Passive Cooling in a Tiny House
Originally published on RMI.org.
By John Matson
As the world warms and the demand for cooling increases, many homes will require an “all of the above” approach to keep cool without further contributing to global warming. That can include high-performance cooling systems that use climate-friendly coolants and consume relatively little energy, as well as building design approaches that offset the need for mechanical cooling in the first place.
This tiny, ultra-efficient Passive House was built in just 10 days in #Australia http://t.co/glUiZVSN1o pic.twitter.com/pjYxo496ti
— The Architect’s Newspaper (@archpaper) February 10, 2015
In this post, we look at some passive cooling strategies that help keep an innovative tiny house comfortable during California summers, without the use of a mechanical cooling system.
Brett Webster, a manager in RMI’s Carbon-Free Buildings program, lives in a 170-square-foot home in Sonoma County, California. Brett and his partner helped design and build the solar-powered tiny house as part of a graduate project, and they have lived in the demonstration home for about five years. The home itself was built on a 24-foot-long trailer and can be hitched up to a truck for relocation. So even though Brett and his partner have lived in their tiny home for years, they have moved twice in that time between Northern California locations (and their respective microclimates).
Strategic Shading
The walls of the tiny house are clad in reclaimed cedar slats over one-inch-thick panels of cork, which provides a layer of continuous insulation, reducing the thermal bridging of the wooden wall framing. Because the carbon sequestered in cork trees can exceed the carbon emissions of producing cork products, cork is often considered a carbon-negative material. The cedar siding is separated from the cork by an air gap, which allows the wooden slats to shade the cork and absorb solar radiation, while slowing the rate of heat transfer directly to the house. The walls of the structure are insulated with recycled denim to further limit heat gain in warm weather and heat loss in cool weather.
Pulley-mounted shade awnings, made from cedar slats to match the siding, cover the largest expanse of glass on the tiny house: a sliding-glass door at the entry to the home. Webster says that the shade structure extends far enough to block solar radiation from pouring through the glass entryway in summer, but it can let in sunlight and heat in winter, when the sun is lower in the sky.
The ability to shade the windows in summer and admit sunlight during the winter is critical to maintaining passive comfort in the house. The windows that the design team chose for the tiny house are well-insulated (low U-value) but are also designed to let the sun’s heat in (high solar heat gain coefficient), because the Bay Area is mostly a heating-dominant climate zone. During the summer, when that heat gain is not desirable, shading the windows is a necessity.
Ceiling and Roof
A layer of BioPCM phase change material in the ceiling acts like thermal mass to absorb and store heat that would otherwise warm the interior space. Adobe buildings and concrete-walled structures similarly benefit from thermal mass that prevents the interior from becoming overheated during the day. But phase change material is lightweight, making it more appropriate for applications like the ceiling of a tiny house, and it doesn’t have the carbon footprint of concrete. (Cement production alone accounts for about 8 percent of global carbon emissions.)
The phase change material, which comes embedded in sheets that can be rolled out between ceiling joists like high-tech bubble wrap, melts from solid to liquid at 77 degrees F (25°C). As it changes phases, the material absorbs a lot of thermal energy, preventing the temperature from exceeding 77 degrees until its heat-absorbing capacity has been reached, like a sponge that can’t soak up any more water.
The tiny house’s roof is designed to harness much of the sun’s energy and reject the rest. A 2.3-kilowatt solar array shades much of the tiny house’s roof and feeds into a Tesla Powerwall to store electricity for nighttime use. The “cool roof” is also covered with a light-colored acrylic roofing membrane to minimize heat gain from solar radiation.
Some Energy Required (But Not Much)
In addition to the passive cooling approaches described above, the tiny house relies on a few efficient electric devices to provide airflow and ventilation. Even though they don’t qualify as strictly “passive” technologies, ceiling fans and other efficient electric devices have long gone hand-in-hand with passive cooling approaches. The ventilation and airflow systems in the tiny house consume very little energy and allow the building to remain comfortable without a dedicated mechanical cooling system.
A high-efficiency overhead ceiling fan consumes 4–18 watts of electricity and ensures occupant comfort in warmer temperatures. “Airflow creates a cooling sensation that’s extremely effective,” Webster says. According to the US Department of Energy, using a ceiling fan can significantly offset the need for air conditioning, allowing occupants to raise the thermostat by about 4 degrees F without sacrificing comfort.
The well-insulated structure is designed to be closed off to the outside during hot days in the summer, so the windows do not provide any natural ventilation during the daytime. The tiny house therefore relies on an energy recovery ventilator to bring fresh air into the house. An energy recovery ventilator uses a heat exchanger to reduce the thermal energy of the outside air before it enters the house, thereby providing ventilation without flushing warm air into the building. In the winter, it does the reverse, using the heat of the outgoing stale air to warm the incoming fresh air.
Unplugging
The tiny house’s passive design and minimal energy requirements for ventilation make it fully capable of going off-grid, especially in the summer months when solar energy is abundant. And even if most of us aren’t ready to commit to living in a 170-square-foot house on wheels, the lessons from Webster’s tiny house and other passive homes provide a powerful reminder: Even for energy-intensive applications like cooling, with thoughtful design, you can do a lot with a little.
Image gallery courtesy of RMI.
Italian electric motorcycle manufacturer Energica has just been handed a lifeline. Previously owned by US company Ideanomics, the famed motorcycle brand entered insolvency late last year after a period of financial duress prevented it from making payroll and continuing production.
Now, a new group of investors from Singapore has stepped in to take over.
The news was shared on Energica’s YouTube channel, and the company confirmed on LinkedIn that “The judicial process undergoing the sale of Energica has received an offer with a significant deposit from investors based in Singapore.” Energica says that the investors, who so far remain unnamed, “are enthusiasts that believe in, and share the common values of Energica.”
While it’s not certain how the buyout and revival will unfold, it appears that Energica is planning on getting the band back together. “If the process comes through successfully,” the company explained, “the same team behind Energica will be entrusted to run the operations, and we will continue creating cutting-edge technologies for our customers.”
With many of Energica’s impressive electric motorcycles already in circulation from years of sales leading up to the 2024 bankruptcy, the company seems focused on starting by supporting those riders. ” Our first order of business is to support the customers and community. The judicial process will be completed in 60 days, and we will continue to share updates during the time.”
Energica rose to fame by building high-performance electric motorcycles in Modena, Italy, and was one of the early pioneers in the premium electric two-wheeler space. Its lineup includes models like the Experia electric touring bike and the Ego sportbike. The company previously supplied race bikes for the MotoE World Cup until Ducati took over the role in 2023.
After being acquired by US-based Ideanomics in 2021, Energica initially benefited from an injection of capital that helped expand production and dealer networks. But Ideanomics itself has faced serious financial trouble, becoming unable to invest in the future of Energica.
Energica’s future prospects seemed dim at the time of its insolvency in 2024, but the uncertainty appears to be clearing with the hope that new owners can breathe fresh life into the company.
Even so, Energica’s core competency is building the fastest, most powerful, and longest range production electric motorcycles the world has ever seen, and that’s not exactly an inexpensive enterprise. Combined with current market trends that favor smaller, lighter, and less expensive commuter-spec electric motorcycles, it begs the question of whether or not a newly revived Energica will find a receptive market, or whether the company will be forced to expand the scope of its products to match better the type of electric motorcycles that are selling today.
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Chinese carmaker XPeng is getting perilously close to bringing its AeroHT consumer eVTOL concept to market, thanks to a $250 million Series B round that’s set to accelerate the company’s modular “flying car” production plans.
XPeng subsidiary AeroHT had its first successful proof of concept test flight ahead of the brand’s annual 1024 back in 2023, where the company unveiled a pair of flying car designs. The X3 is an actual flying “car” that can drive, park, and take off on its own, and a second, modular eVTOL that folds up into the back of an electric van called the Land Aircraft Carrier.
That vehicle pair, shown at CES in January, was set to begin production this year, with the eVTOL component set to begin production in 2026 – and that’s looking a lot more likely thanks to the new infusion of capital!
AeroHT at CES 2025
Xpeng Aeroht raised $150 million in Series B1 funding last August, before launching its Series B2 funding round. The most recent announcement that the company has secured an additional $100 million in its Series B2 funding round brings the total amount raised to more than $750 million, with a $1B pre-revenue valuation.
CNEVPost reports that company aims to establish itself as a commercial pioneer in urban air mobility ahead of a potential IPO – and may get there sooner than later, thanks to several hundred pre-orders at the $280,000 projected price.
Electrek’s Take
Scooter Doll said it best, writing, “this footage (of the AeroHT test flight) is as scary and concerning as it is exciting and awe-inspiring.” Which is to say that these things are real, they seem like they’re getting built, and they seem like they’ll sell well enough to convince at least one or two remaining boomers that the flying car they’ve been promised their whole lives is – finally! – coming to market.
Here’s hoping.
SOURCE: Xpeng, via CNEVPost; gallery photos by the author.
If you’re considering going solar, it’s always a good idea to get quotes from a few installers. To make sure you find a trusted, reliable solar installer near you that offers competitive pricing, check out EnergySage, a free service that makes it easy for you to go solar. It has hundreds of pre-vetted solar installers competing for your business, ensuring you get high-quality solutions and save 20-30% compared to going it alone. Plus, it’s free to use, and you won’t get sales calls until you select an installer and share your phone number with them.
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Flooring manufacturer Beauflor USA just turned on the biggest rooftop solar system by capacity in metro Atlanta — and it’s now powering part of its Georgia factory.
The new 1,040 kW system in Cartersville officially beats metro Atlanta’s previous rooftop solar record of 1,034 kW. The new array produces enough energy to power more than 100 homes. The system is expected to cover about 10% of Beauflor’s electricity needs and cut its carbon emissions by about 920 metric tons annually.
“This solar installation represents our commitment to sustainable manufacturing practices while making sound business decisions,” said Emile Coopman, continuous improvement manager at Beauflor. He added that the system is designed with room to grow: “This is the first step toward more renewable energy.”
The company partnered with Cherry Street Energy to install the nearly 2,000-panel system, which was completed in less than four months. Cherry Street invested $1.8 million into the project and is covering all construction and maintenance costs through a 30-year energy procurement agreement. Beauflor will buy solar power directly from Cherry Street, allowing it to avoid upfront capital costs while still lowering its energy bills.
“As Georgia’s manufacturers ramp up production amid rising costs for grid energy, sophisticated operators seek ways to quickly and sustainably address their energy needs,” said Cherry Street CEO Michael Chanin. “On-site solar with no capital expense delivers just that: reliable, affordable electricity.”
Chanin added that the system’s power output is especially impressive: “The previous record-holder for metro Atlanta’s largest rooftop solar required over 4,000 panels. We’re using less than 2,000 to reliably generate even more power.”
Read more: This is New Jersey’s largest high-rise residential rooftop solar array
The 30% federal solar tax credit is ending this year. If you’ve ever considered going solar, now’s the time to act. To make sure you find a trusted, reliable solar installer near you that offers competitive pricing, check out EnergySage, a free service that makes it easy for you to go solar. It has hundreds of pre-vetted solar installers competing for your business, ensuring you get high-quality solutions and save 20-30% compared to going it alone. Plus, it’s free to use, and you won’t get sales calls until you select an installer and share your phone number with them.
Your personalized solar quotes are easy to compare online and you’ll get access to unbiased Energy Advisors to help you every step of the way. Get started here.
FTC: We use income earning auto affiliate links. More.
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