Numerical simulation of an innovated building cooling system with combination of solar chimney and water spraying system

Abstract

In this study, passive cooling of a room using a solar chimney and water spraying system in the room inlet vents is simulated numerically in Yazd, Iran (a hot and arid city with very high solar radiation). The performance of this system has been investigated for the warmest day of the year (5 August) which depends on the variation of some parameters such as water flow rate, solar heat flux, and inlet air temperature. In order to get the best performance of the system for maximum air change and also absorb the highest solar heat flux by the absorber in the warmest time of the day, different directions (West, East, North and South) have been studied and the West direction has been selected as the best direction. The minimum amount of water used in spraying system to set the inside air averaged relative humidity <65 % is obtained using trial and error method. The simulation results show that this proposed system decreases the averaged air temperature in the middle of the room by 9–14 °C and increases the room relative humidity about 28–45 %.

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Abbreviations

ACH :

Air change per hour (h−1)

C p :

Specific heat of air at constant pressure (J/kg K)

D H2O :

Diffusion coefficient of water vapor into air (m2/s)

E :

Energy term (J)

G sc :

Solar constant (W/m2)

I :

Hourly radiation (MJ/m2 h)

J j :

Diffusion flux of species j

K T :

Hourly clearness index

\(\overline{K}_{T}\) :

Monthly average clearness

P :

Static pressure (Pa)

Pr t :

Prandtl number

R b :

Ratio of beam radiation on the tilted surface to that on horizontal surface

S H2O :

Water vapor added to or removed from the air (kg/s m2)

Sc t :

Turbulent Schmidt number

S m :

Mass source term (kg/s m3)

T :

Temperature (K)

X, Y, Z :

Coordinate system

d :

Chimney width (m)

f i :

External body force in ith direction (N/m3)

h :

Sensible enthalpy (J/kg)

i :

Daily hour (h)

n :

Number of days

t :

Solar time (h)

u :

Direction velocity (m/s)

δ :

Declination

β :

Slope

ρ :

Density (kg/m3)

ρ g :

Reflection coefficient of surrounding ground

φ :

Latitude

ω :

Hour angle

ω s :

Sunset hour angle

μ :

Dynamic viscosity (Pa s)

μ t :

Turbulent viscosity (Pa s)

θ :

Inclination angle measured from the horizontal plane (deg)

θ′:

Angle of incidence

θ z :

Zenith angle

T :

Tilted surface

a :

Absorber

b :

Beam

d :

Diffuse

g :

Glass

h :

Horizontal surface

m :

Maximum

n :

Minimum

oh :

Extraterrestrial radiation on a horizontal surface for an hour period

w :

Wall

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Correspondence to Mehrdad Rabani.

Appendix

Appendix

The details and parameters needed for simulation of the water spraying system in FLUENT software follow as:

  • (a) The “Species Transport Model” should be selected.

  • Define > Models > Species > Transport & Reaction > Species Transport

  • (b) Based on the number of inlet vents, the number of injections should be selected

  • Define > Injections > Create Injections > Set Injection properties

Set Injection properties for present study
Injection type Surface
particle type Droplet
Material Water-Liquid
Diameter distribution Uniform
Evaporating species H2O

Furthermore, regarding the problem conditions, the “Point Properties” that includes diameter, temperature, velocity magnitude, and total flow rate are defined.

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Rabani, R., Faghih, A.K., Rabani, M. et al. Numerical simulation of an innovated building cooling system with combination of solar chimney and water spraying system. Heat Mass Transfer 50, 1609–1625 (2014). https://doi.org/10.1007/s00231-014-1366-5

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Keywords

  • Natural Convection Heat Transfer
  • Chimney Effect
  • Solar Chimney
  • Constant Heat Flux Boundary Condition
  • Solar Heat Flux