GB2383408A

GB2383408A - Heat store for controlling air temperature

Info

Publication number: GB2383408A
Application number: GB0129868A
Authority: GB
Inventors: Carl Mckenzie
Original assignee: RMJM Ltd
Current assignee: RMJM Ltd
Priority date: 2001-12-13
Filing date: 2001-12-13
Publication date: 2003-06-25
Also published as: GB0129868D0

Abstract

Method and apparatus for controlling the air temperature in a space in a building including a heat store formed by at least a part of the building structure, wherein the air is in heat exchange relationship with the heat store so that heat is transferred to or from the air depending on the relative temperature of the heat store. Preferably the heat store comprises a concrete slab. A heat exchanger 11 may comprise a profiled or corrugated section of sheet material 13 which abuts the slab to form a plurality of parallel channels (12, figs 3 and 4) each defined in part by the surface of the concrete. The channels preferably have an input plenum duct 25 and an output plenum duct 23 which connect to ducts in other parts of the building. The output plenum preferably incorporates one or more room diffusers 24 which have a dirt trap and trim flange. The heat exchanger may typically be made from steel, or alternatively from metal, plastics, a composite material or concrete.

Description

Method and apparatus for controlling air temperature perature The present invention relates to a method and apparatus for controlling the air temperature in a space in a building by heating the air and/or absorbing/extracting heat from the air by utilising at least part of the building as a heat sink.

The amount of energy used to heat and cool buildings is becoming an increasing environmental concern throughout the world, particularly since the amount of energy being used is increasing because of increased demands for air conditioning in hot weather, both to improve the conditions in the building for its occupants and also to dissipate the heat generated by the increased use of machinery such as computers in offices. Although the general level of temperature in modem offices has risen to satisfy modem comfort demands, leading to the use of more energy in winter, it is an increasing problem in summer, when the demand for energy for cooling purposes can be greater than the energy needed for heating in winter, even in temperate climates such as the UK.

Traditionally, buildings have been heated by a heating system in the winter and cooled by a separate air conditioning system in the summer. However, systems are known which use a common radiator/condenser which gives out heat in winter when in heating mode but extracts heat in the summer when the system is in air conditioning mode. Underfloor heating systems in which pipes through which hot water is pumped are set in a concrete floor to heat the floor and hence the room are also known. These systems also do not address the problem of the amount of energy being used and dissipated into the atmosphere.

A further problem which exacerbates the problems of unwanted heat and the use of energy to either heat or cool a building is that the temperature in a building varies throughout the day, typically in a normal British summer being below normal comfort levels, 20-25 C, during the night and early morning, when heat is required, rising to a maximum above comfort levels in the afternoon, which creates demands for cooling.

The present invention seeks to alleviate these problems by reducing the emission of energy from buildings by using part of the building as a heat sink in which heat can be

stored and from which heat can be drawn depending on the relationship between interior temperature of the building and ambient atmosphere.

According to one aspect of the present invention there is provided a method of controlling or influencing the air temperature in a space in a building including, providing a heat sink formed at least in part by part of the building structure, treating air by passing it in heat exchange relationship with the heat sink to transfer heat to or from the sink in dependence upon the relative temperature between the air and the heat sink and then to transfer the treated air to the space.

The present invention also provides apparatus for controlling the air temperature in a space in a building including a heat sink formed at least in part by a part of the building structure, a heat exchanger to transfer heat to or from the sink in dependence upon the relative temperature between the air and the heat sink, and ducting means to duct air to an input of the heat exchanger and an output to duct the air from the heat exchanger to the space.

In a preferred embodiment of the invention, the heat sink comprises a concrete slab forming part of the structure of the building and the heat exchanger comprises a profiled or corrugated section of sheet metal abutting the concrete slab to form a plurality of parallel channels each defined in part by the surface of the concrete, the input including an input plenum duct connected to input ends of said channels, the output including an output plenum duct to which output ends of the channels are connected.

In one embodiment, the output plenum duct incorporates one or more floor diffusers through which air is transferred to a room, the diffusers preferably incorporating a conventional dirt trap and a trim flange A preferred embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which :- Figure I shows a typical summer temperature profile over a 24-hour period, Figure 2 shows a floor plan of a building incorporating a plurality of heat exchange units, Figure 3 shows a perspective view of part of the construction of the floor of the building shown in Figure 2,

Figure 4 shows an end view of a section through the floor, Figure 5 shows a side view of a section through the floor, Figure 6 shows a schematic part view of a mounting for a heat exchanger profile sheet, Figure 7 shows the profile of the heat exchanger profile sheet, Figures 8a and 8b show the relationship between the air transferred through the heat exchange air and the temperature of the concrete base at two different air flow rates.

Referring now to Figure 1, there is shown a 24 hour temperature profile for a typical warm English summer day based on temperature readings taken at Kew. It can be seen that at one o'clock in the morning, the air temperature is in the region of 20 degrees C., dropping down to about 16 degrees C. at 6 o'clock in the morning. Thereafter, the temperature gradually climbs until it reaches a maximum of about 30 degrees C. at about 3 o'clock in the afternoon, thereafter declining steadily until it reaches approximately 20 degrees C. at one o'clock in the morning.

A comfortable working temperature for an office environment is in the region of 21- 25 degrees C. and it can be seen that this temperature range is achieved, naturally, only between about two hours in the morning and for two to three hours in the evening after about eight o'clock. Outside these hours, energy must be used either to heat the building in the early morning or to remove heat during the main part of the day. In the past, this has been achieved by using heating in the early morning to raise the temperature to the comfort levels and then to use an air conditioning system to remove heat during the hotter part of the day. In both cases energy is used which eventually is dissipated in the atmosphere with the consequent negative impact on the environment. This is a particular problem in buildings such as hospitals which need to maintain a substantially constant temperature throughout the 24 hours.

Referring now to Figure 2 there is shown in schematic form the floor plan of a building 10 incorporating a plurality of heat exchange units 11 in accordance with the present invention, which are disposed so as to cover almost the entire floor plan of the building. The structure of the building includes a concrete base or floor slab having a float finished upper surface onto which the heat exchange units 11 are secured. Each heat

exchange unit 11 consists of an elongate, substantially rectangular profiled sheet 13 which is formed of 0.7 mm sheet steel and which is typically about 3.5 m long and approximately 760 mm wide, the units being juxtaposed side-by-side so as to cover effectively the entire floor area of the building. There is shown particularly in Figures 3,4, and 7 a cross-section of the profile sheet 13 showing five parallel channels 12 formed between the profile of the sheet and the surface of the concrete, the channels 12 extending in the longitudinal direction of the sheet. Each channel is rhomboid in cross-section having an average width of 116 mm and a height of 19 mm, the largest width being adjacent the concrete. The number of channels and the cross-sectional area of each channel will vary depending upon the size and nature of the installation and the performance required from the heat exchange.

Figure 7 shows the cross-sectional profile for the sheets of the present embodiment but different profiles may be used for different applications. Typically, the sheets will be formed of mild steel but may be of another metal, a plastics material, composite material or concrete.

Referring also to Figure 3, the general construction of a raised floor incorporating the heat exchanger is shown. The sub-base of the floor comprises the structural concrete slab with a float finish on its upper surface. The profile sheets 13, as shown in Figure 6, are placed on the concrete slab with a perimeter seal 14 in the form of a resilient elastomer tube or similar plastics seal extending along the longitudinal side edges of each sheet. The sheet 13 is securely fastened to the concrete slab by mechanical fixing means 15 passing through the perimeter seal 14. No seal is provided between adjacent channels in the sheet, any slight gap between the channels serving to create a degree of turbulence which will assist the heat exchange effect. Floor supporting joists 16 extend in parallel to the channels at approximately 800 mm centres. The floor supporting joists 16 are formed of a lower base batten 16a and a support batten 16b. Subsidiary transverse floor supporting joists 17 extend between the main joists at intervals and rest on the upper surface of the profile sheets 13. Insulating material 18 consisting of 50 mm of mineral fibre insulation or similar covers the profile sheets 13 only. The floor 19 itself consists of a 22 mm plywood deck 20 topped by a conventional floor finish. A service duct 21 for electricity cables or the like may be provided at intervals as required.

Although described as a single sheet, it will be understood that each profile sheet may be formed of a plurality of shorter identical elements joined together by a tape and seal arrangement to form the elongate sheet. Figure 3 shows such an arrangement at reference 22. The identical elements overlap at the join and the overlapping part of one element may be displaced by the thickness of the sheet to provide a smooth surface for the channel.

Generally, the channels are arranged to provide as smooth a flow passage for the air as possible to reduce losses caused by turbulence thereby keeping the energy required to pump the air through the system to a minimum, although in certain cases it may be desirable to create maximum turbulence to maximise heat transfer between the air and slab even at the expense of greater pumping losses.

At the ends of the profiled sheets 13 adjacent to the outer wall of the building, each sheet has an output plenum duct 23 to which all of the channels 12 are connected, with an air outlet in the form of a floor diffuser 24 incorporating a dirt trap and a trim flange. The sheets 13 are disposed under the floor so that the floor diffusers 24 are at approximately 1 metre intervals along the exterior wall. At the inner ends of each sheet there is an inlet plenum duct 25 to which all of the channels 12 are connected and which in turn is connected to an air inlet, which may be atmospheric air. In certain installations the incoming air may be treated by heat exchange and/or drying to put it into a desired condition before it enters the channels. The inlet and output plenum ducts extend across the width of the associated sheet 13 and are therefore approximately 760-800mm in length and their cross-section is approximately 250 mm wide by 65 mm high. Air is drawn from the inlet by pump or fan means (not shown) and transferred through the inlet plenum duct into and along the channels 12 for heat exchange with the concrete slab before being passed into the room through the floor diffusers 24 where it heats or cools the room as the case may be.

Stale air is drawn from the room through outlet ducts located towards the top of the room on the side opposite the floor diffusers 24.

Under test conditions, a sample of the profiled sheet 13 made of steel was installed on a concrete slab with a floor superimposed as described above. The arrangement was allowed to stabilise for 6 days to precondition of the slab by subjecting the test room to the 24 hour temperature profile shown in Figure 1. The room air above the slab and in a void space below the concrete slab, was controlled to 20 degrees C. throughout the tests. The air

supplied for heat exchange with the concrete slab was supplied in a first test at 15 litres per second and in a second test at 30 litres per second. The heat transfer coefficient between the air and concrete slab was 27 W/m2. K for an air flow rate of 30 litres per second and 17 W/m2. K for an air flow rate of 15 litres per second. The maximum cooling effect of the slab occurred between 14: 00 and 15: 00 and produce a six degrees centigrade temperature drop at 30 litres per second air flow and 7.5 degrees C. temperature drop at 15 litres per second air flow. This included the inlet and output plenum ducts where enhanced heat transfer occurs due to the turbulence caused by the abrupt 90 degree change in air flow direction. Excluding heat exchange in these duct areas, the temperature drops were 4.0 degrees C. and 4.4 degrees C. for air flows of 30 litres per second and 15 litres per second respectively. It is envisaged that an increased rate of heat exchange could be obtained by providing deflectors in the channels to create increased turbulence. These deflectors may be provided on the profile sheets or on the concrete slab itself. By casting deflectors into the slab itself, not only would the turbulence be increased but the increased surface area of the slab subjected to the air flow would also serve to increase the heat transfer between the air and the concrete slab, and vice versa. Depending on the installation, the increased cost of providing the deflectors in the material of the concrete slab may be more than offset by the increased savings in heating/cooling costs arising as a result of the improved efficiency of heat exchange.

The test showed that the maximum cooling effect of heat exchange on the air occurs between 13: 00 and 15: 00 hours at which maximum heating of the slab occurs, whilst maximum cooling of the slab occurs between 5: 00 and 6: 00 in the morning.

This is shown more clearly in Figures 8a and 8b. Figure 8a shows the relative temperatures of the slab and the air being supplied to the inlet plenum duct throughout the 24 hours when the air flow is 30 litres per second. The line 26 indicates the air temperature of the air supplied to the inlet air duct while the line 27 indicates the temperature of the concrete slab at various depths. The graph also shows the time lag of the temperature change of the slab relative to the air which is caused by the slower rate of response of the slab to air temperature changes. Figure 8b shows in a similar manner the relative temperatures of the slab and the air supplied to the inlet duct when the air flow is 15 litres per second. The parts of the graph shown as reference A indicate the area where energy is

transferred from the air to the concrete slab and the area shown as reference B shows the area where heat is transferred from the slab to the air. At the higher air flow rate, heat is given up to the air by the slab during the hours of approximately 10: 00 to 9: 00, heat being transferred from the air to the slab in the period from 9: 00 to 20: 00 hours. In Figure 8b, at the lower flow rate, rather less heat transfer takes place.

The results show that the test system is effective in reducing the temperature of ambient air in the building during the hotter parts of the day and increasing the temperature during the cooler parts of the day, with the result that less energy needs be used in heating and/or cooling the building during an average days temperature cycle. Although as described, the air is pumped through the heat exchange system it is possible in certain installations that natural convention may be relied upon to provide the necessary air flow since hotter air is removed from the top of the room where it is at its hottest, and transferred via the heat exchanger, where it is cooled, back to the floor of the room.

Claims

1. A method of controlling or influencing the air temperature in a space in a building including, providing a heat sink formed at least in part by part of the building structure, treating air by passing it in heat exchange relationship with the heat sink to transfer heat to or from the sink in dependence upon the relative temperature between the air and the heat sink and then to transfer the treated air to the space.

2. Apparatus for controlling the air temperature in a space in a building including a heat sink formed at least in part by a part of the building structure, a heat exchanger to transfer heat to or from the sink in dependence upon the relative temperature between the air and the heat sink, and ducting means to duct air to an input of the heat exchanger and an out put to duct the air from the heat exchanger to the space.

3. Apparatus according to claim 2, wherein the heat sink comprises a concrete slab forming part of the structure of the building and the heat exchanger comprises a profiled or corrugated section of sheet material abutting the concrete slab to form a plurality of parallel channels each defined in part by the surface of the concrete, the input including an input plenum duct connected to input ends of said channels, the output including an output plenum duct to which output ends of the channels are connected.

4. Apparatus according to claim 3, wherein the output plenum duct incorporates one or more floor diffusers through which air is transferred to a room, the diffusers incorporating a dirt trap and a trim flange.

5. Apparatus according to claim 3 or 4, wherein the input and/or output plenum ducts is/are connected to ducting which is served from another location and connects to another floor of the building.

6. A method according to any one of claims 3,4 or 5, wherein the sheet material is formed of steel, another metal, a plastics material, composite material or concrete.

7. A method of controlling or influencing the air temperature in a space in a building, substantially as described herein with reference to and as illustrated in the accompanying drawings.

8. Apparatus adapted to control or influence the air temperature in a space in a building, substantially as described herein with reference to and as illustrated in the accompanying drawings.