Conventional Hydronic Boiler with multi-zones

snoop

I am retrofitting multiple zones into my current system and I was thinking that the boiler could be shocked with cold water from 1 zone with hot water on already. I will have a zone thats always on so I may not even need a mixing valve... not sure. So my questions are as follows

1. Do I even need a mixing valve with one zone always on?
2. Should I use a 3 way mixing valve, 4 way mixing valve, or hydronic separator?
3. I read something about close Ts, is that even related to this?
4. Can I get away with only using one pump?

Proposed system design with a 3 way mixing valve

Rich_49

Taco 4 way I Series valve . Can be done with a single circ although Taco only shows P/S piping . Circ should be within the mixed portion of circuits , not where you show it here .

lchmb

what kind of boiler? How big is the added zones? You may be able to just add in a bypass between the supply and return. Add a shutoff on the bypass, if needed it's there...if not..leave it off..

hot_rod

what type of radiators? is it a high mass, high water content system? How accurately is the boiler sized to the load?

If the intent of that thermostatic mixing valve is boiler return protection the pump location is fine. Pump away from the mixed port on those valves.
Be sure the expansion tank connects at the inlet of the pump, air purger at the hot supply out of the boiler.

Formerly

Why is that zone always on?