The PA120 series was concieved after the design-success of the PA160. During development of the PA160 it was discovered that radiators could be more finely tuned for the needs of today's watercooling community, where silence has started to become a major priority. Testing and comparison of the PA160 led to a starting point for PA120 series development. A large portion of the initial discussion and theoretical work leading to the first prototype was done publicly and can be viewed here at Overclockers.com.au (post #171 onwards - Membership Req'd). After the first prototype was produced, development went private for obvious reasons, but a number of further revised prototypes were then created and tested.
After many months of number crunching and testing the final spec for the PA120 series was decided upon. This final design showed a vast improvement over the HE Series... by a significant margin when it came to silent fans. Additional testing confirmed that this margin applied not only to silent fans but to regular and higher airflow fans, up to a 130cfm (approximately) point.
The final spec was slightly "outside-the-box" when it came to regular Radiator construction, thus weeks of tooling changes ensued before the new series could be commerically released to retail. Which brings us to the present day...
The PA120 radiator series features a dual-row dual-pass 120mm form factor, available in single, double and triple sizes, optimised for the fans of today and putting into practice everything learned about watercooling efficiency and performance over the past 3 years. The PA Series boasts from 10-40% better performance over the HE Series. 10% for the high / noisy airflow end of the fan market, and up to 40% for the low airflow / silence end of the market.
What does this mean to you as an end-user? You can retain the same performance for even less noise, or better performance for the same noise over your current radiator. If at the end of the day performance is all that matters to you and noise is of no concern, the new PA Series still offers significant improvements over the HE series. Alternately if silence is the goal, you can now have that too, but with more cooling performance than ever before!