IN SOLAR HEATING SYSTEMS, AND

IMPROVEMENTS RELATING TO SUCH SYSTEMS

This invention relates to extended-dwell transfer conduits for use particularly as a heat-exchange header pipe in a solar heating panel; and to solar heating systems particularly those incorporating such a conduit.

It is a first aim of the present invention to provide a simply constructed means of transferring heat between a conduit arranged to have a fluid passed therethrough and a fluid or solid body outside said conduit. Generally/ the conduit is utilized by being arranged to be surrounded by fluid at a higher temperature than that being passed through the conduit.

According to a first aspect of the present invention, there is provided a conduit comprising a first tube having a closure at one end thereof, a second tube surrounded by and spaced from the first tube, one end of the second tube being spaced from said closure whereby when fluid is supplied at pressure to the other end of the second tube it flows in one direction along the inside of the second tube to said one end thereof and then in the opposite direction through the space between the first and second tubes.

Preferably, said other end of the second tube projects beyond the other end of the first tube to allow for connection to the second tube of supply tubing, although the supply tubing could be connected to the second tube, for example by the latter being screwed on to the supply tubing, if said other ends of the first and second tubes were, for example, flush with one another.

Preferably again, said one end of the second tube is within the first tube, set back from said one end of the first tube but, with appropriate construction of said closure, these two tube ends could be, for example/ flush with one another.

The first tube may have near said other end thereof an outlet duct extending away from the tube axis.

Alternatively, there may be a third tube concentrically surrounding the first tube and held spaced therefrom, there being sealing means for sealing the third tube at the end thereof corresponding to said other ends of the first and second tubes so that the fluid which has flowed in said opposite direction through the space between the first and second tubes then flows in said one direction between the first and third tubes. If said other end of the second tube projects beyond said other end of the first tube, as mentioned above, the sealing means may be a cylindrical cap with a circular hold through the centre of its base or a standard frusto-conical reducer and connected, for example welded, to the outsides of the second and third tubes.

In both cases, the above-mentioned closure may be a cylindrical cap connected, for example by welding, to the outside of the first tube.

There could be one or more tubes surrounding the third tube mentioned above so that the fluid passes one or more times additionally along the conduit. With an even number of passes the outlet will be at the inlet end of the conduit, with an uneven number the outlet will be at the end remote from the inlet.

A particular use of the above-described conduit is in the heat-exchange header pipe for a solar collector panel; other uses such as converting water into steam or super heating steam are described in more detail later.

According to a second aspect of the present invention, there is provided a solar heating system comprising a solar collector, a heat pump or engine arranged to receive energy from the solar collector, and a heat sump connected to receive uprated heat from the heat pump or engine via a heat-exchange medium. The collector may be arranged to transfer heat to the heat pump or engine by circulation of a heat-exchange medium. Preferably, the heat sump contains liquid which may be circulated to heat storage means, heat-radiating means, hot water heating means and/or steam-generating means. The uprated heat may thus be used for one or more of a variety of purposes.

In one arrangement, a duct may pass through the heat sump whereby water may be supplied to the duct, where it is heated, so that hot water and/or steam may be furnished by the heating system, as well as the circulating liquid being used to heat radiators.

The solar heating system according to the present invention can be utilised in a number of applications, for example in a dwelling house or an industrial application where large quantities of water or steam are required; at the same time factory or Office space may be heated. Moreover, the steam may be used to drive an engine, for example a turbine connected to a generator.

Some examples in accordance with the invention are described below with reference to the accompanying drawings, in which:-

Figure 1 is a longitudinal section through a first conduit comprising three concentric tubes;

Figures 2 and 3 are sections of the first conduit, taken as indicated by the arrows II and III, respectively;

Figure 4 is a longitudinal section through a second, modified conduit comprising three concentric tubes;

Figure 5 is a longitudinal section through a third conduit comprising two concentric tubes;

Figures 6 and 7 each show a solar heating system schematically.

In each Figure the wall thickness of the tubes and other parts is represented by a single line. The dimensions given below and the choice of materials are by way of example only since other dimensions and other materials may be employed.

Figures 1, 4 and 5 each show a first copper tube 10 having an external diameter of 22mm and a second copper tube 12, having an external diameter of 15mm, concentrically surrounded by the first tube 10 and held spaced from it by copper spacers 14 which are spot welded to both tubes. In each case a cylindrical copper cap 16 having a flat base 18 with a 1mm drilling 19 therethrough is welded to the left-hand end of the tube 10 and forms a closure for that tube, the part 18 of which closure is spaced from the left-hand end of the tube 12 by about 10mm, so that

when water or some other liquid at pressure is supplied to the right-hand end of the tube 12 it flows from right to left through the interior of the tube 12, and then from left to right through the gap between the two tubes. Also in each case the right-hand end of the second tube 12 pro¬ jects beyond the right-hand end of the first tube 10.

In the conduit shown in Figures 1 to 3 a third tube 20 concentrically surrounds the first tube 10 and is held spaced from it by copper spacers 22 which are spot welded to both tubes. The tube 20 has an external diameter of 28mm and is 20mm longer than the tube 10 and extends beyond both of its ends. Frusto-conical copper reducers 24,26 each comprising a cylindrical portion having an internal diameter of 28mm at one end and a cylindrical portion having an internal diameter of 15mm at the opposite end, and joined by a frusto-conical portion, are pushed over each end of the tube 22, and copper welded to it and to the tube 20 all round. The right hand reducer 24 causes the liquid which has flowed from left to right in the space between the tubes 10 and 12 to flow from right to left in the space between the tubes 12 and 20.

Before positioning the tube 20, a 3mm diameter hole is drilled through both' wall thicknesses of the tube 20, 10mm from the left-hand end, and a copper rod 28 is threaded through both holes, so that it extends diametrically across the inside of the tube 20. In assembling the conduit, the tube 10 is slid to the left until the base 18 of the cap 16 comes into contact with the rod 28, and then the latter is welded to the base 18 and, at both ends, to the tube 20 so as to provide a seal.

The above-described conduit of Figs. 1 to 3 may be mounted horizontally or vertically in situations where heat is to be absorbed from, for example, a steam pipe.

steel chimney or a domestic open fire. In the last case a bank of series-connected horizontal manifolds may form a retro-fitted back boiler, which is very compact and may be used to heat domestic radiators.

Provided that fluid is rising from the conduit the lmm hole 19 in the cap 18 allows air to be vented with the flow, either through a tap or to an air vent mounted higher in the system.

If, on the other hand, the conduit is to be used as a heat-exchange header pipe in a solar heating panel, an outlet to an automatic air vent must be provided, and a typical modification to achieve this end is shown in Fig. 4 where the right hand plain reducer 24 is replaced by a 28mm x 15mm reducing tee 30 connected to the lower end of a 15mm vent pipe 32 which must be at least 200mm in height; the upper end of the pipe 32 is connected to an automatic air vent (not shown) .

In the example shown in Figure 5, the right-hand end of the first tube 10 and one end of a short tube 34 which is of the same diameter of 22mm and in line with it are inserted into the two openings of a T-connector 36, into the third opening of which one end of a tube 38 of the same diameter is inserted. The other end of the tube 38 is inserted into a reducer 40 which receives at its other end a tube 42 of 15mm diameter. An end cap 44 in the form of a cylindrical cup with a 15mm diameter hole through its base is fitted over the tubes 12 and 34. All the parts 34 to 44 are made of copper and the joints between them and the joints between them and the tubes 10 and 12 are welded to make them gas-tight.

The example of Fig. 5 may be used to the same appli¬ cations as that of Figs. 1 to 3.

Given equal pressures, the liquid flowing through the conduits described above will have a residence time in the conduits greater than would be the case with straight tubes 15mm in external diameter and of the same length, so that there is more transfer of heat between the liquid and the surroundings. The conduit of Fig. 4 described above, which is particularly, but not exclusively, for use with solar heating to increase the dwell time in the head of the system, gives a greater heat output from a given-sized system.

The heat transfer efficiency of the above-described conduits may be improved by increasing the number of fluid passes within the conduit by adding one or more alternately- capped tubes of appropriately increased diameter within the outermost tube. In this case each end cap must be drilled to allow air to vent; by choosing a hole of suitably small size only a negligible amount of cooler fluid will pass through to join the hotter, downstream fluid.

The conduits can be used with a sealed loop system, an open-pumped, or a thermo-syphonic system. Use of the conduit in a sealed loop system is preferred because of the high temperature that can be obtained through self- pressurisation. When, used as a method of heating water from a secondary heat source, ie a steam pipe or steel chimney, the conduit can be fed direct from the mains taking into consideration water board regulations, but in this case a descaler should be fitted downstream, for example before the water reaches the conduit.

In the systems of each of Figs. 6 and 7 a dwelling house 50 has a roof 52 on which is mounted a solar collector 54 of the dry clamp type, the panel header 55 which is connected to a heat exchanger or heat sump 56 by a heat pump or engine 58 in a primary circuit. Heat-exchange medium, ie a liquid or an inert gas, flows from the collec-

tor 54 (for example at an average water temperature of 85°F) to the heat pump or engine 58 via a solar flow line 60, and a solar return line 62 conveys the medium back to the collector 54. Heat-exchange medium e.g. "Freon 22", "Essotherm 300" or similar, flows from the heat pump or engine 58 along a line 62 to tubing 64 within the heat exchanger or heat sump 56 and it heats oil in the heat exchanger or heat sump before returning to the heat pump or engine 58 along a line 66. The heated oil passes through flow piping 68 in a secondary circuit through from the heat exchanger or heat pump 56 to radiators 70 and returns from them along return piping 72 provided with a circulating pump 74.

Fig. 6 additionally shows a level-controlled tank

76 and tubing 78 for supplying oil to it and tubing 80 for carrying oil from it to the heat exchanger or heat sump 58, whereby any oil lost in the secondary circuit is replaced. Any overflow from the heat exchanger or heat sump 58 passes up a tube 82 and, if in excessive quantity, into the tank 76.

Fig. 7 shows additional tubing 84, in the heat ex¬ changer or heat sump 56, which tubing carries fresh water supplied by a rising main 86 to which a pressure vessel 88 is connected to allow for expansion. Hot water or steam, or a mixture of the two, leaves the tubing 84 through a tube 90 and flows at mains pressure to hot taps 92 for, e.g. a sink 94 and bath 96.

Fig. 7 also shows an automatic air vent 98, a pressure switch 100, an expansion vessel 102 on a mount 104, a pres¬ sure gauge 106 and a pressure safety valve and pressurizing point 108.