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Posted by HeatPro on November 26, 2005 at 18:12:59:
In Reply to: piping buffer tank into boiler loop posted by Jim on November 26, 2005 at 17:54:03:
The ordinary purpose of a buffer tank would be to give water mass so the boiler has a slower heating response time. If you let the buffer tank work for the other zones; but not the DHW, the entire output of the boiler would have to be absorbed by the indirect heater coil in the summer. In other words, an indirect heat exchanger is usually only absorbing about 50,000 btuh. If the boiler input is larger than that what is the boiler supposed to do with the remaining input? - usually this is what makes the boiler rise in temperature rapidly - which is a sizzling, banging problem with low-mass small-tube boilers.
The better way is to let the boiler heat the buffer tank and take all the partial zone loads off the tank as in loop-subloop design. That is one reason I prefer the buffer-tank with tankless coper inner coil domestic design. The boiler water is in the tank and the domestic water is heated within the tubes passing through the tank. This means that the tank is warmed to domestic water temperature and zones come off that tank. It is an equal-balance circuit design with a recirculation pipe that has an embolism. During the heating season, the tank temperature rises on outdoor reset. The domestic water is taken off a tempering valve.
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