Basic backup generator questions

 I'm looking for some basic information about automatic backup
generators to run on liquid propane.

My house has 200A service, and I'm not interested in a generator that
requires me to pick a fixed number of circuits.  The whole house needs
to be on backup.  I'm not sure at this point what my power needs would
be, but my preliminary guess is that a generator in the 10-15KW range
would be sufficient.

My questions:

1)  What's the lowest power output that's available for whole-house
backup?

2)  How important is liquid cooling versus air cooling in a normal NJ
climate?

3)  How large a propane tank is best?  Besides the future generator,
there's an existing oven/range and a future gas grill to consider.  I
already have a tank for the oven, of course, and I believe it's
capacity is 200 pounds.  It's oversized because after our initial
propane company let us run out of gas on Xmas Eve day a few years
back, then wanted a $100 emergency fill fee to come and rectify the
situation, we requested a tank with a gauge (if possible) from the new
company.  I expect the 200-pound cylinder is the smallest they had
with a pressure gauge attached.

I'm comfortable doing research on details myself, so I'm only looking
for basic pointers, and appreciate whatever helpful answers towards
that end that I get.

  wrote:

It sounds like you are seeking is a "backup only in emergency"
solution.
Please verify that.

It sounds like you don't want to reduce load in an emergency.
Again, please verify that you have no load you could "shed" during an
emergency.


What do you use for HEAT?
Is it an electric heat pump?
If it is, then you need to be sure you can start it.
If not, what fuel do you have on hand and how do you store it today?


You ask:

Wouldn't that depend on the house?
You've implied that you want 200 amps if needed.
Do you really use that much?
Do you know **your** peak load or have an upper bound for it?
How many kwh do you use per month?

Assuming the 200 amp from above, and continuing:
200 amps would be about 24kw, if you really needed all that.

It is likely that your 200 amp service exceeds your actual
consumption.
If you could "get by" with 18kw then this unit might suffice:
http://www.generac.com/Products/Residential/AirCooled/18KW.aspx
Note the fuel consumption.
Note it provides only 18kw which is LESS than the 120volts times 200
amps max that you originally asked to have.

Fuel consumption may exceed 2 gallon per hour.
The above specs 2.85 for only 18kw at max output.

Water cooling would not be needed.
But, you may not find many air cooled units larger than the 18kw.


It would seem 10-14 days might be a good minimum.
that would be
10*2.85*24= 684 gal.
14*2.85*24 = 958gal.
at 80% full, a 500 gallon tank would only give you 400 gallon usable.
If you really use much less than 18kw, then check the other fuel usage
specs.
Do you have storage space for two of them?

It would seem that with some compromises or if your true load is less
than the 24kw,  that a 500 gallon tank and the 18kw air cooled would
"suffice."
But, if your heat is from a heat pump, you need to be sure you have
plenty of capacity to start it.

Best
Phil

 

Wouldn't 200 amps be 48kw? 200A x 240V?

Bob

 

    Well, lets see...  You have to figure in power factor, add in the square
root of 3, correct for RMS, rub your chin for a while and furrow your brows
whilst consulting your slide rule and your trig tables, and finally you end up
with something like...48 kW.  Did I make that clear?

     Seriously, it is very unlikely that the OP needs anything approaching 48
kW.


Vaughn

 
oh good, even better!