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.
Elon Musk confirmed that Tesla is currently in talks with “one major automaker about licensing Full Self-Driving (FSD)”.
Back in 2021, Musk did say that he had early discussions with other automakers about licensing self-driving technology, but that didn’t lead to anything.
Last year, the CEO made an announcement that Tesla would be open to licensing Autopilot and FSD to other automakers.
However, earlier this year, Musk said that “automakers don’t believe Tesla Full Self-Driving is real”.
Now, the CEO has given an update about the FSD licensing effort during the conference call following the release of Tesla’s Q1 2024 results.
Musk announced that Tesla is “in talks with one major automaker about licensing Full Self-Driving.”
The CEO didn’t reveal which major automaker Tesla is talking to, but he did say that there’s “a good chance” a deal is signed this year.
However, Tesla’s management did mention that even if a licensing deal comes this year, it would likely be 3 years before an OEM can implement it into a vehicle program.
Tesla plans to supply its self-driving on-board computers and cameras to OEMs and license them the software, which Tesla currently sells for $8,000 or $99 a month.
Electrek’s Take
I could see Tesla convincing one or two OEMs now that it has v12, which is much more viable than anything it had before – giving a much-needed credibility boost to its self-driving effort.
When it comes to actual automakers, Tesla does seem to be ahead for level 4 autonomous driving. Waymo is obviously ahead as it is commercially deployed already, albeit with a different geo-fenced approach. But it’s also not an automaker.
If we talk about automakers outside of China, other than Mercedes-Benz with its level 3 system, Tesla is leading, in my opinion.
I could see an automaker like Ford being interested. Tesla has been getting closer to the company in recent years, for example, it was the first to adopt NACS. The company also had some bad luck with investments into self-driving, like partnering with Argo Ai, which went under.
The company could be interested in off-loading autonomy completely to Tesla – even though it is a big concession.
I am sure that if it does happen, the move will be criticized because Telsa has yet to achieve self-driving. However, if v12 can build enough confidence to show a clear path to get there, I can see a deal happening quick because as Tesla highlighted, it will take years to integrate the technology into another OME’s vehicle program.
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Elon Musk announced that Tesla may start selling its Optimus humanoid robot next year. The automaker plans to use the robot in its own factory by the end of the year.
A few months ago, Tesla unveiled “Optimus Gen 2”, a new generation of its humanoid robot that should be able to take over repetitive tasks from humans.
The new prototype showed a lot of improvements compared to previously underwhelming versions of the robot, and it gave some credibility to the project, which was laughed off by many when first announced with a dancer disguised as a robot for visual aid a few years ago.
Tesla believed it to be possible by leveraging its AI work on its self-driving vehicle program and expertise in batteries and electric motors. It argued that its vehicles are already robots on wheels. Now, it just needs to make them in humanoid forms to be able to replace humans in some tasks – primarily repetitive and dangerous tasks.
In a previous update on Optimus, Tesla CEO Elon Musk claimed that the “Optimus stuff is extremely underrated.” The CEO said that the demand could be as high as 10 to 20 billion units.
He went as far as “confidently predicting” that Optimus will account for “a majority of Tesla’s long-term value.”
The CEO sees everyone having a Tesla Optimus robot at home on top of them taking over a lot of manufacturing and service jobs.
With the release of Tesla’s Q1 2024 financial results, Musk gave an update on the timing for the rollout of Optimus. The CEO says that Optimus is already performing factory tasks inside its lab. He believes that Optimus will be used to perform real tasks inside actual Tesla factories by the end of the year.
Furthermore, Musk said that he believes Tesla could start selling its Optimus humanoid robot to customers outside of the company by the end of 2025.
The CEO again reiterated that he expects Optimus to represent most of Tesla’s revenue and overall value eventually.
Musk previously said that he expects Optimus to cost “less than half of a car” – so closer to $25,000.
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GreenPower (Nasdaq: GP) today announced the launch of its customizable EV Star Utility Truck, an electric all-purpose utility truck.
The EV Star Utility Truck is upfitted by GP Truck Body, a GreenPower subsidiary, on the GreenPower EV Star Cab & Chassis. The electric utility truck is GP Truck Body’s 10th truck body upfit.
It has a 118 kWh battery, a range of up to 150 miles, and a typical payload capacity of 5,500 pounds that can increase up to 6,000 pounds.
It can DC fast charge at 60 kW in around two hours and has a wireless DC fast charging option. At Level 2, up to 19.2 kW AC, it can charge in around eight hours.
GreenPower’s EV Star Utility Truck can be customized to meet the needs of various vocational applications and utility use cases, including agriculture and landscape, carpentry, construction, electrical, heating and cooling, and plumbing.
It’s equipped with optional power sources, providing accessible power through built-in plugs to accommodate mobile tool charging. Drill need charging? Plug it in on the truck and continue to your next job.
The front box of the EV Star Utility Truck has an optional full pass-through capacity, allowing for oversized tools and supplies. It offers tailored contractor body configurations, coming in a standard bed size of 16 feet, with the option to customize the length.
In addition to the EV Star Utility Truck, GP Truck Body also offers dry freight, refrigerated boxes, aluminum stakebeds, steel and aluminum flatbeds, and service bodies.
Read more: This new electric school bus has a 300-mile range
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