Thermal insulation for steel potable water tanks - do we need it?

[Bjegovic]

Hi all.

My company is dealing with water treatment and supply. We are trying to introduce above ground steel tanks for potable water, instead of most common concrete tanks that are installed below ground.

The problem at hand is do we need to include thermal insullation? Climate is moderate continental, with winter temps below freezing, and summer peaks up to 40C. Sizes of the tanks we are talking about are somewhere between 250 and 1000m3. Turnover rate will be measured in hours, so there is no way that the water can freaze in normal operation. (inlet water temp from underground wells will be above 10 degrees C).

I am concerned that the customers may have complaints that their tap water is too hot in summer, or cold in winter. The potential clients (municipalities, waterworks companies...) are also suspicious. As I know, there is no regulative specifying temperature of potable water.

In Your opinion, do we need thermal insulation for a steel water tank?

 

[cvg]

not likely and this type of tank is quite common in areas with temperatures similar to yours in the US. I haven't heard of anyone complaining about water that was too cold. Warm water in the summer may be an issue and the normal solution is to add ice...

 

[stanier]

Steel tanks are commonly used in Australia without insulation, even at temperatures higher than this figure.

 

[bimr]

Agree with cvg, it is not likely. For what it is worth, I live in moderate continental climate with a surface water supply. I have noticed that the water tends to be colder in the winter and warmer in the summer.

 

[Zambo]

I also doubt that too warm water can be considered a problem. It is worth checking whether there are periods of low turnover, ie. during the night, when freezing could be a problem, this is sometimes the case with rural communities. If freezing is possible then either insulation or a small water heater to cause movement of the water can be used.

 

[Bjegovic]

I did some calculations and @ -25C and tank of cca 500m3, water will start to freeze after 3 days without turnover at all.

since the raw well water is usually above 10C, it seems there is no problem with at least a minimal consumption.

Now i have to address the problem of potential surface freezing during night... maybe an electric mixer or a suitable inlet connection that will cause disturbance is needeed.

 

[JStephen]

NFPA-22 has some information relative to freezing in steel tanks, and heater sizing if heating is required. The application is fire-protection tanks, which normally have zero turnover. Down to a certain minimum temperature, you don't need any heating or insulation.

Municipal tanks in the US are seldom insulated. They usually rely on the water flow to maintain the tank above freezing. This is true of both concrete and steel, both bolted and welded.

Here in the US, water temperature is not an issue- people just deal with it. People in cold climates expect the water to be cold, and people in hot climates expect it to be uncool- it won't normally actually get hot with buried lines. I can see that if you make a CHANGE in water temperatures, you're liable to get complaints.

When placing tanks in potentially freezing conditions, it is best to work the system so that water flows through the tank, rather than putting the tank on a dead-end line. Internals should be minimized. Usually this means internal ladders and float-type gauges are omitted, manway necks are cut flush inside, etc, to avoid problems if you do have a big ice plug that then moves down. I've seen weir boxes on the outside of tanks rather than the inside. Piping connections are normally run through the floor rather than through shell nozzles.