Many times the general contractor will ask the MEP trades to run their equipment to provide temporary heating, cooling or ventilation to allow work to proceed on the project when environmental conditions would otherwise preclude it. The design team, owner, and commissioning provider should be involved in this decision especially if it has not been addressed by the project specifications and other contract documents.
From the owner’s standpoint, the contractor may be operating the equipment for his own benefit, not the owner’s and the proper maintenance and care of the equipment will be considered the contractor’s responsibility during this time. In addition, the owner may want to be sure that the warranty starts from the time that the equipment is accepted, not the time the contractor starts it, even though the equipment supplier may considers the warranty period to start when the equipment starts. The owner may also be concerned with both the local code officials and insurance underwriters. In most cases, these entities will only allow systems to be operated in a temporary state if the building, equipment, and its occupants are protected.
From the designer’s standpoint, the operation of the systems needs to be accomplished in a manner that does not damage or contaminate them. The following list summarizes a minimum level of completion for temporary operation:
· The control and safety system must be complete enough to safely run the unit. Usually this means that freeze and static pressure safeties need to be in place, motor overloads need to be set, and some sort of basic temperature and fan volume control sequence needs to be in place.
· If cooling is to be provided, the lines serving the unit and all the accessories and specialties will need to be complete, tested, insulated and vapor sealed.
· If the temporary heating source is steam or high temperature hot water, then that piping system must also be tested and enough insulation will need to be in place to prevent the tradesmen working on the project from accidentally being burned if they brush up against the piping.
· Temporary filters will need to be in place to prevent contamination of the duct system by construction dust. It is important to note that the nature of this dust may require filtration levels or efficiencies that are higher than what will be required by the normal operation of the system. Additional temporary filters may also be required to protect return ducts at their termination points.
The designer also will be concerned about the loads that temporary operation will place on the system and any central utility systems serving it. These loads could actually exceed those that the unit would see in normal operation. For instance, a system designed for a 30% minimum outdoor air rate may not be able to meet the heating load when it is operated at 100% outdoor air in the middle of the winter to remove construction fumes. In addition, the heating coil piping configurations and control sequences used by the 30% outdoor air system (the normal operating mode) may be unsafe for use at 100% outdoor air without some modification.
From the commissioning providers standpoint, temporary operation will just about always require that the functional testing occur in two phases instead of as one test at the point when the construction of the system is complete. This can have a significant impact on the commissioning budget, plan and schedule.
Another commissioning impact associated with temporary operation relates to the hierarchy of the testing and start-up process (see Section 5 for more details). Subsystems must be complete and ready to run prior to the temporary start-up of the system they serve. Sometimes, in the contractors rush to complete the subsystems, they forget about the need to test. For example, the insulator is applying insulation to the projects piping systems in an effort to prepare them for the temporary start-up, but the systems have not been pressure tested, you may want to meet with everyone to review the difficulties associated with locating a leak when pressure testing an insulated piping system. Remind everyone that there will be a pressure test and clarify who will bear the cost of any repairs, including damage to the work of other trades. Discussing what might happen is easier than a disagreement about what did happen.
At the opposite end of the spectrum, if you discover that the chilled water system is about to be placed in operation for testing or temporary cooling but the insulation work is not complete, you may want to take steps to ensure that the construction team has a plan for:
· Drying the condensation from the piping and equipment prior to insulating them.
· Providing moisture and condensation protection under the uninsulated lines for the work of the tradesmen that are installing ceilings, wall coverings, and floor coverings.
Regardless of the specifics of the temporary operating requirements, prior to releasing the system for temporary operation, the commissioning provider will want to verify that all pre-start and start-up checks have been performed satisfactorily, and that enough of the control and safety system is in place to allow the unit to operate without endangering itself or the occupants of the spaces it serves.