Dynamics of water under pressure/velocity?

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Discussion Overview

The discussion revolves around the effects of pressure and velocity on the freezing point of water, particularly in the context of maintaining operational water systems in a commercial building during cold temperatures. Participants explore practical solutions to prevent pipe freezing, including the use of antifreeze and the implications of water flow dynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks to understand how pressure and velocity affect the freezing point of water, particularly in relation to their building's plumbing system.
  • Another participant suggests that pressure does not significantly impact freezing point and recommends maintaining flow rates according to ASHRAE guidelines instead of using antifreeze.
  • A different participant expresses concern about the dangers of relying on water velocity to prevent freezing, noting that inconsistent flow could lead to ice formation in certain areas.
  • One participant asserts that the freezing point of water decreases with increased pressure, referencing formulas found in physics literature.
  • There is a discussion about the suitability of using antifreeze in the building's chillers, with one participant suggesting that it may not adversely affect the equipment, while another prefers to avoid it due to potential leaks.

Areas of Agreement / Disagreement

Participants express differing views on the role of pressure and velocity in preventing freezing, with some advocating for antifreeze and others cautioning against it. The discussion remains unresolved regarding the best approach to take.

Contextual Notes

Participants mention specific technical guidelines and equipment considerations, but there are unresolved assumptions about the effects of pressure and velocity on freezing, as well as the implications of using antifreeze in the system.

HVACtech
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Hello all, new member here. I am an operating engineer of a 10 story commercial office building in Silver Spring, Md. It's actually right across the street from the Discovery Channel Headquarters building, which is neat.

Anyway, I'm trying to understand the affects on the freezing point of water under pressure and velocity. Basically I try to keep my pipes from freezing by leaving the pumps on when the outside temps drop below 32*F. This keeps the water flowing under a pump pressure of approximately 25psig.
I've searched and found phase diagrams of pure water, but I have a hard time comprehending them.
Can someone help me understand this better? Thank you.
 
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Pressure doesn't much matter. ASHRAE HOF2006 specifies flowrates to be maintained in the pipe with respect to ambient temperature. Why don't you go for antifreeze?
 
You are right by the Silver Spring metro station, red line-to shady grove. :wink:
 
cyrusabdollahi said:
You are right by the Silver Spring metro station, red line-to shady grove. :wink:

Yes indeed. 962 Wayne Ave to be exact.

Quark, some building systems are glycol based systems that won't freeze. Ours is not one of them. Plus, I don't think my centrifugal York chillers would react too well to having antifreeze run through them. I really don't know. If we have a leak somewhere in the building I'd prefer to have plain ol' water everywhere and not antifreeze or glycol.:wink:

Thanks guys. I just leave the boilers on overnight when it gets cold.
 
Contact your nearest York service rep (or check York's technical info on their website) - I'd be shocked if your York chiller cared whether it had water or water/glycol running through it. The only real downside is the specific heat is lower so either you lose a little capacity or you have to increase your flow rates (odds are, your flow rates are too high anyway). Often, chiller literature will give multiple performance tables based on the working fluid.

To me, using velocity to prevent freezing seems very dangerous. Velocity isn't going to be consistent everywhere and all you need is a little ice forming in an eddy somewhere and before you know it your entire system is frozen solid.
 
Last edited:
i think antifreeze is the best solution. and besides i think freezing point varies with pressure and not with velocity, u can find formulas in physics books about it. the higher the pressure the lower the freezing pt.
 

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