Off-Gri(n)d Tiny House

[jebatty]

Dreaming and wishing is moving into a plan: build an energy independent, off the gri(n)d tiny house. Any input, ideas, debunking would be appreciated. I want to make a reasonably mature proposal to an environmental organization to partner on building this, with the goal being that if it works, the organization could expand the concept into living quarters for staff.

Off Grid Tiny House Concept: a livable home that is energy self-sufficient.

Build a shell tiny house, fully insulated and equipped with needed systems (solar hot water collectors and solar panels, hot water hydronics, and basic electric); collect data for one year to determine feasibility and practicality.

1) Dimensions
12' x 16' = 256 sq ft
1 - 3' x 6'8" insulated door (R2+)
3 - 2' x 3' window (R2})
1 - 1' x 12' window (R?)
Tube light

2) Basic features
general lighting: self-contained, rechargeable lamps (Nokero)
1-2 DC lamps for special needs
in-floor radiant
rainwater collection: non-potable water needs
toilet: humanure, composting, evaporative ???
waste (gray) water handling: ??? want to avoid a septic system
DW water storage: 5+ gal ??? (livable tiny house may need a well)
DHW via coil in open hot water storage tank
DC hydronic pump(s): need to calculate energy requirement
DC DW/DHW pump(s): need to calculate energy requirement
cooking: propane gas burner(s) - can this be avoided?
cooking (except harsh winter): Rocket stove-type
solar oven: to be used outside, except harsh winter (could this be built into a wall ???)
solar slow cooker, to be used outside, except harsh winter (could this be built into a wall ???)

3) Preliminary heating requirements: want to be able to provide 24 hours of heat, assuming no solar available, otherwise solar to meet daily demand.
solar hot water collectors, drain back, size to meet design requirement (9400 HDD)
est'd heat loss:
... -15F= 6000btuh = 450 gallons at D40 (design temp, area does experience lower temps occasionally)
... at 0 = 5000btuh = 360 gal water at D40
... at 20 = 3500btuh = 251 gal water at D40
... at 40 = 2100btuh = 151 gal water at D40
estimate 450 gallons of open, insulated storage (3,750 lbs +/-)
450 gallons at delta-T=40 (storage from 140-100F) = 150,000 btu
6000 btuh x 24 = 144,000 btu required storage
open storage: need 60 cu ft (450 gal) (3 x 6 x 3.5 = 63 cu ft)

4) Preliminary electric requirements: need at minimum to supply DC pumps
solar panels, batteries: need to calculate electric requirement and size to meet design
lighting: generally self-contained rechargeable (Nokero)
radio, computer tablet device, cellular/internet connection, other: self-contained rechargeable batteries, NiMH (Eneloop) or Li-ion, etc.
small battery charger: 12V, Nitecore or similar; also multi-voltage output operating from 12V

5) Insulation, other requirements
R30 minimum walls and floor
R50 minimum ceiling
fresh air supply and venting: calculate air exchange requirements and size accordingly

 

[GaryGary]

Dreaming and wishing is moving into a plan: build an energy independent, off the gri(n)d tiny house. Any input, ideas, debunking would be appreciated. I want to make a reasonably mature proposal to an environmental organization to partner on building this, with the goal being that if it works, the organization could expand the concept into living quarters for staff.

Off Grid Tiny House Concept: a livable home that is energy self-sufficient.

Build a shell tiny house, fully insulated and equipped with needed systems (solar hot water collectors and solar panels, hot water hydronics, and basic electric); collect data for one year to determine feasibility and practicality.

1) Dimensions
12' x 16' = 256 sq ft
1 - 3' x 6'8" insulated door (R2+)
3 - 2' x 3' window (R2})
1 - 1' x 12' window (R?)
Tube light

2) Basic features
general lighting: self-contained, rechargeable lamps (Nokero)
1-2 DC lamps for special needs
in-floor radiant
rainwater collection: non-potable water needs
toilet: humanure, composting, evaporative ???
waste (gray) water handling: ??? want to avoid a septic system
DW water storage: 5+ gal ??? (livable tiny house may need a well)
DHW via coil in open hot water storage tank
DC hydronic pump(s): need to calculate energy requirement
DC DW/DHW pump(s): need to calculate energy requirement
cooking: propane gas burner(s) - can this be avoided?
cooking (except harsh winter): Rocket stove-type
solar oven: to be used outside, except harsh winter (could this be built into a wall ???)
solar slow cooker, to be used outside, except harsh winter (could this be built into a wall ???)

3) Preliminary heating requirements: want to be able to provide 24 hours of heat, assuming no solar available, otherwise solar to meet daily demand.
solar hot water collectors, drain back, size to meet design requirement (9400 HDD)
est'd heat loss:
... -15F= 6000btuh = 450 gallons at D40 (design temp, area does experience lower temps occasionally)
... at 0 = 5000btuh = 360 gal water at D40
... at 20 = 3500btuh = 251 gal water at D40
... at 40 = 2100btuh = 151 gal water at D40
estimate 450 gallons of open, insulated storage (3,750 lbs +/-)
450 gallons at delta-T=40 (storage from 140-100F) = 150,000 btu
6000 btuh x 24 = 144,000 btu required storage
open storage: need 60 cu ft (450 gal) (3 x 6 x 3.5 = 63 cu ft)

4) Preliminary electric requirements: need at minimum to supply DC pumps
solar panels, batteries: need to calculate electric requirement and size to meet design
lighting: generally self-contained rechargeable (Nokero)
radio, computer tablet device, cellular/internet connection, other: self-contained rechargeable batteries, NiMH (Eneloop) or Li-ion, etc.
small battery charger: 12V, Nitecore or similar; also multi-voltage output operating from 12V

5) Insulation, other requirements
R30 minimum walls and floor
R50 minimum ceiling
fresh air supply and venting: calculate air exchange requirements and size accordingly

Hi,
You might look at a scheme to get higher R value windows and door. A quick heat loss indicates that they are the biggest loss, and that getting them up to R4 would cut total heat loss by about 25%. R4 windows would be expensive, but R2 windows with R2 or 3 thermal shades might be pretty reasonable.
I don't think that an R4 (or R6) door is too hard to come by these days.

How about rain water collection off a steel roof?

In the heat loss on a small structure like this, internal gains from warm bodies etc helps to reduce the heating requirement -- maybe account for that?

Gary

 

[jebatty]

Excellent ideas. My heat loss calc was pretty rough, and as the plan moves forward I will tighten that up. MN has some cloudy stretches in Nov-Dec, starts to get pretty sunny in Jan-Mar, but of course Jan also is the coldest month usually and the lowest sun angle + sun availability. I likely will intentionally err on the side of more rather than less in planning for winter heating.

With a little luck, I will be able to obtain some very high end windows, plus plastic film and thermal shades may get the windows into the R8 (U-0.12) range. I am going to make the door, wood frame with 1-1/2 or 2" foam core, which would end up R3+ in the frame and R12 in the core.

Warm bodies are significant. I think the plan should be for a single person, working, and gone from the house as much as 12 hr per day. Night with a warm body will be important, and I may have to introduce a heat source to approximate a person to get more accurate data representation.

 

[Vic99]

I like it.

1) Loft for sleeping?
2) What kind of roof?
3) I agree, windows are weak point. You could build a plexi glass type cover to go over the R-3 windows (aren't double pane, argon injected windows R-3). Should be fairly cheap. The plexi would bump to R-4, I think. Could be removable. Plastic over that should be R-5
4) Batteries for solar could get expensive, maybe double cost. Heard they would last ~5 years before replacing, unless you are careful all the time about not draining battery.

 

[jebatty]

1) Loft for sleeping: right now, no. The proposal will be for a shell for data collection. I did work out a preliminary floor plan. The bed will be a "murphy" style bed on one end, fold up against the wall to give floor space during the daytime. I will post the floor plan for comment after I work on it a bit more.
2) Roof: probably metal. Drain back hot water solar collectors on the south-facing roof, with solar panels on the south-facing wall. I still have to work out the btu output and size these for Dec-January in MN, Dec for clouds and often fairly cold in late Dec, and Jan for sun and really cold. This winter weather data for 2012-13 should be quite close to what the plan should be for.
3) Windows: most double pane are in the R2-3 range. There are windows in the R12 range. I hope I can get a lead on a substantial discount or donation of windows well above the R2-3 range. Regardless, more window treatment will be necessary (plexiglass, plastic film, thermal shade, etc. I think windows might be really important for livability in a small space.
4) Batteries: yes, cost; but the plan intends to really minimize electric demand. Check out nokero.com for lighting. I already have 4 of the N220 lights, self-contained rechargebable, and I use these in my home. Put them outside and let them charge in the daytime, up to about 5 hours of light on "hi" brightness at night.These use AA NiMH batteries, so a few spare charged batteries on hand to cover when needed. And cell phone + a tablet (IPad, Kindle, etc.) for phone, media access, etc. also have their own batteries, and they can charge off a 12V system. At this point I see the 12vdc pumps for the heating system being the major draw, and I haven't spec'd these out yet to determine how much electric, solar panels + batteries, I will need. I also have a possible source on lightly used AGM 12v-100ah batteries at a very reasonable cost.

In the end, if this works, it still needs to be livable to a segment of the population. So, the plan cannot be minimalist to the absurd. And, the final "Off the Gri(n)d Tiny House" may have to end up a little larger than 200 sq. ft., although I'm seeing more and more big city apartments in the less than 200 sq. ft. range. A pipeline dream may be a cluster with a central shared area, which is what the environmental organization might move forward on, but I don't want to go in that direction until I know whether a prototype can work.

 

[jebatty]

If I assume no windows/doors, and floor/wall at R30 and ceiling at R50, then heat loss at -15F is 3256 btuH and at -20F it is 3447 btuH. With better window/door performance, and heat from an occupant, perhaps a heat loss of about 4000 to 4500 btuH would be more realistic. I still would be inclined to size water storage at 450 gallons for planning purposes. If data over a year would show that less would provide adequate performance, then it could be down-sized for building an actual living space.

 

[dougstove]

For the composting toilet:
There is a direct tradeoff between the minimum compost volume and the required rate of compost digestion.
A large pool size can compensate for a slow or variable composting rate, or a variable input rate.
A small pool size is lower mass, but needs consistently high composting rates, and can be problematic if the input rate varies.
Depending upon how you built it, the composting mass could serve as a heat source and heat sink, in, for example, an insulated basement.

For true sustainability, a cluster of such houses might share some central facilities, like laundry, and possibly even showers & toilets, to help even out the waste input rates.

Also, re-using grey water can be problematic, since using greywater in a toilet tank can lead to biofilms and even pathogens like Legionnaire's disease. It can be done, but it is not as simple as replacing a treated water input into an ordinary toilet tank.

 

[Highbeam]

If your only real "off-grid" requirement is that you are not directly tied to the grid then why futz around with the other compromises? You have propane so use it. Septic systems work very well with no electric input. Why not just roll up with an RV to your spot equipped with a big propane tank and a septic system?

Is off-grid the best way to describe this effort?

 

[Circus]

At this point I see the 12vdc pumps for the heating system being the major draw​

IF the hot water tank is above the collector and in the heated space you could use a siphon type (most common). You would need antifreeze and a heat exchanger but no pumps. When the sun doesn't cooperate you'll need a camper water heater. I once bought a raty 24 ft camper trailer for $100. It had all the systems so you wouldn't need to start from scratch.

 

[mr.fixit]

Having run a 2.7kw off grid system thru 2 winters now,here's my thoughts.
Those dark days of Nov-Dec-Jan really are hard to get thru on strictly solar.Little by little the batteries get drained and even if you get a stretch of sunny days in a row,its hard to get them back to 100% charged without a generator.

With smaller true sinewave inverters available,and pv panels at more reasonable prices,seems it would be much simpler keeping everything AC? You would be able to use common and easily available pumps,switches,wiring etc. I have a Grundfos Alpha pump in my system that uses very few watts.

As far as batteries go,from what I have read on some of the solar forums,the easily obtainable 6v golf cart deep cycle battery has been found to be one of the lowest lifetime cost per kwh.

I also have a solar hot water heating system in one of my buildings with infloor radiant. The collectors are based off of Gary from Builditsolar's design. The collectors work well,but like the electric,it takes a hit on those long cloudy periods common in the winter here. So you really need a good backup for the heat to.

On the size of the little house,did I once read that it is possible to get too small,where there isn't enough mass in the structure?
Could that affect the heating with infloor ? I don't know about this so that's why I bring it up.

 

[jebatty]

dougstove: I agree on the cluster. We have the land to do this, but we are 15 mi from the nearest towns and most of the jobs. Transportation is a killer if the goal is to get really close to sustainability. I don't plan to reuse grey water, but perhaps in some fashion to use rainwater from a roof collection system, could be sanitized with bleach and used as dish and shower water? The composting toilet needs continuing research on viability., and I'm thinking more of an evaporative toilet design. I think the chance of it working well with heavy use could be problematic, but for 1-2 people should be doable.

Highbeam: Might not be rational in everyone's mind, but in my mind putting an end to use of fossil fuels is a worth goal, thus no desire to use propane unless no other alternative. Septic systems are expensive, in the range of $5000 and up depending on conditions. Would like to avoid that expense. Off the grid may not be the best description, but what I am proposing truly is off the grid + another step towards sustainability. Consider it my passion -- no tie to the petrol-oilman.

Circus: thermosiphon could work. But cost for antifreeze for 450 gallons of hot water storage would be very expensive; thus drainback hot water collectors seems a better way to go, even with required pump(s). Going 120/240 AC is a real possibility, and probably using micro inverters. AC also would make it easy for an emergency backup generator to be used if needed. But I still would need batteries for the times when the sun doesn't shine, and with that going DC may make more sense. .I'm not committed to in-floor radiant, but I think I need to be committed to low temperature radiant. Other low temp radiant ideas? You are in west central WI. If willing, PM me with location and contact info and maybe I could make a visit to talk about your experiences. Thanks.

I really appreciate the input. Maybe someone, and probably so,has already tried this. I would like to learn from others without having to learn what already is known.

 

[Circus]

Circus: thermosiphon could work. But cost for antifreeze for 450 gallons of hot water storage would be very expensive; thus drainback hot water collectors seems a better way to go, even with required pump(s).​

Antifreeze would be used only in the heat exchanger and collector. 80 sq ft of collector wouldn't heat 450 gal.. In January, may heat 30. Maybe.

 

[jebatty]

That's in part why I'm thinking water, drain-back - eliminated the efficiency loss with a heat exchanger. But I agree, this will take some careful planning and sizing.

 

[Circus]

Investigate use of the grid to store summer energy for use in the winter, phase change materials and aerobic treatment.
PS Heat exchangers are efficient. There just isn't much energy to harvest in a Minnesota december.

 

[jebatty]

Maybe it's more accurate to say that I don't see a need for a heat exchanger with the drain-back system. The collectors can directly heat all the water in the storage tank. I have emailed a top solar hot water collector company and asked for its input on the concept, design, etc. It will be interesting to see the response.

 

[wazzu]

Why no outhouse? It would be cheaper and easier.

 

[btuser]

Why no outhouse? It would be cheaper and easier.

Might not be allowed. I've looked into low-impact buildings for camp sites and getaways. My plan was to stick a yurt on a "unbuildable" lot with no utilities and use a composting toilet to avoid septic. No go, not one town would even consider it.

 

[Seasoned Oak]

I like it.

1) Loft for sleeping?
2) What kind of roof?
3) I agree, windows are weak point. You could build a plexi glass type cover to go over the R-3 windows (aren't double pane, argon injected windows R-3). Should be fairly cheap. The plexi would bump to R-4, I think. Could be removable. Plastic over that should be R-5
4) Batteries for solar could get expensive, maybe double cost. Heard they would last ~5 years before replacing, unless you are careful all the time about not draining battery.

For windows i would just make myself some 2" foam interior doors that close over the windows at night. A simple solution.

 

[Seasoned Oak]

Modern composting toilets work very well.Go for months between emptying. Even those sawdust open jobs perform without odor.

 

[jebatty]

I like the foam "doors" to cover the windows, especially at night. Can keep the doors open in the daytime when someone is "at home." I have made and used a humanure toilet using sawdust and planer shavings. Works well also. This is the simplest and least expensive option. An outhouse in our area requires a permit and would be another permanent-type structure, which I would like to avoid. Also must meet septic regulation requirements. It would be worth pricing one just to see what an outhouse install would cost.

 

[EatenByLimestone]

If you are looking at putting the tiny house on an unbuildable lot maybe you can do what other small houses have done and build it on a trailer. Since it is a trailer it doesn't need a Cert of Occupancy.

The main issue I see with a super tiny house is well, it's super tiny. There isn't space for all of the things you are discussing such as waste water heat exchangers and such. For a toilet, how about renting a port-o-let? It would be cold in the winter, but would save lots of space and deal with the problem of waste storage. A well insulated house the size you are talking of will not take much to heat, so propane may be the most environmentally sound way to heat it. With the right amount of insulation, and considering body heat as a source of btus, you might be able to get the house to the point where a 20lb tank would last more than a week. Superinsulated houses use insanely low amounts of energy to heat them.

Matt

 

[Seasoned Oak]

I got an acre in the woods that i cant build permanent on(because of septic,ground water too close to the surface) So im looking at something like this so i can spend time there. But i can legally put up a 20x 30 cabin with no foundation so that is the plan.

 

[jebatty]

Back to basics. The goal of the tiny house concept is "a livable home that is energy self-sufficient." It is a concept experiment, and if it works, the environmental organization may develop it further for staff housing. My goal is 100% solar, no fossil fuels, not even propane. I know this is extreme, but that is the direction I want to move.

I have land to build a mcMansion, if I wanted to; lots of forest for firewood; good soils for a septic system; no permit issues. County zoning will allow the tiny house as a storage building, as I don't intend to live in it, just collect data. It could be re-permitted later as living quarters.

Lots of good ideas have come forward. These are now on my checklist for further development:
1) steel roof for rainwater collection (also collect run-off from collectors installed on the roof).
2) will not reuse grey water, but I need to dispose of it without a septic system -- probably just toss it out on the ground, which I think I legally can do if I do not have a well.
3) windows with foam doors, possibly thermal shades, plastic film, etc. -- need high R-value.
3) toilet options: humanure, evaporative, composting -- but needs to be electric free, unless solar.
4) skytube light -- I know these work very well, but a couple of windows still need to be included to reduce the claustrophobia and provide ventilation.
5) thinking about a small solar fan ventilation system to get rid of humidity and bring in fresh air.
6) thinking more about pressurized hot water solar collectors with antifreeze, not drainback. Pumps for drainback are fairly energy intensive, depending on lift height. A DC or AC circulator in a pressurized system would use much less electricity. I have a 6" x 12" by 100 plate hx, brand new, which could be used. My guess is that approach temperature would be less than 5F.
7) golf cart batteries deserve a good luck. I saw these at a local big box store, 200ah at 20 hour rate, 6v, for $90 each. Two of these would provide about 100 watts of power for 16 hours at 50% discharge, which is about as low a discharge as I would like to see.
8) not decided on a DC solar system or an AC solar system. Micro inverters on each panel are interesting. Efficiency losses on reconverting to DC for battery charging and inverter to provide AC from batteries may be an issue.
9) I do have line voltage available as emergency backup, although a small sine wave generator likely would be the first emergency backup to maintain the off-the-grid concept. I have a Champion 2000w inverter generator.

The major supplier of solar hot water panels has responded positively to my inquiry and will provide me with its input on whether solar hot water, with sufficient storage, can heat the house all winter, or at least to what low temperature this could be achieved. Supplemental energy use is not the goal, but given cloudy, cold Dec and Jan, and sometimes Feb, in my area, it might be unavoidable. Design temp is -15 to -20F, but -30F and colder for brief periods is very likely. This is a critical issue.

 

[Seasoned Oak]

Jebetty
Should also be able to transport on a trailer.Or actually built on a trailer frame. For one thing to get around most septic requirements be should also be mobil in case of flood,fire ect. Given the small size,should not be difficult.

 

[mr.fixit]

Here's a place in Canada that stores up solar heat all summer for use in the winter,large scale. http://www.dlsc.ca/
I think it says it supplies 90% of space heating thru the winter.

When I built one of my buildings with solar hot water collectors,just for experimental purposes I put an insulated sand "pit" underneath the slab.I think it was 4'by4'by 8' with 250' of pex in it.In late summer I heat it up with the solar, thinking the ground under the slab would take longer to get cold as winter progresses.It works but after you stop pumping heat into it ,it dissipates rather quickly.
I thought maybe I could draw some heat out of it early in the winter and put it into the slab,but not so much.

One fall I tried to see how far into the winter I could let that building go strictly on it's solar heat.Of course I didn't keep a log or anything,but from memory it went till Dec. 1st and then it got down below 48* in the building and I needed to use it so the boiler took over and brought it back.
I think with infloor heat,if you let the slab drop down too far,it takes so much to bring it back to normal levels.Now what I do is have the boiler heat the solar storage tank if it drops below 85*.

On the micro inverters you are referring to,I always thought they were strictly for grid tie use?

Big thing on the electric solar system is to know what your daily loads will be and size the system for the lowest producing months,Nov-Dec-Jan-Feb.