Thermodynamic efficiency of low-carbon domestic heating systems: Heat pumps and micro-cogeneration

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Energy and exergy analysis is employed to compare the relative thermodynamic performance of low-carbon domestic
energy systems based on air source heat pumps and micro-combined heat and power (cogeneration) units. A wide range
of current units are modelled under different operating conditions representative of the United Kingdom to determine
the energy and exergy flows from primary energy inputs through to low-carbon heating system and then to end use. The
resulting performances are then analysed in order to provide insights regarding the relative merits of the systems under
the different operating constraints that may be experienced both now and into the future. Although current mid-range
systems achieve comparable performance to a condensing gas boiler, the state-of-art offers considerable improvements.
Micro-combined heat and power units and air source heat pumps have the technical potential to improve the energy
performance of dwellings. The relative performance and potential of the systems is dominated by the electrical characteristics: the grid electrical generation efficiency, the power-to-heat demand ratio and the availability of electrical
export. For total power-to-heat demands below 1:1.5, air source heat pumps have greater improvement potential as
their energy efficiency is not constrained. At higher power-to-heat ratios, micro-combined heat and power units offer
the potential for higher overall efficiency and this generally occurs irrespective of whether or not the thermal energy
from them is used effectively.
Original languageEnglish
Pages (from-to)18-29
JournalProceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy
Issue number1
Publication statusPublished - 1 Feb 2013


  • Heat pump
  • micro-combined heat and power
  • micro-cogeneration
  • exergy analysis
  • domestic heating


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