Combined Heat and Power idea ….. would it work?
I had an idea for a simple combined heat and power system I could build from mostly scrap materials. (To keep it as simple as possible, this one *doesn't* feed back into the grid.) The idea was to use a small water-cooled diesel engine, powered from cooking oil, to turn two generators: a 230 volt alternator and a 24V truck or coach alternator. The latter would be used to charge a bank of lead-acid batteries, in conjuction with a modified computer UPS. The water jacket of the engine would be plumbed into my existing radiator circuit with a 3-port valve to select between it and the gas boiler, and the engine would be controlled by the thermostat.
When the thermostat calls for heat, the engine fires up and heats the radiators, but it also generates 230 volts AC (to run the house electrics) and 24 volts DC (to charge the batteries). When the thermostat is satisfied, the engine is stopped and the UPS switches over to battery power.
If I can get a donor vehicle with an air conditioner, I would use that to transfer the waste heat from the exhaust gases into the main living room of the house as blown warm air heating. The radiator in that room is already fitted with a TRV so would shut down automatically in the presence of extra heat.
Anytime necessary, the gas boiler can be run for heating, and/or the UPS input can be switched over to mains power from the grid.
Would this actually work in practice?
***** UPDATE *****
I intend to refine waste cooking oil for fuel. People will actually pay good money to get rid of the stuff …..
I will only need a two-position switch if I position it at the input of the UPS, to select "real" mains or the AC generator. Operation on batteries would be taken care of by the UPS's own electronics doing what they're meant to.
The idea of the separate 24 volt generator for battery charging is to ease the load on the 230-volt generator. The UPS's own charging circuit will only be rated for charging batteries of a few amp-hours anyway. I might add a third, 12 volt generator for my 12V electronics.
I'm thinking of using open-vented batteries; the air conditioning idea if used would provide me with a supply of de-mineralised water for topping-up. All of this would be located in a coal shed which is attached to my outside privy behind my house.
It may work, but the cost of fuel for the diesel would be high, unless you spend a lot of time collecting and filtering used cooking oil, and you get it free.
But the whole thing is very complicated. How will you switch between 230 volts from the power company and diesel generator and the output from the UPS? you will need a big three position relay. Is the relay switched manually?
And, it looks like it will never operate in the summer, as the only control you have is an air temperature thermostat.
I don't think you need two generators on the diesel. The 230 volt one can be used to charge the batteries via a charge controller, which you need anyway to avoid overcharging the batteries.
Do not use auto batteries indoors, they can leak poisonous gases.
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It may work, but the cost of fuel for the diesel would be high, unless you spend a lot of time collecting and filtering used cooking oil, and you get it free.
But the whole thing is very complicated. How will you switch between 230 volts from the power company and diesel generator and the output from the UPS? you will need a big three position relay. Is the relay switched manually?
And, it looks like it will never operate in the summer, as the only control you have is an air temperature thermostat.
I don't think you need two generators on the diesel. The 230 volt one can be used to charge the batteries via a charge controller, which you need anyway to avoid overcharging the batteries.
Do not use auto batteries indoors, they can leak poisonous gases.
.
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