during a fault condition.

In the waterheater described above, however, in such an event, the water level 22' both in the vessel 1 and the limb 15' of the overflow pipe 15 rises until it reaches an "overflow" level designated by the dashed line 22" in Fig 1 whereupon water flows down the limb 15", via the Ubend 15"', of the overflow pipe 15 and out of the overflow outlet 17.

Overflow of water will continue until the mains cold water is turned off, when the fault can be rectified. Because the overflow water is abstracted from the lower region of the vessel 1, and in particular from the compartment 13, it consists mainly of relatively cool water although it may become slightly heated during its passage through the limbs 15' and 15". Nevertheless, it is unlikely that the temperature of the overflow water (save for the small, initially discharged volume contained in the limb 15') will exceed, say, 200C and, further, much of the stored hot water in the vessel 1 is preserved whereby the heater 2 will operate only intermittently during a fault condition.

As well as serving to vent the vessel 1, the vent pipe 18 acts as an anti-syphon device, thereby preventing syphoning out of hot water from the vessel 1 during an overflow situation. The overflow outlet 17 could (as in prior designs) be located near the top of the vessel 1, as is depicted by the alternative shown in dashed lines at 17' in Fig 1 of the drawings. Likewise, the hot water outlet pipe 6, the inlet pipe 12, the heater boss 3 and the temperature probe 5 could penetrate one or more sides ofthe vessel 1 rather than its base 4. However, as in the waterheater depicted, it is advantageous from a manufacturing and installation viewpoint for all of the connections to the vessel l to be in its base.

Likewise, the provision of the mixer valve 8 and of the pressure regulator is merely preferred. The former, in particular, permits the hot water 22 to be stored at a temperature that is much higher than a safe DHW delivery temperature, whereby the heat capacity of the waterheater is significantly increased.

As noted earlier, the overflow pipe 15 could be located externally ofthe vessel 1, the inlet 16 thereto being defined at the end of, say, a short horizontal section of pipe that penetrates the side of the vessel l and extends into the compartment 13. Such an arrangement has the advantage that heat exchange between the cool overflow water and the stored hot water is avoided.

Claims (6)

1. CLAIM8 1) A storage waterheater which comprises a water storage vessel having a lower, mains cold water inlet and an upper, hot water outlet, level-sensing means located in the vessel at a level therein corresponding to a predetermined normal maximum water level, leaving an expansion air space, vented to atmosphere, above said level, valve means for controlling the flow of mains cold water through said inlet and responsive to the level-sensing means, means for heating most of the water in the vessel, an overflow pipe, and means for inhibiting admixture of incoming mains cold water, as it enters the vessel, with hot water stored in the vessel whereby a zone of relatively cool water is established in the lower region of the vessel, the overflow pipe including a portion which extends generally upwardly from said zone to an overflow level slightly above said normal maximum water level, and the inlet to the overflow pipe being located in said zone whereby, in the event that the valve means remains open because of a fault condition, the level of water in the vessel will rise to said overflow level whereupon relatively cool water in said zone discharges through the overflow pipe via its said inlet.
2. 2) A storage waterheater as claimed in claim 1, in which said means for inhibiting admixture of incoming cold water and stored hot water comprises an enclosure located adjacent the base of the storage vessel, into which enclosure the mains cold water inlet and the inlet end of the overflow pipe extend, the enclosure being formed with an opening for the flow of incoming mains cold water into the vessel.
3. 3) A storage waterheater as claimed in claim 1 or 2, in which the overflow pipe terminates, at the upper end of said generally upwardly extending portion, in a substantially horizontal portion.
4. 4) A storage waterheater as claimed in claim 1 or 2, in which the overflow pipe is generally U-shaped, having a generally downwardly extending portion joined to the upper end of said generally upwardly extending portion.
5. 5) A storage waterheater as claimed in claim 4, in which the uppermost part of the overflow pipe is provided with an anti-siphon vent to atmosphere.
6. 6) A storage waterheater substantially as herein described with reference to the accompanying drawings.