Coordination drawings are the insurance to the HVAC design engineer that the contractor has a well thought out plan for the installation of all the specified HVAC equipment in locations that allows all the above ceiling systems to work correctly. Whew, what a mouth full!
What this means is that the routing and installation locations of the above ceiling systems do not conflict with the routing and installation of all the other systems such as ductwork, roof drains, hot water piping, sprinkler piping, electrical cable trays, electrical conduits, etc. The concept is enormous and typically is done in a wide brush method during the design of the project. All engineers know that the equipment fits perfectly on paper but when the project is out for bid, all of the bidding contractors take the most economical routing for their particular system.
Remember, most projects are awarded on low bid, not on best value. The sprinkler contractor may bid the project assuming pipe runs in the middle of the hall and the HVAC contractor may do the same with his ductwork, setting up the conflict of two things desiring to occupy the same space at the same time. Most of these arguments are settled on the first come basis. Let the sprinkler man do his work first and his piping is in the middle of the hall and vice-versa if the HVAC contractor gets there first.
Back in the day, it was the general contractors responsibility to assure that the systems were fully coordinated and conflicts were minimized. Today, we have a different breed of general contractor that downs the responsibility to the trade contractors or just does not have the experience to know how to put it all together. In their defense, we are all doing more in less time, but that is not me offering an excuse, it is me knowing how the real system works. Too often the general contractor will just issue a directive to “make it work” not knowing the ramifications of such an open ended statement.
So much building construction follows the ready-fire-aim principle that when a more complex project comes along (such as hospital/medical design), chaos follows. Piping or ductwork that could run at the bottom of the joists runs in the middle of the ceiling space effectively creating dead spaces above it which in turn forces the other contractor to relocate or modify his system to suit. The pipe-through-duct detail comes to mind immediately.
Most HVAC design engineers will revert back to the coordination drawing submittal. The equipment designed into the building is rarely the equipment provided by the low-bid contractor. In rare instances, the owner dictates that the general contractor, major sub-contractors and engineers meet at predetermined intervals to discuss the construction progress and iron out any potential conflicts before, not after the fact. A tip of the hat to the wise owner for spending the money to make sure all above ceiling systems are fully coordinated.
Perhaps others in the building industry have different methods to work around this. If so, comment below.