A domestic hot water (DHW) circulation pump driven by a variable frequency drive (VFD, Russian abbreviation ПЧВ) often does not need an external controller: many drives embed a small programmable logic function, exposed through a parameter group labeled "PLC." In the referenced application, that logic lives in parameter Group 13. This reference explains what that group is, how it fits a DHW circulation pump, and how to configure and verify it.
What the PLC Parameter Group Is
Parameter group numbering is vendor- and firmware-specific. Group 13 being the "PLC" group applies to the drive in the referenced application only — on another manufacturer or firmware revision the same function may sit under a different group number or be called "simple PLC," "sequence operation," or "user logic." Before changing anything, open the drive's parameter manual and confirm which group carries the internal PLC function and which firmware it applies to. The group typically contains the enable/selection parameters, step or block definitions (run times, conditions, frequency setpoints per step), and the inputs the logic can read, such as digital inputs, analog feedback, and internal timer values.
Architecture for DHW Circulation Control
The control objective for a DHW circulation pump is to keep hot water available at the draw points without running the pump continuously at full speed. The drive's internal PLC can implement this locally using two evidence-neutral building blocks: time-based operation (run/stop windows, e.g., circulation only during occupancy hours) and feedback-based operation (start or speed up when a temperature sensor in the return line reports water below the acceptable threshold, stop or sleep when the loop is up to temperature). Wiring the return-line temperature sensor to one of the drive's analog inputs removes the need for an external PLC, thermostat contactor, or additional I/O.
Configuration Sequence
- Identify the drive's internal-PLC parameter group from the manual (Group 13 on the referenced unit; verify the number for your model and firmware) and enable the function with its selection/enable parameter.
- Assign the feedback source: map the return-line temperature sensor to an analog input and scale it in the input's parameter set so the logic reads engineering units.
- Define the run conditions in the PLC parameters: the schedule windows and/or the temperature threshold at which the pump starts, and the condition at which it stops or drops to minimum speed.
- Set the frequency limits the logic is allowed to command (minimum speed that still guarantees circulation, maximum per the pump's rating) so the internal PLC cannot drive the pump outside its operating envelope.
- Verify with the pump coupled: confirm the drive starts, stops, and changes speed exactly at the configured schedule times and temperature thresholds, and that the run status and output frequency shown on the keypad match the logic state.
FAQ
What is parameter Group 13 on a VFD?
On the drive in the referenced DHW application, Group 13 is the internal PLC parameter group — it holds the enable, step, and condition parameters for the drive's built-in logic. Group numbering is manufacturer- and firmware-specific, so confirm the PLC group's number in your drive's parameter manual before configuring.
Can a VFD run a hot water circulation pump without an external PLC?
Yes, if the drive includes an internal PLC or sequence function. Configure time-based run windows and a temperature threshold from a return-line sensor wired to an analog input, and the drive starts, stops, and modulates the pump locally.
How do you verify the VFD internal PLC logic on a pump?
Run the system coupled and compare behavior against configuration: the drive should start and stop at the programmed schedule times and temperature thresholds, and the keypad's run status and output frequency must match the active logic state.
