The influence of the human exhalation on flow fields, contaminant distributions, and personal exposure in displacement ventilated rooms is studied together with the effects of physical movement. Experiments are conducted in full-scale test rooms with life-sized breathing thermal manikins. Numerical simulations support the experiments. Air exhaled through the mouth can lock in a thermally stratified layer, if the vertical temperature gradient in breathing zone height is sufficiently large. With exhalation through the nose, exhaled air flows to the upper part of the room. The exhalation flow from both nose and mouth is able to penetrate the breathing zone of another person standing nearby. The stratification of exhaled air breaks down if there is physical movement in the room. As movement increases, the concentration distribution in the room will move towards a fully mixed situation. The protective effect of the boundary layer flow around the body of a moving person disappears at low speed, and is reduced for a seated person placed nearby due to horizontal air movements, which can also cause rebreathing of exhaled air for the seated person. The results indicate that the effect of the exhalation flow is no acute problem in most normal ventilation applications. However, exhalation and local effects caused by movement may be worth considering if one wishes to contain contaminants in certain areas, as in the case of tobacco smoking, in hospitals and clinics, or in certain industries.

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To facilitate the decision‐making and communication, an evaluation method has been devised that incorporates environmental effects of the energy use with thermal and atmospheric indoor climate in a score on an absolute scale from 0–100 %, called the “Eco‐factor”. This factor is based on indicators of physical properties. For the indoor climate part these include mainly the indoor temperature, velocity, and concentration fields. The energy part considers the energy distributed to energy sources, and the environmental effects of the resulting airborne emissions evaluated by Life Cycle Assessment (given by default figures from a database). The tool is used to make an overall assessment of the quality of design alternatives, where the “costs” (energy) is compared to the “benefit” (indoor climate), and to identify possibilities for improvement. The paper shows a model case study of an office building, where choices are considered that must be made in an early design phase.

Problems in office buildings are often related to the design and control of the indoor environment and of the building as an energy system. The often interconnected nature of the above two issues is important to take into account, since, for instance, internal and external heat loads, temperatures, and air change rates affect both energy use and indoor comfort. Thus, to avoid the indoor climate problems, it is essential that energy optimisation is integrated with assessment of indoor climate. An assessment concept based on the so-called Eco-factor has been developed; it can assist building designers in creating solutions of these problems. The assessment concept is meant to be an integral part of new design guidelines for office buildings, which aim to achieve energy efficient buildings with a good indoor comfort and low environmental impact. The building designers have different needs at different stages of the design process. For this reason, the assessment concept makes use of the Eco-factor tool, which is defined so input can be based on both simple and advanced calculations in early and later phases of design, respectively, while still delivering the same output.