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.
HAWESVILLE, KY – May 10
Plant workers drive along an aluminum potline at Century Aluminum Company’s Hawesville plant in Hawesville, Ky. on Wednesday, May 10, 2017. (Photo by Luke Sharrett /For The Washington Post via Getty Images)
Aluminum
The Washington Post | The Washington Post | Getty Images
Sweeping tariffs on imported aluminum imposed by U.S. President Donald Trump are succeeding in reshaping global trade flows and inflating costs for American consumers, but are falling short of their primary goal: to revive domestic aluminum production.
Instead, rising costs, particularly skyrocketing electricity prices in the U.S. relative to global competitors, are leading to smelter closures rather than restarts.
The impact of aluminum tariffs at 25% is starkly visible in the physical aluminum market. While benchmark aluminum prices on the London Metal Exchange provide a global reference, the actual cost of acquiring the metal involves regional delivery premiums.
This premium now largely reflects the tariff cost itself.
In stark contrast, European premiums were noted by JPMorgan analysts as being over 30% lower year-to-date, creating a significant divergence driven directly by U.S. trade policy.
This cost will ultimately be borne by downstream users, according to Trond Olaf Christophersen, the chief financial officer of Norway-based Hydro, one of the world’s largest aluminum producers. The company was formerly known as Norsk Hydro.
“It’s very likely that this will end up as higher prices for U.S. consumers,” Christophersen told CNBC, noting the tariff cost is a “pass-through.” Shares of Hydro have collapsed by around 17% since tariffs were imposed.
The downstream impact of the tariffs is already being felt by Thule Group, a Hydro customer that makes cargo boxes fitted atop cars. The company said it’ll raise prices by about 10% even though it manufactures the majority of the goods sold in the U.S locally, as prices of raw materials, such as steel and aluminum, have shot up.
But while tariffs are effectively leading to prices rise in the U.S., they haven’t spurred a revival in domestic smelting, the energy-intensive process of producing primary aluminum.
The primary barrier remains the lack of access to competitively priced, long-term power, according to the industry.
“Energy costs are a significant factor in the overall production cost of a smelter,” said Ami Shivkar, principal analyst of aluminum markets at analytics firm Wood Mackenzie. “High energy costs plague the US aluminium industry, forcing cutbacks and closures.”
“Canadian, Norwegian, and Middle Eastern aluminium smelters typically secure long-term energy contracts or operate captive power generation facilities. US smelter capacity, however, largely relies on short-term power contracts, placing it at a disadvantage,” Shivkar added, noting that energy costs for U.S. aluminum smelters were about $550 per tonne compared to $290 per tonne for Canadian smelters.
Recent events involving major U.S. producers underscore this power vulnerability.
In March 2023, Alcoa Corp announced the permanent closure of its 279,000 metric ton Intalco smelter, which had been idle since 2020. Alcoa said that the facility “cannot be competitive for the long-term,” partly because it “lacks access to competitively priced power.”
Similarly, in June 2022, Century Aluminum, the largest U.S. primary aluminum producer, was forced to temporarily idle its massive Hawesville, Kentucky smelter – North America’s largest producer of military-grade aluminum – citing a “direct result of skyrocketing energy costs.”
Century stated the power cost required to run the facility had “more than tripled the historical average in a very short period,” necessitating a curtailment expected to last nine to twelve months until prices normalized.
The industry has also not had a respite as demand for electricity from non-industrial sources has risen in recent years.
Hydro’s Christophersen pointed to the artificial intelligence boom and the proliferation of data centers as new competitors for power. He suggested that new energy production capacity in the U.S., from nuclear, wind or solar, is being rapidly consumed by the tech sector.
“The tech sector, they have a much higher ability to pay than the aluminium industry,” he said, noting the high double-digit margins of the tech sector compared to the often low single-digit margins at aluminum producers. Hydro reported an 8.3% profit margin in the first quarter of 2025, an increase from the 3.5% it reported for the previous quarter, according to Factset data.
“Our view, and for us to build a smelter [in the U.S.], we would need cheap power. We don’t see the possibility in the current market to get that,” the CFO added. “The lack of competitive power is the reason why we don’t think that would be interesting for us.”
While failing to ignite domestic primary production, the tariffs are undeniably causing what Christophersen termed a “reshuffling of trade flows.”
When U.S. market access becomes more costly or restricted, metal flows to other destinations.
Christophersen described a brief period when exceptionally high U.S. tariffs on Canadian aluminum — 25% additional tariffs on top of the aluminum-specific tariffs — made exporting to Europe temporarily more attractive for Canadian producers. Consequently, more European metals would have made their way into the U.S. market to make up for the demand gap vacated by Canadian aluminum.
The price impact has even extended to domestic scrap metal prices, which have adjusted upwards in line with the tariff-inflated Midwest premium.
Hydro, also the world’s largest aluminum extruder, utilizes both domestic scrap and imported Canadian primary metal in its U.S. operations. The company makes products such as window frames and facades in the country through extrusion, which is the process of pushing aluminum through a die to create a specific shape.
“We are buying U.S. scrap [aluminium]. A local raw material. But still, the scrap prices now include, indirectly, the tariff cost,” Christophersen explained. “We pay the tariff cost in reality, because the scrap price adjusts to the Midwest premium.”
“We are paying the tariff cost, but we quickly pass it on, so it’s exactly the same [for us],” he added.
RBC Capital Markets analysts confirmed this pass-through mechanism for Hydro’s extrusions business, saying “typically higher LME prices and premiums will be passed onto the customer.”
This pass-through has occurred amid broader market headwinds, particularly downstream among Hydro’s customers.
RBC highlighted the “weak spot remains the extrusion divisions” in Hydro’s recent results and noted a guidance downgrade, reflecting sluggish demand in sectors like building and construction.
— CNBC’s Greg Kennedy contributed reporting.
Danish energy giant Ørsted has canceled plans for the Hornsea 4 offshore wind farm, dealing a major blow to the UK’s renewable energy ambitions.
Hornsea 4, at a massive 2.4 gigawatts (GW), would have become one of the largest offshore wind farms in the world, generating enough clean electricity to power over 1 million UK homes. But Ørsted announced that it’s abandoning the project “in its current form.”
“The adverse macroeconomic developments, continued supply chain challenges, and increased execution, market, and operational risks have eroded the value creation,” said Rasmus Errboe, group president and CEO of Ørsted.
Reuters reported that Ørsted’s cancellation of Hornsea 4 would result in a projected loss of up to 5.5 billion Danish crowns ($837.85 million) in breakaway fees and asset write-downs. The company’s market value has declined by 80% since its peak in 2021.
The cancellation highlights significant challenges currently facing offshore wind development in Europe, particularly in the UK. The combination of higher material costs, inflation, and global financial instability has made large-scale renewable projects increasingly difficult to finance and complete.
Ørsted’s decision is a significant setback to the UK’s energy transition goals. The UK currently has around 15 GW of offshore wind, and Hornsea 4’s size would have provided almost 7% of the additional capacity needed for the UK’s 50 GW by 2030 target, according to The Times. Losing this immense project off the Yorkshire coast could hamper the UK’s pace of reducing dependency on fossil fuels, especially amid volatile global energy markets.
The UK government reiterated its commitment to renewable energy, promising to work closely with industry leaders to overcome financial and logistical hurdles. Energy Secretary Ed Miliband told reporters in Norway that the UK is “still committed to working with Orsted to seek to make Hornsea 4 happen by 2030.”
Ørsted says it remains committed to its other UK-based projects, including the Hornsea 3 wind farm, which is expected to generate around 2.9 GW once completed at the end of 2027. Despite the challenges, the company emphasized its ongoing commitment to the British renewable market, pointing to the critical need for policy support and economic stability to ensure future developments.
Yet, the cancellation of Hornsea 4 demonstrates that even flagship renewable projects are vulnerable in the face of economic pressures and global uncertainties, which have been heightened under the Trump administration in the US.
Read more: The world’s single-largest wind farm gets the green light
If you live in an area that has frequent natural disaster events, and are interested in making your home more resilient to power outages, consider going solar and adding a battery storage system. 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. They have 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 Advisers to help you every step of the way. Get started here. –trusted affiliate link*
FTC: We use income earning auto affiliate links. More.
The Tesla Roadster appears to be quietly disappearing after years of delay. is it ever going to be made?
I may have jinxed it with Betteridge’s Law of Headlines, which suggests any headline ending in a question mark can be answered with “no.”
The prototype for the next-generation Tesla Roadster was first unveiled in 2017, and it was supposed to come into production in 2020, but it has been delayed every year since then.
It was supposed to get 620 miles (1,000 km) of range and accelerate from 0 to 60 mph in 1.9 seconds.
It has become a sort of running joke, and there are doubts that it will ever come to market despite Tesla’s promise of dozens of free new Roadsters to Tesla owners who participated in its referral program years ago.
Tesla uses the promise of free Roadsters to help generate billions of dollars worth of sales, which Tesla owners delivered, but the automaker never delivered on its part of the agreement.
Furthermore, many people placed deposits ranging from $50,000 to $250,000 to reserve the vehicle, which was supposed to hit the market 5 years ago.
The official timelines from Tesla are pretty useless at this point since they haven’t stuck to any of them, but the latest official one dates back to July 2024 when CEO Elon Musk said this:
“With respect to Roadster, we’ve completed most of the engineering. And I think there’s still some upgrades we want to make to it, but we expect to be in production with Roadster next year. It will be something special.”
He said that Tesla had completed “most of the engineering”, but he initially said the engineering would be done in 2021 and that was already 3 years after the prototype was unveiled and a year after it was supposed to be in production:
Musk commented on the Roadster again in October 2024, but he didn’t reiterate the 2025 timeline. Instead, he called the new Roadster “the cherry on the icing on the cake.”
Tesla’s leadership has been virtually silent about the new Roadster since. Two Tesla executives even had to be reminded about the Roadster by Jay Leno after they “forgot” about it when listing upcoming new Tesla vehicles with tri-motor powertrain.
There was one small update about the Roadster in Tesla’s financial results last month.
The automaker has a table of all its vehicle production, and the Roadster was updated from “in development” to “design development” in the table:
It’s not clear if that’s progress or Tesla is just rephrasing it. Either way, it is not “construction”, which makes it unlikely that the Roadster is going into production this year.
If ever…
Electrek’s Take
It looks like Tesla owes about 80 Tesla Roadsters for free to Tesla owners who referred purchases, and it owes significant discounts on hundreds of units.
It’s hard for me to believe that Tesla is not delivering the new Roadster because the vehicle program would start about $100 million in the red, but at this point, I have no idea. It very well might be the reason.
However, I think it’s more likely that Tesla is just terrible at bringing multiple vehicle programs to market simultaneously. Case in point: it launched a single new vehicle in the last five years.
At this point, I think it’s more likely that the Roadster will never happen. It will join other Tesla products like the Cybertruck Range Extender.
FTC: We use income earning auto affiliate links. More.
-
Sports3 years ago‘Storybook stuff’: Inside the night Bryce Harper sent the Phillies to the World Series
-
Sports1 year agoStory injured on diving stop, exits Red Sox game
-
Sports2 years agoGame 1 of WS least-watched in recorded history
-
Sports2 years agoMLB Rank 2023: Ranking baseball’s top 100 players
-
Sports4 years ago
Team Europe easily wins 4th straight Laver Cup
-
Environment2 years agoJapan and South Korea have a lot at stake in a free and open South China Sea
-
Environment2 years agoGame-changing Lectric XPedition launched as affordable electric cargo bike
-
Business3 years agoBank of England’s extraordinary response to government policy is almost unthinkable | Ed Conway