P/S piping in an open system

Robert O'Connor_3

Has anybody used primary/secondary piping in an open/non-pressurized system? I don't see why it wouldn't work, but I wanted to get some other thoughts. Regards,Matt

Kal Row

you mean a pool heater driven off a drain back solar?

you'd could have a problem on real hot days with steam flashing on the solar side of the heat exchanger

Robert O'Connor_3

No, this is in regards to hooking up an open - outdoor boiler unit to a non-ferrous house system. The boiler input would be a secondary circuit off the common piping between the parraleled house zones.

Kal Row

non-ferrous doesnt mean non corosive..

with an open system's constant supply of oxygen, the voltaic battery effect on many of the system's joints doesnt stop, and will corode both sides in short order

start with a flat plate heat exchanger, bronze pumps, and dielectric unions or flanges

need diagrams for more info

Robert O'Connor_3

Back to my original question. Will P/S piping work in an open system. I already use BPHE's in my pressurized boiler tie-ins (and they are quite effective if sized properly). I want to know if P/S will work in a low pressure system. I use it in my pressurized setups but haven't tried it in my open systems. It would simplify some scenarios. My system runs about 3 psi and actually is closed - just low pressure. It technically is not open.

Kal Row

yes...

there is no reason why low pressure should change the physics of closely spaced tee P/S piping
it's a flow isolation temp injection mixing technique as opposed to a pressure balancing technique

S Ebels

Works fine

We've done dozens of O/D wood jobs P/S. Many of them have a main underground loop that goes to several buildings. We constant circ the underground loop and use a secondary to feed whatever is going on in the buildings.

Watch your NPSH in the inlet of your circs. I see lots of burned out 0011's that pulled negative pressure on the inlet side. People try to cheap out using 3/4" or 1" pex while needing a flow rate of 12-15GPM in 200-300 ft of tube. It works for a while but then the circ fries and they wonder why their electric bill took a $30 hike.

You can't cheat physics.

Kal Row

opss... forgot about npsh...

as the pressures get lower - the likelyhood of flashing to steam in the eye of the pump and resultant cavitation, goes up - good idea to put the flow check after the pump in these systems, or use a grunfoss 15-58fc with the check built in to the discharge side