January 10, 2005

Long Burn

A long burn model rocket engine can give about 7 seconds of thrust.
My Pa has a woodstove in a room by the kitchen and does about half the house heating with wood. I used to help split and haul wood when I was growing up, and it was my job to keep the woodbox full. In the fall and spring we would burn punky pithy scrap and bark, poplar and cottonwood even, but the real quality wood was always saved for the dead of winter. Seasoned oak gave good heat for a long time-- the coveted long burn.
Brad Collette writes asking what I know about Swedish stove technology. Well, there is a popular classic model consisting of a cylinder as tall as the room and about 3 feet in diameter, covered in white ceramic tile and filled with sand. At the bottom is the firebox and on top of that is sand for storing heat-- a lot of heat, for a long time. These stoves are apparently very efficient and look great. They are known as 'kakelugn,' literally a ceramic oven, and pictures of some can be found at http://www.nibe.se/brasvarme/produkter/kakelugnar/kakelugnar.htm
According to the sales literature they have the following properties:

5-channel smoke tube for maximum heat transfer to the heat storage chamber
The one-ton stove has a cool-down time of one day
Efficiency of 87 % to squeeze the maximum energy out of every stick of wood
Two burns per day gives a constant heat output of 2 to 4 kW
6 kW output possible for cold-waves
Fast heating possible using the built-in ducts and fan

Our house was built in 1969 when everyone was optimistic and hydroelectric and nuclear power were very cheap in Sweden-- it is heated by electricity! What I've done is replace all the 35-year-old heating elements with newer models, look over doors and windows, and increase the attic insulation from 4 " to 16 ".
My family used to visit a guy's cabin on Rainy Lake and he had built the most beautiful stone/concrete fireplace. Rather traditional looking, but with lots of rocks to hold the heat. If I was really smart I would first build a basement under our house, then put a pool of water there, and store summer heat to use in the winter and winter cool to use in the summer. Brad, how much do you know about heat pumps?


At January 13, 2005 6:20 AM , Blogger Brad said...

We had a heat pump in Texas and it worked great. When we moved to Missouri, I wanted to do a ground-source heat pump, also called geothermal. Same idea but with a buried loop instead of outside heat exchanger and compressor. Ground source is really nice but a bit expensive (about $10k to install the loops). I couldn't justify it.

The house we're building will be heated and cooled with an air source heat pump which is almost as efficient but stops working at around 15 fahrenheit at which time it switches to propane.

I'm hoping to minimize the propane use with a masonry heater. The one I'm putting in is a finnish design by a company called Tulikivi. http://www.tulikivi.com. Same principle as you described, but with an enormous soapstone mass instead of sand. The thing has its own footing and weighs almost 4 tons...and it has a pizza oven!


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