Some Questions for Residential Two-temp System

rossn

I have some design questions relating to the two temp system I'm installing with the rebuild of our home. There will be some radiant floor upstairs and panel rads downstairs and possibly upstairs (where supplemental heat may be needed).

Backstory is I put the distribution and manifolds in the 50% below grade basement several years back, and the basement didn't get finished. With HePEX left exposed to UV, I'm now replacing it, and the heating plan has now changed, which has been a cluster. I greatly appreciate your support on this!

Q1: For the below manifold supply design for the mid-temp, are changes needed, or the supply oversizing in a couple locations fine? With 12F temps forecasted for tomorrow night, I need to reinstall the section in the red dotted box today (already removed).

hot_rod

to make the math easy turn btu into gpm to size tube

Manifold 1&2=27,000 btu/hr. running a 20 ∆ divide by 10,000 so you need 2.7 gpm 3/4 pex is fine.

You largest combination is

garage 25,000

manifold 6. 15,000

manifold 5. 12,000

manifold 4. 12,000

So 64,000 6.4 gpm 1" pex can move 7-8 gpm or so without a problem

No if you chose to run a tighter delta maybe 10- 15 on the radiant, then you need more flowrate. I think you have enough wiggle room in all your sizing examples.

Max. flowrate is at 4 fps feet per second velocity, a comfortable flow rate for pex.

rossn

Thanks @hot_rod ! Yes, 20deg DeltaT. I wasn't sure if any of those supplies to the manifolds needed to get necked down, for pressure equalization or not. For instance if manifolds 6&7 needed to go to 1/2" where they tee off, or if manifold 3 needed to go to 1/2". It's been a while since the initial calcs, so my memory is a bit rusty and this was a good help.

It sounds like overall I can re-use the brass fittings as-is, and not worry about any additional reductions. I'll come back with some related more nuanced questions, but for now, gotta go install :) Thank you.

Edit: The 12,000 BTUs for the garage on M7 are only when-in-the-shop use, so that also gives some wiggle room.

hot_rod

Do the manifolds have flow adjusters? That is where you fine tune individual loops once it is up and running.

rossn

@hot_rod - Yes, they sure do. Uponor stainless variety.

Edit to add: The exception being Manifold 5. Original design was actually for 3 FCU's in this 'breezeway' area between the main house and garage (we discussed in this thread). That design had the 3 FCUs setup with reverse return piping and a single wall mounted TRV to control it. One of the additional questions I had this thread was if I really need to have it on a manifold. There isn't a great location, but I can make one in a thick wall if needed. At this point, for that room, I am leaning towards either panel rads or hybrid baseboard - both of which would be passive at times, and upon demand, forced convection. I haven't quite sorted that one out yet, but do like the passive + forced convection option.

hot_rod

If you add RTVs those are the flow control devise, with built in temperature sensing. Hard to be a TRV for a proportional, non electric temperature control device.

rossn

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