Linking Loxone to my Daikin Altherma 3 through Smart Grid contacts

I want my Daikin Altherma 3 to run when there is surplus solar energy or cheap grid electricity. With Loxone, I want to control when it heats the house and when it heats the water for showers.

The integration now has two connected control paths: Loxone relays connected to the Smart Grid contacts, and pins 30, 34 and 35 connected for off, heating or cooling selection. Smart Grid control is working. The next step is an Arduino that generates pulses for the digital pulse meter input.

Three parts of the integration

flowchart LR
    accTitle: Loxone relay contacts and Daikin X5M terminals
    accDescr: Closing the first Loxone relay connects X5M pin 9 to pin 10 for Smart Grid contact 1. Closing the second connects X5M pin 5 to pin 6 for Smart Grid contact 2. The planned Arduino pulse interface connects to X5M pins 3 and 4.
    subgraph SG1["DAIKIN X5M — SG1 / S10S"]
        T9["Pin 9"] --- R1["Loxone relay contact 1\nCLOSED: connects 9 to 10"] --- T10["Pin 10"]
    end
    subgraph SG2["DAIKIN X5M — SG2 / S11S"]
        T5["Pin 5"] --- R2["Loxone relay contact 2\nCLOSED: connects 5 to 6"] --- T6["Pin 6"]
    end
    HC["Loxone heating / cooling control"] -->|Off / Heating / Cooling| MODE["Daikin pins 30, 34, 35"]
    P["Loxone power value"] -.->|Link TBD| A["ARDUINO — pulse generator"]
    A -.->|Output interface TBD| METER["DAIKIN X5M\nPins 3 and 4\nMeter 2 / S4S pulse input"]

Each relay contact bridges one pair of X5M terminals: 9–10 for SG1 and 5–6 for SG2. The drawing shows the electrical path with the contacts closed; opening a relay breaks that path. The two pairs are separate and are not joined together. “Relay contact 1” and “2” identify their Smart Grid roles, not numbered outputs on the Loxone hardware.

Dashed lines show the planned Arduino connection. Its output interface is still to be designed. The heating/cooling pins are grouped because their individual relay connections are not shown here. Use the manual for your indoor unit to check the terminal assignments.

Heating and cooling selection

I already controlled off, heating and cooling through pins 30, 34 and 35. I also wanted Loxone to control when the hot-water tank heats up.

Those are separate decisions in Loxone: the heating/cooling request and the Smart Grid state. The heating/cooling “off” selection should not be read as switching off the entire unit or disabling all hot-water operation.

What the Smart Grid contacts mean

Daikin documents these combinations:

In the referenced Altherma 3 R F manual, the low-voltage connections are S10S: X5M 9–10, S11S: X5M 5–6, and pulse meter S4S: X5M 3–4. These remain model-specific references, not a confirmed terminal list for my unit. Daikin installer reference guide, pp. 134–136.

Getting the mode selection working

During setup, I initially saw only Vrij bedrijf and Gedwongen uit on the Dutch interface. After troubleshooting the configuration, I confirmed that Smart Grid control was working.

The reference manual selects Smart Grid through [9.8.4] / [D-01] = 3; [9.8.5] displays the received mode. Recommended on uses the pulse-derived limit, or [9.8.8] without a meter. Forced on does not apply that Smart Grid capacity limit. Protection and defrost can bypass the recommended-on limit. Tank buffering can reach the maximum tank temperature, rather than perform a normal reheat cycle. Daikin configuration reference, pp. 216–219.

At that point I had set the fixed limit to 2 kW, with no Smart Grid pulse meter connected. That is power, not an energy budget of 2 kWh. It also does not mean the heat pump must continuously consume exactly 2 kW.

For now, I can switch the Smart Grid mode with the relays and use a fixed power limit. The next step is to make that limit follow the available power.

Next: generate the meter pulses with an Arduino

The meter input is still unconnected. My plan is to let Loxone send a value to an Arduino, and let the Arduino generate the pulse train locally. The existing relay connections stay responsible for mode selection.

Meter 2 distinguishes consumption settings from PV settings: [9.A.2] / [D-09] = 6 means 100 pulses/kWh for PV; 7 means 1000 pulses/kWh for PV. The manual describes this signal as PV production. Daikin energy-metering settings, p. 221.

At 1000 pulses/kWh, the pulse frequency is:

pulse frequency (Hz) = power (kW) × 1000 / 3600

For example, 1 kW corresponds to one pulse every 3.6 seconds. I still need to choose the output circuit and pulse width, and decide what the Arduino should do if it stops receiving updates from Loxone.

Which value should Loxone send?

I still need to work out which power value to send. Solar production and the power being exported to the grid are not the same.

For example, if the house exports 1 kW and the heat pump starts using 1 kW, export drops to zero. The heat pump is still running on solar energy, but an Arduino following grid export would now send a value of zero.

One option is to add the heat pump’s measured consumption to grid export, treating import as negative. I have not tested this yet. I also need to account for the battery and other loads in the house.

How will Loxone communicate with the Arduino?

I have not chosen the connection between Loxone and the Arduino yet. It needs to send the power value reliably and let the Arduino detect when updates stop.

Current status

The relay control is connected and working. Next is the Arduino pulse generator and its connection to Loxone. Once that works, I can test how the heat pump follows the available power.

Installer manual

Daikin Altherma 3 R F — Installer reference guide (English PDF), document 4P629090-1E, June 2024, for ERGA04–08E + EHVH04/08SU18/23E.

The sections relevant to this integration are:

• Pages 134–136: Smart Grid connections and low-voltage wiring.
• Pages 216–219: Smart Grid configuration, operating modes and power limits.
• Page 221: Electricity meter inputs and PV pulse settings.

Check the model designation on the installed unit against the manual before using its terminal references.