It all started back in 2010. Before the current surface mounted air temperature sensor was added to our Player controller circuit board in each digital Heat Siphon.
Back then we used a tiny bead thermistor with long thin bare wire leads to monitor the air temperature. It installed by two screw down terminals and had some field service issues.
For one thing, the small bead on thin wires would get damaged if someone was not careful in removing / replacing the door it was mounted on, second we had some air temperature readings that didn't' make sense and third the screwdown terminals would come loose over time.
We reveiwed the problems and decided to completely redesign this feature going to a surface mounted chip temperature sensor.
That is when we got the idea to use the time and temperature behavior of our Heat Siphon exhaust air to calculate the air temperature using the Player computer program.
Although it gets complicated, it works and we adopted this "COOL LAG ALGORITHM" on All Heat Siphon Digital Models Player controller since May 2011.
Six Years Later:
On March 1, 2016 we finally were awarded US PATENT 9,272,899 "Monitoring and Control System for a Heat Pump" by the US Patent office.