Staple-Up Radiant - Return TRV Control

BuffaloBoiler

Hello,

Long time lurker - first time posting.

System Background: I have a two pipe single zone gravity conversion system using an old oversized cast iron boiler and cast iron radiators. The system is setup for constant circulation with a boiler protection circuit, Grundos Alpha2 pump, and TRVs on every radiator. No outdoor reset, the aquastat range is 130-170F. The setup allowed me to get to 10min burn times 1x/hour and is extremely comfortable.

While the house itself has more than enough radiation I have a 150sq-ft kitchen tile floor that gets cold in the winter. I would like to do a staple-up radiant heated floor to increase the temperature of this floor.

I am hoping to avoid additional circulators, mixing valves, and solenoids to do this. I have come across these European devices that allow small radiant loops to be ran off boiler water temperature directly. Both Danfoss and Oventrop make one. They work by having a TRV adjust flow based on the return water temp.

Below is the one I am considering. It has two TRVs - One to limit return temp and another to modulate flow based on room temp

https://www.oventrop.com/en-GB/productssystems/articledetails/1022734

These devices require a counterflow pattern radiant loop. That makes sense as we are trying to equalize the temperature in the loop as fast as possible. They also assume your radiant loop is embedded in concrete or screed. Both of those things together probably reduce the temperature delta along the loop well.

My questions are around using this in a staple-up job. We know most staple-up jobs are not laid out in a counterflow pattern - the premade heat transfer plates are designed for a single tube per plate.

My plan is to purchase some aluminum plate and stamp out a slot large enough to fit two pieces of pex side by side. I could then lay out the tubing in a counterflow pattern and I would try to maximize the use to these transfer plates to promote temperature equalization.

What are your thoughts on this?

Thanks

Here is a quick sketch of what I was thinking. The red square represent the aluminum plate

EdTheHeaterMan

Interesting device, not familiar with it, but it appears to have all the necessary stuff to work on a small loop. You would need a device for each loop in your floor. 

As far as using the counterflow idea, it is more work placing those loops that way, between each floor joist. Not saying it can’t be done, just that I have installed 3/8" and 1/2" tubing in a staple up configuration and it was not easy to get it there in the standard configuration where you have a u-turn at the end of each joist bay. Now you are going to run all the tubing in one direction at a time in each joist bay in a zigzag pattern. Then once you get half way there make a u-turn and zigzag back to the beginning.  

I see no reason that it won’t work. But why do you need the tubing in a double track aluminum plate?  Why not just put single track aluminum plates closer together?

EdTheHeaterMan

It might look something like this.

BuffaloBoiler

https://forum.heatinghelp.com/discussion/comment/1814362#Comment_1814362

I didn’t think of that - that looks much easier than my idea. Thank you!

hot_rod

I've use the UniBox, it is a handy unit. It is a big piece to put into a wall and thae cover is large.

I think Oventrop pulled out of the US market, so you may need to find one online.

I have not seen the Danfoss version? Do you have a part number?

BuffaloBoiler

Here are the Danfoss units - 2 models - one regulates on return water temp only, the other regulates on air temp only.

https://www.danfoss.com/en-us/products/dhs/hydronic-underfloor-heating/room-controls/fhv-a-fhv-r-thermostats/

Can you share any best practices with the UniBox? How did you lay out your tubing? Was it a staple-up job? Even heat throughout the loop?

I planned on putting the box in a joist cavity and running their remote TRV into the kitchen for air temp control

Kaos

For these types of rad to floor heat conversions, I've had good luck with Ultra Fin. Set the spacing for the water temp you will likely see and the BTU you need out.

Instead of a TRV, I have used zone valve driven by a local floor temp sensing thermostat on such a loop. Works great but does add cost.