Evaluating the Practical Energy Saving Potential of a Personal Cooling System in the Tropics

Cooling the built environment consumes a huge amount of energy, especially in hot and humid climates such as Singapore, where cooling could account for 50-60% of a building’s total energy consumption. Research from the past fifteen years has clearly demonstrated that personal cooling systems are able to provide thermal comfort and energy savings by supplying cooled air directly to the occupants. However, the systems used in previous lab-based experiments relied on central air handling units and complex ductwork to produce and deliver cooled air, making them inflexible and restricting the capability of saving cooling energy in practice.

There have been many attempts to design a portable local cooling device. Yet, existing solutions, such as mini heat pumps and conductive coolers, still suffer the dilemma of practicality and supplying cooled air. To this end, this study first introduces a novel desktop air cooling device that integrates thermoelectric cooler and phase change material. To optimize the practical functions and overall thermal performance, air temperature could be decreased by 3-5°C without any condensation by precisely controlling the cooling surface temperature. Such a plug-and-play device would be one step closer to realizing the potential of personal cooling.

Further, we conduct actual experiments and building energy simulations to quantify the energy-saving potential of applying this device in an office. There are two limitations in past studies that evaluated the energy performance of personal cooling. On one hand, there is a lack of understanding of the practical performance of local cooling devices under diversified operating conditions. For example, the design of thermoelectric coolers mainly relies on theoretical references or standard tests, leading to deteriorated performance in practice. On the other hand, when estimating the impact of personal cooling on the operations of central HVAC systems, previous research is restricted to the change of cooling setpoints, overlooking other factors that affect energy efficiency.

In this study, we integrate the personal cooling device with mixed-mode ventilation, where the space is naturally ventilated under mild outdoor conditions, and the background AC is only turned on when the outdoor temperature exceeds 28°C. The personal cooling devices will be regulated throughout the day to accommodate the thermal comfort requirements. Initial results indicated over 40% energy reduction, which validates the great potential of integrating the proposed personal cooling device and mixed-mode ventilation.