Cold weather!!!

[eljefe281]

Here's a fun question for chem geek...

What does 3500 ppm salt do to the freeze point of water?

[waste]

Jefe, As I recall from an earlier discussion here, having salt in the water does lower the freeze temp, but only negligibly. I realize that you asked for Richard's assesment, complete with the need for some asprin or a strong drink to help the info go down( )

Not fully trusting my memory, I did a search and found this thread http://www.poolforum.com/pf2/showthread.php?t=3355. On page 7 (post #62) MassAttack asks a similar ?, Radish responds (post #68) 'that the difference is negligable' and Poolsean (post #70) says that @ 3000 ppm salt the freeze temp drops from 32 to 30.7 deg (F).

I'm sorry my answer isn't as involved as one that Richard could give, but I'd have to say that @ 3500 ppm the freeze temp will be just under 30.5 deg.

There's the 'quick and dirty' answer, I'll leave it to Richard, or one of the other chemists to give the 'whole story'

[salinda]

Looking in hindsight at the cold winter we have had, I feel a bit of satisfaction and vindication over one thing in particular. This summer, I got a bug over the high (33-35 cents/KW-hr) rates here. We replaced a 2hp whisperflo and a Polaris booster pump with an Ikeric variable speed pump. It is not perfect. I wish that I had the Intelliflow installed instead and I also think that a robotic or even pressure-side with booster would have been more in my comfort zone, but my electric bills for this winter showed that we consistently used 300 KWhr/month LESS this year than last year. Remember the pump ran MANY more hours than last year due to the freeze conditions. Some weeks, it ran almost around the clock. Last year, maybe 2 weeks were like that. That is $100 savings per month. With winter alone, I will make back the high replacement costs I paid in no time.

Hurray!

[chem geek]

Here's a fun question for chem geek...

What does 3500 ppm salt do to the freeze point of water?

Sorry I didn't notice this question to me before now, but the answer is, of course, disappointing. Remember that the freezing point depression for water is 1.86 ºC/m. 3500 mg/l / 58.44 g/mole / 1000 mg/g = 0.060 moles/liter which is essentially 0.060 moles/kg solvent (which is what "m" is...molality).

So 0.060 * 1.86 = 0.11 C = 0.20 F. Yes that's right, the salt in your pool only reduces the freezing point of water by 0.2 degrees Fahrenheit.

Richard