The case of the hydronic project with the three way valve, this weeks case.

RayWohlfarth

There is no case to solve in this weeks case. It will be talking about three way valves and how they are the enemy of hydronic boilers. I will post it Friday @ 6am EST

RayWohlfarth

The case of the hydronic system with 3 way valve is published on YouTube and shows the dangers of using a 3 way valve on a hydronic boiler project. It also explains the difference between mixing and diverting 3 way valves. Here is the link. https://youtube.com/watch?v=wkWfIk5zixU

jumper

Boilers tolerate quite a range of water flow. Old fashioned chillers liked narrower range.

hot_rod

If a 3 way thermostatic is properly selected and applied and used for boiler protection the boiler should be getting full flow up until the return warms, then full flow to the system, and through the boiler.
A 3 way thermostatic return protection mixing valve cannot shut off either side 100% As one port closes down the opposite opens the same amount.

So I’m not understanding how the boiler is ever starved for flow? Or dies😳

Older cast iron gravity system boilers didn’t even have circulators, just buoyancy driven flow, they lasted for decades.

And there are still boilers that use a protection aquastat to keep the circ off until they reach 140, no flow at all?

Perhaps some of the newer low water content thinner casting boilers are more sensitive to having flow equal to a 20 or 30 delta. Most mod cons can handle 30-40 deltas.

PeteA

I finally installed my 3 way valve as a boiler protection device and if there’s any info I can provide about how it’s working or responding let me know.
so far it does do what was explained to me as far as getting the water temp in the boiler up over the 120 degree mark within a few minutes and then I can feel the hot manifold heat up when the valve starts to open and let the flow go up to the house.
My house is not very big and has mainly cast iron radiators so the return side manifold never gets over 100 degrees before the thermostat gets satisfied at 69.
the one thing that is very clear that seem to not match the attached video is that the return pipe that comes off of the mixing valve is always much hotter than the water coming down from the return manifold which tells me that the valve is constantly mixing the hot side with the return side which is keeping the core of the boiler in the 125-130 range which I believe I read is good for the boiler to stay above that 120 temp as long as possible. Hope this helps a little I can take more accurate readings if it would be helpful.

hot_rod

Gpm don’t cannot disappear from a closed loop hydronic system.
With a thermostatic bypass 3 way valve, on cold start 100% of the flow is circulating through the boiler, call it 20 gpm. The circulators only job in the system is to move 20 gpm somewhere somehow.

As the valve sees warm return, some flow is allowed to the system, call it 10 gpm. So where. Is the other 10 gpm? It is still circulating through the boiler.
And the 10 returning from the system is joining the boilers 10 at the valve, so the boiler is still, always seeing 20. But at a more appropriate temperature.

As Dan H has taught us, “what goes into a tee, must come out of a tee”. A 3 way valve is basically an engineered tee, it has some intelligence inside in the form of a capsule of wax🤔

All that happens is temperature variation, there is no restriction of flow. Once again assuming proper valve and application. A 3 way zone valve would be another matter.

The bypass pump Ray mentioned seems to be just putting a second pump in parallel with the system pump, doubling the flow? Unless it has a temperature control function it seems to be treating a symptom not a problem?