Re: OT: Energy=Horsepower-Hours ???

On Tue, 17 Apr 2007 14:53:15 +0100, Eeyore wrote:
MooseFET wrote:
joseph2k wrote:
Don Lancaster wrote:
Eeyore wrote:
Joerg wrote:
Homer J Simpson wrote:
"Joerg" wrote

Even if you plug your Prius into an outlet the coal plant behind that
power grid will still spew gases.

But more efficiently than burning the coal in a furnace.

Usually not.

Invariably not. Average coal to wall socket efficiency is around 35%.

Newest multi cycle coal plants approach 60 percent efficiency.

Further, they can power a heat pump with a SEER of 16 or so that
completely blows away any conventional coal furnace.

How very interesting, in Physics class i had to demonstrate the maximum
possible efficiency for a heat engine. Like all others before me the best
cycle is Carnot with a maximum efficiency of 47 percent. Rankine with
superheat and super-scavenging tops out just below 40 percent. It also
represents the best possible "steam plant" operation. By the time you get
done with transmission losses 35 percent efficiency from fuel to socket is
very good indeed.

Sounds like you took Physics so long ago that combined cycle plants
were not considered.

http://en.wikipedia.org/wiki/Combined_cycle

Efficiency of CCGT plants

The thermal efficiency of a combined cycle power plant is normally in
terms of the net power output of the plant as a percentage of the
lower heating value (LHV) or net calorific value (NCV) of the fuel. In
the case of generating only electricity, power plant efficiencies of
up to 59% can be achieved. In the case of combined heat and power
generation, the efficiency can increase to about 85%.
----
Actual plant reference in First page of Google search:

"ScienceDirect - Energy : Performance effects of combined cycle ...
The plant consists of one Combined Cycle Unit with a designed total
net power output of 457.6 MW and net heat rate of 6695 kJ/kW h
(efficiency=53.8%). ...
linkinghub.elsevier.com/retrieve/pii/S0360544204004633"

These ara all 2 cycle plants with the exhaust of a gas turbine
powering a steam cycle. The coal version is experimental at this
time, AFIK.

If heat is the desired output, nothing will ever beat local fuel to heat
conversion. Efficiency in excess of 90 percent is not very difficult.
Heat pumps can move maybe twice the real energy as provided in input, but
the Carnot limit proves that recovering all the transported energy still
looses total energy.

Better yet:

Use an engine to run the heat pump. Since almost all of the losses of
the engine are heat, if the goal is a heated house, most of the losses
get put to a good use. This should give a far better number than
either a furnace or a heat pump alone.

Local CHP makes a LOT of sense for efficiency reasons. It's another reason why
hybrid cars are the future too.

Indeed, CHP or COGEN as it is usually called here (combined heat and
power generation) was all the rage during the last energy shortage.
Then energy became cheap and plentiful again and many of the cogen
mfgrs got out of the business. No ROI in the first year so no buyers.
When energy gets expensive enough cogen might return to some
popularity - but it dosen't work too well with centrailized large
power plants since there is no practical way to get the heat to users.

Actually all of the losses of an engine are as heat, but it is not all
recoverable heat. An old rule of thumb for diesels that probably goes
back to Otto himself is: 1/3 of the energy delivered to the shaft, 1/3
to the cooling water, and 1/3 out the stack with the exhaust. This is
still pretty close for small diesels, but large turbocharged diesels
do significantly better - 50% efficiency for the current record
holder:

http://people.bath.ac.uk/ccsshb/12cyl/

This engine has record setting efficiency due to its record setting
displacement of 1820 liters per cylinder, which gives it a terrific
volume to surface ratio, cutting way down on heat loss through the
cylinder walls into the cooling water and also reducing friction due
to less rubbing surface area per liter of displacement. To get
anywhere near this efficiency in a small diesel will be very
challenging, simply not possible with a conventional oil lubricated
metal engine due to the low temperatures they can tolerate. There was
a bunch of activity in the development of uncooled ceramic diesels 20
years ago or so, and some notable efficiency improvements made with
ceramic piston caps and cylinder head liners in metal engines. Perhaps
some variant will eventually emerge as a small high efficiency engine
for hybrid vehicles.
.

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