If the secondary flow is greater than the primary flow the return from the loads will mix with the supply from the chillers. This will raise the temperature of the supply water to the loads. This doesnt seem like a good thing.
I always thought the primary should be more than the secondary. Some engineers like a check valve in the decoupler that will not allow the secondary flow to be greater than the primary.
While in a common sense world I would agree with you, however, with some of today's systems and controls schemes things have really been set outside the box.
The one I did recently had two chillers, building divided into two separate loops and all tied together using four pumps. Basically with three way valves at the control level, I can literally run both building sections on a mild day with less than half of one chiller.
The return water temperature sensor controlling the chillers is literally in the decoupling run. This creates a blended return temp of both buildings and it's reset by building total load (using a return water sensor for each building section). The energy used for cooling has dropped in half and the second chiller seldom runs for more than a few hours on the warmest of days.
The system used to be one chiller, one building section with a single pump with full flow going to each chiller/building section.... Ran that way for 12 years. I replaced one of the 40 ton air cooled chillers and talked them into piping it this way and never looked back.
Don't get me wrong, I see your point, but it is not that "cookie cutter" anymore.
I could tell you about the 20 ton FHP system we did, but you wouldn't believe that it actually works and I am too tired to try and explain it right now....:couchhide:
