AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT A SOLAR AIR HEATING SYSTEM WITH A HEAT STORAGE The following statement is a full description of this invention, including the best method of performing it known to me: 1 A SOLAR AIR HEATING SYSTEM WITH A HEAT STORAGE Background The most part of the domestic energy usage is due to heating and cooling electric appliances of low energy efficiency. Room air cooling can be performed using relatively low 5 energy consuming evaporative coolers. In contrast, the issue of room air heating in winter time using energy efficient means was not yet practically resolved. It is, therefore, a prime focus for modem renewable energy developments to supply the domestic market with a competitive and efficient solution for a night-time room air heating. The present patent describes a 100% solar energy powered system for daytime solar heat collection, storing this 10 heat till the night and using it for room air heating during the night. History Using incident solar energy for heating a circulating fluid dates back at least to 1931 as proposed for water heating in patent US 1,814,897. An air heating solar collector was proposed in patent US 2,680,437 from 1945. Both patents describe a solar heat collector 15 surface which absorbs the solar incident heat by thermal radiation heat transfer mechanism. The absorbing surface is positioned inside an enclosure with a transparent cover. A heat transport medium enters the enclosure through an inlet and leaves the enclosure through an outlet. As this medium travels along the absorbing surface, it is being heated by the surface by thermal convection heat transfer mechanism. 20 The basic solar heat collector design described above was further improved in numerous patents. The improvement proposals aimed a better thermal insulation to minimize heat losses from the collector to the environment as described in patent US 3,894,685 and a better heat transfer from the heat adsorption surface to the heat transport medium by maximizing the heat convection as described in patent US 4,054,124 and, also, combinations 25 of these two efficiency improvement strategies. Notably, a drastic increase in the heat exchange and in the collector efficiency can be achieved using a fan for a forced air convection as described in patent US 4,379,449. The collector design from the latter patent successfully addresses the following requirements: construction simplicity, comparatively high thermal efficiency and simplicity 30 of installation. Furthermore, in order to harvest maximum of the available solar energy, the heat absorption surface of the collector should be orthogonal to the incident sun light. This can be achieved using a variable or adjustable tilt of the solar collector as it was proposed in patent US 4,054,124 for a solar water heating system. A solar heat collector should also be supplemented by a heat storage as a peak demand 2 for hot air arises during the night time, i.e. during humans sleep. An idea to use a heat storage for a solar hot air system appeared in patent US 4,324,289. This design forms, however, an integral part of a building and will require a building reconstruction in most cases regarding the existing domestic market. 5 A heat storage using conventional materials (such as stone or water) is of a large mass and volume. The issue of minimizing the heat storage volume can be resolved using Phase Change Materials (PCM) as described in patent US 2,856,506. A PCM heat capacity is many times greater than that of conventional materials due to additional latent heat stored in a PCM during melting and released during crystallization. Therefore, a much smaller heat storage 10 volume and mass is required if PCMs are used. An application of a PCM heat storage for a water heat exchange system is described in patent US 4,219,072. A PCM heat storage of a compact design suitable for an air flow through is described in patent US 4,709,750. There are numerous patents describing solar air heating systems. They incorporate some of the elements and address some of the requirements outlined above such as the patent 15 US 4,379,449. For a domestic market commercialization, however, it is vital to address all the requirements as follows: Objectives A solar air heating system with a heat storage described in this patent is: e able to efficiently harvest and store the solar heat till the night-time and to release the 20 heated air in a humans comfortable temperature range e simple, low cost in construction and easy to install e not demanding any essential dwelling renovations and not occupying much of a room useful space System components (refer Fig. 6) 25 The solar air heating system comprises three main modules (refer Fig. 6): a solar collector (1) for solar heat absorption; a control module (2) for airflow management; a heat storage (3) with a PCM for the heat accumulation, storage and delayed release. These modules can be either separate parts connected by air ducts (4, 5, 6) as shown in Fig. 6 or, alternatively, they can be mounted inside a common collector enclosure (1). The system 30 components are proposed as follows. Solar heat collector design (refer Fig. 1 and Fig. 2) In order to efficiently absorb solar heat by thermal radiation mechanism, the heat absorbing body (10) has a black surface and it is further referred as a 'black body' in this text. The black body (10) is positioned inside of an enclosure (21) in such a way that there is an air 3 gap 'hc' between the black body surface (10) and the enclosure transparent cover (22). To establish an airflow along the black body surface, the enclosure has an air inlet (23) and an air outlet (24). An additional thermal insulation (25) is also desirable to minimise an unwanted heat transfer from the black body (10) to the enclosure (21) and further to the environment. 5 The incident solar heat (11) is absorbed by the black body surface (10) and causes a temperature increase of the black body mass. An instantaneous temperature increase of the black body mass depends primarily on the volumetric air flow and on the air convection heat transfer coefficient as the air removes the heat from the black body. A control of the black body and the air temperatures is, therefore, possible by varying the volumetric air flow and/or 10 the air gap 'hc' in the collector. The collector enclosure (21) was built of acrylic glass, the black body was constructed of several layers of aluminium black mesh. An additional thermal insulation was applied between the cover (22) and the enclosure (21), between the black body and the enclosure (25) and on the collector bottom (26). The black body surface area was about 0.5 m 2 and the black 15 body mass was about 0.6 kg. Heat storage design (refer Fig. 3 and Fig.4) A Phase Change Material (PCM) is kept in thin-walled containers (12) made of possibly heat conductive material. The thickness of the PCM itself, i.e. the container height, is also minimized to facilitate heat transfer through the PCM depth. The PCM mass should be 20 sufficient to absorb the total amount of heat produced by the collector (1) during the daytime. The PCM containers (12) are positioned inside an enclosure (27) in such a way that there is an air gap 'hs' between the containers' surfaces (12) and the enclosure walls. To establish an airflow along the containers' surfaces, the enclosure has an air inlet (28) and air outlets (29). The containers' (12) contact areas with the enclosure should be minimized to avoid an 25 unwanted heat transfer between the PCM (12) and the enclosure (27). This can be achieved using a PCM supporting frame (30) made of a material with a low thermal conduction coefficient. This frame also serves for the air gap 'hs' adjustment used for airflow management. The air flowing through the heat storage enclosure (27) passes along the PCM 30 containers' surfaces (12). This air flow results in a heat exchange between the air and the PCM by the consecutive heat convection and conduction mechanisms if the PCM and the air temperatures are not equal. When the air is hotter than the PCM, the heat is transferred to the PCM and the air cools down. When the air is colder than the PCM, the heat is transferred from the PCM and the air heats up. The essential feature of using a PCM is that PCMs are 4 able to store more heat that conventional materials as it was discussed above. Similarly to the collector, the heat exchange rate can be controlled by varying the air flow and/or the air gap 'hs' in the heat storage (3). Control of the heat exchange rate is especially important when the PCM releases its stored heat, i.e. in the night-time, as this rate governs both the outlet (29) air 5 temperature and the heating process duration till all the heat stored in the PCM is consumed. The containers' supporting frame (30) and the enclosure (27) were built of wood and MDF. The PCM was stored in plastic food containers (12). The total mass of the PCM was of 15 kg but, preferably, should be twice as much for a large bedroom heating needs. The PCM was made by dissolving anhydrous sodium sulfate in water resulting in a Glauber salt solution 10 with a melting temperature about 300 C, i.e. as it was found from testing. Control module design and system operation (refer Fig. 6 and Fig. 7) The control module (2) consists of an air gate (15) and a fan (8). The outlet of the air gate is always connected to the heat storage (3) using an air duct (6). The inlet of the air gate can be connected either to the collector hot air outlet (5) as shown in Fig. 6, or to the room air 15 as shown in Fig. 7. The day operation mode is as follows (refer Fig. 6). The air gate (15) inlet is connected to the collector outlet (5) and the fan (8) is operating. The room air heated up in the collector (1) and driven by the fan (8) enters the heat storage (3) where the heat stored in the air is transferred into the PCM material (12), i.e. the heat storage is being charged. 20 The night operation mode is as follows (refer Fig. 7). The air gate (15) inlet is connected to the room air and the fan (8) is operating. The cold air from the room driven by the fan (8) enters the heat storage (3) where the heat previously stored in the PCM material is transferred to the air and the air heats up, i.e. the heat storage is being discharged. In turn, the heated air flowing out from the heat storage outlet is the proper useful result of the system 25 operation, i.e. it serves humans comfort. The stand-by operation mode is as follows (refer Fig. 7). The air gate (15) inlet is connected to the room air but the fan (8) is not operating. There is no considerable air flow in the system as a free air convection is insufficient to overcome the system pressure drop, i.e. in the control module (2), in the air duct (6) and in the heat storage (3). The heat stored in the 30 PCM (12) is being kept for a further use. The air in the heat storage (3) is still and serves as an additional thermal insulation of the PCM (12). An everyday operation is a sequence of the day mode (charging the heat storage), the stand-by mode (storing the heat) and the night mode (discharging the heat storage). Any valve of an appropriate size and functionality can be used as the air gate (15). A 5 low power fan (8) was installed inside the gate. Such a low power electric device can be easily powered from a small photovoltaic panel equipped with a battery. In this case, the whole system is 100% free solar energy powered. Alternatively, powering a small fan from the electric mains also results in a negligible electricity consumption. 5 The control module (2) can be operated either manually or automatically, i.e. using a timer and temperature gauges. Additional booster fans can also be used to overcome the system pressure drop. System installation and application (refer Fig. 5) The adjustable tilt collector installation design comprises a mounting frame (20) and a 10 window frame insert (31). The window frame insert (31) contains two large air openings to connect the collector inlet (4) and outlet (5) air ducts. The control module (2) is also mounted directly to the insert (31). Additionally, the insert (31) holds the frame joint 'i'. Using such an insert minimizes dwelling alternations required to install a solar system, i.e. it the insert (31) simply replaces a 15 part of a window glass. The mounting frame (20) is a mechanism which enables adjusting the collector tilt angle 'a'. This is possible due to the joins 'i', 'j' and 'k' (refer Fig.5). The back body surface (10) is orthogonal to the incident sun light in order to achieve maximum solar heat absorption. The angle of the incident light changes with seasons and 20 during the day. Daily adjustments of the angle 'a' are not practical. Seasonal adjustments of this angle can further improve the collector efficiency. If the seasonal tilt adjustments are not wanted, the angle 'a' can be set up once equal to the latitude of the geographic location where the collector is installed. The frame (20) was constructed using small aluminum angle profiles. The collector (1) 25 was attached to the frame using bolts. Bolts were also used as joints 'i', 'j' and 'k' (refer Fig.5): the frame inclination was adjusted with these bolts loosened and the adjusted position of the frame was fixed by tightening these bolts. The window frame insert (31) was a wooden board with two large openings. An additional benefit in using the installation shown in Fig. 5 is that the collector 30 outlet duct (5) is as short as possible. Short length of the duct (5) minimizes heat losses to the environment which can be especially large for the hot air leaving the collector. A best application of the system known to me is domestic air heating on a single room scale, i.e. a bedroom night-time heating as discussed in the background section. Other applications are spaces used for humans sleep such as crew cabins, caravans, yachts and other.
6 Statement of newness and distinctiveness (refer Fig. 6 and Fig. 5) The newness and the distinctiveness of the present domestic air heating system is in addressing all the objectives required for a domestic market commercialization as listed in the section 'Objectives' of this patent. This was achieved by using a minimum but sufficient set of 5 design solutions as follows: e The efficiency of the collector (1) operation is achieved using the air flow control as described in the control module (2) design section and by positioning the black body surface (10) orthogonally to the incident sun light (11) using the proposed adjustable tilt mounting frame (20). 10 e The ability to store the heat for the night-time is achieved using the PCM heat storage (3) where the still air serves as an additional thermal insulation whilst the heat is being stored during the stand-by mode of the system. e The system uses cheap and widely available materials, doesn't require complex tools for manufacturing, is comparatively small and lightweight. 15 e The system can be installed by modifying a window frame using the proposed window frame insert (31) with no other dwelling alternations required. The heat storage (3) can be accommodated in an under-bed space. The air duct (6) connecting the control module (2) with the heat storage (3) occupies a very small space in a room. Alternatively, using a common outside positioned enclosure (1) for the collector, the 20 heat storage (3) and/or the control module (2) results in no room space usage.