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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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Tesla Model 3 prototype spotted ahead of rumored design refresh

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Tesla Model 3 prototype spotted ahead of rumored design refresh

A new Tesla Model 3 prototype with camouflage has been spotted in California ahead of a rumored refresh coming next year.

Over the last week, there have been rumors that Tesla is working on a Model 3 refresh that would come during the second half of 2023.

The project is reportedly codenamed ‘Highland’.

For a few years now, Tesla has been integrating its large casting technology into Model Y with single large casting parts replacing dozens of parts in the electric SUV.

This new technology has enabled Tesla to greatly improve manufacturing efficiency with Model Y compared to Model 3. CEO Elon Musk said that Tesla will bring the same technology to Model 3 eventually, but he couldn’t exactly say when.

The problem is that such an update to the Model 3 would temporarily slow down production and Tesla couldn’t afford that while it was still ramping up Model Y production.

However, Model Y production is now starting to exceed Model 3 production and it could be good timing for Tesla to update the Model 3 and use a design refresh to introduce the large from and rear casting.

Now a new Model 3 prototype has been spotted in Santa Cruz, California by Twitter user omg_Tesla/Rivian:

The Model 3 is equipped with manufacturer plates, which would indicate that it is owned by Tesla, and combined with the heavy camouflage in the front and back of the vehicle, it likely points to the automaker testing an updated version of the electric sedan.

However, not much can be discerned from the pictures thanks to the camouflage, which even covers large parts of the headlights.

Nonetheless, some commenters on Twitter did notice what could potentially be a camera embedded in the corner of the front right headlight:

It’s barely visible and therefore unconfirmed, but it would make sense to place a camera around that spot since Tesla’s current self-driving sensor suite has a blind spot around the bumper and it could also help with the creeping forward to see traffic before taking a turn in Full Self-Driving – something FSD Beta has issues with right now.

Tesla has always said that it would keep improving its Autopilot and Full Self-Driving hardware, but current owners who bought vehicles with the promise that self-driving will be enabled through software updates are concerned that Tesla might find that it would need a new sensor suite to achieve the promise.

What do you think about this Tesla Model 3 prototype? Is the camouflage hiding a Model 3 design refresh? A new Autopilot sensor suite? Let us know what you think in the comment section below.

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OPEC+ agrees to stick to its existing policy of reducing oil production ahead of Russia sanctions

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OPEC+ agrees to stick to its existing policy of reducing oil production ahead of Russia sanctions

Led by Saudi Arabia and Russia, OPEC+ agreed in early October to reduce production by 2 million barrels per day from November.

Vladimir Simicek | Afp | Getty Images

An influential alliance of oil producers on Sunday agreed to stay the course on output policy ahead of a pending ban from the European Union on Russian crude.

OPEC and non-OPEC producers, a group of 23 oil-producing nations known as OPEC+, decided to stick to its existing policy of reducing oil production by 2 million barrels per day, or about 2% of world demand, from November until the end of 2023.

Energy analysts had expected OPEC+ to consider fresh price-supporting production cuts ahead of a possible double blow to Russia’s oil revenues.

The European Union is poised to ban all imports of Russian seaborne crude from Monday, while the U.S. and other members of the G-7 will impose a price cap on the oil Russia sells to countries around the world.

The Kremlin has previously warned that any attempt to impose a price cap on Russian oil will cause more harm than good.

Oil prices have fallen to below $90 a barrel from more than $120 in early June ahead of potentially disruptive sanctions on Russian oil, weakening crude demand in China and mounting fears of a recession.

Led by Saudi Arabia and Russia, OPEC+ agreed in early October to reduce production by 2 million barrels per day from November. It came despite calls from the U.S. for the group to pump more to lower fuel prices and help the global economy.

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What’s the status of California’s upcoming $10M electric bike rebate program?

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What's the status of California's upcoming M electric bike rebate program?

California allocated $10 million for a rebate program to help make electric bikes more affordable. But hang on there; it’s not active quite yet.

The move is part of a years-long effort to help reduce the price of expensive electric bicycles for state residents. The ultimate goal is to make it easier for commuters to switch from car transportation to e-bike transportation.

It makes sense when you consider the long list of benefits. From cleaner air to reduced traffic and improved health/fitness, electric bikes solve many of the problems plaguing California (and the rest of the country).

But the path towards a statewide incentive program to reduce e-bike prices hasn’t been quick or easy.

specialized globe haul st e-bike

California has earmarked over $1 billion this year as incentives for electric cars and charging infrastructure, according to Streetsblog. That’s in addition to the billions already put into electric car incentives.

Back in 2019 electric bikes finally got the attention they deserved from lawmakers when California’s S.B. 400 was passed, which included a section that permitted electric bikes to be included in future clean air vehicle incentive programs.

That paved the way for the possibility of statewide e-bike rebate programs, but it didn’t actually create any.

Last year California got one step closer to that goal when it included a $10M allocation in the state budget for an e-bike rebate program. As Assemblymember Boerner Horvath said at the time:

“Making e-bikes more affordable is one of the most effective ways to get Californians out of their cars and reduce emissions. I’m thrilled that the full funding I requested for purchase incentives, education, and training is included in the budget we approved. This program represents a priority shift in the right direction and, once implemented, will help folks from all backgrounds choose a healthier, happier way to get around.”

That was another huge step in the right direction, but it hasn’t yet resulted in an active program.

That’s expected to begin in early 2023, with a number of key guidelines for California’s first statewide e-bike voucher program already laid out.

According to the California Bicycle Association, the program will create a $750 voucher for a standard electric bicycle and a $1,500 voucher for a cargo electric bicycle. There will be additional incentives for anyone whose income is under 225% of the federal poverty level (FPL) or who lives in disadvantaged communities.

But in order to qualify for the voucher, participants’ household income must be below 400% of the FPL, which amounts to $51,000 for a single person and $106,000 for a family of four at current figures.

The program will include Class 1 electric bikes (pedal assist up to 20 mph or 32 km/h) and Class 2 electric bikes (pedal assist and/or throttle up to 20 mph or 32 km/h), but will NOT include Class 3 e-bikes (pedal assist up to 28 mph).

Qualifying bikes must also either be purchased at a local bike shop in California, or online from a company that has “a business location in California”.

The move could see California align with other states that have created or already implemented electric bicycle incentives. Vermont became the first state in the US to offer a statewide e-bike rebate program. Oregon is also working on creating an e-bike incentive program that could soon become law, as New York attempts to do the same.

Many cities such as Denver, Colorado have also implemented their own local programs, though the funding is usually much smaller than statewide programs.

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