That's a Project I have pending and made much easier now I've mastered the esp and real time os. The machine is still in my shed connected up and waiting.
The problem to date (apart from time...) has been finding a device powerful enough and flexible enough to use for the project, this I think is now solved with the esp. I didn't really fancy trying it with a pi or c.h.i.p. although if the esp gives me problems I may try one of them.
By the way, aside from the heat pump controller I have "IOT'd" the controllers for both the solar hot water and solar central heating. With the hot water controller I added statistics for interest and have been surprised that even now in early January I've had just over 25 hours of running time in the last week.