23 05 93: Testing, Adjusting, and Balancing for HVAC

by Sheet Metal and Air-Conditioning Contractors' National Association (SMACNA)

Last updated: 06-03-2009


Most of today's newest HVAC systems are being designed with many more individually controlled temperature zones to improve occupant comfort. Variable speed fans and pumps are becoming more commonplace to provide the exact amount of heating and cooling system capacity in a manner that minimizes overall energy usage. New occupant air ventilation codes are much more restrictive and at the same time building envelopes are becoming much tighter. The combination of constantly changing HVAC airflow rates and increased demand for fresh- and filtered-ventilation air for all occupants is placing more emphasis on fine tuning HVAC system operation.

The building construction industry is experiencing a major growth in demand for experienced and certified testing, adjusting, and balancing (TAB) contractors who can balance today's complex HVAC systems.


TAB contractor servicing an HVAC system

The purpose of testing, adjusting, and balancing (TAB) is to assure that an HVAC system is providing maximum occupant comfort at the lowest energy cost possible.

The following tips are included for initial planning.

Pre-planning for TAB work includes making certain that all the necessary parties and individuals to conduct the work are onboard. The type of building and systems to be tested and a realistic evaluation of what skills the TAB technician possesses are key planning elements.

  • Often, a controls specialist will be needed to operate the system for the TAB technician.
  • The representatives from the original equipment suppliers may be needed as a resource, at a minimum, but for complex equipment and systems or in a new building startup a manufacturer's representative may be required at the site to operate the mechanical equipment.
  • If the building has a facilities manager that individual is typically the most important participant with which the on-site TAB technicians will work. Facility managers have a substantial vested interest in ongoing customer satisfaction—the people who work or live in the building are actual end-use customers—and their satisfaction will ultimately be the key measure of success.

Occasionally, a system cannot be balanced or made to perform in accordance with the contract's design specifications regardless of the number of balancing dampers or valves that can be installed. Competent TAB technicians should be prepared for this possibility and work with the appropriate individuals to formulate recommendations as part of the final TAB report.

It should be made clear that the TAB work is not "commissioning." Most commissioning services are completed by firms having technicians experienced with each of the individual building systems—HVAC, lighting, plumbing, electrical, and security systems.

Commissioning services for any new building construction or renovation are intended to verify all of the above systems—operate properly and meet performance criteria.

Commissioning also includes the testing of all building controls for each mode of operation to verify all systems are being sequenced correctly with each other and that all interlocks are functioning. The commissioning agent must document the results of each equipment test performed as it is completed. These firms will usually subcontract the services of an independent TAB contractor to verify HVAC system balancing as part of their more inclusive commissioning contract.

New Buildings

Testing, adjusting, and balancing of all HVAC systems in a new building is needed to complete the installation and to make the system perform as the designer intended. Assuming that the system design and installation meets the comfort needs of the building occupants, testing, adjusting, and balancing of the HVAC system fine tunes occupant comfort levels while keeping energy use to the lowest level possible. This is extremely important in this era of rising energy costs.

It is important to make sure that all factory equipment startup service has been completed before beginning any TAB work. Most specifications on new building construction usually require a factory representative to be present during the initial startup and adjustment of the mechanical equipment—central boilers, chillers, large variable-speed motor drives, and cooling towers. This initial equipment checkout is also usually required to activate the factory warranties and is not part of the TAB contractor's responsibility. After this initial startup service has been completed, the TAB contractor should be informed that the systems are operating properly, that all safety interlocks and protective devices are functioning, and the systems are ready to be balanced.

The TAB phase of any building construction or renovation is intended to verify that all HVAC water- and air-flows and pressures meet the design intent and equipment manufacturer's operating requirements. It is rare to find an HVAC system of any size that will perform completely satisfactorily without the benefit of final adjustments. This is why it is considered a "best practice" for the designer to specify that TAB work be part of the overall HVAC system installation.

Existing Buildings

There are few buildings in existence that have not experienced changes in internal loads and space layout changes since they were designed and built. These buildings should periodically have their HVAC systems rebalanced to achieve maximum operating performance, efficiency, and comfort.

The TAB Technician

TAB technician designates the person in charge of the TAB work being done on the HVAC system. TAB procedures on a complicated HVAC system require that the TAB technician must be a well-trained, highly-skilled, and knowledgeable individual. This person must know the fundamentals of airflow, hydronic flow, refrigeration, and electricity and be familiar with all types of HVAC temperature controls and refrigeration systems. They must also know how to take pressure, temperature, and flow measurements and be able to perform effective troubleshooting.

The TAB Team

There are TAB jobs that can be done by one person. However, many HVAC systems need a TAB team to complete the TAB work efficiently and in a reasonable time period. It is equally important that the other members of the TAB team be trained and knowledgeable in the basic fundamentals and procedures of TAB work.

Energy Costs and Occupant Comfort

TAB work conducted on existing buildings will often hold opportunities for the attentive TAB technician to identify additional equipment or work for the system being balanced that will increase occupant comfort and decrease building operating costs. An obvious example would be the replacement of single-speed electric fan motors with newer computer-controlled equipment that can more closely follow the required airflow needs over the changing seasons and load variations. Variable-speed electric motors are a relatively new product and the older the building the greater the likelihood and potential for energy-saving and comfort-enhancing opportunity. In some instances, variable-speed motors may consume just 15% of the electricity on an annual basis as an older single-speed motor.

Another example would be when the TAB technician is asked to provide a rebalance of an individual zone due to shifts in internal use. Often, this is a good opportunity to examine the benefits of a complete review of the building's mechanical system and possibly provide complete-building TAB services. Also, changes in one building zone will often result in changes throughout or at least in other parts of the building.

TAB Instruments

Flow measuring hood

Airflow Measuring Instruments

  • Manometers—Used to measure pressure drops which can be translated into flow rates. Available in tube types, both U-Tube and inclined-vertical use a fluid in a tube to represent the difference in pressure between two points.
  • Digital manometers—Can provide very accurate readings at very low pressure differentials, such as across air filters and expansion cooling coils. Can automatically adjust for barometric pressure, store readings with recall in average or total numbers, and some can provide additional functions such as temperature measurements.
  • Anemometers—Available in several configurations—rotating vane, deflecting vane, thermal—and used primarily to measure air velocities at registers, grilles, hoods, coils, etc.
  • Flow measuring hoods—Directly measures CFM of air distribution devices.

Temperature Measuring Instruments

  • Glass tube and dial thermometers—Measurement of air and fluid temperatures
  • Thermocouples—Measures surface temperatures
  • Psychrometers and electronic thermo-hygrometers—Determines relative humidity.

TAB Reporting Forms

The proper use of a consistent set of reporting forms assures that TAB work is being done in a systematic manner that produces documented test results that can be easily understood. The following list is an example of forms with a brief description of each to illustrate the steps in the TAB process. Each project may require fewer or more forms and steps depending upon the TAB project goals and the system complexity.

  • System Diagram—A schematic that depicts the system to be tested, its major components, distribution system sizes, the quantities of flow, the location of regulating devices and terminal units and other relevant data.
  • Apparatus Test Report—Provides details of actual measured flow rates, motor loads and other information that will be useful to compare design to actual system component performance.
  • Coil Test Report—Used to record performance of chilled or hot water, steam, DX, or other types of energy exchange coils.
  • Gas/Oil-Fired Apparatus Test Report—Tracks performance of unit heaters, furnaces, and boilers for use in comparison and as a supplement to factory-provided data.
  • Duct Heater Test Report—Provides documentation of airflow rates across electric furnaces and heater coils and verifies min./max. airflow rates as per required by manufacturers.
  • Duct Transverse Reports—Used as a worksheet for recording velocity pressures in a prescribed manner to determine actual airflow for duct—round and rectangular.
  • Air Outlet Test Report—Provides documentation of preliminary and final air distribution devices and possible reasons for deviations from design.
  • Terminal Unit Test Report—Used to check and document the performance of terminal units.
  • Major Equipment Test Reports—Each major mechanical HVAC device that is present and part of the TAB project—Chiller/Packaged HVAC/Compressor/Condenser/Cooling Tower/Pump/Boiler—is tested and the results recorded according to industry-recognized procedures. Specific test requirements may be requested for any major component to verify operating performance or efficiency.
  • Instrument Calibration Report—Documents the tested accuracy of the instruments used to conduct the TAB project.

Relevant Codes and Standards

  • Energy Systems Analysis & Management—Presents an updated level of technical information necessary for energy conservation and retrofits of today's commercial facilities. This new manual provides building owners, facility managers, contractors, and system designers with the tools needed to evaluate an existing facility for energy savings potential. Items of special interest include performance contracting, CFC refrigeration regulation, and new automation system open protocols. Other topics covered include HVAC heat recovery, energy auditing, operation and maintenance, and indoor air quality.
  • HVAC Systems - Commissioning Manual—A practical how-to guide for contractors, owners, and engineers interested in learning about commissioning for new buildings and re-commissioning for existing buildings. Separate chapters are devoted to the different levels of commissioning, including basic, comprehensive and critical system commissioning. A thorough explanation of re-commissioning leads one through the preliminary investigation, survey and documentation phase, the design and installation of system modifications, and the actual re-commissioning test. The appendix contains a sample HVAC Systems Commissioning Specification, complete from the planning to the final execution stage. Additionally the topics functional performance testing, operator training, MSDS forms and equipment data sheets and O&M manuals are covered. It also includes sample reports and timesaving pre-start and start-up checklists.
  • HVAC Systems - Testing, Adjusting, & Balancing—Presents the basic fundamentals, methods, and procedures, including the necessary tables and charts, to adequately balance a complete HVAC system. A tutorial on air and hydronic systems as well as equipment performance and operation, this comprehensive text covers motor operation, fan curves, pump curves, and fluid flow losses in ducts, fittings, pipes, and air terminals. In addition, variable frequency drives, direct digital control systems, lab hood exhaust balancing and the latest balancing equipment and procedures are presented.
  • TAB Procedural Guide—The TAB Procedural Guide is intended for trained TAB technicians to assure that the appropriate procedures are employed in an effective manner. This new publication includes general as well as specific guidance for both air-and water-side HVAC system adjusting and balancing. Variable air volume, multi-zone, dual duct and exhaust air systems are examples of the systems specifically covered and time-saving forms are included for precise record keeping during the conduct of a TAB project. The guide assists TAB technicians with preplanning and establishing teams so that energy use is minimized whether the work is done in new or existing buildings.

Additional Resources

Trade Associations and Other Organizations

  • American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)—ASHRAE seeks to advance the arts and sciences of heating, ventilation, air-conditioning, refrigeration, and related human factors to serve the evolving needs of the public and its ASHRAE members.
  • National Energy Management Institute (NEMI)—NEMI is a not-for-profit organization that has created a training and certification program to provide the HVAC industry with qualified technicians.
  • Sheet Metal and Air-Conditioning Contractor's National Association (SMACNA)—Located in headquarters outside Washington, DC, SMACNA, an international association of union contractors, has 1,965 members in 98 chapters throughout the United States, Canada, Australia, and Brazil. The voluntary technical standards and manuals developed by SMACNA Contractors have found worldwide acceptance by the construction community, as well as foreign government agencies. ANSI, the American National Standards Institute, has accredited SMACNA as a standards-setting organization. SMACNA does not seek to enforce its standards or provide accreditation for compliance. SMACNA standards and manuals address all facets of the sheet metal industry, from duct construction and installation to air pollution control, from energy recovery to roofing.
  • Sheet Metal Workers' International Association (SMWIA)—SMWIA represents 150,000 skilled craftspersons in the unionized sheet metal industry throughout the United States and Canada.