Dual compressor heat pump

[Acuario]

Well a slight delay whilst I waited for a few bits to arrive to complete the project (the keyboard, a MAX485 and DS18B20 temperature sensor to be precise).

Now all has arrived and I've built the main controller, finished writing and debugging the code and now all that's left is to fit the units - probably tomorrows job.

As the main board has a relay on it I've added a 4th machine (the oil boiler) that can be turned on if we get really cold weather. The main controller has a sensor for the water temperature in the tank and, depending on the temperature, turns on 1, 2 or 3 of the units and if that still isn't enough, as a last resort it turns on the boiler (although this can be disabled). The individual temperature thresholds for each machine are also set by the controller.

As the defrost temperature is difficult to know exactly the controller can re-program the individual slaves to change the temperature the defrost cycle kicks in at.

From the controller you can also set the operating mode (Heat/Cool) and turn on/off the units or force a defrost cycle.

The controller communicates with the slaves via 2 wires (RS485) and checks for existence of the slave and can request its current operative status and the condenser temperature. This is then displayed on the main screen.

So it's built, it should work (it does from my testing) so time to install it all and see if the reality coincides with the theory.