Oh man, I had just typed up a nice reply and I closed the window by accident before posting. Doh! Ill give a brief recap.
I may have been premature in saying you would always flow through your storage with the backup, sorry about that. Im going to need to think about that some more....
Im using a modified PT1 diagram for my setup, which still needs some tweaking. My boiler is a New Yorker (came with the house), and works just fine. If I was buying one outright, I would go with a Buderus. Just my thoughts there.
If you have checks on your circulator already, no need to add a separate gravity check.
That diagram does have the extra zone valve that you dont need. You wont get any flow in that leg of your piping as shown unless there is a call from a circ anyway, so no need to bother putting it all in.
Automatic is what you want for backup, not any manual switching. You have the right thought.
How are you intending to control all of this
I have lost a few posts that way too. Good question and one I have grappled with for some time, but here is what I plan .
I think you are right. Some flow may go to storage. I could envision the load not using all the flow coming from backup, so it would send some to storage if only one zone called for heat and storage tank/backup aquastat circuit energized (closed) ?
For the wood and fossil fuel units I have taco 6 zone circulator control. I will have a couple more zones coming off one of the 3 loads & backup as shown
I need to finalize my plan. I am looking at changing my diagram for the solar tank also, which has two coils and two circs, Both the solar zones and the backup boiler will pipe out of supply and return pipes between boiler load Tee and storage. As I understand it, This type of diagram requires reversing flow in lines between Tee to loads and storage tank. If call for heat to zones was minimal, boiler may supply load and some to storage simultaneously. If no call for heat, flow all goes to storage.
I plan to install a swing check just after boiler but before loads Tee in, to prevent any backflow thru loading unit/wood boiler when no fire. This pipe set up may cause loading of storage with backup boiler, but it will be well insulated, once top of storage tank reaches setpoint, aquastat will turn off the backup, and zones will draw off storage, so excess btu's pumped to storage will not all be lost..
For solar, the200 gal stainless drain down tank has sensor bulb well, I have 2 stage ranco 120v controller with high and low diff controls that will control min tank temp for dhw and supply hi temp load circs if solar tank is hot. The ranco control is not connected to the taco control, so if solar tank is hot, it will pump to storage or zones if calling for heat and if solar tank needs heat, it will pump from supply line between load tee and storage.
Final diagram I'm leaning too is PT3, with solar cirs and back up boiler piped between load Tee and storage tank in supply and return fashion . I have lots of distance between this connection, unlike the diagram. Real driver in decision is distance between my boiler /loads and storage/ solar. Don't want more pipe runs. I don't envision not using storage, Guess I could install a crossover between supply and return lines just before lines enter storage or in event of isolating the storage turn off solar circs. The solar control is independent from other controls. I don't think the solar circs should run if loop is not made thru storage. The backup will be tied to the taco control and will only fire on a call for heat if storage is cold.
Man, it is hard to explain this stuff in writing! Hopefully I'm not sounding like Mr. Haney from green acres ! and this plan will work ok.
You don't think that zone valve is required just ahead of load? It would help without it to lower hea. requirements. Any suggestion/ advice is appreciated
Mark