When talking with customers about advanced vapor compression cooling systems, the subject of noise generation is often brought up as a concern.  Literature from competing Thermoelectric suppliers will state that there are no moving parts on a thermoelectric system and therefore they are silent.  These statements ignore the fact that both vapor compression and thermoelectric-based systems require fans to dissipate the heat.  In both technologies, the fan is the largest contributor to noise.  In equivalently sized vapor compression and thermoelectric systems, however, the vapor compression systems will generate significantly less noise than the thermoelectric counterpart.  There are several factors that contribute to this.

  1. Due to a factor of 4 lower efficiency the thermoelectric device is required to dissipate twice as much heat as an equivalently sized vapor compression system. See the table below. 
TechnologyTypical COP Cooling Provided WattsPower DrawnCoolingWattsPower DrawWattsHeat Dissipated from SystemWatts
Vapor Compression210005001500

            This means that the fan power required to dissipate the heat in a TEC based system will be at least twice that required for an equivalent Vapor Compression based system.  With the fans as the major contributor to noise in both vapor compression and TEC systems, the noise generated by the TEC is significantly higher.  In one application the noise of the system was more than that produced by a thermoelectric system.

2. Further on this point, the heat exchangers themselves are not as efficient for thermoelectric systems.  The heat is generated from a flat plate and conductively transmitted to an extruded heat sink.  This design is less efficient.  For details see the last blog on compact vapor compression systems.  This further raises the fan power required to dissipate the excess heat from a thermoelectric system. 

To illustrate the importance of the noise comparison, multiple customers who have replaced their TEC-based cooling designs with modern vapor compression systems report significant noise reduction.  In one case our customer replaced a thermoelectric cooling system with our vapor compression system and reported a noise reduction from 63 dB to 43 dB.  This equates to a perceived 75% less sound and the equivalent of library background noise.  This is certainly suitable for a medical environment.  63 dB, on the other hand, is loud enough to be annoying and speech masking; definitely not suitable for a medical environment.  Some customers have switched to vapor compression primarily for noise reduction factors, others report the noise reduction as a significant, but not entirely anticipated, benefit of switching to modern vapor compression technology. 

Next time, we will investigate the reliability of modern vapor compression systems

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