Serpentine condensers gain retail cooling market
Retail chains in many countries are reviewing their carbon footprint and are focusing on refrigeration systems, particularly on choosing non-HFC, environment-friendly gases. While transiting to lower GWP refrigerants, among which flammable and mildly flammable gases like propane and HFOs, refrigerant quantity and, correspondingly, gas circuit volumes become essential factors in systems’ design.
In terms of volume, the smallest heat exchangers are microchannel coils with 50% or more refrigerant charge reduction. In turn, serpentine-type, manifoldless microchannel coils offer a further 50% reduction in internal volume.
Further optimization includes the use of microchannel tubes with a minimal hydraulic diameter of the ports to increase heat transfer rates while reducing coil volume to a greater extent. Thin tubes also contribute to lower airside pressure losses. The major disadvantage of serpentine-type designs is high pressure loss on the tubeside. However, this drawback can be overcome with a multi-tube serpentine arrangement.
Serpentine condenser dimensions are limited to the length of a single microchannel tube but large enough (and can be times larger in multi-tube configuration) to satisfy the capacity requirements of small and medium-sized refrigeration devices used in retail cooling applications.
Tangible benefits resulted in the rapidly increased popularity of serpentine condensers in applications like display cases, refrigerated cabinets, cooled showcases, and food and beverage coolers:
- Compatibility with HFC-free and natural refrigerants
- Minimum charge of refrigerant vs. other coil types
- High heat transfer coefficients
- Compact design
- Low cost
At the same time, serpentine coils can be easily distorted during brazing due to the absence of reinforcing parts, thus requiring special assembly fixation techniques to eliminate the issue and keep accuracy in geometry and dimensions.
Besides condenser applications, serpentine coils are perfect as evaporators in retail refrigeration. Being compact, with times higher heat transfer capabilities compared to finned-tube coils, and offering way smaller refrigerant charges, serpentine evaporators recently hit the market with great success.