In a strawberry frozen plant using a ammonia system. It has one compressor, one evap condenser and a ammonia separator which has two pump to over-feed a helicoidal frozen tunnel.

The Te= -20ºc, Tc= 20ºC

The tunnel normally works at 50% of its capacity so does the compressor and some time the refrigeration load goes to 0% due to the lack of strawberry, and compressor stop

I though to install a hotgas by pass between receiver and compressor to keep it working .

However some friends of mine recommend a Variable Frequency Device (VFD) for that application.

What do you recommend me?