I have 3 water temps (estimated @ 132, 91 and 74) and approximately 6 zones I'm looking to set up. The system is a basement in floor slab with about 7 zones of 1/2" pex anywhere from 250-300 per loop. A garage with a similar setup but 6 zones and a staple up (w/transfer plates - "Upstairs" on chart) covering the first floor with various floor types, tile, laminate and carpet (I know not ideal).
Currently I plan to have 3 temps. The temps are estimates I got from building my system using the Uponor software. The highest temp will be on its own branch manifold (BM) with no mixing valve runing off a mod con boiler with ODR. The 91 will be on its own BM with a t-stat mix valve and a circ on the mix side to pull through the valve. Same situation for the lowest temp. I'll be doing a heat exchangers for the garage for freeze protection but this isn't the reason for the post.
My concern as circled in red below is if only my T-stat 2 calls for heat on my 91 degree BM that my flow (.47 gmp) at design condition will be just below what t-stat mix valves seem to rated for. With ODR on the boiler reducing water temp as outdoor temp rises I assume my flow will stay somewhat consistent, but this isn't my main worry right now.
My larger question / concern is that most t-stat mix valves recommend a min flow of .5 GPM. Some like caleffi and Taco rate down to 1 gpm. Talking with some of the folks at their tech support it sounds like the solution is a motorized mix valve that doesn't care about min flow. Curious if this is the most cost effective solution? The rough mix valve pricing ~$115 ish give or take. Moving to motorized approached 3x and adding in ODR is 4x. Not to interesting in going this direction if I can avoid for two reasons, price and complexity. Everything breaks eventually and I'd much rather have a dumb valve with not electronics to fail if I can. Additionally the guys at Taco and Caleffi know there stuff and have been super helpful in their support or online presence to help DIY'ers. I'd prefer to stick with their brands if possible however in this case they don't seem to offer a "dumb" valve that gets down to .5 gpm like others.
Thanks for the input and perspective.