TAKING PART OF A SYSTEM OFF-LINE DOESN'T HAVE TO GET OUT OF HAND.
As with last month, I'd like to introduce a new commissioning term, which isn't exactly mainstream in the commercial and institutional building industry. This time, the word of the month is decommissioning.Although a rigorous process of decommissioning has been standard operating procedure for a number of years at the Pentagon Renovation Program, I have otherwise only heard of it with respect to nuclear power plants, naval vessels, and some industrial installations.
PLANNING FOR DECOMMISSIONING
In very simplistic terms, the decommissioning process, in these applications, is about removing something from service while minimizing/eliminating danger to people and the environment. The same can be said for building systems. When it comes to permanently demolishing existing building systems, including boilers, chillers, air-handling systems, air conditioners, etc., current industry practices are well defined and reasonably enforced, especially with respect to hazardous materials handling and disposal.However, there is very little in the way of standard procedures with respect to partially removing a system from service, either permanently or temporarily. In the case of facility renovations, construction phases (even if there is only one phase) are more often defined by architectural features and/or tenant operations than by building system boundaries. On one side of a construction barrier is a fully functional owner operation (office, classroom, laboratory, patient room, etc.), while on the other side is full-blown construction. This leads to the common scenario of having to maintain "normal" operation of part of an existing building system while removing another part from service.
This may apply to all building infrastructure systems: HVAC, plumbing, electrical power, lighting circuits, fire protection, etc. An HVAC example is when a portion of the area served by a constant volume, terminal reheat air-handling system is under construction while the rest is not. If the AHU is located outside of the construction zone, the construction zone needs to be isolated from the supply and return duct system. In order to maintain "normal" operation in the occupied zones, what happens with the "excess" air no longer needed by part of the building?
A different twist on the HVAC scenario is when the AHU is located within the construction zone but also serves areas outside of the construction zone. The construction zone still needs to be isolated from the system ductwork, while the main supply and return ducts to the un-renovated spaces from the AHU need to remain intact throughout construction. The impact of construction on the outside air intakes should also be considered.
VAV systems offer some flexibility with respect to adding/subtracting zones without causing major upheavals to the system as a whole. However, care must still be taken to ensure that control panels stay "alive," and communication between active terminal units and the AHU remain operational to properly serve the occupied spaces. Conversely, construction zone terminal units should be prevented from influencing the operation of the central air handler.
PHASING OUT GRACEFULLY
The process of decommissioning is all about thinking through, planning for, and documenting these issues before construction starts, not after there is a problem with the occupied zones at the start of construction. Logically, the results of the decommissioning effort should be part of the phasing plan for a project. What systems modifications are required before construction can commence for each phase of the project? Are system bypasses required to avoid the construction zone altogether, e.g., rerouted piping, ductwork, or conduit? What special monitoring and/or control systems should be in place to verify safe and satisfactory operation of the affected systems for the occupied zones? In some cases, decommissioning should be a phase (or multiple phases) of its own in the construction schedule.The HVAC system examples will ring true for most building owners and contractors. Other issues that may be less obvious but no less problematic if not thoughtfully addressed include fire protection (sprinkler) mains that pass through the construction zone to serve occupied zones; central utility piping (steam, chilled water, natural gas, etc.) that passes through the construction zone to serve occupied zones and buildings; lighting control and electrical power circuits that cross phase boundaries; and security and fire alarm conduit and devices serving the construction zone.
Commissioning is a pre-design through construction process intended primarily to mitigate the headaches typical to the end of construction projects of any type. Decommissioning is a pre-design through start-of-construction process intended to mitigate the headaches inherent to the beginning of renovation construction projects.
