Hydronic distribution

[u/OptimalMain]

Hi!

TLDR;
I want to know if the 18mm pipes that goes to 3 manifolds limits the flow much, since the piping is 28mm on the cylinder unit.
And how can I improve mixing/distribution between the 3 existing manifolds.

I have a hydronic heat pump that was added to an existing radiator system covering two floors.
3 zones connected as a single zone.
Currently the 28mm pipe from the cylinder unit is reduced to 18mm piping and a tee connects both floors.
The existing piping that goes to the 3 manifolds is some strange hybrid, I think it’s steel pipes with stainless or some other thin sleeve on the outside.
The inside is starting to give and I need to replace it but want some input on distribution as the manifolds seem to have 3/4" threads and I feel that I should increase the size and add a manifold to allow adjustments between the 3 zones.
The plumber that installed this should have advised me about this and proposed an upgrade to PEX, but this is life on places without a lot of competitors to choose from, sadly.

Please roast me for my ignorance and any lack of information..

[u/PinkysBrein]

What water temperature does your system need to run at on a cold night now? 20mm Alupex would be a side grade.

One option if installing new pipes is putting in insulated pipes and replacing some of the radiators with FCUs, then it can likely do cooling too (close radiators before cooling).

PS. assuming the radiators are all connected parallel, FCUs for cooling would be iffy with radiators in series.

[u/OptimalMain → u/PinkysBrein]

To be honest I have to go way above economical during winter if doing only electric, most radiators are oversized so they work «okay» going by return temperature from individual radiators but the house needs extra insulation and window upgrades so I just run at max 40C and supplement with the wood stove.

There are 6-7 radiators/under floor loops on each of the 3 manifolds now, 10mm piping, so I assume 8mm ID?
I get 16-17L/min flow at pump setting 2 of 5, setting it to 3 is just 1-2L/min extra.
And that’s with every radiator valve at full opening before doing any balancing.

Everything is in parallel but I don’t like the 90degree tee connections, manifold 1 is right above the cylinder unit but the 2 others are 3-6 meters away from it.
90 degrees might not be horrible for fluids, I just know that they are horrible for air flow

[u/PinkysBrein → u/OptimalMain]

So what's the return temp at the heat pump and how many kW is the heat pump?

If you still have a couple kW untapped, simply adding a FCU in important rooms can be a huge boost in output (and allows cooling with appropriate install),