When I try to fix a fusion reactor's efficiency to 100, I need exact -5000K/t to cancel the tempChange. However, liquid helium is cooling at 52800 mB/t and the flow rate should be 0.09469697mB/t. The gate in DE or controller in IC2 fails with such a number(1.89394mB/s, but IC2's controller can only do 2 or 1 mB/s). So there should be some way to deal with such a precision.

Hey there - unfortunately I'm not sure that sort of thing is possible. If the cooling rate is too high, all I can recommend is to use different, less powerful coolers - most of the time you won't need much more than water.

The active cooling as it is now is not super well designed, and will defo change in the future.