GB1587584A - System for supplying heat by means of solar collectors - Google Patents

Description

(54) SYSTEM FOR SUPPLYING HEAT BY MEANS OF SOLAR COLLECTORS (71) We, ROBERT BOSCH GMBH, a German company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a system for supplying heat by means of solar collectors, which is provided with automatically acting means which prevent the development of an inadmissibly high pressure and an inadmissibly high temperature of the heat carrier flowing through the solar collectors when, with intensive solar radiation, the decrease in temperature of the heat carrier represents a consumption of power less than the power offered by the collectors.

In the case of intensive solar radiation lasting for a long period of time, the single- or multi-pane collectors in systems of the above type can attain relatively high temperatures of from 130C to 150C, and in excess thereof, when provision is not made for an adequate reduction in temperature of the heat carrier.

It is very likely that the reduction in temperature effected may be too slight, or may not even occur at all. during summer when the heating system is shut down or when there is only a low consumption of hot water and any heat store employed is fully heated, or when the circulating pump for the heat carrier is rendered inoperative by a power failure, or the system is fully shut down owing to the absence of the operator. Pursuant to the existing safety regulations such as in DIN 4751, closed hot water heating systems must not exceed a temperature of llOC and a maximum pressure of 2.5 atmospheres gauge pressure (including the static water pressure) in the entire system.However, as is evident from the previously mentioned no-load values of temperature of the collectors. the admissible limiting values of the temperature are exceeded to a considerable extent; and the admissible pressure is also exceeded to a considerable extent when using water or mixtures of water and ethylene glycol (antifreezing mixtures).

The known proposals for preventing excessive pressure and temperature of the heat carrier flowing through the solar collectors reside in draining the liquid heat carrier from the collectors when a dangerous situation arises and introducing it into special collecting containers or to allow the heat carrier to evaporate by way of safety valves in the event of excess pressure. Both these measures involve the expensive refilling of the system with the heat carrier. In addition to this, the second method involves the loss of the anti-freezing additives and the additives for protection against corrosion when water mixtures are used as heat carriers.

There is provided by the present invention a system for supplying heat by means of a solar collector through which flows a circulating heat carrier by which heat absorbed in the collector is transferred to at least one heat consumer or heat store capable of intermittent operation and operation at less than the maximum heating capacity of the system wherein for the purpose of preventing the temperature and pressure of the heat carrier exceeding admissible values thereof. there is provided an expansion tank which is connected to the collector but which is arranged to prevent admission thereto of fluid medium from the collector until the temperature in the collector nears or reaches the permissible value and then admits fluid medium from the collector under the pressure developed by steam forming in the fluid medium in the collector.

It is here explained that an expansion vessel per se is a known kind of vessel. It comprises a tank or cylinder containing a loading arrangement, for example a spring loaded piston. to act on the liquid in the tank to maintain a pressure on the liquid. Alternatively it may use a gas cushion for this purpose, the gas cushion being separated from the liquid by a flexible diaphragm. It follows from this that the fluid in any fluid line system connected to the vessel will need to overcome the pressure of the loading arrangement to gain entry into the vessel.

In contrast to known systems, the system in accordance with the invention has the advantage that, in the case specified, the heat carrier is automatically expelled from the solar collectors and reintroduced into them, thus avoiding the expense of restoring the system to operation and avoiding the loss of the heat carrier. After the liquid heat carrier has been expelled from the solar collectors, only a slight pressure rise in the line system is to be anticipated with a further undiminished input of heat, and cannot constitute a danger to the system.

The volume of the expansion tank may be kept relatively small when the tank is connected to the circulating pipe for the heat carrier as near as possible to the bottom inlet of the solar collectors. However, care then has to be taken that the connection point is still located at a sufficient distance from the bottom inlet of the solar collectors to ensure that the heat carrier is present in the liquid phase at this point during any operating state.

One embodiment of the invention is illustrated in the accompanying drawing in which the sole figure is a diagrammatic representation of a system according to the present invention installed in a building.

The system shown in the sole figure serves to heat a house 1 and is a hot water circulating heating system comprising a heating unit 2, a forward flow line 3, and a return-flow line 4 to which the individual space heaters 5 and a domestic water heater 6 are connected.

A battery 10 comprising solar collectors is connected to the heating network in parallel with the heating unit 2 by lines 8 and 9. An anti-freezing agent is added to the circulating heating water. The line 8 leads by way of a circulating pump 12 to a distributor 13 to which an expansion tank 14 and a safety valve 15 are connected. The line 9 includes a distributor 16 connected to a line 17 which leads to a relief valve 18. The line 17 is controlled by means of a shut-off valve 19 in dependence on the temperature of the water in the collectors 10.The arrangement is such that the valve 19 shuts when the temperaturc has reached the boiling point of water, for example, the value of from 105 to I lOC. The temperature is sensed by a temperature sensor 20 which is disposed at the top end of the solar collectors 10 and which also controls a solenoid switch 21 in the electrical circuit of the circulating pump 12. The electrical circuit is interrupted when the temperature of the water in the collectors 10 reaches the above-mentioned value.

The expansion tank 14 is dimensioned such that it can accommodate the increase in the volume of the water upon heating and, additionally, the entire quantity of water in the collectors. The inlet pressure of the expansion tank 14 is chosen such that an average pressure of from 1.2 to 1.4 atmospheres is established in the collectors on removal of the static pressure of the water column between the collectors and the expansion tank. A boiling temperature of the water of from 105 to 110C ensues at this filling pressure; this corresponds approximatelky to the value which is still permissible as an upper limiting value in accordance with the regulations for small closed hot water heating systems.When the collector water reaches this limiting value during intensive solar radiation and no heat is being extracted, the water in the collectors commences to boil and the steam which is formed commences to drive the water out of the collectors into the expansion tank 14. The valve 19 at the same time shuts off the vent line 19, so that steam cannot escape by way of the relief valve 18. There is then only a negligible rise in pressure in the heating network upon a further undiminished supply of heat, it does not constitute any danger to the network. If the collectors cool owing to the fact that heat is no longer supplied, the water can again flow into the collectors from the expansion tank when the temperature drops below boiling point, whereupon the system is again ready for operation.The solenoid switch 21 ensures that the circulating pump 12 cannot be put into operation when the heat requirement is abruptly increased, for example, for the purpose of preparing hot water, when the collectors are operating without water. In this case, the pressure in the heating system might increase abruptly and result in water shocks or similar trouble somc attendant phenomena. The solenoid switch 21 may be omitted when the mass ratio between the water and the material of the collector absorbers exceeds a specific value.

The total working volume of the expansion tank 14 is calculated from the inlet pressure pl. the maximum admissible final pressure p2, the increase in volume of the heating water when it is heated and the water capacity of the collectors. The volume is given by the following equation: V = p2(AV + Vk) p2-pl In the above described embodiment, the tank 14 also serves to reccive circulating heating water on expansion thereof on heat ing of the water; the dimensions of the tank being such as to accommodate the increase in volume of the heating water on heating thereof and the volume of the heat carrier i.e.

in this case, the water of the system passing through the collectors 10, that could be forced into the tank 14.

WHAT WE CLAIM IS:- 1. A system for supplying heat by means of a solar collector through which flows a circulating heat carrier by which heat absorbed in the collector is transferred to at least one heat consumer or heat store capable of intermittent operation and operation at less than the maximum heating capacity of the system, wherein for the purpose of preventing the temperature and pressure of the heat carrier exceeding admissible values thereof, there is provided an expansion tank which is connected to the collector but which is arranged to prevent admission thereto of fluid medium from the collector until the temperature in the collector nears or reaches the admissible value and then admits fluid medium from the collector under the pressure developed by steam forming in the fluid medium in the collector.

2. A system as claimed in claim 1, for a hot water central heating system having heating elements, acting as heat consumers, connected to the heating network wherein the expansion tank is connected also to receive heating water; the capacity of the expansion tank being dimensioned to accommodate the increase in volume of the heating water when it is heated, and the volume of the heat carrier that could be admitted from the solar collector.

3. A system as claimed in claim 2, wherein the heat carrier is water; the solar collector is directly connected in the heating network, and the expansion tank has a single liquid chamber for the water to be accommodated.

4. A system as claimed in any of the preceding claims, wherein the expansion tank is connected to a section of the circulating pipe for the heat carrier to which the bottom inlet of the solar collector is connected, at a point at which the heat carrier is in the liquid phase during any operating state.

5. A system as claimed in any of the preceding claims, wherein there is provided a relief valve at the highest point of the circulating pipe for the heat carrier flowing through the solar collector, and wherein a shut-off valve, controlled by the pressure or the temperature of the heat carrier in the solar collector. is connected upstream of the relief valve.

6. A system as claimed in any of the pre ceding claims, having a circulating pump for the heat carrier flowing through the solar collector, wherein the circulating pump is controlled by a switch in dependence on the pressure or the temperature of the heat carrier.

7. A system according to any of the preceding claims, wherein the solar collector is used in plurality.

8. A system for supplying heat by means of a solar collector, substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. being such as to accommodate the increase in volume of the heating water on heating thereof and the volume of the heat carrier i.e. in this case, the water of the system passing through the collectors 10, that could be forced into the tank 14. WHAT WE CLAIM IS:-

1. A system for supplying heat by means of a solar collector through which flows a circulating heat carrier by which heat absorbed in the collector is transferred to at least one heat consumer or heat store capable of intermittent operation and operation at less than the maximum heating capacity of the system, wherein for the purpose of preventing the temperature and pressure of the heat carrier exceeding admissible values thereof, there is provided an expansion tank which is connected to the collector but which is arranged to prevent admission thereto of fluid medium from the collector until the temperature in the collector nears or reaches the admissible value and then admits fluid medium from the collector under the pressure developed by steam forming in the fluid medium in the collector.

2. A system as claimed in claim 1, for a hot water central heating system having heating elements, acting as heat consumers, connected to the heating network wherein the expansion tank is connected also to receive heating water; the capacity of the expansion tank being dimensioned to accommodate the increase in volume of the heating water when it is heated, and the volume of the heat carrier that could be admitted from the solar collector.

3. A system as claimed in claim 2, wherein the heat carrier is water; the solar collector is directly connected in the heating network, and the expansion tank has a single liquid chamber for the water to be accommodated.

4. A system as claimed in any of the preceding claims, wherein the expansion tank is connected to a section of the circulating pipe for the heat carrier to which the bottom inlet of the solar collector is connected, at a point at which the heat carrier is in the liquid phase during any operating state.

5. A system as claimed in any of the preceding claims, wherein there is provided a relief valve at the highest point of the circulating pipe for the heat carrier flowing through the solar collector, and wherein a shut-off valve, controlled by the pressure or the temperature of the heat carrier in the solar collector. is connected upstream of the relief valve.

6. A system as claimed in any of the pre ceding claims, having a circulating pump for the heat carrier flowing through the solar collector, wherein the circulating pump is controlled by a switch in dependence on the pressure or the temperature of the heat carrier.

7. A system according to any of the preceding claims, wherein the solar collector is used in plurality.

8. A system for supplying heat by means of a solar collector, substantially as hereinbefore described with reference to the accompanying drawing.