# A Review of Small-Scale Vapor Compression Refrigeration Technologies
## 3 Small-Scale Vapor Compression Refrigeration (VCR) Systems
### Components
#### 3.4.1 Compressors
[84] also tested a miniature rolling-piston rotatory compressor (Figure 19) using a hot-gas bypass load stand and refrigerant R134a. The main characteristics of this commercial compressor were 78 mm height, 58 mm diameter, 1.4 cc displacement, and 600 g weight. The tests were conducted by varying the suction pressures, pressure ratios, and rotational speeds, producing the following results: 73-90% volumetric and 44-70% isentropic efficiencies, as well as 2.1-7.4 COP, and a theoretically calculated cooling capacity of 489 W. This compressor was then used by [PERSON] and [PERSON], who considered it the most compact in the market at that time [14], although other studies have demonstrated even more compact compressors, such as a reciprocating compressor that fits within a notebook computer [50]. A small-scale off-the-shelf portable air compressor was used and considerably modified to function as a refrigerant compressor for a portable cooling system [60]. System power was supplied by a 2-stroke compression ignition engine, eliminating the need for an electric grid connection. Several tests were conducted and cooling rates up to 300 W were demonstrated, indicating the air compressor's potential for practical applicability. Figure 19: Miniature rolling-piston rotary compressor [84]. Figure 18: Prototypes of Wankel compressors: (**a**) flat-shaped design and (**b**) lightweight design. The use of linear compressors for refrigeration has been widely studied both in traditional applications such as domestic refrigeration, as well as in small-scale refrigeration due to the advantages over the conventional crank-drive reciprocating compressors [85]. Detailed numerical models have been developed and validated to improve the design and therefore the performance of these compressors [86; 87], as well as experimental tests [55], where a constant-speed, oil-free linear compressor was used for electronics cooling in aeronautical applications, in which the mass flow and cooling capacity were controlled by varying the piston stroke. This same micro compressor was presented by [PERSON] [54]. It is a hermetic linear compressor with cylindrical form and 60 mm in diameter and 160 mm in length that weighs 1.3 kg. The most relevant aspect is its orientation independence, i.e., it can be mounted vertically or horizontally because it does not require any type of lubricant, increasing the practicality of its assembly in reduced areas. Figure 20 shows a schematic of a linear compressor and the one used by [PERSON] [54]. It is possible to find works in the literature comparing the performance of small-scale refrigeration systems operating with different types of compressors [88]. These authors conducted a thermodynamic evaluation of two commercially available portable coolers operating with reciprocating and mini-rotatory compressors. The portable cooler was a 38-liter cabinet originally equipped with a fixed speed reciprocating compressor operating with 42 g of R134a at 60 Hz, while the proposed replacement is a mini-rotary-type compressor with two compression stages evaluated at 40 and 58 Hz. In a brief comparison, the mini-rotary compressor showed better attributes, such as large evaporating temperature range, longer stroke, more compactness, lower mass, and more. It was observed that the system with the original compressor yields higher second law efficiency (by 20%) vs. the rotary compressor. However, the rotary compressor produced a higher cooling capacity, leading to a shorter cooldown time. Based on their results, the authors assert that the performance of the portable cooler using the rotary compressor can be greatly improved with an adequate heat exchanger design. In summary, it can be seen that despite the challenges of compressor miniaturization, there is currently a wide variety of available systems for small-scale applications, where the selection will depend on the operating conditions or even the requirements of weight and dimensions for each application.