Simulation for optimizing timing in unit operation

[alexpwns]

Looking for input on best way to approach this problem:

I have 9 manufacturing units (A-G) that require downtime for maintenance based on there total throughput since last maintenance. This total throughput varies between the 9 units. I have a set total rate I have to maintain through the operation as a whole (this should be modifiable if needed), and my manufacturing units can adjust their flow rates based on how many units are available (not in downtime). Finally, the 9 units are split into 3 groups, and no more than 1 unit from a specific group can have productive downtime (as in, maintenance) at a time. The flow rate through all the units is the same, and its automatically determined based on number of available and running units and the total flow rate needed.

The attached spreadsheet has the information on which units belong to which groups, the total required flow rate, the time for maintenance, the throughput set point for each unit (at which point the unit must go down), and the maximum flow rate through the units.

The variable I'm able to play with right now is when I put the unit back online (I can keep a unit down after maintenance is complete), in order to maintain adequate spacing between when units have to go down for maintenance so I have at least 7 units online most of the time (let's say 90% of the time).

This problem becomes trivial if my total throughput set points are the same for all 9 units, e.g. set at 630000 gallons, then I just have to maintain a distancing of 88200 gallons between units to keep 7 units online. This works out to minimize downtime, so means that as one unit is coming out of maintenance, another would be going into maintenance soon after.
With the maximum throughputs before maintenance different now though, I'm trying to solve what throughput spacing I want to maintain.

I was toying with the idea initializing this with some data at a given date/time, and then allowing the user to enter a "Current Date/Time (MM/DD hh:mm)" at which point the current state of each individual unit would be determined (its current throughput, time since brought online, time until maintenance reqd etc) would be calculated.

Any feedback would be appreciated.

[Metaldrgn]

for me it says the file is corrupt.