Wolf WRS-K

Modbus RTU

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Last updated: 03. 2026

Wolf Official Website

The Wolf WRS-K is a commercial air handling unit (AHU) with heat recovery, controlled via the KLM-M or KLM-L controller. The optional Modbus RTU interface card plugs into the controller’s serial card slot and exposes temperature sensors, fan speed control, room thermostat, CO2 air quality monitoring, and ventilation mode switching to TapHome over RS-485.

The template requires BMS mode (Building Management System) — an initialization script automatically sets the operating mode to BMS (H:214 = 2) when the template is loaded.

Parity inconsistency — The TapHome template configures even parity, 1 stop bit (8E1), but the manufacturer specification states no parity, 2 stop bits (8N2). If communication fails, try switching to 8N2 in TapHome’s Modbus connection settings. The baud rate is 19200 in both cases.

Hardware connection

ModBus interface card

The ModBus interface card has two connections:

Connection block ① — plugs into the KLM-M (part no. 2744747) or KLM-L (part no. 2744746) controller
Terminal block ② — 3-pin pluggable connector for the RS-485 bus

The card is usually supplied pre-installed with the control unit. If retrofitted:

Isolate the KLM-M or KLM-L controller from the power supply
Remove the cover of the “serial card” slot using a screwdriver

Removing the serial card slot cover on the KLM controller

Remove the inner part of the cover with wire cutters

Removing the inner part of the slot cover with wire cutters

Insert the ModBus interface card into the free slot until the connection block clicks into place

Wolf WRS-K Modbus interface card inserted into the KLM-M controller serial card slot

Refit the slot cover
Reconnect the power supply

RS-485 wiring (terminal block)

Wolf WRS-K RS-485 terminal block pinout — GND, RX+/TX+, RX-/TX-

Connect using a 3-wire RS-485 connection via the pluggable terminal block:

Pin	Signal	TapHome connection
1	GND	GND on TapHome power supply
2	RX+/TX+	A+/D+ on TapHome RS-485
3	RX-/TX-	B-/D- on TapHome RS-485

Cable specification:

Type: AWG 20/22, screened
Max length: 1000 m

Configuration

Enabling Modbus communication

If the ModBus interface was supplied with the control unit, it is already configured. For retrofitted interfaces, configure via the BMK programming module:

Press Esc to navigate to the main menu
Select Heating contractor and press Enter
Enter password “1234” and confirm with Enter
Select Other… and press Enter
Navigate to BMS-Protocol using the up/down arrows
Press Enter to highlight, then select ModBus Slave Standard
The transfer rate is automatically set to 19200 and the BMS address to 001
Confirm with Enter, then press Esc to exit

Wolf BMK programming module display — BMS-Protocol set to MODBUS Slave Standard, 19200 baud, address 001

Modbus communication parameters

Parameter	Value
Baud rate	19200
Parity	Even (template) / None (manufacturer spec)
Stop bits	1 (template) / 2 (manufacturer spec)
Data bits	8
Slave ID	1 (default, configurable via BMK)

Modbus TCP gateway

The template uses a ModbusRtuCCU connection type but requires an IP address parameter. This means the WRS-K connects to TapHome through a Modbus TCP-to-RTU gateway (e.g., USR-TCP232 or similar RS-485-to-Ethernet converter). Configure the gateway’s IP address when importing the template.

BMS mode activation

The template’s initialization script automatically writes H:214 = 2 to set the WRS-K to BMS mode. In BMS mode, all setpoints are specified via the Modbus interface — the local BMK programming module cannot override them.

Three operating modes are available:

Value	Mode	Description
0	Manual mode	Set values from BMK module, adjustable via Modbus offsets
1	7-day program	Set values from weekly schedule, adjustable via Modbus offsets
2	BMS mode	All set values specified via Modbus — required for TapHome

The operating mode can also be changed manually via the module’s Set Operating Mode service action.

Device capabilities

Temperature monitoring

The template provides four temperature sensors, all reading holding registers with ×0.1 scaling:

Supply Air Temperature (H:1) — supply air duct temperature after heat recovery and heating/cooling stages. Includes 5 service attributes for supply air humidity (H:9), pressure (H:210), flow rate (H:212), and current setpoints. Also has 2 service actions for setting supply air flow rate and pressure from BMS.
Extract Air Temperature (H:4) — extract (return) air duct temperature. Includes 5 service attributes for extract air humidity (H:8), pressure (H:211), flow rate (H:213), and current setpoints.
Outside Temperature (H:2) — outdoor air temperature sensor
Icing Sensor (H:27) — heat recovery icing-up sensor temperature, used for frost protection

Room thermostat

Room Temperature (H:3 read, H:15 write) functions as a ModbusThermostat — it reads the current room temperature from H:3 and the current setpoint from H:11 (both ×0.1 scaling), and writes the desired temperature to H:15 (×10 scaling). A write-debounce counter prevents readback overwriting the setpoint immediately after a change.

Fan control

Supply Air Fan Speed (H:13 read, H:16 write) — dimmer control, 0–100%, ×0.1 scaling on read
Extract Air Fan Speed (H:14 read, H:17 write) — dimmer control, 0–100%, ×0.1 scaling on read
Fan Mode (H:215 read, H:222 write) — multi-value switch for fan staging:

Value	Mode
0	Fans Off
1	Fans On (single stage/variable) / Stage 1 (multi-stage)
2	Stage 2 (multi-stage fans only)
3	Stage 3 (multi-stage fans only)

Values 4–9 are defined in the template as placeholders but are not used.

Ventilation control

Fresh Air Proportion (H:12 read, H:221 write) — dimmer control for fresh air proportion, 0–100%, factor 1 (no scaling)

Air quality monitoring

Air Quality (CO2) (H:209) — CO2 concentration sensor in ppm, ×0.1 scaling. Read-only.

Service diagnostics

The module exposes 19 coil registers (C:1–C:94) and 5 holding registers as service attributes for monitoring system status:

Digital status indicators (coils):

Central Fault (C:1) — system-wide fault indicator
System Status (C:5) — standby (0) or ready for operation (1)
Operating Status (C:117) — system not in use (0) or in use (1)
Heat Source Demand (C:61) — active heating demand
Enable or Pump, Heat Recovery (C:62) — heat recovery enabled/running
Outside/Supply Air Damper (C:63) and Exhaust/Extract Air Damper (C:64) — damper positions
Pump, Hot Water (C:60) and Pump, Cold Water (C:18) — pump status
Various adiabatic cooling valves and convector heater status indicators

Analog status indicators (holding registers):

Current Set Absolute Humidity (H:24) — absolute humidity setpoint in g/kg
Cooling Source Demand, Stage 1/2 (H:220) — cooling demand stage
Electric Heater Bank Stage (H:232) and Direct Evaporator Stage (H:233) — current stages
Heat Pump Operating Mode (H:255) — not enabled / heating / cooling (requires WRS-K software v3.0+)

Module service actions:

Set Absolute Humidity Setpoint — writes H:26 for BMS humidity control
Set Operating Mode — switches between Manual (0), 7-day program (1), and BMS mode (2)

Additional capabilities

The WRS-K also exposes registers for room air humidity, supply air temperature setpoint, heating/cooling/heat recovery actuating signals, and humidifier control. Additional offset registers allow fine-tuning setpoints in Manual and 7-day program modes. The alarm system covers over 60 fault conditions including fan inverter faults, filter contamination, fire damper status, frost protection, and sensor failures. These can be added in a future template update.

Troubleshooting

No Modbus communication

Check RS-485 cables — verify pin 2 (RX+/TX+) connects to A+/D+ and pin 3 (RX-/TX-) connects to B-/D- on TapHome
Check GND — pin 1 must be connected to the TapHome power supply ground
Verify parity settings — the template defaults to even parity, but the manufacturer specification states no parity. Try both configurations
Confirm baud rate — must be 19200 on both sides
Check the Modbus TCP gateway — verify the gateway IP address and that it forwards RTU frames correctly

Fan speed or temperature not responding

Verify BMS mode is active — the initialization script sets H:214 = 2 automatically, but verify via the BMK module display (should show BMS mode)
If in Manual or 7-day mode, TapHome can only adjust values via offsets — full control requires BMS mode
Check the write-debounce — after changing the room temperature setpoint, the thermostat ignores readback for approximately 55 polling cycles to prevent immediate overwrite

Fan Mode values 4–9

Values 4–9 in the Fan Mode device are placeholder entries in the template and should not be used. Only values 0–3 are valid for the WRS-K. Setting values above 3 may produce undefined behavior.

Available devices

Wolf WRS-K Module

Service Attributes

Central Fault
External System Enable
Hygrostat Humidity
Humidifier Enable
System Status
Operating Status
Pump, Hot Water
Pump, Cold Water
Heat Source Demand
Enable or Pump, Heat Recovery	reads C:62 (Bool); 0=off, 1=enabled/running
Outside/Supply Air Damper
Exhaust/Extract Air Damper
Enable Gas Valve
Enable or Pump, Adiabatic Cooling	reads C:87 (Bool); 0=off, 1=enabled/running
Enable Convector Heater (WO)	reads C:89 (Bool); 0=disabled, 1=enabled
Thermostat, Convector Heater (WO)	reads C:90 (Bool); 0=inactive, 1=active
Water Supply Drain Valve, Adiabatic Cooling	reads C:91 (Bool); 0=closed, 1=open
Pan Drain Valve, Adiabatic Cooling	reads C:92 (Bool); 0=closed, 1=open
Inlet Valve, Adiabatic Cooling	reads C:94 (Bool); 0=closed, 1=open
Current Set Absolute Humidity
Cooling Source Demand, Stage 1/2	reads H:220 (Int16); cooling source demand stage indicator
Electric Heater Bank Stage
Direct Evaporator Stage
Heat Pump Operating Mode	Heat pump mode — Not enabled, Enable heating, Enable cooling (requires WRS-K software v3.0+)

Service Actions

Set Absolute Humidity Setpoint

Set Operating Mode

Wolf WRS-K

Read (module)

#var i := 19;

#WHILE i < 98
# var ans := modbusr(H,i,bool);
# if ans = False
#  addwarning("Chyba na pozicii " + i);
# end
# i := i + 1;
# LOOP
 #return("")

Service Attributes

Zberna porucha

modbusr(C,1,bool)

Externé uvoľnenie zariadenia

modbusr(C,2,bool)

Hygrostat. vlhkosť

modbusr(C,3,bool)

Uvoľnenie zvlhčovača

modbusr(C,4,bool)

Stav zariadenia

modbusr(C,5,bool)

Prevádzkový stav

modbusr(C,117,bool)

Čerpadlo vykurovania

modbusr(C,60,bool)

Čerpadlo chladenia

modbusr(C,18,bool)

Požiadavka na zdroj tepla

modbusr(C,61,bool)

Uvoľnenie alebo čerpadlo rek. tepla

modbusr(C,62,bool)

Klapka vonk./prívodu vzduchu

modbusr(C,63,bool)

Klapka odp./odvodu vzduchu

modbusr(C,64,bool)

Uvoľnenie plynového ventilu

modbusr(C,65,bool)

Uvoľnenie alebo čerpadlo adiabatického

modbusr(c,87,bool)

Uvoľnenie ohrievača vzduchu (WO)

modbusr(C,89,bool)

Termostat ohrievača vzduchu (WO)

modbusr(c,90,bool)

Vypúšťací ventil prívodu vody adiab. chladenia otvorený

modbusr(C,91,bool)

Vypúšťací ventil vane adiab. chladenia otvorený

modbusr(C,92,bool)

Ventil prívodu vody adiab. chladenia otvorený

modbusr(c,94,bool)

Aktuálna pož. hodnota absolútnej vlhkosti [g/kg]

modbusr(H,24,int16)*0.1

Požiadavka na zdroj chladu stupeň 1/2

modbusr(h,220,int16)

Stupeň el. ohrievacieho registra

modbusr(h,232,int16)

Stupeň priameho výparníka

modbusr(h,233,int16)

Prevádzkový režim tepelného čerpadla

modbusr(h,255,int16)

Service Actions

Zmena pož. hodnoty abs. vlhkosti [g/kg]

Parameters: paramater (1–10000 p)

modbusw(H,26,int16,p/10)

Nastavenie prevadzkoveho rezimu

Parameters: Parameter1

modbusw(H,214,int16,Abr1)

Fresh Air Proportion Dimmer

Fresh air proportion control — adjustable 0–100%

Air Quality (CO2) Variable Read-only

CO2 concentration sensor in ppm for indoor air quality monitoring

Extract Air Temperature Temperature Sensor Read-only

Extract air duct temperature with humidity, pressure and flow rate service attributes

Service Attributes

Extract Air Humidity

Extract Air Pressure

Extract Air Flow Rate

Current Set Pressure, Extract Air

Current Set Flow Rate, Extract Air

Extract Air Temperature

Read temperature

MODBUSR(H, 4, Int16) * 0.1

Service Attributes

Vlhkosť odvodu vzduchu [%r.H.]

modbusr(H,8,int16) * 0.1

Tlak odvodu vzduchu [Pa]

modbusr(h,211,int16)

Objemový prietok odvodu vzduchu [m³/h]

modbusr(h,213,int16) * 10

Aktuálna pož. hodnota tlak odv. vzduchu [Pa]

modbusr(h,217,int16)

Aktuálna pož. hodnota prietok odv. vzduchu [m³/h]

modbusr(h,219,int16)

Extract Air Fan Speed Dimmer

Extract air fan speed control — adjustable 0–100%

Extract Air Fan Speed

Read level

var ret := MODBUSR(H, 14, Int16) / 1000;
counter := counter - 1;
if counter <= 0 or ret = Le
    return(ret);
    
else
    return(LE);
end

Write level

counter := 55;
MODBUSW(H, 17, Int16, Le * 1000)

Supply Air Fan Speed Dimmer

Supply air fan speed control — adjustable 0–100%

Supply Air Fan Speed

Read level

var ret := MODBUSR(H, 13, Int16) /1000;
counter := counter - 1;
if counter <= 0 or ret = Le
    return(ret);
    
else
    return(LE);
end

Write level

counter := 55;
MODBUSW(H, 16, Int16, Le * 1000)

Room Temperature Thermostat

Room thermostat — reads current and desired temperature, writes setpoint to BMS register

Room Temperature

Read temperature

MODBUSR(H, 3, Int16) * 0.1

Read desired temperature

var ret := MODBUSR(H, 11, Int16) * 0.1;
counter := counter - 1;
if counter <= 0 or ret = Se
    return(ret);
    
else
    return(Se);
end

Write desired temperature

counter := 55;

MODBUSW(H, 15, Int16, Se * 10);

Supply Air Temperature Temperature Sensor Read-only

Supply air duct temperature with humidity, pressure and flow rate service attributes

Service Attributes

Supply Air Humidity

Supply Air Pressure

Supply Air Flow Rate

Current Set Pressure, Supply Air

Current Set Flow Rate, Supply Air

Service Actions

Set Supply Air Flow Rate

Set Supply Air Pressure

Supply Air Temperature

Read temperature

MODBUSR(H, 1, Int16) * 0.1

Service Attributes

Vlhkosť prívodu vzduchu [%r.H.]

modbusr(H,9,int16)

Tlak prívodu vzduchu [Pa]

modbusr(h,210,int16)

Objemový prietok prívodu vzduchu [m³/h]

modbusr(h,212,int16)

Aktuálna pož. hodnota tlak prív. vzduchu [Pa]

modbusr(h,216,int16)

Aktuálna pož. hodnota prietok prív. vzduchu [m³/h]

modbusr(h,218,int16)

Service Actions

Zmeň pož. hodnotu prietoku prív. vzduchu [m³/h]

Parameters: parameter (1–10000 par)

modbusw(h,225,int16,par*10)

Zmeň pož. hodnotu tlaku prív. vzduchu [Pa]

Parameters: Parameter (1–10000 par)

modbusw(h,223,int16,par)

Icing Sensor Temperature Sensor Read-only

Heat recovery icing-up sensor temperature for frost protection monitoring

Fan Mode Multi-value Switch

Fan stage selector — Off, On/Stage 1, Stage 2, Stage 3 for multi-stage fans

Values / States: Ventilátor vypnutý · Ventilátor zapnutý · Ventilátor stupeň 2 zapnutý (viacstupňové ventilátory) · Ventilátor stupeň 3 zapnutý (viacstupňové ventilátory)

Fan Mode

Read switch state

var ret := MODBUSR(H, 215, Int16);
counter := counter - 1;
if counter <= 0 or ret = Mu
    return(ret);
    
else
    return(Mu);
end

Write switch state

MODBUSW(H, 222, Int16, Mu);
counter := 55;

Outside Temperature Temperature Sensor Read-only

Connection: Modbus RTU • 19200 baud• 8E1 • Slave ID: $[SlaveId]

Possible improvements (18)

H:5 Air Quality (Mixed Gas) — Air quality mixed gas sensor, factor 0.1, unit V
H:6 Set Room Transducer — Set room transducer temperature, factor 0.1, unit °C
H:7 Room Air Humidity — Room air humidity, factor 0.1, unit %r.H.
H:10 Current Set Supply Air Temperature — Current set value supply air temperature, factor 0.1, unit °C
H:23 Current Set Relative Humidity — Current set value relative humidity, factor 0.1, unit %r.H.
H:28 Actuating Signal, Heating — Heating actuating signal, factor 0.1, unit %
H:29 Actuating Signal, Cooling — Cooling actuating signal, factor 0.1, unit %
H:30 Actuating Signal, Heat Recovery — Heat recovery actuating signal, factor 0.1, unit %
H:31 Actuating Signal, Humidifier — Humidifier actuating signal, factor 0.1, unit %
H:32 Extract Air Temp After Humidifier — Extract air temperature after humidifier for adiabatic cooling, factor 0.1, unit °C
H:33 Actuation Signal, Reheating — Reheating actuation signal, factor 0.1, unit % (requires WRS-K software v3.0+)
H:25 Set Relative Humidity from BMS — Write relative humidity setpoint from BMS, factor 0.1, unit %r.H.
H:221 Set Fresh Air Proportion from BMS — Write fresh air proportion from BMS, factor 1, unit %
H:224 Set Pressure, Extract Air from BMS — Write extract air pressure setpoint from BMS, factor 1, unit Pa
H:226 Set Flow Rate, Extract Air from BMS — Write extract air flow rate from BMS, factor 10, unit m³/h
H:18 Offset Set Temperature — Temperature offset for manual/7-day modes, factor 0.1, unit K
H:19 Offset Set Speed, Supply Air Fan — Supply air fan speed offset for manual/7-day modes, factor 0.1, unit %
H:20 Offset Set Speed, Extract Air Fan — Extract air fan speed offset for manual/7-day modes, factor 0.1, unit %

Download Template

Sources

Wolf WRS-K Modbus Interface — Installation and Operating Instructions
wolf.lt 2026-03-20
PDF