Is this a reasonable radiant control panel design, and do I need to add a mixing valve?

axolLearner

DIYer here who's spent a lot of time learning/reading on this site! I think I've figured out what I need, but would love to get some advice before I spring for the parts.

I built a shed with ~1550ft ~1450 ft of 1/2" pex in slab this summer. Will be a single zone closed-loop, heated with a wall-mounted LP boiler that has a heat control to output 100-140F, running 50% glycol.

The panel I'm building myself is almost identical to the one in the picture in terms of layout.




So, 1" L copper piping. Has 2 pumps (P/S loop of sorts - that purge valve seems to act similar to a 2, close tees setup?) as required by the boiler's 2 year warranty, but I wouldn't really hesitate to void said warranty if folks thought there was a better way?

If that checks out, 2 questions:
1) Can I replace the $90 PVC wye strainer with a more typical $30 brass one, or bad idea?

2) Do I need a 3-way mixing valve on the manifold intake to protect the concrete. I've seen a lot of builds without them, and some with them in the exact spot I placed it in the image. A thermostatic mixing valve with a check because of my secondary pump placement. Would it be bad to set my boiler temp low (~110F), instead of getting one? Or should I spend the $100?

Also, Don Holohan has a video on using mixing valves like this, and how they can cause cavitation with the pump in the secondary loop if the hot-supply is cut off completely. That said, I would put a manual valve in, and could just make sure I never set it fully closed? (Can't really find a 1" diverter valve he mentions)...

Thanks for the wisdom!

hot_rod

Is it a boiler or tankless  water heater you are considering? That temperature range sounds like a water heater. Tankless water heaters are not an ideal heat source for hydronic

Do you have a heat load number for the shop?

A shop that size consider a tank type LP water heater, then all you need is a pump , air sep , expansion tank.

HomerJSmith

Why would you need a mixing valve unless you had a sys operating at 2 different temperatures?
I like to pump into the greatest pressure loss. In your photo of a P/S sys, I would like to see the pump moved to the hot water supply to the manifolds instead of on the return from the manifold to the boiler sys. Why would you need a strainer at all?
Likely your boiler has programing for a boiler pump and distribution pump with all the programing for temperatures, ramping and Outdoor Reset. A real boiler.
Glycol percentage seems high. How many circuits are on your manifold? I hope all your loops are less than 300 ft. and have an O2 barrier.

axolLearner

hot_rod said:

Is it a boiler or tankless  water heater you are considering? That temperature range sounds like a water heater. Tankless water heaters are not an ideal heat source for hydronic

Do you have a heat load number for the shop?....

Yeah! So, the actual shop is just over 2200sqft - concrete crew was young, I don't think they knew the standard 1ft on center for 1/2" pex runs, so it's a bit short, (that's the impression I get? I'm no expert, just a learning here).

2 heat load calculators put me between 50-80kbtu (Northern WI). I was looking at a 120kbtu LP high-efficiency boiler - on sale and can get a good business credit from the local energy company if I use a true high-efficiency boiler. I've read enough on here to be dissuaded from using a tankless waterheater like the Takagis.

I have a lean-to expansion I want to do within the next 2 years if things go well, which I'd probably add pex and maybe radiators in. Is it a bad idea to preemptively oversize a little like that?

hot_rod

Just run the Takagis at the temperature you need for the slab. It may have outdoor reset control built in , so it will modulate itself as far as supply temperature

No need for a mixing valve, and the panel should work if the boiler pump meets Takagis requirement?

If it is non barrier tube, use two stainless pumps and a RadiantPro expansion tank, which is coated inside.

axolLearner

HomerJSmith said:

Why would you need a mixing valve unless you had a sys operating at 2 different temperatures?...

I read that a few folks add one before in-slab installations to make sure there's not too much temperature shock. Do you think the heat transfer is slow enough that it doesn't matter?

HomerJSmith said:

Why would you need a strainer at all?

I thought the strainer would be cheap bit of fool-proofing to keep anything from flowing into the boiler if corrosion happens or foolishness etc.

HomerJSmith said:

Glycol percentage seems high. How many circuits are on your manifold? I hope all your loops are less than 300 ft. and have an O2 barrier.

Oxygen barrier, 5 runs 250, one of almost 300, but if I understand correctly, it should've had 2 more runs... Honestly, I'm working with what the concrete guys gave me. I really wish I'd laid the pex myself. Glycol - I'm in Northern WI, where we can get weeks of -40F windchill on a bad winter. You think I can get away with a little less? I was looking at some of the Hercules cryo-tek mixes.

hot_rod

If the slab is warm when power goes out, you should have a day or more of heat in the concrete to prevent freezing. If you are away for extended periods, glycol may be wise.

Look at the spec on the glycol you are considering, the protection varies from brand to brand.

There is a freeze and burst temperature. 30-35% may be adequate with a good, non diluted brand.

axolLearner

That sounds wise - it would help extend pump life, right?

I may be gone for a rare week here or there, but have family and folks who could stop in and check it and a backup generator that could run for a few hours while it gets back up to temp.

Thank you for all the advice, hot_rod

Zman

Do you have a boiler picked out? Do they have a suggested piping drawing?
I don't love your layout:

• I would pipe the expansion tank with an isolation and purge valve. It is also good practice to not put the tank right below a sediment trap like an air sep. Offsetting it to the side the purge is a good idea.
  
• The exp tank would work better on the secondary and would allow both circs to "pump-away".
  
• The pressure relief should be at the boiler.
  
• I am not sure you need a strainer on the system. I sure wouldn't use a PVC one.
  
• There is no need for a mixing valve on a single zone mod/con boiler system. I would run the boiler on an outdoor reset and let it take care of temp control.
  
• Are you planning to use a glycol feeder to keep it topped off?
  
• 50% glycol is a lot. 30% is pretty standard.
  

hot_rod

axolLearner said:

That sounds wise - it would help extend pump life, right?

I may be gone for a rare week here or there, but have family and folks who could stop in and check it and a backup generator that could run for a few hours while it gets back up to temp.

Thank you for all the advice, hot_rod

I’ve had shops in winter climates all my life and never used glycol. Sounds like you have back up monitoring with family nearby. I’d go without personally, your call.

As zman noted, the relief valve is on that panel because they sell them with tankless water heaters. Most boilers will have a relief valve included.

Big Ed_4

Flip one of the manifolds to piped in on the reverse end . It will equalize the pressures across the loops ...

GroundUp

Are you planning to use that Laars Mascot FT boiler like is in the photo? They don't come in 120k, nor does any boiler that I can think of readily. Your load for 2200 SF is likely under 60k if the insulation is even mediocre, probably closer to 30k if well insulated. Some boilers have an internal circulator, including the Laars, which would eliminate the need for the primary circ in that HydroSmart panel. The strainer is useless on all accounts, and as has been said, 30-35% glycol is typical. You don't need or even want 50%. Honestly, you'd probably be best off scrapping the entire idea of this HydroSmart junk and pipe the system as shown in the manual of whichever boiler you choose to install. It'll be cheaper and more effective. And no, you don't need or want a mixing valve.

hot_rod

Lochinvar has a 55 and 80,000. The building is at 2200, and an addition is being considered planned, so a bit oversized may be okay