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Building Simulation 2023, 16(7): 1173-1185 https://doi.org/10.1007/s12273-023-1023-3
Research Article | Issue | Published: 11 May 2023

Numerical investigation of impinging jet ventilation in ICUs: Is thermal stratification a problem?

Show Author's Information Lei Wang1,2,  Zhiqiang Wang3,  Sirui Zhu3,  Zhe Zhu4,  Tao Jin1,  Jianjian Wei1,2( )
Institute of Refrigeration and Cryogenics/Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province, Zhejiang University, Hangzhou, China
Center for Balance Architecture, Zhejiang University, Hangzhou, China
The Architectural Design & Research Institute of Zhejiang University Co, Ltd, Hangzhou, China
Zhejiang Modern Architectural Design and Research Institute Co, Ltd, Hangzhou, China
Keywords:
air change rates, impinging jet ventilation, heat sources, respiratory particles, lock-up phenomenon
Cite this article:
Wang L, Wang Z, Zhu S, et al. Numerical investigation of impinging jet ventilation in ICUs: Is thermal stratification a problem?. Building Simulation, 2023, 16(7): 1173-1185. https://doi.org/10.1007/s12273-023-1023-3
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Abstract Full text About this article

Intensive care units (ICUs) are the high incidence sites of hospital-acquired infections, where impinging jet ventilation (IJV) shows great potential. Thermal stratification of IJV and its effect on contaminants distribution were systematically investigated in this study. By changing the setting of heat source or the air change rates, the main driving force of supply airflow can be transformed between thermal buoyancy and inertial force, which can be quantitatively described by the dimensionless buoyant jet length scale ( lm¯). For the investigated air change rates, namely 2 ACH to 12 ACH, lm¯ varies between 0.20 and 2.80. The thermal buoyancy plays a dominant role in the movement of the horizontally exhaled airflow by the infector under low air change rate, where the temperature gradient is up to 2.45 ℃/m. The flow center remains close to the breathing zone of the susceptible ahead, resulting into the highest exposure risk (6.6‰ for 10-μm particles). With higher heat flux of four PC monitors (from 0 W to 125.85 W for each monitor), the temperature gradient in ICU rises from 0.22 ℃/m to 1.02 ℃/m; however, the average normalized concentration of gaseous contaminants in the occupied zone is reduced from 0.81 to 0.37, because their thermal plumes are also able to carry containments around them to the ceiling-level readily. As the air change rate was increased to 8 ACH ( lm¯= 1.56), high momentum weakened the thermal stratification by reducing the temperature gradient to 0.37 ℃/m and exhaled flow readily rose above the breathing zone; the intake fraction of susceptible patient located in front of the infector for 10-μm particles reduces to 0.8‰. This study proved the potential application of IJV in ICUs and provides theoretical guidance for its appropriate design.


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About this article

Numerical investigation of impinging jet ventilation in ICUs: Is thermal stratification a problem?

Show Author's information Lei Wang1,2, Zhiqiang Wang3, Sirui Zhu3, Zhe Zhu4, Tao Jin1, Jianjian Wei1,2( )
Institute of Refrigeration and Cryogenics/Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province, Zhejiang University, Hangzhou, China
Center for Balance Architecture, Zhejiang University, Hangzhou, China
The Architectural Design & Research Institute of Zhejiang University Co, Ltd, Hangzhou, China
Zhejiang Modern Architectural Design and Research Institute Co, Ltd, Hangzhou, China

Abstract

Intensive care units (ICUs) are the high incidence sites of hospital-acquired infections, where impinging jet ventilation (IJV) shows great potential. Thermal stratification of IJV and its effect on contaminants distribution were systematically investigated in this study. By changing the setting of heat source or the air change rates, the main driving force of supply airflow can be transformed between thermal buoyancy and inertial force, which can be quantitatively described by the dimensionless buoyant jet length scale ( lm¯). For the investigated air change rates, namely 2 ACH to 12 ACH, lm¯ varies between 0.20 and 2.80. The thermal buoyancy plays a dominant role in the movement of the horizontally exhaled airflow by the infector under low air change rate, where the temperature gradient is up to 2.45 ℃/m. The flow center remains close to the breathing zone of the susceptible ahead, resulting into the highest exposure risk (6.6‰ for 10-μm particles). With higher heat flux of four PC monitors (from 0 W to 125.85 W for each monitor), the temperature gradient in ICU rises from 0.22 ℃/m to 1.02 ℃/m; however, the average normalized concentration of gaseous contaminants in the occupied zone is reduced from 0.81 to 0.37, because their thermal plumes are also able to carry containments around them to the ceiling-level readily. As the air change rate was increased to 8 ACH ( lm¯= 1.56), high momentum weakened the thermal stratification by reducing the temperature gradient to 0.37 ℃/m and exhaled flow readily rose above the breathing zone; the intake fraction of susceptible patient located in front of the infector for 10-μm particles reduces to 0.8‰. This study proved the potential application of IJV in ICUs and provides theoretical guidance for its appropriate design.

Keywords: air change rates, impinging jet ventilation, heat sources, respiratory particles, lock-up phenomenon

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Publication history
Copyright
Acknowledgements

Publication history

Received: 29 December 2022
Revised: 19 March 2023
Accepted: 23 March 2023
Published: 11 May 2023
Issue date: July 2023

Copyright

© Tsinghua University Press 2023

Acknowledgements

Acknowledgements

This study was financially supported by the National Natural Science Foundation of China (52178092) and the Basic Research Funds for the Central Government “Innovative Team of Zhejiang University” under contract number (2022FZZX01-09).

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