Projet MICRO 15 kWh Système de micro-cogénération et de ventilation adapté aux logements à très faibles besoins énergétiques (2009)

« MICRO 15 kWh » ProjectMICRO-COGENERATION AND VENTILATION SYSTEM ADAPTED TO VERY LOW ENERGY DWELLINGSThe aim of this project is to study a micro-cogeneration system especially adapted to low energy buildings (eg. Passive houses, Minergie or Effinergie) while maintaining the thermal comfort of the occupants and lowering the environmental impacts. The system under study combines a wood-pellet fueled micro-cogeneration unit with a hot water storage tank and an air heating device with individual room temperature control. The micro-cogeneration unit, supplying heat and power at the same time, is already on the market, whereas the air heating device has been specifically designed for this project.First, each element of the system has been studied one by one and then modeled. Finally these models have been coupled in order to evaluate the energy performance of the whole system by simulation, and to optimize its design as well as the sizing of each element and the control strategy of the pumps, fans, etc. The operation of a wood-pellet fueled micro-cogeneration Sunmachine unit has been characterized using a test bench specifically designed for this project. The results of this characterization have been used to develop an empirical model which has been implemented into the building thermal simulation software, COMFIE. After the model was carried out, a parametric study has led to the sizing of the hot water storage tank in order to optimize the combined production of heat and water.Air heating with individual room temperature control is still not widespread. The prototypes which have been carried out comprise an insulated case with an air recycling fan, two air inlets, three or five hot air outlets (according to the type) and a water-air heat exchanger at the inlet of each ventilation duct. These prototypes have been improved, leading to a system which fulfills the energy requirements as well as the functional and industrial specifications set at the beginning of the project. The final prototype is now under test and the product will soon be marketed.The system under study needs to maintain the thermal comfort of the occupants. That is why the indoor environment has been specifically studied. The model of the air heating system has been integrated into the TRNSYS software and coupled to a model of thermal behaviour of the human body. This model takes into account the main aspects of thermal control of the human body: On the one hand, the physiological thermal control (perspiring, shivering), which influences the thermal state of the occupant body taking into account its physiological reactions, on the other hand, the behaviour control (changing in the clothing, changing of the heating temperature setpoint), represented by a simplified model. This model simulates the behavioral reaction of an occupant when he is not satisfied with the indoor conditions.The results show that the micro-cogeneration unit under study has limited performance (HHV thermal efficiency: 50%, HHV net electrical efficiency: 9%). Although it is one of the lowest-powered unit available on the market, this device seems to be more suitable for an apartment building of 4 to 6 dwellings than for a very low energy, single-family dwelling. A demonstration project of this kind of building has been studied. The control of the air heating system which has been designed can maintain a suitable thermal comfort level in winter and intermediate heating seasons. Summer comfort can also be improved by using an earth-to-air heat exchanger or free-cooling. These techniques can be studied using the software tool which has been carried out. The wood-pellet based, micro-cogeneration unit generates electricity during peak power load, subsequently lowering the demand of thermal electric generation and the induced CO2 emission.