scope:

Preface

This book presents system performance evaluation and design guidelines for displacement ventilation.

The authors first reviewed the literature concerning the performance of traditional displacement ventilation. Since U.S. buildings have different layouts and larger internal heat gains than those studied in the literature, it was necessary to develop design guidelines for displacement ventilation for U.S. buildings under different climatic conditions.

The design guidelines present two important models that were not available in the literature: a model to calculate the temperature difference between the head and foot level of an occupant and a model to determine the ventilation effectiveness at the breathing level. The investigation developed the models from the results of 56 cases of displacement ventilation obtained by a computational fluid dynamics (CFD) program. Those cases include a wide range of thermal and flow conditions similar to those found in U.S. offices, classrooms, and workshops. The CFD program was validated by six sets of detailed experimental data obtained from a fullscale environmental chamber simulating a small office, a quarter of a large office with partition, and a quarter of a classroom. The data include airflow patterns and distribution of air velocity, temperature, contaminant concentration, and turbulence. The validation also used some data obtained from the literature. The CFD program was also used to assess the performance of displacement ventilation, such as airflow pattern and distributions of air temperature, percentage dissatisfied due to draft, predicted percentage dissatisfied, contaminant concentration, mean age of air, and ventilation effectiveness. The investigation also conducted energy and first costs analysis.

The results show that a displacement ventilation system can provide a thermally comfortable indoor environment at a high cooling load through careful design. The indoor air quality in a space with displacement ventilation is better if the contaminant sources are associated with the heat sources. The displacement ventilation system can also save energy but requires a separate heating system if it is applied to building perimeter zones. This book presents a ten-step design guideline to design the displacement ventilation system for U.S. buildings.