Being armed with information from bidding to system start-up will help the HVAC contractor make it around the sustainable world.
Here a cable tray installed in front of the air column unit needs redirecting. The low voltage contractor needs to be aware of the impact of their cable tray installation and not impede the airflow directly in front of the column unit.
THE BIDDING PROCESS
It is important to understand that a sustainable project can still be a profitable one for the contractor. While the written specifications can sometimes be overlooked, these documents, especially with regard to commissioning, include an immense amount of information that will cost both time and money. It is important that the time required to fulfill all commissioning requirements is accurately accounted for in a contractor’s bid.Unfortunately, the project team spearheading the bidding process still has an eye on the final cost of the project. If one contractor states the commissioning process will take 500 hours to complete and another affirms it can be done in 300, it’s possible the lower bid will win out. When the commissioning process is underway, the design team will make sure all commissioning items meet the written specification, whether it takes 300 or 1,000 hours.
Read the specifications. As the commissioning process becomes more of a standard project component, contractors will be able to gauge time more accurately and bids from contractor to contractor will fall in line with each other.
Another costly and time-consuming process involves reaching IAQ demands during construction. The requirement for fulfilling this credit may be buried in a specification or at the end of a bid form as a box to check for compliance. However, meeting this requirement can be costly in a project with as many as a 1,000 terminal boxes over a three-year construction process.
The requirement states that all mechanical equipment with a return air grille shall be protected and all mechanical fan systems provided with a MERV (minimum efficiency reporting value) 8 filter throughout construction. Over a period of three years, multiple sets of filters can be required to keep equipment protected. The best bet is to account for the number of filter changes needed both throughout construction as well as the final filters replaced after construction - all in the original bid.
In following sustainable and green practices, ductwork should be wrapped and off the floor at the work site before it is installed.
MATERIALS SELECTION AND PROTECTION
In the world of LEED, material selection is essential. While carpet, paint, and wall coverings will bear the primary burden, duct sealants and adhesives cannot be overlooked. Engineers need to see submittal information for these materials to verify that VOC contents meet LEED requirements. Submittals need to clearly indicate this information.Equipment protection at the construction site is equally important. There is an enormous amount of effort put forth by the design team to provide a building with superior IAQ. Ductwork that is going to deliver this superior air quality needs to be clean when it is installed. Ductwork, fans, and other mechanical equipment should be kept off the floor of a construction site that, at times, can be dirty and wet.
Shown is a plenum floor installation in progress. Note that the envelope and columns are properly sealed at the perimeter.
EFFICIENCY IS KEY
In the past, engineers focused on such things as air quantities, velocities, and electrical requirements when reviewing equipment submittals. In the sustainable world, more submittal information is monitored, such as EER values, pressure drops, fan efficiencies, and other items that contribute to the overall energy efficiency of the systems.The submittal process is easier for all parties if the equipment specified matches the equipment purchased and installed. In the real world, during an open bidding process, the contractor will search for comparable equipment at a better price. It is important to understand the specifying engineer is held to the same commissioning standard as the contractor. Any equipment changes need to be well documented and will not be accepted during commissioning unless the equipment submitted meets or exceeds designated performance criteria.
Shown is a typical “swirl” floor diffuser in an underfloor air distribution project. A system started with temperatures too cold will cause occupants to reduce or completely close their individual air diffusers and the impact can be difficult to recover from.
COORDINATION WITH ALL TRADES
With more energy-efficient systems there can be additional coordination needed that other subcontractors may overlook. It is important to know these issues upfront since the success of the HVAC system performance can be dependent on the success of installations by other trades.For example, an underfloor air distribution (UFAD) system will be affected by the quality of the plenum floor installation, the electrical distribution, and the low voltage cable tray position. If the plenum floor is not properly sealed, air leakage can be significant enough to greatly impact both occupant comfort and the system’s energy performance. Conduit penetrations in walls, floors, or any underfloor baffling can result in similar problems. Keep an eye on the issues before they become your problem.
With many UFAD systems, air column units are used to maintain the pressure under the floor. These column units are often placed at the building core to reduce the architectural impact of the HVAC system. Date closets are positioned at the building core for the same reason. The low voltage contractor needs to be aware of the impact of their cable tray installation and not impede the airflow directly in front of the column unit.
Coordination on the engineer’s part is also important when locating underfloor cable trays with respect to floor diffusers. Oftentimes cable trays are not placed in the exact location that they are drawn on the plans. A 5-inch-deep cable tray cannot fit under a floor diffuser that extends 8 inches into a 12-inch raised floor. The floor diffuser placement should win out in most scenarios. The placement of the diffuser is more critical in a UFAD system than in an overhead air system.
NEW TECHNOLOGIES CAN BE CONFUSING
Because of the heightened focus on energy efficiency, manufacturers and engineers are looking for new ways to cut energy expenditure. This is often done through the implementation of new technologies.One such new technology involves ECM (electronically commutated motor) in fan-powered terminal units. ECM technology reduces power consumption at reduced airflows. A minor efficiency improvement on small equipment installed at large quantities can have a significant improvement in overall systems efficiency. They operate differently than a PSC (permanent split capacitor) induction motor. The test and balance contractor should be aware of these differences and the appropriate way of balancing them. Equipment manufacturers for newer technology systems should be consulted early on to avoid any time-consuming missteps.
SYSTEM START-UP
Proper system start-up is essential with new technology systems. Building occupants will enter their new facility with not only great expectations but, at times, minor skepticism. First impressions are crucial.In the underfloor air example, all individual air diffusers should be in the “open” position with warmer underfloor air temperatures. A system started with temperatures too cold will cause occupants to reduce or completely close their individual air diffusers and the impact can be difficult to recover from.
CONCLUSION
As the sustainable world simply becomes more lived in, many of the issues facing HVAC contractors today will be resolved. But, being armed with the right information as a result of communication and coordination with all trades can help accelerate this process for the HVAC contractor.From bidding to system start-up, the green world is yours for the taking.
Publication Date:05/18/2009
