Optimizing the position of insulating materials in flat roofs exposed to sunshine to gain minimum heat into buildings under periodic heat transfer conditions

Transforming waste disposals into building materials to investigate energy savings and carbon emission mitigation potential

This work aims to enhance the energy cost-saving potential of conventional mud-brick by including natural waste materials as insulators. The solid waste materials considered for mud bricks are rice husk, sawdust, coir pith, and fly ash. This work investigates the structural and thermoeconomic performance of four types of insulated mud bricks and three roofs of ferrocement, clay, and ceramic materials. The thermal properties of walls and roofs were measured as per ASTM D 5334 standards. The utilization of solid waste in mud bricks enhanced the structural properties and air-conditioning cost-saving potential of the mud bricks. The results also showed the mitigation of greenhouse gas emissions with the usage of insulated bricks for buildings. The rice husk mud-brick wall showed better results of higher time lag, lower decrement factor, higher air-conditioning cost-savings, acceptable payback periods, and higher annual carbon mitigation values of 11.11 h, 0.24, 1.74 $/m², 1.17 years, and 33.35 kg/kWh, respectively, among all the studied multilayer walls. Among the roofs, clay tile roof showed a lower decrement factor (0.989), higher time lag (0.73 h), higher air-conditioning cost-savings (2.58 $/m²), lower payback periods (0.61 years), and higher annual carbon mitigation (21.73 kg/kWh). The results are in designing eco-friendly and energy-efficient envelopes for buildings.

Strategic design of wall envelopes for the enhancement of building thermal performance at reduced air-conditioning costs

A strategy is proposed for the design of wall envelopes to improve unsteady thermal performance in non-air-conditioned buildings and to reduce energy costs in air-conditioned buildings. The thermophysical properties of building materials (e.g., burnt bricks, mud bricks, laterite stone, cinder concrete, and expanded polystyrene) were measured experimentally using a thermal analyzer. A total of 28 combinations for composite walls were designed with expanded polystyrene as an insulation material based on seven criteria and were subjected to 8 different external surface heat transfer coefficients, which were tested for unsteady thermal performance parameters and air-conditioning cost-saving potential. In this paper, unsteady thermal transmittance obtained from admittance method has been employed to compute cost saving potential of air-conditioning for the various wall envelopes. The use of C-H₅ design at a 2 m/s wind speed was found to increase the decrement lag of burnt brick, mud brick, laterite stone, and cinder concrete composite wall envelopes by 48.1%, 49.0%, 59.5%, and 47.0%, respectively, relative to the common wall design (C-H₁) in non-air-conditioned buildings. The laterite with a C-H₅ design offers the highest annual energy cost savings (1.71 $/m² at 2 m/s), the highest life cycle cost savings (18.32 $/m² at 2 m/s), and the lowest payback period (4.03 yrs at 2 m/s) in all tested building materials for air-conditioned buildings. The overall results of this study are expected to open new paths to deliver simple design strategies for energy-efficient buildings.

Influence of orientation, glazing proportion and zone aspect ratio on the thermal performance of buildings during the winter period

The objective of this study is to assess the effect of orientation, glazing proportion and aspect ratio of building zones on heat fluxes through their surfaces, under specific environmental conditions. The investigation is carried out for thermally-insulated building zones with a varying facade orientation corresponding to each cardinal point, during the winter period in the northern Greek region. For this purpose, three glazing-to-facade ratios (GR) are taken into account; along with the glazing ratio the influence of the glazing U value is also considered. Regarding the impact of the fenestration layout geometry, five different building aspect ratio profiles are examined. Thermal fluxes are assessed for two different indoor temperature settings, while the operation of the heating unit is assumed to be continuous. The transient thermal analysis with its mathematical formulation and solution are based on the thermal-network modelling approach, while the solar heat gain through glazing relies on the sunlit-pattern approach; in this way, the stricken by the solar rays glazing area is projected onto any interior surfaces to form the so called "sunlit" areas. As the orientation, glazing proportion and aspect ratio of the building zone vary, so do the sizes and shapes of the illuminated "sunlit" areas. Accordingly, the delivered into the zone direct solar energy and its diffused and ground reflected components can be determined. The adopted methodology provides a more accurate determination of solar heat gain with respect to glazing proportion and orientation as well as zone aspect ratio. With regard to surface orientation, glazing proportion and aspect ratio, computer results demonstrate the improvement of the thermal performance for a building zone with a south oriented glazing surface, as well as the deterioration for the other surface orientations; relative increases/decreases in the energy fluxes of a rectangular shaped building zone compared to a square-shaped building zone can reach up to 50%/100%.