Abstract: The present invention includes a heat storage tank (1) with a built-in suction chamber (2), a first heat source unit (R-1) and a first pump (P-1) for pumping up water from the high-temperature side (3) of said heat storage tank (1) and supplying the chilled water into said suction chamber (2), a low-temperature heat exchanger (5) for exchanging heat between water and an antifreeze solution, a second pump (P-2) for pumping up water from said suction chamber (2) and supplying the water chilled by the antifreeze solution in said low-temperature heat exchanger (5) to the low-temperature side (4) of said heat storage tank (1) and a second heat source unit (R-2) and a third pump (P-3) for cooling the antifreeze solution in an antifreeze solution tank (6) and feeding it to said low-temperature heat exchanger (5), and is designed to variably control the flow rates of said first and second pumps (P-1 and P-2) in dependence upon their suction temperatures.

Abstract: A tube type freezing unit of the present invention employs as a low-temperature heat accumulating material an aqueous solution of bromide of a low concentration. A plurality of thin tubes are accommodated in a shell, and a non-freezing liquid or a refrigerant is passed into the shell around the tubes. A sherbet-like slush is generated in a freezing mode by filling the tubes with the aqueous solution of bromide of a low concentration which serves as the low-temperature heat accumulating solution and then by passing a non-freezing liquid having a temperature of about -5.degree. C. or a refrigerant whose vaporization temperature is about -5.degree. C. around the tubes which contain the aqueous solution of bromide in a stationary state. The aqueous solution of bromide does not freeze. So, the sherbet-like slush is generated in the solution. An aqueous solution of bromide of a low concentration has a freezing point of about -1.degree. C.