Delta P in chilled water loop at various heights

[kailaster]

Hello. In a secondary chilled water loop serving a 10 story building, what is the effect of feet of head on the delta p of the loop. For example, pumps are in the basement and 15 psi dp is measured at the roof. What are the likely dp readings on floors 9,8,7, etc.? Chilled water usage is equal on each floor and on the roof.

 

[btrueblood]

Lower floors will (all else being equal) see higher dp, because they are closer to the pump (less head loss due to friction along the pipe). The elevation will change the static pressure, but shouldn't affect dp.

 

[drawoh]

kailaster,

I would expect [Δ]P to be around 4.3psi per ten feet of elevation. This is a surprising question to be asked by a mechie.

--
JHG

 

[Compositepro]

drawoh, elevation affects the pressure in the riser and down-comer exactly the same so the affect on delta P is zero.

 

[Jboggs]

OK, I'm not a piping guy but I'll bite. Wouldn't the delta-P be the same all the way up? The actual pressure in both lines will vary with depth, right? So, whatever the actual pressure is at the bottom of any line the pressure 40 ft up will vary by a fixed amount, right?

 

[LittleInch]

Ft of vertical head is irrelevant. Delta p at the same level is not affected.

Ft of pipe length is the key. Friction creates the difference.

Just think what happens when there is no flow. Thet is no dp in a closed loop system.

Now in a flowing system thet is a dp from pump suction to pump discharge. This is maximum at the pump and gradually reduces to zero at the midpoint of the circuit. This is the 15 psi mentioned by the OP.

Now what the dp is at other floors we can't say because we don't know what the dp is at the pump.

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