WA Preforming TAB in a Once-Dormant Hospital

The building was actually a campus, and consisted of a central utility plant (CUP) serving two main buildings and a medical office building. The last construction phase of the original project was completed in 2010, so the age of the equipment, technology, and devices (balance valves, etc.) were all relatively modern and conducive to re-use. There were a few new components in the form of new variable air volume boxes (VAVs) and laboratory-grade supply and exhaust air valves for operating rooms (ORs), but for the most part all equipment was existing. The building was to be retrofitted with a new building automation system (BAS).

The base mechanical system consisted of a variable primary chilled water system, heating water and boilers, central station air handlers, hot water terminal units, laboratory air valves, exhaust fans, and room pressure monitors.


Our bid and contract stipulated a thorough pre-demolition evaluation of the main equipment measurements, and evaluation of any existing terminal VAV units and exhaust fans that were to be reused. This was a very critical task because it helped identify issues with mechanical equipment that would prevent the systems from achieving the very strict standards required of any healthcare or surgery environment.

Our engineers and technicians made key discoveries early in the game that included, but were not limited to:

  • Clogged coils
  • Seized pumps
  • Failed control devices and senors
  • Required sheave changes
  • Bad bearings
  • Leaking ducts
  • Missing dampers
  • Malfunctioning fire dampers

We were also able to identify and propose solutions when we noticed discrepancies with the intended new sequence of operations and the actual capability of the existing equipment. Another key part of this pre-demolition phase was an evaluation of all the pressure-critical rooms such as ORs, isolation rooms, and dirty and clean utility rooms. We were able to identify missing door sweeps, malfunctioning room pressure monitors, and compromised room envelope issues that likely would have prevented the hospital opening on time.

As with any project these days, the schedule was extremely aggressive, so the identification, and more importantly resolution, of all the issues mentioned above were imperative to the owner achieving their goals. Our team made it our highest priority to maintain regular (weekly), clear and concise deficiency reports complete with room numbers, pictures, dates, and responsible parties. Online reporting software proved to be invaluable for this. Regular on-site meetings and conference calls clarifying these items were also an important part of the project and included in our bid.


Once final construction and controls updates were underway, the final TAB began in phases following right behind the controls contractor. We have not always had luck with this strategy because, frequently, what the controls contractor reports as ready and what is actually ready for TAB are two different things.

It mostly worked here, though, for two reasons: the controls contractor had a very capable on-site project manager who we communicated with directly and regularly, and our team was diligent in communicating issues promptly and with detail.

We attacked the project in this order with some simultaneous overlap:

  • Terminal units grilles, registers and diffusers
  • Hydronic plant and coils
  • Exhaust systems grilles, registers and diffusers
  • Ducted return
  • Critical pressure rooms
  • Air handler performance
  • Sensor calibration
  • Sound testing
  • Commissioning support

We understand some may approach a project differently, but we feel this plan served us and the client well. It also cannot be understated how important project setup and a rigorous review of drawings and submittals were to the success of this project.


As a general rule, our firm will not begin any meaningful final water balance on a variable volume system until the differential pressure (DP) sensor (or sensors) is in place and communicating back to the BAS. We subscribe to a method of water balance that takes into account the flow, pressure drop, and length of pipe for each coil in the system and then assign a rank or "demand" factor to that coil. We then begin balancing the system in that strict order. This makes the operation of the DP sensor very critical to our success and results in a very efficiently balanced final product. We like to have an inordinate amount of input as to the location of the sensor(s). DP sensors located in the CUP near the pumps do not work nearly as well as those located out in the system near to critical (not necessarily most remote) branches or coils.


On this project, both the owner and engineer mandated that the terminal unit heating coils were not to be balanced. They were presumably referring to key ASHRAE studies (Taylor S, Stein, J. "Balancing Variable Flow Hydronic System," AHSRAE Journal, October 2002.) and experience on previous projects in this decision. The assertion is that any small coil with its own controlled feedback loop does not need to be balanced, and in fact is detrimental to do so because coil performance is nonlinear. We too have had some experience and success with this method but have been reluctant to adopt it as our own policy because of the following:

  • Invariable installation issues lead to substantial troubleshooting time that might as well be carried as balance labor.
  • Relying on this method assumes careful analysis has been done in the selection of pipe sizes and control valve authority.
  • With those qualifiers in mind, we did acquiesce to the owner's wishes. Our heating water balance labor consisted of verifying air and water temperatures and measuring flow ultrasonically at approximately a dozen critical or problem coils. Balance labor in this regard was not entirely eliminated.


There is a tendency for construction managers to put off the balance of the ducted return air. Understandably, there is a priority in closing off the return and protecting the ducts and coils with filter media while copious amounts of dust are being generated from flooring and wall construction. However, it has been the experience of our firm that balancing ducted returns is the most time and labor consuming portion of the work. Putting it off to the end can have a severe impact on scheduling deadlines. We made it a point to collaborate with the construction manager on staging the balance of the return air so that adequate time was allotted for our task and all equipment was protected. A key part of making this staggered approach work was verifying the location and availability or return air branch dampers and, where necessary, having the contractors install them.


As is the case with any healthcare project, the correct room pressures and air changes per hour (ACH) in the ORs and isolation rooms become the linchpin of a smooth building turnover. This is not just due to state health requirements, but also for facility sustainability. Most competent TAB professionals are aware of the requirements and subsequent challenges that arise in this phase. It seems that the most emphasis is placed first on the ORs, and rightfully so. However, we have seen that it is the central sterile (or sterile processing) room that can present the most challenges and this project was no different. These rooms are designed with passthrough bays for sterilizing machinery that are inherently leaky.

They are also often bookended by two other rooms with their own very specific pressure and ACH requirements. We encourage our technicians to focus on these rooms first to identify and resolve room envelope and design issues as soon as possible. Also, be wary that because of their large footprint and wide-open space, construction managers tend to use these as material storage areas during construction, which greatly inhibits the TAB contractor.


This was a very ambitious project for all parties involved and, in the end, a successful one. We relied heavily on our experience in hospital and surgery centers. More importantly though, we applied said experience early in the drawing and document review stage. A project this unique also provided our firm with many new opportunities to learn and expand our knowledge base and we have tried to share some of that here.