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Energy saving potential of a fresh air pre-cooling system using radiative sky cooling

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Abstract

To achieve required indoor air quality, fresh air supply in buildings should meet relevant standards and regulations. However, the handling of fresh air introduced a cooling load that takes up a large portion of building energy consumption, especially in tropical and subtropical areas. A proper way should be employed to reduce the cooling load of fresh air. Radiative sky cooling, which is the process that an object cools itself by emitting thermal radiation to outer space without any energy input, is a cost-effective and eco-friendly technology. In this work, a fresh air pre-cooling system using radiative sky cooling is proposed to reduce fresh air cooling load. The system, consisting of filters, a radiative air-cooling system, an air handling unit (AHU), fans, etc., is installed on the rooftop of the modeled building. Six cities in low-latitude areas are selected and investigated. Results show that with the radiative air-cooling system installed, annual cooling energy consumption of the modeled building can be reduced by around 10% in most cities. For arid areas, e.g., Abu Dhabi, the system has even better performance with 19.34% annual cooling energy saving.

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Abbreviations

A :

total radiative cooling surface area (m2)

c :

speed of light (m/s)

\({c_{{\rm{p}}\_{\rm{air}}}}\) :

specific heat capacity of the air (J/(kg·K))

C air :

heat capacity rates of the air (W/K)

C duct :

heat capacity rates of the duct (W/K)

d e :

hydraulic diameter of the duct (m)

f :

Darcy friction factor

g :

gravitational acceleration constant (m/s2)

h :

Planck constant (J·s)

h inner :

heat transfer coefficient inside the duct (W/(m2·K))

h upper :

heat transfer coefficient above the upper surface (W/(m2·K))

I bb :

blackbody radiance (W/m2)

I direct :

direct normal solar radiance (W/m2)

I diffuse :

diffuse horizontal solar radiance (W/m2)

I solar :

total solar irradiance (W/m2)

k air :

thermal conductivity of air (W/(m·K))

k B :

Boltzmann constant (J/K)

L :

length of the duct (m)

N :

cloud cover

Nu :

Nusselt number

Pr :

Prandtl number

P atm :

absorbed atmospheric radiation (W)

P net :

net cooling power (W)

P non-rad :

heat loss due to conduction and convection (W)

P rad :

energy emitted from the radiative cooling surface (W)

P solar :

absorbed solar irradiance (W)

PWV:

precipitable water vapor (cm)

ΔP :

pressure drop along the duct (Pa)

Q fresh :

fresh air cooling load of the modeled building (W)

q v :

volume flow rate of the air (m3/s)

Re :

Reynolds number

RH:

relative humidity (%)

S :

friction loss (m)

T amb :

ambient temperature (K)

T design :

indoor cooling setpoint temperature (K)

T en :

temperature of the duct at the entrance (K)

T outlet :

outlet temperature of the air (K)

T s :

radiative cooling surface temperature (K)

ΔT m :

logarithmic mean temperature difference (K)

t d :

dew point temperature (°C)

u :

velocity of the airflow (m/s)

v :

wind speed (m/s)

W fan :

fan power (W)

α s :

solar absorptance of the radiative cooling surface

ε atm :

emissivity of the atmosphere

ε s :

emissivity of the radiative cooling surface

η f :

fan efficiency

λ :

wavelength (µm)

ρ air :

density of the air (kg/m3)

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Acknowledgements

Dongliang Zhao acknowledges the support from the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20200373).

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Authors and Affiliations

  1. School of Energy and Environment, Southeast University, Nanjing, Jiangsu, 210096, China

    Dikai Xu, Hua Qian & Dongliang Zhao

  2. Pôle Universitaire Leonard de Vinci, 12 Avenue Léonard de Vinci, Courbevoie, 92400, France

    Sébastien Boncoeur

  3. Department of Civil and Architectural Engineering, University of Wyoming, Laramie, WY82071, USA

    Gang Tan

  4. Ningbo Ruiling Advanced Energy Materials Institute Co., Ltd, Ningbo, 315500, China

    Jingtao Xu

  5. Engineering Research Center of Building Equipment, Energy, and Environment, Ministry of Education, Nanjing, China

    Hua Qian & Dongliang Zhao

Authors
  1. Dikai Xu
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  2. Sébastien Boncoeur
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  3. Gang Tan
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  4. Jingtao Xu
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  5. Hua Qian
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  6. Dongliang Zhao
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Correspondence to Dongliang Zhao.

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Xu, D., Boncoeur, S., Tan, G. et al. Energy saving potential of a fresh air pre-cooling system using radiative sky cooling. Build. Simul. 15, 167–178 (2022). https://doi.org/10.1007/s12273-021-0802-y

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  • DOI: https://doi.org/10.1007/s12273-021-0802-y

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