It occurred to me today that I don’t think I have as yet talked about hot water. I am not sure why as it seems to be pretty central to operations at Ling’s Meadow.
We had always planned to experiment with a rocket stove to heat water for the shower and sinks, but in year one time ran away with us and we had to make do with a homemade solar panel system. If we are honest it only ever really took the chill off the cold water unless we had a few days of scorching weather.
It was a pretty simple design, using two radiators painted black under a glass cover to transfer heat to the hot water tank. Water was drawn through the system by thermosyphon (the natural circulation caused by heating the water). We had no way of monitoring the actual temperature of the water apart from the screams of the campers using it.
In year two we upgraded, and made the system more efficient, by detecting the temperature of the water in the panels and using that to turn a pump on and off. The pump forced water through the system better than the thermosyphon and transferred heat to the tank more efficiently. The problem with the improved system is that it didn’t (and still doesn’t) get the water hot enough for a decent shower, but did heat it just enough to keep the water at a temperature where Legionella became a risk factor (we use temperature and regular emptying of the tank to control Legionella). But, by now we had added in our new wood-fired rocket stove and this was able to take over, continue heating the water and boost the temperature to safe and shower comfortable levels (60 degrees or more).
Rocket stoves are designed to be a very efficient way of burning wood. This means that we use reasonably small quantities of kindling for the amount of heat that is produced. The stove produces a secondary burn of the gases created by the wood fire so you get more heat for your money. We have adapted a design for a rocket mass heater but rather than heating space it is heating water. Our stove is made up of a domestic radiator inside a 55 gallon steel barrel. Hot gases from the wood fire flow through the burn chamber into the steel barrel and circulate around the radiator, heating the water running through it. The gases then exit through a chimney. The heated water runs through pipes in the hot water tank and transfers its heat to the water stored there. This is the same principle as a domestic hot water system (pre ‘on-demand’ boilers). When it was first built, we used thermalite blocks to build the burn chamber and a reclaimed stove pipe we found in the shed for the chimney.
This year we replaced the thermalite blocks with harder wearing aircrete equivalents and storage heater blocks to form the burn chamber. These seem to be holding the heat a lot better. Neel also rewrote the computer software (its all run on an Arduino) so that the pumping rate in the system adjusts with temperature changes. This allows us to regulate the temperature of the circulating water to improve efficiency and also safety.
Since we built the stove, we have talked and pondered about the pros and cons of insulating the steel barrel, and many campers have asked us about this too. We hoped it would raise efficiency, but worried it would reduce the draw and the effectiveness of the rocket effect. A few weeks ago we wrapped some left over insulation around the barrel to experiment, and found that both things were true – the stove is harder to light, but the increases in efficiency far outweigh that trouble. The amount of wood we have to burn to get the tank to 60 degrees is reduced considerably. It also reduces the amount of trips to the stove to add more kindling! In addition, now that we have neatened up our first attempts at insulation, the stove looks almost like the body of a metal robot!
The top of the steel barrel is a great place to heat kettles of water for washing up, boil potatoes etc. The insulation got in the way of this for a while but we have now cut a hole through to reveal the top of the steel barrel again. We initially lined the square hole in the insulation layer with a wooden frame (your kettle sat inside this) but we had to swap this for a metal version as the wooden one got a bit too hot/charred! It just goes to show that the rocket stove is working though. A wooden lid neatens everything off and provides rain protection.
We have retired the solar element of the system for now as it just can’t keep up with the new boy in town – our wood fired rocket stove. Although Neel (sitting opposite me as I write) has reminded me that nothing is ever retired, it is just on hold.
We are still limited by the size of our hot water tank, so we don’t have enough hot water to provide a hot shower to all every day. We get the rocket stove going each morning so that campers have hot water that evening and (depending how enthusiastically used) the following morning. The success of the system relies on sharing and consideration and so far it seems to be working thanks to the enthusiasm and communal spirit of our guests.
