Minimizing heat transmission loads and improving energy efficiency of building envelopes in sub-Saharan Africa using bio-based composite materials

Richard Opoku,George Y Obeng,Jo Darkwa,Samuel Kwofie

doi:10.1016/j.sciaf.2020.e00358

Richard Opoku, George Y Obeng + Show 2 more

Open Access

https://doi.org/10.1016/j.sciaf.2020.e00358

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Abstract

Increasing effect of climate change coupled with global warming has necessitated the need for mechanical cooling in buildings to provide indoor thermal comfort. Many countries in tropical climates, particularly in sub-Saharan Africa, use sandcrete blocks for constructing building envelopes which have relatively high thermal conductivity. This leads to increased heat transmission through the building walls resulting in increased building electricity consumption using air-conditioners. This study focused on opportunity of minimizing the thermal conductivity of sandcrete blocks by mixing it with available bio-based local materials, specifically treated sawdust and palm fibers. Experiments were conducted to determine the thermal conductivity, compressive strength and densities of sandcrete mixed with 10%, 20%, 30% and 40% of treated sawdust and palm fiber to form building block composites. The study results showed that incorporating the bio-based material into the sandcrete decreases its density and thermal conductivity, thereby decreasing the wall heat transmission load. Using a minimum standard limit of 3 MPa for compressive strength for building envelopes, the composite samples: S10, P10, P20 and P30 were found to be appropriate to be used to minimize wall heat transmission. The composite of 70% sandcrete with 30% treated palm fiber (P30) exhibited the best thermal performance with 38% reduction in thermal conductivity compared to the control sandcrete block. Maximum wall heat flux reduction of 52 W/m2 was attained at peak load with the composite P30 compared to the control sample P0 (100% sandcrete). In addition, using the degree-days cooling for Ghana, the analysis indicated maximum electricity saving potential of 453.40 kWh per year for an office space cooling using the sandcrete-palm fiber composite P30 as the building envelope.

Highlights

Electricity consumption of residential, commercial and public buildings in tropical climates is dominated by airconditioning equipment to provide indoor thermal comfort [1,2,3]
Recent research and development in the building industry are focused on sustainable energy efficient building materials that minimize wall heat transmission load in order to reduce the electricity consumption and the corresponding operational cost of buildings [7,8], and in addition reduce CO2 emissions associated with electricity use in buildings [9,10]
The thermal conductivity values for the composite blocks obtained in this work compare well with the values (k = 0.44 −1.02 W/m K) reported in the works of [29,40,41]

Summary

Introduction

Electricity consumption of residential, commercial and public buildings in tropical climates is dominated by airconditioning equipment to provide indoor thermal comfort [1,2,3]. Air-conditioning equipment could consume as much as 60–80% of electricity used in commercial and public buildings in hot-humid climates [6]. It has been demonstrated that PCM can be used to reduce and control fluctuations in indoor temperature of buildings during the hot summer days [18]. In the work of Ramakrishnan et al, [19], they reported annual energy savings potential of 16–25% in commercial buildings in major Australian cities using thermal energy storage cementitious composites (TESC) to reduce peak indoor temperatures by approximately 5.6 °C during summer design days

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