Ask why heat pumps were long considered unsuitable for cold climates and you will hear about efficiency falling as temperatures drop. True — but there is a second, more physical failure that almost nobody puts in the marketing, and a 2022 patent is built around it: water.
Here is the mechanism that creates the problem. An air-source heat pump extracts heat from outdoor air by running cold refrigerant through an outdoor coil. Air carries moisture, and when that moist air gives up heat to a sub-freezing coil, the moisture condenses — and then freezes. Ice builds on the coil, chokes the airflow, and the pump's performance craters. The system has to periodically run in reverse to melt the ice (a 'defrost cycle'), which wastes energy and, in the worst case, the meltwater refreezes and the unit jams.
Steven Winter Associates' grant US11333395B2, "Condensate removal system for cold-climate heat pumps," attacks this directly. Rather than just managing the defrost cycle, it addresses getting the condensate water away from the unit before it can refreeze and disable the system. It is plumbing, essentially — and in a cold climate, plumbing is what separates a heat pump that works in January from one that quits.
Why this is the right kind of patent to take seriously: the barriers to cold-climate heat pump adoption were never purely about the thermodynamic coefficient of performance. They were about reliability in real winters — the unit that ices over and stops heating is worse than useless to a homeowner in a cold snap. Solving the water problem is solving an adoption problem.
The broader read: the heat-pump patents of the early 2020s show the industry methodically removing the cold-climate asterisks one by one — better refrigerants, smarter defrost, and unglamorous condensate handling like this. None of these is a headline. All of them, together, are why 'heat pumps don't work in the cold' has gone from conventional wisdom to outdated claim.