Zone Valve Question

[hagakure]

http://www.thisoldhouse.com/toh/vide...045338,00.html

I've been in plumbing for a year and a half, doing new construction in large apartment buildings here in NYC but don't have much experience yet with heating systems other than large fan coil units and only set up the radiators, so the logistics in the mechanical room still confuse me a bit.

I watched this video and I was wondering how the water 'knows' which pipe to go through? He put zone valves on the return lines, but wouldn't he have the same problem he describes in the beginning, that the water won't go up the new 1/2'' line due to water choosing the easiest path? All he did was put valves on the returns. There's still only 1 line coming out of the circulator pump, supplying 3 different lines.

I understand he installed thermostats but wouldn't the smaller line still perform poorly in comparison to the other radiators, due to water "choosing the easiest path"?

Shouldn't the system be pressurized?

Thanks

[jadnashua]

All hydronic heating systems need to be pressurized to some degree to prevent the water from flashing to steam in the boiler. It depends on how high up it needs to pump, how much pressure it needs.

You often need to balance the lines so you can get the desired flow in each branch. You can do that with separate valves, then, once a loop is opened, the flows should be able to be balanced and you'll get even heat to all. Now, if the head is too high, you may need a bypass loop/valve to keep things within range of acceptable if say only one zone was calling for heat.

[hagakure]

I still don't see how the 'loop' would balance out the pipes if there's still 1 smaller pipe. He says the water will flow through the path with the least resistance so the smaller line would still be under-performing.

Would what he did work, the way he did it, to solve the problem which was the new addition, with a radiator being supplied by a smaller line? I don't see how it would.

[Terry]

The Zone valve is used to either shut down a line, or to scale it back.
If the two 3/4" lines are shut off, and the 1/2" opens, then the water can only circulate through the 1/2"

[Tom Sawyer]

There is every chance that the zones will not balance properly and that's why purge & balance valves are installed on each zone.

[hj]

IF you have zone valves, you do NOT need balancing valves, because the thermostats will control the flow of water. The pump should be adequate to circulate through all the lines simultaneously. And a good technician, if he installed TWO zone valves on the existing system, would have added a thermostat so the three zones could operate independently.

[hj]

What a scmuck! He did NOT have to cut the 1 1/4". All he had to do was cut the 3/4 " and 1/2" lines and install the zone valves in them.

[jadnashua]

If all zones are open and not balanced, the one with the biggest head or restrictions may not get much of any flow until the others shut down. On a day when they need to be operating for long periods of time, the zone with the biggest restrictions may end up being quite cool since little flow will go there; thus, balancing things can help. It can get worse when you have multiple levels, but some will naturally flow by convection.

[Tom Sawyer]

Thank you jadnashua, you saved me the effort

[hagakure]

If all zones are open and not balanced, the one with the biggest head or restrictions may not get much of any flow until the others shut down. On a day when they need to be operating for long periods of time, the zone with the biggest restrictions may end up being quite cool since little flow will go there; thus, balancing things can help. It can get worse when you have multiple levels, but some will naturally flow by convection.

So what he did wouldn't have actually solved the problem he mentioned in the beginning of the video, which was the non balanced water supply?

If the zone valves are stopping the circulation, I don't understand why they would stop the water supply from going up the 2 larger pipes.

[jadnashua]

To flow when the pump is on, the loop has to be open and that is controlled by the zone valve(s). Now, assuming all zones are open, you won't necessarily get good flow through all of them and that's why you may need balancing valves. It's one thing if they are all on the same floor, the same length, and the same number of restrictions (elbows, radiators, etc.). Whichever zone(s) has(have) the lower resistance (head) when open will get the higher flow. Now, you can balance things somewhat with pipe sizes, but elevation changes, fittings, and other restrictions will also come into play. The larger the pipe, the lower the resistance, and the more it will flow.