GB2241568A - Boilers - Google Patents

Abstract

In an electric boiler for use as part of a hot water heating system, the boiler including a heat store so as to be capable of being heated by off-peak electricity, the boiler tubes 24 - 27 have manifold connections 37 to 39, 41 to 44, which are contained within the overall lengths of the tubes. The ends of the tubes are closed. This means that unbroken panels of top and bottom insulation can be used with the boiler tubes as part of the normal insulation for the heat store, thereby avoiding a problem with prior designs where boiler tubes extended through the heat insulating material, which necessitated assembly of at least one manifold on site. <IMAGE>

Description

Boilers This invention relates to boilers, especially electrically powered boilers.

Boilers have been proposed in which boiler tubes extend through a heat store surrounded by insulation material and heated by electrical means.

The heating of the boiler is usually carried out during periods of the daily cycle when electricity is available at a reduce cost.

The applicants first considered implementing such a system with design shown in Figures 1 and 2. The boiler had four upstanding boiler tubes 1 to 4 surrounded by side insulation panels 5, 6 and front and rear insulation panels (not shown). The inlet pipe 7 connected to the tubes by a manifold 8 and a manifold 9 fed an outlet pipe 10.

The boiler was designed to be assembled on site as follows.

The welded assembly of four tubes and lower manifold was placed in the cabinet, and a panel of insulation 11 was threaded over the four tubes. The bricks (not shown) and the front, rear and side insulation panels were assembled, and a top insulation panel 12 was the threaded over the four tubes. The top manifold was then fitted into the gland nuts 13 to 16 which were loosely threaded to pipes la to 4a at the upper ends of the boiler tubes, and compression sealed to the pipes by tightening the nuts.

The aim of the present invention is to simplify the assembly of an electric boiler.

The invention provides an electric boiler, comprising a heat store, electrical means for heating the heat store, heat insulating material surrounding the heat store, a plurality of boiler tubes extending through the heat store, and a first manifold which includes portions which communicate with the sides of the boiler tubes, the adjacent ends of the boiler tubes being closed and terminating inside the heat insulating material.

With such manifold connections to the boiler tubes, it is no longer necessary to thread the insulation over the tubes. If a second manifold includes portions which communicate with the sides of the boiler tubes, and the adjacent ends of the boiler tubes are closed and terminating inside the heat insulating material, it is not necessary for the insulation at either end of the tubes to be perforated, and the assembly of boiler tubes and manifolds can be factory assembled. For example, the assembly could be welded together and pressure tested prior to despatch to the location where the boiler was to be assembled. Further, the boiler tube assembly could be withdrawn from the electric boiler if necessary for maintenance.

The first and/or second manifold may communicate with the region outside the heat insulating material by means of portions which extend around the periphery of the heat insulating material adjacent the respective ends of the boiler tubes.

A domestic hot water system including an electric boiler, constructed in accordance with the invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 3 is a schematic view of the hot water system; Figure 4 is a perspective view of the electric boiler in partially assembled state; Figure 5 is a perspective view illustrating the positions of the bricks when the boiler has been assembled; Figure 6 is a perspective view of the boiler tubes; Figure 7 is a perspective view of an alternative arrangement of boiler tubes; Figure 8 is a front view of the boiler tubes of Figure 7 positioned in the boiler; Figure 9 is a perspective view of the lower insulation for the tubes of Figure 7; and Figure 10 is a plan view of the top course of bricks.

Referring to Figure 3, the hot water system is powered by an electric boiler indicated generally by the reference numeral 17 which heats a primary water/steam circuit indicated generally by the reference numeral 18, which in turn heats a secondary hot water circuit indicated generally by the reference numeral 19 by means of a heat exchanger 20.

The boiler is intended to be powered by off-peak electricity which is available at certain periods during a 24 hour period from a separately metered power source at a reduced price.

A water pump 21 pumps the hot water in the secondary circuit around fan-assisted water pipe coils 22, 23. The secondary circuit could include hot water radiators or other heat dissipation means, positioned within the rooms to be warmed.

The primary water/steam circuit consists of four water/steam boiler tubes 24 - 27 arranged at the corners of a square (see Figure 6) and a heat store consisting of a stack of bricks 28. The heat store is surrounded by insulation in the form of a top panel 29, a bottom panel 30, side panels 31 and 32 and front and rear panels (not shown). The bricks are heated by means of heating coils 33.

When the bricks have been heated to a high temperature, water is allowed to pass from a reservoir tank 34 by means of a control valve 35 by gravity into the lower end of the boiler tubes, where the water is evaporated into super-heated steam. The steam gives up its heat in the heat exchanger 20 and condenses back to water which is collected in the reservoir tank 34. The control valve 35 enables the return condensed flow to be interrupted so that all the primary circuit water is retained in the reservoir 34 in order that the withdrawal of heat from the primary circuit can cease. Contraction and expansion of the primary water is allowed for by standpipe 36, but a closed flexible membrane or pressurised tank could be used instead if desired. The secondary water circuit is provided with a conventional header tank (not shown).

Referring to Figures 4, 5 and 6, the upper manifold consists of tubes 37, 38 which are welded to apertures in the sides of the boiler tubes 25 to 27, and intermediate section 39 and an outlet section 40. The lower manifold consists of tubes 41 to 44 which are welded to apertures in the sides of the boiler tubes, and an inlet pipe 45 into which the tubes 41 to 44 connect.

All these tubes are welded at the factory and the boiler is delivered with the tube assembly in position. The upper and lower ends of the boiler tubes are closed.

The upper and lower insulation panels 29, 30 have recesses to locate the tube end portions. They also have peripheral recesses 29a, 30a, to allow inlet pipe 45 and outlet section 40 to communicate with the region outside the boiler to connect to the primary water circuit. The side insulation panels 31, 32 are shown partly removed in Figure 4.

It will be apparent that, because the boiler tubes and manifolds do not extend through apertures in the top and bottom insulation panels, the fitter does not have to assemble the manifolds on site.

The rest of the installation is as follows. With the panels 31, 32 completely removed, those bricks in the first course which lie to the left of the tubes 24, 25 are inserted into the cabinet. Because the thickness of the panel 31 is greater than the depth of the semi-cylindrical recesses which engage the tubes, there is sufficient room for the bricks to be inserted. They are then displaced sideways until their recesses engage the tubes 24, 25. Next, the bricks of the lower course that lie to the right of the tubes 24, 25 are inserted, and pushed adjacent to the ones already in the cabinet.

The same procedure is then applied for the bricks of the first course which surround the tubes 26, 27, which are not shown in Figure 5.

Having inserted the first course of bricks, the fitter then inserts the element 33, which lies in the four sections of the horizontally extending grove 46 which is formed in the upper surface of the bricks.

Since the bricks to the right of the tubes 24 and 25 and those to the left of the tubes 26 and 27 are in contact with each other when inserted, it follows that the bricks to the left of the tubes 26, 27 have to be held above the first course and with the recesses in engagement with the tubes 26, 27 and then lowered vertically to be installed. It will be apparent that this is not possible with the uppermost course of bricks since there is no room above the uppermost course for the bricks to the left of the tubes 26, 27 to be held. This situation is dealt with by providing just two bricks 47, 48 of reduced width in the direction from side to side of the boiler, the width reduction being greater than the depth of the recesses that engage the boiler tubes, so that these bricks 47, 48 can be inserted in a front to back direction level with the other bricks of the top course (Figure 10).The gap thus left is then filled with a pair of keying bricks 49.

As an alternative to the boiler tube assembly shown in Figure 6, the boiler tube assembly in Figure 7 may be adopted, in which the connections to an outlet pipe 50 are by means of individual tubes 51 to 54. To accommodate the tubes 51 to 54, the bottom insulation panel has recesses for the tubes (Figure 9), and this arrangement is also shown in Figure 8. The construction of Figure 7 has the advantage that there is a certain flexibility in the tubes 24 to 27, allowing greater tolerances to be provided in the recesses in the base insulation 29.

When all the bricks have been inserted, and are in contact with the tubes 24 to 27, the side insulation panels 31, 32 are inserted, and the inner faces thereof may be faced with stainless steel to assist this operation.

The heating coil end leads for each course are connected to the electrical supply terminals and the front slab of thermal insulation is mounted over the front face of the storage mass. An outer metal panel is mounted over the front insulation completing the construction of the outer casing.

Each brick has proportions roughly of length twice its width and three times its thickness. A clay or chemically bonded mineral mixture containing in excess of 95% magnesium oxide is used to make the brick, this material having particularly suitable storage properties of heat retention and thermal conductivity heat storage on the one hand and for the withdrawal of heat into the water/steam primary circuit on the other hand.

Of course, modifications may be made without departing from the scope of the invention. Thus, for example, the manifold arrangement for the bottom of the tubes shown in Figure 7 may be used for the tops of the tubes if desired. Equally, additional boiler tubes 24 to 27 may be provided if desired.

Claims (9)

1. An electric boiler, which comprises a heat store, electrical means for heating the heat store, heat insulating material surrounding the heat store, a plurality of boiler tubes extending through the heat store, and a first manifold which includes portions which communicate with the sides of the boiler tubes, the adjacent ends of the boiler tubes being closed and terminating inside the heat insulating material.

2. An electric boiler as claimed in claim 1, in which there is provided a second manifold which includes portions which communicate with the sides of the boiler tubes, and the adjacent ends of the boiler tubes are closed and terminating inside the heat insulating material.

3. An electric boiler as claimed in claim 1 or claim 2, in which the first and/or second manifold and respective boiler tubes form a welded assembly.

4. An electric boiler as claimed in any one of claims 1 to 3, in which the first and/or second manifold communicates with the region outside the heat insulating material by means of portions which extend around the periphery of the heat insulating material adjacent the respective ends of the boiler tubes.

5. An electric boiler as claimed in any one of claims 1 to 4, in which a manifold comprises tubes which extend laterally from the respective boiler tube and portions to a common tube.

6. An electric boiler as claimed in any one of claims 1 to 5, in which the boiler tubes are upstanding and the insulation beneath them has recesses to seat the tubes.

7. An electric boiler as claimed in any on of claims 1 to 6, in which the boiler tubes form part of a primary circuit, connected by a heat exchanger to a secondary hot water heating circuit.

8. An electric boiler substantially as herein before described.

9. A hot water system including an electric boiler as claimed in any one of claims 1 to 8.