The purpose of this project is to add some extra controls for the DIY Fujitsu air-to-water heatpump:
- The COP (coefficient of performance) of the heatpump is really bad when running on low power. Force the heatpump to idle state when the output power need is low
- Disable the 6 kW backup immersion heater when the heatpump is in idle state. Normally this heater turns on when the heatpump does not produce warm enough water
- Cheat the heatpump to not defrost every 35 minutes on cold weather, but only when it's necessary
- Control the heating cable on the defrost water drain pipe
- Automatically start the air-to-air heatpumps when the outdoor air gets cold enough, i.e. when the air-to-water heatpump is not powerful enough. Also shut them down when the weather gets warmer
- Provide temperature logging using xPL messages
The DIY heatpump project can be found here (sorry, in Finnish): http://lampopumput.info/foorumi/index.php?topic=10949.0
- Arduino Duemilanove
- Arduino Ethernet shield
- 4-channel relay board
- 4x DS18B20 1-wire temperature sensors
- 2x16 characters LCD display, based on the Hitachi HD44780 driver
Relay 1
- Controls the heatpump defrost cheating
- Connects a 68kOhm resistor in parallel with the outdoor unit's pipe temp sensor, to prevent the unit from defrosting
- One of the 1-wire sensors measures the pipe temp, and the relay is controlled by the difference between the outdoor air and pipe temp temperatures
- See the function 'awhpDefrostSignal'
Relay 2
- Controls the sewer pipe heating, and also the compressor heating cable
- By default the heating is on practically from October to March, now it's only running when really needed
- This relay does not control the heating directly, but just shows two different (fixed) temperature values to Ouman EH-203, the real relay and program is on the Ouman side
- See the function 'sewerHeatingCableSignal'
Relay 3
- Controls the 6 kW backup heater
- Well, actually it's the Ouman EH-203 which controls the heater, based on boiler temperature measurements
- The purpose of this relay is to 'cheat' the temperature measurement so that the backup heater will not turn on when the heatpump is not running
- So this relay connects a resistor in parallel with the Ouman's NTC resistor, so that Ouman will see higher temperatures
- See the function 'awhpState', for the handling of the 'BACKUP_HEATER'
Relay 4
- Controls the heatpump, by connecting either 0 Ohm or 2.2 kOhm in series with the indoor unit's inlet air sensor
- The heatpump is set to 27 degrees, so with 0 Ohm resistor it will try to produce cooler than 30 degrees C, and with 2.2 kOhm resistor it will try to produce about 37 degrees C
- The purpose of this relay is to let the heatpump idle when it's running on very low power
- When the boiler gets warm enough, let the heatpump idle until the boiler has cooled down a bit
- Experience has shown that the heatpump runs on very poor COP on low power, so the whole point is to get better COP out of the heatpump
- See the function 'awhpState', for the handling of the 'AWHP_RUN'
