The RTD-20 is for control of AHU DX Heating and Cooling Coils: The RTD-20 ERQ operation mode gives a linear 0-10 VDC capacity control of the range of ERQ condensers for cooling and heating coils within air handling units (AHU). Simultaneous control with Modbus is possible.
Overall system set up
The BMS system will consist of a DDC (Direct Digital Controller) controller, a sensor and the RTD-20 to control the demand level of the AHU:
- With the DDC controller and the temperature sensor a PI loop is implemented which outputs the Voltage to the RTD-20 input S3.
- The PI loop uses a setpoint and the temperature sensor as inputs.
- The output of the loop should be scaled to the 0 - 10VDC range.
- The output is wired to the S3 input of the RTD-20 interface.
- '0' VDC will run the ERQ condenser at minimum capacity (30% demand), 10 VDC at maximum capacity.
- Sensor:
- Neither R1T nor the BRC remote controller's space sensor are used for control of the DX coil.
- Instead an air sensor located in the supply, conditioned space or return path is used.
- This is why at start-up of the RTD-20 (which must be set as MAIN P1P2 device) the field setting 10(20)-02-03 is automatically written by the RTD-20.
- The value 10-2-03 means that the unit is controlled from the MAIN remote controller sensor. The RTD-20 is the MAIN remote controller in this configuration and generates a simulated temperature.
- Based on the input Voltage at S3 the RTD-20 generates a simulated setpoint value which is sent to the AHU in order to generate the required capacity from the coil
In summary, you require a DDC controller with a Setpoint and a Temperature Sensor as inputs to a PI loop, with the output of the loop scaled to a 0-10V that is wired to input S3 of the RTD-20 in ERQ mode.
Which EKEQ control box to use?
The RTD-20 can be used with control boxes EKEQMCBA and EKEQDCBA. Please contact Daikin Technical Support for further information on which control box suits your requirements and how many RTD-20 interfaces you need for your application.
Installation
Please see the article How to install the RTD-20, as well as the details below.
DIP switches
- DIP switches 1 and 2 must be in On position.
- DIP switch 3 must be in Off position.
- DIP switch 4 can be either in On or Off position:
- Off: Relay R1 closes on Unit Running
- On: Relay R1 closes on Unit Defrost
DIP switches 5 - 8 must be set if a Modbus network address is required, otherwise they can be left in Off position.
*Note: The RTD-20 in ERQ mode does not have an Interlock mode like the RTD-10 interface.
P1P2 network
In ERQ mode the RTD-20 acts as MAIN P1P2 remote controller. Therefore only one RTD-20 can be connected.
Please note that the RemCon must be configured as SUB P1P2 device. For information on configuring as MAIN/SUB P1P2 device please see the article How to switch the RTD interface to P1P2 Main or P1P2 Sub device .
Modbus
For control with Modbus please use the Modbus Holding Registers listed in the attached RTD-20 instructions.
For monditoring please use the listed applicable Input registers in the attached RTD-NET installation instructions.
Note that a non-zero value in Holding Registers H8001-H8004 overrides only the respective (physical) input.
Input registers In10001 - In10006 can be useed the to read values of analogue inputs S1-S6.
Inputs S1 - S6
The functions and Voltage ratings for inputs S1 - S6 are listed in the RTD-20 installation instructions on pages 4 and 19.
S3: 0V at S3 will run the ERQ condenser at minimum capacity (30% demand).
- Important: Please note the maximum allowed power rating listed in the RTD-20 installation instructions on page 4 (Maximum Rating 12VDC).
S4: Pull -Down mode: This mode enables the unit to decrease it's minimum evaporating temperature in cooling. Pull-down mode simply increases cooling output capacity by about 30%.
S5: External Mode Source: Closing input S5 of the RTD-20 in ERQ mode only allows for manual heat/cool changeover with the BRC (the other BRC functions are completely locked), or via the heat/cool A/B/C terminals on the outdoor unit or BS box.
- Note that the BRC hast to be in SUB P1P2 mode.
How to control the condenser
To set the capacity of the ERQ condenser you need to use either input S3 of the RTD-20 or Modbus.
Custom Case Solutions: What if...?
Q: You have a BMS controller with only four available outputs and need to use it to control 4 stages of heat pumps with 4 ERQ RTDs. Therefore, you can only enable, but not increase demand. Is there a solution with which to can enable, rotate and set demand according to your needs?
A: There are 3 options to fulfill your requirements.
a) Apply external power on S3 (in case you want to have constant demand)
b) If you want to control your demand, then connect:
Output1: Stage1 & Stage2
Output2: Stage3 & Stage4
Output3: Heating enable (for all stages)
Output4: Demand S3 for all stages (output configured as analog)
c) You can use following non-standard solution: With your current wiring, change Default Demand by writing Holding Register 11205 through Modbus. Values: 300=30%, 1000=100% (writing Default Demand can be done only once). Apply Default Demand by short circuit on input S6. When there is short circuit on S6, setting the Demand through input S3 is disabled. Open circuit on S6 will enable input S3 again.