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With a super-airtight house, indoor air quality is a big concern. When the windows and vents are all closed, we get headaches, even though we do our best not to introduce VOCs into the house by buying a minimum of plastic, and off-gassing any new purchases before bringing them indoors.


In the summer at 9000 ft in Colorado, we simply keep the windows open, as long as there isn't smoke wafting in from a wildfire to the west of us. But in the winter, it gets very cold here, so leaving windows and doors open isn't an option.


Our house had two passive air vents when we bought it, one in the bedroom on the east end of the building, and one in the office on the west end. The little bit of fresh air that comes in through that vent in the bedroom is delightful, but we found that passive ventilation just wasn't sufficient to keep the air in the house fresh.


First we tested for radon, and found it was much higher than the recommended limit. We installed the smallest wattage radon fan we could find (50W), but running continuously it's a big load. With only 2.5 kW of generation before installing our 5 kW ground mount, we've had to turn it off for days at a time when it is cloudy.


Next, we added a pair of Lunos e2 heat recovery ventilators. It's ingenious technology. In the same size opening as our passive vents, there's a small round fan. Two paired units are installed at opposite ends of the house (we have them at the east and west ends of our large central room so they ventilate the whole house). One is pulling air in, while the other pushes it out, and they switch directions approximately once per minute. The warm house air heats the body of the fan as it exits, and then the fan heats the cold air coming in from outside. The result is that 85% of the heat energy is retained, while fresh air is introduced to the house, and the air pressure indoors remains the same as outdoors.


The Lunos HRV has the advantage over other HRVs that it requires no ductwork. If you have a larger multi-room house, you'll probably want a different type of HRV, but for our house, which is basically just one big room, this solution was ideal. We added the rotary switch made by 475 High Performance Building Supply, which also sells the HRVs, to make it easier to control the speed of the fans. This HRV solution uses much less power than the central units do, and is much less expensive. The pair use only 3W of power on low (twice that on high), and cost about $1K.


The fans are easy to install. You'll need a power drill with a hole bit the diameter of the fan to cut the hole in the wall (a little over 6"). Make sure to avoid the studs! Once you have a hole, the fan assembly simply slips into it, and the wires from the controller have snap connectors to attach to the fans. You'll need to run 3 wires (or telephone wire) from the controller to each of the pans. We employed the CAT-5 wiring already in the ceiling to route the power from the controller to the remote fan, to avoid a wire run across the ceiling. (If you do this, note that you'll need to use a twisted pair for each of the 3 conductors to carry sufficient current.)


The only downside we have found to the Lunos HRV solution is that the fans are not silent, nor is the sound white noise, since the fans switch direction every minute. On high, they are about as loud as the compressor on our refrigerator. On low, they are barely audible, but they don't give much improvement in indoor air quality. For now, we are running them on high in the daytime all winter, and turning them down at night. We haven't decided what our next step in indoor air quality improvement will be. We may add a second pair of Lunos fans on the north and south sides of the room, so we can keep them all on low, or we may add more of the passive vents.


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Updated: Feb 5



A bit about us: Cat (left) is a PhD Electrical Engineer and Solar Photovoltaic System Designer, and Ota (right) is a PhD Environmental Scientist. We are both educators and former teachers who are drawn to inspiring ourselves and others. Specifically, we are passionate about solving the climate crisis through behavioral change and popularizing new technology. And having fun doing it!


We were living in Los Angeles and decided to move to Colorado because Cat loves the Rockies and Ota suffered a chemical injury 10 years ago that left her unable to tolerate air pollution, even in minute amounts. Finding a mountain house with fresh air straight off the Continental Divide was a win-win for us.


We were already making some climate-friendly lifestyle choices while living in LA -- Cat was biking to work and Ota was working from home and making her own soap -- but in making this move we decided to go all out and try to live as fuel-free as possible. So we bought a small, off-grid, highly insulated house at 9000 ft in the Colorado Rockies, close to the activities we enjoy, and set about demonstrating to ourselves that we could create a lifestyle we love, save money, AND generate as little greenhouse gases as possible.


This climate action map documents the elements of how we created our climate-friendly home. We hope that it inspires you to do the same, though of course not all of the steps we took will be relevant to your context. Our lifestyle is a work in progress, as yours is. The important thing is that we are all working to reduce our emissions as much as we can, and helping each other do so!


Please don't hesitate to contact Cat if you'd like to create a similar map for your climate-friendly lifestyle project. We'd love to showcase a variety of people's projects on our site, which is a totally non-profit labor of love for the planet and all her creatures.





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When we bought our 1200 square foot off-grid house in 2020, it had a small photovoltaic system. The system was designed for a single frugal person back when solar panels were relatively expensive, and consisted of 2.5 kW of solar panels on the roof tilted to capture the winter sun, a 120V Outback inverter, and a new 20 kWh bank of sealed lead-acid batteries.


Actually, why the batteries were new is a story in and of itself. The previous owner had been carefully maintaining his giant lead acid batteries for years past their usual end of life, to the point where the inspector red-tagged them. There were hot spots where some of the batteries were older than the rest, and as they charged, they were emitting clouds of hydrogen sulfide gas, indicating that the electrodes were breaking down. So we asked the seller to replace them with new batteries, and he did, with smaller sealed ones that we could more easily manage.


We went into our first winter with 10 kWh of storage capacity, since lead acid batteries can only be discharged 50%. We found that staying out of the bottom 50% of the battery capacity was tricky, because just understanding where we were involved reading a graph of the battery voltage versus discharge. There were no bars or percent readout like your phone battery. It was more like checking the voltage on rechargeable 1.5 V batteries to judge how charged they are -- not an exact science. Since on a sunny day our 2.4 kW array would generate about 8 kWh of energy, refilling the batteries was pretty quick, but discharging them was discouragingly quick, too. And we discovered that lead acid batteries like to be trickle-charged, even when they are full, so a lot of our generation was just going into "floating" the batteries!


In order to save our batteries, we had to reduce our loads, which involved unplugging the refrigerator and finding alternatives for food storage (more on that in a different article). On several cold nights we found ourselves turning off the main breaker for the house to preserve the batteries, grilling dinner outside in the snow, and then playing board games by lantern light in front of the propane fireplace. Not the modern fuel-free lifestyle we wanted to show was possible in our demonstration project!


We were able to run our electronics to work from home, a few lights and the well pump, but that was about it. Even when the batteries were full, the inverter couldn't handle running multiple loads at once (accidentally turning on the microwave while the well pump was running was enough to flip a breaker), and we wouldn't be able to change to electric cooking, since electric stoves require a 240V system.


We considered connecting to the grid, since there is a power pole on the edge of our property, just 600 ft from the house. But the cost for grid-tying would be $25K, including trenching to the house, meter, etc., not to mention the monthly bills for the rest of our lives. We could buy a lot of solar PV system upgrades for that $25K, we decided, have no power bill, and not participate in the carbon emissions of Xcel Energy's coal-fired power plants!

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