After doing energy modeling for my own earthship, here are some of my conclusions on the best ways to keep the house warm without requiring any artificial heat in winter in the coldest city in the world here.
First, thermal buffer zones. In winter at night heat transfer occurs from the inside to the colder environment outside. Practically what happens is heat in the inner air circulates around the living space and makes contact on a window or the ground where a heat exchange occurs. Air can freely waft through the room to a surface which interfaces with the external environment. Still air is an insulator. Relatively still air has about an R-1 value per inch. Completely still air has about an R-3 value per inch. A lot of insulation works on the principle of trapping still air to take advantage of these facts. A packaged earthship or vol. 1 earthship had the living space and the external environment. People inside walk around and hot air travels to the glass and there is heat loss. If we have the living space in an envelope with almost no direct contact with the outside environment, then thermal buffer zones are created. Generally people don't walk through the thermal buffer zones at night. The global model has buffer zones in the 2nd greenhouse and optionally in the 3rd greenhouse. However, if we can encase the entire living space in thermal buffer zones (to the south, north, east, west, above and below), the results are improved. This is one of the best ways to deal with cold sub-arctic climates.
Second, maximize solar gain. An earthship or passive solar house is heated by solar gain. Therefore, if we're in a cold climate, we have to maximize solar gain--period. In Mongolia I was in an unheated room in early January. The room only had 2 single pane windows. In the room I had a bike with a thermometer. Around noon and until about 1:30 - 2:00 it was in direct sunlight. The high of the day was about -20C. In the sun it reached over +20C/70F. In a cold climate it's absolutely necessary to maximize the solar gain during the day. If it's too much, we can always draw shades. If it's day time in winter, what can obstruct solar gain? There are various things. One pane of standard width (6mm) glass reduces the amount of solar gain by 10-15% depending on construction assuming there is no tinting or covering. We went into some local glass stores and they were even selling quadruple glazing (4 panes with air between them). If you had quadruple glazing over the living space, the 2nd greenhouse and the outside of the 3rd greenhouse, that's 12 panes of glass light has to travel through. If we say the glass is completely clear and we optimistically assumed 90% of the solar gain passed through each layer, the best case scenario would be that 28.2% of the sunlight reaches the living space. If we assume 85%, then 14.2% reaches the living space. If condensation, ice, snow or dirt is present on the glass, even less. If we had used a total of 3 panes of glass, 72.9% of the solar gain would enter the living space, which is over 2.5 times as much solar gain, which becomes heat at night time.
Third, minimize heat loss at night. Earthships in middle latitudes, like New Mexico, are probably warm enough at night, even on the coldest nights. Using insulated glazing is OK in such environments. Double insulated glazing might be OK is many places where some heat loss at night is acceptable. It may not acceptable in winter in the coldest city in the world or sub-arctic climates. If we use single pane glass, we get 72.9% of the solar gain. Once the sun goes down we cover one (or more) of the windows with thermal curtains, which can have over R-10 value. These curtains must seal around the edges. A good strategy is also to trap about 25cm of air between the glass and the curtains. This way we maximize solar gain, but trap that extra heat inside the house. The best way is to put the curtains on automated control, so they open in the morning, close around sunset or dark periods (whenever heat loss occurs) and open at sunrise automatically. Quadruple glazing may have R-7. If may have more with certain gases (which leak after years of use). It costs at least 4 times as much as single glazing, which could be tens of thousands of dollars more. R-7 is OK, but not warm enough in sub-arctic environments. Also, once condensation infiltrates that kind of glass, it generally remains until maintenance is done.
Fourth, thermal mass. Thermal mass can store heat over time. Heat absorbed during the day can radiate into the living space at night. It also stabilizes the temperature in the room. Without thermal mass artificial heat in cold climate is pretty much necessary. Even in earthships if we have a tire wall in the air locks to the east or west, the airlocks can stay warm due exposure to the sun and the thermal mass in the whole tire wall.
Fifth, heat storage. Some locations closer to the poles don't have enough sunlight, so they can store solar gain in the form of heat in a hot water tank, then spread it into the living space when needed. This makes it possible to build earthships in Alaska, Scandanavia and Europe. I assumed I would need it in Mongolia, but though it's very cold in January, the day is 8.5 hours long on the shortest day and solar gain is fairly constant. My energy model concluded that it's not necessary at all.
Sixth, insulation. How warm is it under your floor? Many places in middle latitudes it's well above freezing down under the frost line not too far below the surface. In middle and northern Mongolia there's permafrost down there, maybe 15 meters deep or more. It is about +0C down there. If I didn't insulate the floor, then heat would be constantly sucked out of the living space into the ground. Therefore, floor insulation is necessary. Without some floor insulation artificial heat is necessary (or heat storage with a radiator system), and floor insulation is probably less money and trouble than constantly heating the place. If the floor is mostly below the frost line, then if you put some vertical insulation around the perimeter, that will keep things above freezing all the time. Even in southern Canada it might be OK. The living space might not be +20C, though. I modeled our situation. 15cm of floor insulation is pretty much necessary if the roof is done well at R-75. Just increasing the thermal wrap wall doesn't negate the necessity of floor insulation. Materials high in thermal mass typically have high conductivity, so without enough insulation heat will quickly be drawn out of the living space. Heat rises so the roof is where the most insulation needs to be. Also wooden doors have very little insulation r-value, so they are like thermal holes. Having a wall of windows with no covering has an inadequate r-value. There are thermal shutters. The problem with earthships is they have to go somewhere when open, so sliding shutters (pieces of insulation) reduce the window area and incoming solar gain during the day (unless one found a way to get them off the front face during the day).
A neighbor showed me his stash of bottles. He had 3-4 bags of juice bottles, which I took. He had practically a dumpster's worth of pickle jars (or similar products). They just seem less than optimum, being short and wide, making a larger honeycomb. Usually I skip those jars. I suppose they would work. I suspect we have enough can/bottles for the bond beam and interior of the house. I'm mainly collecting for a property wall or edging where wine bottles and vodka bottles would work best. (There are vodka bottles everywhere here.) Any ideas on what to do with pickle jars?
I've made several posts about third greenhouse glazing angles, electric car batteries used with solar PV panels, etc. http://groups.google.com/group/earthships_en?hl=en
This is a bit of a diversion again, but could be a cheap way to supplement power off-grid using bike wheels. I got this off the icebike email list.
The quality way to do this is to use a Shimano dynamo hub on an old beat up rim and just step the power up to 12v. This appealed to me being a cyclist. It would be great to find ways to recycle old bike parts. It would add more outer space landing look to your earthship.
Dynamo bike hubs and battery packs
The concept isn't exactly new and neither is this product, but the Busch & Müller "e-werk."
This collects electricity from a dynamo bike hub into a battery. It's one way to decrease reliance on a home solar PV system and enable earthship off-grid living for small appliances like charging cellphones and other small DC devices. This would require not only this device, but a dynamo hub, so the whole package could cost as much as $250.
I've already read "Water From The Sky", but wasn't clear about details for our location. Many of the details, like the silt catch, were designed with Taos, NM in mind and need some adjustment. Taos has a frost depth of 18" (0.45 meters). I'm dealing with a frost depth of supposedly 1.9 meters as some say. They have that pic of a wonderful silt catch on top of a cistern. In Taos it can get cold, but the average high in January is above freezing. Even then they said it could possibly freeze up a little. If it froze a little there in January, It would definitely freeze in Mongolia, where rivers are completely frozen blocks of ice until the end of March.
So I was dealing with the situation that even if I have a well insulated cistern that it has an opening. I can't even close it for the winter, because as we use water inside, it has to relieve pressure. They also say in that book that metal funnel shaped silt catches will eventually rust and develop holes, so they suggested plastic tubs filled with pebbles as an alternative. The tubs were close to 18" deep. So even if some cold winter air got down through the tub into the cistern, the water is quite a big mass and warm below the frost depth line, even insulated.
I was frustrated when looking at Dan Richfield's 18" cistern riser, because I doubted they had a 2 meter version of that, even if I took 2 1 meter risers. We will check out the water tank places locally. (We know where they are.) Then it occurred to me that I could simply get 2 industrial strength new plastic garbage cans and stack them on top of the cistern opening and do some sealing to prevent dirt from entering the cistern.
Since I want to build in a cold arid climate where 80% of the precipitation is in about 4 summer months, I don't need to be concerned about collecting any snow melt, and need a very large capacity. I wanted to build tire cisterns. If I collect water off the roof and it falls through 2 meters of silt catch, and I want to have the bottom of the cistern at or above the ground floor in the house. That leaves 1 meter or less height fully below the frost depth and above the floor. Most of the large capacity tire cisterns are tall and wide. If I built one cistern, it might need to be extremely wide of 10 meters or more and it would be hard to put a strong lid on it that wouldn't collapse.
I was looking for a cistern design that was 1 meter high or less and large capacity. Eventually it occurred to me that I could use tires behind the thermal wrap in a multiple U design using the smaller tires often found on Asian cars 195 or less, which are considered to be too small for earthship tire walls in the dwelling place. Each U could be maybe 2 meters in width with a common (greenhouse analogy) area to drain towards the center. This way I could easily secure a strong cistern top with rebar and cement over each U. Since 2 tall garbage cans could easily hold the largest storm, I could have one entry point over one U, and perhaps have another insulated cover with a pipe riser from another point to inspect the contents or even climb into the cistern if necessary.
So far this sounds great, because not including piping to/from the cistern there is almost no cost besides cement, sand, 2 big garbage cans and maybe the other riser with an insulated cap to gain entry. It would take the labor to pound hundreds of tires, though.
So, the idea is: put the 1 meter high cistern with 2 meters of earth over it. It would be completely insulated on the inside. It would have a riser of 2 or more pebble filled plastic garbage cans as a silt catch. Even though air could find it's way down into the cistern, I'm hoping that the water won't freeze.
Let's say one cistern U is 1 meter (3.28 ft.) tall, 8 feet long towards the north, 6 feet wide (U sidewall to sidewall) not including tires. Even though U's might be curved and lose space the juncture between each cistern U will compensate for that. These are adjustable. We could easily make them 10 feet if we're short on capacity. 6 feet wide will give up a strong roof over each U. I figured one of these will contain about 1100 gallons.
UB gets about 10" of precip. a year. Maybe less. The airport reported 25" one year. Some places like weather.com report as low as 7-8". If we built a 2000 sq. ft. (large) roof, what is the likely maximum amount of water the roof could produce at 10"? I figured about 12,000 gallons. If we tried to contain the entire year's worth of rainfall, how many 10' long cistern U's would we need? 11.2. If we say a tire is 2' wide and we have 10 walls between 11 tire cistern U's, this would have to be 88 feet long including the tires.
Without a finished global model book what's an earthship sailor to do? Become an intern like Dan Richfield? http://www.youtube.com/watch?v=iI9LInmNfpE and hire EB staff during your build? He's got great practical details in his videos that EB kind of glossed over. I like the multiple U design. It's got more thermal mass for a cold climate. In a sunny cold climate we need to collect as much sun energy in thermal mass as we can get. Admittedly the weaknesses that I can tell are: you can't overhang the roof at all over the greenhouse, and the front of the U sidewalls are vulnerable, and the transition from the main roof to the greenhouse can be straight as I want, but it's a little trickier. I want multiple U's with 1st greenhouse glass like the packaged earthship, which became the global model. I was worried if I put up 9 courses of tires and then dig the little foundation for the non-weight bearing 1st greenhouse glass that it's going to cause the dirt under those front tires to weaken, but we'll be putting concrete in there anyway. They run that footing all the way to the sidewalls on the packaged earthship. Even one of the "existing earthships" in the back of volume 1 implemented it. We definitely need the 1st inner greenhouse in Mongolia in my opinion.