The heat island phenomenon in major cities is partly due to the excessive use of concrete and brick, which causes many problems regarding thermal comfort and energy expenditure. The thermal behaviour of the envelope wall material depends on its density, heat capacity, and thermal conductivity, and its effect on the heat island intensity (HII) is reported in this paper. Experiments and simulations were carried out on the four most popular building materials: brick, aerated concrete, wood with glass-wool insulation, and glass fibre-reinforced concrete with glass-wool insulation, with each material having a dimension of 1 m × 1 m. Experiments to analyse the thermal behaviour of the wall materials were performed by exposing each material to heat radiation from 2 × 1000 W halogen lamps for 4 h, followed by 4 h of cooling. The HII simulations were carried out in a simple urban kampong in a tropical area using Energy2D software. Heat flow analyses confirmed the thermal behaviour of the four walls, which can be categorised into two types: heat storage of block wall (BW) type and heat flow inhibition of insulated sandwich wall (ISW) type. The BW type showed 0.32 °C higher indoor air temperature than the ISW type, while the HII simulation showed ISW to be 0.74 °C higher than BW; however, both types increase the intensity and need mitigation treatment. The results of this study are important for the technological approach for dealing with local warming to lower the energy expenditure of poor people in an urban area. Keywords Urban heat island • Thermal behaviour • Block wall type • Insulated sandwich wall • Urban kampong List of symbols ρ Density c Specific heat κ Thermal conductivity avg Average density c avg Average specific heat avg Average thermal conductivity T so Outer surface temperature T si Inner surface temperature T m1 Temperature of the core wall at a depth of 2.5 cm T m2 Temperature of the core wall at a depth of 7.5 cm T m3 Temperature of the core wall at a depth of 12.5 cm P so Heat flow at outer surface P m1 Heat flow at a depth of 2.5 cm P m2 Heat flow at a depth of 7.5 cm P m3 Heat flow at a depth of 12.5 cm P si Heat flow at inner surface T ao Outdoor air temperature T ai Indoor air temperature T ac Outdoor air temperature above the canopy layer

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Controlling the thermal behaviour of buildings is very important because it affects the energy use in the buildings and impacts the thermal environment of the area. Thermal behaviour of the building is determined by the type and composition of the building material. This paper shows the thermal behaviour of several types and composition of commonly used building wall materials, i.e. brick, aerated concrete, laminated wood with glass wool insulation, and gypsum with glass wool insulation. For the thermal behaviour measurements, we used wall models exposed to halogen lamps of 2000 watts for 4 hours heating and 4 hours for cooling with a measurement interval of 5-15 minutes. Data retrieval using 8 thermocouples mounted on the surface and inserted inside the wall. The observed thermal behaviour phenomena are the heat flow on the walls, the time delay, and the heat capacity. The results show different maps of the thermal behaviour on the walls and indicating the need for additional thermal insulation material to control the heat release to the outside and inside of the building.

Study of heat exchanger system using phase change material (PCM) for air conditioning system application in buildings is still very rare. The potential application of natural materials such as coconut oil as heat storage and heat exchangers in buildings in the tropics is quite large because the melting point of this material is in the human comfortable temperature range and a relatively large heat enthalpy corresponds to the stored heat. The heat exchange of such materials is strongly influenced by its thermal conductivity so that the heat flow rate greatly affects the effectiveness of heat exchange. This paper shows the role of cell size on the effectiveness of coconut oil as the heat exchanger. The experiment was conducted by measuring the temperature of coconut oil cell with diameter 4 cm, 5 cm, 6 cm, 8 cm, 12 cm and 16 cm in the natural air environment. The temperature was measured using thermocouples for 2 × 24 hours with a data retrieval interval for 15 minutes. The results showed that cell size provides different responses to changes in environmental temperature, so that its role as a heat exchanger can be designed according to its needs.