The Perils and Paradox of Panoramic Sunroofs (Tianmu)
Why do some car owners resort to using umbrellas, wearing straw hats, or placing rags on their car roofs? The answer lies with owners of cars equipped with panoramic sunroofs (Tianmu), who face their own personal "roasting" experience every summer. Temperatures inside the car can reach scorching levels, sometimes even hot enough to fry an egg.
Why Panoramic Sunroofs Get So Hot
There are two main reasons why panoramic sunroofs can make car interiors so hot.
- Transparency: They allow direct sunlight and its associated heat to enter the vehicle.
- High Specific Heat Capacity: The glass used in panoramic sunroofs has a high specific heat capacity and thermal conductivity. This means it absorbs and stores a significant amount of heat compared to metal. The glass then radiates this heat, further warming the interior air.
Unlike traditional sunroofs, panoramic sunroofs often cannot be opened. This prevents ventilation and creates a positive feedback loop where heat accumulates at the top of the car, while cool air from the air conditioner struggles to reach the roof. This results in passengers experiencing localized heat, especially those who are taller.
The Rise of Panoramic Sunroofs
Despite the "烫头" (scalding head) problem, more and more new cars are equipped with panoramic sunroofs as standard. In 2024, nearly half of new energy vehicles (NEVs) feature this design. However, dealerships and manufacturers often emphasize the panoramic view and "high-tech" appeal, while downplaying the heat issue.
Why Car Companies Promote Panoramic Sunroofs
Car companies are keen on promoting panoramic sunroofs due to several advantages:
-
Space Saving: In the electric vehicle (EV) era, battery packs consume significant vertical space inside the car. Panoramic sunroofs offer a way to reclaim headroom. By replacing the metal roof and sunroof mechanisms with a thin glass panel, manufacturers can save about 5 cm of space. This allows for a lower chassis and better aerodynamics, without compromising interior space.
-
Weight Reduction: Panoramic sunroofs are lighter than traditional car roofs. A glass roof saves approximately 4kg compared to metal. Installing a standard sunroof, however, can add between 20 and 90kg due to the glass, sunshade, rails, and mechanical components. "Full panoramic sunroofs" which can be opened entirely can add even more weight (close to 50kg).
-
Safety: Despite being glass, panoramic sunroofs are designed to be as strong and rigid as metal roofs. They feature reinforced rings that distribute impact energy to the A, B, and C pillars of the car, offering comparable protection.
-
Cost Effectiveness: Panoramic sunroofs are relatively inexpensive. While a small sunroof can cost between 1,000 and 3,000 yuan, and a full panoramic sunroof system can range from 3,000 to 10,000 yuan, a panoramic sunroof averages only around 1,500 yuan.
-
Marketing Appeal: Panoramic sunroofs are attractive to consumers. The seamless integration of the windshield and roof, offering an unobstructed view of the sky, appeals to the perception of "high-tech" and luxury.
Attempts to Mitigate the Heat
Car companies have attempted to mitigate the heat problem with solutions like:
-
Double-Layered Silver-Coated Glass
-
Multi-Layer Light-Shielding Structures
-
Variable Tinting Smart Glass
-
Low-E Laminated Glass
These technologies can effectively block UV and infrared rays. However, they struggle to address the core issue: the glass itself heats up and radiates warmth. Even with advanced coatings, the temperature near the roof remains elevated, and the benefit of such technologies are only really felt further away from the sunroof.
Solutions and Recommendations
The best solution for the "烫头" problem is to either avoid buying a car with a panoramic sunroof altogether or to choose a model with a retractable sunshade. If neither is possible, owners can:
-
Slightly open the windows: This increases airflow and reduces heat accumulation near the roof.
-
Use a sunshade: Purchase and install a physical sunshade to block direct sunlight.
-
Improvise: Employ creative solutions such as cardboard, newspapers, or even grass to cover the roof and provide insulation.
{#