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.
Hot on the heels of the Fiat 4×4 Grande Panda Manifesto comes another subcompact Stellantis compact with electric drive and off-road ambitions. Meet the Opel Frontera GRAVEL – which might be our best look yet at the next-generation electric Jeep Renegade coming in 2027.
Based on a lifted Frontera EV and riding on a set of bespoke, 7×16″ Borbet CWE wheels wrapped in aggressive AT tires, Opel says its all-electric Frontera GRAVEL’s emissions-free driving makes it ideally suited for “soft-roading” nature drives (their words, not mine), with a rugged, adventurous 4×4 appearance.
Those rugged, Jeep-like good looks are backed up enhanced by the usual overland accessories, including a front-mounted winch, side storage boxes at the rear, and a lattice-style roof rack. A slew of accessory lights mounted on the Thule Canyon XT carrier and hood, as well, for excellent nighttime visibility off-road and (presumably) retina-searing intensity on-road.
“The new Opel Frontera is already standout,” says Rebecca Reinermann, Vice President of Marketing for Stellantis’ Opel and Vauxhall brands. “It is rugged, practical, and perfect for families and everyday adventures. But with the Frontera GRAVEL show car, we’ve pushed the limits, imagining a tougher, more daring, trailblazing version. This concept is built to fire up our fanbase and test the demand for a bolder, more rugged Frontera in the future. It’s all about freedom, adventure, excitement and pushing boundaries.”
Like the recent Fiat concept mentioned at the top of this post, the production Frontera EV is based on Stellantis’ “Smart Car” BEV-native platform, and features a 113 hp electric motor and more than 300 km of WLTP range (about 185 miles) standard, with the “long range” version able of traveling up to 400 km (about 250 miles) between charges.
Either version comes with the “Pure Panel” digital cockpit featuring dual 10″ displays. For a few dollars quid more, the GS trim adds automatic climate control and Intelli-Seat front seats. And, if Mopar Insider has any idea what’s up, it might actually make for a decent little Jeep Renegade replacement (below).
Electric Jeep Renegade rendering
The Opel Frontera first came to our attention last October, when it became the first new EV from Stellantis to be offered with both ICE and battery power, for the same price – making EV price parity an objectively real thing.
Jeep parent company Stellantis has already confirmed that a new Jeep Renegade that’s priced below the upcoming Jeep Compass EV would be coming to the US as a 2027 model, and it’s expected to share its mechanicals with both the Frontera and Fiat’s recently teased Grande Panda Manifesto. If that does anything for you, let us know in the comments.
Opel Frontera GRAVEL gallery
SOURCES | IMAGES: Mopar Insider, Stellantis.
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Year after year, a seemingly endless raft of all-electric concept bikes wearing Honda badges have made their way across the motor show stage without ever making it onto the dealer showroom. But now, it’s here: this unmissable, cafe racer-inspired electric Honda motorcycle is the company’s first – and you can buy it!
We got our first look at this first-ever production electric motorcycle from Honda back in March, when leaked type-approval documents hinted at a 75 mph 125 cc-class motorcycle with cafe racer styling and a “WH8000D” designation first surfaced. It was clear, then, that Honda was seriously working on a for-real electric motorcycle – what wasn’t clear was when (or even if) it would ever see productions.
The wait is over
The new Honda E-VO is available in dual- or triple-battery versions that feature either 4.1 or 6.2 kWh of battery capacity. On the triple-pack version, riders can enjoy up to 170 km WMTC (about 105 miles) of riding. Recharging takes about 2.5 hours on a standard outlet or about 90 minutes on an L2 (like the Harley-Davidson backed Livewire or Vespa Elettrica electric bikes, DC fast charging is not available).
Both battery configurations drive a motor with a peak power of 15.3 kW, or about 20 hp. And, like all electric motors, all the torque is available at 0 rpm, giving the Honda E-VO in-town performance similar to much higher (than 125 cc) displacement bikes.
In addition to superior stop-and-go performance, the Honda E-VO offers riders a number of other innovative (for a motorcycle) features, including a 7-inch TFT instrument display paired with a second 7-inch TFT screen for navigation, music, tire pressure, and battery SOC information. The smaller battery pack version of the E-VO includes a front dash cam, while the larger model has both a front and rear dash cam as standard equipment.
The Honda E-VO is available in the black and off-white color schemes (shown). Prices start at 29,999 yuan, or about $4500 for the 4.1 kWh version, and 36,999 yuan (about $5100) for the 6.2 kWh triple-pack version.
Electrek’s Take
Yes, this is a Chinese-market bike built by Honda’s Chinese Wuyang venture. No, we probably won’t ever get something like this in the US, where a raucous, 113 hp 600 cc CBR600RR is somehow positioned as a “good starter bike” by cowards with 3″ wide chicken strips on their tires. That said, if the motorcycle industry as-a-whole wants to survive in North America, zippy, affordable, lightweight motorcycles are exactly what’s needed.
Here’s hoping we get something like this stateside rather sooner than later.
SOURCE | IMAGES: Wuyang Honda; via Ride Apart, the PACK.
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Westerners in-the-know look longingly at the affordable, value-packed electric cars rolling out of China – but what could you get if money was no object? If you were to spend 100,000 US American dollars on a Chinese EV, how good could these Chinese cars really get? Huawei’s 852 hp Maextro S800 is the answer.
Packing up to 852 hp and a cutting-edge technology stack developed by Huawei, Chinese luxury brand Maextro revealed its latest entry into the Mercedes-Maybach EQS and Rolls-Royce Spectre segment of ultra-luxe EVs, the S800, back in February. Now, it’s officially on sale, priced at 708,000 and 1,018,000 yuan (approx $97,500-140,000), and ready to make an entrance.
As I wrote at the car’s launch, the Maextro S800’s bespoke, purpose-built platform doesn’t share any parts with a lesser offering in the Huawei lineup in the same way a Mercedes or BMW or Volkswagen does with a Maybach, Rolls-Royce, or Bentley, respectively. And, while I admit that that may not mean much to you and me, I maintain that it might to the people shopping six- and seven-figure cars. And that might be especially true to people willing to shell out that kind of cash for a car in China’s generally lower-priced market.
That seems to be the kind of upmarket experience people of the People’s Republic want, if the S800’s two thousand initial orders (in just two days) are and indication. And, lucky for those buyers, the Maextro is set to deliver plenty in return.
The vibe is immaculate
Those well-heeled buyers will get a choice of EREV or “pure” battery electric powertrains good for between 480 and 852 all-electric horsepower. 32 ADAS sensors including both radar and lidar compliment a suite of cameras analyze the road ahead and feed data to Huawei’s ADS road perception system, which is constantly adjusting torque distribution, suspension compression and rebound, and front and rear steering to deliver a tech-driven chauffeur experience that Huawei insists is second to none.
Huawei says its robotic driver is pretty handy when the weather gets nasty, too, thanks to an advanced sensor array that helps to increase the detection distance in rain, fog, and dust by 60% compared to the benchmarked competition.
While the car is its passengers around, they’ll get to enjoy luxurious, reclining rear seats with next-level mood lighting handled by a fully independent rear passenger system that supports intelligent track lighting, gesture dimming, and a panoramic “starry sky” moonroof that includes meteor shower effects.
The Maextro S800 also offers intelligent privacy glass and a unique door-closing function are also controlled with advanced gesture controls, in case you needed reminding that China is living in the year 3000 while the US is being plunged headlong into the 1940s by a pack of pseudo-conservatives too old to realize their gold standard policies will do nothing but hurt a fiat economy that’s consistently proved out the basic hypotheses behind modern monetary theory over the last five or six decades – but that’s a lot for an EV blog.
Instead of that, let’s ooh and ahh over the Maextro S800’s ultra-luxe interior in the photo gallery, below, then keep the debate to the relative merits of one of these over, say, a Mercedes-Benz EQS in the comments.
Huawei Maextro S800 gallery
SOURCES | IMAGES: Huawei Central; CarNewsChina.
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