1. Field of the Invention
This invention relates to a device for collecting solar heat by the use of a vacuum tube type heat collector having heat collecting plates and heat medium tubes.
2. Prior Art
This type of device is designed to accumulate a high-temperature heat medium in a heat accumulating tank by repeated operation of transferring a heat medium heated to high temperatures by a vacuum tube type heat collector to a heat accumulating tank and of feeding a low-temperature heat medium in the heat accumulating tank to a heat collector. Generally, the heat medium is circulated by a circulation pump between the heat collector and the heat accumulating tank, and the pump is driven when the temperature of the heat medium heated at the outlet portion of the heat collector is raised higher than a specified temperature or when the temperature on the side of the heat collector is higher by comparison between the heat medium temperature at the bottom of the tank and that at the outlet portion of the heat collector.
The vacuum tube type heat collector provides the advantage that the collector permits the free installation thereof in various ways such as horizontal installation, but it has the counterbalancing disadvantage that the point of space wherein the temperature is highest inside the heat collector is difficult of easy measurement as opposed to a plate type heat collector.
Under examples of heat controlling devices for a conventional vacuum tube type heat collector are included a device for controlling heat collection by an insolation sensor, a device for controlling heat collection by the temperature of a header portion (confluence of pipes through which a heat medium passes), and the like.
FIG. 1 shows a conventional type device for controlling the collection of heat by an insolation sensor. A low-temperature sensor 2 is disposed in the heat accumulating tank 1, and the insolation sensor 4 is installed in matching relation with respect to a degree of inclination of a heat collecting plate 3. The insolation is sensed by the sensor 4 and is compared by a heat collection controlling unit 5 with the low-temperature sensor 2 on the bottom side of the heat accumulating tank 1, and when it is approximately judged by the controlling unit 5 that collection of heat is possible, a pump 6 operates to collect heat.
A device for controlling the collection of heat by the temperature of the header portion is of the construction in which the header is provided with a sensor so as to sense the temperature of the header and that of the heat medium inside the header and in which when the temperatures of the header and the heat medium in the header become higher than the temperature of the heat accumulating tank to a certain set value, the heat collection pump operates and when the temperatures become lower than the set value, the pump ceases to operate.
FIG. 2 shows a flow chart representing the control of the above-mentioned device using an insolation sensor. In the figure, the reference character TL designates a temperature in the heat accumulating tank 1 detected by the low-temperature sensor 2, and I designates an insolation detected by an insolation sensor 4. FIG. 3 shows a relation between the insolation I and the temperature TL in the heat accumulating tank 1. Both of the aforementioned devices relate to a method of sensing the rough temperature in the insolation sensor and the header portion respectively, and, when the insolation sensor is used, the relation between the insolation and the temperature describes a secondary curve as shown in FIG. 3, and the characters I and TL are not brought into a relation of linear proportion. When the temperature of the header portion is sensed, transfer of heat from the heat collecting unit is delayed, thus the devices being reduced in performance, and positive control becomes impossible. When the insolation is reduced, or when the weather conditions change, or when the temperature of the open air is reduced, the devices are subject to external conditions to render it impossible to make accurate control.