Thermosiphon
Tuesday, September 16th, 2008
Jeff,
I want to install a simple gravity fed hot water tap in my remote cabin. I am not electrified at this location. My idea is to have a water containment vessel (probably not sealed) above the heat source and copper tubing running out of the bottom of the vessel dropping to about 15 coils around a wood stove pipe. When I open the tap (which is at the lowest point) the water flowing around the coils will heat to a temp relative to the amount of heat the stovepipe is generating. Will this system work, or will the water thermosiphon back into the vessel and provide me no water at the tap? Do I need a sealed system with an inlet and outlet in the water vessel to circulate water as it heats? Thanks for the help.
Richard P.
Richard:
What you described is not a thermo-siphon system, you are just passing the water around a hot pipe when you open the lower faucet and this is not safe. Without water flow, the water in the copper pipe wrapped around the stove pipe will quickly heat up and turn to steam, then “shoot” out of the tubing and back into the elevated tank.
For a thermo-siphon system to work and not overheat, you need a constant water “flow:” around the copper piping and up into the side of the tank near the top (but still below water level). The bottom end of the copper coil is connected into the bottom of the elevated tank which has to colder water (heat rises).
Your hot water supply piping to faucets should be a separate pipe connected near the top of the tank (also below the water level). As the water is heated in the coil, it will rise and enter the top of the tank, while colder water enters the coil from the bottom of the tank.
If you decide to make this a closed system and under pressure, you will need a separate temperature relief valve and a pressure relief valve, but I recommend that you keep it simple and not pressurize the tank.
Make-up cold water can be a separate cold water line connected near the bottom of the tank using either a manual valve or a “commode” type float valve to let more water in as the water level drops.
Be safe,
Jeff Yago
