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Avoiding freezing in water tanks
2

Avoiding freezing in water tanks

Avoiding freezing in water tanks

(OP)
What are the most common systems to avoid freezing in  water storage tanks i.e fire water storage tank...?

thanks

RE: Avoiding freezing in water tanks

Immersion heater?

Don
Kansas City

RE: Avoiding freezing in water tanks

(OP)
With insulation obviously right? Is that the most common system, or is that the "industry standard"

RE: Avoiding freezing in water tanks

The few that I have seen were just mounted underground.  Fixes the heat and insulation problem.  But if yours is already installed above it doesn't help much

RE: Avoiding freezing in water tanks

Derek

I've seen the immersion heater.  The other thing I've seen done is to have a bypass system which pumps water out and back into the tank to keep the water flowing ... and maybe add a bit of heat from the pump.  Of course, this only works if you don't have really deep freezes.

Patricia Lougheed

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RE: Avoiding freezing in water tanks

(OP)
of the three options:

underground tank
immersion heater
water return

which of these options is the cheapest. Obviously not the underground tank, but of the other two?

Also, which of these systems is most common in fire water storage, or recommended by the NFPA?

RE: Avoiding freezing in water tanks

Depending on the volume and insulation, you can probably get an immersion heater for under a grand...maybe even a couple of hundred bucks if the tank is small and/or insulated.  Take a look at McMonkey-Carr.

Don
Kansas City

RE: Avoiding freezing in water tanks

It depends on what is available.

Per NFPA 22, tanks in many southern areas don't require anything.

Otherwise, it's a matter of balancing cost of insulation against energy costs.

Bayonet heaters can be used; separate water heaters with pumps can be used; steam coils can be used.  You can inject steam directly into the water, for that matter.

RE: Avoiding freezing in water tanks

Depends on the size of the tank and the average ouside temperature ( not wind-chill). The larger the tank, the more probable that with an AVERAGE outside temperature over 1 day period above 32, the water would not freeze; during that period, the outside temperature could drop below 32 and the tank would have sufficient thermal capacity to remain above freezing.

If you post the tank size, the region you live in, then a cost effective solution could easily be suggested here. It may be just as simple as a layer of insulation and a cheap immersion heater which would be used only during sustained below freezing condition over days.

For example, where I am in southern CT, so far the average temperatures over any 24 hour period this winter season has been below freezing, so the layer of insulation would have been sufficient to maintain above 32 in the tank without turning on the heaters.

RE: Avoiding freezing in water tanks

I've been to southern CT this winter.  I froze.

Mike Halloran
Pembroke Pines, FL, USA

RE: Avoiding freezing in water tanks

Add salt?

RE: Avoiding freezing in water tanks

quote:"I've been to southern CT this winter.  I froze.


Mike Halloran
Pembroke Pines, FL, USA


Mike,

Southern CT is not Pembroke, but by any objective measure it aint that cold there.

And by the way, I meant to say that AVERAGE temperatures over any 24 hour period so far has been ABOVE freezing, not as I stated.

RE: Avoiding freezing in water tanks

I suggest you get a copy of NFPA to insure you meet all applicable requirements.

There are some handleld fire extinguishers used on aircraft that use water. We used to use "anti-freeze" in these. Not sure why you couldn't do the same in your application.

RE: Avoiding freezing in water tanks

(OP)
Quote: "If you post the tank size, the region you live in, then a cost effective solution could easily be suggested here. It may be just as simple as a layer of insulation and a cheap immersion heater which would be used only during sustained below freezing condition over days."


The tank is 433,000 GAl (1039 M3). We are talking about south of buenos aires in Argentina. the lowest 24h average temperature would be about -10 degrees C (14 F)

RE: Avoiding freezing in water tanks

Have you thought about a thermal loop underground?

Charlie
www.facsco.com

RE: Avoiding freezing in water tanks

If your tank is an open system, using compressed air to bubble up through the water (breaks up the surface tension and is what we use in our tanks). I also use a diaphragm pump (air powered) to make a loop system to pump water within the tank to minimize stratification.This is if I don't have a larger supply of air CFM readily available. Immersion heaters do work well if you have the power available or if it is a closed system.

RE: Avoiding freezing in water tanks

Unfortunately, with an average temp of 14 F over 24 hrs, you will need an insulation blanket. Without one,I calculated that you would need a heat source of about 100,000 BTUH. With an insulation  blanket R=6, the heat source would be 1/6 of this or about 16,000 BTUH. Tapping hot water off of an existing boiler would do the job, or even a 5Kw electric immersion heater would do it with a simple thermostat control and a setpoint of say 35 F. But the long thermal time constant would limit/obviate the heater usage as explained below.

The calculation assumes a spherical container which, from your data yields a radius of 20 feet and a thermal time constant of 15 days (meaning it would take 15 days for a tank at 45 F to drop to 25 deg with an outside average temp of 14 F without insulation and 90 days with R=6.

So the benefit of insulation is that if the average temperature over about a few months is above freezing, you probably won't need to turn on the heater.

RE: Avoiding freezing in water tanks

Corection:
The example of the thermal time constant should be:
If the OT is 14 F and the tank is 45 F, then without insulation it would take 12 days to reach 32 F. With a blanket, R=6 it would take 24 days to start freezing without the heaters.

RE: Avoiding freezing in water tanks

The type of heater required by NFPA 22 is largely dependent on the heat source.  Electric heaters are supposed to be pumped circulation types, where steam coils can be immersed.

Your tank is not required to be insulated, but in any practical sense it will need to be, and is probably more cost effective in the capital equipment let alone the long term to do so.

NFPA 22 has tabulated heat loads for tanks of varying proportion and capacity that will specify the heat load including insulation, temperature and wind factors.

In summary, NFPA 22 is a one-stop-shop to solving this problem and should be your primary resource.

RE: Avoiding freezing in water tanks

Well no one's mentioned so I will - what's wrong with a little freezing in a water tank? I have passing knowledge of water tanks in southeast Alaska.  I don't believe any of the large ones are insulated. With proper design they can function OK with a floating layer of ice and accumulation along the walls.  It does take away from your storage volume though.

RE: Avoiding freezing in water tanks

(OP)
CarlB, I agree with you that in some cases, who cares. The problem is that in this case it is a fire water tank, And it would kinda suck if the turbine is on fire or a 200,000 bbl. crude storage tank is on fire, and shoot theres no water.

I want to thank all of you for your help. I really appreaciate all the ideas that arrived. When i really started searching, we found that in our case, NFPA only accepts one answer, insulation and a heater.

Once again, tanks (chessy joke) for all the expertise of our faithful eng-tips friends

RE: Avoiding freezing in water tanks

Man....don't know where you are writing from, but in Canada this is almost a trivial problem.

You can add common anti freeze also known as ethylene glycol in a concentration approximately 1:4 with water.  This makes the system good to -40C.  If you are talking about a tank with potable drinking water, then you need to bury the tank below the freezing line.  Typically this is six (6) feet or so.

The other way of doing it is head to your local corner grocery and buy a bottle off the shelf.  Works every time!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

RE: Avoiding freezing in water tanks

Common antifreeze is considered a hazardous material.

It's probably illegal to allow it to flow down city sewer systems.

TTFN

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RE: Avoiding freezing in water tanks

...not to mention putting out fires with it.

Don
Kansas City

RE: Avoiding freezing in water tanks

If it such a hazardous material, then why is it commercially available at gas stations: PetroCanada, Shell, Esso (Exxon Mobile), not to mention hardware outlets such as Canadian Tire, WalMart, Home Hardware, etc?  Would the federal government allow such wholesale hazardous material "known" to be problematic?

Interesting!  What would you boys recommend as an automobile anti freeze for your radiators, rated -45C?

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

RE: Avoiding freezing in water tanks

Just because it's sold in a store doesn't somehow magically render it "non-hazardous".  You can buy herbicide, rat poison, brake fluid, paint stripper, engine degreaser, and dozens of other nasty potions over the counter.  That doesn't mean that you can merrily flush them down a toilet.

It had already been reported by the OP that a heater and insulation is the only acceptable answer for the NFPA anyway.

Don
Kansas City

RE: Avoiding freezing in water tanks

For cockroach:

The question isn't to to protect a few gallons in a closed loop system from freezing, it's for a large storage tank (433,000 gal) that supplies water for fire fighting!

Not sure the "owner" would want to purchase 100,000 gallons of antifreeze to provide a 1:4 mixture,  also not sure any wildlife (or people) in the area would appreciate having tens of thousands of gallons of antifreeze being sprayed in the open air.

Ethelyne glocol is hazardous, and that's why it should be properly handeled and disposed of, even in small quantities (in my state, it's illegal to dump ANY quantity of antifreeze, including from a treated radiator, in the environment or sewer).

RE: Avoiding freezing in water tanks

If money is an issue, and I appreciate the scale of economy argument, then your problem has now become increasingly complex.  Probably the best thing to do is to have designed the system correctly in the first place, acknowledging thermal variations in water temperature is an issue due to seasonal influences.

One response was to increase the salinity concentration of the water volume.  Probably price will be an issue here also.  Another has suggested water heater and mixers for stirring the volume.  Probably you need worry about the electrical bill on a monthly basis.

Short of throwing ice cubes at the fire, I guess you have a real problem.  Sorry nothing matched your particular specifications for a viable solution set.  Good luck with it, none-the-less.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

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