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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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Daily EV Recap: 10,000 ton electric container ship

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Daily EV Recap: 10,000 ton electric container ship

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)

Joby completes pre-production eVTOL testing, segues into production prototype flight certification

A fully-electric 10,000 ton container ship has begun service equipped with over 50,000 kWh in batteries

This German startup is pioneering recyclable wooden wind turbine blades

US updates EV tax credit rules, enabling more electric cars to be eligible

Watch this autonomous excavator build a 215 foot retaining wall

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Daily EV Recap: 10,000 ton electric container ship

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You’re reading Electrek— experts who break news about Tesla, electric vehicles, and green energy, day after day. Be sure to check out our homepage for all the latest news, and follow Electrek on Twitter, Facebook, and LinkedIn to stay in the loop. Don’t know where to start? Check out our YouTube channel for the latest reviews.

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Republicans introduce bill that would hand US EV lead to China

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Republicans introduce bill that would hand US EV lead to China

Republicans have introduced a bill to eliminate the US EV tax credit in the Inflation Reduction Act, with the effect of slowing US progress on EV manufacturing, thus handing the lead in EV manufacturing to China.

How the Inflation Reduction Act helps American health, economy & manufacturing

The Inflation Reduction Act included hundreds of billions of dollars of climate spending, much of which was allocated to EV tax credits, both for personal and commercial vehicles. These credits were an extension and expansion of the $7,500 EV tax credit first introduced in 2008.

But those credits were limited to 200,000 cars per manufacturer, a cap which some manufacturers had hit and more were going to hit. So the Inflation Reduction Act improved access to those credits, removing the cap and setting up a way for the credits to be available upfront at the point of sale, meaning that lower-income buyers can qualify for the credits and get them immediately instead of waiting to file their taxes.

However, it limited the credits in some important ways as well – namely, by ensuring domestic production of electric vehicles in order to qualify, and setting limits on high-income buyers so the credits go to people who need them rather than those who don’t.

It also added a $4,000 used EV tax credit, which is limited to even lower income groups.

There are ways around some of these limitations and some restrictions have been loosened to allow industry to catch up. But these restrictions have nevertheless fueled a renaissance in American auto manufacturing, with many manufacturers announcing new factory investments in the US.

In fact, since President Biden started his EV push, oer $210 billion has been invested in new or expanded factory projects, which will create EV 250,000 jobs, with more to come.

These commitments stand to make the US into an EV manufacturing powerhouse – we’re already doing pretty well in EV production, largely led by Tesla. But Chinese EV production and demand are rising rapidly and automakers are waffling in the face of it – so government must be clear that we are committed to building this industry long-term.

The IRA also represents the largest climate commitment made by any country in the world, ever, by dollar value. The hundreds of billions of dollars allocated, largely to EV-related tax credits but also to many other climate programs, are a commitment still unmatched by any other country. As an added bonus, the bill actually brings in more revenue than it costs due to tax reforms targeting wealthy corporate and individual tax cheats.

Republicans are lying about their bill’s effects

So, no wonder that republicans, a party that seems to actively oppose anything that would benefit American manufacturing or the environment that Americans live in, would introduce an act to eliminate much of the benefit from the Inflation Reduction Act.

The new act, fittingly called the “ELITE” Vehicles Act (surely named for republicans’ elite fossil fuel donors which it aims to benefit at the expense of everyone else), aims to eliminate the clean vehicle credit for new, used, and commercial electric vehicles.

The act was introduced by John Barrasso, a republican senator from Wyoming who has received $526,425 from the oil & gas industry in this senate election cycle. Not only that, but Wyoming’s main industries are all tied to oil, putting the lie to the assertion that this act is intended to do anything more than benefit an industry which is responsible for millions of deaths per year.

The act’s advocates say that IRA credits – which are limited to lower-income buyers, particularly the used EV credit – are a giveaway to the wealthy (who don’t qualify for them), and that the credits allow Chinese EVs into the US (which they in fact explicitly disallow through the domestic manufacturing provisions mentioned above).

Notably, the act doesn’t do anything to get rid of the $760 billion in subsidies received by polluting industry each year in the US. This could be done through making polluters pay for the pollution they cause. If subsidy elimination were the act’s main concern, then that’s a rather big target that the act ignores – because, of course, the fossil fuel industry wouldn’t like it if their free license to harm the health of Americans were revoked.

The actual effect of rolling back these credits would be to make EVs less affordable for Americans, to ensure that those same Americans have more misery forced on them by pollution from the industry that bribes Barrasso, and to discourage American EV manufacturing and consumer uptake which would have the effect of handing over the lead in global EV manufacturing to China.

How Chinese auto benefits and the US is harmed by repealing the EV credit

Chinese EV manufacturing and consumer demand are both currently skyrocketing, and China is rapidly increasing exports of EVs to overseas markets – particularly Europe at the moment.

But Chinese companies would love to sell EVs in the US, and would likely love to see the government tack $7,500 onto the price of US-built EVs, which would only make Chinese-built EVs much more competitive to the pocketbooks of the American consumer. Barrasso’s bill would do exactly that – make Chinese EVs more competitive, and the US auto industry less so.

And since EVs provide local air quality benefits, which stands to reason and which we’ve already seen in areas with high penetration, reducing EV adoption would also make Americans sicker and fill up American hospitals more.

While Barrasso claims that the bill would do the opposite of the things that it would actually do, it’s hard to believe that anyone would be ignorant enough to believe it would actually have the effects he claims. We don’t think that even he thinks that – we think he’s just playing politics, and saying whatever will make his fossil overlords happy.

In short, John Barrasso, author of the act, is lying to protect the industry that bribes him.

So far, the act has only been introduced in the Senate, and has not made it through committee or to a vote. It is sponsored by 19 republican senators, many of whom come from states with significant oil industry presence. If somehow passed, it would almost certainly be vetoed by President Biden, so it is not likely to make it into law under the current government (though that could change in November, which is something to keep in mind when filling out your ballots).

But even if it doesn’t make it into law, it still functions as a way for republicans to show their intent – to cost you money, to harm your health, and to hand the keys of the future of the auto industry over to the country which the US considers its main geopolitical rival.

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Daily EV Recap: 10,000 ton electric container ship

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Record number of EV chargers installed in the UK last quarter

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Record number of EV chargers installed in the UK last quarter

A record number of public electric vehicle charging stations were installed in the UK this quarter, as charging companies struggle to keep up with the growing number of plugin cars on British roads.

Almost 6,000 new EV chargers were installed in the UK during the first three months of 2024, according to quarterly figures from data company Zapmap and published by the UK’s Department for Transport. Approx. 25% (about 1500) were DC fast chargers.

There were nearly 60,000 public vehicle chargers energized and active in the UK as of April 1st, up nearly 49% compared to 2023 and nearly 2x the number of public chargers available in 2022. Ben Nelmes, CEO of automotive think tank New AutoMotive, says the recent expansion of the UK’s electric vehicle charging infrastructure has brought public charging to areas that had previously been poorly served. This is thanks, in part, to local governments gradually taking advantage of central government grants to put more EV chargers in the ground.

“I think there is a coming together of two things,” Nelmes told The Guardian. “Some of the barriers have been mitigated. And the private sector has woken up to the opportunity.”

Another tidbit from that Guardian article was a survey conducted by the Electric Vehicle Association of some of the UK’s one million plus EV drivers. The survey found that only 6% of EV drivers in England reported experiencing range anxiety either very often or fairly often, while 94% of EV drivers said they had range anxiety occasionally, rarely, or never.

Electrek’s Take

Electric Cab London
The all-electric TX Black Cab: Credit: LEVC

More than half of the more than 15,000 famous London “black cabs” are now electrified (effectively EVs with range-extending ICEs on board), with the majority of London’s largest taxi and minicab services committed to operating fully electrified fleets by 2025.

Let that serve as your gentle reminder that EV sales are down, except at Ford, Cadillac, GMC, Kia, Hyundai, Toyota, Nissan, Honda, Acura, Volvo, Chrysler, etc. …

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Daily EV Recap: 10,000 ton electric container ship

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