[Stoves] Anticipating future markets for stoves and fuels

[Tom Miles]

Crispin,

In concept you are describing what larry Dobson built in the 1970s and
called the Grendle. 

Alternative Sources of Energy Magazine, 1980, The Grendle Report 

 The Mother Earth News Guide to Home Energy, 1980, An Amazingly Efficient
Sawdust Stove

It was a "hanging grate"  furnace with an afterburning chamber for wet bulk
fuels like sawdust and hog fuel that would burn efficiently. Heat transfer
to the house was through hot gas in roman-style hypocaust ducting.
http://en.wikipedia.org/wiki/Hypocaust

Grendle was followed by Helen and Gertrude. 

Since then Larry has built a dozen different designs, some of which can be
seen at: 

http://www.stiltman.com/html/energy_from_waste.htm

It seems to me that for stick wood your hybrid cross-draft design would be a
useful heat generator for a bench heating system. 

Tom

 

 

From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: Thursday, June 23, 2011 9:47 AM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Anticipating future markets for stoves and fuels

 

Dear Tom

Thanks for the industry update.

The device I am thinking of is called the Rocket Mass Heater. Just found the
email.  I did not see much 'rocket' about the design but it may be that the
name is an older use of it. Not sure. He says Larry was working on it, or
something that inspired it.  The guy is Daniel Roggema. He has been working
on stoves for about 35 years, by my reckoning. I do not know much about him
though we have corresponded a number of times. There is an Apro' publication
from 2006 called Rocket Mass Heaters that describes at least one version of
it.

The interesting part of the design is the use of an insulated chimney riser
and a heat exchanging drop, with no chimney exhaust. I have not seen this
before, but it is hard to know when it was first used. There are many
strange things in the old libraries. Made from tincanium the thing looks
dangerous, but the principle makes sense: you use the heat rising in the
insulated part to push (under a low pressure) gases horizontally under
sleeping benches. The benches are made from pounded (crackable/shrinkable)
clay so having a positive pressure in them sounds really dangerous. But
again, the principle is sound. 

According to my analysis, it should be possible to make a condensing furnace
in this manner without a fan, meaning we should be able to get >92%
efficiency as a heater. This holds open the possibility that in Nepal,
switching from an open fire to a stove would actually increase the system
efficiency, even though nearly all the heat from the open fire is deposited
into the room. It might be too expensive or heavy but should work. In
Mongolia it would be affordable.

Combined with a good combustor, the up-down system in a tight stove should
decrease the total heat requirement by reducing the excess air ratio in the
stove (and air exchanges in the room), ergo, less fuel required.

It is on the agenda for this year's work.

Regards

Crispin

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