Steps in Commissioning
Commissioning a make-up air unit begins with an inspection of the unit, its components, and the installation to verify everything was installed correctly and meets the design requirements. The next step is to follow the unit’s initial startup instructions. Most manufacturers ship units with an instruction manual, wiring diagram, and checklist which provides an area to document the initial start-up. Tempered units with heating or cooling capability will also come with a quick start guide to assist with unit adjustments and startup as examples seen below. (Figure 1) Some manufacturers also use helpful aids such as QR codes posted on the quick start guide that are linked to unit manuals and start-up videos.
For example, Greenheck provides quick start guides and step by step instructions for unit commissioning. The company also created instructional videos to assist with start-up procedures for indirect and direct gas-fired units along with other helpful videos.
Air Balancing Benefits
During the initial start-up of a make-up air unit, one of the most important details is verifying proper air balancing and adjustment. “testing, adjusting, and balancing,” or TAB, involves measuring air and water flows, adjusting dampers and valves, and setting sensors. TAB contractors test the CFM output and adjust it according to the provided schedule or contract documents. For example, make-up air units in warehouse, data centers, and other industrial applications often have short duct drops to a discharge diffuser. Overestimating external static pressure is possible in this application. If the makeup air unit utilizes a forward curved fan, it can result in too much airflow and over current the fan motor. Two options are available to correct this issue—making adjustment with sheaves and belts or using a variable frequency drive (VFD). Selecting the proper sheaves and belt to adjust airflow according to specifications can be challenging. However, the use of a VFD allows for quick and accurate TAB by allowing the technician to make speed adjustments without ordering and installing new belts and sheaves.
In most cases, TAB is performed prior to start-up to allowing the technician to make final adjustments according to airflow. Air balancing can help diagnose many issues affecting the performance of the entire HVAC system. Some issues identified by the TAB inspection include:
• A building with negative pressure (Difficulty opening outside doors)
• Over-pressurizing a building (Outside doors not shutting entirely or staying open)
• Over current of the fan motor, causing make-up air unit circuit tripping or alarm
• Undersized ducts
• Duct Blockages
• Ductwork with multiple or sharp turns
Startup and commissioning Benefits
Warehouses, distribution centers and many other applications emphasize the importance of proper startup and commissioning. However, TAB and unit commissioning may not be standard practice in many instances. Smaller projects such as kitchens, office studios, and small business storage facilities may not have technicians familiar with make-up air start-up and operation. Make-up air units may not operate correctly when installed without proper start-up procedures completed causing dissatisfaction for the end-user. Avoidable technical and customer service issues identified by make-up air start-up include:
• Heating capability jeopardized by not reaching design temperature rise
• Overheating or over cooling a space or short cycling
• Increased operating costs due to excessive outside air above schedule requirements
• Ignition failure or low flame signal due to burner pressure differential
• Refrigerant system failure due to sub-cool and superheat temperatures
• Communication issues or no control of the unit caused by failed installation of field wiring
Make-up air startup and commissioning should always be performed by a certified technician or licensed commissioning agent.
Start-up and commissioning achieves proper unit performance and provides in-depth documentation to aid in future service or warranty concerns. Commissioned make-up air units avoid operational issues and perform more efficiently creating fewer operating costs. Studies performed by Portland Energy Conservation; Inc. (PECI) indicate average operating costs of commissioned buildings ranged from 8% to 20% below that of a non-commissioned building.
Air balancing and commissioning makes for satisfied customers by providing easy operation and energy efficiency while extending the life of the unit. When a make-up air unit operates as designed, it provides the heating, cooling, and peace of mind that every HVAC customer expects from the equipment.