This is an idea for a type of fuel powered heat pump for
heating and cooling a home.
The benefits:
It can fueled by anything which can power an engine
(natural gas, propane, diesel fuel, wood gas, etc.).
It will be more fuel efficient than either a single stage
absorption heat pump or
an engine powered reverse Rankine cycle heat pump.
It should be simpler and less costly to construct than
either a double absorption heat pump or a two stage
heat pump.
It can operate completely independently of the
building's electrical system, making it ideal for off grid
homes or in areas where the grid is unreliable.
The background:
In a conventional reverse Rankine cycle heat pump,
gaseous refrigerant is moved from the (low pressure)
evaporator to the (high pressure) condenser via an
electrically powered mechanical compressor.
In an absorption heat pump, gaseous refrigerant flows
(at nearly constant pressure) from the (low pressure)
evaporator into the absorber, is absorbed into the
absorbent liquid, is pumped to the (high pressure)
generator (where it is boiled off by a heat source), and
flows (at nearly constant pressure) into the condenser.
The heat is most often supplied by a simple gas or oil
burner.
The idea:
Take the fuel which would be burned for the absorption
heat pump, feed it into an internal combustion engine
(spark or diesel, depending on the fuel).
The waste heat from the engine (the exhaust, coolant,
or preferably both) is used to boil the refrigerant out of
the absorbent in the generator.
The mechanical power from the engine is used to drive
both the pump (used to move liquid from the absorber
to the generator), and a mechanical refrigerant
compressor located between the generator and
condenser, and any other fans or pumps the system
might need, and an electrical alternator.
The power from the alternator charges a battery, and
powers the fuel injectors, spark/glow plugs, etc.. The
battery operates the electric starter motor and provides
voltage to the thermostat.
By using two stages of refrigerant compression (thermal
then mechanical), instead of just one, greater
efficiency should be obtainable than one would have in
a single stage.
In comparison to using the fuel solely for heat (and using
thermal compression) or solely for mechanical power
(and using mechanical compression) the other stage can
be thought of as being approximately "free."
However, this two stage compression is much less
complicated and less costly than either two stages of
heat pumps, or a double effect absorption heat pump.
Furthermore, since the refrigerant coming out of the
mechanical compressor will be hotter than the liquid in
the generator, that refrigerant can pass through a extra
heat exchange coil in the generator, transferring some
heat to the liquid absorbent, before the refrigerant
continues on to the condenser. By making productive
use of even more heat that would otherwise be
considered waste, in a manner similar to vapor
recompression distillation, efficiency is further
increased. I'm not entirely sure whether this particular
feature would be cost effective (it's just an extra coil of
copper tube, but I'm not sure how much it will actually
improve efficiency), so a production version of the
system might or might not have it.
The Drawbacks:
Not all thermostats work with 12 volts.