Towards a better tinyhouse

Inventing to freedom?

The Tiny System V. 0.5 (draft)

with 3 comments

After I finished writing this I remembered it is really dwellings in the city that matter, I mean whatever the issue it is that you care about 95% of people (including me) really don’t have the option of being in a rural area, where this would be suitable. Off grid is interesting and a nice idea but it’s not that useful, so I was going to draw this in sketchup, but I think I will not, and save that time for something else tinyhouse related. What we really really need is to overcome the barriers to in-city tinyhouses.

Also I’m going to try a little harder to refrain from wasting time on off grid rural area stuff. Especially because more likely than not off grid tinyhouses would be used for wasteful second homes by the wealthy more than anything, unfortunately, although probably not full time homes like this is made to support, so I guess it’s not that bad, but still.

Okay, so this is only a rough design. I’m not saying it’s the best way to do it, but I’ve been wanting to design this sort of thing and I never seem to have the time that I would need to do a more thorough job.

The goal here is to provide Electricity, clean water including hot water, a fridge and freezer, space heating, ventilation, a toilet solution, greywater disposal, and laundry solution for an off grid tinyhouse of about 250 square feet including the loft, at the lowest cost I can manage while still keeping it eminently buildable. Insulation would be just to code, with 1.5 sq meters of windows.

Basically I’m trying to get the outline down, then I would build a simulator in excel and find the appropriate component sizes. Sometimes though you sort of need to have at least some idea of the numbers, e.g. should you add a regenerative heat exchanger (one brand is “EcoDrain”) to the hot water system or not? Well, it could reduce the size of the hot water tank. But by how much is what matters. So those kind of decisions are based on estimations from previous experience with e.g. the solar heater and photovoltaic spreadsheet things where I could get some idea of the numbers involved (looks like there is no point in a heat exchanger, really).

The description is also sort of clogged with ideas that occured to me or were remembered while writing it, but I think that is good. While I think this would work as is, the cost can always be reduced, and maybe the size sometimes might need to be. As you’ll see, it is all about saving some money here and there which really adds up, there is no silver bullet (although and inexpensive and low maintenance heat engine for providing electricily would really help).

Of course with anything like this there needs to be some assumptions made about the usage per day, so I made it the way I would want it, and I would build something like this if I could get a place to go off grid, and maybe with an eye towards experimenting with water recycling, but I guess most people aren’t interested in that.

This is the unit size, so only for one person, but you could upsize things approritately for 2 people at less than 2x the cost. Once you start upsizing it it might turn out to be a good idea to use some of the methods mentioned of getting the size of the thermal collectors and water tanks under control a bit better, I guess, though at slightly higher cost.

Obviously you could save some money by being even more aggressive with conservation. The pricing is also based on mostly new parts, so like anything you can save a lot of dough with used stuff.

Use overview:

60 liters of water each day 40 is hot at maybe 45 degrees, with low flow faucets of course, and the shower should have a navy function (some low cost shower heads have this built in anyway) in case you want to free up extra water for some reason.

Average electric usage during worst case month in winter is 2036 Wh per day, no more than 1000 Wh during the night, see below for details.

Heat is kept at at least 22 degrees all year round. Allowing the temperature to go down when you are not home or are asleep would reduce the size of the thermal collector and heat storage tank. The physiological optimum for sleeping is apparently about 18 degrees anyway so that’s the way to go. Have the heating (and cooling) radiator and ventilation output in the loft so when you are asleep the ventilation, heating and cooling can be turned down without detriment to comfort.


The precipitation collector is the “snow capable precipitation collector” (see post) with a separate smaller but similarly desgined collector and melting/storage tank made from known-nontoxic material, for water that will actually be consumed. You might have a filter system for it too, probably a combo ultrafilter and some granular activated carbon, removes any taste and pathogens or other particles, get the water tested before going to town with anything more expensive, it is probably fine.

The reflector for the thermal collectors doubles as the collector for drinkable water, probably made from aluminum or galvanized steel.

Methods of reducing cost of the electrical system:

– Use X-10 ($9 each) or wall switches wired to the electrical outlets switched by the user, or both, to disconnect appliances, eliminating their standby power draw, another option might be to have 3 or 4 separate electrical circuits in the house, i.e. groups of outlets, that are wired to relays or x10 modules after the circuit breakers so they can be disconnected while the user is away or asleep. Could be a motion sensor in the house to determine this, there may be x10 motion sensors available.

– Get a PLC with a power save mode feature if practical.

– The freezer stores energy as frozen water, which is far cheaper than storing it as electrical energy in batteries. Suppose batteries are $0.3 per watt hour, a small freezer uses 212 kWh per year or 0.58 per day, so to keep it cold for a 3 day cloudy period would take $522 of battery (actually more because you can’t use the whole capacity of the battery) I have a 3.5 Cuft freezer right here and it looks like the wall insulation might be 3 inches thick, suppose it’s closed cell polyurethane spray foam, which I think it usually is, it should have a U value of maybe 0.3 let’s suppose the surface area is 2.5 m2 , then the ice has to absorb 27.75 watts of heat energy to keep it cold , a kg of water is 92.5 Wh to melt, so to get you through 3 days takes 21.6 Kg of ice, which is less than a cubic foot so you still have plenty of space in the freezer, and it’s next to free.

The fridge is a normal cooler, which uses a loop of tubing which goes under the lid of the freezer, around just under the lid (probably attached to the lid) and then back to the cooler, to extract cold from/dump heat into the freezer by convection (so the tubing coil inside the cooler has to be a bit lower than it’s counterpart in the freezer). Inside the cooler, the tubing would also be surrounded with some water, immersed in a container of water or surrounded by a bottle filled with water, say, so that water freezes to the tubing. This starts to impedes the flow of heat into the tubing wall if the water in the bottle/container get to 0 degrees. This way the interior of the freezer can’t get below 0, which is close enough for a fridge, and you can look in there and see water frozen to the tubing so you know it’s all working.

You could also use something like for redundancy, so you know if the temperature got too high for some reason, like someone mucked up the tubing or something, and the food might not be safe to eat. Or you could use a temperature sensor connected to the PLC and the PLC could beep or something if the temp got too high.

The freezer might also have a temperature sensor in it, and be on/off controlled by the PLC, and of course it would stay off at night, coasting on the frozen water. The frozen water would have sugar mixed in, say 6 liters with enough sugar to prevent it from freezing at -10, 9.1 liters that freeze at -13 and 7.5 that freezes at -18 (recommended freezer temp) so the temperature inside the freezer changes depending on how much water is frozen, and the PLC can know, and bump up it’s priority for electrical demand if it is low, might be unneeded.

Obviously in winter you have cold on tap, so that could be taken advantage of maybe to reduce the size and cost of the photovoltaic system a bit (maybe by 25%, eyeballing it), except if the freezer needs to be kept at -18, only surrounding the outside of the freezer with cold air or water in tubing would be available, so it would still take some electricity, and I seem to recall that the freezers can be damaged if the ambient temperature is too low. Definitely want to check that though. You could put a convection loop outside the house, which then comes inside and into the freezer, shaded and at a level so that only if it was colder outside than inside the freezer would convection occur. Like a thermosiphon. Similar deal for the fridge perhaps. For another version maybe.

Looking at Sundanzer units etc it is pretty clear that it is at least a couple hundred bucks cheaper to do it this way even after the cost for the extra electricity, because they charge $800 or so for the things. Plus you get both a fridge and freezer.

– The ventilation takes a quite significant amount of energy if powered solely from the solar panels, so you would probably orient the intake and output vents outside so that the prevailing winds blow through them a bit to help with that. I looked into trying to do it all with wind power, and the various passive ventilation products that are available, and they do not do more than 40% better really than just orienting the ventilation intakes appropriately (i.e. you could try to harvest the energy in a large wind cross sectional area, then use that to turn a fan, or what these things do is try to use aerodynamics, with no moving parts (well the roof turbine things use moving parts but they cost a fortune anyway so are pretty much off the table) to transfer kinetic energy from a large air volume to a smaller volume, but they don’t increase the energy in the small volume by more than 40% or so from what I have found, mostly what they are made to do is regulate the flow of air to a fairly constant level and keep water out).

You might figure out a clever way to make it so that the vents automatically are oriented if the wind changes direction, or use a windcatcher or something similar. Climate data includes wind direction so could check to see if there is any point in this. Suppose the wind velocity, and this info is included in the climate data, is 1 m/s, if you have an “effective free area” for the ventilation holes in the side of the house (an this number goes down if there are any constrictions or bends in the air flow path), of say 150 cm2 i.e. the equivalent of a hole in the wall with an area of 150 cm2 you can take that area, multiply by the wind velocity and that is the ventilation rate you will get. So the obvious thing to do is make that EFA nice and high so even if it is not too windy out there is still enough ventilation. To calculate the liters/second (or cubic feet / second) you should aim for, take the volume of the house and multiply by 0.3 for okay ventilation, but 1 is good ventilation (“air changes per hour or ACH”. Suppose the interior volume of the houe is 83 cubic meters, 3000 cu ft, we need 0.46 to 1.4 cu m per minute. Average windspeed in minnesota is 4.7 m/s so 150 cm2x4.7m/s, 4.2 cubic meters per minute. And it very rarely goes below 1 m/s so not bad. So looks like ventilation could be provided this way, but trees etc will reduce the windspeed a lot of course, so I leave some electricity for ventilation in the electric section.

The problem with this is two things: with a “plain” approach during windy periods there would be too much ventilation, resulting in excessive heat loss with no benefit. That could be solved with a valve and a way to measure airflow, so the plc can constrict the flow appropriately, or a better yet with some sort of passive mechanical mechanism, that would be a point to improve for a later version.

The other problem is noise. How do you let air into a dwelling but keep noise out? I mean you need a hole in the wall, right. Well, there are at least 2 ways I know of and would really be interested in any others out there: use a bellows like mechanism with doors that open and close so that there is never actually a contiguous path between the indoors and the outdoors. That seems like a real bother and mechanically complex.

The other way which is more common, is to have a sort of silencer unit, which forces the airflow to take many bends, with fiberglass or another material that absorbs sound lining the inner walls of the silencer, so the sound waves have to reflect many times off of the absorbent surfaces at the corners, 10 or 20 corners depending what lines the walls and the Dba of reduction you need (or STC), each time losing some energy, before they enter the dwelling. Insulated flex duct is sometimes used (with the insulation being the sound absorbent stuff), need to watch out for the smell of the duct, if it releases VOCs that would suck. Another way is to force the air to go through the porous, fibrous material directly, but this has issues with air quality because stuff gets stuck in the fiberglass etc. although I suppose it would be fine for the outgoing path.

Obviously that is going to restrict airflow. In fact you can buy “acoustic vents” that are made to do exactly this sort of thing, and the reputable manufacturer’s include an EFA figure for each product. However you can make your own too with some fiberglass, flex duct, caulk and MDF (medium density fiberboard, doesn’t change shape with humidity), cheaper and with a much higher EFA. I have been trying to get a good design for this, so far not successfully. I’m stuck on the finding out how high the fraction of sound energy that reflects at each corner for a certain type of insulation, but there some links that I added to the ” lighter soundproofing” post down at the bottom that help a bit. I also would really like to know how those commercially available acoustic vents work so maybe I can find some patents or something.

– Electric cooking is not done during the wost months of winter except I budgeted 10 minutes a day for the microwave. Otherwise it would be by propane probably only, unless you can find efficient appliances, which do not seem to be common. During summer there is such an excess of electricity you can use rice cookers etc., it might make sense to have the PLC monitor this and disconnect them if they are used excessively so these would not infringe on the state of charge of the battery, limiting use of other more important appliances later on. During the hottest days that energy would probably be used by the air conditioner instead, I would have to check the requirements and include the efficiency of the electrical air conditioner with various temperature drops, which I didn’t bother with for the off grid air conditioning post, just assumed the worst.

– There is usually about 2 times as much electrical energy per day on average in the middle summer months as the worst case winter, according to the graph in cheaper photovoltaics post so there should be ~2036 Wh to spare on these days, which is more than enough to run it all day judging from my experience with the off grid ac spreadsheet, certainly when coupled with thermal inertia approach, which can make use of the space heating tank, since it is already connected to the radiator.

-Potentially there could be 2 inverters, there are cheap UPSs available for $60 or so which might be used as an inverter for the low peak load stuff, because the average power useage is less than 100 watts, and then the stuff like microwave and so on could have a separate inverter. The SAM thing has graphs of efficiency vs. rated load that show this might not make sense, depending on the cost of the extra inverter, though. Depends on of you want to be able to use e.g. the microwave *and* a kettle at the same time, raising the peak useage to a high level. At 10% load it looks like they are still 90% efficient. Also, the ups ones might be inefficient so that would sort of ruin the plan. Something to look into with a spreadsheet, though. Also, the ventilation fan and PLC is DC, and if the lighting is LED it might as well be too.

This uses a solar thermal panel of about 8 square meters, with greenhouse plastic. If things seem to be working out a few years down the road when the plastic has worn out, upgrade to polycarbonate panels.

The hot water system uses a thermoregulatory valve thing, also called an anti scald valve, to regulate the temperature of the water down to a safe level (45 degrees) even when the temperature of the storage reservoir is higher than that. It does so by mixing heated water that has passed through the stainless steel tubing in the reservoir with cold water. The thing is, the reason the temperature of the hot water tank has to be higher than 45 degrees is that the tank is essentialy mixed, over periods of more than a few hours i.e. there may be a thermal gradient, with it hotter up towards the top for some reason or another, but over several hours the heat will, even though there is no convection, be pretty much evened out throughout the tank due to conduction of heat through the water, and there would no longer be any significant thermal gradient.

What that means is that it’s not unreasonable to assume as an approximation that the tank will be fully mixed. So if we assume that the minimum acceptable water temperature is say 45 degrees (40 is I think a comfortable shower temp) then only the heat used to heat the water supply tank above that temperature is usable.

The energy stored in the tank is 4*gramsofwater*degreesrise*/3600=energyinWh. We can assume in winter that the incoming water to be heated is 0 degrees, we are using 40 liters a day, we need a 45 degree temperature rise, which is 2000 Wh. The tank is loosing heat, too, it’s an exponential decay but I’m to lazy to find it exactly, supposing it is insulated to U 0.3 and has a surface are of 2 m2 it’s -10 out, it will be less than 3888 Wh, so to be able to get through 3 days 6000+3888=9888 Wh should suffice. Yikes. An awful lot of energy, but if the heat is stored at 35 degrees above the hot water temperature, or 80 degrees when going into the cloudy period, then 260 liters should do it. So again to find a more accurate figure you’d want to simulate it with weather data, but there’s the approximate figure.

If you bought a 250 liter tank, they want, uh, $1020. Yeah. So they can keep it, and we’ll just make our own out of plywood and styrofoam and plastic and and PU spray foam and some stainless steel tubing and the anti scald valve.

If you wanted to you could place the hot water tank indoors and then get hot water a bit faster at the tap. Using narrow gauge plumbing would also help with that, we do not have to worry much about the flow constriction that would result since the plumbing lines are short and the pump is plenty powerful and the flow rates are quite low to begin with due to low flow faucets (which also increase the waiting time). Plus then that heat that was lost would be reduced, and recycled as space heat for the house. But also a potential air conditioning problem in summer, I would have to check, not if it was well insulated. And it takes up space. And it might leak. And it is very heavy. So I put it outside, but close to the house. Maybe you could switch it depending on the season, with some effort to drain and move it.

The reason there are stainless steel tubes running through the tank (actually for all 4 storage tanks) instead of allowing hot water to just flow out of the tank is to deal with the pressure differential, and as explained in the heating system post, the antifreeze need. Unlike a normal hot water tank, the tank itself cannot withstand any pressure as it is just a plastic lined box.

The bulb pump and valve and vertical tube (top section that comes out of the tank would ideally be transparent PVC tubing) extenting from the tubes leading from the thermal panel is to store, and eventually remove bubbles (just open the valve and squeeze the bulb to pump out the bubbles and then close the valve), the reason there is the valve is that the one way valves buit in to the bulb pump usually leak a bit which would let air in), and ideally to see them through the tube wall. If too much air got in there it could prevent convection which would prevent recharging of the heat reservoirs.

One problem with a thermosiphon system is that you have no control over the output temperature. With a separate thermal collector for the 3 different heat loads, there would be periods when the panel connected to the hot water reservoir was perfectly capable of outputting water above 0 or 22 degrees, but not 45 degrees, or whatever the present temperature of the tank is. Which means it could charge the space heating tank or snow melting tank, but because it is not connected that heat it could be outputting is wasted. The one for the space heating tank could put out 0 degree water but would not because it is not connected to the snow melt tank.

With a single panel and a 3 position valve you can have only one panel, and use the area more efficiently so the total panel area is smaller. Using temperature sensors and a pump could get it down more, but but then you have to pay for that (which is not much but still, increases part count too). So I decided to go this route. However if you have a limited about of land area, or not that much sun area, or it turns out the bubble thing is a problem valves and pumps may be the way to go. They would also allow you to put the thermal panel at a slant and eliminate the reflector, but I don’t know that would be very beneficial.

The PLC controls the tracking of the photovoltaic collector, so knows the approximate amount of incoming sunlight from the light sensors used by the panels, and has an ambient temperature sensor for the outdoor temperature. It also has a clock in it for approximate time of day information, and it reuses this information, to make a decision about where to route the water from the solar thermal collector to. It has the airflow sensor for the ventilation, so knowing the approximate ventilation rate and the outdoor temperature, it can estimate the temperature of the space heating tank from how often the valve to allow heating water though the radiator needs to be turned on, and whether it can be charged now. Then it also knows approximately when the panel is capable of outputting water that could charge the hot water tank, and some set fraction of the time it connects the panel to the tank. When the space heating tank is full enough, the rest of the time it directs heat to snow melting. Or you could have temperature sensors in the tanks.

The radiator would be indoors just near the output of the ventilation system, which would probably be up in the loft so the ventilation can be turned down at night. This way the radiator can easily be harnessed for use for air conditioning from a tank of cold water because a big, slow fan (therefore efficient) could be directed at it. As it stands, I didn’t use thermal inertia or evaporative cooling because there is that extra electricity, and that makes it a bit easier to build, but if you wanted to free up that electricity the electric air conditioner would use, that’s a cheap way to do it. Also for air conditioning at night you might want to cool a tank of water down and use that. As it stands there is no cooling at night. Really hot nights don’t happen often, and if they do use the evaporative bedsheets thing mentioned in the AC post.

The ventilation heat exchanger is an aluminum core one. The amount of heat required for melting snow is about 5600 Wh per day and for heating probably worst case 38 kWh without a heat exchanger, 15 kWh with, much of which is recycled for snow melting, so the limiting factor is the space heating not the snow melting, and it makes sense to save the heat with the exchanger, reduces the size of the heat storage tank and the solar thermal collector (energy needed for hot water is 3 kWh/day and is essentially all reused for snow melting so again it is the space heating that is the limiting factor). I think they are pretty cheap, about $40. You can make your own too out of aluminum foil but I would think it is not as good.

Defrosting of the heat exchanger is done by opening a valve of some sort on the intake side of the ventilation after the heat exchanger, by an RC servo. This causes the cold air from outside to no longer flow through the exchanger, rather just right into the house, but the hot air at 22 degrees from inside still flows, so it warms the exchanger and melts the frost, the exchanger should be tilted so the water can drip out. Obviously this will result in some cold air coming out of the vent inside the house, might have to deal with that somehow so it doesn’t blow on the user. This same valve or at least the same servo is also used to throttle airflow.

The wastewater and waste air from the house go through tubes near the bottom of the non drinkable water collection tank, inside the tank they should maybe dip down to the bottom, then come up again to exit, giving up heat through the walls of the tubes to melt snow.

The water then flows into a network of throughs, not tubes, and onto the garden or lawn, which would be under the rainwater collection surface. Troughs so that they can’t get clogged. If ice builds up, you can clear it out easily. In winter I guess the water would not sink into the ground really, so there needs to be some accommodation for the spring. Depends how fast it melts, and I would have to check how much the ground can process. Maybe shading it could help slow down the thaw.

Another way might be to let the greywater freeze in a slightly insulated tank. Then, in summer it melts slowly, to avoid overloading the ability for the ground to process it. And is of course refrigerated in the meantime, reducing bacterial growth hopefully enough. If not, use an ozonation thing. The tank would have to be about 11 cubic meters though, to get you through 6 months of discharging, which means it can’t really be a shallow pan thing, you’d need a pump to pump it up to the level of the tank.

An interesting notion if the tank is 11 cubic meters, 2 meters high, 2.4 meters wide and long, 21.2 square meters of wall, insulated u 0.3 , assume 20 degree differential over 120 days that’s 1216512 Wh of heat lost, and it stores 10 cubic meters of ice, so 925000 Wh, and we use maybe if we use 5000 Wh per hot day for air conditioning, well maybe with more accurate reckoning for the heat lost or better insulation the ice could be used for air conditioning in summer, if you had a reason to free up that extra electricity. Also for refrigeration. Once you realize you can make big cheap water tanks, there are a lot of things you can do with them.

There are certainly cheaper ways of doing things all this stuff that I haven’t thought of, though, I’m sure. I’m not saying I think this is all the best way, just trying to figure out a good way.

What would really be interesting is if you could combine this with the “soap bubble insulated greenhouse” and grow all your own food too all year round… the roof of the greenhouse could be the rainwater/snow collector.

If you input the cost of the different system components, such as the cost per m2 of solar collector, thermal collector, a formula for the cost of the water tanks, etc. then have all 50 years or so of climate data, and set your requirements, e.g. no running out of power more than one day every 3 years on average, not going into low power mode more than once a year on average, no running out of heat every x often, you could use a nonlinear optimizer to find a nearly optimally priced system that meets your requirements. There is a free evolutionary algorithm plugin for Calc I think, though I haven’t tried it, and I have used one in excel before. I expect the optimization would take a day or more, but whatever.

Also, it’s clear that while you can save some money here and there, and it all adds up, it takes quite a bit of thinking. So it would be nice to have some standard systems, open source designs that would be perpetually being improved, for various climates and needs, with spreadsheets to simulate operation. Just download the one for your general climate, cut and paste the right climate data in for your exact area, set the pricing if the defaults are not quite right, hit Optimize, leave it for a day, and the system tells you what you should build, and it would be a fraction the price of a more conventional off grid system.

The obvious problem being that rather than benefiting the social fabric or environment, wealthy people would just use them to make second (or third) off grid homes in pristine wilderness areas, spend the balance of what they saved on gas and and skidoos and snowmobiles, and destroy the surrounding environment with them.

Maybe it would make more sense it a nonprofit sold kits priced on income level and took the profits and did something useful with it… but then that applies to so many things. Or we could try to get the culture of rampant overconsumption under control so the wealthy felt no need for second homes.

Or maybe that’s why I should stop wasting my time thinking about this and think about homes in the city instead, which let’s face it are about 100 times as important. Unfortunately the wealthy and inconsiderate are causing problems there too.

Anticipated electrical energy consumption during the worst case winter month, (only rough estimates):

lights 196
ventilation 280
micriowave 166 (10 minutes 1000 watts
water pump 10.4
PLC and other system components : 144
PC 260
task light 50
cell phone 15
misc 125
laundry 140
freezer +fridge 580 (might be higher)
Total about 2038 Wh average during the worst month in winter.

During the summer there is a lot of extra energy from the panels, twice as much during the peak when AC is desired so ther should be plenty of electricity for that, have to double check with spreadsheet. During the summer in the periods during which there is no AC needed there is also enough electricity for rice cookers, electric kettles and so on.

The air from the dehydrate pasteurize toilet obviously has to be kept separate from the incoming air so make sure there is a suitable pressure diffferential across the heat exchanger using the ventilation fan. Could potentially also have a separate circuit for it with a small extract fan, since the heat that escapes will be recycled to melt snow anyway.

I don’t know, maybe half of it is used at night, so you’d have maybe 1200 Wh battery just to get you through the night normally.

Power save mode 1 in which the fridge and most of the ventilation, some of the sytem load, most of the lights and laundry loads are not allowed , but the misc, pc and other is retained: 555 Wh per day.

Then you might want *another* power save mode, 2, that would only be used once every few years when there really was a 3 day cloudy period, that would be just the PC and 80 Wh for the PLC or something. You get the idea though, instead of having abattery so huge it can get you through a 3 day cloudy period that only happens once in a few years, just go without some stuff once every few years and it’ll save some dough on the battery. The obvious problem is predicting that you are now entering that 3 day period, and need to start with into power save mode now, however you could conceivably get the PLC to get weather forecast information through your computer over the internet, as the PLC will have an either RS232 USB bluetooth or ethernet port. Alternatively you could figure out a method of going into power save mode when the battery reaches a certain level or something maybe…. but you might get a lot of false alarms then. Hm. What you really want to know is the future with regards to how much power there will be from the panels and what the user demands will be, using the last 50 years of climate data to try to make some degree of predictions based on time of year etc. might help some.

The photovoltaic array uses 2 of the collectors mentioned in “cheaper photovoltaics” though that’s a bit more than you need. By the way the amorphous panels bring the improvement ratio from 2.4 to 3 at 85 degree max temp, so that is the way to go if you can get them at the right price. Still haven’t checked the impact of wind.

Price estimate (very rough, excludes parts that are more part of the house, e.g. interior plumbing, also taxes and shipping excluded):

3 position valve: $60

Space heating system: $185
(8 Sq meters of collector plus reflector, $10
5 cu meter Tank, $80
Tubing plastic, $20
Tubing stainless steel. $30
Thermostat valve: $40
Temp sensor connects to plc: $10
Bulb pump and valve: $15
Radiator: $20)

water heating system: $135
(Tank, $40
Tubing plastic, $20
Tubing stainless steel. $40
Bulb pump and valve:$15
Thermo reg valve: $20)

Plc: $200
relays or x10 modules to cut off power reducing standby loss or control pumps: $60
Freezer: $180
Cooler: $40
non drinkable collector: $200
drinkable water collector : $200
Water filter: $100
Water pump, demand mode: $70
Photovoltaic collectors: $800 Could be reduced $200 with freezer thermosiphon thing
Battery: $400 could be reduced with power saving during night and cloudy periods
Inexpensive stirling engines burning veggie oil would greatly reduce both the above, and need no inverter potentially as some have 60 hz ac output.
Electronics for photovoltaics, mppt charge controller and inverter: $400? Hopefully that could be brought down with shopping around and looking into upses, might be able to use the built in battery charger too if enough capacity, need to know the efficiencies to decide, mppt still needed $130
DC Ventilation fan: $40
regen Heat exchanger: $40
Valve for defrost with rc servo for actuator: $55
ventilation system airflow sensor, could be the fan actually maybe depends if can freewheel with the airflow, either with back emf or muffin fans usually have rpm sensors built in, so: $30
Troughs for greywater: $130?
Laundry: $350 (used washing machine, centrifugal dryer is not needed if it has a 1200 rpm spin cycle so reduce to $200)
Toilet, dehydrate pasteurize (used electric slow cooker for pasteurize takes 150 Wh per 2 weeks maybe so included under “misc” in electric demand section): $80?
misc stuff have forgotten etc. :$200


Air conditioner, cheapest and smallest model around see post on AC watch the eff.: $150

temperature sensor option $5 also hot maybe water tank thermostats

cheap thermostatic valve :


Written by gregor

February 6, 2011 at 19:51

Posted in Uncategorized

3 Responses

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  1. Wow! The amount of thought you put into this is amazing. Unfortunately, I have a report to write and don’t have time to digest all the details. I will keep it in mind though as I think you are on to something!

    Ps. I’ve seen a lot of homemade air-conditioners from fans circulating cold water through copper wire that is weave through the fan grid. Perhaps this will work in place of an air-condition with less wattage. I haven’t tried it yet, but will try it this summer.

    Thank you!


    February 6, 2011 at 21:56

    • Yes, that is what what you would be doing of you were to use the giant greywater tank as ice for ac in summer.


      February 7, 2011 at 11:00

  2. I hope you’ll focus on both rural and city. I’m interested in tiny houses in the city out of pure interest even though it’s not my lifestyle choice. I’m hoping you’ll still cover rural too since lots of people have the ability to work anywhere and the movement to live simply in smaller houses out away from the cities is ongoing and very strong.

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