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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

MODELLING OF ADVANCED COMBINED HEAT AND POWER SYSTEMS IN BUILDING APPLICATIONS

Maria Anna Chatzopoulou
Clean Energy Processes (CEP) Laboratory, Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

Christos N. Markides
Clean Energy Processes (CEP) Laboratory, Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

Abstract

Buildings are responsible for almost 40% of the energy consumption in the EU, and more than 50% of this consumption is due to the provision of heating and cooling. Cogeneration of heat and power (CHP) has been identified as a key technology for the provision of thermal and electrical energy, due to its higher efficiency compared to separate systems. However, studies investigating the performance of CHP systems often model the technologies using constant efficiency rates or curve fits from manufacturers' data. This paper presents detailed thermodynamic models developed for a CHP unit comprising a reciprocating internal combustion engine (ICE) coupled with a subcritical organic Rankine cycle (ORC) unit. The tool simulates the operation of the prime movers providing reliable estimates of the system's thermal and electrical output, along with the available heat for recovery. An optimization exercise is then performed to maximize the power output of a CHP-ORC system, investigating alternative working fluids, for varying exhaust-gas stream conditions leaving the ICE. The exhaust-gas stream of a 2.5 MWel CHP unit, has been used to drive an ORC unit. The optimization results indicate that up to 166 kW can be generated by an ORC using R1233zd, at a heat source temperature of 623 K. This results in an increase of the system's power-to-heat ratio of 67%. Consequently, the CHP-ORC system operation can be decoupled from the heating demand of the building, maximizing its efficiency and energy savings, in periods when traditionally the CHP heat output would be wasted.

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