By Ali Dashti
One world Trade Center, NY [1]
Have you ever wondered what your house would be without windows? I bet many of us picture ourselves in our dream home sitting around sipping on coffee in the morning, gazing through the windows, and observing a garden, the highway, or people watching in an urban city. We often value this serene experience of gazing out a window that draws natural light. Throughout many civilizations in the past, architects included some sort of opening for natural light to enter. We can see those openings embedded in the pyramids of Egypt, Greek temples in Athens, and in structures of our current times. Marvelous skyscrapers, such as the Burj Khalifa in Dubai-made entirely out of glass- or the One World Trade Center in New York City, are an indication of today’s prosperity and advancement. Glass and windows with enormous skylights and floor-to-ceiling windows in residential apartments are an architectural trend. This unfortunately comes at a great price to our primary home, our planet Earth.
Throughout the evolution of architecture, window systems have always been a major player in energy loss when compared to other components of a building’s envelope. Keeping that in mind, a significant attribute dictating modern advancements in construction and architecture is indoor air quality and climate control. Engineers and scientists along with companies and investors have worked together for years to come up with a system that enables us to be at home, comfortable in our nightgowns, enjoying a warm cup of tea while a blizzard is a window thickness away from us. This system is known as heating, ventilation and air conditioning (HVAC). With this system being so precise, we can create winters in cold harsh deserts like in Dubai’s indoor Ski resort or a hot and humid sauna room in freezing Alaska. This exponential demand of climate control in different buildings throughout various geographic locations has a significant cost to the energy consumption. This results in great use of fossil fuels triggering our worst nightmare: an increase in our carbon footprint via CO2 emissions. Scientists indicate that reducing an individual’s carbon footprint can help decrease greenhouse gas emissions and slow the effects of climate change.
According to the U.S Department of Energy, HVAC systems consume up to 48% of the total household energy usage. During winter, the heating system represents up to 42% of a typical household monthly usage. Air conditioning alone contributes to 8% of the total electricity generated in the U.S at a cost of over 15 billion dollars. Environmentally, the demand for heating, cooling, and hot water contributes to over 40% of all U.S. carbon emissions [2].
This data about the energy demands of building heating and cooling is increasingly untenable in the context of climate change. If the demand in air conditioning continues to increase throughout the years, it will trigger more waste gas byproducts released from gas and coal from power generation facilities. This alarming scenario creates a positive feedback loop just like the melting Arctic ice cap. Several scientists have predicted that the energy demand for indoor cooling could increase tenfold by 2050.
Now our purpose as members of our primary home, planet Earth, is to use our resources to innovate possible solutions to this dilemma. Just how we created these glorious civilizations that are degrading the planet, we can still use those same powerful tools to implement solutions and attempt to restore what we’ve lost. One key method to reduce demand in HVAC systems is to reduce the heat loss or gain in buildings. With regular walls enclosing a building, you can always add more layers, just like putting on a sweater, scarf, or a jacket to stay warm. When you are dealing with a window on the other hand, transparency is the primary requirement and the addition of layers is no longer simple. The materials you consider in your window system require specific building standards. You ask now, then what do we do?
A team of researchers, including myself Ali Dashti, led by several professors from different disciplines (Mechanical Engineering, Chemistry and Materials Science departments) at UCLA are currently working on a promising solution. The proposed method involves developing a material that will meet all the standards required for a coating on a window and provide outstanding performance in regulating energy of a building. Think of the perfect jacket for a freezing night during a camp out. this material will be the perfect jacket to your windows.
The material our team is working on is known as silica aerogel. It can achieve a rate of heat dissipation less than half the rate of insulating materials commonly used in buildings, such as glass wool or foam glass. With this material, we can imagine windows being as effective as a brick wall surrounding them. Coating this material onto single pane windows would save 1.2 quads of heating energy per year corresponding to 1.2% of the US yearly energy consumption. This is equivalent to 12 billion dollars per year. Now, we need to consider the challenges to manufacture those silica aerogels and implement a strategy to scale this production and commercialize it to the public [3,4].
During production, three major benchmarks will be analyzed for this material to pass as a coating system to windows with: insulation capability, transparency, and strength. Although silica aerogels have outstanding insulating properties, they are also blurry and commonly used for insulating containers or pipe systems, not windows. The optical properties of silica aerogels are governed by two central characters, phonons and photons. Phonons are vibrational waves that carry heat, while photons are light carriers. The Aerogel structure is made of a network of silica nanoparticles connected to each other, like pearls of a necklace. The nature of this pearl-like-necklace structure creates empty spaces known as pores in between. This porous structure is what triggers its insulating capability as the phonons scatter when they move through the interface between the emptiness and the solid nanoparticles, thus increasing the structure’s overall insulating performance. Photons scatter in a similar matter; the difference here would be that light is inhibited from traveling. When light scatters within a structure, the transparency is affected and usually reduced [5].
Our team at UCLA will need to optimize the perfect nanoarchitecture of the silica aerogel to achieve the best optical transparency for a window along with promising insulating properties. This can be done by reducing the photon scattering for the light to pass and increase phonon scattering to prevent heat passing. We concluded that higher porosity, which is an indication of the amount of void space within the structure, will allow more phonon scattering along with reduction in pore size. The challenge discovered with these conclusions was their effect on how strong this material will be while varying porosity and pore size. For a window solution to be commercialized to the public, specific strength requirements are needed, such as withstanding wind, human or animal interactions. When you increase porosity however, you are also increasing the amount of emptiness within the structure, which reduces its strength significantly. Our team is working on finding the best combination of porosity for preventing enough scattering of phonons; the perfect pore size to allow enough light to pass, and last but not least, the overall strength to withstand coating requirements for window solutions.
The figure above demonstrates the relationship between strength indicated by the maximum flexural stress and rigidity indicated by the young’s modulus with respect to porosity (porosity is the percent of emptiness in the silica aerogel). Using these plots, we can analyze and study the physical properties these coatings have in variation of pores and emptiness.
As demonstrated, developing such structures have proven to be challenging. These challenges hold a moral obligation that needs to be tackled by our society so as to ensure that we reduce the negative impacts on Earth. It is easy for us to forget and focus on our shallow problems, for example, a client demanding his architect to install bigger windows in the middle of a desert solely for cosmetic purposes. This client should think about that decision on a bigger scale and how it may impact the environment.
Energy consumption, as it applies to windows and buildings, is a crucial factor to climate change on our planet. Your choice of material for your window, facade, or roof could have a great impact on our primary home, planet Earth, and the future generations. Careful consideration to what materials to use or apply during the design stage of your dream house is as important as the implementation and construction stage. Let us build and innovate our cities with elegance yet environmentally clean designs.
References
- nabpilot.org/one-world-trade-centers-new-broadcast-transmission-facility/
- www.energy.gov/
- Galy et al., Computer generated mesoporous materials and associated structural characterization, Computational Material Science, 156-167, 2019
- Marszewki et al., Thick Transparent Nano-particle-Based mesoporous silica monolithic slabs for thermally insulating window materials, ACS Applied Nano Materials, 4547-4555, 2019
- Marszewki et al., Controlling Thermal Conductivity in Mesoporous Silica Films Using pore size and Nanoscale Architecture, The Journal of Physical Chemistry Letters, 2020
Ali is part of the 2019-2020 INFEWS program cohort and a PhD Student in the Mechanical Engineering at UCLA. The blog is part of the INFEWS Social Media Series.