HI Josip,

I started a new thread to continue the discussion on system design and maintenance..

I have seen a lot of systems being sold to owners that are supposed to be "energy efficient". Here is a highlight of the last one I heard about: Single suction pressure maintained by 4-5 big screw compressors (1000 HP +, +/- 750 kW) each.

Back pressure regulator valves on all of the higher temperature evaporators. Condensing temp. = 95F (35C) design for summer.

Most of the evaporators are operating at much higher temperatures than the lower suction pressure was being maintained at. The compressors were sized to operate at the low suction pressure for a very small percentage of the total loads.

The owner was told this is the most efficient system they could buy. So they did. Now they are beginning to wonder if it was true. Several big screws operating at part load!

To me this system falls in the category you labeled #1. Cheap for first installed costs. Expensive to run.

A much better job of engineering could have been done but... This seems to be the way most systems are being sold.

I think if the owners were more aware (and better informed) of the differences in operation and first installed cost they would make different decisions.