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Investigation of the thermal performance of coconut fibre composite with aluminium reflector cooling roofs


Global warming and depletion of petroleum resources have made the scientists to focus on new passive cooling techniques to reduce the indoor temperature of residential and commercial buildings. This paper explores the benefits of using coconut fibre composite as a passive cooling roof and quantifies those benefits in terms of heat flow changes through field experiment and compares them to the base case of standard roof in arid regions. The research also focussed on the usage of this material in combination with radiation reflectors such as aluminium and the effect of air gap between coconut fibre composite and aluminium reflector on the energy efficiency of the buildings. Experimental investigation showed a substantial reduction in room air and concrete roof slab temperature of coconut fibre composite with aluminium reflector room in comparison with the conventional roof. A maximum reduction of 5.99 °C (16.59%) and 8.39 °C (23.8%) were observed in room air and roof slab temperature of coconut fibre composite–aluminium roof with an air gap of 40 cm between them. It was also observed that as the air gap between coconut fibre composite and aluminium reflector is increased, the room air and roof slab temperature were reduced due to enhanced convective cooling. Compared to a standard roof, the indoor air temperature of coconut fibre composite roof was reduced by a maximum of 2.2 °C (5.86%), 2.9 °C and 5.99 °C (16.59%) for 0, 20 and 40 cm air gap between the coconut fibre composite and aluminium reflector, respectively. It is convincingly demonstrated that the coconut fibre composite roof with aluminium reflector can significantly affect the indoor air and roof surface temperature of the roofs during the hot summer days.

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ρ :

Density (kg/m3)

C p :

Specific heat capacity (J/kg K)

T :

Temperature (K)

λ :

Thermal conductivity (W/m K)

Q :

Heat source (W)

ϕ :

Heat flux density (W/m2)

μ :

Dynamic viscosity (Pa s)

λ r :

Thermal conductivity of the aluminium sheet (W/m K)

h o :

Convective heat transfer coefficient between outdoor air and aluminium reflector (W/m2 K)

T o :

Outdoor air temperature (K)

T re :

Temperature of external surface of the reflector (K)

T gap :

Temperature of air in the gap (K)

T ri :

Temperature of internal surface of the reflector (K)

α r :

Absorption coefficient for solar radiation

ε r :

Surface emissivity

σ :

Stefan–Boltzmann constant: σ = 5.67e−8 (W/m2K4)

T sky :

Sky temperature (K)

E :

Solar radiation (W/m2)

h a :

Convective heat transfer coefficient in air gap (W/m2 K)

T c :

Temperature of composite (K)

r :

Ratio of surface emissivities


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Correspondence to V. Vinod Kumar.

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Kumar, V.V. Investigation of the thermal performance of coconut fibre composite with aluminium reflector cooling roofs. Environ Dev Sustain 22, 2207–2221 (2020).

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  • Global warming
  • Coconut fibre composite
  • Heat flux
  • Reflectors
  • Thermal comfort