| 摘要 |
PROBLEM TO BE SOLVED: To make the flow of heat medium proper at all times even under different installation conditions by controlling the rotational frequency of a pump based on an arbitrarily selected reference temperature and a detected temperature of an objet to be melted or the heat medium. SOLUTION: When a snowfall sensor 1 detects snowfall, a boiler 3 and a pump 4 start to operate and heat medium is circulated in a heat medium pipe line 2. In this case, when a detection temperature of geothermal sensor 5 is lower than a first reference temperature, the rotational frequency of the pump 4 is set one (1). When the detection temperature is not less than the reference temperature but lower than a second reference temperature, on the other hand, the rotational frequency is set two (2). Further, when the detection temperature is not less then the second reference temperature, the rotational frequency is set three (3). The flow per unit time in the line 2 becomes high as the temperature of heat medium becomes high according to variation of viscous coefficient, in this case. An arbitral target flow rate can be maintained by reducing the rotational frequency of the pump 4 in order according to a rise in the detection temperature.
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