Automatable 3-way Valve For Solar/tankless System

Q: We are building a (solar) drainback hot water system which we are coupling with a tankless (gas) water heater for backup. If the solar system is providing water at/above desired temperature (e.g., water heater output temp), we want the water to bypass the water heater altogether. Otherwise, send the "pre-heated" water to the tankless for a temperature boost. This seems straightforward enough: use a 3-way valve (e.g, L-port) that has a single input and 2 outputs, only one of which will be in use at any given time. I've located an electrically operated valve suitable for this purpose, but am now at a loss as to how to make it switch. I'd appreciate suggestions for specific "thingie" (manufacturer and part number) that will switch the valve, as appropriate. It would also be helpful if temperature out of the solar system could be reported to my automation system (for data collection, if nothing else). Appreciate any suggestions,

A: Why not just set the gas DWH to a lower temp then the Solar. Let say a 8'f diff. That way the backup system will only kick in when needed. The small amount of gas needed to bring you solar up a few degrees now and then would be small. No change in the plumbing.... The other thing you might want to try - especially if your hot water tank is some distance from your gas heater - is some sort of delay on the gas heater to give the hot water time to arrive at the tap. It's only a little bit each time, but it will be nearly every time, and that will add up over a month. Unfortunately, I have no idea how you would do that - but someone will probably post with the technicalities. It's also a very good investment to insulate all the hot water pipes. The foam tubes that slip over the pipes are very cheap. I would suspect that the payback would be measured in months. If the pipes are in place and you have to slit the foam tubes to put them on, make sure to tape them closed - just a long spiral of black electrical tape.

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