An indirect freeze concentration system operating in accordance with a reversibleheat pump cycle includes a first tube-tube heat exchanger and a second tube-tube heat exchanger . Heat exchange between a selectively supplied feed stream and a low pressure low temperature refrigerant enables a solvent from the feed stream to freeze within the first tube-tube heat exchanger while vaporizing the low pressure low temperature refrigerant . A first compressor receives and compresses the low pressure vapor refrigerant to an intermediate pressure . Heat exchange between a pre-formed frozen solvent and the intermediate pressure refrigerant within a second tube-tube heat exchanger melts the frozen solvent and partially condensing the intermediate pressure refrigerant. A second compressor receives and compresses the vapours of the partially condensed intermediate pressure refrigerant to a high pressure refrigerant . Heat of the high pressure refrigerant is rejected to ambient temperature to obtain a condensed refrigerant which is re-circulated to the first tube-tube heat exchanger