GB2428781A

GB2428781A - System and method using solar radiation to control the temperature of an environment

Info

Publication number: GB2428781A
Application number: GB0515146A
Authority: GB
Inventors: Hugh Dudley Harwood
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-07-22
Filing date: 2005-07-22
Publication date: 2007-02-07
Also published as: GB0515146D0

Abstract

An apparatus for transferring energy from solar radiation to at least one energy transfer fluid comprising a corrugated surface 210, a plurality of conduits 220, 222, 224, 226, 228 and a means for absorbing solar radiation. The cross sectional area of each conduit may be varied with moveable surfaces 230, 232, 234, 236, 238. Preferably, the apparatus incorporates a radiation loss reduction screen 240, a reflective blind 250, and a weather protection cover 260. Also, a system for controlling the temperature of an environment comprising means for absorbing solar radiation, means for transferring energy from the absorbed solar radiation to at least one energy transfer fluid, means for extracting energy from the at least one energy transfer fluid, means for transferring the extracted energy to a working medium and means for using the working medium to heat a predefined environment.

Description

A system and method for controlling the temperature of an environment The

present invention relates to a system and method for controlling the temperature of an environment and, in particular, for a system and method using solar radiation to control the temperature of an environment.

It is evident that there is a general concern both as to the extent of the emission of carbon dioxide into the atmosphere from the combustion of carboniferous fuels and of the possible ending of the supply of those fuels.

At present, combustion is largely employed to provide space heating in commercial and domestic premises. The essential quantities of energy from sources not involving the combustion process, for example energy from tidal or wind power, are severely limited by the basic facts that such are not only essentially intermittent in quantity and extent, but also are uneconomic and present substantial undesirable ecological consequences even in the very restricted areas in which they can be employed. Their contribution to the problem is therefore essentially only symbolic One remaining source of energy is the direct harnessing of the sun's radiant energy. However, the direct radiant energy supply is, by definition, generally intermittent. Also in winter, when the greatest demands for space heating occur, the supply is at a minimum, and moreover it is very largely absent during night time and when fog, low cloud or snow storms occur. It is therefore essential to examine and evaluate the weaknesses of present methods of garnering the sun's radiant energy and also to provide more efficient methods of harvesting that energy and better methods of employing that harvested energy for space hating than are at present in general use.

It is very evident that in temperate climates the extent of radiant energy received directly from the sun at the earth's surface is not only intermittent in time but also in intensity even during daylight hours. Obviously, too in any one time zone there is a strong diurnal variation superimposed on an even larger monthly variation. In addition, both from the domestic and the commercial aspects there is usually a very strong demand for heat energy at the two ends of the day, and this compounds the position especially during the winter solstice.It is, therefore, essential in any system relying on solar heating, to employ some form of heat storage which is at least sufficiently substantial to even out the effects of time and intensity variations in the garnering of heat and preferably as well to even out the effects of variation in the demands.

There are many known systems for converting solar radiation into usable heat.

However, in most systems the thermal connection between the absorption surface and the heat-transfer medium is inefficient.

In most of the known systems there is a substantial distance between at least a considerable proportion of the absorption surface and that of the tubes containing the heat-transfer fluid. Because of the thermal resistance involved in that intervening space, and also of the closely associated blackbody radiation loss back into space, this separation must inevitably lead to a large loss of efficiency in the transfer of the absorbed energy. Additionally, the separation leads to the inevitable loss of collector efficiency caused by the use of flat collecting surfaces and this must inevitably lead to a particularly substantial loss of collector efficiency during the morning and evening due to the oblique angle of radiation incidence, and moreover that just at those times when the demands for heat are greatest.

In one known design the heat-transfer fluid is required to boil so that the associated gaseous fluid should reach the upper portion of the device, and, there condensing, deliver up the associated latent heat. However, in such a design, towards that upper end this gaseous fluid occupies an increasing proportion of the enclosing tube cross-section and inevitably decreases the transfer efficiency of the heat energy actually garnered by the device. Still further, in some such designs the absorbing surface, is only thermally connected to the tube containing the heat-transfer fluid by a series of spot welds. In addition, the outputs of these individual sources are located in a line along which another heat transfer fluid is caused to flow. It is therefore inevitable that the temperature gradient between this fluid and the heat sources located therein must become progressively smaller as the fluid passes along the top of the tubes and hence yet a further loss of efficiency is inevitable.

Furthermore, in such systems, if the heat-transfer fluid does not reach the boiling point temperature then no energy transfer whatsoever is produced, and the heat stored in the liquid begins to be dissipated by radiation back into space.Additionally, as the temperature of the heattransfer fluid is increased the temperature differential between the heattransfer fluid and the absorption surface must become correspondingly less, and then also must the efficiency of the heat energy transfer. Additionally, this feature is aggravated by the fact that the internal fluid system is significantly pressurised thus increasing the operating temperature still further.

Many known systems use heat-transfer fluids containing large quantities of noxious fluids to prevent any form of growth in the fluid and which will seriously reduce the surface tension of the mixture leading to a strong tendency to "weep" at any weak point in the fluid circuit. This therefore is also likely to involve human contact with such a noxious fluid.

A common method of transferring energy stored in a heat-transfer fluid in domestic and also in many commercial enclosures, is to pass that fluid through radiators. In fact, these devices only radiate a little heat, just sufficient to ensure that a static location near them is rendered uncomfortable. Most of the heat transferred from such devices takes the form of convection currents rising vertically to the ceiling. It is evident that the efficiency in warming the ambience at personal level is very poor and that in order to achieve any reasonable efficiency at all that the actual temperature of that heat-transfer fluid must be quite substantially higher than that of the desired air temperature in that enclosure, a factor which inevitably involves a corresponding reduction in efficiency in the source of supply. Such radiators have a reaction time to any sudden change in temperature in that enclosure that is undesirably long because of the substantial quantity of heat energy stored in that volume of heat-transfer fluid located in the enclosure.

Furthermore, with such a system it is not possible rapidly to differentiate between changes in temperature in different portions of such an enclosure, for example as is often caused by the ingress of a sustained burst of sunshine right across to the opposite room boundary whilst that portion in the shadow remains largely unaffected.

There are also a number of situations where in highly localised conditions supplies of pure, i.e. sterile, air at an adjustable temperature, rate of flow and direction thereof are in some cases almost essential and in others highly desirable, such as in a hospital type ward, or in large offices, and simultaneously such air provides a barrier against unwanted fumes such as from passive smoking or as in the case of hospital wards of airborne infections.

We have appreciated that solar radiation provides a cheap and usable source for providing energy for space and water heating. However, the problems of the prior art systems show that it is problematic to harness sufficient energy to make such a system commercially viable. Additionally, known systems are inefficient in the transfer of energy between the absorption surface and the heat-transfer medium.

During the colder months in temperature climates the amount of the sun's radiant heat is always small and even then is spasmodic in both length of time and in intensity, yet it is during such months that the demands for heat are greatest. It is therefore important that these small heat quanta be harvested efficiently and this in turn implies that an adequate temperature must be achieved even in such circumstances. This fact therefore also implies that the heat capacity of the harvester per se together with that of the heat transfer fluid be quite low and only a gaseous fluid can provide such a property. However, in turn this implies that when substantial irradiation is available, a correspondingly large gas flow is required. One solution to this problem is to provide multiple systems acting in parallel, one employing a gas as the transfer fluid, another a liquid transfer fluid, the rate of flow of each fluid being separately controlled for optimum efficiency.

An alternative system is to provide just one garnering device and more than one store, each containing the necessarily limited volume of fluid, gaseous or liquid, any one of which can be utilised according to the conditions then prevailing. The problem can also be eased in that the effective cross sectional area of the channels, and hence the heat capacity of the transfer fluid therein, can be substantially reduced by causing the base boundary of the channel to protrude to a substantial extent into that channel space by anyone or more of those methods known to those skilled in the arts; the prevailing requirement being that the heat capacity of the channel per se be not then significantly increased, in which case compressed air could be one of the elements employed for operating this change. Such an embodiment could be employed to provide greater efficiency than any one or more of the systems heretofore described.

Alternatively, a system may be provided in which reservoirs containing different heat transfer fluids are stored in just one harvesting device and the particular fluid best employed at any one time is automatically selected. Furthermore, the effective cross sectional area of the individual harvesting channels again can be automatically altered as necessary and hence the associated heat capacity of the volume of the heat transfer fluid under the same area of harvester. Such a temporal change in effective cross sectional area of the individual channels can be effected by changing the shape of the channel base boundary, so that instead of being a plane surface it protrudes significantly into the space above it. It is of course essential that this surface also has a low heat capacity and this operation can be provided by such means as a gaseous medium forcing that boundary upwards by any one or more of those means known to those skilled in the art.

Such a device could be employed in any one or more of the systems heretofore described.

Embodiments of the present invention provide a solar heating system which may employ one or more heat transfer fluids to transfer heat between a radiation absorption surface and a working medium. The system controls the rate of heat flow around the system in each heat transfer fluid independently in order to provide an efficient performance of the system regardless of the operating environment and the required temperature of the working medium.

Figure 1 is a diagram showing the main components of an embodiment of the invention.

Figure 2 is a cross-sectional representation through a heat transfer device used in an embodiment of the present invention.

Figure 3 is a longitudinal cross-sectional representation of an energy transfer device used in an embodiment of the present invention.

Figure 4 is a representation of a heat exchanger used in an embodiment of the present invention.

Figure 5a is a cross section through an inlet/outlet channel for the working medium.

Figure 5b is a cross sectional plan view through an inlet/outlet channel for the working medium.

Figure 6 shows the flow of system data around an embodiment of the invention.

Figure 1 is a diagram of an embodiment of the present invention which is used to control the temperature of a predetermined environment using energy derived from solar radiation. The system includes two heat transfer fluids contained in separately closed loops which flow around the system. Further embodiments may use a single heat transfer fluid or more than two fluids. The fluids transfer heat between a heat transfer device 110 and a heat exchanger 150. The heat transfer device absorbs incident solar radiation and converts the radiation into heat. The heat is then transferred to the heat transfer fluids. and they flow around the system to the heat exchanger. As the fluids flow through the heat exchanger, the heat exchanger transfers the heat from the heat transfer fluids to a working fluid.

The working fluid is then used to control the temperature of an environment. The required temperature of the environment is selected by a user.

In order to provide the temperature required in the environment, the system monitors the flow of heat around the system and adjusts the flow of heat in accordance with the requirements. The system monitors the temperature of the heat transfer fluids in at at least two positions within the system. Typically, the temperature is monitored just before and after the heat is transferred into the fluids using sensors 120 and 130. These sensors enable the system to determine the change in temperature and, hence, the heat absorbed by the fluids within the heat transfer device.

The output temperature of the working fluid from the heat exchanger and the temperature of the environment are also monitored using temperature sensors 160 and 170 respectively. The measurements from all temperature sensors, as well as the selected user requirements, are directed to a central control unit 180 which monitors the temperatures to determine whether the user requirements are being achieved.

The system includes a number of features to control the rate of flow of heat around the system. These features are controlled by the control unit 180 in order to provide the output conditions required by the user. The system includes at least one pump 140 to control the rate of flow of the heat transfer fluids around the system. Preferably, separate pumps are provided for each heat transfer fluid in order that more accurate control of the flow of heat can be achieved and that the system can operate in the most efficient way in the specific operating conditions. Additionally, a fan is provided to control the rate of flow of the working fluid through the heat exchanger.

The heat transfer device is also able to control the energy input into the system and the features that provide this control are discussed in detail below with respect to figure 2.

The central control unit controls the pumps, fans and the heat transfer device in response to the temperature measurements in order to obtain the temperature requirements of the user.

In order to provide improved performance, preferred embodiments of the present invention include a heat pump positioned such that it removes heat from the heat transfer fluid before the fluid enters the heat transfer device. That removed heat may be transferred to a later portion of the sytem. (i.e is not lost or wasted) Such a heat pump removes heat from the fluid entering the heat transfer device in order to reduce the temperature of the heat transfer fluids as they enter the device. Since the temperature of the heat transfer fluid entering the device is reduced, the potential thermal gradient within the conduits of the device is increased. The increased thermal gradient in the conduits improves the heat transfer efficiency particularly in those conditions where the radiation intensity is low but the demand for heat energy is high.

The individual components of the solar heating system are now described in detail.

Figure 2 is a cross-sectional representation through a preferred embodiment of the heat transfer device. The heat transfer device includes an absorbing surface 210 which is suitable for absorbing solar radiation. In preferred embodiments, the absorption surface should be made from a material having a thermal heat capacity which is low compared with that of the associated volume of heat- transfer fluid. This choice of material allows that any sudden short increase in temperature of the absorption surface due to an increased burst of incident radiation, is substantially transferred to the fluids and provides a corresponding change in the temperature of the fluids. This factor is particularly important in conditions where the supply of incident radiation is low or intermittent. Examples of preferred materials to be used for the absorption surface include thin aluminium sheeting coated with small anodised aluminium granules and sprayed matt black; for the transparent version an acrylic resin sheeting can be used.

If the absorbing surface is flat it cannot absorb a significant proportion of incident radiation at glancing angles as the radiation is almost entirely reflected from such a surface and this is the case even if the surface is matt black. . In order to improve the absorption factor for the radiation, the absorption surface should be positioned so that it is as normal an angle as possible to the direction of the incident radiation. During the hours of daylight, the position of the sun with respect to the surface and, hence, the angle of incidence of the radiation on the absorption surface, changes over 180 . In order to maintain the level of absorption as the position of the sun changes, preferred embodiments of the invention provide a corrugated absorption surface.

It is preferable that the profile of the cross-section of the corrugation takes the form roughly similar to that of a triangle, although the flanks thereof need not be flat. Further embodiments include curved corrugation. When installed for use, the device should be positioned such that the lines forming the apices of the corrugations should be aligned as near to the north-south direction as possible in order to maximise the absorption of the incident radiation throughout the daylight hours as the sun moves from east to west and, in particular, in the early morning and late evening. The inclination in the vertical plane may not always be open to choice but where it is, the variation in any demand should also take precedence.

In the north-south direction, the flanks of the absorption device need not be straight but, for example, may take the form of a triangular saw tooth with the steeper portion facing roughly southwards so that the angle of incident radiation from the sun during winter is more normal to that portion of the absorption surface and, thus, maximise the absorption efficiency. Such irregularities may cover part or the whole of the appropriate surface.

In preferred embodiments of the invention, the absorption surface is made as thin as possible and of as low specific heat as possible in order to optimise radiation absorption and transfer to the heat-transfer medium.

In order to increase the absorptive power of the absorption surface, the absorption surface may be coated in part or in whole by a thin layer of small particles. Preferably the particles are thermally conductive and affixed to the surface in a thermally efficient manner. The particles may be sprayed matt black to improve absorption further. Such coating of the surface is designed to resemble emery cloth and prevents reflection of radiation at lower angles of incidence. A similar effect may be obtained by including dimples on the absorption surface which may be blackened.

Beneath the absorbing surface are a plurality of conduits 220, 222, 224, 268 and 228 through which the heat transfer fluids flow. Typically, the heat transfer fluids are separated from each other and flow through distinct channels. The absorption surface forms at least part of at least one surface of each conduit.

Heat is transferred from the absorption surface to the heat transfer fluid by bringing the heat transfer fluids into contact with the absorption surface and relying on the conduction of heat. Preferably, the walls of the conduit should be of a low heat capacity in order to reduce the heat conducted away from the fluids.

In preferred embodiments, the conduits have a hollow wall which is vacuum pumped or filled with gas to better thermally insulate the conduit and prevent heat loss through the walls of the conduit.

In use, the rate of flow of the transfer fluid through the absorption and heat- transfer device should be controlled such that the heat-transfer medium is brought into contact with the absorption surface. The heat energy in the absorption surface is efficiently transferred to the heat-transfer fluids by conduction. The heat-transfer fluids are then pumped from the heat transfer device towards the heat exchanger.

The conduits of the energy absorption and heat-transfer device for each heat transfer fluid are connected together at their inlet and outlet points such that they start from, and are finally collected into, a single stream even though the individual rates of flow may differ and an intervening heat exchanger be required.

Each heat-transfer fluid is then caused to flow through each of its group of conduits in the device connected in parallel at equal rates of volume flow for any particular fluid.

The efficient transfer of heat from the absorbing surface to the heattransfer fluid depends on the flow of the heat-transfer fluid being turbulent in order that as much of the fluid as possible is brought into contact with the surface and that the heat content is fairly uniformly distributed throughout the entire volume of the fluid. It is envisaged, however, that the rate of flow of that fluid be so controlled that the temperature at the exit of the heat transfer device be substantially that of an intended value, It is evident that if the surfaces of the conduits through which the fluid flows are smooth then at some low rate of irradiation on the upper reception surface the corresponding rate of fluid flow will become quite slow and, therefore, laminar in nature. In this case the transfer of even that low rate of irradiation to that fluid will become extremely poor.

In order to maintain turbulence in the fluid, preferred embodiments of the invention include irregularities in one or more of the conduit walls to generate turbulent flow and which serve to extend downwards the rate of flow at which laminar conditions must prevail. In addition, other irregular surfaces may also be provided on the substrate surface.

It should be noted that whilst extra power will be required from the pumping system to provide turbulent flow conditions than would be needed for laminar flow, that this extra power is by no means lost for it must all reappear as heat in that fluid, for heat has the lowest form of entropy, and it is therefore all recovered subsequently in the heat exchanger. The size of the turbulence then generated becomes smaller as the transverse velocity gradient is increased so that at higher rates of flow, when turbulent flow would be the norm, the effect of the irregular surfaces on the flow becomes correspondingly small.

Preferred embodiments of the invention include at least one moveable surface for each conduit 230, 232, 234, 236 and 238 which is moveable in order to vary the effective cross-sectional area of the conduit through which the heat-transfer fluid flows. In preferred embodiments of the invention the cross-sectional profile of the conduit through which the heat transfer flows is adjustable over a very wide range. Typically, one of the walls of the conduits may be movable in order to increase or decrease the cross-sectional area through which the heat transfer fluid may flow. The change in cross-sectional area of the conduits produces a change in the volume of the transfer fluid contained within each conduit and, hence, the magnitude of the temperature change of the heat-transfer fluid can be controlled. The cross-sectional area is controllable by the control unit in dependence on the user requirements and current operating conditions of the system.

One potential area in which energy may be lost from the system is from convection losses from the upper surface of the absorption surface. These losses can be reduced by installing, just above the absorption surface, a radiation loss reduction screen 240. Preferably, the radiation loss reduction screen is rigid and is of a similar contour to the absorption surface 210. An important feature of the radiation loss reduction screen is that it does not prevent the incident radiation from reaching the absorption surface. Therefore, the screen should be essentially transparent to the wavelengths of the incident solar radiation. In preferred embodiments of the invention the screen is corrugated in order to minimise reflections of the incident radiation. Another important feature of the screen is that it should reflect back radiation emitted from the absorption surface in order that this energy is retained by the system. Therefore, in preferred embodiments of the invention the inner surface of the radiation loss reduction screen is treated so that it heavily reflects the long radiation wavelengths emitted from the absorption surface. The radiation loss reduction screen is preferably located closely above the absorption surface by thin spacers 245 which can be of a reflective surface and which may extend effectively right across the absorption surface. Preferably the spacers are spaced at sufficient intervals along the length of the corrugated surfaces such that they inhibit the formation of convention currents above the absorption surface. The screen should not only be as transparent as possible but the dielectric constant thereof should also be low in order that the inevitable energy reflection produced by the relative impedance discontinuity in the transmission path be minimised.

Since the material of the screen must present a different transmission impedance to the incident electro-magnetic waves than that of the air, there will be a correspondingly small magnitude of reflection of the energy by the screen.

However, in preferred embodiments of the invention the angle subtended by the corrugations can be so designed such that the energy reflected from the surface is substantially incident at an angle normal to the surface of the adjacent corrugation. Such an arrangement provides a corresponding ease of entry of that reflected energy into the system even though onto a different part of the absorption surface.

In order to prevent heat losses from the fluid in the device when little or no radiant energy is available and to prevent unwanted radiation from reaching the absorption surface when no further energy is required, part or whole of the absorption surface may be covered by one or more radiation attenuators, for example a type of blind 250. Preferably, such a blind consists of a material resistive to heat conduction wherein the fronts and/or rear surfaces are reflective so that radiation is both poorly received and poorly transmitted. The position of the radiation attenuator, whether fully open, closed or in an intermediate state, is controlled by the control unit in dependence on the amount of radiation required to be input into the system having regard to the user requirements and the current operating conditions.

Typically, embodiments of the present invention will be exposed to the effects of the elements and preferred embodiments of the invention include a weather protection cover 260 positioned over the heat transfer device in order to protect the device from the effects of the weather. Preferably, this cover should be corrugated to match the device which it covers.

Preferred embodiments of the system include at least two temperature sensors associated with each heat transfer fluid which are positioned around the inlet and outlet of the energy transfer device and are in good thermal contact with the heat transfer fluid. In preferred embodiments they are positioned in the flow of the heat transfer fluids or oncontiguous surfaces. These sensors monitor the temperature of heattransfer fluid as it enters and exits the energy transfer device. The temperature sensors are linked to the central control circuit which controls the operating conditions of the system.

If, at any time, the temperature sensor devices indicate that the temperature of the heat-transfer fluid exceeds either of the upper or lower prescribed limits, the pump can be activated to increase the rate of flow of fluid through the energy absorber until the desired temperature is restored. Alternatively, when atmospheric and loading conditions mean that the temperature exceeds the predefined limit, then heat attenuators in the form of the blinds, can be partially or wholly closed in order to cover the absorption surface and to prevent the transmission of heat energy either into or out of the system.

Embodiments of the invention may incorporate one or more heat-transfer fluids.

The heat-transfer fluids are kept separate throughout the system and are directed through specific groups of conduits of the energy transfer device at specific rates of flow.

Figure 3 is a cross-sectional representation of the energy transfer device of Figure 2 showing the conduits in their longitudinal sense along the line AA of Figure 2. Preferably, the rate of flow of each medium around the system is controllable independently and the cross-sectional area of the conduits of the different heat-transfer fluids can be adjusted as discussed above. The advantage gained by using multiple heat- transfer mediums is that these can be selected to have different specific heat capacitances which will produce different temperature changes in a constant volume of the material for the same input energy. Therefore, the energy transfer to the heat-transfer medium can be optimised in different radiation conditions and temperature conditions.

Examples of Heat transfer fluids The obvious contender for a heattransfer fluid is water; it is cheap, freely available, neutral in pH value, possesses a very high specific heat and has an adequately high boiling point. However, the freezing temperature of 0 C is problematic when used in regions in which the temperature drops below this value. In known systems, this problem is overcome by adding substantial concentrations of an antifreeze compound. However, this substantially lowers the viscosity of the mixture and leads to weeping of the fluid from the slightest weak spot in the system. This limitation is still further exacerbated by the necessity of adding to that fluid an even more noxious substance designed to inhibit any organic growth in that medium. In spite of these additives it seems that, in practice, provision also has to be made to empty the system of this fluid, when the atmospheric conditions so demand, into a container located inside the enclosed space and to return it to the system at other times, thus not only adding to the capital cost of the system but also introducing another very real potential source of failure.

Preferred embodiments of the present invention can employ water as the heat- transfer fluid but instead of those noxious fluids cited above being added thereto, sufficient urea is added to ensure that whatever the temperature of that fluid, it is always a saturated solution. Inevitably this must involve a redeposit of that compound at the lower temperatures and this effect can always be accurately located by ensuring that an adequate quantity of undissolved urea is always present at the coolest point in the fluid circuit; recrystalisation will then always take place at that location. A solution of urea has as eutectic of c. - 11 C and the solution is non ionic, any leakage thereof is biodegradable, non toxic and in that concentration the associated very high osmotic pressure produced renders it sterile.

Alternative or additional heat-transfer medium include the group of fluids designed for hydraulic transmission. Typical properties are: Specific heat 0.66, Freezing temperature - 55 C, Boiling temperature 250 C and flash point of at least 120 C. This liquid would of necessity be completely sterile, no problems from seepage are likely to arise and the change in viscosity over the temperature range involved is not excessive.

Gaseous heat-transfer is especially useful in climates where temperatures are known to fall to extremely low values in winter. It can be profitable there to replace a liquid heat-transfer fluid by a gaseous one, in which case dry air is the obvious choice. In order to ensure the closed circuit necessary to provide a very low humidity level it will be necessary to include a largely passive volume store, such as a bellows type, large enough to accommodate the ensuing changes in volume of that gas at the different temperatures expected. In view of the much lower specific heat it is evident that a much greater rate of volume flow will be necessary for most purposes. Examples of suitable gases include air and nitrogen.

When a gaseous fluid is thus employed as a primary heat-transfer fluid, in general it will be advantageous to employ a secondary liquid heattransfer fluid close by and inside the premises, the transfer of energy being carried out by the usual heat transfer device. Implicit in such a scheme is the assumption that the primary heat-transfer fluid, whether liquid or gaseous, does not change its state, e.g. congeal or vaporise, at the temperatures involved. It is also evident that when that fluid is employed to cool the atmosphere in an enclosure, that some tubing will be essential to dispose of the associated condensation produced in the associated heat-transfer equipment.

A large source of wasted energy in presently known systems is that they require that the transfer fluid, for example, water in boilers, reach temperatures far beyond that required by the user. In contrast, preferred embodiments of the present invention need only provide a temperature of the heat transfer fluid at a value required for the domestic purposes of a user, typically around 50 C.

Typically, even such a magnitude as 50 C will only be reached at just one portion of the absorption surface and it follows that the temperature averaged over the whole surface is obviously very much lower even than that value. In view of the fact that, according to Stefan's law, the radiation from a blackbody is proportional to the fourth power of the temperature it follows that unwanted re-radiation losses from the present invention are very small compared with those of prior art systems. Therefore, embodiments of the present invention provide more efficient systems. Additionally, preferred embodiments of the present invention do not start to circulate the heat-transfer fluid until it has reached the operating temperature.

Preferred embodiments of the present invention can employ gases as the working medium and pump the gas directly into the environment at the required temperature rather than using radiators as in the prior art. Such embodiments also provide a much more efficient circulation of warm air within the environment rather than relying upon a static condition as produced by hot water radiators to provide very local heating and also which, of necessity, have far too long a heat time constant for the required rapid ambient temperature control.

Figure 4 shows a heat exchanger 400 used in preferred embodiments of the present invention. The heat exchanger is designed to transfer heat between the heat-transfer medium 410, 420 and a stream of gas 430. In preferred embodiments the gas is air. The rate of flow of gas into the heat exchanger is controlled by a fan 440 which is connected to the central control unit of the system. A temperature sensor 450 is also positioned at the output side of the heat exchanger to monitor the temperature of the environment and/or of the gas.

It is desirable that the temperature sensor has a low thermal capacity in order that it can quickly react to any sudden changes in the atmospheric temperature.

In use, the heat exchanger should be mounted above head height. The warmed gas issuing from the heat exchanger can be divided into more than one stream, each of which may be directed over a wide range of angles in both the horizontal and in the vertical planes. Such devices enable the direction of the warmed gas to be controlled. Additionally, the relative volumes of air issuing from any one of the streams can separately be controlled. As many devices as desired can be provided within an environment and mounted at such a height that, unlike the condition when radiators are used, the entire floor area of the enclosure may now be utilised. Even the pipe carrying the heat-transfer medium can be mounted at such a height.

As a further improvement to such a system, one or more of such heat exchangers can have the outputs coupled to a conduit whilst a more or less contiguous conduit can carry a stream of cold gas, eg air. For this purpose it can often be an advantage that the sources of such warm and cold gas be external to the building. Such a double conduit can be routed to cover any or all of the stations occupied by personnel, who can then adjust the mixture issuing therefrom in both temperature, in quantity and in angle to suit their own particular preferences at any one time. Clearly such a system is absolutely vital in hospitals where in most of the wards the danger of airborne cross infection is very great, quite apart from the well known fact that even patients in adjacent beds often have substantially different needs, and also in offices where in addition to the dangers of airborne infection from one member of staff to another, is also is that of passive smoking, illicit or otherwise. It is well established that the atmospheric conditions preferred by the individual members of the staff are often very different, and that even that their choice may vary throughout the day.

It then follows that the provision of conditions which can easily be changed will lead not only to better staff health but also psychologically, resulting in significantly better staff efficiency and that at very little capital cost or running cost either.

When a substantial volume of gas is being passed through the heat exchanger it is important to avoid causing a nuisance so that no complaints are engendered by neighbouring parties from the noise inevitably associated with such an operation. This essential condition can simply be achieved by means of two devices. The first consists of ensuring that the onset and cessation of any audible noise level has a sufficiently long time constant that the change of condition does not protrude itself on the consciousness. Such a time constant can for example, easily be provided by ensuring that the rotor axle of the compressor fan provides to the electric motor a sufficient moment of inertia, if necessary, by coupling one or more flywheels to it. Such a device being a pure mass reactance will not consume any electrical power at all, the associated electrical load being in perfect quadrature with the power consumed by the resistive element and, moreover, is failproof. The second device is to so construct at least the ends of the fan input and output gas conduits to have a substantially rectangular cross-section. However, concentric circles or elipses may also be used. Acoustic absorbent material, suitably protected against the effects of the airflow, is affixed to at least the end regions of each of the two long walls on the internal faces of the conduits and these will ensure the very rapid attenuation with distance of sounds generated by the fan during its operation.

Additionally, the conduits may include walls, again coated with acoustic absorbing material, which protrude into the channel, typically from the ends, different distances. The different length walls absorb sound waves of different frequencies.

Figures 5a and 5b show an example of such a sound absorbing conduit. Figure 5a is a cross-section through the channel looking along the longitudinal axis and Figure 5b is a cross-sectional plan view of a part of the channel.

The long internal faces are represented by 510 and 520 and the internal walls 530, 540 and 550 protrude different distances into the channel to absorb sounds of different wavelengths. Typically the acoustic absorbing material is covered by an essentially acoustically transparent airflow restraining layer.

The associated fan rotary acceleration and deceleration is made to have sufficiently long period by, for example, ensuring that the rotating member has such a moment of inertia compared with the driving torque, that the time taken to reach the final angular velocity is adequately long. This can be achieved by, for example, attaching effectively to the fan axle one or more fly wheels of adequate moments of inertia.

Figure 6 is a circuit showing the flow of data around the solar heating system.

The central control unit receives temperature readings from temperature sensors measuring the first heat transfer fluid (HTF1), HTF2, the output temperature of the working medium and the temperature of the environment. The control unit processes the measurements and sets the position of the radiation attenuation, the cross-section of the conduits for the heat transfer device and the speed of the pumps and fans accordingly. The current status of each of these is also fed into the central control unit.

It will be clear to those skilled in the art that figure 6 is merely an example of an embodiment of the invention and that, in further embodiments, the central control unit may receive data from only some of the identified sensors or further data from additional sensors.

In further preferred embodiments of the invention which are located in premises through which a substantial volume of warm air is circulated, the effluent air which would otherwise be vented directly into the external space, is passed through a heat exchanger with associated heat pump and the heat thus absorbed is fed back into the system elsewhere. The air is finally vented and, thus, at least a substantial portion of the heat which otherwise would have been wasted is reclaimed, thus implying a smaller original input. In the case of domestic type situations the main recoverable heat is probably that from the hot water used in baths, showers and wash hand basins. The waste water from such can temporarily be stored, preferably in a circular conical shaped vessel [having a large central plug-controlled vent] into which such warm water can temporarily be stored whilst in a similar manner to that described above, the heat energy can be substantially extracted. A central control plug would ensure a very rapid discharge, helpful in ensuring a clean exit of the effluent to the usual site.

At any time some heat is radiated from cloud cover but this is small compared with that from the sun's direct radiation. Furthermore, there are numerous occasions in winter particularly during a still night when the sky is at least largely cloudless, exposing a space at almost zero degrees. At any time of the day or night, in contrast to this condition, the sky may be completely obscured by low cloud, fog or a precipitation of snow.

It therefore becomes evident that as far as is practicable in any particular case it is highly desirable to provide heat storage devices of sufficient magnitude to bridge over lapses in heat reception. Fortunately, there is another easily tapped and universally available major reservoir of heat derived also from the sun's radiant energy, which is evident in the temperature of the atmosphere itself.

Even during conditions of fog or low cloud the water in the associated droplets has a very high thermal capacity and, in addition, that air is then quite saturated with water vapour which has a large latent heat of condensation. In preferred embodiments of the invention, large volumes of this water-laden air can be passed through an appropriate heat exchanger whose external surfaces may be coated with a water repellent substance and the heat stored in the water is then transferred into the system. Under these conditions and at any time of the day or night, and preferably with the help of a heat pump, all the latent heat contained in that water vapour as well as that heat stored in the droplets of water can thus be extracted until the temperature is well below 0 C without involving solidification.

During weather conditions accompanied by significant snow precipitation the air is always relatively warm again because of the large associated latent heat of solidification from the vapour involved and here again the water vapour content in that air is also quite high so that at least to some extent, the same factors apply whatever the time of day or night.

A still further advantage of such a system should here be noted in that when the climatic conditions are reversed, and the temperature in the enclosure is now deemed to be excessive, then the input/output fluid terminals to this heat exchanger/heat pump system may be reversed, and the now cold heat-transfer fluid employed to cool the atmosphere in the enclosure to the desired extent.

It is evident that in temperate climates there are a number of occasions when the supply of radiant heat from the sun falls far short of that required, whether for domestic or for commercial purposes. Such conditions will include coverage by fog, by low cloud, a significant snow fall or even the existence of a still clear night revealing a sky at almost zero degrees. When such conditions prevail there is still a large source of heat derived previously from the sun's radiation. For example, in foggy or low cloud conditions not only does the extensive presence of so many droplets of water in a given volume of air very greatly increase the specific heat thereof but as well, by definition, the air is completely saturated with water vapour whose latent heat of condensation adds substantially to the energy potentially available. Even during a snowstorm the large mass of water vapour yielding up the latent heat thereof to become a solid medium ensures that at any such time the air temperature is relatively high as well as quite moist.

In order to extract sufficient heat from such a medium it is evident that substantial volumes of air must flow rapidly through a heat exchanger, and the heat preferably being extracted by means of a heat pump in the usual manner. If the external surfaces of this exchanger are coated with a water repellent film there is no reason why the water droplets should not be cooled to such an extent that they become a super cooled fluid, well below the normal freezing point temperature, meanwhile the substantial latent heat of condensation of the saturated air is also extracted.

It is quite evident that, at least in general, it is definitely preferable that when a certain excess quantity of heat is available for storage that this excess should be stored at a relatively high temperature in a quite finite volume of fluid than at, say, a lukewarm temperature in a much larger volume of fluid. In view of this fact it is proposed that the heat stores should consist of at least more than one unit, the first unit being heated fully to the predetermined temperature before the heat supply is diverted to another unit. If the first store/s is/are thus kept for domestic' use then the fluid in the remainder can be restricted to providing heating, in which case the fluid can be different, e.g. preferably have a lower freezing temperature such as would be provided by a concentrated solution of urea. In commercial premises it would appear convenient that at least the major store/s be located at the same level as that of the previous boiler house. In the case of domestic applications, however, the advantages of distributed loading on the loft rafters is apparent, as opposed to that involved from just one large volume.

When at any one time the whole store has been filled with fluid at the temperature for which there is optimum efficiency, there is no reason why, if excess irradiation is still available, that the storage process should not be recommenced at a higher storage temperature right up to the higher safe limit, even though the garnering efficiency will not now be quite so high.

In further embodiments of the invention, the solar radiation is absorbed by a radiation absorbing material included within the actual heat transfer medium itself. The absorbing element could consist of an aerosol or dust or coloured vapour in the case of a gaseous heat transfer medium or of an emulsion, colloidal solution or soluble dye in the case of a liquid heat transfer fluid. Alternatively the fluid colour or colour density is made sufficiently high to absorb radiation eg deep blue. In embodiments including such heat transfer mediums, the corrugated cover of the heat transfer device (210 in figure 2) would then be made of as transparent a substance as possible to the incident radiation as well as having as low a dialectric constant as possible so that the inevitable transmission medium discontinuity involved does not produce a serious attenuation in the magnitude of the energy transmitted inwardly. Such embodiments would benefit from the transparent covering being corrugated since this increases the time period for which the incident radiation is substantially normal to the surface. Although the material is transparent, reflection of incident radiation is reduced when the radiation is incident on the surface at a normal angle.

Embodiments of the system employing radiation absorbing material in the heat transfer medium inherently have the fundamental advantage that the radiant energy would be absorbed throughout the whole body of the heat transfer fluid.

Such embodiments may not require irregular surfaces to generate turbulence since energy would be absorbed throughout the fluid. Additionally, such embodiments with a transparent ceiling on the conduits may have at least one dark inner surface to absorb additional radiation and transfer this to the fluid.

It will be clear to those skilled in the art that the connections of the heat transfer system can simply be reversed in order to cool the environment in hot weather.

Claims

Claims 1. An apparatus for transferring energy from solar radiation to at

least one energy transfer fluid comprising: a corrugated surface; a plurality of conduits, suitable for carrying energy transfer fluids, wherein the corrugated surface forms at least part of each conduit; and, means for absorbing solar radiation; wherein, the apparatus is adapted such that at least one energy transfer fluid can be passed through the conduits and energy can be transferred from the means for absorbing solar radiation to the energy transfer fluid by bringing the fluid into thermal contact with the absorption means.
2. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claim 1 wherein the means for absorbing solar radiation is the corrugated surface.
3. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claim 1 wherein the corrugated surface is transparent to solar radiation and the means for absorbing solar radiation forms at least part of the conduit or is carried within the fluid.
4. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claims 1, 2 or 3 wherein the corrugations of the corrugated surface are substantially triangular shaped.
5. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claim 4 wherein portions of the sides of the substantially triangular corrugations are curved.
6. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claims 1, 2, 3, 4 or 5 wherein the means for absorbing solar radiation is coated with energy absorbing particles.
7. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claims 1, 2, 3, 4, 5 or 6 wherein the means for absorbing solar radiation includes dimples.
8. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid wherein the means for absorbing solar radiation is formed of a material having a heat capacity lower than that of the energy transfer fluids.
9. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claims 1, 2, 3, 4, 5, 6, 7 or 8 wherein the cross sectional area of the conduit can be altered.
10. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to any of claims I - 9 wherein the conduits include irregularities on their inside surfaces.
11. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claims 1 - 10 wherein the conduits have hollow walls.
12. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claim 11 wherein the walls are vacuum pumped.
13. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to any of claims 1 - 12 further comprising a radiation loss reduction screen.
14. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claim 13 wherein the radiation loss reduction screen is corrugated.
15. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claim 13 or 14 wherein the radiation loss reduction screen can be penetrated by solar radiation but reflects radiation emitted from the absorption surface.
16. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claims 13, 14 or 15 wherein the radiation loss reduction screen is located above the means for absorbing solar radiation.
17. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to any of claims 1 - 16 further comprising the means for selectively preventing solar radiation from reaching the absorption surface or leaving from it.
18. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to claim 17 wherein the means for selectively preventing solar radiation from reaching the means for absorbing solar radiation or leaving from it has a higher thermal resistance and at least one of the surfaces has a reflective nature.
19. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid according to any of claims 1 - 18 further comprising a weather protection cover.
20. An apparatus for transferring energy from solar radiation to at least one energy transfer fluid substantially as herein described with reference to the accompanying figures numbered 2 and 3.
21. A system for controlling the temperature of an environment comprising; means for absorbing solar radiation; means for transferring energy from the absorbed solar radiation to at least one energy transfer fluid; means for extracting energy from the at least one energy transfer fluid: and transferring the extracted energy to a working medium; and, means for using the working medium to heat a predefined environment.
22. A system for controlling the temperature of an environment according to claim 21 wherein the energy from the absorbed radiation is absorbed by at least two energy transfer fluids.
23. A system for controlling the temperature of an environment according to claim 21 or 22 wherein the means for absorbing solar radiation is an absorption surface.
24. A system for controlling the temperature of an environment according to claim 23 wherein the energy is transferred from the absorbed solar radiation to the at least one energy transfer fluid by positioning the energy transfer fluids in thermal contact with the absorption surface.
25. A system for controlling the temperature of an environment according to claim 21, 22, 23 or 24 wherein the energy transfer fluids are carried in conduits and at least part of the conduit is formed by the energy absorption surface.
26. A system for controlling the temperature of an environment according to claim 21, 22, 23, 24 or 25 wherein the means for absorbing solar radiation is carried within at least one energy transfer fluid.
27. A system for controlling the temperature of an environment according to claim 21, 22, 23, 24, 25 or 26 further comprising means for monitoring the temperature of the energy transfer fluids before and after the energy is transferred from the absorbed solar radiation to the at least one energy transfer fluid.
28. A system for controlling the temperature of an environment according to claim 27 further comprising means for controlling the rate of flow of the energy transfer fluids through the conduits in dependence on the monitored temperatures of the at least one energy transfer fluid.
29. A system for controlling the temperature of an environment according to claim 28 wherein the rate of flow of the or each energy transfer fluid is controlled independently.
30. A system for controlling the temperature of an environment according to any of claims 21 - 29 wherein the means for absorbing solar radiation and transferring the energy to at least one energy transfer fluid is the apparatus of any of claims I - 20.
31. A system for controlling the temperature of an environment according to any of claims 21 - 30 comprising means for extracting energy from the energy transfer fluids before transferring energy from the absorbed solar radiation to the at least one energy transfer fluid.
32. A system for controlling the temperature of an environment according to any of claims 21 - 31 wherein the working medium is air.
33. A system for controlling the temperature of an environment according to any of claims 21 - 32 wherein one of the energy transfer fluids is a saturated solution of, preferably, urea.
34. A system for controlling the temperature of an environment according to any of claims 21 - 33 wherein one of the energy transfer fluids is dry air.
35. A system for controlling the temperature of an environment according to any of claims 21 - 34 wherein the means for transferring the extracted energy to a working medium is a heat exchanger and the working medium is a gas.
36. A system for controlling the temperature of an environment according to claim 35 further comprising a fan to draw gas through the heat exchanger and into the environment.
37. A system for controlling the temperature of an environment according to claims 35 and 36 further comprising channels suitable for carrying gas to and from the fan and through which the fan draws the gas.
38. A system for controlling the temperature of an environment according to claim 37 wherein the cross-section of at least the ends of the channels are substantially rectangular shaped.
39. A system for controlling the temperature of an environment according to claims 37 or 38 wherein the internal walls of the channels are coated with an acoustic absorbent material.
40. A system for controlling the temperature of an environment according to claims 37, 38 or 39 further comprising further walls within the channels which protrude along part of the length of the channel.
41. A system for controlling the temperature of an environment according to claim 39 wherein the further walls protrude from the ends of the channels and towards the fan.
42. A system for controlling the temperature of an environment substantially as herein described with reference to the accompanying figures.
43. A method for controlling the temperature of an environment comprising the steps of; absorbing solar radiation; transferring energy from the absorbed solar radiation to at least one heat transfer fluid; extracting energy from the at least one energy transfer fluid: transferring the extracted energy to a working medium; and, using the working medium to energy a predefined environment.
44. A method for controlling the temperature of an environment comprising the step of energy from the absorbed solar radiation to at least two energy transfer fluids.
45. A method for controlling the temperature of an environment according to claim 43 wherein the step of absorbing solar radiation is performed by an absorption surface.
46. A method for controlling the temperature of an environment according to claim 45 wherein the step of transferring energy from the absorbed solar radiation to the at least one energy transfer fluid is performed by positioning the energy transfer fluid in thermal contact with the absorption surface.
47. A method for controlling the temperature of an environment according to claim 43, 44, 45 or 46 wherein the energy transfer fluids are carried in conduits and at least part of the conduit is formed by the energy absorption surface.
48. A method for controlling the temperature of an environment according to claim 43, 44, 45, 46 or 47 wherein the step of absorbing solar radiation is performed by absorbing means carried within at least one energy transfer fluid.
49. A method for controlling the temperature of an environment according to claim 43 - 48 comprising the further steps of monitoring the temperature of the energy transfer fluids before and after the energy is transferred from the absorbed solar radiation to the at least one energy transfer fluid.
50. A method for controlling the temperature of an environment according to claim 49 comprising the further step of controlling the rate of flow of the energy transfer fluids through the conduits in dependence on the monitored temperatures of the at least one energy transfer fluid.
51. A method for controlling the temperature of an environment according to claim 50 comprising the further step of controlling the rate of flow of the or each energy transfer fluid independently.
52. A method for controlling the temperature of an environment according to any of claims 43 - 51 wherein the steps of absorbing solar radiation and transferring the energy to at least one energy transfer fluid are performed by the apparatus of any of claims 1 - 20.
53. A method for controlling the temperature of an environment according to any of claims 43 - 52 comprising the further step of extracting energy from the energy transfer fluids before transferring energy from the absorbed solar radiation to the at least one energy transfer fluids.
54. A method for controlling the temperature of an environment according to any of claims 43 - 53 wherein the working medium is air.
55. A method for controlling the temperature of an environment according to any of claims 43 - 54 wherein one of the energy transfer fluids is a saturated solution of, preferably, urea.
56. A method for controlling the temperature of an environment according to any of claims 43 - 55 wherein one of the energy transfer fluids is dry air.
57. A method for controlling the temperature of an environment according to any of claims 43 - 56 wherein the step of transferring the extracted energy to a working medium is performed by a heat exchanger and the working medium is a gas.
58. A method for controlling the temperature of an environment according to claim 57 further comprising the step of drawing gas through the heat exchanger and into the environment using a fan.
59. A method for controlling the temperature of an environment according to claims 57 or 58 wherein channels are used to carry gas to and from the fan and through which the fan draws the gas.
60. A method for controlling the temperature of an environment according to claim 59 wherein the cross-section of at least the ends of the channels are substantially rectangular shaped.
61. A method for controlling the temperature of an environment according to claims 59 or 60 wherein the internal walls of the channels are coated with an acoustic absorbent material.
62. A method for controlling the temperature of an environment according to any of claims 59 - 61 further comprising further walls within the channels which protrude along part of the length of the channel.
63. A method for controlling the temperature of an environment according to claim 62 wherein the further walls protrude from the ends of the channels and towards the fan.
64. A method for controlling the temperature of an environment substantially as herein described with reference to the accompanying figures.