Hybrid Hydronic Systems – The Circuits Pt.1

Okay, now that the primary loop is established, there are a few exceptions to go over.

1. I show most of my zoning of secondary circuits as zoning with valves, but you can also zone with pumps which can be a great way to do it, but pumps are expensive and this is usually only cost effective if you are doing fewer but larger zones.
2. The water fill usually occurs at the air-compression tank, but on my last drawing I showed it as filling at the return side. This is usually seen on older boilers, on new installs or modulating boilers it is best done at the tank.
3. On this post, I am showing the concept behind secondary circuits, not the exact science. So don’t run off and install per this drawing as the balance will be off!

The primary circuit just cycles hot water like a rotary circles cars in traffic. The secondary circuits are like the side streets that draw as the demand requires. With this setup, you can mix higher temp radiators in a system with lower temp hydronic floors and not starve the one or overheat the other…

Basically you are zoning the different types from one another.

This is how the secondary loops connect to the primary

If you feel lost or overwhelmed, this should help. If your house is old and has an original radiator-heat boiler system, then the radiators are probably the primary circuit. The pipe leaves the boiler and goes on a loop with each radiator having a branch supply and branch return. It is unlikely that the system has any connections between supply and return that are not a radiator of some sort. This was a simple way to pipe the system and required only one pump (albeit a relatively big one) to circulate the water.

The bummer of it is that room-by-room temp control is more difficult and is a bit of a fumbling science. Also, air problems are shared by every component in the system. And if all that was not enough, one thermostat controls the whole thing! Simple, but not very accurate and a waste of energy.