Two speed fan
 

I have a question..
The majority of machines I have hacked to convert to heat pumps have had single speed condenser fans. I have just 'inherited' two Fuji 7kW machines that have 2 speed fans.

My question is why two speed? What is the advantage of running the fan at a lower speed? Just energy saving?

Many of the non-inverter units have a "low noise" mode that runs both the indoor and outdoor unit fans slower. This is sometimes used in "economy mode" as well. In low noise mode, the compressor usually runs full out on demand, but in economy mode, it runs for some amount of time before timing out for a few minutes and then restarting. Some of the stuff has a setpoint profile built in as well, where the moving parts cycle depending on fuzzy logic.

Ok, thanks, that makes sense. The machine was one with conducts and the control panel does have an 'Energy save' button so I guess that's what it was for.

It doesn't sound like I need to implement the 2 speed strategy as I'm doing air to water so no inside noise and I want to reject as much cold (or heat in the summer) as possible. I'll leave it running full speed.

Some of those two speed systems employ techniques to lower that output of the scroll compressors even though they are running at full RPM. One method I remember is the medium pressure port.

The low speed option does increase efficiency since it lowers the number of cycles but more importantly is the increase in comfort since there is less temperature swings.

Some commercial units slow down the condenser fan if cooling is still needed at lower outdoor temperatures.