| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent freezing of a circuit by a method wherein when the water temperature in a circulation circuit or the outside air temperature lowers to a check reference temperature and a given time elapses after a circulation pump is stopped, the circulation pump is operated and when the lowest water temperature during that time is below a reference water temperature, the circulation pump is operated for a time longer than the check operation time. SOLUTION: The water temperature by a water temperature sensor is stored at a lowest water temperature memory and an initial water temperature memory, a timer is reset, and a circulation pump is operated at ST2. A water flow switch transmits a water flow detecting signal at ST3 and further, when the time measured by a timer is shorter than a check operation time at ST4, operation to re-store the detecting temperature of a water temperature sensor changing with the lapse of time stored in a lowest water temperature memory is repeated until a check operation time elapses at ST5, and a most cooled water temperature in water residing in a circulation circuit is stored in the lowest water temperature memory at SE6. When the water temperature is below a reference water temperature at ST9, the pump is operated for 60 minutes and water in the circuit is circulated at ST10 to reliably prevent the occurrence of freezing.</p> |
