part load in evaporator and condenser

[wta12]

I still don't fully understand because you neither describe your system correctly nor the problem.

One method to keep a minimum condensing pressure is a Head Pressure Control that lets you flood the condenser with refrigerant and simultaneously (if necessary) pressurize the liquid receiver. For this array to work you also need a correctly sized liquid receiver.

You can get information on these types of valves from the manufacturers and lots of help from posts here.

My schematic in left of photo
_revers_vody.jpg
. We use for water cooled screw chiller with dry cooler. evaporator water in/out 12/07oC, condenser water in/out 45/50oC. in cooling mode we use chilled water from evaporator (keep the leaving evaporator water temperature), condenser connect to dry cooler. In heating mode, use water from condenser and evaporator connect to dry cooler (keep the leaving condenser water temperature).
My situation like this the entering evaporator water temperature often lower than designed at part load. So i want unloading (reducing capacity) chiller but the ambient temperature still high so the condensing pressure/temperature need be keep high enough. So how to unloading chiller in this case with the refrigerant cycle control ?
Thanks