Hi Ian.
This is what Samsung Tech Support emailed me in response to several questions (my emphasis):
On 17/11/2023 17:27, Aftersales Technical Support wrote:
Hi Sarah,
Thanks for the email.
Thermo on / off hysteresis for WL flow temperature is around 2K, this combined with an anti-restart timer of around 5 minutes will dictate the off state time before the heat pump starts again.
The 405* FSV’s are for a PWM circulation pump, it’s called inverter pump in the FSV list, it’s a type of water circulation pump that can be used on the system that will modulate the flow rate slightly in heating mode. It doesn’t relate to inverter control in the heat pump sorry.
The minimum turn down for your unit 4KW.
Best regards
Nick Kirwan
I guess I took his word for the 50% turndown (my ASHP is 8kW), and I don’t have any fancy monitoring equipment to verify inverter frequencies, but I believe him because I’ve never seen sustained thermal duty (as calculated from Q = m * Cp * deltaT on the circulating fluid) below about 4kW, or compressor power consumption below about 50% of the figures in the Samsung capacity tables (EHS Technical Data Book).
The one thing I would retract is my comment that at turndown the compressor has a poorer effieciency. This was based on early observations (I don’t have performance curves for the DS2BB5033FVA), but data from several subsequent test runs suggest that there is little change in efficiency across the speed range (no more than a few %).
Maybe the 16kW unit behaves differently?