Avoiding freezing in water tanks 2

[DerekLJ]

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

thanks

 

[eromlignod]

Immersion heater?

Don
Kansas City

 

[DerekLJ]

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

 

[BusaJames]

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

 

[vpl]

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

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[DerekLJ]

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?

 

[eromlignod]

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

 

[JStephen]

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.

 

[IRstuff]

How cold are we talking? Is the water even recirculated? How about adding PG?

TTFN

FAQ731-376

 

[zekeman]

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.

 

[MikeHalloran]

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



Mike Halloran
Pembroke Pines, FL, USA

 

[IFRs]

Add salt?

 

[zekeman]

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.

 

[mechengdude]

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.

 

[DerekLJ]

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)

 

[FACS]

Have you thought about a thermal loop underground?



Charlie

http://www.facsco.com

 

[n2entropy]

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.

 

[zekeman]

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.

 

[zekeman]

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.

 

[KiwiMace]

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.