For a domestic CHP load of 1 kW, the positive Brayton cycle requires minute turbomachinary, which
would have inherently low turbine and compressor efficiencies due to leakage at the rotor tips [11].
However, the inverted Brayton cycle has a lower specific output for a given turbine unit, i.e. a lower
output power per unit mass flow. Consequently, for a given electrical output, the system mass flow and
thus the required turbomachinary would be much larger than for the positive cycle. This allows better
component efficiencies. Hence, for low output power applications such as domestic CHP, the inverted
Brayton cycle might be preferred. Another overall advantage of the inverted cycle for domestic CHP is
safety. It would not require pressurizing the present domestic gas supply. Furthermore, if a leak occurred
in the unit, air would be drawn into the system, rather than fumes being exhausted into the house. The
feasibility of the inverted cycle for domestic use was analyzed to evaluate cycle efficiencies at low output
powers. This showed that for an output power of 1 kW an efficiency of 25% was possible by recirculating
the exhaust gases back into the system. Clearly, much work is needed before the suitability of the inverted
cycle gas turbine for domestic CHP can be established, including the construction of safe and reliable
demonstration model
For a domestic CHP load of 1 kW, the positive Brayton cycle requires minute turbomachinary, whichwould have inherently low turbine and compressor efficiencies due to leakage at the rotor tips [11].However, the inverted Brayton cycle has a lower specific output for a given turbine unit, i.e. a loweroutput power per unit mass flow. Consequently, for a given electrical output, the system mass flow andthus the required turbomachinary would be much larger than for the positive cycle. This allows bettercomponent efficiencies. Hence, for low output power applications such as domestic CHP, the invertedBrayton cycle might be preferred. Another overall advantage of the inverted cycle for domestic CHP issafety. It would not require pressurizing the present domestic gas supply. Furthermore, if a leak occurredin the unit, air would be drawn into the system, rather than fumes being exhausted into the house. Thefeasibility of the inverted cycle for domestic use was analyzed to evaluate cycle efficiencies at low outputpowers. This showed that for an output power of 1 kW an efficiency of 25% was possible by recirculatingthe exhaust gases back into the system. Clearly, much work is needed before the suitability of the invertedcycle gas turbine for domestic CHP can be established, including the construction of safe and reliabledemonstration model
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