Re: Whole house generators (slightly OT)

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Tue, 17 Oct 2006 15:42:41 GMT, "BruceR" <razrbruce@xxxxxxxxxxxxxxx> wrote
in message  <RR6Zg.13181$gU6.10463@xxxxxxxxxxxxxxxxxxxx>:

>So, I think it's time for big honkin' generator to serve the whole
>house.  I've been looking at the Generac line and I'm considering a
>35,000 watt unit to serve my 200amp home.  I'd appreciate any info or
>suggestions that any of you have to offer.  I'd like to run it off
>Natural gas with LP gas as a backup.

When I was using generators to power scientific labs in the field, I quickly
gave up on carbureted generators (gasoline, NG, LPG) because they were too
slow to respond to load changes caused by air conditioners and pumps. When a
heavy load kicked in, the UPS's powering the electronics would cycle.
Eventually the batteries in the UPS's would become discharged and the lab
electronics would recycle or worse.

This was in the 1980's and NG/LPG/gasoline generators may have improved, but
ABIK, the physics still favor fuel injection.

Diesel, which is always 'fuel-injected', is fast to recover from a load
because at 1800 rpm on a 4-cycle engine, there are 450/60= 75 injections/sec
(i.e., opportunities for load adjustment) so with electronic fuel injection,
the amount of fuel injected can in theory be adjusted for every AC cycle.
This in turn reduces the nominal KW rating of the genset that you actually
need to buy compared to NG/LPG/gasoline.

(Thar's steady-state KW's and then thar's *real* KW's ...  ) Big flywheels
help a lot, but I found no useful comparative specs on _dynamic_ performance.
Hopefully this has changed for the better.

Since you are planning to allocate space for backup LP cylinder(s), you would
may not lose space with diesel compared to the NG+LNG approach, esp.
considering that the energy density of diesel is about 50% higher than that
of LPG, so combined with the requirement for cylindrical (not rectangular) LP
tanks, you can store twice as much energy in the same volume/area with diesel
than with LPG. IME, with good housekeeping diesel fuel isn't unacceptably
smelly.

... Marc
Marc_F_Hult
www.ECOntrol.org