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The Design Intent Document Lives On

Last month this column described the design intent document (DID) and how it is the backbone of the commissioning process. A good DID, however, can have great value beyond the life of the design and construction project. It can be an invaluable operations and maintenance (O&M) reference throughout the life of the systems.

As 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 everyone on the team, i.e., designers, owner, contractors, commissioning consultant, operations and maintenance 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 75oF, it can be assumed that no one should expect them to be able to cool to 72oF under design conditions. Similarly, if a space is to be ventilated at the rate of 0.25 CFM/ft2, it should be understood that the systems can not provide 0.5 CFM/ft2 of outside air.

This 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 understand 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 can not provide him with a 68oF space, the O&M people can look up the DID and find out that the space temperature design criteria was 75oF. They need to tell the occupant that the system is incapable of achieving his 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 nor 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.

The DID, therefore, is a dynamic document needing maintenance and updating not only during design and construction but during the life of the building as well. The commissioning consultant is often the “keeper” of the DID during design/construction, but the owner should consider assigning someone else to continue maintaining and updating the document through all of the inevitable renovations and additions. This building “history” can be a valuable asset when it comes time to transfer ownership of the building.

Finally, in order for the DID to “live on,” the operations and maintenance staff need to be trained on what it contains and how it can be used. This is non-traditional training that is typically conducted during the construction phase by the commissioning agent but should, if at all possible, include the design engineers as well. On-going training for the O&M staff is also critical. Handing new employees a copy of the DID for a building would be a great way to introduce them to their new “home.”

 

COMMISSIONING: GETTING IT RIGHT

Engineered Systems, August, 2000

Rebecca Ellis, PE, LEED AP, CCP, CxA
President
Questions & Solutions Engineering
1079 Falls Curve
Chaska, MN  55318
rteesmag@QSEng.com