Douglas Woods

Are large metal buildings and light-straw-clay the perfect companions?

The latter is a heavy insulation material that requires substantial thickness and weight, about 2x thick and 20x heavy of glass fiber for the same R value.

Can the cost advantages of light metal buildings and light-straw-clay be combined to create affordable energy efficient multistory buildings?

Light metal building example
https://www.texshed.com/50-x-100-x-16-commercial-warehouse-metal-building-v3Vo.html , $80,000 for 5000sqft "shell" is $16/sqft.

Commercially, how much does it cost per cubic ft to make light-straw-clay bulk or panels?

I cannot find one online, so I devised one.
Will it work?
How is its efficiency?
Is it better to point the propane flame to the waste at bottom of waste bowl?

Phil Stevens wrote:Have you built a J-tube according to the dimensions known to work? There are several factors at play, so it's a good idea to start with a tried and true configuration and then experiment to see how far you can depart from the basic design, changing one parameter at a time to figure out if it will work or not.

Just by looking at the plan, I think the feed tube is too tall and will be prone to creating a reverse stack effect and working against the desired flow. I'm not sure I understand the air holes in the barrel holding the rocks...is this a secondary combustion chamber? Sending the combustion gases directly through a bunch of rocks will remove too much heat from that zone, hampering the burn and stalling the draft.

Sorry my illustration is far from clear, the bottom holes are for flue to pass into the barrel.
Combustible gases might ignite at 500'F. Rocks need to be above this temperature in order not to kill the flames. Maybe use 500F as the start point of refueling cycle, so the next batch of fuel will always begin with relatively hot rocks. Cold-start with propane or electric heat.

The design goal is a rocket mass heater for small spaces, requiring minimum construction work, using masonry stove body, and a 55 gallon barrel containing crushed rocks as heat storage.

Do you think the following design will work as a rocket mass heater? 55 gallon of crushed rocks is around 1000lb (450kg). The floor would need support from below.

I guess there could be a drafting problem when the rocks are cold, could be solved by adding an electric draft fan on top of barrel.

The fuel box size should be designed such that one batch of fuel will heat rocks to a relatively high temperature, such as 1200°F, then we close the throttle and let the barrel radiate heat to the room, until it cools off.

Any other possible issues and improvements to this design?

Michael Cox wrote:Industrially, solids are burned using a fluidised bed. Dry the slurry, crush it to power or lumps. Tip it into a vertical tube, and blow air into the bottom. You are aiming for just enough velocity to suspend the particles to be burned without blowing them out of the top. You obviously need a source of ignition as well.

This system if done properly is clean burning and robust, but needs to be designed well and would be sized for large scale use. Think, toilet waste from a medium sized community. Not and individual toilet. You run into all sort of problems of scale trying to burn tiny masses of material - heat loss to the fabric of your incinerator etc... You would need to supply large amounts of external energy (heat) and have a super insulated system to ensure a clean and safe burn. Way beyond the technical capabilities of a typical cheap DIY system.

We have used composting system here with great success. Incredibly low tech - literally a few plastic buckets and some sawdust free from the local sawmill. Look up the "Humanure Handbook" - available as a free pdf.

Allow me to calculate the energy cost of incineration here:
Average urine production in adult humans is around 1.4 L of urine per person per day, and 0.4 kg of feces.  For simplicity, we assume this is 1.8kg of water.
specific heat capacity of water is 4.184J/gram/Celsius , plus 2260 J/gram for vaporization.

Boiling 1.8kg of water to vapor from 24C room temperature costs (76*4.184+2260) * 1800 = 4640371 J = 4.64MJ = 1.29 kWh

So it use 1.29kwh per day. The capital cost for generating this power is around 200W of solar panels. If it costs $3/w to install solar panels, the capital cost for energy is $600 per habitant, which is much cheaper than septic tank + leechfield system.

If the heat is generated by burning propane, "combustion of propane produces about 50 MJ/kg of heat". Because propane fire is not 100% efficient, let's say 50% efficient, it uses around 0.2kg (1/15 of a gallon) of propane per day, or $0.2 per day, $73/year fuel cost.

Gerry Parent wrote:Hi Douglas,
Before delving into the complexities of your plan, have you ever tried a much simpler bucket compost method?
An internet search for "humanure” willbring up lots of good information.

Thanks for mentioning this, Gerry. Unfortunately, compost toilet is culturally incompatible with many residents and regulatory bodies. While desiccating and incineration is widely known as a reliable way of disinfecting, composting is not.

Septic tanks and leech fields are not affordable for everyone.
Flushing toilets need water, inconvenient for arid areas like the Mojave and Arizona-Sonora deserts, and RVs.
These calls for housing and RV designs that do not discharge black water.

While gray water can be discharged as landscape irrigation,  human waste must be sanitized.
There is already several incineration toilets on the market, but they are far from affordable.
Given we already know the design of masonry heaters, how to build heat-resistant masonry incineration toilets?

Let's say, we use electric heat to dry and ignite human waste and discharge the stinky gas up the flue.
I guess the part that have contact with both wet human waste and fire must be sheet steel. Other parts can be masonry.
How to design such metal/masonry incineration toilets? Any existing designs to copy from? Is an ash drawer necessary?

John C Daley wrote:Yes its possible, using a pond with a glass roofing apon which the evaporating water can condense and trickle away to a container.
A similar process can be used to catch dew at night.

This web page explains the mechanics of the process
Solar water still

And another which I found by searching for 'grey water distillation'
grey water distillation

The 1st video is not an evaporation pond but a specific water absorbing material. The 2nd video is too expensive, concentrated solar is about 2x more expensive per kw than solar PV.

Have anyone successfully used an evaporation pond to turn gray water back to potable water?

60-100 miles north of Los Angeles, Mojave Desert is a vast, largely uninhabited land with relatively nice weather.

Right now the difficulties for homesteading is the lack of water supply and lack of precipitation.

Mojave has very little precipitation during months of April to October, it cost a lot to store enough rainwater for half a year.

Water have to be trucked in. There are city water 10-30 miles away at the grocery store, so it's possible to bring a tanker trailer of maybe 500 gallons to fill up at grocery store.

We can use incineration toilets to save toilet flushing water, so let's only count gray water (everything not toilet)
Even with navy shower of 3 gal/person/day, showering takes 12 gal for a family of 4, 500 gallons don't last long.

What if we use a solar evaporation pond under a greenhouse? A 1ft shallow pond that can be bulldozed up, bury in a layer of anti-seepage film, and have a very low rise (maybe 3ft) greenhouse over it, and then use a dehumidifier inside this green house to condense evaporated water?

My estimates: cost of anti seepage film is $0.5/sqft, cost of greenhouse dome $2/sqft,  1 sqft can evaporate 0.1 gallon of water per day under clear sky.

If 30 gallon is used each day, we need 300sqft of evaporation pond, costing $750 in above ground materials or maybe $1500 if labor is calculated.