Commissioning: The Eternal DID (August 2000)
DID overviewAs a summary of last month, the DID is the definition of how the owner expects the building systems (hvac, for example) to perform upon completion of the project. It represents the objectives of the project from a systems performance standpoint and is intended to improve communications and keep designers, the owner, contractors, commissioning consultant, O&M staff, etc., working towards a common goal.
Either by direct inclusion or by indirect exclusion, the DID can also be used to document what the systems are not intended to do. For example, if offices are to be cooled to 75˚F, it can be assumed that no one should expect them to be able to cool to 72˚ under design conditions. Similarly, if a space is to be ventilated at the rate of 0.25 cfm/sq ft, it should be understood that the systems cannot provide 0.5 cfm/sq ft of outside air.
Consult the DID OftenThis interpretation of the DID will be particularly useful to the operators of the building systems after the contractors have left the site. If the O&M staff understands what the systems where intended (and not intended) to do, then they can more intelligently address occupant complaints. For example, if an occupant complains because the hvac system cannot provide him with a 68˚ space, the O&M people can look up the DID and find out that the space temperature design criteria was 75˚. They need to tell the occupant that the system is incapable of achieving the desired condition, and that, if the occupant has a problem with that, he should bring it up with the building owner who set the design criteria.
It is not the O&M personnel’s responsibility to apologize for design decisions or to “fix” systems that are not broken. Too many building systems, especially hvac, become all messed up after years of the O&M staff trying to meet various occupant requirements by “tweaking” the system out of balance and out of control. The DID can be a tool that helps them maintain the building systems as intended and not try to “squeeze” more out of the systems than can be expected.
The DID can also be used by future renovation design teams to understand the “existing” systems and to be sensitive to their limitations and control system operation requirements. This is beneficial to the building owner in a couple ways. First, the design team will have to spend less time (and less of the owner’s money) searching for information about the original design intent and trying to read the minds of the long-gone original design engineers. Second, the new systems or modifications to the existing systems designed by the renovation engineers will be less likely to disrupt or change the proper operation of the systems.