Creating better HVAC systems in old laboratories and university buildings

TAB insights

• Testing, adjusting and balancing (TAB) firms are vital for assessing and optimizing complex HVAC systems in lab buildings, which ensures efficient operation and performance.
• Upgrading outdated HVAC controls is essential because of component unavailability. Collaboration between TAB and controls teams is crucial for successful integration and improved system efficiency.

As the heating, ventilation and air conditioning (HVAC) industry continues to evolve, there are more opportunities to improve the effectiveness and efficiency of commercial buildings that consume a substantial amount of energy.

A university teaching lab is a great example of a building that relies on complex HVAC design and installation to operate effectively and efficiently. There continues to be a need and desire for university science and lab buildings, both for new construction and existing facility upgrades. As some of these existing buildings approach 30 years or older, the new challenge facing the industry is to properly upgrade the HVAC critical components, such as direct digital controls, air terminals, air handling units (AHUs), energy factors, pumps and chillers.

Starting with the infrastructure components, many of these buildings are designed with energy recovery wheels, coils and night or occupancy setbacks, all to reduce the energy costs while still meeting the needs and expectations for a laboratory building. When it comes to determining the current performance of the existing infrastructure, using a testing, adjusting and balancing (TAB) firm that can help assess the current conditions is a must.

Air to air energy recovery wheels are very popular and highly efficient in these 100% outside air laboratory buildings. While very efficient at reducing energy use, they also need proper maintenance on a frequent basis to ensure the proper performance of the system. Many times, wheel degradation can affect the supply and exhaust fan performance. Assessing the purge cubic feet per minute (CFM) and total fan performance is essential. Manufacturers provide performance data with purge CFM that needs to be independently verified. As these laboratory HVAC systems have redundancy, excessive purge CFM can eliminate or considerably reduce system redundancy (see Figure 1).

Figure 1: An air handling system energy recovery wheel in poor condition after 25 years. Courtesy: Jeremy Johnson, CxA

Equipment assessments to identify replacements

Variable air volume (VAVs) offer pressure independent control and reliability in these applications. Proper TAB is critical and is required after any building automation system (BAS) controls upgrade. The components of the terminals are simple, but there can be severe consequences if they are not operating correctly. Buildings at least 30 years old usually need BAS upgrades where the local VAV controller is replaced.

However, other components of the controls and duct leakage should also be measured and assessed by a TAB firm. For example, the VAV flow ring is essential for proper operation. If only replacing the existing VAV controller, a designer may miss the condition of the flow ring and include cracked tubing or dirt laden ring, which will have severe consequences to properly TAB the air terminal. To prevent these kinds of instances, a full and detailed assessment is needed (see Figure 2).

Figure 2: A commercial heating, ventilation and air conditioning variable air volume terminal that was retrofitted with a new airflow pitot sensing device. Courtesy: Jeremy Johnson, CxA

Some typical design applications have a campus type of chiller water and steam distribution. Establishing the building gallons per minute, differential pressure and maximum capacity requirements ensures that the building can properly heat, cool, humidify and dehumidify.

Lab fume hoods can most likely be found in university teaching labs. There are many different types of fume hoods that operate at low velocity, 60 feet per minute (FPM), or standard velocity, which is100 FPM. Other controls schemes include VAV with occupancy, night setback or active sash control. The biggest challenge that fume hoods face in the industry is to provide a safe environment for the researchers while still being efficient as possible. This is easier said than done with a system that typically exhausts 100% of its air into the atmosphere and replaces it with outside air being introduced into the building or lab through the HVAC system. Modern products and approaches to control concepts have changed through the years and should be reevaluated if newer technology can benefit an existing building (see Figure 3).

Figure 3: A high performance, or low flow, laboratory fume hood seen in university buildings. Courtesy: Jeremy Johnson, CxA

One of the biggest reasons why HVAC controls are replaced in 30-year-old buildings is that the components or supports are no longer available from the supplier. These are called legacy or outdated controls. So, when a component breaks, it’s up to the maintenance team or vendor to apply a bandage the best they can. This is an absolute injustice to a building that conceptually needs to operate independently for the comfort and safety of its occupants. But even on a more practical note, Band-Aid fixes are temporary, which leads to further patches and systems that become untenable to manage.

Pre-TAB steps and criteria

Procuring a TAB firm to help assess the existing conditions is an important part of any HVAC building upgrade. Not only will they help identify systems that no longer are working and find ductwork that leads to nowhere, but they also are a vital part of determining whether existing systems have the ability for future capacity planning.

When it comes to pre-TAB there are important criteria that should always be considered. One of the first is existing duct integrity; how much of the original duct sealant remains, if any? Are the existing fire or smoke dampers still operational and compliant? These are just two examples of components of the existing HVAC system that are often assumed to be reusable, but in many cases are only partially functional.

In the case of an existing laboratory building, open duct chases can be rusted out because of chemical exhaust through the fume hoods that reacts with ductwork installed 30 years ago. These chases need to be examined with cameras, if possible. Static pressure profiles between floors can identify areas of significant static loss.

During the pre-TAB, it is critical to verify that the AHU performance is still intact. Many times, performance values are pulled from old schedules or old TAB reports. In many cases, the report from 30 years ago will not be indicative of current performance. A fresh set of data at the fan must be collected to ensure that the project goals can be accomplished.

Another point of investigation should be the condition of the current energy recovery wheel. How are the seals and brushes? Is the wheel dirty or damaged? This is a great opportunity to meet with the facilities team and review any existing issues that could become hurdles during final TAB. Reviewing existing and known deficiencies allows the entire construction team to be ready for existing challenges in the project (see Figure 4).

Figure 4: A Generation 1 direct digital control building automated system as seen from the front-end. Courtesy: Jeremy Johnson, CxA

Next, the performance at the terminal units needs to be verified on both the air and hydronic sides of the HVAC systems, in conjunction with current controls. During this part of the pre-TAB, building conditions can be noted like accessibility and serviceability, condition of the control valves, water condition and pipe scaling. With gathering of on-site drawings, HVAC original equipment submittals and other maintenance reports that may also be available. None of this due diligence can be accomplished from a desk and must be part of a field pre-TAB site visit.

Creating a new design with TAB insights

Once the on-site visit is conducted and the TAB data has been refreshed, the new design review can be started. This desk review should be inclusive of maximum or peak condition demands for ventilation and minimum flow conditions as well sequence of operation, if the situation calls for it. Modern laboratory HVAC systems have occupancy controls that incorporate proximity sensors on the fume hoods and interaction with GEX (general exhaust registers in the lab) for the purpose of constant pressure control from labs to corridors.

Riser airflow diagrams should be compared with contract drawings for the purpose of matching up space discharge cubic feet per minute (DCFM) requirements with the terminal units DCFM serving those areas. Additionally, once verified design feet per minute velocities should be checked for the main and zone ducts to look for possible distribution duct that could be a larger static loss than originally anticipated. During this step it’s also a good idea to look at any diversity that has been built into the new HVAC laboratory design to ensure that the TAB plan incorporates this into its approach for final TAB.

Reviewing the new supply and exhaust fan submittals is an important step to understand the amount of total static pressure the fans can produce. The final step is to make sure the tolerance levels specified that the TAB team will balance to are achievable. Be mindful that sometimes tolerance levels of 5% are not achievable based simply on the terminal units that have been approved for the equipment installed. Terminal units are very accurate when calibrated, however many off the shelf models can only control for a tolerance of +/- 7% to 11%. If these terminal units are applied to a 5% tolerance job it will not work and if found should become a request for information to the design team immediately.

After all the VAV controls have been modified or replaced and the infrastructure upgrades are complete, the TAB firm can calibrate the new controls and optimize the air system static pressure setpoints and water system differential pressure setpoints.

For calibration of the new controls, it’s not just about calibrating the BAS to read the same as the capture flow hood. This process of TAB captures a moment in time that is an important document for future generations to use and benefit from, known as total system balance. Documenting final operating conditions, such as damper positions, component static pressure profile, thermal capacities and motor brake horsepower (BHP) usage are a few of the real measurables on how the HVAC system performance. If the fan motor BHP exceeds the design intent, there may be a bigger issue that needs to be addressed.

Optimizing the pressure setpoints of both air and water has great value in the operating energy of the building. An AHU or engineering fundamentals system that operates with all the air terminal dampers 50% open wastes energy and is not properly set up. For a properly balanced system, the critical run air terminal should be no more than 80%-90% open during a full cooling test. There is usually only one chance to get this right, as the full cooling or max capacity test only happens once.

Controls verification by the TAB firm has great value with the BAS control upgrades for a university teaching laboratory. While the TAB firm is performing the TAB, taking the extra time to verify the controls components and document the conditions can be done during this step. With a BAS controls upgrade, there may not be the same quality assurance as with a new construction process. Having controls verification written into a controls upgrade is valuable to the project and the future of the building.

As filtration of the HVAC duct system and components have evolved over the years, new challenges, such as particulates from forest fires and concerns about coronaviruses, face the industry — requiring higher required filter differential pressures. These frequently have severe consequences on the performance of older fans, especially in a building that was sized for cooling loads decades ago. Measuring the filter differential pressures and comparing to the design provides insight to the performance.

The specification will sometimes call for TAB planning or project drawings to be completed on as-built drawings. However, this is not realistic because as-built drawings are often not completed or uploaded to today’s construction portals before TAB begins on projects.

Outside air needs to be verified in the peak cooling conditions, at minimum conditions and possibly at some other sequences in between. Today’s buildings operate in more than just minimum and maximum conditions and today’s engineers have developed additional energy saving sequences for different times of the year and regions of the country. Outside air cannot be measured with one reading anymore.

The decision to upgrade building equipment, which is often because of controls, is one that involves a lot more than simple replacement and restart. TAB surveys in advance and early in the design process will help ensure the building owner is satisfied with the investment.

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