GB2253896A

GB2253896A - Improvements in hot water storage vessels

Info

Publication number: GB2253896A
Application number: GB9105502A
Authority: GB
Inventors: Richard Martyn Griffiths
Original assignee: IMI RANGE Ltd
Current assignee: IMI RANGE Ltd
Priority date: 1991-03-15
Filing date: 1991-03-15
Publication date: 1992-09-23
Also published as: GB9105502D0

Abstract

A hot water storage vessel, for example a copper cylinder, is thermally insulated by a non-CFC-blown foam material having in intimate contact with most or all of its external surface a separately formed, substantially non-permeable membrane. The foam may be a polyurethane foam and the membrane may comprise a plastics or metallic sheet or film secured to the foam surface by adhesive or strapping. Alternative the membrane may comprise a dried varnish or lacquer coating.

Description

Improvements in Hot Water Storage Vessels This invention relates to hot water storage vessels and more particularly to such vessels, especially but not exclusively cylinders, provided externally with thermally insulative lagging.

It has for many years been standard practice to factory-insulate copper hot water storage cylinders with a polyurethane foam. Conventionally this has been done by spraying a foamable precursor composition, including a blowing agent, onto most of the external surface of the cylinder. This results in a very effective insulating layer, typically between 20mm and 60mm thick (in order to comply with BS 699, 1566 and other specifications), adherent to the external surface of the cylinder.

Alternatively, such foam insulation may be moulded onto the cylinder or applied as "strap-on" pre-formed, eg pre-moulded, sections.

Hitherto, the blowing agent used to produce such foams, in whatever form, has conventionally been a chloro-fluoro carbon, for example the material known in the art as "CFC R.1l". However, the use of such materials is now controlled by the Montreal Protocol because of their allegedly detrimental effect on the "ozone layer" and the use of alternative blowing agents is, at the very least, desirable. One alternative suggestion is to use carbon dioxide as the blowing agent which is generated, during the curing step, by the reaction of water with the isocyanate monomer contained in the pre-cursor composition.

One desirable feature of CFC-blown polyurethane foam, in particular CFC R.ll-blown foam, is the foam's ability to retain the CFC in its cells after blowing and this improves the overall insulating properties of the foam since CFCs generally have better insulating properties than, say, air or, indeed, than most proposed substitutes. A second desirable feature of CFC-blown foam is that a skin tends to form on its outside surface and again this improves the long term insulating properties of the foam by preventing migration of the CFC from the cells into the atmosphere. Foams utilising certain alternative blowing agents do not, we have discovered, possess this feature. As a result of the above, many alternatively blown foams have inferior insulating properties and thus, other things being equal, greater thickness of foam have to be used.For example, in the case of carbon dioxide-blown foams, around 50% extra thickness may be required in order to achieve the same insulating properties as CFC-blown foams. This, of course, adds to manufacturing costs and increases the external dimensions of the cylinder which may give rise to difficulties in siting it in a restricted space such as an airing cupboard.

It is an object of the present invention to improve the thermal insulating properties of a foam-insulated hot water vessel, for example a cylinder, and especially of hot water vessels insulated with foam that has been blown using agents other than CFCs, whereby the amount of extra thickness may be somewhat reduced.

According to one aspect of the present invention, therefore, there is provided a hot water storage vessel, for example a cylinder, having on at least a major part of its external surface a thermally insulating foam, for example a polyurethane foam, at least a major part of the external surface of the foam having thereon a separately formed, substantially non-permeable membrane.

The substantially non-permeable membrane, by which we mean substantially non-permeable at least to gaseous substances, is preferably a sheet or film of plastics material, but other thin materials may be used, including for example metal sheet or foil or a composite metal/plastics sheet or foil.

The substantially non-permeable membrane may be located on the external surface(s) of the foam by means of, for example, an adhesive, or may be retained thereon by, for example, strapping.

Alternatively, for example, it may comprise a membrane formed by the application to the external surface of the foam, for example by spraying, brushing or dipping, of a liquid film-forming material such as a varnish or lacquer compatible with the foam, followed by drying. As yet a further alternative, the membrane may be applied to a moulded foam by an "in mould" technique ie by coating the inside of the mould with the membrane material which then preferentially adheres to the external surface of the foam upon removal from the mould.

In a preferred embodiment, however, the membrane preferably comprises a heat-shrunk plastics sheet or film, for example, a polyethylene sheet or film. Where, as is usual, the hot water storage vessel is in the form of a cylinder, for example of copper or steel, the membrane may conveniently be in the form of a tubular plastics sheet or film, initially having a diameter slightly greater than the external diameter of the insulated cylinder, which is located at least over the cylindrical outer surface of the foam and is then heat-shrunk into firm contact with the outer surface of the foam.

In an alternative, but less preferred, embodiment, the membrane is in the form of a rectangular sheet which is wrapped around the outer surface of the foam with the free, vertical sides of the sheet being seam welded or otherwise secured together. In that case, an optional, subsequent heat-shrinking step may be effected where the sheet comprises a heat-shrinkable plastics material.

As will be appreciated, the invention is applicable to storage vessels of any shape, however the foam insulation has been applied to it, eg by spraying and blowing, moulding or by the application of pre-moulded sections of foamed materials.

According to a second aspect of the present invention, there is provided an insulating foam material, for example a pre-moulded section adapted to be applied to the external surface of a hot water storage tank and, adherent to its external surface, a separately formed, substantially non-permeable membrane.

Tests have shown that the application of a membrane in accordance with the invention may increase the insulating performance of, in particular, non CFC-blown insulating materials, relative to like foam materials without such a membrane, by around 10% in the short term and possibly more in the long term bearing in mind that the migration of the blowing agent is substantially prevented. Equally, however, the application of such a membrane may improve the performance of CFC-blown insulating foam materials and the invention includes same within its scope.

In addition, the application of such a membrane improves the appearance of, in particular, non-CFC blown foam materials.

Claims

CLAIMS:

1. A hot water storage vessel having on at least a major part of its external surface a thermally insulating foam, at least a major part of the external surface of the foam having thereon, in intimate contact therewith, a separately formed, substantially non-permeable membrane.

2. A vessel according to claim 1 wherein the membrane comprises a plastics sheet or film.

3. A vessel according to claim 1 or claim 2 wherein the membrane comprises a metallic sheet or foil.

4. A vessel according to any one of claims 1 to 3 wherein the membrane is secured to the external surface of the foam by an adhesive.

5. A vessel according to any one of claims 1 to 3 wherein the membrane is held in place by strapping.

6. A vessel according to claim 1 wherein the membrane comprises a dried, liquid film-forming material, such as a varnish or lacquer compatible with the foam, formed by applying the liquid material to the foam followed by drying.

7. A vessel according to claim 1 or claim 2 wherein the foam is moulded into the vessel in a mould and the membrane is applied in situ in the mould by lining the inside of the mould with the membrane material which is adapted to adhere preferentially to the external surface of the moulded foam upon removal from the mould.

8. A vessel according to claim 2 wherein the membrane comprises a heat-shrunk plastics sheet or film.

9. A vessel according to claim 8 which is in the form of a cylinder and wherein said heat-shrunk sheet or film is in the form of a tubular sheet or film initially having a diameter slightly greater than the external diameter of the insulated cylinder, the tubular sheet or film having been located over at least the cylindrical outer surface of the cylinder and then heat-shrunk into firm contact with the external surface of the foam.

10. A vessel according to claim 2 or any claim appendant thereto wherein said plastics sheet or film comprises a polyethylene.

11. A vessel according to any one of claims 1 to 10 wherein the foam is a non-CFC-blown foam.

12. A vessel according to any one of claims 1 to 11 wherein the foam is a polyurethane foam.

13. A pre-formed thermally insulating foam material for application to a hot water storage vessel in order to insulate same, the material having adherent to a surface thereof a separately formed, substantially non-permeable membrane.

14. A material according to claim 13 wherein the membrane/foam material is as defined in any one of claims 2 to 12.