The use of passive perfluorocarbon technique for air flow measurements has been developed and tested. The building and testing of the system took approximately one year. The reproducibility of the analysis was tested during the period. The results show that the relative standard deviation of the analysis for parallel samples is less than 7 % for each tracer in most of the cases. A drift of calibration was noticed, but it can be allowed for by using reference samples with known amounts of tracers. The accuracy of the method was tested in controlled laboratory conditions.

Tracer gas techniques have become widely used to measure the ventilation rates in buildings. The basic principle involved is that of conservation of mass (of tracer gas) as expressed in the continuity equation; by monitoring the injection and concentration of the tracer, one can infer the exchange of air. Although there is only one continuity equation, there are many different experimental injection strategies and analytical approaches. These different techniques may result in different estimates of infiltration due to uncertainties and biases of the procedures.

What does the designer of a future energy-efficient building ask of the air flow specialist? - Static predictions of air flow patterns and optimization of thermal comfort and indoor air quality at design conditions will not be enough for him. The paper suggests that time-dependent air flow simulation is imperative to respond to tomorrows design needs. Different physical timescales for air flow patterns in spaces will be discussed. Heat capacity by components, different types of heat transfer, varying occupancy, control inputs etc. give rise to disparate time scales.

The IEA Annex 18 Demand Controlled Ventilating Systems-(DCV-Systems) with 9 participants are just in the middle of the work. Reviews are indicating energy conservation possibilities in the range of 8-40% in experiments and even more in theoretical studies. Most of the case studies will start this autumn with sensor tests, test room studies, and trials in occupied spaces. In the testrooms will be simulated the conditions in dwellings ---and offices with various ventilating systems. Almost 30 occupied buildings will be involved in tests in dwellings, offices, auditoria, and schools.

Annex 14 -Condensation and Energy- started in April 1987, with a take of meeting in Utrecht, The Netherlands. The annex itself was born after a moisture-workshop in September 1985 at the Laboratory of Building Physics, KULeuven, Belgium.