Reverse flow in dump zone

[twitch]

I have 21' of baseboard as a dumpzone in my boiler room for overheat / no power heat dissipation. It runs from my boiler supply (high end) to the boiler drain connection (low end). If the boiler drifts too far over the high fan limit setpoint, an aquastat opens the connection to the zonevalve which opens up the dump zone.

I observed this the other day, and noticed that the pipe got hot on the drain connection side first rather than the supply side. As far as I can tell, the water was flowing from the low end to the higher supply end, and it doesn't really make sense. I'm guessing it isn't a problem, because the water was flowing, and the heat was being drawn off the boiler.

Not really looking for a fix, just an observation.

 

[Nofossil]

That does seem odd. Any chance that the standing water in the outlet-to-high point was colder on the average that the water in the high point-to-drain half of the loop?

 

[twitch]

That's quite possible. The zone valve is only about 3' from where it connects to the boiler supply, so only a few feet of water would be warmed, whereas the drain side is completely unobstructed.

Just to note that the circ pump was running at the time, not sure if this would have any affect.

 

[Jim Post]

On overheat w/power does your circulator still have power? If the pump is pumping towards the boiler and the overheat zone opens the water will choose the path of least resistance and could flow backwards?? through your overheat loop. Just guessing, I didn't study your piping layout too close but I believe that is how my power loss overheat setup would work. Without power, the hot water flows out the supply up through my fin tubes and back to the return by gravity. I have a 3-way valve that will only allow flow to the gravity overheat loop if power is lost. I have an aquastat that turns on my largest zone if I am overheating with power available...not very common but it can happen.

jp

 

[twitch]

Yes, my pump still has power, and it was running when I observed the odd flow. My first overheat zone is the air handler that heats the house, the second is the dump zone. I have the aquastats set pretty close to my high fan limit, so when the temp drifts a little above the set zone, it first dumps heat to the house then the dump zone. I set them close to draw heat from the boiler so it won't idle as much. I'm not sure if this is really helping or not, but it sounded good in theory. I think it might be flowing backward because the pump was running at the time?? As long as it draws heat from the boiler, I'm not going to worry too much.