I also wanted to add some other thoughts. I feel the system should be designed to work efficiently under all of the operating conditons; summer/winter & full load/part load.

All too often I see systems designed for the worse case (summer & full load) with little regard for the other conditions.

The way I see it, the systems should be designed for efficient operation all of the time, not just at one point.

Any control system used should simply provide the means to sustain the optimum operating conditions during those periods, and as loads change.