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Numerical study on supply parameters’ influence on ventilation performance of a personalized air conditioning system for sleeping environments

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Abstract

Personalized air conditioning systems are widely used in sleeping environments, where a sleeping human body is always immobile through night. The ventilation performance optimization of air conditioning system becomes necessary, and the influences from different supply air parameters were investigated in this study, including supply air flow rate and temperature, supply air outlet height and fresh air flow rate. To understand the effects of supply air parameters on ventilation performance, the occupied zone air flow field, air change efficiency, CO2 concentrations and CO2 concentrations distributions inside the room were numerically studied. It was indicated that placing the supply air outlet at lower levels of 1.1 and 0.8 m could directly deliver cooling air to the thermal manikin, leading to a much higher air change efficiency of around 70%. The air temperature of the occupied zone could not be well cooled down for the supply air outlet at a height of 0.8 m. Meanwhile, the higher supply air flow rate may cause significant draft risk. Finally, considering the ventilation performance and draft risk, a set of the supply parameters is suggested for this personalized air conditioning system.

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Abbreviations

C :

Convective heat loss (W m−2)

C p :

Specific heat at constant pressure (J kg−1 K−1)

C oz :

CO2 concentration in the occupied zone (ppm)

C r :

CO2 concentration in the return air (ppm)

C res :

Sensible heat loss due to respiration (W m−2)

C s :

CO2 concentration in the supply air (ppm)

D i,m :

Mass diffusion coefficient (m2 s−1)

E :

Total energy (J)

\(\overrightarrow {g}\) :

Gravitational acceleration (m s−2)

H s :

Height of the supply air outlet (m)

\(\overrightarrow {{J_{{\text{j}}} }}\) :

Diffusion flux of species j (Kg m−2 s−1)

k eff :

Effective conductivity (W m−1 k−1)

L R :

Lewis ratio (K kPa−1)

M :

Metabolic heat production (W m−2

m :

Mass of the external wall (kg)

Q f :

Volume flow rate of supply fresh air (L s−1)

Q s :

Volume flow rate of supply air (L s−1)

S ct :

Turbulent Schmidt Number

S i :

Rate of creation by addition of species i (kg m−3 s−1)

t :

Air temperature (ºC)

t o :

Average air temperature in an occupied zone (ºC)

t r :

Return air temperature (ºC)

t s :

Supply air temperature (ºC)

t sk :

Mean skin temperature (ºC)

t uz :

Air temperature in the unoccupied zone (ºC)

v :

Air velocity at a measurement position (m s−1)

Y i :

Mass fraction of the species i

ρ :

Air density (kg m−3)

μ t :

Turbulent viscosity (Pa∙s)

\({\upmu }_{\text {eff}}\) :

Effective dynamic viscosity (Pa∙s)

\(\overline{\overline{\tau }}\) :

Stress tensor (Pa)

\(\overline{\overline{\tau }}_{{{\text{eff}}}}\) :

Deviatoric stress tensor (Pa)

Φ i :

Arbitrary scalar

Г i :

Diffusion coefficient

\(S_{{\phi_{{\text{i}}} }}\) :

Source term of the scalar

τ e :

Local mean age of the air in the exhaust

\(\left\langle {\overline{\tau } } \right\rangle\) :

Room average age of air

τ o e :

Local mean age of the air in the exhaust of the occupied zone

\(\left\langle {\overline{{\tau_{\text o} }} } \right\rangle\) :

Average age of air in the occupied zone

CFD:

Computational fluid dynamics

DR:

Draft risk (%)

OACE:

Occupied air change efficiency (%)

SST:

Shear stress transport

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Funding

The study was supported by Shandong Provincial Natural Science Foundation, China (Project No.: ZR2020ME170), the Fundamental Research Funds for the Central Universities (Project No.: 18CX02077A).

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Authors and Affiliations

  1. Department of Gas Engineering, College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao, Shandong, China

    Mao Ning, Yu Hao & Zhuang Jiaojiao

  2. School of Mechanical Engineering, Beijing Institute of Technology, Beijing, China

    Song Mengjie

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  1. Mao Ning
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  2. Yu Hao
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  4. Song Mengjie
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Correspondence to Song Mengjie.

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Ning, M., Hao, Y., Jiaojiao, Z. et al. Numerical study on supply parameters’ influence on ventilation performance of a personalized air conditioning system for sleeping environments. J Therm Anal Calorim 147, 11331–11343 (2022). https://doi.org/10.1007/s10973-022-11332-5

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