Impacts of Phased Construction on Mechanical Systems

Occasionally we have a project where construction is completed in two or more phases, often as a result of funding constraints, occupied spaces (for renovations), or site limitations.  For example, construction on one wing of the building may be completed before a second wing is started.  Another common type of phasing is shell and core, where the building shell & interior are completed separately.

Phasing can have unexpected impacts on mechanical and other building utilities if not carefully planned, or could add unnecessary duplication for some trades. A few examples include:

Testing, adjust, balancing (TAB): Usually, HVAC balancing will need to be repeated for each phase.  Designers should consider whether a “preliminary” balancing is acceptable for the early phases, with more comprehensive TAB at the end of the project. The preliminary TAB should be sufficient to ensure adequate heating, cooling, and ventilation for the affected area until the final TAB is implemented.

Building controls (BAS): Similar to TAB, controls work will need to be repeated for each phase. There may be a preliminary level of controls implementation required for the first phases, with comprehensive integration and commissioning at the end of the project to fine-tune the building controls.

Impacts of reduced loads: Running a building’s HVAC at very low part loads can be risky for certain types of equipment such as chillers, potentially leading to short cycling, oil return issues, surge, etc. Ensure that the heating and cooling plants can handle the temporary conditions during the first phase, and consider staging multiple smaller units in place of larger systems.

Learning from early phases: In essence, the first phase can serve as a “mock-up” for the whole project.  Future wings can be fine-tuned based on the initial installations. Allow for design flexibility in subsequent phases to take advantage of potential improvements and avoid problems.

These are just a few impacts of phased construction on mechanical systems, not to mention equipment staging, temporary heating and cooling, dust control, etc. With careful planning, we can minimize surprises and unnecessary replication in multi-phase projects.