Designing a General Purpose Heat Pump Controller

[AC_Hacker]

Originally Posted by jeff5may

...For the first version of a controller, I would like to use an uno. ...

Great, Radio Shack has them, about 8 blocks away...

Originally Posted by jeff5may

I have a good question for you: what kind of data is the thing you will be controlling this unit with going to be sending and receiving? Switch states? readings of what frequency? Keep alive sgnals?

I hope I'm talking approximately the same language...

For the very simplest application, I want to control a water-to-water heat pump... heating only, no cooling.

What I can envision as the most basic function is:

1.) Delayed (1 min) startup at power-up, then...

2.) Look for a "heat-required" signal from a separate thermostat.

3.) If "heat-required" signal is FALSE, do nothing.

4.) If "heat-required" signal is TRUE, start the loop water pump 30 seconds before indoor loop water pump. During this time, monitor the temperature of the water at the output of the ground loop HX.

[* NOTE: The controller needs a minimum HX output temp variable, to be used to assure that the HX does not freeze. For now, I think it should be 37F. That could be tweaked later *]

If the HX output temp measures <= 37F, keep loop water pump running, and wait 10 minutes, then re-measure.

If HX output temp measures > 37F then...

[* NOTE: we need to build a fail safe into the system such that if a value or value range from a thermistor (or 1-wire) that would occur if the sensor failed or a sensor wire broke, the unit would shut down and issue an ERROR light *]

5.) Start indoor water pump, and run for 30 seconds. After 30 seconds...

6.) Start compressor.

7.) Run until "heat-required" signal is FALSE, then...

8.) Cut both compressor and outdoor loop pump.

9.) Continue running indoor loop pump another 5 (variable here?) minutes.

10.) Continue monitoring "heat-required" signal


This is the first cut, so I'm open to feedback.

Best,

-AC