chilled ceiling

Thermal comfort and indoor air quality (IAQ) play a vital role in creating a pleasant and healthier indoor environment for occupants. The supply air conditions and the concentration of CO2 contaminant present in the supply air can decide the comfort level and purity of air in indoor environments. In this study, an effort was made to investigate the combined effect of a chilled ceiling and displacement ventilation (CC-DV) air conditioning (A/C) system that would possibly achieve good thermal comfort and IAQ in a proposed office building subjected to hot and humid climatic conditions.

The performance and effectiveness of any ventilation and cooling strategy depends largely on the method of air distribution and heat removal system. The consequences of poor air distribution and cooling systems are draughts, air stagnation, large temperature gradients and radiation asymmetry. These factors are the chief cause of the occupants' dissatisfaction with their thermal environment, and are major contributors to the so-called 'sick building syndrome'. Cooled ceilings combined with displacement ventilation, sometimes known as 'comfort cooling', has gained popularity in recent years.

A new ventilated cooledbeam system concept with free cooling has been installed and monitored in a retrofitted office building in the Wartsila NSD Finland complex in Vaasa, Finland. Good indoor air quality and individual room temperature control has been achieved using ventilated cooled beams. Both cooling- and supplyair distribution functions were integrated in the same room unit. No extra costs were incurred for the low-energy system's freecooling loop.

The paper presents some of the findings from a broader investigation aimed at determining thermal comfort design conditions for combined chilled ceiling/ displacement ventilation environments. A typical chilled ceiling/ displacement ventilation office has been created within a laboratory test room, in which the ceiling temperature can be varied over a range of typical operating values; the thermal comfort of eight female test subjects was then measured in the test room over the range of ceiling temperatures.

The influence of a cooled ceiling on the air quality in a displacement ventilated room is examined by means of CFD. The objective of the study is to examine how the flow field in a displacement ventilated room is influenced when a cooled ceiling removes a major part of the total heat load, and in particular to examine the effect on the contaminant distribution and the indoor air quality. The simulations show that the inclusion of a cooled ceiling has a significant impact on the flow field but only a minor influence on the personal exposure in this study.

This paper presents general guidance on designing for thermal comfort in combined chilled ceiling/displacement ventilation environments. Thermal comfort measurements involving 184 human subjects were carried out in a laboratory- based test room, constructed to resemble a normal office and equipped with a combined chilled ceiling and wallmounted displacement ventilation system.