Thermosiphon Central Heating

The standard drip coffee maker is a remarkable machine. Perhaps the most remarkable thing is the lack of remarkable things within. As machines, they seem durable at a level not attained by much else, especially consumer products that handle water. We have 4 dead examples in a cupboard here at work. They're not actually dead, someone just dropped the glass carafe. The local diner has an example from the late '60s that as far as I can tell has been in continuous 24Hr operation since it was bought.

The key lies in simplicity. The business end is a heated tube in the base. Cold water is fed to this from a tank and when the temperature rises above boiling point the steamy-water mix expands and is forced up to the coffee basket. This water is replaced by more from the tank, usually via the only moving part: a one-way valve.

Central heating systems, the type with water pipes and radiators, are a lot like coffee machines. They have a gas boiler on the ground floor/basement that heats water, this is then electrically pumped to the radiators. Sadly the durability isn't in the same league as coffee makers. Their reliability is also lower, since they rely on a gas supply AND an electrical supply to function. Should electricity be unavailable or the pump malfunctioning, you might freeze to death despite a plentiful supply of fuel. This would be embarrassing.

To prevent such embarrassment, I recommend a coffee- maker inspired pumping mechanism. The gas boiler heats water which is ejected up to the top of the radiator in the highest room. Here it fills the radiator until it overflows down the return pipe to the radiators on lower floors and ultimately the main tank. Flow can be regulated by manual and thermostatic valves as normal. To simplify the system further, the one-way valve should be eliminated. To do this, the holding tank and/or heating coil should be designed as a fluid inerter <link>. When the boiling water rapidly expands, the supply-side inerter will dramatically bias the pumping in the desired direction, a Tesla valve could also be added for the cool factor, depending on how cool you find inerters or Tesla valves.

To dramatically increase the effectiveness of the system, water can be replaced with mercury. Radiators operating at ~350C can be smaller and mercury has excellent inertance and antimicrobial characteristics.