Dynamics of water under pressure/velocity?

[HVACtech]

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.

 

[quark]

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?

 

[Cyrus]

You are right by the Silver Spring metro station, red line-to shady grove.

 

[HVACtech]

You are right by the Silver Spring metro station, red line-to shady grove.

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.

Thanks guys. I just leave the boilers on overnight when it gets cold.

 

[russ_watters]

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.

 

[eaboujaoudeh]

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.