Automotive Passenger Heating

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The internal combustion engine produces heat energy. The vehicle interior heating system captures the heat from the engine and transfers the heat to the passenger compartment using heat exchangers. The hot coolant from the engine is transferred to the heater core located under the dash board as soon as the engine is started and before the thermostat opens. The passenger compartment need to be heated immediately during cold weather conditions or maintained at 70F, the most comfortable temperature for humans. A fan motor is placed in front of the heater core to force air into a complex large heating and AC duct assembly that distributes air to various locations inside the passenger compartment.

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The forced heated air can be used to defrost and windshield, which is a safety feature. The air can be automatically controlled by an active computer or manually controlled by a passive mechanical system. Extra air duct plumbing, heater cores, coolant hoses, and other controls can be used to distribute hot coolant and hot air into rear passenger compartments far way from the heat generated by the engine.

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Coolant Flow and Types of Heat Exchange

Engine Cooling System Animation

Convection

The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat. Convection was the original design method for cooling and heating system heat transfer.

Heat Exchanger

Equipment that transfers heat from one medium (such as water) to another (such as air). Heat exchangers, such auto radiators, are active devices that consume power in doing their work. The heat exchanger in the front of the car is called the radiator and is used to maintain engine temperature. The heat exchanger used in the passenger compartment is called the heater core and is primarily used to heat the passenger compartment.

Heater Core

The heater core is the primary method of heating the passenger compartment using hot liquid to heat cooler air. The ambient temperature in a confined or sealed space can be controlled using a hot or colder air supplied by the heating and air conditioning system.

Heater Control Valve

The heater control valve can be actively controlled by a computer to blend the amount of hot coolant entering the heater core, or the valve can be a passive manually controlled valve. Typically the climate control system does not need hot air when the passenger compartment is too hot. The heater core hot coolant control valve will either automatically or manually shut off hot coolant tot he heater core. Many modern designs allow hot coolant to always enter the heater core but use the heater and AC air ducting to control the amount of hot air blending with cool air by opening or closing the heater blend door.

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Heater Control Valve in car

Automatically Controlled Blended Heater Control Valve. This type of valve can be automatically controlled to blend the amount of hot coolant entering the heater core.

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Image of 4 - Port Heater Control Valve

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Air Ducting - controls and directs air to various air vents. The climate control module can automatically open and close air blend doors to control and direct air to vents. The hot air can be blended with cool air from the outside of the vehicle or with cool air from the air conditioning system. The blend doors can be controlled by using electronic motors with potentiometer type sensors on the doors used to determine door position. The temperature of the interior and the relative humidity can be measured using thermistors. The blend doors can also be actuated using vacuum controlled servos.

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The image above shows the integration of electrical and mechanical components. The image below shows the electronic schematic diagram.

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Most of the testing and electronics are contained in the climate control head. The climate control head is an electronic control module that controls the heating and air conditioning system. The driver or passenger can input their desired temperature and the computers active various motors to direct heated or cooled air. Temperature sensors monitor the compartment temperatures to maintain the desired temperature.

Front view of a climate control unit.

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Rear view of a climate control unit.

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The image below shows a blend door.

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The image below shows a blend door actuator.

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How and Auto HVAC System Works - Good Animation of Ducting

How a cooling system can be used to transfer heat.