Propane consumption rate 2

[sodengineer]

Hi All
I'm from the Civil side of the forum, but I'm working on a project far from civilization and it requires solar power. I'm NOT here for the solar power question but for a heat quesiton. This system will push electricity into a battery. I need to keep the battery from freezing through the winter. This will be an inexpensive (I hope) automotive battery. The problem is that it will be located at 8500 ft in Wyoming and will be inaccessable from November to June. I want to keep the battery from freezing in the winter. I will have it in an insulated box, but I'm still concerned about freezing. If I put a small propane heater (I'm thinking of something that would be essentially a pilot light that would run all winter, or even something as simple as a "bernz o matic" torch connected to a 5 or 10 gallon tank.

Is something like this doable?
Is there a specific "heating box" made for batteries and I can avoid this whole cobb together process?
How much propane (gallons) would I need to run something like this?

Thanks
Mike

 

[pmover]

sodengineer,

since ya have solar power, a 50 or 100-W light bulb will do just fine. a charged & well-maintained battery is not likely to freeze. so, if the solar power genset can deliver the power, no need for propane. remember, all your attempting to do is keep the battery slightly warmer than the surroundings.

fyi, many outhouses in AK use small 100-W heaters to provide some warmth. also, there are 50-W heaters placed below typical auto batteries that apply heat to the battery when plugged in (a few hours before starting the vehicle).

hope these ideas help you.

Good luck!
-pmover

 

[imok2]

How about a battery wrap(warmer)
go here

http://www.apelectricshop.com/p-60-057148-generac-guardian-36-battery-warmer-wrap.aspx

 

[sodengineer]

Thanks for the idea.

I had thought of that, but I figured I would be running the risk of discharging the battery just to keep it warm. This is a remote site, nearest "real" electricity is 15 miles. So, I would have to use battery power to run the warmer.

I was looking for an independent source of heat.

 

[IRstuff]

Well, you can do the math.

Energy density of LPG is around 13kWh/kg.

If we assume a 50 W load for 8 months, you get 329 kWh. 50W is 170 BTU/hr, which is roughly a stove burner on very LOW.

So, you'd need about 25.5 kg of LPG, or 11.6 gal.

However, running an unattended burner seems highly dubious at best.

TTFN

FAQ731-376

 

[sodengineer]

That is exactly what I needed, thanks!

I will enclose the entire operation in a vented box with a separate vent for the batt.

Yes, I'm in the process of making a financial contribution to Eng Tips now.

 

[tkordyban]

Seems to me you may be throwing away more energy heating the battery in the winter in Wyoming than you gain from the solar photovoltaic panels. How much sun is available in Wyoming during the winter anyway? If you are going to bring propane to the site, just use propane to generate the power you need at the location. If I were you I'd do a sanity check to see if the solar energy part of this project makes sense. Also, from a safety standapoint, consider that batteries being charged can outgas hydrogen under certain fault conditions. An open pilot light and a collection of hydrogen gas seems to be a bad combination. Even an electronic igniter for the propane would be bad if the hydrogen is not vented away properly. Even if you do away with the propane heater entirely, make sure you vent the hydrogen.

 

[sodengineer]

Thats why I'm going to separately vent the battery.

Actually, many many days are clear, cold and, believe it or not, sunny, yes, there are some cloudy, snowy days, (hence the battery), but the battery should get me through a week of no sun.

Thanks for the help.

 

[Compositepro]

Consider putting the battery underground. This is common practice in cold climates for water pumps, hydrants, and propane tanks. The boiling point of propane is -40F. If it gets colder than that there will be no pressure in the tank. If you insulate well over the battery the ground will keep it warm.

 

[btrueblood]

Might have to dig pretty deep at 8500' in Wyoming winters. But agree with Compositepro on principal.

 

[sodengineer]

<<have to dig deep>>

There is a reason they are called the "Rocky Mountains" so I might have to shoot a hole, but I like the idea. The contr. should have a front end loader for a lot of the other work, so this shouldn't increase the cost (too much). I will use a prefab box with an insulated lid, and run the cables underground.

EXCELLENT IDEA.

As a Civil, I prefer siimpler systems that run on things like gravity, the heat of the earth, etc., rather than omplex mechanical systems.

 

[btrueblood]

sod,

Would love to know what the frost depth is there, are there charts for that kind of thing?

 

[IRstuff]

Don't forget that you'll still need to vent the battery compartment so that there's no hydrogen buildup.

Even if the ground temperature is cold, you'll still be ahead by getting out of the cold air convection, etc., and with high-performance insulation, like maybe a VIP (

http://www.glacierbay.com/products/thermal_insulation.html),

you might get by with considerably less heat input requirement to keep the battery warm, maybe only a few watts.

The VIPs are pretty nifty, a vacuum aerogel sealed in an external shell, resulting in heat transfer coefficients lower than anything else available.

TTFN

FAQ731-376

 

[IRstuff]

A quick calculation. If you get the thickest available VIP, the htc will be 0.086 W/m^2-K. Assuming 6 ft^2 of insulation and a 60ºC delta (which ought to be pretty worst-case), the heat loss is 2.9 W.

TTFN

FAQ731-376

 

[btrueblood]

One more worry - there is likely to be a fair bit of snow cover during winter at that elevation, and that snow will melt someday. Make sure your hole is well drained.

 

[sodengineer]

WRT the snow....

Concur with the need to drain, but it isn't as bad as one would think. It is on a slight ridge that "generally" blows clear.

Getting sufficient fall to drain the hole to the surface may be a problem, but if I can shoot the rock and fracture it enough I should be able to just get it to drain into the subsurface.

BTW, where I am, 6000' frost level is about 3', so we put our foundations at 4'+. I will probably do the same here.

 

[KiwiMace]

Here's an article discussing a remote arctic acoustic station with similar issues to what you are describing, although the duration was only a few days.

From E-NZ, a New Zealand engineering magazine.

 

[IRstuff]

With a higher ambient surround temperature, the amount of heat required to keep well above freezing is commensurately less. If the ambient is 0ºC, and the desired temperature is 20ºC, the heat loss would be about 1/3 of the calculated value above, resulting in less than 1 watt of heat loss, so, about 80 mA from a 12 V battery.

TTFN

FAQ731-376

 

[chicopee]

sodengineer, don't forget to capitalize on the higher ambient temperatures due to the "Shanook" (I hope that it's speeled correctly) winds during winters.

 

[sodengineer]

Actually, I spell it Chinook (like the helicopter), but I know what you mean.