Micro-CHP

The desire to make a contribution in terms of environmental sustainability and the reduction of harmful emissions is spreading faster and faster, also thanks to the continuous development of new technologies. For many years, cogeneration has been one of the technologies with the greatest added value in terms of improving energy efficiency, because it combines the simultaneous production of electricity and heat. To date, machines with medium and large dimensions are more widespread, despite the fact that micro-cogeneration systems suitable not only for industrial and tertiary applications but also for the residential one are increasingly present on the market.

To make the most of the efficiency characteristics of the cogeneration machines, it is essential that the design of the entire equipment, especially towards thermal requirements, allows the system to work for the greatest number of hours per year, avoiding that heat is dissipated towards the environment.

To ensure greater flexibility in the relationship between the thermal production of the cogenerator and the user’s thermal consumption profile, the combination with phase change material (PCM) thermal batteries is envisaged.

Thanks to our devices, the heat is transferred to a specific storage medium, is stored and then returned when necessary; these three phases are not necessarily distinct from each other, they can in fact be simultaneous and repeated within the same cycle. An accumulation system is characterized with some fundamental parameters:

• efficiency, given by the ratio between the energy discharged and that stored
• the storage capacity, that is the quantity of energy that can be stored
• the power with which the storage is able to release the stored energy
• the length of time within which the energy can be stored inside the battery without significant energy losses

The combination of the thermal storage can be achieved on both large and smaller systems; in the first case, since it is a question of complex applications (industrial or advanced tertiary), it is necessary to proceed according to a storage model distribution to the sub-users with less constant withdrawal profiles, while for micro-cogeneration plants it is possible to directly install the thermal storage downstream of production heat.

For simplicity of calculation, this case study will refer to an application with a micro-cogenerator.

In general, to correctly design a cogeneration plant, it is essential to know the profiles (hourly) of both electrical and thermal consumption, becuase they are the most critical and binding factors in the final sizing of the machine. The higher the precision of the starting data, the more certain the result will be obtained, especially from the point of view of the economic return.