Half a croissant, on a plate, with a sign in front of it saying '50c'
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Non-electric cogeneration

Like Combined Heat, Cooling, and Power, but no power.
  [vote for,

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.

goldbb, Jun 22 2011


       Also available from GOLDCO corporation: portable stand alone units for cooling or heating outdoor entertainment venues.   

       When ordering, make certain to specify the fuel: gasoline, diesel, or propane.   

       For alternative fuels, you may order a version of the heat pump powered by an external heat source and a power take off; it is the buyer's responsibility to connect his or her heat engine to the heat pump.   

       To power the heat pump using biomass, GOLDCO recommends using a "GEK Power Pallet," designed by All Power Labs, which has a PTO, and can be set up for CHP.
goldbb, Jun 22 2011

       "Cogeneration" always looks wrong without a hyphen. I like hyphens. My great great aunt Robert had three in her surname, and we've kept them ever since in a small ivory box next to the spigot mortar.
MaxwellBuchanan, Jun 22 2011

       I don't Completely understand this idea but if it's based off of old HVAC technology you should be able to create a working model if you've got the money
EdwinBakery, Jun 23 2011

       The idea is not without merit; but -   

       The working fluids for absorbtion and compression refregerators are radically different in their physical properties.   

       Having said, that, using the "waste" heat from the engine to drive an absorbtion heatpump is quite practicable. Energy could also be harvested by, for example, a thermopile (Seebeck effect).   

       There are problems if this is intended for domestic use; footprint, noise, maintainance. The initial cost of the plant, plus installation, will be large.   

       The usual mutterings about economies of scale apply too.   

       The trick would be to make the system flexible, depending on climatic conditions.   

       In the winter, you probably want electric power, hot water, and domestic heating.   

       In summer, you probably want electric power, hot water, and domestic cooling.   

       The engine gives you rotational mechanical energy, and waste heat. It makes the most sense to convert the rotational energy directly into electrical energy.   

       This leaves the heat, which comes out in two ways; fairly high grade heat through the exhaust, and low grade heat through circulating liquid. Pressurised glycol systems can work quite happily at up to 100C.   

       Providing the management system can make sure that the primary powerplant doesn't overheat under rapidly changing load conditions, then there's probably quite a lot of mileage in this idea.   

       The obvious fuel is methane.
8th of 7, Jun 23 2011


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