Micro Generation - Combined Heat and Power Generation

Micro CHP is a device which generates electrical energy and heating simultaneously at domestic or shall commercial building level in accordance with the ESB network's definition.

Micro Combined heat and power generation system (aka CHP or cogeneration ) if operated on natural gas provides very high energy efficiencies. The generated low voltage electrical power can be used to supplement the home electrical energy supply which is generally about 27% to 35% of the total home energy usage. But by far the reason people are over enthusiastic about CHP s is its ability to generate large amounts of thermal energy usable for space heating. In reality this is the waste product of the electrical power generation process through the operation of a heat engine. The production of electricity in CHP s is secondary in a micro generation system.

Thermal energy for space heating

Space heating utilizing the waste heat of CHP s has been demonstrated to increase the fuel efficiency of Micro Generation up to 90%. The CHP units use the thermal energy wasted under normal conditions in conventional power generation units for space heating. Every kwh produced by Irish grid is said to generate 600 kg of CO 2 gas. Use of natural gas and biomass in micro CHPs will reduce the green house gas emissions while improving the carbon foot print.

Heat engines and energy efficiency

Heat engines by it's very nature produce only about 35% useful work. Balance energy content of the fuel is simply wasted away during operation. In most applications this will be as low grade hot water. The fuel being invariably a non renewable fossil fuel (such as natural gas, propane, diesel, petrol etc.) wastage of 65% or so is not conductive for good home economy and also the carbon foot print of the house, if the purpose is to generate electrical energy. The heat recovery of the waste heat through heat exchangers enables it to be utilized for space heating and hot water. This raises the power generation systems efficiency level to about 90%. It so happens therefore in micro CHP s used in domestic and small commercial applications the heating needs govern the generation of electricity if 85 to 90 % efficiency is aimed at.

Low Grade waste Heat for Home Heating

In a micro CHP units the hot water thus generated will be used for space heating, which constitutes the biggest portion of home energy usage during the colder seasons. The electricity generation is secondary in the system as at best it would be equivalent to about 35% of the energy stored in the fuel. The electricity generated will be in excess of the home's requirement in the heating seasons while in the hot seasons when you really need electricity (but not heating) it will be in short supply.

If you are in Ireland