Electrical Connection

MiniHPC Placement

MiniHPC is installed in a modular distribution box with a DIN rail of at least 9 modules wide. We recommend placing it as close as possible to the heat exchanger to avoid the need for extending the cables to the supplied NTC temperature sensors and the flow sensor (the cables are 2 meters long). Additionally, it is advisable to position the distribution box so that it is easily accessible, ideally at eye level.
If there are multiple devices inside the distribution box along with the MiniHPC, such as circuit breakers, auxiliary relays, electricity meters, etc., the MiniHPC should be placed on the far right side of the distribution box. This is because the WiFi antenna is located on the upper right side of the MiniHPC and could be interfered with by nearby devices.
We also recommend routing power cables and low-voltage cables to the NTC sensors and the flow sensor along separate paths to reduce electromagnetic interference.

Connecting MiniHPC and the Outdoor Unit

The outdoor unit has a terminal block with connections 1 + 2 + 3 + PE (N + communication + L + PE), which match the terminals on the MiniHPC labeled as Outdoor. The terminals of the outdoor unit and the MiniHPC are connected using an appropriate cable with a conductor cross-section of at least 4x0.75mm².

Temperature Sensors T1 - T6

T1 NTC sensor should be placed indoors in a location not exposed to external heat sources such as fireplaces, sunlight, stoves, etc. This sensor can be replaced with a Bluetooth wireless Xiaomi Mijia temperature and humidity sensor (LYWSD03MMC) with the alternative ATC firmware.

T2 NTC sensor is installed at the heating water input to the heat exchanger. This sensor is mandatory if temperature control uses the T2 temperature setting.

T3 NTC sensor is installed at the heating water output from the heat exchanger. Similarly, this sensor is mandatory if temperature control uses the T3 temperature setting.

T4 NTC sensor is installed after the output of the electric heating element.

T5 NTC sensor is placed inside the DHW tank in a designated area for such a sensor. This sensor is mandatory if the DHW heating is enabled.

T6 NTC sensor is installed on the output of the liquid refrigerant pipe at the bottom left of the heat exchanger. This sensor is mandatory.

We recommend attaching temperature sensors T2, T3, T4, and T6 to the pipes using aluminum tape and insulating them with thermal insulation.

I1 is a pulse input for the water flow sensor. The sensor is powered by 5V DC. The default pulse count for the sensor is set to 476 pulses per liter (for type YF-B10). This value can be adjusted in the flowmeter calibration menu I1 based on the type of flowmeter used. The sensor connector is plugged into the pin connector with the locking tab facing down so that the tab fits into the slot on the circuit board below the connector. When connecting, you may need to slightly lift the connector. When disconnecting, the connector must be lifted further to release the locking tab.

Relay Outputs R1 - R5

R1 is an output relay intended to switch the electric coil in the DHW tank. The relay's switching terminals are accessible on terminal R1. The relay has a 10A load capacity; if the coil exceeds the maximum current, an external auxiliary relay or contactor must be used. The DHW heating coil is switched when the outdoor unit exceeds one of the conditions set in the menu 3.4 DHW HP conditions, which can be, for example, a higher temperature than the air conditioning can achieve in functions such as 3.3 Anti-legionella.

R2 is an output relay designed to switch the electric heater in the heating circuit when the outdoor unit cannot provide enough capacity to heat the building. If the relay's load exceeds 10A, the heater must be connected through an external auxiliary relay or contactor. The conditions for activating the electric heater are set in the Electric Heater R2 menu. By default, this heater is disabled!

R3 is the output for connecting the circulation pump in the heating circuit, with a directly switched phase terminal.

R4 is the output for connecting the 3-way valve for DHW heating.

R5 is the output for connecting the 3-way valve for cooling.

The R4/R5 output has four terminals: N, L4/5, L, and PE. The L terminal is permanently powered with 230V, and the L4/5 terminal switches 230V via a relay. Most 3-way valves switch water flow by having the L and N terminals permanently connected. In this case, water is directed through outlet A by default, and after applying voltage to L4/L5, the flow is redirected to outlet B. When L4/L5 is disconnected, the flow returns to outlet A. Some 3-way valves, however, have two phase inputs and switch water flow depending on which phase input is powered. In this case, an auxiliary switching relay is required between the R4/R5 terminals and the 3-way valve.

An alternative defrosting function for the external unit's chassis can be set for the R1, R2, R4, or R5 outputs. To connect this function, a two-wire cable from the outdoor unit must be connected to one of these outputs. This allows control of the external unit's chassis heating, as most air conditioners are pre-set to activate this heating permanently below +2°C, which is often unnecessary and increases power consumption. More information on the connection and settings can be found in the menu 8.5 ODU heating cable.

Outdoor terminals connect the outdoor unit to the MiniHPC controller. The MiniHPC, along with peripherals connected to terminals R3, R4, and R5, is powered from these terminals. These outputs are protected by a shared 3A fuse.

Volt-Free Inputs S1 and S2

S1 is a volt-free input for connecting a flow switch sensor. This sensor activates when a preset flow rate is reached and deactivates when the flow drops below this threshold. We recommend using the flow sensor on input I1 for precise flow measurement, as it allows for calculating the heating performance and COP.

S2 is a volt-free input terminal for connecting an on/off wired thermostat. When connected, heating or cooling conditions must be modified for this input.

Do not apply any voltage to these inputs; they are designed for external volt-free switches or transistor-based switches on external energy meters with S0 output.

An alternative function for connecting an external energy meter with a digital S0 output can be set for the S1 or S2 inputs. By default, the input energy data is sent by the outdoor unit. However, this data may not be 100% accurate and does not account for the power consumption of the circulation pump or the external unit's heating. Therefore, we recommend connecting an energy meter with S0 output (e.g., DDS238-1) to the outdoor unit's power supply input, which can be connected to the S1 or S2 terminals. The selected output and pulse count per kWh are configured in the menu 7.4 input power.