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Room air stratification in combined chilled ceiling and displacement ventilation systems.

Author(s) : SCHIAVON S., BAUMAN F., TULLY B., et al.

Type of article: Article

Summary

Radiant chilled ceilings with displacement ventilation (DV) represent a promising integrated system design that combines the energy efficiency of both sub-systems with the opportunity for improved ventilation performance resulting from the thermally stratified environment of DV systems. The purpose of this study was to conduct laboratory experiments for a typical U.S. interior zone office to investigate how room air stratification is affected by the ratio of cooling load removed by a chilled ceiling to the total cooling load, ?, for two different chilled ceiling configurations. The experiments were carried out in a climatic chamber equipped with radiant panels installed in the suspended ceiling. In the first test configuration representative of thermally activated slab applications, 12 panels covering 73.5% of the ceiling were used. During the second series of tests, 6 panels covering 36.7% of the ceiling were used, representing a typical installation of metal radiant panels. The cooling load removed by the panels varied between 0 and 73 W/m2 (based on radiant panel area) or between 0 and 28 W/m2 (based on room area). The average mean water temperature of the panels varied over a more moderate range of 20–24°C for the 12-panel tests and over a colder range of 16.5–22.6°C for the 6-panel tests. The displacement ventilation airflow rate varied between 1.65 and 4.03 l/(s m2), and the supply air temperature was kept constant at 18°C. The results showed that increasing ?, the relative amount of the cooling load removed by the chilled ceiling, reduced the total room stratification. However, a comparison between the colder 6-panel tests and the warmer 12-panel tests indicated that average radiant surface temperature (mean chilled water temperature in panels) was a stronger predictor of stratification performance. When smaller active radiant ceiling areas are used (e.g., for a typical radiant ceiling panel layout), colder radiant surface temperatures are required to remove the same amount of cooling load (as a larger area), which cause more disruption to the room air stratification. Despite the impact that the chilled ceiling has on stratification, the results indicate that a minimum head–ankle temperature difference of 1.5°C in the occupied zone (seated or standing) will be maintained for all radiant ceiling surface temperatures of 18°C or higher.

Details

  • Original title: Room air stratification in combined chilled ceiling and displacement ventilation systems.
  • Record ID : 30003586
  • Languages: English
  • Source: HVAC&R Research - vol. 18 - n. 1-2
  • Publication date: 2012/02
  • DOI: http://dx.doi.org/10.1080/10789669.2011.592105

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