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I was reading about a shuttered car factory. It has to be heated through the Michigan winter to prevent the fire preventing sprinkler system from freezing. It is a big drafty building and expensive to heat. It seems wasteful to heat a huge unoccupied building to keep a pipe full of water for freezing.
propose a method to keep pipes from freezing during periods when the building they are in is not heated. Currently sprinklers are set along pipes that dead end - as the case for any pipe terminating in a faucet or other outlet. If there were a set of return pipes, hot water could be made to circulate through these pipes. On returning to the source the same water could be heated again and reused.
It would be expensive though not prohibitive to build in a parallel return circuit. Another option would be to connect these hot water sprinkler pipes at the far end to the cold water pipes, and use the cold pipes for the return. With this method, one could also keep hot and cold nonsprinkler pipes (washrooms etc) from freezing as well. There could be a valve opening the connection between hot and cold supply pipes. There would be no risk of contaminating clean with waste water. The water system would work fine if you forgot to switch the valve back, but you might get a mix of hot and cold from each tap. This would be cheap, and done for the cost of the connection valves and the pump. Certainly it is cheaper to heat water in a pipe than an entire building.
Hot water dissolves minerals and leaves them behind as it cools. However, a closed circuit using the same water over and over could use softened water or have additives to help dissolve minerals. In this siutation the hot water circuit would help dissolve and carry away any mineral buildup in the pipes.
[bungston, Apr 15 2009]
[gnomethang, Apr 16 2009]
||Or one could use heat-trace tape, which I am astonished nobody at the Michigan plant has thought to do. But this idea has merit. [+]
||seems like a good idea. don't know how this compares with installing dry pipes and electronic detection for price. I would hope that somebody has looked at the expense of heating an empty building. Don't be so sure that it's only the sprinkler system they are protecting from freezing, pipes here, pipes there, traps and dips everywhere, a truly drainable water system is really really rare.
||Ditto [gisho] - I thought that was why the good Lord invented freeze protection trace heating - linky
||I was thinking of this idea again recently after seeing an article in the paper that encouraged people to gather the water wasted while waiting for showers to turn hot, tote it outside and pour it on plants. The shower getting hot thing is wasteful. Why not a circuit which, when turned on, routed water back to the hot water heater tank until water in the line leading to the shower was hot? Maybe a different idea than the above, but the same tyrannical principle.
||That would be a traditional 3 port system [bungs]. Many/Most commercial buildings do this so that water is available at source at the correct temperature. It gets rid of cold spots and thermal lag in a 2 port system.
You do get more of a chance of thermal losses and you need to keep a pump running all the time to circulate water but it may work for a domestic arrangement since you are probably waiting for your boiler to actually fire and start heating water.
Some thermostatic 3 port mixing valve could do this.