FR2466719A1 - Solar water heating installation - has reservoir partly charged with nitrogen for automatic frost protection and additional instantaneous heat exchangers high efficiency - Google Patents

Abstract

The solar collector (1) is connected to a heating coil (5) in a hot water storage tank (4). A reservoir (12) is interposed on the flow pipe (3) between the collector and storage tank coil. A connection (18) is taken from the top of the reservoir (12) to join the flow pipe (3) at its outlet from the collector. A non-return valve (19) prevents flow to the reservoir. Water is circulated by the pump (7). During the initial filling of the circuit a level of water AA is obtained. Above this level the system is charged with nitrogen. When the pump is started by the temperature control system the nitrogen is displaced by water, the fuel in the reservoir falling to BB. Conversely when the pump stops the nitrogen displaces the water and the upper, exposed part of the system is protected against frost damage.

Description

The present invention relates to installations for producing hot water using solar heat.

It is known that installations of the kind in question include in principle one or more sensors in which a heat transfer fluid is circulated which comes to heat a tank playing the role of a hot water accumulator. The heat transfer fluid can be constituted by the water itself that one wishes to heat, but this has various drawbacks and it is therefore preferred to use for this purpose a particular fluid (which can moreover be water or an aqueous solution ) by providing an intermediate exchanger, such as for example a coil arranged inside the tank.

The known installations pose a whole series of problems which have so far been unable to be satisfactorily resolved.

The first of these is the risk of frost.

It is certainly possible to use as a heat transfer fluid a liquid which does not freeze at the lowest temperatures likely to be encountered, or even a gas such as atmospheric air, but this complicates the installation. It is generally preferable to provide an automatic emptying system in cold weather that is not sunny * This solution however requires that when the sun shines again the installation be restored to working order.

Another problem poorly resolved to date is that of the instantaneous efficiency of the sensors, that is to say of the ratio between the amount of heat collected by the heat transfer fluid in the sensor considered and that which the latter receives from the sun. . It is observed in practice that this ratio decreases as the inlet temperature of this fluid rises. The heating of the water in the balloon therefore slows down, which means that excessively powerful sensors must be provided, all conditions being equal.

The third problem is that when the sun starts to shine, especially in the morning, you have to wait a while before you can take hot water from the tank. Indeed if as soon as the exchange coil is heated, water streams tend to rise in the balloon to create a hot zone at the top of it, where the outlet pipe opens, at at the beginning these nets cool a lot as they rise and it is therefore necessary that all the water in the balloon has started to heat up appreciably before the aforementioned zone can form sufficiently.

 According to a first characteristic of the invention, in a solar installation for producing hot water comprising a tank, a separate circuit of water playing the role of heat transfer fluid, an exchanger between said circuit and the tank, (for example a coil arranged in the latter) and a circulation pump not constituting a sealed closure when stopped (for example a centrifugal pump), provision is made to interpose on the path of the heat transfer water between the sensor and the exchanger an intermediate tank containing a mattress of gas, preferably nitrogen, so that when the pump stops, the water from the heat transfer circuit comes to collect in said tank, while the gas rises in the sensor whose emptying is thus ensured. It is understood that under these conditions a simple temperature detector is sufficient to avoid any risk of freezing in the sensor and the pipes which are associated with it, it being admitted that the tank and the balloon are arranged in a lo cal where this risk does not exist.

 Advantageously, a device sensitive to the difference between the temperature of the sensor and that of the balloon is used as a detector, this device thus acting to put the first into action only when it is capable of supplying heat to the second.

 According to another characteristic of the invention, a first auxiliary heat exchanger is provided, interposed between the cold water supplying the balloon (water from the local distribution, for example) and the water from the heat transfer circuit which returns to the sensor. leaving the main exchanger (coil) provided between this circuit and the tank. Consequently, when hot water is taken from the tank, the cold water which the latter receives in exchange cools the water of the heat transfer circuit returning to the sensor, the instantaneous efficiency of which is thus increased.

 Finally, according to a third characteristic of the invention, a second auxiliary heat exchanger is provided between the water of the heat-carrying circuit which leaves the sensor to go to the main or serpentine exchanger and the water taken from the tank. We understand that so when the sensor is working, but the water in the tank is not yet at the desired temperature, this second exchanger ensures its heating, which allows the installation to be used as soon as the sun begins to shine , without having to wait for the ba-llon to warm up.

The appended drawing, given by way of example, will allow a better understanding of the invention, the characteristics which it presents and the advantages which it is capable of providing.
The single figure of this drawing shows in schematic form a heating installation according to the invention.

The installation shown comprises a sensor 1, which is assumed to be produced in the usual form of a suitably inclined flat panel, comprising a black rear wall 1a and a front window 1b which form between them a space 1c in which one circulates water from the heat transfer circuit between a lower inlet pipe 2 and an upper outlet pipe 3. On the other hand, there is shown in 4 the balloon intended to contain the water heated by said circuit. This ball contains a coil 5 forming the main exchanger. Its lower end Sa is connected by a pipe 6 to a circulation pump 7, of the centrifugal type, the outlet pipe 8 of which leads to a first auxiliary exchanger 9 from which the aforementioned inlet pipe 2 leaves.

As for the outlet pipe 3, it leads to a second auxiliary exchanger 10 which a pipe 11 connects to a reservoir 12. The bottom of the latter is connected by a pipe 13 to the upper end 5b of the coil 5.

 The auxiliary exchangers 9 and 10 can be of any type. For the sake of clarity of the drawing, they have been represented as comprising two flat elements in contact with each other, but this is only symbolic. The second element of the exchanger 9 receives by a pipe 14 the cold water intended to supply the tank 4, for example water from a local distribution (city water) and for this purpose it is connected to the bottom of this tank by a pipe 15. As for the second element of the exchanger 10, it is connected on the one hand to the top of the tank 4 by a pipe 16, on the other hand to the distribution of hot water by a pipe 17.

From the top of the tank 12 there is a pipe 18 which leads to the inlet of the outlet pipe 3 through a non-return valve 19 oriented so as to block the flow towards the tank 12. The latter contains a nitrogen blanket which , mime during the coldest, is at a pressure higher than that of the atmosphere in order to avoid any reentry of air.

 The lines 2, 3 and 18 have a slope ensuring the flow of the liquid from the sensor when there is nothing to prevent it. On the other hand, the entire installation, except the sensor 1 and part of the pipes 2, 3 and 18, is inside a building that is supposed to be kept at a temperature above OOC. The wall of this building is shown schematically at 20 through which lines 2, 3 and 18 pass.

 Two thermometric probes 21 and 22 are arranged at the top of the sensor 1 and of the tank 4, these two probes being connected by electric lines 23 and 24 to a comparator 25 which controls the starting and stopping of the motor 26 of the pump 7.

 During assembly of the installation, the reservoir 12 was filled with water to a level A-A located in its upper part, leaving sufficient space, as will be understood later. This water, intended to play the role of heat transfer fluid, fills. Of course the coil 5, the pump 8, the corresponding element of the first auxiliary exchanger 9 with the pipes 13, 6 and 8. It rises to the level AA in the inlet and outlet pipes 2 and 3. The rest of these and the sensor 1 itself are filled with nitrogen.

 As soon as the first probe 21 detects a temperature higher than that of the second 22, the comparator 25 starts the motor 26 and consequently the pump 7. The water then circulates in the heat transfer circuit 8-9-2-1- 3-10-12-13-5-6, the nitrogen being discharged through line 3 into the tank 12 inside which the level drops to BB. The coil 5 is supplied with hot heat transfer water and it heats the consumption water contained by the tank 4.

If the sensor 1 is capable of giving a temperature above 1000C, the risk of boiling is avoided by sending the signal from the first probe 21 to a level comparator 27, suitably calibrated, which stops the motor 26, for example around 900C.

When water is drawn from the tank 4 during the operation of the pump 7, this water passes through the second auxiliary exchanger 10 and therefore if it is not at a sufficiently high temperature, it heats up in the presence of l very hot heat transfer water leaving the sensor 1. Thus, in the morning, even if the tank 4 no longer contains water at a sufficient temperature, hot water can be obtained as soon as the sun has started to shine, without have to wait for a general warm-up of the ball.

The water which is thus withdrawn from the balloon 4 is obviously replaced by cold water coming from the pipe 14. This water passes through the first auxiliary exchanger 9 and it heats up by cooling the heat transfer water even more or less hot or lukewarm pumped by the pump 7. The sensor 1 therefore receives relatively cold water and its instantaneous performance is thereby increased.

The heating of the tank 4 is therefore faster and the solar heat is better used.

 When the temperature of the first probe 21 becomes lower than that of the second 22, the motor 26 stops. The water in the heat transfer circuit therefore returns to the reservoir 12 through the pipe 2, the first exchanger 9, the pipe 8, the pump 7 then stopped, the pipe 6, the coil 5 and the pipe 13. The level in the reservoir 12 goes back up to AA.

 The valve 19 prevents any untimely re-entry of water into the pipe 18 which thus remains reserved for nitrogen to allow it to fill the sensor when the sensor is emptied.

 It is understood that under these conditions when the sensor 1 does not receive solar radiation, it in no way risks freezing, any more than the outside parts of the pipes 2 and 3, since the second probe 22 is always at a higher temperature at OOC and that the water from the heat transfer circuit is drained as soon as that of the sensor drops below this limit.

 The invention has therefore made it possible to very simply resolve all of the problems set out above.

 Of course the reservoir 12 must be of sufficient capacity so that when the pump is started and the sensor 1 is filled with the parts of the pipes 2 and. B located above level A-A, there is still an appreciable amount of water in its lower part (that is to say so that level B-B is clearly above its bottom). 'In addition, it is necessary to take into account the expansion of the heat transfer water between the lowest temperature of the building and the maximum temperature of the sensor and the tank at the end of heating, this expansion tending to raise the levels AA and BB. on the other hand, the nitrogen blanket must be large enough for these expansions to have no significant influence on its pressure, which is then solely a function of the natural temperature of the gas and can therefore be provided.

It should moreover be understood that the foregoing description has been given only by way of example and that it in no way limits the field of the invention from which one would not depart by replacing the execution details described by all other equivalents. It is understood first of all that the liquid used for the heat transfer circuit could be other than pure water. Aqueous solutions of mineral or organic substances, hydrocarbons with a low freezing point, etc. could be used. The gas forming the gas blanket could be other than nitrogen. This is how air can work when there are no oxidation problems.

The type of sensor can be any. Since the reservoir 12 contains hot heat-carrying water in service, it could in some cases be placed inside the tank 4 so that it contributes to heating the consumption water contained therein. Finally, it goes without saying that the installation may include auxiliary heating means in the event of insufficient solar energy, such as, for example, electrical resistors incorporated in the tank 4 and controlled by suitable detectors.

Finally, although it has been more or less implicitly assumed during the present description that the hot water stored in the tank was intended to be sent to dispensing taps for bathrooms, kitchens, etc., It is quite obvious that one could also use it for a central heating installation by providing a sufficient volume for the balloon which would then become a real tank.

Claims (6)

R E V E N D I C A T I O- N S 1. Installation for producing hot water by using solar heat, of the type comprising at least one radiation sensor, a hot water storage tank, a heat transfer liquid circuit transferring heat from the sensor to the tank via '' a main exchanger, such as a coil disposed inside said tank, a circulation pump mounted in this circuit, this pump, for example of the centrifugal type, does not form a sealed closure when stopped, and detector means temperature controlling the start of the plant shutdown, characterized in that on the circuit of the heat transfer liquid, between the sensor and the main exchanger associated with the tank is interposed an intermediate tank containing a gaseous mat and located at a level lower than that of the sensor, so that when the pump stops, the liquid of the circuit comes to collect in this tank, while the gas rises in the sensor whose draining is thus assured.  2. Installation according to claim 1, characterized in that the tank is arranged in a room not involving the risk of freezing.  3. Installation according to claim 1, characterized in that the detector means respond to the temperature difference between the tank and the sensor so as to stop the pump when the sensor is cooler than the tank and to restart it in the reverse case.  4. Installation according to claim 1, characterized in that the gas blanket consists of nitrogen.  5. Installation according to claim 1, characterized in that it comprises an auxiliary exchanger through which pass on the one hand the cold consumption water entering the tank and on the other hand the heat transfer liquid returning from the main exchanger to the sensor . 6. Installation according to claim 1, characterized in that it comprises a second auxiliary exchanger through which pass on the one hand the hot consumption water leaving the tank, on the other hand the heat transfer liquid going from the sensor to the main exchanger .