[TenTec] emergency power via generator

[k9zw at mac.com]

On Wednesday, March 07, 2007, at 02:00PM, "Dr. Gerald N. Johnson" <geraldj at 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