Head loss of OWB + elevation?

[heppm01]

I am redoing the mess of a "hydronic system" the previous owner of my house put in. Right now I am trying to (re)size the primary circulator. This pump is supplied from the OWB via 100' of 1" PEX and switches to 1" copper inside the basement for the P/S tees, and then returns to the OWB via 100' of 1" PEX. The design targets 7 GPM at 160 degrees, with a 20 degree delta on the return.

I think I have a pretty good handle on the head loss for the piping, but I'm not sure what to do about the OWB. Is there a head loss associated with this? It is open to atmosphere, and I find myself making arguments on both sides. Even if there is head, I have no idea what it is - not even the ballpark.

Also, the OWB is about 10' higher than the circulator. I'm not sure if this makes a difference or not - again, I can argue both ways.

Any insight would be appreciated.

Thanks,

Matt

 

[sgschwend]

There is always loss, sounds like you have a good handle on the elevation loss.

My guess is that the outdoor water boiler would have a significant loss if it has a restriction in the heat exchanger or any other piping. It the thing is one big water jacket then I would say the amount of loss should be very small. What does the manufacture say?

 

[heppm01]

Actually, I don't have a good handle on the elevation thing - that's why I asked. I understand the implications in a closed system (there are none), but in an open system I'm not so sure.

The OWB is a Northland - pretty much a big barrel of water with a firebox in the middle. I've not had very good luck getting info from the manufacturer about other issues; they seem a little put off by the fact that I am not the original owner. I guess it wouldn't hurt to try again.

 

[heaterman]

If the OWB (open system) is higher than the circ you will have virtually no other head other than that developed by the tubing. Think of it this way.....the fluid in the tube has a down hill run to the circ and an uphill run back to the OWB. They cancel each other out. The water will seek it's own level in the tube. You would have additional head present only if you were trying to move the water back to a point higher than the water level of the boiler.

 

[heppm01]

Great, that's what I was hoping to hear.

I was probably over-analyzing things, because I was worried that the atmospheric pressure pushing down on both the supply and return columns entered into it somehow.

 

[heaterman]

Great, that's what I was hoping to hear.

I was probably over-analyzing things, because I was worried that the atmospheric pressure pushing down on both the supply and return columns entered into it somehow.

It does. The thing to remember is that both tubes are connected to the same vessel which is open to that atmosphere. Equal pressure on the inny and the outty means nothing happens. The circ is the only thing that can change the pressure in the lines and make the water move.