Design and simulation of a microturbine trigeneration system incorporating hydraulic storage and an inverse Brayton cycle

Integrated micro-power systems that can provide electricity, heating and cooling (i.e. trigeneration) have the potential to provide greater overall efficiencies than traditional micro-cogeneration power systems with separate cooling devices. With rising grid power rates, small-scale trigeneration has the potential to be economically attractive. The majority of trigeneration systems under development and in use utilize expensive components such as absorption chillers suitable for medium to large-scale trigeneration, which are not economically suitable for small-scale applications.;A study was conducted to assess the thermodynamic and economic performance of the proposed system compared to systems currently used, such as individual generation provided by an air conditioner, high efficiency natural gas furnace, and grid power. Simulations were run for a full year based on actual external temperature, electrical, and thermal loads for a single family detached dwelling located in Winnipeg, Canada. The output of the microturbine studied is 10 kWe, suitable for a domestic household, however the system is easily scaled for larger commercial applications. The majority of the components in the system studied are off-the-shelf products. Performance data was generated using MATLAB(TM) while economic performance was determined with time-based simulations conducted using SIMULINK(TM). The system allows energy islanding by providing for all household energy needs throughout the year, however integration with a power grid is optional. It was found that the operating costs for the proposed trigeneration system in an energy islanding mode of operation were equivalent to or less than individual generation (air conditioning unit, natural gas furnace, grid power) during heating modes of operation, and more expensive for cooling modes of operation. The yearly energy cost for the trigeneration system exceeded the total cost of running individual systems by 30 to 48 percent, however there remains much room for improvement to the trigeneration concept. All economic data was based upon fair market energy prices found in central Canada.;To bring the economic benefit of trigeneration to small-scale users without incorporating expensive components, an inverted Brayton cycle (IBC) is employed which makes use of the expander section already present in a microturbine. A hydraulic accumulator, indirectly charged by a microturbine, provides pressurized air, which is passed through the expander section of the microturbine and cooled due to expansion; simultaneously providing power and cooling flow. As the microturbine is indirectly fired, the flow passing through the engine or IBC can be directly vented into the household, eliminating the need for additional heat exchangers.