Circulation system for a commercial vehicle

The circulation system (100) has a cooling circuit (10) that supplies first fluid (F1). A heating circuit (20) supplies second fluid (F2). A first heat exchanger (WT1) performs heat exchange with heating circuit, when first fluid is fed. The heat exchanger prevents communication with heating circuit, when first fluid is not fed. An expansion element (EO) of cooling circuit expands second heat exchanger (WT2) for receiving the first fluid fed from cooling circuit. The expansion element bypasses the second heat exchanger, if first fluid is not supplied to the second heat exchanger.