For decades, glass has been used to protect consumers in automobiles from external conditions such as rain, wind and bugs. In the last few decades, developments in glass technology have enabled glass to provide significantly more value to car companies and consumers. Glass technology has allowed cars to become quieter, to protect consumers from harmful ultraviolet (UV) rays, to remain cooler in the summer, and to provide a user interface for various displays, among other benefits.

The most recent developments in glass technology have been recognized by the state of California in its drive to reduce carbon dioxide (CO₂) emissions. California recently approved a regulation that will require energy-efficient glass in all vehicles sold in California, starting with the 2012 model year. It is expected that other states will follow suit, and the annual reduction of national—and, ultimately, global—CO₂ emissions could be in the billions of kilograms.

Efficiency and Comfort

One of the most pressing issues in the world today is climate change. Scientists around the world have concluded that greenhouse gas emissions need to be controlled, and the automobile has been identified as a major contributor of CO₂ emissions. In response, the automotive industry has developed several technologies that reduce CO₂ emissions. Some of the most common of these technologies involve the source of power for the engine.

The introduction of hybrid electric vehicles (HEVs) was received enthusiastically by the media and environmentalists. The interest shown by consumers, as well as the support provided by governments around the world, has led to the development of plug-in hybrid electric vehicles (PHEVs) and complete electric vehicles (EVs). All of these technologies, along with others that help with the propulsion of the vehicle, have been demonstrated to provide a direct link to fuel consumption and hence to CO₂ emissions.

Traditional metrics of measuring fuel consumption have centered around the fuel efficiency associated with propulsion of the vehicle. In reality, several other sources of fuel consumption exist that are not directly related to the movement of the vehicle.

The vehicle also acts as a sanctuary for consumers while they are in it. The consumer expects to be safe, secure and comfortable while in the vehicle. Vehicle manufacturers have gone to great lengths to ensure that consumers are as comfortable in the vehicle as they would be in a home or office environment.

The climate control systems in vehicles, for example, can be far superior to those found in most homes in the U.S. When a consumer gets into a car that has been sitting in the sun for a while, the vehicle’s air conditioning system is so powerful that it cools the extremely hot interior down to a comfortable temperature in minutes. The large air conditioning systems required for this level of cooling consume a lot of energy. Highly sophisticated glass technology can be used to reduce this energy consumption.

Background

Enlarge this picture Figure 1. Normalized solar power distribution.

Solar energy consists of three segments (see Figure 1). The UV spectrum makes up only about 5% of the total energy, but it has been shown to cause skin cancer with extensive exposure and can also cause damage to interior materials used in vehicles. Comprising about 43% of solar energy, visible light is what enables us to see and is thus regulated for vision glass applications. The remaining 52% of solar energy comes in the infrared (IR) spectrum, which can therefore be a significant source of heat in vehicles if it is allowed to enter the vehicle.

Glass technology has long been used to reduce the heat load in automobiles. The use of solar-absorbing glass has provided significant improvements over the clear glass that had been in use for many decades. Solar-absorbing glass soaks up the solar energy and then re-radiates it. In a moving vehicle, most of the absorbed energy is convected away by the wind. However, in a parked or slow-moving vehicle, a lot of that energy gets radiated into the vehicle.

Enlarge this picture Figure 2. By reflecting the IR energy away from the glass, glazing reduces the absorbed energy in the glass and thus reduces the energy radiated into the vehicle.

To address this situation, a glazing technology was developed several years ago that reflects the IR portion of the solar spectrum while still allowing the visible light to be transmitted.* By reflecting the IR energy away from the glass, the glazing reduces the absorbed energy in the glass and thus reduces the energy radiated into the vehicle (see Figure 2). The glazing reflects over 400% more energy from the surface than conventional absorbing glass.

Sputtering technology is used to deposit nano-layers of several materials to achieve the IR reflective performance. The glass produced using this technology can reject more than 50% of the solar energy while a vehicle is parked.

Testing conducted in conjunction with the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) has shown that use of the glazing in a vehicle can reduce internal breath air soak temperatures by as much as 5°F. This reduction in interior soak temperature leads to an 11% reduction in the air conditioning compressor load, and thus a 2.2% improvement in fuel economy over the U.S. Environmental Protection Agency (EPA) test cycle that includes the use of air conditioning.

The reduction in soak temperature also means that the consumer is more comfortable when first entering the vehicle, and the vehicle is able to reach an acceptable temperature sooner once the air conditioning is turned on. Testing by the NREL showed that the time to comfort can be as much as 30% faster.

* Sungate IR Reflective glazing, developed by Pittsburgh Glass Works (then PPG Industries).  

A New Solution

Enlarge this picture Figure 3. The new glazing was shown to reduce the breath air soak temperature by as much as 12°F.

Recently, a new automotive glass glazing was developed that takes this performance even further.** The technology rejects almost 97% of IR energy while still maintaining the 70% visible light transmission required for automotive vision glazing.

The solar heat load reduction of the new glazing was tested in a vehicle as part of a project led by the Society of Automotive Engineers. The NREL-run study was designed to look at the impact of heat load reduction on the air conditioning workload and the fuel economy of the vehicle. The new glazing was shown to reduce the breath air soak temperature by as much as 12°F (see Figure 3). This head load reduction would reduce the air conditioning workload by as much as 25%. It has been shown by the NREL and the EPA that a 30% heat load reduction can save the U.S. 2.5 billion gallons of fuel and over 22 billion Kg of CO₂ emissions annually.

Enlarge this picture Figure 4. The glazing configuration vehicle had the highest impact in the UDDS drive cycle.

As vehicles become more fuel efficient, heat load reduction technologies become even more important. When the engine is optimized for the highest levels of fuel efficiency, the relative amount of energy used for auxiliary loads, such as air conditioning, grows higher. To test this concept, a study was conducted with the NREL on a Toyota Prius hybrid vehicle that was modified to be a PHEV. Testing was done with a simulated heat load reduction using a glazed windshield and rear window. The base case was the vehicle with standard glass. The two configurations were run through an EPA Urban Dynamometer Driving Schedule (UDDS, for city driving) and a US06 Drive Cycle (for highway driving).

The vehicle with the new glazing had the highest impact in the UDDS drive cycle, with the adjusted, utility-factor weighted fuel economy increasing from 36.8 mpg for standard glass to 42.9 mpg for the glazed glass, a difference of 6.1 mpg (see Figure 4). In addition to this fuel savings, the temperature in the vehicle was still cooler for the glazed case by 4.5°F after the vehicle had run through its drive cycles with the air conditioner on for both cases.

Multiple Benefits

Testing has shown that developments in advanced automotive glazing can help improve vehicle efficiency while increasing consumer comfort. In addition, solar load reduction technologies can save consumers money in the form of reduced fuel expenses while also reducing greenhouse gas emissions and U.S. dependence on foreign oil in the process.

For additional information, contact Pittsburgh Glass Works, LLC at 30 Isabella St., 5th Floor, Pittsburgh, PA 15212; e-mail info@pgwglass.com; or visit www.pgwglass.com.