DHW recirc line head resistance question...

[quizzical1]

Hi All,

We were discussing whether or not adding recirc branches in parallel to the main loop would work like resistors in electronics in that the resistance lowers, or would a larger recirc pump be required due to the added frictional losses to the extra pipe lengths?

TIA

Q~

 

[Artisi]

Not clear to me what you are asking, however seems you need to be giving a lot more data for reasonable comments.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

It works like resistors.

In parallel resistance goes down. In series it goes up. [pre][/pre]

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

The resistor part of your question is understood, but what are you asking hydraulically - effect of splitting flow to the same destination?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[quizzical1]

Sorry guys, as an example:

Say you have 1/2” copper pipe configured into a square pipe line 12’ x 12’ standing vertically with a recirc pump circulating the water. If you add branches like rungs on a ladder across the line from rise to return would the pump need to be increased to accommodate additional branches within this loop due to added pipe friction loss or would the additional flow paths make up the difference and pump stays same size?

 

[Latexman]

And, what of the total flow as you add branches? Same? Initial flow x # of branches?



Good luck,
Latexman

Engineers helping Engineers

 

[quizzical1]

Constant pressure of 5 - 10 psig. There will be valves in each rung opening and closing depending on temperature sensed

 

[PEDARRIN2]

Unless you are using some type of balancing flow controller, the water will flow in the path of least resistance, likely the shortest loop/route. You will not get much of any flow in the other branches. In a DHW/DHWR loop system, the branches which are not part of the loop/route with the most friction do not add any friction to the pump calculation. They will add flow, though.

I typically calculate the each loop's heat loss to determine the flows required. The longest loop is where the pressure drop calc starts, since it is typically the worst case. I then add/subtract the other loops' flows and recalculate the pressure loss based on the added/subtracted flows. Typically the most change occurs in the later parts of the recirculation section since it has the smallest pipe and the largest flow.