Friction loss to vertical pipes in a closed system?

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Discussion Overview

The discussion revolves around the treatment of friction loss in vertical pipes within closed heating systems. Participants explore the implications of elevation loss due to gravity and its relationship with frictional losses in the system design.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses concern about treating vertical pipe lengths as horizontal and questions whether this approach is valid in the context of closed systems.
  • Another participant asks if the pressure difference due to elevation has been estimated compared to frictional losses, suggesting that elevation loss could be significant.
  • A participant notes that pressure loss due to elevation is much higher than friction loss, indicating that elevation loss is a result of gravity and should be considered in calculations.
  • There is a discussion about the necessity of pump sizing in relation to elevation changes, with a suggestion to perform calculations that include elevation to compare results.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether elevation loss should be disregarded in closed systems. Some argue it should be considered for accurate pump sizing, while others believe it may not need to be factored in at all.

Contextual Notes

There are unresolved assumptions regarding the impact of elevation on overall system performance and the specific conditions under which friction losses are calculated. The discussion does not clarify the exact scenarios where elevation loss may or may not be significant.

Who May Find This Useful

Engineers and designers involved in the design of heating systems, particularly those working with closed-loop systems and fluid dynamics.

TSN79
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So in designing closed systems, mostly heating systems, I realized today that I've probably been doing one thing wrong all these years. In such a system one doesn't take elevation loss due to gravity into account since you "get it back" on the way down. This I've always been aware of, but what I've still been doing is treating the vertical lengths of pipe as if they were horizontal, that is applying to them a friction loss per meter. Can someone just confirm that I can stop doing this? I'll just go back to my corner and be ashamed...
 
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Have you estimated how much of a pressure difference is involved as a result of the elevation differences, as compared with the frictional losses?

Chet
 
Chestermiller said:
Have you estimated how much of a pressure difference is involved as a result of the elevation differences, as compared with the frictional losses?

Pressure loss due to elevation would be much higher than the major head loss per meter. Elevation loss is just a result of gravity, 9,8 kPa/m in addition to the friction loss, compared to about 0,15 kPa/m in the horizontal piping. But I believe the elevation loss doesn't need to be considered at all in a closed circulating system.
 
What about when you select the fan? Doesn't it need to have enough ooomph to get significant air flow to the upper floor(s)?

Chet
 
Chestermiller said:
What about when you select the fan? Doesn't it need to have enough ooomph to get significant air flow to the upper floor(s)?

It's a central heating system, so there is a water circulation pump, not a fan.
 
TSN79 said:
So in designing closed systems, mostly heating systems, I realized today that I've probably been doing one thing wrong all these years. In such a system one doesn't take elevation loss due to gravity into account since you "get it back" on the way down. This I've always been aware of, but what I've still been doing is treating the vertical lengths of pipe as if they were horizontal, that is applying to them a friction loss per meter. Can someone just confirm that I can stop doing this? I'll just go back to my corner and be ashamed...

Technically you should consider the elevation changes so you can size your pump correctly. I imagine that since it's a closed loop system that is being constantly recirculated that you'll end up with the same answer. Why not just run a couple of hand calcs and do one like you've been doing it and then one that includes the elevations and see what the results tell you?

CS
 
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