If I understand your question, I'll answer this way just in casejrv8984 wrote:Somehow I missed that the supply and return from a zone are supposed to be the 4 pipe diameters from each other, I suppose it's because it seems counterintuitive to be returning cold water to the main loop before supplying the next zone.
Question, if I have all the hots for the 4 zones 6" apart, and then immediately continue with my cold returns 6" apart, and there's never anymore than 6" between any tee, would that work?
4 pipe diameters for the supply and return of a single zone, then a larger distance of some sort between that "set" and the next "set" of supply and return tees for another zone.
Does that help?
FYI. Counterintuitive? Maybe. It leverages the idea of zoning, in which different zones will likely have different call for heat cycles. Even when neighboring zones are calling for heat at the same time, you run 1" zones (like I do), then you are returning 1" of 20F cooler water (ideally) from that zone into a constantly replenished 1.25" primary loop.
1.25" has almost double the flow of 1" and almost 4 times the flow of 3/4" so the returning water is diluted as it is reintroduced into the primary loop.
Before you go too far and because of your initial request for a 26 gpm pump, I suggest to take a look at this page and pay particular attention to the "laminar flow" section: https://highperformancehvac.com/boiler-piping-flow-pipe-sizing/
In a nutshell, water "sleeves" itself with an insulating layer at the outer edge of the cross-section. That's a good thing, helps prevent heat loss to the room. BUT...when the flow is too high, that layer can get too "thick" and stratifies the circulating water.
The big problem here is heat cannot transfer from the pipe to the radiant and the boiler can't get heat into the water at efficient rates.
You have to find the happy medium. Not too fast, not too slow
This is one reason cooling systems in a vehicle MUST create turbulence, to break up this problem.
Note for the purists (you know who you are, LOL). I know this is not an exact explanation of the situation, but it does accurately depict the effects and what must be done to avoid it
I've added a PDF attachment to this post that should answer a lot of questions for you, concerning BTUs in different diameters of pipe, etc. Notice that 1.5" can carry 1.8 times the BTUs that 1.25" does (pg 13). It also has some PEX stuff in it that you might find helpful.
I'm going to paste this one table from that page:
According to the table, if you are looking for 170k, the 1.25" PEX only carries 150k at 20F delta-T (return vs supply temp, the BTUs used in your zones).
Even at 30F difference, it's only 270k BTUs. You have 300k boiler? At 0.8 * 300k = 240k, so it might handle it. I haven't figured out the flow rate, but I'm assuming the table is corrected for max flow rates of piping. You can always target a higher delta-T, but the zones *should* take care of this, with the limit being the coldest days with all the zones running. (Many of us crank up our boiler temps and warm our houses, overriding our setbacks)
Here's a chart showing the Min and Max flow rates for various piping types and diameters
Here is a snip of the PEX chart:
According to the chart, PEX 1.25" is Min: 5.6 gpm and Max 11.2 gpm
That is another problem with the 26gpm pump you requested. But not to worry, the resources I'm giving you are for hydronic systems and a lot of the gotchas are factored into the data.
Is this all starting to make more sense now? It's not near the steep mountain that it might have seemed initially
Numbers can be your friend, too