Centrifugal Compressors During Fast TransientsTransient studies for compressor systems allow the prediction of the compressor system behavior during fast transients such as they occur during emergency shutdowns. For the system simulations, the compressor behavior is assumed to be quasi-steady-state. This means in particular that the steady-state compressor flow-head-efficiency-speed map remains valid. During well instrumented emergency shutdown tests conducted on a centrifugal compressor system under realistic operating conditions, data showing the headflow-speed relationship of the rapidly decelerating compressor were taken. These data are compared with steady-state head-flow relationships taken at a number of speeds. This allows the determination of the relative deviation between the transient and steady-state head-flow-relationships and thus answers the question of the validity of steady-state assumptions during rapid transients. The impact of the fast transients on efficiency and consumed power, which can be derived from the speed decay of the system, as well as the impact of nonstationary heat transfer are also evaluated and reported.

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. An air accumulator provides pressurized air, which is passed through the expander section of the same microturbine used to charge the accumulator. The air passing through the IBC is cooled due to expansion, simultaneously providing power and cooling the 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. The size of the cycle studied is on the order of 10 kW(e), suitable for a domestic household; however, the system is easily scaled for larger commercial applications. The majority of the components in the system being studied are “off the shelf” products. A feasibility study was conducted to ensure that the proposed system is economically competitive with systems currently used, such as individual generation provided by an air conditioner (A/C), a high efficiency natural gas (NG) furnace, and grid power. Simulations were run for a full year based on the actual external temperature and the electrical and thermal loads for a single family detached dwelling located in Winnipeg, Canada. Performance data were generated using MATLAB™ while the economic performance was determined with time-based simulations conducted using SIMULINK™. The system is designed to allow 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 (A/C unit, NG furnace, and grid power) during heating modes of operation and were more expensive for cooling modes of operation. The yearly energy cost for the trigeneration system exceeded the individual generation costs by 30–40%; however, there remains much room for improvement to the trigeneration concept. All economic data were based on fair market energy prices as found in central Canada.

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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. An air accumulator provides pressurized air, which is passed through the expander section of the same microturbine used to charge the accumulator. The air passing through the IBC is 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. The size of the cycle studied is on the order of 10 kW(e), 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. A feasibility study was conducted to ensure the proposed system is economically competitive with 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. Performance data was generated using Matlab™ while economic performance was determined with time-based simulations conducted using Simulink™. The system is designed to allow energy islanding by providing for all household energy needs throughout the year, however integration with a power grid is optional. It was found the operating costs for the proposed trigeneration system in an energy islanding mode of operation were marginally higher than individual generation (A/C unit, NG 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 individual generation costs by 30 to 40%, however there remains much room for improvement to the trigeneration concept. All economic data was based upon fair market energy prices as found in central Canada.

Transient studies for compressor systems allow the prediction of the compressor system behavior during fast transients such as they occur during emergency shutdowns. For the system simulations, the compressor behavior is assumed to be quasi steady state. This means in particular that the steady state compressor flow-head-efficiency-speed map remains valid. During well instrumented emergency shutdown tests conducted on a centrifugal compressor system under realistic operating conditions, data showing the head-flow-speed relationship of the rapidly decelerating compressor was taken. This data is compared to steady state head-flow relationships taken at a number of speeds. This allows to determine the relative deviation between the transient and steady state head-flow-relationships, and thus answers the question of the validity of steady state assumptions during rapid transients. The impact of the fast transients on efficiency and consumed power, which can be derived from the speed decay of the system, as well as the impact of non-stationary heat transfer are also evaluated and reported.