The assignee ranking for this dataset covers 100 companies, with the leader holding 133 of the 955 records in scope. The top 5 assignees combine for 38.0% of all records and the top 10 for 50.3%, so while there is a clear leading group, roughly half the field is held outside that group. This pattern is typical of an industrial hardware sector where a handful of established HVAC and refrigeration manufacturers file heavily but a long tail of smaller entrants still contributes meaningfully.

Filings rose from 49 records in 2017 to a peak of 82 in 2022, and the clearest complete-year growth window shows a 91% increase from 22 records in 2021 to 42 in 2024. The apparent decline in 2025 and 2026 is a reporting artefact: publication typically lags filing by around eighteen months, so the most recent one to two years are always undercounted at the time of any snapshot. Read the trend through 2024 as the reliable signal, not the tail years.

F25B, covering refrigeration and heat pumps generally, touches 54.9% of the 955 records in this dataset, making it by far the most crowded subclass. C09K (refrigerant materials, 15.6%) and F25J (gas liquefaction and separation, 15.0%) follow at roughly a third of that density. Because records can carry multiple IPC codes, these percentages describe density relative to the full record count rather than shares of a single pie, and they signal where claim space is occupied rather than where the underlying technology is more advanced.

US20220380648A1, assigned to Daikin Industries and published in December 2022, claims a refrigeration cycle apparatus built around a standard compressor-condenser-decompression-evaporator circuit enclosing a small-GWP refrigerant. Its significance is less about novel hardware architecture and more about tying that conventional circuit topology to low-GWP refrigerant charge, which is the same claim pattern that recurs across much of the F25B-heavy portion of this dataset. Anyone drafting hardware claims in this space should check how closely a proposed circuit and refrigerant pairing tracks this structure.

The subclasses with lower filing density relative to F25B's 54.9%, namely C09K materials (15.6%), F25J gas separation (15.0%), and smaller categories like F28D heat-exchange apparatus (4.1%), represent comparatively less-claimed territory. Combined with the fact that roughly half of all 955 records sit outside the top 10 assignees' 50.3% share, there is real room for a well-targeted composition or separation-process claim to avoid the densest prior art. The safest approach is to treat F25B as occupied ground and look at how a refrigerant composition or gas-separation angle can be claimed independently of core cycle hardware.