GB2225369A - Preventing or eliminating damage to buildings caused by heat bridges - Google Patents

Abstract

The temperature of the building or that of some internal walls of the building is raised above a critical temperature. Apparatus is placed on the external surfaces of the walls of the building or on the internal surfaces of walls between rooms at different temperatures. Surfaces or walls (1, 2), are heated by electrical resistance heating means placed on the covering or under the covering of the walls (1, 2), e.g. by an electric resistance wire network which covers the 'mouths' of the heat bridges and their surroundings, the plate being fixed to the surface of the walls (1, 2) in the vicinity of the heat bridges, and the terminals (4) of the resistance wire or the resistance layer are connected to a low voltage supply (6). <IMAGE>

Description

Method and Apparatus for Preventing or Eliminating Damage to Buildings Caused by Heat Bridges to Buildings Caused by Heat Bridges The present invention relates to a method and an apparatus for preventing damage to buildings arising as a result of thermic bridges, e.g. the formation of mould, mildew and rot, wherein the temperature of the building or that of some internal walls of the building is increased above a critical temperature. The apparatus may be placed on the external surfaces of the walls of the building or on the internal surfaces of walls between rooms of different temperatures.

The above-indicated kind of damage in buildings may frequently appear as a consequence of energy-saving steps and the existing dwelling habits; their cause is mainly the so-called heat bridges. Heat bridges are of great importance, because the building materials, building methods, and ventilation modify their effect disadvantageously. In general, heat bridges (also called herein thermic bridges) occurring in buildings are dependent on the materials or the geometry of the buildings and their thermodynamic behaviour differs considerably from that of surfaces free of heat bridges. Heat convection increases, while the internal surface temperature decreases, adjacent these heat bridges.

Frequently, this decrease in temperature is so big that the internal surface temperature falls below the dewpoint, and regular precipitation of moisture appears. In consequence of the regular precipitation of moisture, the wall becomes damp, its thermal conductivity deteriorates, and hereby the phenomenon expands over the heat bridge to those areas which are free of heat bridges and thus, favourable conditions for mould-formation are produced.

In most cases the distribution of the heat at the heat bridges is worse than in a plane wall fee of heat bridges, which is the result of the fact that the convectional conditions become worse at the heat bridges. The exchange of energy also decreases due to some geometrical relations e.g. in corners where interradiation occurs.

Without exceptions, the loss of heat is bigger at the heat bridges, and the unfavourable precipitation of moisture can be prevented by increasing the internal temperature. On the other hand, this increase in the internal temperature disadvantageously modifies the loss energy of the building to such an extent that it is inadmissible from the point of view of the economy.

The following methods have been used to stop mould formation so far: - The most frequently used method includes the removal of the wallpaper, the chemical destruction of the moulds, and then the repapering of the wall, and is essentially a palliative treatment. The drawback of this method is that it does not terminate the cause of the mould formation, and therefore the mould appears again. The hygienic circumstances do not change permanently, and for this reason the walls have to be repapered every year.

- Although the heat insulating layer applied to the inside of the rooms raises the surface temperature, only the site of the mould formation is being altered in this way. On the edges of the inside heat insulation the mould appears again, because the surface of the wall gets colder than the previous temperature. This method is more expensive than the previous one, but it is also not permanently effective.

- From the point of view of the building physics, a heat insulating layer applied to the outside of the building is the best solution, but its significant disad vantage that the heat insulating layer has to cover not only the mouldy walls but the whole facade.

The object of the present invention is to eliminate the above-mentioned imperfections and to provide most simple and economic method and apparatus.

According to the invention there is no need to warm up the whole room to a high temperature by wasting of energy unnecessarily, but it is sufficient to ensure that the temperature of the wall at the inner surface of the heat bridges does not fall below the dewpoint.

Therefore the surroundings of the heat bridges on the surfaces or in the walls are heated by resistance heating placed on the covering or under the covering of the walls.

The apparatus according to the invention includes an electric resistance wire means disposed adjacent the 'mouth' of the heat bridges and their surroundings so as to form a network; or a plate supplied with an electric resistance layer which covers the 'mouths' or 'approaches' of the heat bridges and adjacent to their surroundings, fixed on the surface of the wall which is in the vicinity of the heat bridges, and the terminals of the resistance wire or the resistance layer are connected to an electric voltage supply.

The invention will be described in more detail, by way of example only, with reference to the accompanying drawing, wherein the single figure, Figure 1, demonstrates an embodiment of the apparatus according to the invention mounted to the junction of two walls.

The figure shows a plate 3 supplied with a resistance layer placed at the junction of a wall 1 provided with a window and a wall 2 perpendicular to the wall 1.

Some parts of the plate 3 expand to the adjoining areas of the ceiling (which cannot be seen in the figure) and adjacent to the walls 1, 2. The terminals 4 of the plate 3 are connected with conductors 5 to a voltage supply 6, which is advantageously a safety extra-low voltage source.

The heating, according to the invention, is only used on the surface determined by the geometrical dimensions of the heat bridge with a power output calculated by considering the heat flux density distribution gained on the base of the multidimensional thermological examination of the building construction.

The heating can be carried out by fitting up electric heating, which is expediently supplied with safety extra-low voltage.

The heating elements, dimensioned in this way, can be either bonded to the internal surface of the heat bridge or can be built into or behind the mortar or plaster or into the wall. The heating elements placed on the surface can be painted or wallpapered over.

Since the heating elements work with safety extra-low voltage on low temperature from the point of view of electric shock protection and fire protection they are safe. Their operation can be regulated automatically as a function of the outside and inside temperature and the internal degree of humidity, so that the internal surface temperature cannot fall below the dewpoint according to the existing thermophysical conditions.

The heating element may be a 0.5 mm thick plate made of an epoxy resin and coated on one of its sides with a conducting resistance layer. As a consequence of the electric current, heat is developed in the homogeneous conducting resistance layer, which uniformly distributes it on the whole surface. In order to assure the electric connection to the conducting resistor, silver layers may be applied (e.g. by screening) to both ends of the plate. The electric connections can be formed to the silver layer by means of soldering or soldering tabs.

The epoxy resin plate cut out to the given size has to be fastened with screws or stuck to the heat bridge. The plate fixed to the wall or to the ceiling can be either wallpapered or painted. Its advantage is the uniform distribution.

As a safety extra-low voltage current source a transformer can be used with mains primary voltage, and with adjustable secondary safety extra-low voltage.

Comparing the invention with the previous methods it has the following advantages: - it stops mould formation lastingly and does not damage the building construction; - the non-recurrent expenditure of the realization is markedly less than the costs of known methods used so far; - it needs energy for the operation only in the heating season, and within the heating season only in certain periods, - the cost of energy required for a year of operation is much less than the expenses of the yearly fumigation and wallpapering of the rooms, as well as less than the cost of production of other heat insulating materials used for the same purpose; - from the point of view of 'building biology' it has favourable features; - it is suitable for preventing defects in structures under construction.

The invention is not limited to the example described, but includes all the possibilities falling within the scope of the attached claims in which reference numbers have been used purely by way of illustration but without any scope-limiting effect being intended thereby.

Claims (14)

1. A method of preventing or eliminating damage (e.g.

mould formation) to buildings caused by heat bridges, wherein the temperature of the building or that of some internal wall(s) of the building is increased above a critical temperature, and wherein the areas at and adjacent the heat bridges situated in the walls and its surroundings are heated by electric resistance heating.

2. Method according to claim 1, wherein at least one suitably-sized heating element is placed on, around and/or under the area of the heat bridges.

3. Method according to claim 2, wherein the heating element is fixed to surface of the surroundings of the heat bridges by sticking or with screws.

4. Method according to claim 2 or 3, wherein the heating element is a base plate or sheet coated with an electrically conductive resistance layer.

5. Method according to any preceding claim, wherein the terminals of the resistance heating means or elements is or are connected to a safety extra-low voltage source.

6. Apparatus for preventing, reducing or rectifying damage, especially due to mould formation, to buildings, which apparatus is placed to the warmer surface of the external walls of a building or of the walls between rooms at different temperatures, comprising an electric resistance wire heater means which covers the mouths of heat bridges and their surroundings with a network; or a plate or sheet (3) supplied with an electric resistance layer which covers the mouths of or 'approaches' to the heat bridges and their surroundings and is fixed on that surface of the walls (1, 2) which is in the vicinity of heat bridges, and terminals (4) for the resistance wire or the resistance layer connected to a voltage source (6).

7. Apparatus according- to claim 6, wherein the plate (3) supplied with an electric resistance layer is an epoxy resin, e.g. Bakelite (Trade Mark) plate coated with a graphite conducting layer.

8. Apparatus according to claim 7, wherein the terminals (4) of the graphite layer are connected to terminals of a safety extra-low voltage source (6).

9. Apparatus according to claim 8, wherein the safety extra-low voltage source (6) is the secondary coil of a mains transformer.

10. Apparatus according to any of claims 7 to 9, wherein the terminals of the graphite layer are silver layers placed on two opposite ends of the graphite layer.

11. Apparatus according to any of claims 6 to 10, wherein the plate (3) supplied with an electric resistance layer is fixed to the inside surface of the walls (1, 2) with screws or by sticking.

12. Apparatus according to any of claims 6 to 11, wherein the plate (3) supplied with an electric resistance layer is covered over by a layer (e.g. mortar, plaster, coat of painting, or wallpaper) which covers the other parts of the internal surfaces of the walls (1, 2).

13. A method according to claim 1 substantially as herein described with reference to and as shown in the drawings.

14. Apparatus according to claim 6 substantially as herein described with reference to and as shown in the drawings.