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Renovation of existing buildings, in order to reduce energy consumption, represents a big market inEurope. As the first efforts often concentrate in improving insulation and airtightness of the buildingenvelope, important insufficiencies of ventilation can appear, generating health risks for the occupants and a degradation of the frame. Taking into account the difficulties to insert ductworks in existing buildings, it can be easier to use distributed ventilation systems for room-by-room ventilation instead of centralised systems.

On the way to the solution of our energy-problems, the conditioning of buildings is the most importantsector. We have to create new buildings, that produce more energy than they need in the course of ayear, so called plus-energy buildings and we have to perform large-scale retrofitting of existing buildings. Priority must be given to increasing energy-efficiency. Having fulfilled this, the implementation of renewable energy has to be undertaken.

One of the topics studied in the European IEE-ASIEPI project (www.asiepi.eu) is the way envelopeairtightness is dealt with in the EPB-regulations of the Member States. To this end, a number of surveyshave been made among the participating countries. Also a quantitative comparison on a samplebuilding has been performed. The results of this study are used in the development of an instrumentto compare the energy performance requirement levels among the Member States.

Thermal bridges increase the building energy demand for heating and cooling. For well insulatedenvelopes and buildings with increased energy efficiency, the influence of thermal bridging on theenergy consumption is of major importance. Here the ratio between the thermal bridging effect and the overall thermal losses increases compared to low or medium insulated buildings and it is possible that the effect of thermal bridges on the energy demand compensates or even overtakes, for instance, the energy gain provided by thermal solar collectors for domestic hot water.

Since 1991 has Sweden regulations on compulsory inspection of ventilation systems (OVK). Thereasons to issue these regulations were many studies on poor indoor climate and health problems for building occupants. The studies have shown also that poor upkeep and maintenance have led to a decline in the performance of existing ventilation systems. If, in the future, we do not look after ourventilation systems properly and adapt operation and maintenance to current user habits, then evenmore buildings will become problem buildings.

In 2005 the first Energy Efficiency Plan for South Africa was developed by the Department of Mineralsand Energy. This plan sets the target for energy efficiency improvements of 12% until 2015. Onepoint of the strategy is to improve the energy performance of public buildings like schools. Manyschool buildings in South Africa are inadequate to provide a suitable learning and teachingenvironment for students.

The influence of ventilation on the energy performance of a building is generally considered to be quite high. It rises clearly, when a building contains large-volume spaces. A famous example building for that is the Reichstag building in Berlin, housing the German parliament. The huge plenary hall in the buildings centre, which occupies only 4% of the total net floor area but 20% of its net volume, is equipped with a powerful air-conditioning system.

The Energy Policy Act of 2005 (EPAct05) requires that federal building energy-efficiency performance standards be revised. New federal buildings must be designed to achieve energy consumption levels at least 30 percent below the levels established in the currently applicable version of standards published by the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) Standard 90.1 or the International Energy Conservation Code.

The current rate of consumption across Europe is leading to environmental problems. We need toreduce our impact to nature - our ecological footprint - by two thirds to achieve a sustainable andglobally equitable level. There is a strong need for more efficient and sustainable buildings. At present it is difficult to define the performance of buildings in an objective way to efficiency and sustainability. Goal of this project is to examine and to understand differences between different green building assessment rating systems approaches when applied to high performance buildings.

The indoor air quality is a very important issue and it generally depends on the airtightness of theshell, the ventilation rates, the deposition and the resuspension rates of the particles and the internalsources as well.The whole experimental procedure took place in a PASSYS test cell, which is located at the University Campus of Athens.