# A Review of Small-Scale Vapor Compression Refrigeration Technologies
## 3 Small-Scale Vapor Compression Refrigeration (VCR) Systems
### Small-Scale Vapor Compression Applications
#### 3.1.2 Personal Cooling  
When we talk about personal cooling, it is important to mention that there has been an evolution in the last three decades in the way in which individuals have been seeking to create a comfortable thermal environment: we have been moving from the use of HVAC systems, through \"task ambient conditioning (TAC)\" strategies, followed by \"personalized environmental control systems (PECS)\", and more recently, \"personal thermal management systems (PTMS)\" [59]. In other words, there has been a transition from controlling the climate of an entire space to creating a micro-climate in a localized area, until reaching the point of developing wearable cooling systems that only focus on the comfort of the human body, as can be seen in Figure 16.  
Figure 15: Illustrative representation of the meso-scale VCR system.  
PTM systems are important because they can help individuals exposed to high-temperature environments, such as firefighters, soldiers, and other hazardous duty and chemical-spill personnel, increase productivity, increase the duration of missions, reduce fatigue, and improve safety by reducing thermal stress [60]. We next outline some research works focused on this topic.  
[PERSON] et al. [61] designed and manufactured a miniature vapor compression refrigeration system for microclimate control applications using a Wankel compressor, a miniature air-cooled multi-channel parallel-type condenser, a spiral-tube-type evaporator, and a capillary tube. The dimensions and weight of the equipment were 260 \(\times\) 250 \(\times\) 120 mm\({}^{3}\) and 2.85 kg, reaching 4 kg when a high-performance lithium battery was added. Experimental tests were performed to determine optimal R22 refrigerant charge (100 g) and capillary tube length (1000 mm). Additional tests were conducted to evaluate the effect of compressor speed on system performance. The results show that the miniature refrigeration equipment provided 300 W of cooling with a COP above 2.0 at 40 \({}^{\circ}\)C ambient temperature. [PERSON] et al. [62] presented follow-up work evaluating the influence of refrigerant charge and capillary length on system operating conditions (superheating, subcooling, operating pressures, and temperatures). The results show a compression ratio above 3.0, cooling capacity above 300 W, and COP of 2.3.  
[PERSON] and [PERSON] [60] designed, fabricated, and tested a wearable personal cooling system including an engine-driven compressor and a wearable evaporator. The system was assembled in a backpack-type configuration with a total mass of 5.3 kg and measuring 318 \(\times\) 273 \(\times\) 152 mm\({}^{3}\). The authors found that the system can provide 178 W of cooling for 5.7 h in an ambient temperature of 43.3 \({}^{\circ}\)C. An even more compact wearable system was proposed by [PERSON] et al. [63] with 190 \(\times\) 190 \(\times\) 100 mm\({}^{3}\) overall dimensions and 2.75 kg in weight. The system includes a liquid cooling vest and therefore demands an additional pump, and yet the system is lighter and more compact. The system reached a cooling capacity of 260 W and a COP of 1.62 under an ambient temperature of 50 \({}^{\circ}\)C and a cold-water temperature of 24 \({}^{\circ}\)C. The study also analyzed the influence of the expansion valve opening, and the mass of refrigerant charge in the system, finding an optimal mass of 120 g of R134a. The system incorporated a microchannel plate-fin-type evaporator.  
The development and study of small-scale VCR systems for personal cooling will continue to grow in the following years for at least two reasons: (1) extreme weather is becoming more prevalent in many areas of the world due to climate change, and (2) technological development and progress in new manufacturing techniques will allow the creation of increasingly compact vapor compression refrigeration systems, leading to improved portability and wearability.  
Figure 16: Conditioning area moving closer to the human body.