GB2108249A - Catering water boilers - Google Patents

Abstract

A water heater for supplying nominally boiling water in catering establishments has an enclosed main tank 11 with a header tank, 12 just above it. A draw-off tap 17 is provided at the top of the main tank which tap extends into the main tank via a pipe portion 16, an extension of which is surrounded by an electric immersion heater 20. In a second embodiment the two tanks are formed by dividing a deep pan member by means of a diving bell member with the space between the two members forming a connection between the two tanks. <IMAGE>

Description

SPECIFICATION Catering water boilers The present invention concerns water boilers for use in catering establishments and in other bulk users of boiling water.

In catering establishments there is a need for a constant supply of hot water for making beverages etc. There are several ways of providing such a supply but each has its own advantages and disadvantages. An enclosed tank can be at superatmospheric pressure and be dangerous unless it is vented to atmosphere releasing clouds of steam. An open topped tank even if provided with a lid tends also to emit steam. Thus boilers in the form of tanks are associated with release of steam which is wasteful of heat and a nuisance. In addition heat is lost from the walls of the tanks. Heating a pipe through which water flows on demand leads to problems in synchronising the heating and the water flow and heat is wasted by having to heat the pipe each time. In most cases more heat is wasted than with a properly lagged tank. In general boiling water is not required to make drinks but a somewhat lower temperature is adequate; nevertheless the water is referred to as boiling and the equipment as boilers and due to time lags in the control of heating the near boiling water does boil at times due to thermal inertia in the usual on-off thermostatic control. The present invention aims at supplying a boiler with the minimal heat loss by reducing steam emission and heat transfer through the wall of the boiler.

According to the present invention, a water boiler comprises main tank and a header tank, the main tank having associated with it heating means and being enclosed except for a first connection for conducting water from the header tank to the base of the main tank and a second connection for releasing any steam into the header tank together with a draw-offfor drawing offthe hot water.

It is important that the first and second connections do not form a thermosyphon loop and one way of avoiding this is to have the second connection discharge through through an air gap into the header tank. The header tank is relatively cool and so any discharged hot water from the main tank is cooled. It is preferable that the second connection passes through the water in the header tank being cooled thereby to minimise any steam passing through the second connection. Conveniently the header tank has a lid. It is greatly preferred that the heating means is an electrical immersion heater within the main tank and disposed adjacent the draw-off point so drawn-off water passes through the immersion heater. Imagine starting with both tanks full of cold water, when the heat heating means is operating the water in the main tank is heated and any water drawn-off has its temperature boosted. Any expansion of the water in the main tank is relieved by water flowing into the header tank through the second connection due to the lower inertia associated with the second connection. As water is drawn off from the main tank, the water from the header tank refills the main tank passing down the first connection to the bottom of the main tank (any heat.lost to the header tank is thus returned). The bottom of the main tank is therefore cool and even if it rests on a thermally conductive surface the heat loss would be small; moreover the bottom tends to cool any external casing enclosing the boiler. Since only the top of the main tank is hot with the bottom remaining cool, the mean temperature of the tank is somewhat lower than that of the boiling water and thus the tank tends to lose less heat.

Whilst all development has been concentrated on boilers in which the tanks are discrete tanks with the connections being in the form of pipes, all being of brass, and in which the header tank is spaced a small distance above the main tank, other ideas are under evaluation. Some form of lagging the first connection as it passes through the main tank, or of otherwise separating the first connection from the main tank, may be useful in preventing a chilling effect on the water in the main tank. Again it may be possible to have a tall deep pan-like member divided into the two tanks by a diving-bell-like member with a space between the walls of the two members serving as the first connection and forming a cold water jacket around the main tank; since the hot water is totally enclosed in cold water the overall heat loss is low but the hot water tends to be chilled by the cold water and thus the diving-bell-like member should be made of a thermally insulating material.

Embodiments of the present invention will now be described, by way of exam ple, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic vertical section through a boiler, and Figure 2 is a similar view through another embodiment.

The boiler of Figure 1 comprises a main tank 11 and a header tank 12. The main tank is made of brass or copper and is totally enclosed except for a first connection 14 leading from the base of the header tank to the bottom of the main tank, a second connection 15 from the top of the main tank leading through the header tank and bending over at its top end to discharge water from the main tank through an air space on top of the water in the header tank, and a draw-off tap pipe 16 leading to a draw-offtap 17. This pipe 16 is provided in the top wall 18 of the main tank and has associated with it a stub pipe 19 within the main tank through which stub pipe drawn-off water has to flow. Surrounding the stub pipe there is an electrical immersion heater 20 which heats the stub pipe and the water in the main tank.

This heater can be controlled manually and/or thermostatically but thermostatically is preferred.

The filling of both tanks can be controlled automatically and/or manually through a water inlet 21 into the header tank since if the main tank is empty any water in the header tank will flow into the main tank displacing any air through the second connection.

An outer stainless steel casing 22 encloses both tanks and mounts the tap 17. Surprisingly some tests showed that thermal lagging material between the tanks and the casing increased heat loss but such lagging material can be used if desired.

Various sizes of these boilers can be provided ranging from a small domestic size of say four pint capacity wherein when two cups of hot water are required two pints of cold water have to be poured into the header tank to a large industrial size plumbed into a water supply with automatic level control in the header tank. At least in the smaller sizes, access to the header tank is needed and a removable lid 23 is provided. In the larger sizes with automatic water control, a lid is not essential and the header tank can have a closed top but an overflow is desirable. Such an overflow or a removable lid vents the header tank to atmosphere. To avoid spillage down the side of the header tank, the header tank is in sealing relationship with the casing.

Boilers in the catering trade do not normally supply water at boiling temperature (1 000C) but somewhat below (say 88"C) but nevertheless if the hot water is vented at atmosphere they emit copious amounts of steam, possibly due to unavoidable thermal inertia of the heater and due to localised overheating. In the present arrangement, even when it is adjusted to supply boiling water, the second connection which serves as a vent is in heat exchange relationship with the cold water in the header tank and thus any steam in the second connection merges back into the water and the vented hot water is dumped into the cold water in the header tank. In some tests at the worst conditions the water in the header tank reached 60"C but no steam was observed escaping past a metal lid 23.

Despite the absence of thermal lagging the outer casing remained cool to the touch.

Instead of having a stub pipe 19, it is possible to dispose the heater so that normal convection would result in the drawn-off water being heated preferentially. It is possible to sense when water is being drawn off from the position of the tap or by sensing water flow and use this to switch on the heater overriding the thermostat or to switch on a booster heater (in larger sizes). The draw-off pipe and the second connection are disposed so that after the main tank is initially filled to cover the heater, it is impossible to draw off water so as to uncover the heater indeed the main tank remains full at all times.

In use the heater is switched on after the main and header tanks are filled for a pre-determined heating time sufficient to establish a bank of heated water in an upper level of the main tank. If the boiler is unused for some time, the header tank may become warm but not too hot and this merely results in the feed water being pre-heated as the water in the header tank is later drawn into the main tank. When hot water is drawn off, the feed water is introduced at the bottom of the main tank with the bank of hot water becoming shallower with the heater being called into play to restore the depth of the bank.

The boiler shown in Figure 2 is theoretically similar but differs in the method of construction. A deep pan-like member 30 with removeable lid 223 is divided into a main tank 211 and a header tank 212 by a diving-bell like member 31. This member 31 is of, or is lagged with, a thermally insulating material such as impermeable foamed plastics material or is of a double wall construction as shown at the top of this me-mber in Figure 2 and can be ballasted if desired so it will not float in water. A first connection 214 between the bottom of the header tnak and the bottom of the main tank is provided by a clearance between the walls of the two members and a gap between the bottoms of the two members. The member 31 can rest on the bottom of the member 30 with the said gap being provided by means of scallops 32 or other cutaways. A second connection 215 in the form of a thermally conductive tube leads from the top of the main tank through the header tank to a turned over end to discharge any water expelled from the main tank on top of the water in the headertankthrough an air gap. A downward extension of this second connection in the form of a tubular mesh 33 beyond the top of the main tank to impede steam bubbles entering the second connection; the aim is to stop the latent heat of the steam leaving the main tank and heating the header tank whilst at the same time permitting the escape of air and steam in the form of layers not bubbles. It is important to vent off steam layers since whilst the steam will condense as the temperature falls it is possible that water will be drawn off before the temperature falls and this would result in the emission of steam. Instead of using a tubular mesh, other arrangements are possible such as merely castellating the bottom of the second connection's downward extension so water can escape through the slots forming the castellations. The member 31 has a draw-off duct 216 leading to a boss 34 formed on the member 31 to which can be sealingly connected a draw-off tap 217 or a pipe leading to the draw-off tap. This duct can be moulded into the member 31 in the form of cross-bores or could be in the form of a downwardly open groove in the part of the memberforming the top wall of the main tank leading to a central bore in the boss 34. It is envisaged that this boss could be the only anchoring point for the member 31 and if it is it must be strong enough to withstand inertial stresses whilst the boiler is being transported and also to prevent the member 31 trying to float. Of course, the boiler could be packed during transport to minimise inertial forces and the member 31 could be ballasted to avoid flotation forces. As in the first embodiment, the draw off duct is surrounded by a stub-pipe depending into the maintankwhich minimisesthe amount of steam drawn off with the water, an electrical immersion heater, a thermostat, and possible also automatic water feed. It will be appreciated that the member 30 is merely a deep pan with a few holes in it (all bar one being above the water level) and everything is either part of, or mounted on, the member 31 with a few interconnections to be made; thus the boiler is simple to make. If, by suitable insulation or by suitable setting of the thermostat, the temperature of the water in the header tank can be kept down even in the worst case to an acceptable level, it may be possible to dispense with an outer casing and/or external lagging, since there is a cold water jacket.

Claims (12)

1. A water boiler comprising a main tank and a header tank, the main tank having associated with it heating means and being enclosed except for a first connection for conducting water from the header tank to the base of the main tank and a second connection for releasing any steam into the header tanktogetherwith a draw-off tap for drawing off the hot water.

2. Awater boiler according to claim 1 wherein the heating means is an electrical immersion heater which is disposed close to where the water is drawn from the main tank.

3. A water heater according to claim 1 or claim 2 wherein the water is drawn off at the top of the main tank.

4. A water heater according to claim 3 wherein surrounding the water-take-off point there is a stub pipe depending into the main tank.

5. A water boiler according to any one of the preceding claims wherein the second connection passes through, and is cooled by water in, the header tank.

6. A water boiler according to any one of the preceding claims wherein the header tank is enclosed but vented to atmosphere as by a removable non-sealing lid.

7. A water boiler according to any one of the preceding claims wherein the first connection passes through the main tank.

8. A water heater according to claim 7 wherein the first connection at least where it passes through the main tank is thermally insulating or insulated.

9. A water heater according to any one of the preceding claims wherein both tanks are enclosed in a common outer casing.

10. A water heater according to any one of the preceding claims wherein the two tanks are defined by a pan-like member divided into the two tanks by a diving bell like member.

11. A water boiler according to claim 10 wherein the diving bell like member thermally separates the two tanks.

12. A water boiler substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.