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.
Renewables and nuclear provided 40.9% of the world’s power generation in 2024, passing the 40% mark for the first time since the 1940s, according to a new global energy think tank Ember report.
Renewables added a record 858 TWh in 2024, 49% more than the previous high in 2022. Solar was the largest contributor for the third year running, adding 474 TWh to reach a share of 6.9%. Solar was the fastest-growing power source (+29%) for the 20th year in a row.
Solar has doubled in just three years, providing more than 2,000 TWh of electricity in 2024. Wind generation also grew to 8.1% of global electricity, while hydro – the single largest renewable source – remained steady at 14% of global electricity.
“Solar power has become the engine of the global energy transition,” said Phil MacDonald, Ember’s managing director. “Paired with battery storage, solar is set to be an unstoppable force. As the fastest-growing and largest source of new electricity, it is critical in meeting the world’s ever-increasing demand for electricity.”
Ember’s sixth annual Global Electricity Review, published today, provides the first comprehensive overview of the global power system in 2024 based on country-level data. It’s published alongside the world’s first open dataset on electricity generation in 2024, covering 88 countries that account for 93% of global electricity demand, as well as historical data for 215 countries.
What drove the rising power demand
The analysis finds that fossil fuels also saw a small 1.4% increase in 2024 due to surging electricity demand, pushing global power sector emissions up 1.6% to an all-time high.
Heatwaves were the main driver of the rise in fossil generation, accounting for almost a fifth (+0.7%) of the increase in global electricity demand in 2024 (+4.0%), mainly through additional use of cooling. Without these temperature effects, fossil fuel generation would have risen by only 0.2%, as clean electricity generation met 96% of the demand growth not caused by hotter temperatures.
“Amid the noise, it’s essential to focus on the real signal,” continued MacDonald. “Hotter weather drove the fossil generation increase in 2024, but we’re very unlikely to see a similar jump in 2025.”
Aside from weather effects, the increasing use of electricity for AI, data centers, EVs, and heat pumps is already contributing to global demand growth. Combined, the growing use of these technologies accounted for a 0.7% increase in global electricity demand in 2024, double what they contributed five years ago.
Clean power will grow faster than demand
Ember’s report shows that clean generation growth is set to outpace faster-rising demand in the coming years, marking the start of a permanent decline in fossil fuel generation. The current expected growth in clean generation would be sufficient to meet a demand increase of 4.1% per year to 2030, which is above expectations for demand growth.
“The world is watching how technologies like AI and EVs will drive electricity demand,” said MacDonald. “It’s clear that booming solar and wind are comfortably set to deliver, and those expecting fossil fuel generation to keep rising will be disappointed.”
Beyond emerging technologies, the growth trajectories of the world’s largest emerging economies will play a crucial role in defining the global outlook. More than half of the increase in solar generation in 2024 was in China, with its clean generation growth meeting 81% of its demand increase in 2024. India’s solar capacity additions in 2024 doubled compared to 2023. These two countries are at the forefront of the drive to clean power and will help tip the balance toward a decline in fossil generation at a global level.
Professor Xunpeng Shi, president of the International Society for Energy Transition Studies (ISETS), said: “The future of the global power system is being shaped in Asia, with China and India at the heart of the energy transition. Their increasing reliance on renewables to power demand growth marks a shift that will redefine the global power sector and accelerate the decline of fossil fuels.”
Read more: Made-in-America solar just got a big win in Louisiana
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.
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The next-gen LEAF is almost here, and it’s looking better than ever. This isn’t the electric hatch you are used to seeing. Nissan’s new LEAF EV has more range, a fresh crossover design, and yes, it can finally charge up at Tesla Superchargers with an NACS port. With the official reveal just around the corner, someone already spotted the new LEAF at a Tesla charger in Canada.
Nissan is launching the new LEAF in the US and Canada
A little over a week ago, we finally got our first look at the third-generation LEAF. Nissan’s iconic electric hatch has grown into a “sleek and spacious family-friendly crossover.”
The US and Canada will be the first to see the reimagined LEAF later this year. It will join the Ariya in Nissan’s North American EV lineup as it looks to spark growth in one of its most important markets.
Based on the CMF-EV platform, the same one underpinning the Ariya, Nissan promises the new LEAF will have “significant range improvements.” Although no other details were revealed, Nissan’s vehicle programs chief, Francois Bailly, told TopGear.com that it’s expected to have WLTP driving range of up to 373 miles (600 km).
It will likely be lower on the EPA scale, but anything even close to 300 miles would be a major improvement over the current 212 EPA-estimated miles offered on the 2025 LEAF SV Plus.
The next-gen LEAF will also be Nissan’s first EV to feature an integrated NACS charging port. With its official debut later this year, the new model is out for testing and was just caught testing at a Tesla Supercharger in Canada.
If you didn’t know what vehicle it is, the LEAF is hardly recognizable. The new image from KindelAuto gives us a closer look at the new crossover design. It almost looks like a Tesla sitting in front of the charger.
The new LEAF is one of 10 new and refreshed Nissan vehicles set to launch in the US and Canada. It will arrive later this year, followed by the fourth-gen Rogue in 2026, which will be available as a PHEV for the first time.
Nissan also plans to build a new “adventure-focused SUV” at its Canton, Mississippi, plant in late 2027. The teaser shows what appears to be a rugged electric Xterra. We’ll have to wait for more details on that one.
Nissan will reveal additional info about the upcoming LEAF mid-year. Check back soon for more updates.
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The Port of Barcelona launched the Ecocat Tres, a highly efficient, all-electric commuter ferry powered by Molabo’s ARIES i50 electric motors.
Ecocat Tres is the latest zero-emission ferry in Bus Nàutic’s growing electric fleet, providing clean transportation between the Drassanes and Llevant wharves. In just its first three months, the Bus Nàutic service logged over 125,000 sustainable trips. Operated by ALSA and backed by the Port of Barcelona, the initiative offers locals and visitors an eco-friendly way to travel, cutting down on road congestion and air pollution in the bustling city.
Built by Spanish shipbuilder Metaltec Naval, Ecocat Tres is a 15-meter aluminum catamaran that carries up to 84 passengers. It even includes a rooftop deck, offering extra seating and a breezy ride across the port. The ferry runs every 15 to 30 minutes for at least 12 hours each day, with the entire trip taking about 10 minutes.
Under the deck are two powerful 48V Molabo ARIES i50 motors, enabling the electric ferry to hit a top speed of 12 knots. Cruising at its regular operational speed of 5 knots, Ecocat Tres can run efficiently for up to 21 hours on a single charge, making it highly reliable for daily commuters.
Molabo’s motors have a low-voltage setup, which makes them safer to maintain compared to traditional high-voltage electric systems. Passengers also enjoy a smoother, quieter ride thanks to significantly reduced noise and vibrations onboard. Azimut Marine supplied the full propulsion and energy system, which includes two ARIES 50 kW electric drives, 36 batteries providing a total of 216 kWh, fast chargers, and integrated solar panels. Impressively, solar power alone can cover up to 40% of the ferry’s energy needs.
Ecocat Tres will cut around 90 tons of CO2 emissions each year, making a positive impact on Barcelona’s ambitious climate goals.
Port of Barcelona president José Antonio Carbonell said, “This 100% electric, zero-emission passenger ferry is helping us reshape mobility in the port and accelerate the decarbonization of our operations.”
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FTC: We use income earning auto affiliate links. More.
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