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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.

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.


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IEA downgrades oil demand growth forecast as prices heat up on elevated Middle East tensions

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IEA downgrades oil demand growth forecast as prices heat up on elevated Middle East tensions

An oil pumpjack is shown near the Callon Petroleum vicinity on March 27, 2024 in Monahans, Texas. 

Brandon Bell | Getty Images

The International Energy Agency on Friday downgraded its forecast for 2024 oil demand growth, citing “exceptionally weak” OECD deliveries, a largely complete post-Covid-19 rebound and an expanding electric vehicle fleet.

In its latest monthly oil market report, the IEA said it had revised down its 2024 oil demand growth forecast by around 100,000 barrels per day (bpd) to 1.2 million bpd.

The global energy watchdog said that it expected the pace of expansion to decelerate even further to 1.1 million bpd next year “as the post-Covid 19 rebound has run its course.”

The IEA’s report comes amid a rebound in oil prices on elevated Middle East tensions, with energy market participants closely monitoring the prospect of supply disruptions from the oil-producing region.

Iran, which is a member of the Organization of the Petroleum Exporting Countries, has vowed to retaliate after it accused Israel of bombing its embassy in the Syrian capital of Damascus earlier this month.

The attack has ratcheted up tensions in a region already grappling with the ongoing Israel-Hamas war. Israel has not claimed responsibility for the attack.

International benchmark Brent crude futures with June delivery traded 0.8% higher at $90.45 per barrel on Friday at 9:30 a.m. in London, while U.S. West Texas Intermediate futures with May delivery rose nearly 1% to trade at $85.84 per barrel.

“We’re seeing the surge in [electric vehicle] sales, especially in China and also in Europe, really taking into gasoline demand, but also in the United States,” Toril Bosoni, head of oil industry and markets division at the IEA, told CNBC’s “Street Signs Europe” on Friday.

“There has been a lot of talk about sales not increasing as much as maybe was expected, but EV sales and increased fuel efficiencies in the car fleet is lowering gasoline demand, at least in advanced economies and particularly in China.”

Asked about some of the main concerns relating to oil supply security, Bosoni replied, “We are watching, obviously, the Middle East very closely. The continued tanker attacks in the Red Sea is of key concern, but also escalating tensions between Iran and Israel, and then we’re seeing tensions between Russia and Ukraine continue, with attacks on Russian refineries.”

“So, there are several tension points in the oil market today that we’re watching very closely that could have major impacts … if there would be any significant outages,” she added.

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Tesla unveils new Sport Seats to absorb Model S Plaid’s insane power

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Tesla unveils new Sport Seats to absorb Model S Plaid's insane power

Tesla has unveiled new Sport Seats for the Model S Plaid to absorb the electric supercar’s insane power better.

While it’s in the form of a family sedan, the Model S Plaid could easily pass as an electric supercar with its 1.99-second 0 to 60 mph acceleration.

That’s more power than anyone would need, but it is fun.

Some Model S Plaid owners even like to take the fun to the racetrack. When cornering, you can really feel the Gs on the racetrack.

Tesla’s Model S seats are comfortable, but they are not designed for super-spirited driving, which the rest of the vehicle enables.

Today, Tesla decided to address the issue with the release of new Sports Seats:

They obviously feature much more pronounced side support. Here are the main features of the seats:

  • Increased lateral support
  • Modular seat architecture for comfort & support, plus same 12-way power adjust, heating & ventilation
  • High performance suede for increased grip & reduced weight

Here’s another look at the new seats:

The seats are now standard for the $90,000 Model S Plaid and included on all cars built since the beginning of the month.

Electrek’s Take

We had known new sports seats were coming to the new Model 3 Performance, which is expected to be unveiled any day, but it makes sense that the Model S Plaid would get them first.

The vehicle’s level of performance deserves sports seats.

I am surprised that Tesla is making it standard rather than a paid option, but we’ll take it.

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Daily EV Recap: China looks to export EVs by the hundreds of thousands

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Listen to a recap of the top stories of the day from Electrek. Quick Charge is now available on Apple PodcastsSpotifyTuneIn and our RSS feed for Overcast and other podcast players.

New episodes of Quick Charge are recorded Monday through Thursday and again on Saturday. Subscribe to our podcast in Apple Podcast or your favorite podcast player to guarantee new episodes are delivered as soon as they’re available.

Stories we discuss in this episode (with links):

Formula E again delays debut of 600kW mid-race charging

This lamppost EV charger just went commercial in the US

Tesla releases more details on Powerwall 3, confirms cheaper stack coming

Electric cars are saving Americans billions — even people who don’t drive them

China is exporting so many EVs that it needs more ships – a lot more

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