The development of ORC based micro-CHP systems to retrofit the current combi-boilers is receiving noticeable attention from research centres and companies due to the huge dimension of the potential market. Recognizing the importance that the evaporator has on the technological/ commercial success of these systems, and instead of avoiding the problem through the adoption of alternative restricting solutions (i.e. indirect vaporization process), it seems reasonable to face the challenges associated with the development of a specifically designed ORC-evaporator capable to directly use the hightemperature combustion gases to perform the vaporization of the working fluid (direct vaporization). In an attempt to overcome those challenges and fulfil this technological gap, that is believed to be preventing the widespread use of these systems, this paper presents and discuss some of its main design principles. From those principles emerged a hybrid topping/bottoming) CHP configuration in which the thermal energy is produced stepwise: firstly in the ORC-condenser and then in a post-heater, that is integrated on the ORC-evaporator, directly with the combustion gases. A model of this configuration was developed to determine the fraction of the CHP water heating process performed in the post-heater that maximizes the primary energy savings (in more than 20%) and ORC net power output (in more than 5%) for a wide range of CHP operating conditions. When compared to a standard CHP configuration, this solution show benefits for the greater part of those conditions. Besides solving the safety issue posed by the ORC-evaporator requirements and the performance benefits shown, this configuration has an additional positive side effect: the decrease of the combustion gases’ temperature before they reach the organic fluid heat-exchanger section in the ORC-evaporator that leads to a reduction of the risk of the working fluid thermal degradation.     «

The development of ORC based micro-CHP systems to retrofit the current combi-boilers is receiving noticeable attention from research centres and companies due to the huge dimension of the potential market. Recognizing the importance that the evaporator has on the technological/ commercial success of these systems, and instead of avoiding the problem through the adoption of alternative restricting solutions (i.e. indirect vaporization process), it seems reasonable to face the challenges associate...     »