Background In Europe, about 50 percent of CO2 emissions are the result of energy use in buildings. The EU Council Directive on Building Energy Performance approved in December 2002 continues the work begun by Directive 93/76/EEC (SAVE) on improving performance in this area. One of the main tasks to be fulfilled by Member States calls for more rational energy consumption in buildings to reduce CO2 emissions. Energy use by ventilation and fans accounts for almost 10 percent of total energy consumption in the EU. Hybrid ventilation combines features of both mechanical and natural ventilation; they tend to use natural air intake through wall inlets in combination with mechanical extraction. A hybrid system switches automatically from one mode to another at different times of day, or at different seasons of the year to provide the necessary indoor air quality in an energy-efficient way. It is estimated that the introduction into building practice of hybrid ventilation systems for residential buildings across Europe would lead to energy savings in the long term of approximately 64 PJ - and 3.6 mega tonnes of CO2 - per year. Objectives The overall objective of the ECOVENT project was to reduce CO2 emissions through the development of innovative ventilation systems with reduced energy consumption. This demonstration project aimed to design and implement a form of ecologically-friendly hybrid ventilation system for Latvia using the knowledge and experience of French and Swedish firms. It particularly sought to prove the suitability of the systems in Latvia, a country characterized by a cold climate with relatively high humidity. To test the system during all four seasons, the implementation would be monitored over a full year. Dissemination activities would serve to transfer the newly designed technologies into the building practices of other countries in the Baltic region, thus promoting the wide usage of ventilation systems with low energy consumption and good indoor air quality. Results Unfortunately the project was not able to carry out the installation of the two different hybrid ventilation systems. Although it was able to install one of them in a building in Latvia, delays meant that monitoring over a full year was not able to take place and therefore specific results and conclusions were not achieved. The project identified three apartment buildings to be used in the project. They were each intended for a different use: one to install the AERECO hybrid ventilation system; one to install the venticonvector hybrid ventilation system; and one to use as the control to enable successful monitoring of the results of the two systems. An agreement was signed with the owners of the three buildings to carry out the installations and building drawings and energy consumption estimations for each building were carried out. In cooperation with the Swedish expert partner and progressing through a process of drawings, computer simulation and the building of a prototype, the project team designed and manufactured an AERECO hybrid ventilation system to be tested in Latvia. This is a system which uses humidity regulated inlets installed in walls or windows to manage the transition from natural to mechanised ventilation. The system was installed in the allocated building. Unfortunately, the project was not able to complete the design and production of the second hybrid ventilation system. Furthermore, due to delays in the other stages of the process, the total monitoring time of the AERECO system and the control building was only able to cover a period of seven months. This prevented full results and conclusions being arrived at. Despite the failure to finish the project, Riga Technical University and Environmental Engineering AB have agreed to continue research on the basis of the ECOVENT project ideas. The project developed a website and presented papers at a series of international conferences.