P/S piping question

Jamie_6

I'm a bit confused about how P/S piping works in theory.

• The purpose of closely spaced tees is to hydraulically separate two separate portions of a hydronic system. Meaning if one side of the system is on and “pumping” the flow rate and water temperature of that system can not affect the flow rate and water temperature of the system it is separated from! In essence they can not see each other.


Can the secondary loop be tied to bull of one Tee, and to the straight of the other Tee?

• Not a good idea! The reason we are connecting these tee’s so close to one another is that we do not want to get flow through the portion of the system that we are trying to separate from one another. We want to give the water the path of least resistance to insure we are doing so. We actually try to allow for 10 times the primary loops pipe size on both sides of our primary tee’s.


Could the two Tees be replaced with two closely spaced back to back Y fittings, or even a very large volume manifold with four ports?

• We’ve never used y’s on heating systems so I do not know! But, Caleffi does make a large volume manifold called a Hydraulic Separator which alleviates the need for primary secondary piping and also eliminates the need for a primary loop pump.


Is the PONPC the same regardless if the ports on the Tees are transposed?

• This is the tricky question! It depends on what you are piping as your primary and what you are piping as your secondary. If the boiler is the secondary to your primary loop then you would want to pump away from the closely spaced tees. Allowing for a normal Point of no pressure change configuration from “Pumping away.” Although, if you are piping a portion of the system (say a radiant heat zone) as a secondary to a boiler loop. Then you would want to be upstream from your PONPC configuration.

Hope this helps..


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Unca Pete

P/S piping question

I'm a bit confused about how P/S piping works in theory. Could the two Tees could be replaced with two closely spaced back to back Y fittings, or even a very large volume manifold with four ports? Is there any magic to using a Tee? Can the secondary loop be tied to bull of one Tee, and to the straight of the other Tee? Is the PONPC the same regardless if the ports on the Tees are transposed? Am I visualizing this right?

Brad White

Jamie nailed it.

Nothing to add.

John Ketterman

No, there is nothing special about a tee. You can use any three-way, such as a Y. You can connect any side to any port of a tee. The only requirement is that the tees should be close together so there is negligible friction (head) between them.

In principle there is a bit more friction for water rounding a corner compared to going straight, but it is small (you can look up the head due to an elbow of the same pipe diameter). You can't have both primary and secondary go straight through a tee anyway, one of them has to turn 90o. It just doesn't matter enough to worry abut.

Rich Kontny_3

Typically

With P/S you try to make the secondary piping the course of the most resistance to avoid unwanted flow! The primary piping has the course of the least resistance! Secondary flows can be boilers in a modular type arrangement or zones of a system that are intermitent in use versus the primary piping's continuos use.

Rich K.

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