Persona: Senior Thermal Systems Engineer & Mechatronics Specialist
Review Panel Recommendation: This project would best be reviewed by a panel consisting of Thermal Design Engineers, Portable Power Specialists, and Advanced DIY Fabricators. The synthesis of vapor-compression refrigeration, custom heat exchangers, and Arduino-controlled solar harvesting provides a multidisciplinary case study in high-efficiency personal climate control.
Abstract
This technical demonstration outlines the design and fabrication of a wearable personal cooling system utilizing a miniature vapor-compression cycle to chill water circulated through a silicone-tubed vest. Moving away from less efficient forced-air cooling, the system leverages the superior thermal conductivity of water to provide significant heat relief (approx. 24W lift) at a lower temperature differential, thereby improving theoretical cycle efficiency.
The hardware stack includes a miniature brushless-DC rotary compressor, a custom-brazed evaporator/chiller assembly constructed from dual CPU cooling blocks, and a 32V lithium-ion power supply. A significant portion of the analysis focuses on solar integration, detailing the V-I characterization of a 50W solar array and the implementation of a custom Arduino-based control circuit. This circuit utilizes current-sensing logic via a load resistor to manage compressor start-up torque and protect sensitive components from over-voltage using a MOSFET-based linear regulator. Empirical testing confirms the system's ability to maintain a comfortable micro-climate in high-ambient conditions (Florida) and its potential for thermal energy storage in water/ice reservoirs.
Project Summary: Portable Vapor-Compression Liquid-Cooled Vest
0:00 Liquid vs. Air Cooling: Vapor-compression systems for personal use are more efficient when applying cooling directly to the torso via liquid rather than blowing air. Water has 25x the thermal conductivity of air, allowing the refrigerant loop to operate at higher evaporator temperatures (21–24°C) while still providing effective relief.
1:51 Custom Chiller Fabrication: The evaporator/water-chiller interface is fabricated by brazing two 40mm copper CPU cooling blocks together. One block carries the propane refrigerant; the other circulates the coolant water. The assembly was pressure-tested to 10 bar.
4:51 Component Integration: The system utilizes a 120mm condenser fan from a tabletop ice maker, a miniature rotary compressor, and a 60cm capillary tube for flow restriction. The final refrigeration unit is compact enough to be belt-mounted.
6:07 System Charging and Performance: Following a vacuum purge, the system was charged with propane. Bench tests showed steady-state temperatures reaching -10°C at 30V/1A.
8:20 Power Distribution: The unit operates on a 32V bus (dual 4-cell Li-ion). Two LM2596 buck converters step down voltage to 12V for the water pump and 10V for the condenser fan to optimize power consumption.
9:11 Thermal Lift Measurement: Calorimetric testing via a known quantity of water measured a peak refrigeration power of 24W with 26.4W of input, indicating a Coefficient of Performance (COP) of approximately 1.0.
10:11 Vest Construction: 15 meters of 3/16-inch silicone tubing are woven into a porous high-visibility mesh vest using zip ties. The design prioritizes surface area contact with the torso while preventing tube kinking.
11:08 Field Testing Results: Real-world testing in Florida's ambient conditions confirmed that the system provides a noticeable chill, making the user "uncomfortably cold" in indoor settings and providing significant relief in direct sunlight.
12:24 Solar Characterization: A 50W (dual 25W) solar array was characterized using a custom V-I curve tracer. Due to winter sun angles, the panels peaked at 38W. Open-circuit voltage reached 49V, exceeding the 40V limit of the ESC and buck converters.
14:54 Solar Control Logic: An Arduino-controlled relay system was implemented. Since open-circuit voltage is a poor indicator of available power, the system shorts the panels through a 50-ohm resistor to measure current. The compressor only engages when current exceeds 0.75A.
16:16 Voltage Regulation: A MOSFET-based linear regulator with a Zener diode on the gate is used to clip the input voltage at 40V, protecting the drive electronics from solar voltage spikes.
18:11 Thermal Energy Storage: The system was successfully used to chill a one-gallon water reservoir via solar power. Future iterations will focus on phase-change energy storage (ice) to recover cooling power at night using only minimal wattage for the pump.