Is my piping for gas hot water radiator boiler fine?

mariusz6100

I wanted to ask for feedback on my piping diagram for a hot water boiler for a converted gravity cast iron radiator system using the system bypass approach. I modified the Weil McLean system bypass to use a mixing valve rather than manual valves, moved the expansion tank on the supply line and added an air and dirt separator. I also moved the circulator on the supply side after the separator. I think this is a more efficient set up but I wanted to ask for your thoughts.

WM Provided System Bypass Diagram

Modified System Bypass Diagram

Ironman

How would circulation be induced in the bypass loop with the circulator outside of it?

Look closely at the factory diagram and you’ll see the difference.

mariusz6100

I looked at the drawing and thats why I am asking. Since the circulator is pumping away from the separator, it would drive flow through the bypass/mixing loop. Any path that connects supply to return should see the pressure difference, so water will circulate through it, even though there’s only one pump on the supply side after the separator. The pump’s pressure difference would drive all paths at once, proportionally to their resistance and the valve position.

Big Ed_4

The circulator should be between the tees on the boiler side…

Alan (California Radiant) Forbes

The "alternate circulator location" has the bypass on the discharge side of the pump. Your diagram has the mixing valve on the suction side. Proper placement of the pump has a lot to do with the Cv rating of the mixing valve.

That's not to say it won't work, but it might not be stable. Give it a go and report back. We're always learning here.

EBEBRATT-Ed

I don't believe it will work with your drawing. The pump discharge is coming back to the common port on the three-way valve.

The water is trying to get back to the pump

When the valve is open to the boiler return the water goes through the boiler to the pump. When the valve is open to the boiler supply the water will go backwards through the three-way valve with no flow through the boiler.

Leave the three-way valve where it is and pipe the branch of the valve to a tee in the pump discharge pipe.

Ironman

https://forum.heatinghelp.com/discussion/comment/1872451#Comment_1872451

No, the pump is on the wrong side of the Tee. It has to be within the loop.

hot_rod

What is the intent of the bypass in your application?

Unless you are connecting to a high mass system, large pipes and cast radiators, or a concrete radiant slab, it doesn't have much value. Copper fin tube rarely needs a boiler protection valve, same with air handlers, they are low mass, heat up quickly.

If you do need a bypass to protect the boiler a temperature sensing approach is a better option.

The bypass valve or piping cannot adjust to the changing temperatures.

As an example, you have a large pipe, maybe converted gravity system, cast iron radiators.

A call for heat comes on, 68° water flows back to the boiler.

A properly sized boiler will be able to lift, increase that temperature 5 maybe 10 degrees at design flow rate.

Put some numbers to it:

How much bypass would you adjust to mix the boiler required return to 130F, or with a bypass pump, how do you mix 68 return with 78 supply from the boiler to get to 130°F?

You would need to manually close of most if not all flow to the radiators to allow the boiler to catch up. Then open it up so the system eventuallky gets the 100% flow it needs.

What a thermostatic 3 way does is bypass the distribution system completely until the boiler can keep up with the cold return temperature rise. Iy "slips the clutch" allowing just the amount to the system as the boiler can keep up with.

These valves are included in some copper boilers, some Weil boilers, pool boilers, etc. They work and are an inexpensive solution

A temperature solution to a temperature problem. An example of how a thermostatic protection valve works.

Some boiler manufacturers are starting to acknowledge bypass pumps or piping may not get the job done.

So they show a "factory kit" that actually will not work for the same reasons, the load is never disconnected from the boiler. The bypass pump cannot raise the return temperature to the boiler with cold water coming back. As long as the load is still pumping. Which is omitted from this "Best Alternitive" for some reason?

This is how a variable speed setpoint pump will work for return protection.

Fig 7-15a is the non workable solution, setpoint bypass pump

Fig 7-15b shows them pump properly applied, as a "thermal clutch" Through the closely spacd tees, the load can now be "disconnected" from the boiler. The BVS pump will sip off what it needs to keep that return sensor happy.