Re: Efficiency of utilities
- From: "Max Demian" <max_demian@xxxxxxxxxxx>
- Date: Mon, 17 Nov 2008 12:28:20 -0000
"larkim" <matthew.larkin@xxxxxxxxx> wrote in message
news:fdee4262-82c1-40ca-80cf-d1dd3e3914d0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I have a wife who is becoming obsessive about the use of electricity
and gas, and consequently is pushing up my requirement to know
something about these things.
One thing I've been puzzling recently is why we are told that electric
heating is "less efficient" than gas heating. Is that really true?
Or is it that a) electricity is more expensive per kWh, so to achieve
the same output is more expensive or b) electricity carries high(ish)
level of transmission losses on the way to my house, whereas gas
arrives in an "unused" state, and therefore I get nearly all of the
benefit of its heating ability I use it to power my boiler?
There's not just the cost/losses in transmission of electricity: the
generation of electricity from (e.g.) gas is inherently inefficient - I
don't think they've ever achieved much more than about 50% efficiency - the
rest is lost in those great cooling towers they have at power stations, or
possibly used in "neighbourhood heating" schemes if there is a housing
estate nearly - though it usually is wasted.
(Theoretical, not just engineering considerations limit the efficiency of
electricity generation - heat is a "low grade" of energy as it is "random",
whereas electricity is a "high grade" of energy as it is "directed".)
On a similar vein, there is the standby / mobile phone charges etc
arguments. If (as my physics teacher once said) energy cannot be
created or destroyed, just converted from one form to another, we must
be "using" the energy. If they heat up, we're using the heat, if they
buzz then isn't that sound energy converted into heat through the air
(?), if they have a small LED on them doesn't the light again convert
to heat energy (save for the part that disappears through the windows
as visible light). So aren't they equally "efficient" as an
electrical heater?
The efficiency figure looks at the *useful* output of a device, e.g. forward
motion of a car, or light output of a lamp.
The "waste" heat *may* be able to be used, for example the heater of a car
using waste heat of the engine; similarly the heat output from a domestic
appliance might reduce central heating costs if it is controlled with an air
thermostat - but only in the winter months.
--
Max Demian
.
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- Efficiency of utilities
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