From Concept to Reality: The Crucial Role of Testing, Adjusting, and Balancing (TAB) in HVAC Design

In the process of testing, adjusting, and balancing (TAB), qualified engineers and technicians meticulously document data and establish preliminary and final airflow, water flow, and temperatures for all components of a heating, ventilating, and air conditioning (HVAC) system. This process may also extend to domestic water, smoke control, steam and industrial process water systems. Total system balancing ensures that all components of the HVAC system work in conjunction with the control system, and that all modes of temperature control and ventilation operate per the design intent at optimized and responsible energy-consumption rates. The true value TAB represents is energy optimization over the life of a building. When a building goes unbalanced, critical HVAC systems can run unchecked for years, conditioning air unnecessarily and wasting money.

TAB firms are independently certified, usually by one or more governing bodies that adhere to strict guidelines and standards that require the use of calibrated instrumentation. These bodies also stress independence, qualifications, accuracy, repeatability, ethics, integrity and continuous training.

At the most basic level, TAB firms test, adjust, and balance all mechanical components of HVAC equipment to achieve design air and water flow while also striving to maintain the equipment’s optimal energy usage, noise, and vibration levels. In particular, they validate and certify the outside air ventilation rates of indoor environments according to ANSI/ASHRAE standards 62.1 and 62.2. In order to accomplish this, TAB firms must have all the latest construction documents, drawings, as-builts, submittals, and specifications before starting or being asked to begin work on a project.

Prior to mobilization and after all information on the approved equipment has been collected, the test and balance engineer should submit a written plan outlining the TAB activities to be performed on the project. This gives the engineer of record (EOR) the opportunity to approve the methods and procedures, as well as raise awareness for the construction team on what the expectations will be when TAB begins. The TAB plan should state exactly how the equipment is to be exercised and in what sequences the testing will occur; for example, allowing the controls contractor to be prepared to place the air-moving equipment into all design sequences, not just maximum load conditions.

Once all equipment is properly started and all controls and automation complete, TAB technicians and engineers set about gathering data and information on every air handler, fan, heat exchanger, water and direct expansion coils, motor, duct, air register, valve, and more. To establish a baseline performance, they meticulously document preliminary measurements of the airflow, water flow, pressure, temperature, electrical data, and energy consumption of the HVAC system and equipment. Certified and trained technicians adjust dampers, valves, variable frequency drives, sheaves, belts, and building control systems to achieve the design flows as specified by the design engineer and to meet the building owner’s design-intent document.

A large part of the TAB process happens while testing and adjusting the building automation system (BAS, BMS, EMS, controls). Accordingly, TAB firms should have complete access to the BMS, and this assertion should be made clear in the project specifications. The TAB firm must test all HVAC control systems and identify when a system does not conform to the specified sequence. Point verification documents that every point is operational and calibrated. Point verification also includes documenting that each point is correctly labeled and reporting correctly to the graphic interface.

TAB, almost by definition, is meticulous. This attention to detail makes TAB professionals adept at discovering issues with the systems they test. By distributing “deficiency reports” or “punch lists” regularly, or as they encounter issues, TAB firms should promptly communicate all issues they encounter with as much detail as possible so that the responsible parties can set about resolving identified issues. It is the responsibility of the construction manager and other subcontractors to manage and correct these issues and report back to the TAB firm.

Once all fieldwork is completed and final adjustments made, the TAB firm begins assembling the final test and balance (or TAB) report. This document is the final record of all performance conditions for the building’s systems. The report is certified by the firm’s test and balance engineer or other certified professional with a signed and sealed stamp. This report should also include an executive summary or a narrative describing the project and any unusual issues, system idiosyncrasies, and critical system setpoints to best maintain the building’s performance. Final reports also include a record of the instruments used, along with their respective dates of calibration. All instrumentation used should be calibrated within the last 12 months.

Regarding the building and its mechanical systems, the lead TAB technician is often the most knowledgeable member of the construction team at the completion of a project. Because TAB technicians and engineers are so proficient at uncovering issues, there is a tendency for other trades to surreptitiously delegate all quality assurance to the TAB scope of work. This is a mistake and invariably leads to a major bottleneck in the construction schedule and a lower-quality end product. An excessively long list of deficiencies is usually a symptom of poor quality control or a compressed construction schedule.

When approaching TAB activities on a project, each employee must have the proper training and education to properly test systems, and report that the designed systems and sequences are functioning as designed and providing design capacities. Each project specification must have a detailed TAB specification, including qualification requirements of firms submitting proposals. The qualification requirements demand resumes of individuals that will be assigned to the project with their educational background, certifications of their training, experience level on previous projects and recommendations.

When it comes time to determine pricing for TAB projects, many factors can affect the cost: the mechanical complexity of the system being installed, how many modes of operation are being programmed into the sequence of operation (SOO), and last but not least, access to the equipment to be tested, adjusted, and balanced. Square-foot pricing can range greatly, depending on whether the project is (for example) an elementary school or a laboratory. It is not unheard of to find square-foot pricing ranging from $1.25 to $4.00 or more, based on geographical location and complexity of the project scope.

The scope of work being requested should include current drawings, approved equipment submittals, project-specific specifications, and finally, an executive summary highlighting the TAB report that is to be submitted at the completion of work.

New construction comprises most of the workload and experience of TAB firms. A TAB firm may cover projects ranging in complexity from single-unit retail spaces to ISO 3/class 1 cleanroom laboratories.

The most successful new construction projects engage a TAB firm early in the process to assist in the review of the design documents as they pertain to being able to properly test the systems’ application. On large projects, owners and construction managers should endeavor to include the TAB firm in discussions regarding scheduling and key dates, performing observations of systems being installed, and assisting with pre-testing components.

TAB work is most successful when it is completed “by system” rather than “by phase,” which should be considered when scheduling TAB on multi-phase projects. The TAB process cannot be skipped, diminished, or compressed in favor of commissioning activities, building inspections, or owner occupancy. The TAB firm should also have adequate access to controls and other energy management systems that are part of their testing scope.

To avoid project delays, owners and operators should also see that the firm has adequate access. TAB firms, in turn, should provide the construction team with regular updates regarding progress and deficiencies. Having meetings and discussing deficiency reports can be highly beneficial so that the construction team can delegate the issues to the proper subcontractor for quick resolution. A new building with any type of mechanical complexity will not operate correctly without engaging a competent TAB professional.

Existing building TAB should be approached with a very specific mindset. Normally, a pre-demo survey is conducted on any of the systems to be tested by TAB after construction is complete. A pre-demo survey will allow the engineer to better understand the condition of the equipment and whether it can be rescheduled for use in the building.

When HVAC systems are reused and repurposed, they often involve a blend of old and new technologies. When this occurs, a TAB design review must be initialized to make sure that the two technologies can be utilized together. Newer technology like pressure independent control valves cannot be mixed in with traditional balancing valves because system fluctuation can cause constant pressure-dependent valves to fail with lower than design flow. This is just one example. Once the pre-demo and design reviews are completed, the standard TAB methodology is the same as that of new construction projects.

Unfortunately, in situations where a pre-demo survey has not been conducted, it may not be discovered until the end of a project that an existing pump or fan is not performing as anticipated.

Depending on the size of the project, a request for proposals or a request for qualifications may be required. It is important TAB specifications identify who will select the TAB firm (owner or general contractor). It is equally important that the specifications identify how deficiency items will be handled.

TAB firms occasionally partner with commissioning firms to provide a level of third-party independence regarding the functional performance of a building. Since TAB firms strive to achieve optimal building conditions, it is not a conflict of interest for TAB and commissioning entities to work together.

When the mechanical contractor hires a TAB firm, a conflict of interest could present itself: the mechanical contractor could change the TAB firm’s scope, which is in conflict with the specification, or not submitting the same report submitted by the mechanical contractor.

The TAB firm is responsible for testing all the systems covered by the design documents. When deficiencies are found, the TAB firm is not responsible to correct the deficiencies but will often be able to make suggestions about possible remedies for troubleshooting the problem.

The TAB firm is not responsible for changing belts and drive components on systems that are purchased and installed by the contractor. Proprietary control hardware components or software required to operate the BMS controls shall be provided to the TAB firm, or the controls contractor will assign a person(s) to manipulate the control system as required to complete the TAB work at no cost to the TAB firm.

Pressurization is the combination of air movement within a building and the introduction of properly filtered and conditioned, heated or cooled, return and outside, air and exhaust air. The quality of pressurization of a building will deteriorate over time when systems are not maintained. For example, dirty or improperly installed filters, a reduction of outside air, and improper distribution in the supply of return and/or outside air are just a few of the contributing factors to building inefficiency.

The TAB firm must identify how the difference in outside air versus exhaust for the total building, each floor and areas designed to be pressurized (positive or negative to adjacent spaces). Ideally, after the building TAB is complete, all pressurized areas are operating as designed, with each floor being slightly positive to atmosphere and the building slightly positive, theoretically.

Building pressures change due to buoyancy, doors opening and closing and outdoor wind effect. Building pressures should be set to 0.05” w.c. at the end of TAB. The only time this can be measured is on a day without wind. A 10 mph wind will overcome the 0.05” w.c. pressure.

A client should have high expectations for their TAB firm, depending on the specification requirements. At a minimum, the TAB firm should be able to provide the following information:

• Firm capabilities statement.
• Past work experience.
• Example reports from a similar sized-and-scope project, and written procedures.
• Methods for how the work is to be accomplished along with resumes and pertinent experience of key role players should be provided as well.

All of this documentation will assist the engineer of record (EOR) in selecting the most qualified TAB firm for the project.

Experienced, certified TAB technicians are well versed in many aspects of the mechanical, electrical, and plumbing (MEP) disciplines: knowledge of fans and pumps, the associated affinity laws, electrical systems, and optimizing the performance of HVAC equipment, as well as how to test each component and sequence controlled by the BAS system. Understanding these engineering principles also gives TAB technicians insight into the engineer’s design intentions and the goals of the building owner’s use of the indoor environment.

TAB technicians will also have knowledge of sound and vibration analysis, including techniques that allow facility managers and operators to forecast equipment failures and measure, with confidence, how the equipment is performing against manufacturer-provided data.

TAB technicians can also perform work in niche environments like cleanrooms and food and medicine manufacturing, and they can calculate air changes per hour for suite validation and performance review. Other areas of expertise belonging to certified TAB technicians include print reading, document management, troubleshooting equipment and systems, thermal measurements, and more.

TAB firms are one mechanism to realize an engineer’s design. Without the efforts of a TAB firm, a design is just a concept, not a reality. Once a building owner or operator engages with a certified, independent TAB firm, they will immediately start to develop an unbiased view of the design, installation, and performance of their HVAC system.

The most important reason for bringing on an independent TAB firm very early on in the project is the positive impact TAB can have on the design, life cycle, and energy use of an HVAC system. Now more than ever, correct ventilation rates, responsible energy consumption, and longer equipment lifespan are critical to the long-term profitability of a building. TAB firms should be a priority on any project, which will be made clear after developing an understanding of what they do and how vital the energy savings can be.