When it comes to freezing the tanks, it is the amount of heat used to
vaporize the gas (phase change from liquid to gas uses up a huge amount of
heat) vs. the stored heat in the mass of the liquid and the tank itself.
Obviously at those cold outdoor temps, the tank is not going to be helped by
getting any heat from the ambient. So if you have a huge tank and a
relatively small draw - it works.
Still might not be able to start the engine though.
These are two different issues entirely.
A well designed engine, especially if kept warm and insulated will start up
when a poor one will not. Nothing to do with freezing the tanks - you have
not even used any gas yet when starting the engine.
This is why the Coleman design is insulated and heated. Or the engine could
be run indoors in like a barn or something.
My original point was, and is, that improperly installed or designed propane
engines will not start in really cold weather, when other engines, like
gasoline, will start, and thus that is a valid consideration when choosing
which one you want.
Of course a badly maintained gas engine with thick tar-like oil won't start
either ! So, you have to do something right somewhere !
Gary
----- Original Message -----
From: <k9zw@mac.com>
To: <geraldj@storm.weather.net>; "Discussion of Ten-Tec Equipment"
<tentec@contesting.com>
Sent: Wednesday, March 07, 2007 3:22 PM
Subject: Re: [TenTec] emergency power via generator
>
> On Wednesday, March 07, 2007, at 02:00PM, "Dr. Gerald N. Johnson"
<geraldj@storm.weather.net> wrote:
> >On Wed, 2007-03-07 at 14:47 -0500, Gary Hoffman wrote:
> >> Propane powered generators will not start in freezing cold weather.
They
> >> must be insulated and heated. Keep that in mind.
> >
> >Not true. But the propane tank must be large enough. Too small a tank
> >won't have enough vapor at low ambient temperatures. My 5 KW Onan needs
> >at least a pair of 100 pound tanks. They typical house 500 or 1000
> >gallon tank WILL supply adequate propane at all temperatures for the
> >propane fired generator.
> >>
>
>
> Depends on how deeply the temperatures dip where you are located.
>
> We've out run twinned 100lb tanks running a modest sized Onan. But then it
was showing -32F on the gauges.
>
> At -45F at an Oxbow Wis Cabin we found warmed 100lb tanks lasted less
than 30 minutes until they couldn't keep up.
>
> Ready to cringe? The solution is to bring 100lb tanks indoors and let
them warm.
>
> There are charts for production per 100lb (and other sized) tanks at
various temps & at various level of fill.
>
> We've eliminated the problem with a horizontal 500lb tank, and kept
connections to add-on other tanks if needed.
>
> Isn't it the amount of surface area, rather than absolute tank size that
solves much of the problem?
>
> I've been told that the basic rule of thumb is that for every 30 degrees
you drop you need to double your tank surface area if the tanks are pretty
full, and double them again if the tanks are less than 30% full.
>
> As most tank draws are a fraction of what the tanks can produce without
frosting down, I would expect that one shoudl start knowning that at summer
temperatures your genset would run on part of a 100lb tank's surface area.
>
> I am sure there are definative engineering sources for the problem, but
thought I would pass on experience & what the rule of thumb repeated around
here was.
>
> 73
>
> Steve
> K9ZW
>
>
>
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>
>
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