Science 101: warm air rises while cold air sinks. This simple fact makes it harder to warm up a car during the winter. The basic automotive climate control system provides heating, but it also makes the air too dry. Hyundai and Kia recently unveiled the world’s first infrared knee warmer.
The core element the infrared knee warmer used is carbon fiber. Carbon fiber is a very efficient material for heaters because it has low heat capacity (the amount of heat energy needed to raise the temperature of an object or unit of matter by one degree Celsius). Hyundai and Kia filed patents in Korea, the U.S., China, and Germany, regarding the structure and the system of their infrared knee warmer. Senior Research Engineer Sola Chung in Total Thermal Management Research Lab talks about it.
Q. Tell us the story of the development of the infrared knee warmer.
The customers have been telling us the old car heaters are not strong enough to warm lower bodies. Besides, they were not heating the air fast enough. People in Korea and, especially in Russia, demanded a new heating system for their cars because their feet were always soaking wet for constant snowing. The warm air coming out from the heater underneath their seats did not stay and kept rising.
One option for the new heating system was to use a radiant heat warmer. The problem here was that it would cost more money to put more parts in a car. It also needed new materials to bear much higher temperatures. After years of development, we finally created the infrared knee warmer. The Hyundai Venue and Kia Seltos will be the first to have the system, and we will expand its use for other models in the future.
Q. How effective is the infrared knee warmer?
We tested the system at an outside temperature of 0 degrees Celsius. The driver’s knees were as warm as 23 degrees Celsius under the conventional climate control system, and the knee temperature did not exceed 25 degrees Celsius even after 15 minutes. On the other hand, the temperature of the driver’s knee exceeded 35 degrees Celsius after the warmer was turned on(6cm between the knees and the warmer). Normally people start to feel the warmth from 34 degrees Celsius. We expect women and toddlers, who are more sensitive than men, will especially like the infrared knee warmer since it does not make the air dry.
Q. How efficient is the infrared knee warmer?
Unlike internal combustion vehicles use the heat from the engine, electric vehicles use PTC heaters that have automatic power adjustments in response to the in-cabinet temperature conditions. The problem is that the PTC heaters are not very fuel-efficient (the vehicle’s range declines 20%). It gets more important in Korea, where the Government offers financial incentives for increasing the vehicle’s range.
When seven auxiliary infrared heaters are placed in a cabin at an outside temperature of -7 degrees Celsius, it decreased 17% of the energy used, compared to when using the PTC heater only. The range increased by 15% when simulated.
Q. The warmer uses carbon fiber heating wires. What are the advantages of it?
Carbon fiber has a rapid temperature rise since it has low heat capacity. Besides, carbon fiber infrared heaters are more energy-efficient than others. They also protect the passengers’ skin from burns because they contain less energy.
Q. Why are the wires curvy-shaped?
There are more wires in the same amount of space compared to a linear structure. You can also put more touch sensors in a warmer for better performance.
Q. Tell us about the structure of the heating system.
An infrared warmer comprises five major components: base to put wires in, carbon fiber wires for heating, electric circuits to supply power, touch sensors, and cover. Inside a warmer are a controller and a temperature sensor to regulate a setpoint.
Q. Is there any safety device for the warmer?
Firstly, touch sensors attached to the heating element prevent the skin from burning. While the warmer can reach operating temperatures of up to 110 degrees Celsius, it won’t harm your skin because of its low heat capacity. The anti-burn system controls the temperature below 45 degrees Celsius within 3 minutes after the touch sensor detects human skin. Also, the warmer emits less energy when the outside temperature rises. The chances of burning your skin are very slim.
Q. Is there any safety device for the warmer?
We used Polyethylene terephthalate (PET or PETE) in the form of fabric to cover the heating wires. This material is commonly used for making plastic bottles. After a lot of experiments, we concluded that the material for the wire cover should feature low heat capacity. Leather, for example, has relatively higher heat capacity, which means it stores heat energy well and can burn your skin. Non-woven fabric, on the other hand, has a low heat capacity and it also can be aesthetic for being a cover material.
Q. Can you use carbon fiber for other purposes?
The carbon fiber heating element has advantages over other materials. Some automakers are using it for seat warmers because of its high energy-efficiency. We, too, have considered putting the material next to a center console or inside a door trim. The cost efficiency is also increasing, so we expect that its use will grow rapidly.
Q. Is there another heating element?
Aside from the carbon fiber heating element, we are developing thin carbon films for heating. We think the film type will make it much easier for us to work with. Once it is proven to be efficient, safe, and strong enough, it will be applied to future products. So far, we are trying to develop carbon films that are high-temperature resistant.
Q. Can the infrared warmer work as the main heater of a car?
The structure of a cabin will change soon. This is one of the reasons why we are considering other applications of in-cabin infrared warmers. So far, we think using infrared warmers as auxiliary devices is best suited for vehicles’ climate control systems.
Q. What do you think the future climate control systems will be like in self-driving vehicles?
In my opinion, the climate control system will be much more efficient it is attached to the ceiling of a cabin. We expect that glass materials may replace metals, and it might be harder to install a climate control system on the ceiling. A cross-shaped frame on the roof will make it feasible then.
Having new climate control systems installed inside the seats is another option. Just like ventilated seats we use now, it will be efficient to maintain the body temperatures of the passengers. It will not be easy to design such seats, though. We will do our best until we could make everything our consumers want possible.
Photographs. Yoonsik Kim