Making provisions for a future in-floor radiant zone

HydronicRookie

I hope to someday tack-on an additional zone to my recently-installed (not yet complete) hydronic system.

In this first stage, manifolds are running tube to and from cast-iron radiators throughout the house and the future/additional zone will be in-floor slab radiant in the basement.

What I'm not sure of is whether the eventual in-floor zone will be sufficiently pumped by the existing Alpha. If not, should I then branch off and cap just before the system circulator?



Any other provisions I might be forgetting?

Many thanks for everything thus far. I will upload photos when its all said and done. Cheers!

Harvey Ramer

I would use the "or here" spot if possible. You'll have to do the math. Figure your heat load on each emitter and then figure out the flow to each emitter. Figure out how much head pressure on the longest run of tubing that the circ will see at the required flow for that run. Add all your flows from all the circuits together and then see where your head and flow intersect on the pump curve chart for the Alpha. Add in the radiant and see what happens. Or just post the flows and head loss on here.

By the way. Make sure that boiler pump has a flow check in it. Otherwise the DHW pump will make the water go backwards through the boiler loop instead of through the boiler.

I just had to help out a local contractor who made that mistake. He was beating his head against the wall trying to figure it out. His genius advisor at the supply house told him exactly how to pipe it.

Harvey

Paul Pollets

For flow purposes, it's better to eliminate the 2 way zone valves and let the system run on constant circulation, like Viessmann suggests in their piping schematics. Their should be a variable speed pump on the system side of the Caleffi hydraulic separator. Make sure the LLH sensor is strapped to the supply outlet of the Caleffi unit. The radiators use TRV's for individual zoning and the thermostat has 1 setting. You can setback for evening temps or install the vitotrol thermostat. Now the system works at peak efficiency. A 1.4 heating curve is a good place to start for radiators.

Rich_49

Rookie , If this drawing is accurate you'll want to connect that expansion tank to the supply header after the Caleffi Sep4 . The way it is now depicted will do you no good unless I am missing something , it looks as if it is hooked to cold make up water .

@Paul . I did not see where he stated he was using TRVs , in fact zone valves are clearly depicted . A variable speed pump could still certainly benefit this system but in a constant circulation situation it would not be good . You also neglected to say he would require bypasses somewhere in the system for that configuration . Now I must ask why a 1.4 curve is a good starting place ? Wouldn't performing the heat loss at a high and low OAT temp , determining what the rads would require at each condition and setting the curve at the RIGHT place be a better starting point ?

Ironman

You'll need to create a separate temp zone for in slab radiant. You should use either a smart mixing valve or variable speed injection mixing (preferred) to control the slab temp. Both methods will use outdoor reset, which when properly set, will match the load to the proper supply temp. It must be done this way because the slab is high mass and takes a long time to heat up and cool down (the flywheel effect). If you supply water that's too hot, the slab will continue to give off heat for hours after the stat is satisfied and the space will over-heat.

I would recommend you go to Tekmar's site and read their essay on variable speed injection mixing. Naturally, they have the control to do it. Taco's I valve is the other acceptable choice.

Zman

Good points Harvey. Both the boiler and the DHW circs need check valves. I've done that once and seen it done many times.

If you want to leave yourself the most options, I think it make sense to pipe it at the location you have colored black.

One reason is that the radiant loops will likely be longer than the radiator loops. This will make balancing the zones a little tricky.

You also may want to run the radiant loop at a lower temp. If you pipe it where I am describing, you could add mixing easily.

Carl

HydronicRookie

@Harvey Ramer‌ I had a feeling I'd simply have to crunch the numbers. I attempted to do so the first time around and wasn't getting Resistance to Flow numbers that made sense so I gave up with my fingers crossed that the alpha will be able to handle the three zones. Now in adding the fourth, I guess there is no way around it and I should try again. I'll look back at my spreadsheet and get back to you. Thanks again! All my circulators came with check-valves and they're already slotted in ready to go - I could see how it would be a tricky thing to troubleshoot as they're basically hidden from view.

@Paul Pollets‌ , I actually was planning on implementing constant circulation, as the valves you see there aren't the typical on/off valves but more-or-less equivalent of a TVR for each zone (the TVR route was proving cumbersome and expensive so I went this way with some advice from @SWEI on this forum). The plan is to have a modulating thermostat on each floor sending a 1-10DVC current , proportionally controlling the openness of the zone valve.

@Rich‌, for the positioning of the expansion tank, I'm just following the Viessmann schematic (apparently its the PONPC, as the circulator is pointed towards the boiler).

@Ironman‌ , thanks for the tip on injection mixing. I see the benefits are faster temperature response times (up to 4x), while going the 3-way mixing valve will impede flow a bit. I guess either way, I still need to crunch the numbers and see whether another circulator will be needed.

@Zman‌ , thanks for the input. I was wondering why mixing would be easier if I branch off before the distribution circulator - is it because, in the event that I add another circulator it won't interfere with the other one too much? Its tempting to just tack-on the new zone at the end of the header for simplicity's sake, but I've learned simplicity doesn't always correlate with proper function in hydronics.

Zman

If you are creating a mixing loop, the circulator must be within the loop. If you put the circ on the outside, when the valve throttles down it no longer circulates.
If you are running the same temp, similar head resistance and you have circulator capacity, you can run it as you are suggesting.
Carl