primary/secondary multizone valves

shredmaster

Weil Mclain cga5 installation manual, the recommended primary/secondary piping has two circulator pumps, one on the supply and another one on the returns. for zone valved system, usually there is only 1 circulator either on the supply or return. Does anyone know why there is a second circulator? also, do they have to run at the same time when the zone valve call for heat? see attached file for the diagram.

EdTheHeaterMan

On the zone valve illustration, I see three circulators. One in the primary loop with the zone valves (Primary loop is the one with the Expansion tank) and two on the boiler (Secondary) Loop

One of the two is marked as an alternate location. The one near the Expansion tank (12) is the location installed at the factory on package units.

The Alternate is a better location. unless you are operating above 200°F. Then the other location is preferable

Don't use both, but you need to select one or the other location.

I hope this answers your query.

EdTheHeaterMan

Why do you need to use a Primary Secondary design?

One good reason is because you have a large water volume system, this will take a considerable time to get the water up to an acceptable return water temperature. By operating the system for longer times with cold water (less than 130°F) returning to the boiler, there is a risk of condensation of flue gasses. This condition over time will cause premature failure of the cast iron on the flue (AKA the dry side of the cast iron boiler sections).

By operating the short circuit directly back to the boiler via the balancing valves the boiler temperature can rise more quickly so the return water to the boiler will be above the recommended 130°F. So the boiler Circulator (14) will move that secondary loop thru the short circuit to keep the boiler hot.


The Circulator (3) on the primary loop keeps the water moving thru the zones when one is open and calling for heat. The balancing valves on the secondary loop will then determine how much of the secondary (Heated) water is introduced to the zones.
YES both (3 & 14) need to operate at the same time

Now if one of the zones is old-time high water volume radiators and the other zone is copper tube baseboard, there is a slightly better design than the one pictured here. If the system is all copper tube type baseboard, you probably don't need primary secondary.

shredmaster

I have copper tubes with cast iron radiators for the first and second floor, and the basement will have baseboards. I'm using it mainly because it's the preferred method in the manual.

if the boiler circulator (secondary) is blending the hot from the supply with the cold returns, does that means secondary pump needs to turn on whenever one of the zones calling for heat?

the alternate solution in the manual seems to be easier and only use one circulator. I could go with it if it's suitable.


thanks a lot for the answer.

shredmaster

I will have 3 zones in my system. if all the zone valves call for heat, will the balance valves adjust the amount of hot water send to primary/secondary accordingly? maybe that just means the pumps will work harder, curious to see how does that works.