This dataset identifies 9,899 published records between 2015 and the August 2026 cut-off that combine district heating and cooling terminology with core thermal-system components such as heat exchangers, thermal storage and working fluids. That figure counts published documents in scope for this search, not every patent that touches district energy in any way, so a differently scoped search string would return a different total. Patent families, rather than raw document counts, are the fairer unit for cross-jurisdiction comparison because they neutralise continuation and multi-country filing behaviour.

The ranking covers 100 companies counted in records, with a single leader holding 355 records and a steep drop to 130 by fifth place and 106 by tenth. The top five combined account for 1,052 records, 10.6% of the 9,899 in scope, and the top ten reach 1,636 records, or 16.5% — a real but not dominant concentration. Beneath that group sits a long tail of single- and few-filing entrants, so competitive mapping should not stop at the named leaders.

Filings rose from 497 in 2017 to a peak of 555 in 2020, then declined to 328 by 2024 — a 38% drop across that three-year span, the last period with complete data. Figures for 2025 and 2026 look lower still, down to 51, but that reflects publication lag of roughly 18 months rather than an actual collapse in filing activity. The honest read is a cooling-off after a 2020 peak, not a technology in decline.

F24D, domestic heating systems, carries the largest share at 21.1% of the 9,899 records in scope, followed closely by F01K steam and thermal power plants and F28D heat-exchange apparatus, each near 14.3%. Refrigeration and heat pumps, air conditioning, gas turbines, heat-exchanger details and separation processes each contribute between 5.8% and 7.6%. Because records often carry multiple IPC classes, these shares sum to more than 100%, reflecting how heavily district heating equipment claims overlap with adjacent mechanical classes.

Relative to the dense F24D, F01K and F28D classes, sub-areas such as thermal storage load-shifting controls, working-fluid selection for low-grade waste heat recovery, and sensor-fusion approaches to leak and heat-flux detection show comparatively lighter claim density. Hybrid solar-thermal district loops and heat pump integration with legacy networks are active but not yet saturated. These are directional signals from the class composition data, not a guarantee of allowability, and any specific concept still needs a targeted prior-art search before filing.