Spraying on Energy Efficiency

Spraying on Energy Efficiency

An aerosol spray can.
Photo by PiccoloNamek, used under Creative Commons Attribution ShareAlike 3.0.

the heat loss from a typical house
The above illustration shows the heat loss from a typical house.
Image courtesy of action 21

Professor Jo Darkwa, Research Associate Oliver Su and PhD student Tony Zhou with their heat-regulating material. The material can be manufactured small enough to be sprayed or much bigger, like the one shown here.
Image courtesy of the University of Nottingham Ningbo China's Centre for Sustainable Energy Technologies

You can buy sprays to hold hair in place, protect skin from sunburn, and remove grass stains from white baseball uniforms. You can also buy sprays to eliminate odors, etch circuit boards, and sooth sore throats. So, maybe it isn’t too surprising that in the next few years you might be able to buy a spray that could dramatically increase the energy efficiency of your house.

If you have ever slept next to a drafty window during the winter, you know that heat escapes through buildings. But heat sneaks out of buildings in many ways, not just through drafty windows. Heat also escapes through ventilation systems, roofs, doors, and walls. According to some estimates, walls are responsible for up to 35% of the heat that escapes from un-insulated houses. Adding insulation to walls can dramatically reduce heat loss. Spraying the walls with a new material being developed by team of scientists from the University of Nottingham Ningbo China could reduce energy consumption and reduce electricity costs even more.

The material, called novel non-deformed energy storage phase change material, is designed kind of like a pharmaceutical tablet, with something called a phase changing material (PCM) on the inside surrounded by a coating. In this context, phase refers to the physical state of the material—for example solid, liquid, or gas. A phase change occurs when something changes from one state into another, such as from a liquid to a gas. In phase changing materials, a change in temperature causes the material to change from a solid to a liquid or vice versa.

As the temperature around a solid rises, the solid absorbs heat and its temperature increases. When the temperature of the material reaches a certain point, it starts to melt. The material continues to absorb heat as it melts, but that energy goes into the phase change. This means that the temperature of the material stays about the same during the melting process. Later, if the temperature around the liquid falls below the melting point, the liquid solidifies and releases the heat that it absorbed earlier. In this way, phase-changing materials can store energy.

If it takes a lot of heat to turn the solid into a liquid after the solid reaches its melting point, then you can store a lot of energy. This is the key to using a phase changing material to increase the energy efficiency of your house.

One of the challenges in creating energy efficient buildings is regulating the temperature—you want to take advantage of the heat from the sun that hits the building during the day and the cool air at night. However, you also want to maintain a comfortable temperature inside the house for 24-hours a day. If only you could store the heat that hits the house during the day and use it at night! This is where PCMs come in.

Imagine a wall containing a PCM that is “set” to absorb heat anytime the temperature in the room rises above 70°F. During the afternoon, when the sun is out and the room heats up, the PCM absorbs extra heat that causes its temperature to rise. When its temperature reaches the melting point, extra heat is still absorbed by the PCM, but it now goes into the phase change. In the evening, when the sun sets and the room cools to below 70°F, the PCM begins to solidify and releases the heat that it absorbed earlier in the day, which brings up the temperature in the room.

PCMs are nothing new, but the scientists at the University of Nottingham Ningbo China made some key improvements to existing PCMs and the coating that bring this idea closer to reality. The details of their design aren’t public, but they found a way to optimize the responsiveness of a PCM to heat and the time when extra heat is released. In addition, they found a way to manufacture the material at low cost and using materials local to their area, which makes it an attractive option for widespread use. The material can also be manufactured in different sizes and shapes for different applications.

The material isn’t ready for commercial use just yet, and researchers are still working on manufacturing it in spray form so that it can be used on already existing walls. They are also looking into how it can be mixed with paint or incorporated into wallpaper. In addition, the temperature at which the PCM starts absorbing heat is currently set during manufacturing, but ideally scientists would like a design that lets a user set whatever temperature he or she would like.

The potential applications of this new material go beyond regulating the temperature of buildings; scientists are also trying to incorporate the technology into electronics, lighting, and solar panels. All of these applications are limited by temperature—when their temperature is too high they become less efficient. If the new material can be used in these applications and sprayed onto walls, the material could dramatically reduce the amount of energy used by buildings.

For more information, check out these resources:
The University of Nottingham UK: Scientists invent heat-regulating building material
Read more about the details of the material in this press release from the University of Nottingham.

The University of Nottingham China: University invents heat-regulating building material
Find out more about this project and the University of Nottingham’s investments in energy research.

Zona Land Education: Changing of phase (or state)
Learn more about phase changes and their dependence on heat.

University of Colorado PhET Simulation: States of matter
Explore the difference three main states of matter (solid, liquid, gas) with this fun simulation.

Wikipedia: Phase-change materials (PCM)
Learn about specific phase-change materials, such as salt hydrates and fatty acids.