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.
More than $14 billion in US renewable and EV investments and 10,000 new jobs have been scrapped or put on hold since January, according to a new analysis from E2 and the Clean Economy Tracker. The reason: growing fears that the Republican-majority Congress will pull the plug on federal clean energy tax credits.
In April alone, companies backed out of $4.5 billion in battery, EV, and wind projects right before the House passed a sweeping tax and spending bill that would gut the federal tax incentives fueling the clean energy boom. E2 also found another $1.5 billion in previously unreported project cancellations from earlier in the year.
Now, with the Senate preparing to take up the so-called “One Big Beautiful Bill Act,” E2 says over 10,000 clean energy jobs have already vanished.
“If the tax plan passed by the House last week becomes law, expect to see construction and investments stopping in states across the country as more projects and jobs are cancelled,” said Michael Timberlake, E2’s communications director. “Businesses are now counting on Congress to come to its senses and stop this costly attack on an industry that is essential to meeting America’s growing energy demand and that’s driving unprecedented economic growth in every part of the country.”
Ironically, it’s Republican-led congressional districts – the biggest beneficiaries of the Biden administration’s clean energy tax credits passed in 2022 – that are feeling the most pain. So far, more than $12 billion in investments and over 13,000 jobs have been canceled in GOP districts.
Through April, 61% of all clean energy projects, 72% of jobs, and 82% of investments have been in Republican districts.
Despite the rising number of cancellations, some companies are still forging ahead. In April, businesses announced nearly $500 million in new clean energy investments across six states. That includes a $400 million expansion by Corning in Michigan to make solar wafers, which is expected to create at least 400 jobs, and a $9.3 million investment from a Canadian solar equipment company in North Carolina.
If completed, the seven projects announced last month could create nearly 3,000 permanent jobs.
To date, E2 has tracked 390 major clean energy projects across 42 states and Puerto Rico since the Inflation Reduction Act passed in August 2022. In total, companies plan to invest $132 billion and hire 123,000 permanent workers.
But the report warns that momentum could grind to a halt if the House tax plan becomes law. Since the clean energy tax credits were signed into law, 45 announced projects have been canceled, downsized, or closed entirely, wiping out nearly 20,000 jobs and $16.7 billion in investments.
What’s more, Trump’s Department of Energy announced today that it was killing more than $3.7 billion in funding for carbon capture and sequestration (CCS) and decarbonization initiatives. Eighteen out of 24 projects were awarded through DOE’s Industrial Demonstrations Program (IDP), which was made law in the Inflation Reduction Act. It aimed to strengthen the economic competitiveness of US manufacturers in global markets demanding lower carbon emissions, while supporting US manufacturing jobs and communities.
Executive Director Jason Walsh of the BlueGreen Alliance said in a statement in response to today’s DOE announcement:
The awarded projects that DOE is seeking to kill are concentrated in rural areas and red states. American manufacturers are hungry to partner with the federal government to bolster US industry. The IDP saw $60 billion worth of applications during the program selection process, a ten-times oversubscription.
President Trump claims to be a champion of American manufacturing, but today’s announcement is further evidence that he and his Secretary of Energy are liars.
Read more: Global energy giant RWE halts US offshore wind because of Trump
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A Tesla prototype was spotted at the Fremont factory in California, sparking speculation that it’s the new “cheaper Tesla”, but it looks like a regular Model Y.
A drone operator flew over the Fremont factory this week and spotted a Tesla prototype with light camouflage on the front and back ends.
The vehicle is making a lot of people talk on social media and the media as many think it could be a new “affordable model” coming to Tesla.
Other than the camouflage, the vehicle looks just like a regular Model Y:
It’s likely one of two things: a new “stripped-down Model Y” or a Model Y Performance.
Model Y Performance is the only version that Tesla hasn’t launched since the design changeover earlier this year.
The “stripped-down Model Y” is what will replace Tesla’s upcoming “affordable models.”
We have been reporting on this new vehicle program from Tesla for a while now.
It came to life just over a year ago as a pivot for Tesla after CEO Elon Musk canceled two cheaper vehicles that Tesla was working on, commonly referred as “the $25,000 Tesla”. Those vehicles were codenamed NV91 and NV92, and they were based on the new vehicle platform that Tesla is now reserving for the Cybercab.
Instead, Musk saw that Tesla’s Model 3 and Model Y production lines were starting to be underutilized as Tesla faced demand issues. Therefore, Tesla canceled the vehicles program based on the new platform and decided to build new vehicles on Model 3/Y platform using the same production lines.
We previously reported that these electric vehicles will likely look very similar to Model 3 and Model Y.
In recent months, several other media reports reinforced that, and Tesla all but confirmed it during its latest earnings call.
Considering this looks like a regular Model Y, it could be the new cheaper and less feature rich Model Y:
Some people are claiming that this vehicle looks smaller than the Model Y, but it’s difficult to tell as the black camouflage on the ends can confuse the eye.
It looks like a very similar size when it passes near other Tesla vehicles:
What do you think it is? Let us know in the comment section below.
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![Lumina hopes this 32-ton dozer makes them the Tesla of heavy equipment [video]](https://i0.wp.com/electrek.co/wp-content/uploads/sites/3/2025/05/lumina_2.png?resize=1200,628&quality=82&strip=all&ssl=1)
San Francisco-based founder Ahmed Shubber wants to emulate Elon Musk’s success in the electric construction equipment world – and he hopes his new, 32-ton electric bulldozer is enough to make the world sit up and take notice.
Since launching his company, Lumina, in 2021, Shubber has raised more than $8 million and grown the company’s global (!?) headcount to 26 people. That fruit of that team’s labor is the machine seen here. Dubbed “Moonlander,” the first-of-its-kind prototype occupies the physical footprint of something like a Caterpillar D6, but packs the blade and performance of the larger, more powerful Cat D9.
“A D6 could not push that blade,” David Wright, Lumina’s head of UK operations, told the assembled media at the Moonlander’s launch last week. “We can have that blade full of material, full dozing seven to nine cubic meters of material, for eight to 10 hours.”
Moving all that mass takes a lot of power – but getting that power back into the Moonlander’s batteries won’t take a lot of time, thanks to the machine’s 300 kW charging capability.
“Even if you spend all morning heavy dozing and you’re a bit worried about how much juice you’ve used — well, your operators are going to take a union-mandated lunch break, right?” asks Wright. “Plug it in, and in 30 minutes, you’ve put 50% of power back in again.”
Shubber says Lumina is working to raise from $20-40 million for its Series A round to develop the company’s next electric equipment asset: a 100-ton electric excavator called Blade Runner. And, in a truly Tesla-like fashion, Shubber says he’s on track to hit an ambitious $100 million revenue target sometime in the next 24 months.
And, of course, the Blade Runner will feature state-of-the-art autonomous operating technology (because: of course it will).
We’ll see how that unfolds in 2 year’s time, I guess. In the meantime, check out this Lumina promo video for Moonlander, below, then let us know what you think of Shuber’s take on an electric job site in the comments.
Lumina ML6 electric dozer video
SOURCE | IMAGES: Lumina; via Business Insider, Earthmovers Magazine.
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