My complicated DWH system...
Posted by Jacob Boles on May 05, 2004 at 14:42:53:
I'm working on connecting a solar hot water before a takagi tankless heater. The solar water heater will get up to 160 degress so between them is a mixed valve set at 120. The tankless is also set at 120.

1. when the solar is > 120 degrees, everything should be fine since the tankless wont fire.
2. if the solar temperature is low (<70 degress) the tagaki will fire and heat it to 120 degrees to meet demand.
3. If the solar is between 70-120 degress, arises the problem. The tankless has a minimum fire of 20,000 BTUs. So the water will not be heated all at low flow rates (like a sink). Luke warm water until the solar empties down.

To fix this problem i'd like to have a way to bypass the preheated water and instead use cold water to go to the tankless. Would a TEE with a electric gate valve with a temperature control connected to Cold do this function? Can a gate valve be controlled by an aquastat??

Does anyone have any advice?

Another obvious solution is to turn off the tankless in the summer months and use the solar exclusively(and vice-verse in the winter) to solve the problem. An automatic way would be better though (and I like challenges).



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