Thermischer Komfort bei Quellluftströmungen

• Thermal comfort of displacement ventilation

Möhlenkamp, Martin Georg; Müller, Dirk (Thesis advisor); van Treeck, Christoph Alban (Thesis advisor)

1. Auflage. - Aachen : E.ON Energy Research Center, RWTH Aachen University (2019)
Book, Dissertation / PhD Thesis

In: E.ON Energy Research Center 74. Ausgabe : EBC, Energy efficient buildings and indoor climate
Page(s)/Article-Nr.: 1 Online-Ressource (xxxv, 237 Seiten) : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2019

Abstract

Displacement ventilation systems are used for cooling and air conditioning in rooms with high occupancy to achieve good air quality and high thermal comfort. The use of displacement ventilation in an occupied zone is limited by the vertical temperature gradient ΔT/Δy in K/m, and its use is recommended at temperature gradients of up to 3 K/m in current standardisations ANSI/ASHRAE Standard 55 [2013] and up to 4 K/m in DIN EN ISO 7730 [2006]. In recent studies, the effect of the vertical temperature gradient ΔT/Δy and the mean room temperature Tm on thermal comfort have proven to be independent. In realistic displacement ventilation environments, an interaction of these parameters exists. The objective of this research is to increase the range of the application of displacement ventilation and propose new design criteria. New experimental investigations conducted under constant and reproducible boundary conditions are necessary for the revaluation of the thermal comfort of displacement ventilation. To this end, a modular test chamber, the Aachen Comfort Cube (ACCu), was constructed. Test subjects were subjected to a variation in vertical temperature gradients from ΔT/Δy = 1 K/m to 12 K/m and mean room temperatures of Tm = 20 °C, 23 °C and 26 °C. Finally, the results were statistically analyzed. In total, 822 test subject evaluations are included in the study. Factors such as gender and age were examined more closely. The results of this study reveal that the effect of the mean room temperature is larger than the vertical temperature gradient. The optimum of a mean room temperature for a seated position (M = 1.0 to 1.2 met) and a light to moderate degree of clothing (Icl = 0.6 to 0.9 clo) is between Tm = 22 °C and 24 °C. In a displacement ventilation system with a low temperature gradient (Tm = 23 °C, ΔT/Δy = 1 K/m), approximately 82% of the test subjects are satisfied with the environment. For single body parts and overall thermal comfort, the percentage of dissatisfied persons (PD) increases nearly linearly for higher vertical air temperature gradients and all mean room temperatures. More statistically significant results for local instead of global evaluation, and for thermal sensation instead of thermal comfort evaluations, were found. Based on the comfort classes according to the standard DIN EN ISO 7730 [2006], new recommendations for vertical temperature gradients can be designed. In conclusion, higher vertical air temperature gradients of up to 8 K/m can be tolerated in displacement ventilation concepts. Moreover, between 0 K/m and 8 K/m, the PD increases by approximately 10%. This PD corresponds to the comfort class C. The previous one-dimensional dependency cannot be confirmed; in fact, the results suggest a multi-dimensional dependency of the vertical temperature gradient ΔT/Δy and the mean room temperature Tm. These findings deviate significantly from current recommendations. The air change rate is geared to new ventilation concepts in the aircraft industry and is thus significantly higher than in the building sector. A transferability to real rooms is partly possible. Further studies should be condructed on this issue.

Institutions

• E.ON Energy Research Center [080052]
• Chair of Energy Efficient Buildings and Indoor Climate [419510]