WO2016150856A1

WO2016150856A1 - Determining the u-value of a wall or other construction element

Info

Publication number: WO2016150856A1
Application number: PCT/EP2016/055978
Authority: WO
Inventors: Eric Atherton
Original assignee: Senico Limited
Priority date: 2015-03-26
Filing date: 2016-03-18
Publication date: 2016-09-29
Also published as: EP3274679A1; GB2536702A; GB201505226D0

Abstract

A method and an apparatus are disclosed for determining the U-Value of a wall (or of any other construction element having two opposed substantially flat surfaces). The method comprises: measuring the initial temperature of both wall surfaces at two positions which are substantially opposite each other on either side of the wall, and either, if the two measured temperatures are different, modifying the temperature of a first closed volume defining a first predetermined area of wall surface surrounding at least one of said positions by applying energy to heat or to cool the first volume and the first area of wall so that the temperature of the area of wall is substantially uniform and substantially the same as the initial measured temperature on that side of the wall or, if the two measured temperatures are substantially the same, modifying the temperature of a first closed volume defining a first predetermined area of wall surface surrounding at least one of said positions by applying energy to heat or to cool the first volume and the area of wall so that the temperature of the area of wall is substantially uniform and differs from the measured temperature: and using the measured temperatures, the first predetermined area and the heating or cooling energy to determine the instantaneous U-Value.

Description

Determining the U-Value of a wall or other construction element

FIELD OF THE INVENTION

The present invention relates to the methods and apparatus for the determination of the "U value" of a wall of a building or the like.

BACKGROUND ART In the field of building physics, U-value (or U-factor) is the term used to describe the heat transfer coefficient of a building element (e.g. a wall); it is a measure of the rate of heat loss or gain through the material of the building element. The unit of U-Value is W/m²K. The lower the U-factor, the greater the material's resistance to heat flow and the better is the insulation quality of the building element. The U-Values of the elements forming the exterior of a building determine the building's fuel consumption, C02 emission, cooling load or running cost.

Figure 1 shows in cross-section a part of a typical building 1 having walls 3 and a roof 5; there is a temperature difference (dt) between the interior 7 of the building and ambient or atmospheric temperature outside 9 the building. In the drawing, the internal temperature is greater than that outside the building, so there is a heat loss, or flux, (H_t) in the direction of the arrow (if the ambient temperatures were reversed, the heat flux would be in the other direction). The heat transmission through the building wall (or any similar construction element) can be expressed as:

H_t = UA dt (1) where

H_t = heat loss (W) U = "U-value" (W/m²K)

A = wall area (m²)

dt = temperature difference (K)

Techniques are known to extend the above expression so as to allow for construction elements formed of more than one layers, such as that formed by bricks and mortar in many walls. The typical U-Value for a wall, 150 mm thick of poured concrete having a density of 2.2xl0⁶ kg/m³, is about 3.9 W/m²K; for a wall 250 mm thick made of brick the U-Value is about 2.0 W/m²K.

Measurement of U-Value is frequently carried out during building surveys, for example so as to predict heating costs, or to determine the "before and after" effects of adding insulation, etc. and it is important that the U-Value be determined quickly and accurately. Known ways of determining U-Value involve using temperature sensors on the internal and/or external surfaces of the wall (or other construction element), together with sensors for measuring the ambient temperature on either side of the wall; on at least one surface of the wall there are usually several, spaced temperature sensors so as to enable measurements of heat flux to be taken over an area of the wall, rather than simply a point reading. Usually the readings are taken over a period of time, often days or even weeks in order to obtain accurate values; although this allows accuracy, it is too slow to be accomplished in the normal building survey, which is usually conducted in no more than an hour or two. One factor which has a significant bearing on the speed of determining U-Value is the thickness of the wall or other construction element; combined with the normally low thermal conductivity of conventional wall material(s), the equilibration of heat flux through and temperatures in/on the wall following a change in the ambient temperature on one or both sides of the wall takes a significant time, and any U-Value readings taken before equilibration is completed will be inaccurate (which is why U-Values are normally only measured accurately over a long period of time, so that equilibration errors are allowed for).

The accuracy of U-Value measurements is affected by such factors as the

inhomogeneity of or variation in many building elements (they may contain voids or regions of greater or lesser density, or heating pipes or other building utilities, all of which can give a U-Value reading which is not representative of the wall over its entire surface) and variations in ambient temperature. Fluctuations in temperature over time have already been discussed, however there are very often variations in temperature over the surface area of the wall as well as through its thickness, for example because the air inside a room is usually warmer towards the ceiling than towards the floor, or because part of an external wall is in sunlight and part in shade; in these circumstances the heat flux is not directed squarely across the wall, as shown in Figure 1, but instead is angled other than at 90° to the surface of the wall. This can mean that when a U-Value reading is taken over a relatively small surface area the U-Value determined may not be representative of the wall as a whole (because the thermal difference across the wall at one point differs from that at other points).

There is a need to be able to determine the U-Value of a wall (in what follows any reference to a "wall" or "walls" should be construed as encompassing any form of construction element, such as a roof, floor, door, window, etc.) more quickly and/or accurately than conventional techniques and devices allow. SUMMARY OF THE INVENTION

The present invention arises partially from the recognition that, where there is a temperature difference through a wall and also a temperature gradient along the wall surface then the isotherms within the wall are not parallel to the surface of the wall, and therefore their intersection with the wall surface at or adjacent the area where the U-Value reading is being made introduces error into the U-Value measurement. It is also prompted by the realisation that the thickness of the wall is one of the main factors which prevent rapid and accurate U-Value measurements to be made, and that reducing the wall thickness would enable an improvement in speed and/or accuracy. Actively modifying the temperature of the wall surface(s) can effectively reduce the wall thickness, in temperature distribution terms, as will be explained.

The present invention therefore provides a method of determining the U-Value of a wall (or of any other construction element having two opposed substantially flat surfaces) comprising: measuring the initial temperature of both wall surfaces at two positions which are substantially opposite each other on either side of the wall, and either, if the two measured temperatures are different, modifying the temperature of a first closed volume defining a first predetermined area of wall surface surrounding at least one of said positions by applying energy to heat or to cool the first volume and the first area of wall so that the temperature of the area of wall is substantially uniform and substantially the same as the initial measured temperature on that side of the wall or, if the two measured temperatures are substantially the same, modifying the temperature of a first closed volume defining a first predetermined area of wall surface surrounding at least one of said positions by applying energy to heat or to cool the first volume and the area of wall so that the temperature of the area of wall is substantially uniform and differs from the measured temperature: and using the measured temperatures, the first predetermined area and the heating or cooling energy to determine the instantaneous U-Value.

Such an arrangement is effective, where there is a temperature difference through the wall and also a temperature gradient along the wall surface and hence the isotherms are not parallel to the general plane of the wall, of changing the temperature distribution within the wall so that the isotherms adjacent one side of the wall (the side of the wall on which the first area is located) are brought parallel, or closer to parallel, with that surface of the wall and/or the general plane of the wall.

A succession of instantaneous U-Values may be monitored and recorded in a processor or data store until the difference between successive instantaneous U-Values reaches a threshold amount, and taking the last U-Value determined as the final U-Value of the wall. Where the structure reacts sufficiently quickly, this allows a speedy U-Value measurement to be made. Alternatively, a succession of instantaneous U-Values may be recorded over time until sufficient information has been acquired to extrapolate a representative U-Value, and extrapolating the final U-Value of the wall from the recorded information; this is where the structure is such that temperature stabilisation takes too long, in which case extrapolation can be carried out using known techniques.

Where the two initially measured temperatures are different, the method further comprises modifying the temperature of a second closed volume defining a second predetermined area of wall surface surrounding the other of said positions by applying energy so as to heat or cool the second volume and the second area of wall so that the temperature of the second area of wall is substantially uniform and substantially the same as the initial measured temperature of the said other position. Where the two initially measured temperatures are substantially the same, the method comprises modifying the temperature of a second closed volume defining a second predetermined area of wall surface surrounding the other of said positions by applying energy so as to heat or cool the volume and the second area of wall so that the temperature of the second area of wall is substantially uniform and differs from the measured temperature of the said other position.

Preferably the arrangement is such that on one side of the wall the temperature is lowered, whilst at the same time on the other side the temperature is raised. This brings the temperature distribution inside the wall more quickly into equilibrium, certainly as compared to applying heat (or cold) to only one side of the wall as the re-distribution of the isotherms has to reach only from the surface of the wall to its centre from each side, and the quantum of heat energy to achieve a notable change is less than when applying a temperature difference on only one side of the wall.

The method may further comprise modifying the temperature of at least one third closed volume defining a third predetermined area of wall surface surrounding the first and/or second predetermined area of wall and applying energy to heat or cool the third volume(s) and the third area(s) of wall so that the temperature of the third area(s) of wall is/are substantially uniform and/or substantially the same as the measured temperature of the surrounded first and/or second predetermined area of wall. In this way, concentric regions or areas are defined on the surface of the wall. Control of the heating or cooling is carried out in two control loops; the first of these maintains the temperature of the inner part of the outer area the same as the temperature of the central or core area, at a higher or lower temperature than the initial measurement, whilst the second, on the other side of the wall, either maintains the temperature of the inner part of the outer area the same as the temperature of the central or core area at the initial measured temperature, or modifies it in the opposite direction (cooling or heating) compared to the modification on the other side of the wall.

The invention also provides an apparatus for measuring the U-Value of a wall comprising a first temperature sensor for mounting to and for measuring the temperature of a surface of one side of the wall and two temperature sensors for mounting to and for measuring the temperature of two spaced points on a surface of an opposite side of the wall to the first temperature sensor and thereof, a first enclosure adapted to be held against the said opposite surface so as to enclose a volume of air against a predetermined area of the wall and so as to surround one of the two temperature sensors on said surface, a heater/cooler adapted to heat or to cool the volume of air and a processor operatively connected to the temperature sensors and the heater/cooler, the processor being adapted to control and monitor the energy supplied to the heater/cooler, to monitor the temperatures sensed by the sensors, and to determine the instantaneous U-Value using the sensed temperatures, the first predetermined area and the heating or cooling energy.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example and with reference to the accompanying figures, in which;

Figure 1 is a schematic cross-sectional view of a part of a typical building illustrating heat flux through a wall; Figure 2 shows a section of wall with temperature sensors attached;

Figure 3 shows a section of wall with a thermal management apparatus in accordance with the invention in place;

Figure 4 is a detailed view of the thermal management unit of Figure 3, and

Figure 5 shows the placement of an apparatus in accordance with the invention in place on both sides of a wall.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 2 shows a wall 1 in its initial state, prior to the measurement process. The internal temperature profile of the wall depends on the current and previous external temperature and convection acting on the wall outer surface 9 and the current and previous internal temperature and convection acting on the wall inner surface 10, the thermal conductivity of the wall 1, and the thermal mass of the wall 1. Isotherms 2 are shown, each line being the locus of points at the same temperature ("contours") within the wall. The exact pattern of the isotherms 2 shown is indicative only, as this temperature profile depends on many variables.

Surface temperature sensors 3 and 5 are attached to measurement module 7 on the wall outer surface 9; preferably this attachment is releasable, using adhesive tape or the like, so that the sensors can be removed from the wall without damaging any decoration. Surface temperature sensors 4 and 6 are attached to measurement module 8 on the wall inner surface 10 and are located opposite the corresponding temperature sensors 3 and 5 and measurement module 7.

Air temperature sensors 11 and 12 are attached via short posts to measurement modules 7 and 8 respectively.

Portable IT device 60 (see Figure 5) receives temperature information from both measurement modules 7 and 8 via any suitable wireless standard for exchanging data over short distances. Measurement modules 7 and 8 are identical apart from their serial numbers, so the operator of Portable U device 60 can identify which measurement module is on the wall inner surface and which on the wall outer surface. Measurement modules 7 and 8 also contain physical location devices, preferably small coils designed to generate or detect a specific medium frequency magnetic field, so that each can detect the location of the other. Which device is the transmitter, and which is the receiver is determined by the user through the portable IT device, so that the user is able to position the second measurement module installed to be exactly opposite the first measurement module to be installed by referring to the intensity of the received local signal displayed on the portable IT device 60. A gravitational sensor in each of the measurement modules 7 and 8 (the output of which is displayed portable IT device 60) allows the modules to be oriented so that the corresponding temperature sensors are directly below the measurement module, and hence also aligned.

The temperature sensors 3, 4, 5 and 6 are preferably physically small and of very low thermal mass so as to disturb the surface convention and heat flow in the wall as little as possible. Temperature measurements are logged and displayed as trends on the portable IT device 60. The two thermal management units, 50 and 51 are both identical, but identifiable through unique serial numbers. One thermal management unit is allocated for use on the wall inner surface 10 and the other is allocated for use on the wall outer surface 9.

The two thermal management units are then placed over their corresponding sensors as shown in Figure 3, where temperature sensors 4 and 6 are on the wall inner surface 10, are covered by thermal management unit 51 and positioned so that the central axis of thermal management unit 51 aligns with the temperature sensor 4.

The thermal management unit 51 contains a core enclosure 26 that along with the wall inner surface 10, creates a core chamber 22. Similarly, guard enclosure 28 along with wall inner surface 10 creates a guard chamber 24. The positioning of thermal management unit 51 is such that it measures the temperature of the wall at the inner edge of the guard chamber 24. Temperature sensor 4 measures the temperature at the centre of the core chamber 22.

Referring to Figure 4 it can be seen that guard seal ring 43 acts to seal guard enclosure 28 to wall inner surface 10. Core seal ring 44 acts to seal core enclosure 26 to wall inner surface 10. Guard seal ring 43 and Core seal ring 44 are composed of soft rubber, and have a wedge shape profile so that they effectively prevent exchange of air, and also define a precise limit and hence surface area of each chamber.

Guard fans 40, 41 and core fan 42 rotate as indicated by the arrows in the drawings and are effective to circulate air within the guard chamber 24 and core chamber22.

Peltier devices 34 and 35 can transfer heat between the guard chamber 24 and the surrounding air in either direction. Peltier device 38 can transfer heat in either direction between the guard chamber 24 and the core chamber 22.

Heat sinks 30, 32, 31, 33, 36, 37 are connected to Peltier devices 34, 35, 38 to aid heat transfer from the either side of the Peltier devices to the air surrounding the devices.

Heat flux sensor 46 is sandwiched between Peltier device 38 and heat sink 37. This precisely measures direction and quantity of the total heat flow into/out of the core chamber 22. Core enclosure 26 and guard enclosure 28 is preferably made of a thin structurally robust, thermally insulating material with relatively low thermal mass such as a glass loaded composite material.

Connecting rods 15 serve only to mechanically attach the core enclosure 26 to the guard enclosure 28 to form the thermal management unit 51. The connecting rods 15 are small diameter, and do not substantially impede the air flow within the guard chamber 24.

Figure 5 shows a preferred way of deploying the two thermal measurement modules, 7 and 8 and the two thermal management units, 50 and 51 to measure the thermal conductivity of the wall 1 of a house. Each thermal management unit 50 and 51 is supported by an adjustable telescopic leg 53 and 52 respectively. The upper section of each telescopic leg holds control modules 53 and 52 respectively that are wired to the sensors, Peltier devices and fans within the thermal management units. The control modules contain the necessary electronics to drive the Peltier devices and fans and also receive signals from temperature sensors (not show) monitoring air temperature within the core chamber and the guard chamber. Other sensors, for example airflow speed sensors, can be incorporated into the core and guard chambers for enhanced information and control.

The control module 53 is also wired to heat flux sensor 37. The control module 53 contains rechargeable lithium batteries to enable reasonable operating time. As the temperature differentials across the Peltier devices are small, they behave as efficient heat pumps and current consumption is relatively small.

The upper ends of control modules 53, 52 are attached on hinged connectors joining them to thermal management units 50, 51. The lower end of each telescopic leg 54, 55 terminates at a hinged connector joining it to foot plates 56, 57 respectively. The foot plates have a soft rubber lower surface designed for high coefficient of friction on a wide variety of surfaces. The hinged connectors and telescopic legs allow the height of the two thermal management units to be adjusted to suit differing conditions.

Each control module 53, 52 contain a radio link to the portable ΓΓ device, so that a control programme in the portable IT device 60 can receive, store and process information from, and also control, both the measurement modules 31 and 32 and also the control modules 52 and 53. Figure 3 shows the isotherms 2 when the control programme has been managing the heat flow in the wall 1 for a relatively short period. It can be seen that the isotherms in the region of the centre of the wall 20 are substantially parallel with the walls. In particular, they are parallel in the coaxial cylinder of wall 19 that is coaxial with the same diameter as, the core chambers 21 and 22. Because the isotherms are parallel with the wall within and immediately surrounding the coaxial cylinder of wall 19, there is negligible heat is flowing either in or out of this region and the coaxial cylinder of wall 19 can be considered as isolated from the rest of the wall, with known cross sectional area. The heat flow through this cylinder is substantially the same as that measured by heat flux sensor 46 in the thermal management unit 51. As the effective cross section area, the heat flux, and the temperature differential across the wall through temperature sensors 3 and 4 are all known, all the information necessary to calculate the thermal conductivity of the wall material is available. There is also confirmation and a quality indication from the thermal management unit on the other side of the wall that should be reading an equal and opposite heat flux. To obtain the required isothermal profiles two control loops are active. In the first control loop, the temperature obtained from temperature sensor 6 is controlled so that it matches the temperature obtained from sensor 4. This control is effected by varying the heat flow into guard chamber 24 generated by Peltier devices 35 and 34. In the second control loop, the temperature sensed by temperature sensor 4 within the core chamber 22 is maintained at the original value from this sensor when it was in free air prior to attaching the thermal management unit 51. This control is effected by varying the heat flow into the core chamber 22 by varying the heat flow through Peltier device 38. Two comparable control loops are also implemented using the corresponding sensors and Peltier devices on the other side of the wall within the thermal management unit 50. If the initial temperature difference between temperature sensors 3 and 4 is sufficient to obtain reasonably accurate U-values, then the above control loops strictly applies, and this minimises the thermal disturbance of the wall, so that only enough energy is put in to make the isotherms parallel within the central region. If on the other hand the initial temperature difference between 3 and 4 is too low for accurate U-value measurement, then the control temperature set point for the highest temperature side is increased by a certain small amount (of the order of a few degrees C), and the other control set point temperature, being lower of the two on the other side of the wall, is reduced by the same amount. The key point is that the total amount of thermal disturbance, particularly at the centre line of the wall, is minimised by putting substantially equal and opposite heat inputs into either side of the wall to obtain an enhanced "delta-t".

Table of References

It will of course be understood that many variations may be made to the above- described embodiment without departing from the scope of the present invention. For example, the various chambers are described above as being circular, however these could be square, rectangular, or any other shape. There may be a plate or thermal conductor within the volume to assist in transferring heat to or from the surface of the wall; however, this adds weight to the apparatus and presents difficulties in ensuring good contact and thermal conduction with the wall. Also, the invention is described and shown in Figures 3 and 5 as having enclosed volumes on both sides of the wall; this is because it is felt that this is the most practicable way of providing an apparatus of sufficient accuracy, ease of use and at reasonable cost. It will be apparent to those skilled in the art that the invention could also be carried out, albeit less accurately, by having an enclosure on only one side of a wall.

Where different variations or alternative arrangements are described above, it should be understood that embodiments of the invention may incorporate such variations and/or alternatives in any suitable combination.

Claims

A method of determining the U-Value of a wall having two opposed surfaces, the method comprising: i. measuring the initial temperatures of both wall surfaces at two positions which are substantially opposite each other on either side of the wall and either; a. if the two measured temperatures are different, modifying the temperature of a first closed volume defining a first predetermined area of wall surface surrounding one of said positions by applying energy to heat or to cool air in the first volume and the first area of wall so that the temperature of the first area of wall is substantially uniform and substantially the same as the initially measured temperature on that side of the wall, and modifying the temperature of a second closed volume defining a second predetermined area of wall surface surrounding the other of said positions by applying energy so as to heat or cool the second volume and the second area of wall so that the temperature of the second area of wall is substantially uniform and substantially the same as the initial measured temperature of the said other position; or b. if the two measured temperatures are substantially the same, modifying the temperature of a first closed volume defining a first predetermined area of wall surface surrounding one of said positions by applying energy to heat or to cool air in the first volume and the first area of wall so that the temperature of the first area of wall is substantially uniform and differs from the initially measured temperatures, and modifying the temperature of a second closed volume defining a second predetermined area of wall surface surrounding the other of said positions by applying energy so as to heat or cool the volume and the second area of wall so that the temperature of the second area of wall is substantially uniform and differs from the measured temperature of the said other position; and ii. using the measured temperatures, the first predetermined area and the heating or cooling energy to determine the instantaneous U-Value.

2. A method according to Claim 1 comprising monitoring a succession of instantaneous U-Values until the difference between successive instantaneous U-Values reaches a threshold amount, and taking the last U-Value determined as the final U-Value of the wall.

3. A method according to Claim 1 or Claim 2 comprising recording a succession of instantaneous U-Values over time until sufficient information has been acquired to extrapolate a representative U-Value, and extrapolating the final U-Value of the wall from the recorded information.

4. A method according to any one of Claims 1, 2 or 3 further comprising modifying the temperature of at least one third closed volume defining a third predetermined area of wall surface surrounding the first and/or second predetermined area of wall and applying energy to heat or cool the third volume(s) and the third area(s) of wall so that the temperature of the third area(s) of wall is/are substantially the same as the temperature of the surrounded first and/or second predetermined area of wall.

5. A method according to Claim 4 comprising circulating air within the first, second and or third volumes so that the heating or cooling is assisted by air convection.

6. A method according to any preceding claim wherein the first and second volumes and/or the first and/or second areas are substantially the same

7. A method according to any preceding claim comprising releasably attaching the temperature sensors to the wall surface.

8. A method according to any preceding claim comprising measuring the temperatures of both wall surfaces at two positions on either side of the wall, at least one position on one side of the wall being substantially opposite a position on the other side of the wall, the first and second volumes being located so as to surround the two positions which are opposite each other.

9. A method according to any preceding claim wherein the modification of temperatures comprises heating or cooling the first volume, and cooling or heating the second volume

10. Apparatus for measuring the U-Value of a wall comprising a first temperature sensor for mounting to and for measuring the temperature of a surface of one side of the wall and two temperature sensors for mounting to and for measuring the temperature of two spaced points on a surface of an opposite side of the wall to the first temperature sensor, a first enclosure adapted to be held against the said opposite surface so as to enclose a volume of air against a predetermined area of the wall and so as to surround one of the two temperature sensors on said surface, a heater/cooler adapted to heat or to cool the volume of air and a processor operatively connected to the temperature sensors and the heater/cooler, the processor being adapted to control and monitor the energy supplied to the heater/cooler, to monitor the temperatures sensed by the sensors, and to determine the instantaneous U-Value using the sensed temperatures, the first predetermined area and the heating or cooling energy supplied.

11. Apparatus according to Claim 10 comprising a second enclosure adapted to be held against the said opposite surface so as to enclose a second volume of air and , the first enclosure and to surround the other of the two sensors, the second enclosure defining a second predetermined area of the surface of the wall and having a further heater/cooler adapted to heat or to cool the second volume of air, the processor being operatively connected to the further heater/cooler, and being adapted to control and monitor the energy supplied to the further heater/cooler and to determine the instantaneous U-Value using in addition the energy supplied to the further heater/cooler.

12. Apparatus according to Claim 10 or Claim 11 comprising a third enclosure adapted to be held against the said one side of the wall so as to enclose a third volume of air and to surround the first sensor, the third enclosure defining a third predetermined area of the surface of the wall and having a third heater/cooler adapted to heat or to cool the third volume of air, the processor being operatively connected to the third heater/cooler, and being adapted to control and monitor the energy supplied to the third heater/cooler and to determine the instantaneous U-Value using in addition the energy supplied to the third heater/cooler.

13. Apparatus according to Claim 10, Claim 11 or Claim 12 wherein the processor is adapted to record a succession of instantaneous U-Values over a period of time until the difference between successive instantaneous U-Values reaches a threshold amount, and to output the last U-Value determined as the final U-Value of the wall.

14. Apparatus according to any one of Claims 10 to 14 further comprising a control circuit operatively connected to each of the first temperature sensor and to the two temperature sensors, and adapted to transmit the sensed temperatures to the processor.

15. Apparatus according to Claim 14 further comprising a position locator associated with each control circuit, the position locators being adapted to communicate with each other and to measure the distance between them and/or their relative locations, and an audible and/or visual alert to indicate to an operator when the control circuits are located substantially opposite each other on opposite sides of the wall.

16. Apparatus according to any one of Claims 10 to 15 comprising a resilient seal provided around the edge of the or each enclosure and adapted to engage against a surface of the wall so as substantially seal the air within the respective volume.

17. Apparatus according to any one of Claims 10 to 16 comprising a fan within the or each volume to circulate air within the volume and to

18. Apparatus according to any one of Claims 10 to 17 further comprising a selectively telescopic leg attached at one of its ends to the exterior of the enclosure outside the volume enclosed and at its other end to a foot adapted to rest on the ground so as to hold the enclosure against the wall.