How does water velocity affect a hydronic system? This weeks video

RayWohlfarth

While we focus on gallons per minute and feet of head, improper water velocity in a hydronic system can cause uncomfortable areas, air accumulation, and erosion of the metal causing leaks. Hope you enjoy the video

https://www.youtube.com/watch?v=zAiG3XWPXnk

Peregrine

thanks you

Tim_D

High velocity does not decrease heat transfer at the heat emitter. If there is a differential between the heat emitter and the space, heat will flow. Many seem to think that at some arbitrary velocity the btu's become afraid to jump off of the bus which is not so. In fact, at higher velocities or said differently, smaller differentials the average temperature across the heat emitter is slightly higher which leads to more output. Number 30 Slantfin gives off 540 buts/ft at 170f and 610 btu/ft at 180f. 4gpm at a 20 degree differential and 8gpm at a 10 degree differential would both deliver 40 mbtu's. I am not advocating for 8gpm through 3/4 baseboard, As Ray stated, velocities over 4fps can be problematic.

hot_rod

Always different opinion. Fast moving water has no problem releasing the heat energy. In any type of heat emitter. The limitation is usually flow velocity through the piping. It's hard to rationalize slow moving fluid not transferring heat, and also fast moving water not transferring heat.

500 X flow X ∆T

I've been to a number of Robert Bean seminars. he has mentioned velocity up to 5 fps. Above that you start to hear the water.

Piping over 2" is sized by pressure drop, not velocity. As you mentioned 8 even 10 fps is not uncommon in larger pipes.

Nice presentation, you have a DJs voice :)

RayWohlfarth

Thanks @Peregrine

@hot_rod and @Tim_D I would normally agree with you I had an apartment building with zone valves for each apartment They had huge 3/4 hp pump I got called there When I arrived only one zone was calling The owner turned the boiler temp up to 200 degrees There was little heat coming from the baseboard I partially closed the ball valve until there was a 20 degree delta t As soon as I did that the baseboard started heating Weirdest thing I ever saw.

@hot_rod Dj lol my kids would disagree Thanks

hot_rod

200 SWT, 1 delta= 199.5 AWT with SlantFin #30 that is 710 btu/ft

200 SWT 20 delta= 640 btu/ft

Maybe the heat from choking down the flow from a 3/4 hp circ, to 2 gpm? running it off its curve, cavitating?, to one zone warmed it up more😯

RayWohlfarth

@hot_rod Not sure what it was. The owner and the tenant kept asking When is the heat coming on. The delta t for the zone was 2 degrees F before adjusting the valve. It was a strange service call

Alan (California Radiant) Forbes

I would have liked to see pressure gauges on each side of the pumps to see the actual pressure drops vs. calculated.
TACO 007’s are such a “gentle” pump; hard to image them over pumping.
With all our knowledge, there are many weird things that happen on jobs that confound us and are beyond explanation.

RayWohlfarth

@Alan (California Radiant) Forbes Thats what I love about this industry is that I learn something new every day sometimes in a humbling way.