Pool surface feeezing

[Mam262]

Hello,

My pool is winterized and I currently have my mesh safety cover on my 30K gallon gunite pool. The water is 4 inches above the top of my light fixtures. Over the next 4 days we are going to have freezing temps with two days in the mid 20’s and two days in the low teens.

Question, should I be concerned about the pool surface freezing thick enough to damage the lights being that the water surface is only 4 inches above the lights? I have no concept of how thick the ice is when the surface freezes?

Should I consider adding water?

Thank you,
Mike

 

[ajw22]

No. Any ice is not going to get over 4” thick. By Monday your temps are going to be up to 50.

 

[mas985]

What is going to be the average temperature over the entire day each day?

What is the current water temperature?

Has freezing started?

Once freezing starts, you can use an empirical formula to estimate the rate at which the ice will grow. This requires the number of freezing degree days which is the difference between the average daily temperature and 32F. You will get about 1" per 15 FDDs. So assuming an average of 20F, one day is 12 FDDs. So to get 4", would require about 5 days. But that is after freezing starts.

 

[PoolguyinCT]

In the northeast, ice is approaching 12”.

Your lamp & pool will be fine. If possible keep water below tile band.

 

[ajw22]

 

[Mam262]

What is going to be the average temperature over the entire day each day?

What is the current water temperature?

Has freezing started?

Once freezing starts, you can use an empirical formula to estimate the rate at which the ice will grow. This requires the number of freezing degree days which is the difference between the average daily temperature and 32F. You will get about 1" per 15 FDDs. So assuming an average of 20F, one day is 12 FDDs. So to get 4", would require about 5 days. But that is after freezing starts.

There is a very thin layer of ice now, probably 1/8 inch.

Tomorrow avg temp is 31
Wednesday avg temp is 18. = 14 FDD
Thursday avg temp is 8 = 24 FDD
Friday avg temp is 14 = 18 FDD
Saturday avg temp is 21 = 12 FDD
Sunday avg temp is 36

That is 68 FDD / 15 = 4.5 inches of ice which puts my light fixture 1/2 inch in ice.

Should I be concerned?

Thank you very much for your help!

 

[ajw22]

@Mam262 please correct the spelling of your city in your profile.

 

[Mam262]

@Mam262 please correct the spelling of your city in your profile.

Corrected. Thanks for catching that.

 

[mas985]

Ice grows from the bottom but lifts the other ice as it grows as water cannot be compressed. The change in volume from water to ice is about 9% growth. However, in a pool, the area is confined so all that volume growth occurs in the height which means about 4.13" of water is consumed making 4.5" of ice. [EDIT] Fixed math error.

However, even if the ice does reach the light, it doesn't mean the light will be damaged. Again, the ice grows upward and I think you would be ok up to about half way through the light as there is room for the ice to move upward. However, once the ice gets below the mid-point of the light, it could potentially, crack the lens.

 

[Mam262]

Ice grows from the bottom but lifts the other ice as it grows as water cannot be compressed. The change in volume from water to ice is about 9% growth. However, in a pool, the area is confined so all that volume growth occurs in the height which means about 3.5" of water is consumed making 4.5" of ice. Therefore, the ice/water line is about 1" above the light after those 4 days. Keep in mind these are estimates and can vary some.

However, even if the ice does reach the light, it doesn't mean the light will be damaged. Again, the ice grows upward and I think you would be ok up to about half way through the light as there is room for the ice to move upward. However, once the ice gets below the mid-point of the light, it could potentially, crack the lens.

Thank you very much!

 

[mas985]

I made an error in the ice/water line calculation. It is actual about 4.13", not 3.5". So it would be just touching the light.

 

[Mam262]

I made an error in the ice/water line calculation. It is actual about 4.13", not 3.5". So it would be just touching the light.

I really appreciate your time/efforts. Thank you.