A critical appraisal of the use of displacement ventilation in commercial buildings

Abstract

The work in this thesis examines recent research and current design practice relating to the use of displacement ventilation in commercial buildings to assess the degree of success that has been achieved. The findings show that there is uncertainty in several areas of performance. The major area of concern is the inability of this method of ventilation to maintain thermal comfort in typical commercial office conditions due to restrictions on supply airflow rates. Attempts to overcome this problem with supplementary cooling devices have presented a risk of negating the air quality benefits and the nature of these risks are exposed using smoke visualisation techniques. It is concluded that it is inaccurate to describe the use of displacement ventilation system as such, when used in combination with any form of chilled ceiling device.

A feasibility study is completed to examine the performance of an alternative form of air supply diffuser, namely a textile diffuser. This indicates that it may be possible to provide a displacement ventilation system that will maintain thermal comfort and good air quality in typical commercial office conditions without the need for supplementary cooling devices. Further experimental work results in data confirming the performance characteristics of the textile diffuser used for displacement ventilation supply.

It is established that it is technically feasible to provide a displacement ventilation system with a volume flow rate sufficiently high to provide 50 W/m² of cooling capacity. Additionally, at this flow rate, the displacement flow regime is established to the full height of the occupied zone, to ensure the desired air quality in the space. It is concluded that the low draught risk associated with textile diffusers make them the preferred option for any low level supply system.

Date of Award	Feb 2000
Original language	English