GB2342985A

GB2342985A - Airgrid

Info

Publication number: GB2342985A
Application number: GB9822961A
Authority: GB
Inventors: Nicholas Ian Barnard
Original assignee: OSCAR FABER GROUP Ltd
Current assignee: OSCAR FABER GROUP Ltd
Priority date: 1998-10-20
Filing date: 1998-10-20
Publication date: 2000-04-26
Also published as: GB9822961D0

Abstract

A device (50) for insertion in a void between a thermally massive structural building component (10) and an adjacent non-structural element (24) defining at least part of a conditioned space is disclosed. The device for insertion, which may take the form of a grid, grill, lattice or grating with high surface emissivity, has a form factor as viewed from the thermally massive structural building component such that heat energy is preferentially transferred via device (50) between building component (10) and the air within the void. The device (50) may be located in a false ceiling or floor space, where the thermally massive building component (10) may consist of a concrete ceiling or floor slab.

Description

AIRGRID The present invention relates to building structures and to a method and device for controlling the temperature of an interior space defined by such structures.

In modern buildings, thermally massive structural elements such as concrete slabs are increasingly being used in conjunction with natural ventilation, mechanical ventilation and air conditioning systems to store heating and/or cooling energy. The most common type is shown in figure 1. The concrete slab 10 is exposed to the conditioned space 12 and direct heat exchange takes place between the air and the slab.

The system can be employed to make use of the"free" cooling which is available at night as a result of low ambient temperatures (often referred to as"night cooling"). Cool outside air is circulated through the building at night, lowering the temperature of the slab as the air comes into thermal contact with it in the conditioned space. This stored cooling is then available for use during the following day to offset heat gains in the conditioned space. Circulation of air through the space can be by natural and/or mechanical ventilation.

The performance of the slab 10 in terms of storing and discharging the potential cooling (and heating) available is dependent on three main factors: 1) the volume flow rate of cool night air introduced 2) the rate of heat transfer at the slab surface 3) the efficiency of the slab in storing the cooling.

Commonly it is the second of these which is the governing factor in determining performance. This is because the conductivity of concrete is relatively high and the concrete generally has sufficient thermal mass to store the cooling introduced. For further discussion on this point, refer to Dynamic Energy Storage in the Building Fabric, Barnard N, Building Services Research and Information Association Technical Report TR 9/94, ISBN 0 86022 372 8.

During the day, the cooling effect felt by the occupants will be both radiative 14 and by convective cooling of the air 16. Representative values for the radiative and convective surface heat transfer coefficients are 5 W/m2K and-2-3 W/m2K. The product of these and the temperature differentials, the slab/space radiant temperature differential and the slab/space air temperature differential respectively, gives the radiative and convective heat transfer per m2. However, radiant and air space temperatures (and hence the temperature differentials) are normally relatively close, and so the sum of the heat transfer coefficients (-7-8 W/m2K) can reasonably be used as an approximate comparative measure of overall cooling performance.

It should be noted that both radiant and air temperatures affect the thermal comfort of occupants, approximately in equal measures-refer to CIBSE Guide A (Design Data, The Chartered Institute of Building Services Engineers 1986, ISBN 0 900953 29 2) for further information on comfort, space temperatures and heat transfer.

At night the radiant temperature in the conditioned space is of little concern if it is unoccupied, so the process of interest is the transfer of heat from the slab to the air (see figure 2). Direct convective heat transfer (downward heat flow) will be negligible as the slab will be warmer than the air below. The heat transfer path will be via radiation 18 to upward facing surfaces such as the floor and vertical surfaces such as the walls in the conditioned space 12, and then by convection 20 to the air from these surfaces. Slab to air heat transfer performance will be a function of the surfaces available, varying from -2 W/m2K for an open plan space (1 m2 of floor area per m2 of ceiling area) to-4 W/m2K for a cubical cell (1 m2 of floor area + 4 m2 of wall area per m2 of ceiling area). This is based on a value of-2-3 W/m2K for both upward convective heat flow at horizontal surfaces and horizontal convective heat flow at vertical surfaces.

A value of-0 W/m2K is assumed for downward convective heat flow at horizontal surfaces.

Using an exposed concrete slab in this manner is potentially a very low cost way of controlling temperature rises in buildings, particularly in combination with natural ventilation. However, there are two inherent problems; aesthetic appearance and acoustic performance. Whilst composite decking systems commonly contain sufficient thermal mass to act effectively as night cooling stores, many are unsuitable for exposure in terms of visual appearance.

A hard exposed surface will reflect sound, and so an exposed slab or composite decking will have low acoustic absorption.

Partial solutions are available. Open grid ceilings, often referred to as open cell ceilings, can be used to maintain reasonable thermal exchange between the slab and the conditioned space whilst providing a degree of visual concealment of the slab or composite decking above. However, open grid ceilings themselves may in many cases not be considered desirable aesthetically. Special baffles can be used to absorb sound and improve acoustic performance but will add to the cost of an installation.

False ceilings have been widely installed because they potentially provide an acceptable finish both aesthetically, for example by concealing services, beams, decking, and integrating with lighting, and acoustically. However, they act to thermally isolate the slab from the conditioned space and greatly reduce the rate of heat transfer which will take place. The principal daytime heat transfer paths between the cool slab 10, the air in the ceiling void 22, a false ceiling 24 and the warm conditioned space 12 are shown in figure 3. Heat transfer during the day is by the following route; radiation 26 and convection (at the slab surface 28 and at the ceiling top surface 30) across the ceiling void 22 from the top surface of the false ceiling 24 to the surface of the slab 10; conduction through the false ceiling 24; and radiation 32 and convection 34 to the bottom surface of the false ceiling 24 from the conditioned space 12 below.

Assuming a false ceiling conductivity of about 3 W/m2K, the effective overall surface heat transfer coefficient is about 2 W/m2K, greatly reduced from the exposed slab value.

Night-time cooling by circulation of cool air from outside the building into the conditioned space 12 is illustrated in figure 4. The rate of night-time cooling of the slab 10 is reduced to about 1 W/m2K.

The main heat transfer paths are radiation 38 from the slab 10 to the false ceiling 24 and radiation 36 from the bottom surface of the false ceiling 24 to the horizontal and vertical surfaces in the conditioned space 12 which then warm the air by convection 20.

Natural or mechanical air circulation 40 between the void 22 and the conditioned space 12 can be used to provide an additional convective heat transfer path (see Figure 5). However, the radiative element 26,32 of the surface heat exchange (the majority) is still intercepted by the false ceiling 24. Although some conducts through the ceiling 24 and so into the conditioned space 12, heat transfer is still significantly less than for the case of the exposed slab illustrated in figures 1 and 2. The overall surface heat transfer coefficient for daytime heat transfer to the slab is estimated to be about 4 W/m2K.

This is based on the simplifying approximation that a relatively high rate of air circulation 40 between the void 22 and the conditioned space 12 is achieved. At night, as shown in figure 6, when the slab 10 is warmer than the air in the conditioned space 12 the value of heat transfer out of the slab is estimated as about 2 W/m2K.

The present invention seeks to address the problems of the prior art. To this end, particular embodiments of the invention provide a device which can be used to increase the rate of heat transfer between a concealed slab, composite decking system or other thermally massive structural building component and the air in the adjacent air gap or void. Other embodiments provide a building structure within which the device is used and a method of providing more efficient temperature control of a conditioned space.

According to a first aspect of the present invention there is provided a device for insertion in a void between a thermally massive structural building component and an adjacent non-structural element defining at least part of a conditioned space, the device for insertion having a form factor as viewed from the thermally massive structural building component such that heat energy is preferentially transferred via said device between said thermally massive structural building component and the air within said void.

Preferred embodiments of the device are set out in the claims appended hereto.

The invention also extends to a building structure comprising a thermally massive structural building component and an adjacent non-structural element defining at least part of a conditioned space, the thermally massive structural building component and the non-structural element defining a void therebetween in which the device is positioned.

According to a further aspect of the present invention there is provided a method of providing temperature control of a conditioned space in a building in which a void is provided between a thermally massive structural building component and a non-structural element defining at least part of a conditioned space, the method comprising the steps of positioning such a device in said void and passing air between an outside of the building and an inside of the building so that air passes air between the void and the conditioned space.

Preferred embodiments of the building structure, and of the method of providing temperature control, are also set out in the dependent claims attached hereto.

A number of embodiments of the present invention will now be described by way of example with reference to the accompanying drawings of which: Figure 1 is a cross sectional view of a concrete slab of the prior art, exposed to a conditioned space, and showing heat flows during daytime cooling of the conditioned space; Figure 2 is the cross sectional view of the arrangement of figure 1, showing heat flows during night-time cooling of the slab; Figure 3 is a cross sectional view of a concrete slab and false ceiling of the prior art, showing heat flows during daytime cooling of the conditioned space; Figure 4 is the cross sectional view of the arrangement of figure 3 showing heat flows during night-time cooling of the slab; Figure 5 is a cross sectional view of a concrete slab and vented false ceiling of the prior art, showing heat flows during daytime cooling of the conditioned space; Figure 6 is the cross sectional view of the arrangement of figure 5, showing heat flows during night-time cooling of the slab; Figure 7a is a plan view of a first embodiment of the invention, in the form of a grid; Figure 7b is a cross-sectional view of the grid of Figure 7a; Figure 8a is a plan view of a second embodiment of the invention, in the form of a grille; Figure 8b is a cross-sectional view of the grille of figure 8a; Figure 9 is a cross-sectional view of a concrete slab and vented false ceiling with the grid of the first embodiment of the invention installed therebetween, and showing heat flows for daytime cooling of the conditioned space; Figure 10 is the cross-sectional view of the arrangement of figure 8, showing heat flows for nighttime cooling of the slab; Figure 11 is a plan view of a false ceiling void showing intake and exit vents for outside air, crossflow of natural ventilation and positions of ceiling vents; Figure 12 is a cross-sectional view of a profiled ceiling slab and vented false ceiling with the grid of the first embodiment installed therebetween; Figure 13 is a cross sectional view of a concrete floor slab and a false floor, showing heat flows for daytime cooling of the conditioned space; Figure 14 is a cross-sectional view of the arrangement of figure 13, but showing heat flows for night-time cooling of the slab; Figure 15 is a cross-sectional view of the arrangement of figure 13, with the grid of the first embodiment installed in the false floor void, showing heat flows for daytime cooling of the conditioned space; Figure 16 is a cross-sectional view of the arrangement of figure 15, showing heat flows for night-time cooling of the slab; and Figure 17 is a cross-sectional view of a ceiling slab and a vented false ceiling in which chilled ceiling panels are installed, showing heat flows for cooling the conditioned space.

An embodiment of the device of the present invention is shown in plan view in figure 7a and in cross sectional view in figure 7b. In this embodiment the device takes the form of an open grid 50. In a second embodiment shown in plan view in figures 8a and in cross section in figure 8b the device takes the form of a grille 52. The grid, grille or other embodiment of the invention such as a lattice or grating is designed to maximise radiant heat exchange with the surface of a thermally massive structural building component, typically a ceiling or floor slab, and convective heat exchange with the surrounding air.

Requirements for maximising radiant heat exchange are high surface emissivity and form (or shape or view) factor. The emissivity of a surface is a measure of its ability to absorb and emit radiant heat energy.

Form (or shape or view) factors relate to the proportion of the radiation leaving one surface which impinges on another. (For calculation of these refer to the CIBSE Guide C, Reference Data, Section C3 Heat Transfer, The Chartered Institution of Building Services Engineers 1986, ISBN 0 900953 31 4. Also see the above referenced"Heat Transfer"by J. P. Holman).

Preferably, the device is constructed and positioned adjacent to the thermally massive structural building component in such a way that the form factor of the device from the building component is at least 0.5.

High surface area and fin efficiency are preferable for maximising convective heat exchange of the device of the present invention with the surrounding air.

Fin efficiency is a measure of the heat transfer performance of the fin relative to an equivalent fin with infinite conductivity. (For calculation of fin ef f iciency refer to"Heat Transfer"by J. P. Holman).

High fin efficiency is relevant to elements aligned vertically as most radiant heat exchange with the slab will be at the top of these elements, whereas heat exchange with the air will take place over the whole surface area, analogous to fin heat flows. High thermal conductivity is important to ensure the whole surface area is used effectively for heat exchange, by transferring heat between the top and bottom of the elements.

The open structures of the grid and grille embodiments of the device allow a convective air flow and enable air to pass through the device so that air cooled convectively at the slab surface can be used to cool the conditioned space in addition to that cooled by the device surfaces. A suitable material for the grid or grille of the described embodiments is a metal such as steel or aluminium, with a high emissivity finish such as matt black paint. Suitable dimensions for the described embodiments are a 50mm spacing of the vertical elements with a depth of 50mm. For the grid, this provides a surface area of four times the grid plan area. Preferably, the device surface area is at least equal to the grid plan area.

Materials with lower thermal conductivities, including plastics and similar materials, could also be used, particularly for grids with small construction depths.

Plasterboard may also be used. If the device is constructed from a material of lower thermal conductivity, it may be suitably coated or finished with a coating or finish that has itself a high thermal conductivity.

The grid of the first embodiment may be constructed in a manner similar to that for an open grid ceiling tile. Conveniently, the device may be installed in a false ceiling void using the same support hangars and system as the false ceiling, or attached to or integrated with ceiling tiles, or supported independently. The described embodiments of the present invention are suitable for retrofit in old buildings as well as for new build applications.

Embodiments of the present invention in the form of building structures making use of the device will now be described. The grid embodiment of the device is shown to be used in these applications, although the grille or any other embodiment could equally well be used.

Figure 9 shows the grid 50 of the first embodiment of the present invention positioned horizontally in a ceiling void 22, between a thermally massive structural building component, in this case a concrete slab 10 above, and a false ceiling 24 below. The false ceiling is vented to allow a circulation of air 40 between the ceiling void 22 and the conditioned room or other space 12 below.

The main heat transfer mechanisms for daytime cooling of the air in the ceiling void 22 and in the conditioned space 12 are shown. The slab 10 is cooler than the air in the ceiling void 22 and in the conditioned space 12, following earlier night-time ventilation of the conditioned space 12 with cool night air. Air circulation 40 carries heat from the warmer air of the conditioned space 12 to the cooler air of the ceiling void 22. The grid 50 is designed to maximise radiant heat exchange 54 with the surface of the cooler slab 10, cooling the grid, and allowing convective heat exchange 56 to cool the surrounding air. Radiant heat exchange 58 between the device 50 and the false ceiling 24 cools the false ceiling with some subsequent radiant heat exchange 32 between the false ceiling 24 and the fabric of the conditioned space. Convective heat exchange 28 moves heat from the air in the ceiling void 22 to the slab 10. Convective heat exchange 34 moves heat from the air in the conditioned space 12 to the false ceiling 24.

Based on previous assumptions plus a slab/grid form factor approaching unity, a high fin efficiency and a grid surface area of about 4 times the area of the exposed slab, the overall surface heat transfer coefficient is estimated to be about 6 W/m2K. This is about 80% of that for an exposed slab.

For the daytime cooling of the air in the conditioned space illustrated in figure 9, only a relatively small vent area of about 10 is required in the false ceiling to achieve a reasonable rate of natural air circulation 40 (buoyancy driven) between the ceiling void 22 and the conditioned space 12. Thus the aesthetic appearance and acoustic performance of a full false ceiling may be largely maintained. Means of achieving the vent area include use of perforated ceiling tiles, ceiling tiles with punched holes, open grid ceiling tiles, or ceiling grilles to replace some of the existing tiles. These approaches are suitable for retrofit as well as new build applications. A mechanism for modulating the vent area either automatically or manually can be used to provide control over the rate of heat transfer and therefore the cooling output of the system. One means of achieving this is to use closeable ceiling grilles with rotating blades for damper type operation.

The grid also promotes heat transfer performance at night, estimated at about 4 W/m2K out of the slab if the cool night air that is circulated through the conditioned space also circulates adequately through the ceiling void 22. This is illustrated in figure 10, in which the grid 50, thermally massive slab 10 and false ceiling 24 are positioned in the same way as shown in figure 9. The main mechanisms for night-time cooling of the slab are convective transfer 62 of heat from the grid 50 to the air in the ceiling void 22 followed by radiative heat transfer 60 from the slab 10 to the grid 50. Radiative heat transfer 64 warms the false ceiling, which in turn convectively warms the air in the void. Convective heat transfer 30 from the false ceiling to the air cools the false ceiling.

The vents bringing in air from outside the building for the purposes of cooling the slab at night may be advantageously positioned to introduce the flow of cool night air into the ceiling void rather than into the conditioned space. This will increase the cooling stored in the slab and reduce cooling in the conditioned space, improving the storage performance of the system and reducing the risk of overcooling the conditioned space. Systems of the prior art are commonly controlled to stop night venting of outside air if the temperature in the conditioned space falls below a low limit that is comfortable for occupation, typically about 20 C. Reducing the ventilation of cold air into the occupied space while maintaining ventilation into the ceiling void extends the period of night venting and therefore increases the amount of cooling which can be stored in the thermally massive building structure. If a low temperature limit cutoff control of night venting is not provided, reducing the entry of cold air into the conditioned space by careful positioning of the vents in the false ceiling reduces the likelihood of overcooling the conditioned space at night. Overcooling may necessitate the use of heating prior to occupancy or otherwise may cause discomfort to the occupants.

A suitable arrangement showing false ceiling vent locations 70 relative to intake and exit vents 72 for cross flow of natural ventilation in the ceiling void is shown in figure 11. The false ceiling vents 70 allow ventilation between the ceiling void and the conditioned space. The intake and exit vents 72 controllably allow ventilation of the ceiling void with air from outside the building. The plan shows the false ceiling vents 70 located away from the flow paths 74 of cold intake air. This ensures that the cold night air will travel a reasonable distance in the false ceiling void, taking heat from the grid and the slab, before it can enter the conditioned space.

This both acts to warm the air before it can enter the conditioned space thereby reducing the risk of overcooling, and increases the rate of cooling of the slab.

As an alternative to natural ventilation, fans or other means may be used to mechanically circulate the air between the ceiling void and the conditioned space. Such means may also be used to mechanically ventilate the ceiling void for night-time cooling. Fan speed modulation may be used to facilitate control of heat exchange.

Embodiments of the invention may also be used in buildings which incorporate profiled slabs or profiled composite decking systems. Such a profiled slab 80 is illustrated in figure 12, which also shows a grid 50 of the present invention located below the profiled slab 80, and above a false ceiling 24. The grid follows the contour of the profiled slab, which has a greater surface area than a slab with a flat surface, and therefore emits more radiation for given temperature and surface characteristics. Appropriate profiling and location of the grid 50 can be used to radiatively couple more effectively with the profiled slab, enhancing convective heating or cooling of the air in the ceiling void 22. Without the use of an embodiment of the present invention in this way a significant proportion of the slab radiation would be reabsorbed by a neighbouring slab or decking surface and not utilised in heating or cooling the air in the ceiling void. The estimated effective overall surface heat transfer coefficient for day cooling of the system shown in figure 12, when the surface area of the profiled slab is 1.7 times that of the ceiling plan area, is estimated to be about 10 W/m2K. The value for night storage is estimated at about 8 W/m2K.

Corresponding values for the same profile exposed to the conditioned space but without use of the grid device of the present invention are estimated at about 9 W/m2K and about 5 W/M2 K.

If significant stratification is expected to occur within the ceiling void in which the grid is located, the vertical location of the grid can be adjusted to suit. Placing the grid at low level in the void will benefit storage performance at night as the grid will be in contact with cooler air. Vents to allow air into and out of the void may be located to encourage air flow over the grid.

By providing a low resistance route for heat flow between the slab surface and the air, the device of the present invention can also be used to improve the performance of other types of night cooling system.

One such type of night cooling system is shown in figure 13. Supply air 82 is ducted into a pressurized false floor void 84 where it comes into thermal contact the top surface of the concrete slab 10. Heat exchange takes place between the air and the slab before the air then passes from the pressurized void 84 into the conditioned space 12 via diffusers 88 in the false floor 86. Air is subsequently extracted from the conditioned space by some other means (not shown) and either discharged or recirculated. This system can be employed to make use of night cooling in a similar manner to that described for the exposed slab system.

Cool outside air is circulated through the building at night, lowering the temperature of the slab as the air comes into thermal contact with it in the false floor void. This stored cooling is then available for use during the following day to cool warm daytime supply air as it comes into thermal contact with the slab surface. The cooled air then passes into the conditioned space, offsetting heat gains.

Air flow regimes for these systems are often such that convective heat transfer at the surfaces is predominantly natural (rather than forced). As the slab is cooler than the supply air during the day, negligible natural convective heat transfer takes place at the slab surface for day cooling (heat flow into the slab). Supply air cooling is reliant on radiation 90 between the slab 10 and the false floor 86 and convection 92 at the false floor 86. The overall effective surface heat transfer coefficient for day cooling is estimated at about 2 W/m2K.

For night storage, illustrated in figure 14 which shows the same building structure as figure 13, convection 94 will take place at the surface of the slab 10 as it cools to the air, resulting in an overall effective surface heat transfer coefficient of about 2 to 3 W/m2K. These values are relatively low and, as a consequence, the efficiency of the heating/cooling exchange between the supply air and the slab is poor, typically of the order of 50%. This ratio is termed the heat transfer effectiveness. As an example, if the slab were at 20 C and the supply air entered the void at 10 C, all of the cooling available would have been transferred if the supply air exited the void at the slab temperature of 20 C, However, with an effectiveness of 50%, the air will exit the void at an average temperature of 15 C and only half the cooling available in the supply air will have been transferred to the slab.

One solution to improve heat transfer, and provide control over when the heat transfer is to take place, is to use elements to form paths at the slab surface through which air is directed as shown in EP-A-0,678,713. A second solution is to utilise building elements with preformed hollow cores through which air is directed as shown in GB-A-2, 208,922. Both of these create highly turbulent air flow to give high air/slab forced convective heat transfer.

Introduction of the device of the present invention into the floor void provides a further solution for improving heat transfer performance by creating an enhanced heat transfer route between the slab surface and the air. Figure 15 shows the grid 50 of the first embodiment of the present invention installed in a false floor void 84 between a thermally massive slab 10 and a false floor 86. Air 82 enters the pressurized false floor void and leaves through diffusers 88 or other vents in the false floor 86 to enter the conditioned space 12. The main heat transfer mechanisms for daytime cooling of the supply air are shown. Radiation 96 between the grid 50 and the slab 10 cools the grid. The grid will then convectively cool 100 the air and cool the false floor 86 by radiation 98. The false floor 86 will also convectively cool 92 the air in the floor void 84. At night, as illustrated in figure 16, the air in the floor void 84 will convectively cool 102 the grid 50 which will radiatively cool 104 the slab 10. In addition, the air will convectively cool 94 the slab directly. Based on previous assumptions the overall s

As discussed above for ceiling void installations, the vertical position of the device could be adjusted to suit if significant stratification is expected to occur. Location of a grid at high level in the false floor void (where thermally stratified air is warmest) would be preferred for efficient daytime cooling of the air. Conversely, location of a grid at low level would be preferred for storage of cooling at night.

Provision of both is not favoured as the low level grid would tend to mask the high level grid. However, one compromise solution to improve the performance of both cooling and storage is to alternate grid sections at high and low level. A second approach is to provide a full grid coverage at high level, but only partial grid coverage, such as 30W of the total area, at low level to limit the masking effect. Vents to allow air into and out of the void may be located to encourage air flow over the grid.

Rather than using low ambient air temperatures at night for cooling, cooling generated by mechanical systems can also be stored in the building fabric.

This has a number of benefits including: -the ability to make increased use of off-peak electricity tariffs -facilitating load shifting to limit maximum demand and thereby reduce plant size -increasing efficiency by enabling the operation of the cooling system during periods of low ambient temperature such as at night, rather than at the dictates of an applied load.

Similarly, heat energy such as that generated electrically or by burning of fossil fuels can also be stored in the building fabric. The ability to facilitate load shifting and make increased use of off-peak tariffs is particularly beneficial where the heat energy is generated from electricity. Excess heat energy which might otherwise be wasted, including that from space heat gains and combined heat and power (CHP) machines, can be stored for later use.

Embodiments of the present invention can be used to enhance the performance of any such system where heating or cooling is stored in the fabric of the building.

The slab may also be heated or cooled by water circulating within pipework embedded in the slab. A device of the present invention may then be used to transfer heat between the slab and air adjacent to the slab.

Embodiments of the invention have been illustrated which enhance heat exchange at horizontal surfaces associated with floor and ceiling voids, using concrete as the thermally massive material for storage. However, embodiments of the invention could also be used adjacent to vertical surfaces such as those associated with wall cavities. Underground supply ducts or trenches used as air supply paths are another potential application with both horizontal and vertical surfaces. Apart from concrete, other materials could equally be used for storage including brick, steel and Phase Change Materials (PCMs).

Increasing interest is being focused on the use of PCMs, and research is ongoing to develop wallboards, concrete blocks and the like which incorporate PCMs.

Embodiments of the invention are also of benefit in some applications where a thermally massive structural building component is not required. For example, in one embodiment the invention can be used in conjunction with chilled ceiling panels 110 to increase output from the panels. One such embodiment is shown in figure 17, which illustrates a concrete ceiling slab 10, a false ceiling 24 and a grid 50 located between the slab and false ceiling. Such chilled ceiling panels normally rely on radiant cooling 112 of the conditioned space 12 and, to a lesser extent, convective cooling 114. The device of the present invention 50 placed above the chilled panel 110 radiates 116 to the chilled panel leading to convective cooling 56 of the air in the ceiling void 22. The cooled air is then circulated 40 into the conditioned space 12 to provide additional cooling.

Claims

CLAIMS 1. A device for insertion in a void between a thermally massive structural building component and an adjacent non-structural element defining at least part of a conditioned space, the device for insertion having a form factor as viewed from the thermally massive structural building component such that heat energy is preferentially transferred via said device between said thermally massive structural building component and the air within said void.
2. A device as claimed in claim 1, wherein the device when positioned in said void has a form factor of at least 0.5 as viewed from said thermally massive structural building component.
3. A device as claimed in claim 1, in which the surface area of the device for insertion is at least equal to the device plan area.
4. A device as claimed in claim 3, in which the surface area of the device is at least four times the device plan area.
5. A device as claimed in any one of the preceding claims, wherein heat preferentially follows the path of being convectively transferred from the air in said void to the device and then being radiatively transferred from said device to said thermally massive structural building component, when the air in said void is warmer than the surface of the thermally massive building component.
6. A device as claimed in any one of the preceding claims, wherein heat preferentially follows the path of being radiatively transferred from said thermally massive building component to the device and then being convectively transferred from said device to the air in said void, when the surface of the thermally massive building component is warmer than the air in said void.
7. A device as claimed in any one of the preceding claims wherein the device is formed as a grid, a grille, a grating or a lattice.
8. A device as claimed in any one of the preceding claims wherein the device has one or more apertures for the flow of air therethrough.
9. A device as claimed in any one of the preceding claims wherein the device has one or more fins.
10. A device as claimed in any one of the preceding claims wherein the device is made from a material with a high thermal conductivity.
11. The device as claimed in any one of the preceding claims wherein the device is made from a material selected from the list comprising metal, aluminium, steel, plastic and plasterboard.
12. A device as claimed in any one of the preceding claim wherein the device has a high emissivity finish.
13. The device as claimed in any one of the preceding claims wherein the device is coated with a paint of a colour which absorbs electromagnetic radiation.
14. A device as claimed in any one of the preceding claims, the device having a coating which has a high thermal conductivity.
15. A device for insertion in a void between a thermally massive structural building component and an adjacent non-structural element defining at least part of a conditioned space, the device being substantially as herein described with reference to the accompanying drawings.
16. A building structure comprising a thermally massive structural building component and an adjacent non-structural element defining at least part of a conditioned space, the thermally massive structural building component and the non-structural element defining a void therebetween in which a device of any of claims 1 to 15 is positioned.
17. A building structure as claimed in claim 16 wherein the thermally massive structural building component forms a part of a ceiling, a floor, a wall, an underground supply duct, or a trench used as an air supply path.
18. A building structure as claimed in claim 16 wherein the non-structural element is a false ceiling.
19. A building structure as claimed in claim 18 wherein the device is attached to the false ceiling.
20. A building structure as claimed in claim 18, in which the device is integral with the false ceiling.
21. A building structure as claimed in claim 18, in which the device is independently supported.
22. A building structure as claimed in any one of claims 18 to 21, the false ceiling further including chilled ceiling panels.
23. A building structure as claimed in claim 16, in which the non-structural element is a false floor.
24. A building structure as claimed in claim 23, wherein the device is supported using the same floor stools as the false floor.
25. A building structure as claimed in claim 23, in which the device is attached to the false floor.
26. A building structure as claimed in claim 23, in which the device is integral with the false floor.
27. A building structure as claimed in claim 23, in which the device is independently supported.
28. A building structure as claimed in any one of claims 16 to 27 wherein the device is arranged within the void so as to utilize thermal stratification of air in the said void.
29. A building structure as claimed in any one of claims 16 to 28 wherein the device is positioned to provide partial coverage of less than 50*1 of the total plan area at a first level which is close to the thermally massive structural building component and to provide in excess of 50% full grid coverage at a second level which is close to the non-structural element.
30. A building structure as claimed in any one of claims 16 to 29 wherein the thermally massive structural building component is a flat slab, a profiled slab, or a composite decking system.
31. A building structure as claimed in claim 30 wherein the device is adapted to follow the profile of the thermally massive structural building component.
32. A building structure as claimed in any one of claims 16 to 31 wherein the thermally massive structural building component is formed from concrete, brick, steel, stone or a phase change material.
33. A building structure as claimed in any of claims 16 to 32 further comprising vents to allow air to pass between an outside of the building structure and the conditioned space or the void.
34. A building structure as claimed in claim 33 further comprising means for mechanically forcing air through the vents.
35. A building structure as claimed in claim 34 wherein the means for mechanically forcing air through the vents includes a fan.
36. A building structure as claimed in claim 35, in which the fan speed may be modulated to control the rate at which air passes through the vents.
37. A building structure as claimed in any of claims 16 to 34 wherein the air passing inside the void is air recirculated from the conditioned space.
38. A building structure as claimed in claim 34 wherein the vents are positioned in said nonstructural element so as to minimise the entry of cold air into the conditioned space during night venting of the void with air from outside the building.
39. A building structure substantially as herein described with reference to the accompanying drawings.
40. A method of providing temperature control of a conditioned space in a building in which a void is provided between a thermally massive structural building component and a non-structural element defining at least part of a conditioned space, the method comprising the steps of positioning a device as claimed in any one of claims 1 to 15 in said void and passing air between an outside of the building and an inside of the building so that air passes between the void and the conditioned space.
41. A method as claimed in claim 40, further comprising mechanically forcing the air from the outside of the building into the inside of the building.
42. A method as claimed in claim 41, further comprising adjusting the rate of flow of air from the outside of the building into the inside of the building.