UFH and Rads - system design

[HughF]

I'm going for UFH in 100mm slab in the extension (south facing), tied to the mesh on 50mm stilts, new rads in the rest of the house (as it's a retrofit)... Whole lot will be driven from a 9kW (max) ASHP running in weather comp mode.

 

I can't size the rads for the UFH flow temp so I'm going to set the weather comp up to suit the rad sizing then use a blending valve and pump station at the UFH termination.

 

I want to do this without a LLH or buffer if possible (for efficiency and space constraints) but I'm pretty sure I'm going to need at least some sort of hydraulic separation between the different flow rate emitters.

 

Anyone have any input on this? Should I make allowances in the design for a buffer or LLH?

[JohnMo]

You could run you piping to the rads and use two close coupled tees on the return line to supply the UFH.  So the return water out of the rads if no UFH is on would flow direct back to the UFH.  If UFH is on, water would be borrowed from the return via the first tee, then after flowing through the UFH would return to the radiator return via the second tee.  Using the close couple tee there is hydraulic separation, between to boiler pump and the ufh pump.

 

You will need to find the min flow rate and system capacity for heat pump and make sure the system is big enough and there is enough flow

 

Run the whole lot as a single zone, will keep the system from short cycling.  

[HughF]

3 hours ago, JohnMo said:

You could run you piping to the rads and use two close coupled tees on the return line to supply the UFH.  So the return water out of the rads if no UFH is on would flow direct back to the UFH.  If UFH is on, water would be borrowed from the return via the first tee, then after flowing through the UFH would return to the radiator return via the second tee.  Using the close couple tee there is hydraulic separation, between to boiler pump and the ufh pump.

 

You will need to find the min flow rate and system capacity for heat pump and make sure the system is big enough and there is enough flow

 

Run the whole lot as a single zone, will keep the system from short cycling.  

Assume that you meant 'So the return water out of the rads if no UFH is on would flow direct back to the ASHP'?

 

The setup with close-coupled T's in the return line makes perfect sense, cheers. I'll design around this.

 

I was planning on having all the heating emitters on a single zone but manifold plumbed, just so I can easily balance at the manifold (I have the manifolds already, and all the mlcp pipe)....

[JohnMo]

You are correct, my typo

[joth]

3 hours ago, JohnMo said:

Using the close couple tee there is hydraulic separation, between to boiler pump and the ufh pump.

 

Nit: isn't it hydronic separation (not hydraulic)

 

[Gus Potter]

3 hours ago, JohnMo said:

You could run you piping to the rads and use two close coupled tees on the return line to supply the UFH. 

The close coupled tee is a good concept.. I experimented with this.. it worked for some of the time but not all the time. My rads have TRV's so things / flows were always changing.. or maybe I should stick to other stuff.. I probably know enough about plumbing to be dangerous!

 

I made a home made manifold to test how I could couple an old council house up with a modern extension with UFH. It's working great so what luck! Photo uploaded

 

 

[JohnMo]

9 hours ago, joth said:

 

Nit: isn't it hydronic separation (not hydraulic)

 

No I think my use of words are correct.  You are not separating cooling systems, you are separating multiple pumps from interaction with each other.

[HughF]

On 02/09/2022 at 23:08, Gus Potter said:

The close coupled tee is a good concept.. I experimented with this.. it worked for some of the time but not all the time. My rads have TRV's so things / flows were always changing.. or maybe I should stick to other stuff.. I probably know enough about plumbing to be dangerous!

 

I made a home made manifold to test how I could couple an old council house up with a modern extension with UFH. It's working great so what luck! Photo uploaded

 

 

No trvs for us. the doors are always open to all the rooms, the house is tiny and we don’t have the luxury of unused rooms 🤣

[HughF]

Done a quick sketch, anyone care to comment? Single manifold set shown for the rads, I’ll probably have one upstairs and one downstairs.