GB1559676A

GB1559676A - Thermostatic control apparatus for solar heating systems

Info

Publication number: GB1559676A
Application number: GB4087775A
Authority: GB
Original assignee: ROBINSONS OF WINCHESTER Ltd
Current assignee: ROBINSONS OF WINCHESTER Ltd
Priority date: 1976-10-06
Filing date: 1976-10-06
Publication date: 1980-01-23

Description

(54) THERMOSTATIC CONTROL APPARATUS FOR SOLAR HEATING SYSTEMS (71) We, ROBINSONS OF WINCHESTER LIMITED, a British Company, of Robinson House, Winnall Industrial Estate, Winchester, Hampshire, 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 solar heating system in which a fluid, such as water, is heated by causing it to flow through a solar collector exposed to direct solar radiation and diffuse sky radiation.

Such systems are used for, or as auxiliary to other heating means for, swimming pools, domestic water heating and other purposes. It is importont that the system should only be operative when the temperature difference between the fluid entering and leaving the solar collector indicates a nett heat gain, and various automatic control devices are known for rendering the solar collectors in- operative, for example by stopping the flow of fluid therethrough, when the ambient conditions are such that there is no such net heat gain.

The present invention has for its object to provide a thermostatic control apparatus for solar heating systems which is simple and inexpensive to manufacture while providing efficient response to the variable factors of the ambient conditions. The variable factors which exist are: 1) Intensity of the direct solar radiation 2) Intensity of the diffuse sky radiation 3) Air temperature 4) Wind 5) Precipitation, e.g. rain 6) Temperature of the fluid in the re servoir 7) Flow rate of the fluid through the system 8) Various heat loss from the collector.

This is a function of the particular collector and depends on variables 1-7 for its instantaneous value.

Variable 7 is of a similar order of maG- nitude for most swimming pool systems, and thus, for such systems, is not a significant variable.

The invention consists in a thermostatic control apparatus for solar heating systems, comprising a thermostat of which the sensing element or medium is contained in a casing or housing, of a heat-conducting material and having a heat-absorbing external surface, which is positioned in front of a heat-reflecting surface so that, in use, solar radiation and diffuse sky radiation will both be directly incident on and reflected from the reflector on to the casing or housing, said casing or housing being exposed to the atmosphere whereby the temperature of the casing or housing, and thus the response of the thermostat. is dependent upon the intensity of the incident and reflected solar radiation and diffuse sky radiation, the air temperature and the wind.

The housing or casing is preferably so dis posed, in use, that it is also exposed to any precipitation whereby the thermostat is also responsive to variable factor 5.

When the thermostat, responsive to these variable factors, detects a temperature of or above that required for solar pick-up, it sends a control system to render the solar heating system operative. When it detects a temperature below that required for solar pick-up, the solar heating system is turned off.

The heat-reflecting surface is conveniently a polished sheet metal reflector which may be curved or polygonal in cross-section in one plane perpendicular to said surface and substantially linear in planes perpendicular to said one plane.

The casing or housing may comprise a generally rectangular sheet metal box having a matt black external surface. A con- ventional thermostat, such as used for controlling domestic central heating systems, is mounted in the box which may have opening providing limited air ventilation of the box. The box is mounted on a support and spaced in front of the reflector at a position which may be loosely described as the "focus" of the reflector. The reflector is provided with a mounting bracket so that it can be mounted with its principal axis inclined upwards.

The thermostat may optionally be equipped with a heating resistance, connected to respond to the temperature of the reservoir, e.g. a swimming pool, and associated with the sensing element to have the effect of turning down the switching tem pe.-atu.c of ili thermostat by a few degrees, e.g. 5"C, when the resistance is energised. The resistance is energised when the temperature of the reservoir is below a set value and is switched off when the reservoir reaches its normal desired temperature, whereby a higher intensity of sun is required to make the solar heating system operative when the reservoir is already heated to its normal temperature, than when its temperature is below the set value.

If desired the thermostat may incorporate an accelerator heater, associated with the sensing element, which is switched on when the detected temperature is below that required for solar pick-up, thereby providing auxiliary heating to make the thermostat respond more precisely at the desired minimum temperature.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, in which: Figure 1 is a side view of one embodiment of control apparatus according to the invention, Figure 2 is a front view looking in the direction of arrow A in Figure 1, Figure 3 is a perspective view of the apparatus from the front and one side, Figures 4 and 5 show modifications.

Referring to the drawings, the apparatus comprises a polished sheet metal reflector 1 having three substantially planar sections la, ib, ic, adjacent sections being inclined to one another at an included angle of 135 as is shown in Figure 2. The reflector is mounted on a bracket 2 so that the central section ib is inclined at 45 to the horizontal.

Supported in front of the reflector 1 by a bracket 3, secured to the central section 1 h of the reflector, is a rectangular sheet metal box 4 having a removable cover portion 5. The external surface of the box has a matt black or other finish having heat absorbing properties so that the box will be heated by the direct and diffuse solar radiation which is both directly incident on the box and is reflected thereonto by the reflector.

Enclosed within the box 4 is a thermostat, (not shown). This may be a proprietary thermostat, such as a Satchwell TLX type, e.g. Tax2356 or Tax2651, as used for controlling domestic central heating systems, the electrical connections to which are provided by a cable 6 passing through a hole in the back of the box 4.

In use, the apparatus is preferably installed with the reflector oriented as shown in Figure 1 and facing due south. In Figures 2 and 3, the areas 4a, 4b, 4c represent images of the box 4 as reflected in the sections la, ib, ic respectively. It will be apparent from a comparison of these two figures that as the sun moves in azimuth, the areas of the back and walls of the box 4 on which the sun's rays are directly reflected increase as the sun is further away from the due-south positon, thus compensating to some extent for the reduced intensity of the sun's rays as the sun rises and sets.

As the box 4 is exposed to the atmosphere, its temperature, and thus the response of the thermostat therein, is also dependent upon the air temperature, and the cooling effects of wind and rain, mist or other precipitation.

As above described the thermostat may also include means for making its operation responsive to the temperature of the reservoir. It may also include an accelerator heater for more precisely controlling the switching-on temperature.

The response of the thermostat may control the starting and stopping of a pump.

Alternatively, and preferably, it controls the operation of a motorised 3-way valve, or other valve system, which enables a fluid flow, for example through the filtration system of a swimming pool, at all times, the flow or part thereof only being directed through the solar collectors when the detected temperature is sufficient for solar pick-up.

While a particular embodiment has been described, it will be understood that various modifications may be made without departing from the scope of the invention. For example, the reflector need not comprise planar sections; it can be partly flat and partly curved, or entirely curved, e.g. parabolically, in one or more planes. Further, the casing or housing need not be a rectangular box. It may, as shown in Figure 4, be formed as a cylindrical casing 7 having a heat-absorbing external surface and containing the sensing element of the thermostat. The sensing element may control contacts in the enlarged compartment 8 at the end of the casing 7, or the casing may com- prise a thermostatic bulb containing a sensing medium, which is black to absorb radiation, and which is connected by capillary tubing to remote thermostat switching mechanism. The W-range of Satchwell thermostats are suitable for this embodiment.

Again, as shown in Figure 5, the casing or thermostatic bulb 7 (or 4) could be moun ted within a transparent or translucent tube 9, conveniently of plastics material, having the reflector surface 1 applied on the outside or inside surface of the tube 9.

WHAT WE CLAIM IS:- 1. A thermostatic control apparatus for solar heating systems, comprising a thermostat of which the sensing element or medium is contained in a casing or housing of a heatconducting material and having a heat-absorbing external surface, which is positioned in front of a heat-reflecting surface so that, in use, solar radiation and diffuse sky radiation will both be directly incident on and reflected from the reflector on to the casing or housing, said casing or housing being exposed to the atmosphere whereby the temperature of the casing or housing, and thus the response of the thermostat, is dependent upon the intensity of the incident and reflected solar radiation and diffuse sky radiation received, the air temperature and the wind.

2. Apparatus as claimed in claim 1, wherein said casing or housing comprises a generally rectangular metal box having a matt black external surface and is mounted on a support so as to be spaced in front of the heat-reflecting surface.

3. Apparatus as claimed in claim 2, wherein the casing or housing has openings providing ventilation of the box.

4. Apparatus as claimed in claim 1, 2 or 3, wherein the heat-reflecting surface is a polished metal reflector which is curved or polygonal in cross-section in one plane perpendicular to said surface and is substantially linear in planes perpendicular to said one plane.

5. Apparatus as claimed in claim 4, wherein said reflector is made of sheet metal.

6. Apparatus as claimed in any preceding claim, wherein the housing or casing is disposed, in use, so that it is also exposed to any precipitation.

7. Apparatus as claimed in any preceding claim, wherein the housing or casing also contains a heating resistance associated with the sensing element of the thermostat.

8. A thermostatic control apparatus for solar heating systems, constructed substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.

9. A thermostatic control apparatus for solar heating systems, constructed substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

10. A thermostatic control apparatus for solar heating systems, constructed substantially as hereinbefore described with reference to Fig. 5 of the accompanying drawings.

11. A solar heating sytem comprising a solar collector in combination with means for interrupting the flow of fluid therethrough and an apparatus as claimed in any preceding claim connected to control said interrupting means.

12. A solar heating system as claimed in claim 11, including means mounting the control apparatus with the heat-reflecting surface facing substantially due South and with its principal axis inclined upwardly.

13. A solar heating system, as claimed in claim 11 or 12, including an electric heating element associated with the sensing element of the thermostat, and means responsive to the temperature of the liquid in the reservoir heated by the system for energising the element substantially as and for the purpose hereinbefore described.

14. A solar heating system as claimed in claim 11, for heating swimming pools, substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ted within a transparent or translucent tube 9, conveniently of plastics material, having the reflector surface 1 applied on the outside or inside surface of the tube 9. WHAT WE CLAIM IS:-

1. A thermostatic control apparatus for solar heating systems, comprising a thermostat of which the sensing element or medium is contained in a casing or housing of a heatconducting material and having a heat-absorbing external surface, which is positioned in front of a heat-reflecting surface so that, in use, solar radiation and diffuse sky radiation will both be directly incident on and reflected from the reflector on to the casing or housing, said casing or housing being exposed to the atmosphere whereby the temperature of the casing or housing, and thus the response of the thermostat, is dependent upon the intensity of the incident and reflected solar radiation and diffuse sky radiation received, the air temperature and the wind.