Due to the little loss heat of modern (diesel) engines during warm-up, PTC (Positve Temperature Coefficient) heaters are used to guarantee the fast warm up of the cabin. The inner resistance of the PTC increases for higher temperatures, therefore the heating power is automatically reduced for high temperatures (caused by high inlet temperatures, low mass flows, …).
Usually the PTC is positioned next to the conventional cabin heater and is mainly used during the warm up phase of the engine. To reduce the fuel consumption, the PTC is deactivated if the heating power of the engine is sufficient. Due to the characteristic of the inner resistance which will reduce the current and therefore also the heating power for higher temperatures, no additional emergency shut of system is required.
In this example the model of the PTC is reduced to an air-side point mass, including the thermal inertia and heat transfer coefficient. The amount of heat is calculated by the inner resistance (2D map) and a calculation controller.
Additionally the heater will be turned off if the cabin (air ducts) temperature exceeds 60 deg.Usable from release: KULI 9.1-0.01