Thick film heating technology
The three heating methods used in new energy vehicle air conditioner heaters can be divided into three types according to the heating medium and heating method: air heating, water heating, and heat pump.
1. PTC Air Heater: Air heating method (heating element is resistance wire or PTC): The electric heating component is arranged in the air outlet channel of the air conditioner, and the air flows directly through the heating component and is heated and then blown into the car cabin.
2. PTC Water Heater: Water heating method (heating element is PTC or thick film heating): The heating element is arranged in the liquid flow channel of the component, and the heat is brought to the heat exchanger in the air outlet channel by circulating the heated liquid. The air flows directly through the heat exchanger, heated, and then blown into the car cabin.
3. Heat pump method: Although the energy efficiency ratio is relatively high when the ambient temperature is low in winter in northern regions, heating cannot guarantee the normal use of the vehicle, so it has not been used in domestic passenger cars.
The air heating method has the characteristics of a simple system and an easy layout. Because the temperature of the air heat exchange interface is high, the heating comfort of the passengers is not strong. In addition, the electric heating components entering the passenger car cabin pose a great safety hazard.
The water heating method can effectively improve the heating comfort of the passengers. The electric heating components are in the front cabin of the car, which is safer and more reliable, but the component manufacturing technology is more difficult. From a safety perspective, the water heating method is the mainstream of the future development of new energy vehicles.
Classification and characteristics of water heaters for new energy vehicles: From the perspective of the heating elements used, water heaters can be divided into two technical routes, PTC and HIC. Both types of products have mature applications in listed new energy vehicle models. PTC water heaters are represented by Eberspächer in Germany, and HIC thick film heating is represented by Webasto in Germany.
Due to their simple structure and few heat exchange interfaces, HIC thick film water heaters have the characteristics of high heat exchange efficiency, small size, and lightweight. It has the advantages of stable positive value, no power attenuation, and low thermal capacity and thermal resistance. Its good controllability and electrical performance without starting current impact are more obvious than PTC heating. The heat transfer efficiency of the HIC thick film heater is higher than that of the PTC heater can be explained by the theory of the second law of thermodynamics (entropy increase principle). Because the entropy of an isolated system never decreases automatically, and entropy increases in an irreversible process. In the heat transfer environment of a water heater, the heat transfer process conforms to the irreversible process described by the second law of thermodynamics, so the heat transfer efficiency mainly depends on the heat transfer temperature difference between high and low temperatures during the heat transfer process. When the fluid temperature is heated to the operating temperature (60-90℃), the operating temperature of the core heating element of the PTC heater is about 250℃, while the operating temperature of the core heating element of the HIC thick film heater is about 200℃. Therefore, the HIC thick film has a lower exchange temperature difference than the PTC, so it has a higher heating (heat transfer) efficiency (that is, less entropy increase).
