CompressingAir Illustration.xls
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1/ Power an air compressor with 13.38 kWh of electric energy to produce heating for a household's daily hot water consumption
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The electric energy is converted to heat energy at about 60 C to produce 270 litres of hot water at 55 C and compressed air cooled to 25 C and 8 atmospheres.
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See the spreadsheet below for calculations of thermal energy needed to supply 270 litres of hot water per day for a household or business.
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2/ The compressed air produced at 25 C and 8 atmospheres (absolute) pressure may be used for driving compressed-air tools.
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See the spreadsheet "AirCompressor" for the calculation of the energy used by the compressor and the volume of air it compresses.
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3/ The compressed air instead may be used in a solar-air turbine to deliver 24.55 kWh at 100% thermal efficiency by compressing it adiabatically to 32 atmospheres
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before heating it further with an external thermal energy source at constant pressure then
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expanding it adiabatically before finally outputting it at 25 C and 1 atmosphere pressure.
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See the spreadsheet "AirHeatEngine" for the calculation of the conversion of heat energy to 24.55 kWh electrical energy at 100% conversion efficiency
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with the compressed air that was produced while providing a household or businesses daily hot water requirements.
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Note that while the conversion of thermal energy to electrical energy can achieve an efficiency of 100%, the total efficiency takes into account the 13.38 kWh consumed
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to produce the compressed air. The overall efficiency for this model is (24.55 - 13.38) / 24.55 =
45.5%
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A household / business using -
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hot water per day
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270 litres
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Delivery temperature
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degrees C
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Final temperature
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55
degrees C
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Change in temperature
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35
degrees C
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Energy per degree per mL
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4.184
Joules per degree C per mL
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Energy per day
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39.5388
MJ per day
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Joules in a kWh
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3.6
MJ per kWh
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kWh per day for hot water
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10.983
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