Heat transfer fluid system for a vehicle

A heat transfer fluid system for a vehicle comprising an electric energy supply system, the heat transfer fluid system comprising:

• a heat transfer fluid circuit arranged for controlling a temperature of the electric energy supply system by means of a heat transfer fluid, and
• a heat transfer fluid storage tank defining a tank volume for the heat transfer fluid, the heat transfer fluid storage tank comprising:
• a partition dividing the tank volume into a first volume and a second volume, and
• a biasing device,
• wherein the partition is movable to/from any position between a minimum heat storage position corresponding to a minimum second volume, and a maximum heat storage position corresponding to a maximum second volume,
• wherein movement of the partition away from the minimum heat storage position corresponds to storing energy in the biasing device, and movement towards the minimum heat storage position corresponds to releasing energy from the biasing device;
• and
• the heat transfer fluid system further comprises:
• a valve assembly comprising one or more valves, the valve assembly being controllable to provide an electric energy supply system heating state of the heat transfer fluid system wherein release of energy from the biasing device produces a flow of heat transfer fluid from the second volume to the first volume via the heat transfer fluid circuit for heating the electric energy supply system.