Improving Thermal Comfort in a Tropical Bedroom Through Wall Insulation and Solar Reflective Paint

Measurements of temperature and thermal comfort were done for a bedroom in tropical Malaysia, where the owner had mounted internal wall insulation panels on the lower part of the East-facing wall. Additional energy optimisations were explored through annual building simulations using the IESVE software.

Introduction

Maintaining thermal comfort in residential buildings is a major challenge in Malaysia's hot and humid climate, where solar heat gains often lead to elevated indoor temperatures and increased cooling energy demand.

This study focuses on a bedroom in The Estate, a residential high rise condominium in Bangsar South, Kuala Lumpur. The room has dark-painted external concrete walls, which are exposed to direct morning sunlight. Because concrete absorbs and stores solar heat, the wall continues to release heat into the room even after the period of direct solar exposure, contributing to prolonged overheating and reduced occupant comfort.

To mitigate this issue, 60 mm insulation panels had been installed on the lower section of the east-facing wall behind the bed (Figures 1 and 2). The objective of this study was to assess the effectiveness of the existing insulation and to investigate potential improvements in thermal comfort and energy performance.

Figure 1: Existing insulation panels installed on the lower section of the east-facing concrete wall behind the bed area

Methodology

The study combined on-site measurements with dynamic thermal simulations using IESVE to evaluate the bedroom’s thermal performance.

Measurements were carried out in March 2026. Two temperature loggers were installed on the exposed concrete wall and on the insulated wall section to monitor surface temperatures. In addition, a Comfort Cube was used to continuously measure indoor environmental conditions, including air temperature, humidity and thermal comfort indicators such as Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD). The floor plan and measurement equipment are shown in Figure 2 - 4.

Figure 2: Floor plan and measurement placements

Figure 3: Temperature loggers installed on the concrete wall and the insulation panel (left). Figure 4: Comfort Cube to monitor the thermal comfort (right).

To complement the field measurements, a digital simulation model of the bedroom was developed in IESVE software. Several East-wall configurations were simulated, including the existing partially insulated wall, an uninsulated wall, full-wall insulation and reflective white-painted external walls. These simulations were used to estimate the annual cooling energy consumption and potential energy savings, while also evaluating the thermal comfort under each scenario.

The measurements were carried out under typical occupancy conditions. The air conditioner was operated between 8:00 pm to 10:00 pm to pre-cool and dehumidify the bedroom before sleeping, while the ceiling fan was used from 12:30 am to 8:00 am during the night. The same operating schedule was applied in the IESVE simulations.

Results

The measurements confirmed that solar radiation was the dominant source of heat gain in the room. The thermographic image was taken on a sunny morning of the East-facing bedroom wall at 11 am, by which time a considerable amount of heat is seen to be coming through the window as well as through the uninsulated part of the wall.

Figure 5: Thermographic image clearly shows that the insulated panels reduce heat influx into the bedroom on a sunny morning (11 am)

The continuous surface temperature measurements in Figure 6 show that the exposed concrete wall consistently reached higher surface temperatures than the insulated wall section. The insulation not only reduced the heat flow through the wall but also dampened temperature fluctuations on the interior surface. As a result, temperature differences of up to 5–6°C were observed during the afternoon and evening (Figure 7), demonstrating the effectiveness of the insulation in limiting heat transfer and moderating temperature peaks within the room.

Figure 6: Measured surface temperatures of the exposed concrete wall (orange) and insulated wall section (blue)

Figure 7: Temperature difference between the surface temperatures of the concrete wall and the insulation panel

Thermal comfort measurements indicated that the room experienced significant overheating during daytime hours. PMV values reached approximately +2, corresponding to warm conditions (Figure 8), while PPD values exceeded 80%, indicating that most occupants would likely experience thermal discomfort (Figure 9). Thermal comfort improved in the evening when the when the air conditioner was in operation and throughout the night with just the use of a ceiling fan.

Figure 8: Measured PMV values showing significant thermal discomfort during daytime hours

Figure 9: Measured PPD values indicating that more than 80% of occupants would likely be dissatisfied during peak overheating periods

The simulations show that the highest thermal comfort is achieved in the pre-cooled bedroom during the sleeping hours 12:30 am to 8:00 am with the use of a ceiling fan. During the two hours of pre-cooling the bedroom with air-conditioning (8:00 pm to 10:00 pm), the bedroom gets a bit too cool for comfort.

The simulation results supported the measured findings. Partial wall insulation reduced heat transfer through the east-wall and improved thermal comfort compared with the uninsulated case. Full east-wall insulation provided the highest percentage of hours within the ASHRAE-55 thermal comfort range and therefore delivered the best overall thermal comfort performance among the insulation scenarios. The simulations also showed that reflective white exterior wall finishes could further reduce solar heat absorption and lower annual cooling energy demand. Depending on the scenario, annual energy savings of more than 20% were predicted compared with the original uninsulated walls (Figure 10).

Figure 10: Simulated annual energy consumption (bar chart) and energy saving percentages (red) for the different scenarios compared to the wall without insulation. As well as with white wall (WW) exterior wall paint.

Summary and Conclusion

This study shows that solar heat gains through the East-facing external wall have a significant impact on indoor temperatures and thermal comfort in the investigated bedroom.

Both the field measurements and the IESVE simulations confirmed that wall insulation is an effective passive strategy for reducing heat transfer into the room. While the existing partial insulation already improves the wall’s thermal performance, the simulations indicate that extending the insulation across the entire East-wall would further improve thermal comfort. In addition, applying reflective white paint on the external walls was found to further reduce cooling energy demand.

These findings highlight how relatively simple retrofit measures can improve occupant comfort while also reducing the energy required for air conditioning in tropical residential buildings.

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Acknowledgements:

• A big thank you to Stephanie Bacon for her hospitality and for letting us undertake the temperature datalogging her bedroom.

• Thank you to Gregers Reimann (IEN Consultants) for organising this study

Author of article, Amelie Hottner, and Stephanie Bacon during measuring equipment installation in bedroom (18 March 2026)