I wonder if the buffer tank should move to the retrun side of the chiller, and the chiller draws from the top and loop return is to the top, but the bypass is to the bottom of the tank. That way you get the warmest water to the chiller most of the time even when below minimum load.

I assume to lengthen minimum cycle times you might run the chiller to start at 44-45F and shut off at 40F.