2020-11-21

Wood Heat: Rocket Stove Mass Heater solution

 My friend Amir has a Zome Village Hipcamp North of Mt. Shasta.

https://www.hipcamp.com/california/georges-amir-kunzler/zome-village-group-campsite

I was thinking of camping there.


Objective

He asked me how I'd stay warm. I took it as a challenge. How can I stay warm from 6 pm - 6 am without having to wake up to feed the fire?


[ It's not the first time I've considered this question. I have a long-standing interest in aquaponics. One of the major cost of raising warm-water fish is the cost to warm the tank.]


Hot compost

I'm particularly fond of the idea of using hot compost to generate heat. A pile of manure and woody material of sufficient size (at least 4' x 4' to start) must be kept moist and it will reach 140 degrees, sufficient to sterilize weed seeds, and the end product is a valuable soil amendment. Although manure may be free, unless it is at hand there is a time and energy cost to transport it to the site. Minor maintenance includes keeping the pile moist and turning the pile once or more during the 4 to 6 weeks of composting, and building a new pile as needed.

Hot compost can directly heat a greenhouse, or living space, or heat indirectly with a heat exchanger. A properly maintained hot compost pile does not have an offensive odor.


Woody debris

Amir has a lot of woody debris on his property that needs to be cleared for fire safety. So there's plenty of fuel at hand.


Design criteria

Minimize the amount of fuel needed to burn.

Even where there is an abundance of fuel, there are still time and energy costs associated with collecting, storing, and preparing the fuel (reducing to usable size). Also, it takes time to tend a fire.

Minimize the burn time

To increase safety and reduce time that the fire must be monitored.

Minimize the smoke

Burning dry wood at a high temperature protects air quality.

Maximize the amount of heat generated

Preheat the air coming into the intake.

Maximize the amount of heat captured

Heat thermal mass, which is stable, rather than air, which is not.

Insulate

Insulate the thermal mass, and the human.

Human factors

Keep the operator dry, provide affordances to feed fuel.

Minimize ash

Dispose of ash properly. Ash makes a good insulation.

Safety

Isolate the fire from anything flammable, provide for water bucket and shovel.


Rocket stove

A rocket stove is simply a stove designed to channel air flow to maximize the burn, there are endless design variations.

The Kelly Kettle is one.

https://www.kellykettle.com/


Why buy when you can build?

I felt I could build a decent stove for less than what I would pay to buy.


This rocket stove video is among my favorites.

https://www.youtube.com/watch?v=FMhUFthG4bU

8 Simple Rocket Stoves”


The 4x4 rocket stove

No stove is needed to create a rocket stove. Simply drill a chimney into a block of wood.

Burning pieces of 4x4 has numerous advantages: the fuel is compact, so it stores easily. It's clean (no barks, no bugs). Because of uniform size and material, we can estimate the burn time, a hour per inch of diameter. I used a 1-1/2" paddle bit. A drill press would help.

It has some disadvantages. It has to be purchased and transported, cut and drilled.

Duct rocket stove

Duct is available in 4”, 6”, and 8” diameters, with endless accessories. Advantages: inexpensive, readily available, easy to build and modify. Disadvantages: heavy, bulky, must be purchased, transported and stored.

This seems the preferred solution for this site. Purchase a chipper. Collecting and chipping fuel takes time. Consider periodically moving the stove to minimize fuel transport.

Identify the camping spot. Minimize the distance between the stove and the living space. And, provide for heat exchange between the hot water and the insulated living space.

Minimize the space I need to heat. Isolate sleeping space from living space.

Insulate with Reflectix and / or survival blanket.


Oils hold more heat

Oils hold more heat than water. Mineral oil is satisfactory. Specialty thermal oils are available. The thermal advantage does not justify the cost in my opinion.


Solution: A 20-gallon drum

Twenty gallons of water weighs 166 pounds, nearly as much as I do. A 20-gallon drum or tank of hot water should hold sufficient heat long enough to keep me warm during sleeping hours.







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