| 摘要 |
A solar water heating system under normal operating conditions permits water to be circulated by a pump from a hot water storage tank through a one-way check valve and a solar collector back into the hot water storage tank when energy can be transferred from the solar collector to the water passing through. When the solar collector drops to a temperature where it is no longer desirable to transfer energy to the water, the pump ceases operation. If the outside ambient temperature drops further to a level where the water in the system affected thereby would be in danger of freezing, the pump is electrically energized by means of a freeze sensor to circulate the warmer water from the storage tank through the solar collector back to the tank. The water storage tank has a standby electrical heating unit. If electrical power fails, causing the pump to cease operation, a flow bypass means is opened to permit water to have reverse flow from said tank through said solar collector and back into the tank by natural convection. The reverse flow bypass means permits reverse flow due to convection around the one-way check valve and the pump, if the pump is one which provides a restriction to reverse flow.
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