<LONG>
I've changed the subject, thus if you're reading this, don't complain.
On Sun, 19 Sep 1999 HI100@xxxxxxx wrote:
:Acer wrote :
: >>>I have not used my air-conditioner for years and if I were poor I
: definitely would not use it as it costs a bundle in extra gas.<<<
:
:Only in stop-n-go city driving; negligible increase in gas use at cruise
:speeds.
:
:Acer,
: I seem to remember a number of close to 10HP so for a moderate size
:car running say 50-100HP cruising, about 10% reduction. Which is about what I
:used to see and about what I see on rentals..
10%? That still seems rather large. Admittedly, I have not read texts or
am I an engr yet.... Supposing that you normally get 20mpg (measured,
not EPA estimates) at cruise. 10% would be .2mpg, correct? Oh, wait,
you're talking HP, not MPG. Still, 10HP sounds too optimisic. For
reference, the current Dodge Caravans have a cooling capacity equal to
that of an A/C designed for an 1800 sq. foot house (literature).
Converting 10HP to watts, that's 7.6kW, a LOT of power. Maybe it is
correct, but it sounds not to me.
Whether I'm correct or incorrect above, it doesn't matter; we're concerned
about MPG in the end (or km/L for those across the Pond ;-)). Even if the
10 0.000000igure you quote is spot on, you're losing .2MPG--instead of 20, it's
now 19.8. Negligible.... (each PSI of under inflation looses you more
mileage). Cross winds, car loads, "wake" effects from semis, blah blah
probably account more.
Another way to show this is not
:a small amount of energy think of the extra radiator area which is added to
:get rid of the heat (Of couses since this is a heat pump this is not all
:wasted energy but still).
Most prolly negligible. At cruise, there is enough airflow to take care of
things. (nitpick: if the a/c is started up at startup, whether in winter
to de-fog or in summer to cool, the added heat produced by the condensor
is adding to the coolant, decreasing time to warm up to op. temp. Yes, it
is most likey negligible again)
Or just remember that the air conditioner has a
:special kick in switch to supply extra juice to prevent the car from stalling
:at idle when the airconditioner is on.
...I believe only for smaller engines. Some engines also have a relay to
cut out the compressor under large (or wide open) throttle openings to use
all avail. power to drive the car (since you're at WOThrottle, you
obviously want to go and need that go). If a compact car doesn't have such
a cutout, then the a/c switch is often termed the "turbo boost" switch;
cut it out, and whoohooo, more power! <G>
Speaking of which, winter is around the corner: denser and colder
air->"cold charge"->more power :-) Each degree celcius cooler adds either
.5 or 2 HP, not sure. Double the fun if you have a turbo/intercooler setup
as the intercooler gets more efficent, to the point where the injectors
can't supply enough fuel causing a lean mixture and risk of overheating
the heads ;-) (yes, this has actually happend)
Mike Butler (or any engineers or car nuts) feel free to jump in and tell
me I'm wrong, which I may be. Email too will be most welcome if you don't
want to add to list traffic. I'm all for it :-)
/Acer "steppenwolf" Victoria
--
"Nothing left to win / And nothing else to lose." --U2
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