Tuesday, June 21, 2011

Cook Stove Water Heater

Today Nicholas and I took a break from incinerators, and he took me around Kampala to show me one of his other projects. He has developed a cook stove that also boils water to make it safe for drinking and warm for bathing. In Kampala/developing Africa, most cooking is done on either wood burning or charcoal stoves. Electricity is very expensive, and there is not very much to go around. Since the water is not safe to drink from the tap, a lot of people resort to electric water heaters to clean their water for consumption and bathing. This is a huge drain on electricity and is not only expensive but also takes valuable electricity from other parts of the city where it might be needed for more important applications. To combat this issue, and to utilize power from cooking that would typically just go to waste, this water heating system was developed. The cook stoves traditionally consist of a clay "bowl" filled with charcoal with a grate on top. Instead of this clay bowl, Nicholas created a stove that had hollow walls that water could enter to be heated. The system is basically a closed loop driven by the steam generated in the cook stove. Cool water from the bottom of the water tank enters the cook stove where it is heated. Because of the rise in temperature in the cook stove, the increased pressure drives the heated water out of the stove and into the top of the water tank that used to be only cool water. Because of the temperature difference, the cool water and the hot water don't really mix because of the temperature difference, but soon because of non return valves that stop back flow, the whole tank of cool water is replaced with clean, hot water. Pretty cool stuff. This system greatly reduces electricity use, and because of the insulation in the tank, the water can be kept hot for several days. The different stoves varied in size, and one of the stoves Nicholas installed, is designed so that it delivers hot water all over the house.

Here is a picture of the whole system. This is a pretty small version. On the left you can see the cook stove. The two tanks are on the right. Water is loaded from the tap into the tank on the top (most versions do not require you to pour in the water by hand). This tank feeds cool water into the bottom of the tank on the bottom. Because of gravity, new cool water from this tank can only enter the bottom tank when water is let out of the bottom tank from the tap (seen right next to Nicholas's hand). You can see pipes that come out from the bottom of the tank, into the stove, then back to the top of the tank. This is the "closed loop" I was talking about. For this system, one batch of charcoal in the stove can heat up an entire tank of water (about 35 L). Pretty impressive.

Here is another version that uses two different stoves to heat the water. In this version, the feeder tank (blue tank in the above picture) is located on top of the house. Again due to gravity, this allows the hot water to be delivered all over the house.

Here is a close up of the stove. That bowl around the charcoal is hollow. You can see where the pipe carrying cool water enters on the left of the stove, and then the boiled water leaves the stove on the right and returns to the top of the tank.

At the end of the day Nicholas and I stopped by the metal shop to check on an incinerator that has been in the construction process since I've been here, but today it's finally finished. Either tomorrow or Thursday, Nicholas and I are going to head over to Kibale which is on the western side of Uganda some 400 km away. We are going to spend a couple of days there installing the incinerator and training the workers on operation procedures. Hopefully we can convince the hospital administrators on the importance of monitoring it's operation and the sorting of their waste. Hopefully it'll be a successful trip. I'm looking forward to seeing a new part of Uganda.

- Stokes

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