Microturbines are a relatively new technology with significant applications in green building design. By using natural gas as a fuel (also diesel or propane), microturbines generate electricity and hot water, rather than just one or the other. In this way, about 80% of the energy value in the fuel is converted to useful work. Microturbines can range from 25 kilowatt (kW) output to 500 kW, have low emissions of nitrogen oxide, are about 20% to 30% efficient in producing electric power and can produce hot water at 120°F to 175°F, a range quite suitable for a number of uses, including swimming pools and service water.

Microturbines offer a number of potential advantages over other technologies for small-scale power generation. These include a small number of moving parts, compact size, light weight, greater efficiency, lower emissions, lower electricity costs and ability to use waste fuels such

Microturbines at 60 kW power output are about the size of a large refrigerator. They are typically installed in group of five or more, to match demand for hot water and electricity in a building.

as biodiesel. They can be located on sites with limited space for power production, and waste-heat recovery can be used to achieve total system efficiencies of more than 80%.102

Microturbines typically come in 60 kW modules, about the size of a large refrigerator. By coming in small modules, it is easy to assemble a group of microturbines into an onsite power system and to match the electrical and thermal output to the building's demands. For example, the turbine's heat output can be used for water heating in a hospital or hotel, a facility type that requires lots of hot water on a 24/7 basis. If there is a swimming pool that gets a lot of use, any excess hot water can be used to heat the pool (which loses heat mainly through evaporation).

Other facilities that can benefit from microturbines include data centers, schools and colleges, food-processing or manufacturing plants, supermarkets and even sewage treatment plants.

The benefits of microturbines today are the same as those of cogener-ation systems; they are cost-effective whenever there is a connected thermal load that uses heat most of the time. The electricity generated by the microturbines displaces the purchase of energy from a utility, at full retail rates; and the heat displaces natural gas that would have to be purchased otherwise just for a single purpose. In many cases, there is less air pollution and lower carbon dioxide emissions than from conventional generation.

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