I am wondering if there is a list of materials that I would need to monitor an air to air heat pump. The current bundle on the shop is for air to water heat pumps.
Hello @hunterdartmouth and welcome! We dont have a solution for air2air that accurately measures heat output but you can use the EmonTx4 to measure electric consumption and three temperature sensors, outside temperature, air in and air out of the indoor fan unit. That alongside the datasheet air volume rates through the fan unit could allow you to estimate some ranges for power output…
Another approach could be to attach a temperature sensor to the metal body of the refrigerant to air heat exchanger in the fan unit to try and get the condensing temperature and then use the carnot equation to estimate COP? E.g: https://docs.openenergymonitor.org/heatpumps/basics.html#carnot-cop-equation
Both approaches will have significant error margins but may be useful enough to see what is happening?
Thanks, I wonder if there is scope with the Emon hardware to add a hot wire air speed sensor, which could measure m/s and then we could do some math on the size on the opening? What do you think?
The indoor units usually have a rated air flow at certain levels, measuring the rotation speed of the fan could be another way to have a continuous data point by finding a way/formula to corelate everything.
Have in mind the air temp sensor that is on top or next to the coil already measures a temp higher than the actual room air temp and makes the machines stop earlier.
Could also be possible to see if there is a correlation between amp draw on the blower motor and air flow. Then one could have a current transducer installed on the blower motor.
All good ideas… feels like the challenge is to calibrate the setup somehow? Could be done with a room heat up test vs an electric fan heater perhaps? Measure room temperature accurately with multiple room temperature sensors, power input to the electric fan heater and outside temperature and do alternate heating periods with the a2a and electric fan heater?
Older thread but very interesting. Also have an air to air setup. Also in a balanced heating/cooling climate. (USA)
Are there no in-line refrigerant heat meters? I realize that they would require skilled labor to install (pump refrigerant down, vacuum, flare etc).
Does anyone know what would actually be needed here? Going to be different for centralized ducted blower systems than for mini-splits.
For ducted systems I’m thinking some airflow and temperature monitoring in the ducts could be useful? Perhaps something could be done with pressure differentials?
For calibration in minisplits perhaps a flow hood over the whole unit could give airflow to power draw for the blower motor mapping?
Another approach that would work for cooling might be to run a resistance heater in a battle with the cooling system. Then, since one knows the output of the space heater, one could know the output of the cooling system for a given power draw? Obviously only useful for calibration, not for live long term monitoring 
Blows my mind that there are not more data available in the boards themselves. For example it would be nice to at least know what different heads in a multi split system are calling for?