Ventilation That Makes Labs Safe and Energy-Efficient
Commissioning is great business for consulting engineers. One problem, however, is selling clients on why they should pay extra for commissioning. But if the building is a laboratory, then the sales job becomes much easier.
This is because safety is paramount in a lab and depends on properly operating ventilation systems to protect occupants and—in the case of bio-containment labs—the environment.
The modern laboratory is composed of many systems and subsystems bound together in complex ways. These systems are in turn made up of many components. And while each component may have been checked at the factory prior to shipment, and rechecked after installation, one small failure can bring down the whole system. In addition, setup and programming for all of these components to act in unison is often by trial and error. Even after these components are working together, more is required to get these systems optimized for peak performance.
Not only new facilities benefit. In fact, existing laboratories can gain much from commissioning.
First, a few definitions are in order. Re-commissioning is applying the process to buildings that have been previously commissioned. Retro-commissioning involves facilities that have never been commissioned before.
Existing labs can benefit from re-commissioning and retro-commissioning. Their building systems operate round-the-clock, which means that operating costs are high due to the intense energy used by the many complex subsystems involved.
Consequently, simple adjustments can yield large savings. One area ripe for savings involves determining acceptable minimum lab air change rates and having systems set back at night to these values, when many labs may be over-ventilated.
The consulting engineer should keep in mind that certain tasks in retro- and re-commissioning may need to be subcontracted, including air and water balance associated with measuring, verifying and adjusting flows. A temperature control contractor might be needed to download and modify programs, calibrate field devices and adjust set points.
Whether old or new, laboratories are often designed in modular configurations for flexibility, where addition or removal of walls quickly creates larger or smaller work spaces. Each module has its own thermostat, but when several modules are combined into one space, these thermostats can "fight" with one another.
In one project, for example, three bays were combined into one large lab. Retro-commissioning during after hours revealed that HVAC equipment in the center bay was blasting hot air, while equipment in the outboard modules was blowing large quantities of cold air—all in an attempt to maintain different temperature set points. This air was then being pulled out of the building through the general exhaust valves, as the fume hoods were all in their minimum positions.
In other types of facilities, the energy consumption by thermostats "fighting" isn't usually as great, because their systems are often recirculating air, but in the laboratory, one is dealing with 100% outside-air systems. In the example, by giving all three thermostats the same set point or by temporarily giving control of all three HVAC zones to one thermostat, a significant amount of energy was saved.
But energy efficiency isn't the only thing that commissioning can do for labs.
By design, laboratories are configured to control airflow to protect the health and safety of workers and the surrounding environment. This is normally accomplished by creating pressure gradients within the lab so that clean air moves toward more contaminated environments and then out of the facility through either chemical or biological filters or through tall, high-velocity stacks.
Getting these pressure gradients set up under various operating conditions is a prime reason to involve a commissioning agent in the construction process.
In one case, while commissioning a laboratory that had an attached office complex, it was observed and recorded that air moved properly between the corridors separating the two areas, moving from the office portion toward the laboratory wing. However, after hours, when the office air-handling units were shut down, it was noticed that the airflow reversed directions and moved from the lab into the office space. Rebalancing of the corridor airflows surrounding the laboratory space corrected this problem.
Of course, this type of problem could have also been caused by restroom exhaust fans in the office areas not being interlocked to shut down with their respective air handlers after hours.
Most labs are designed to operate at a negative pressure, but some require positive pressurization. For example, we had a clean room requiring positive pressure that was adjacent to a cluster of biosafety Level 2 labs and also opened onto a corridor. The room tested positive with respect to the corridor and also to a workroom that opened to a biosafety lab. Things looked good—until the door between the workroom and the biosafety lab was closed. At this point, the clean room was negative with respect to the workroom. Again, air balance work resolved the issue. Open doors between adjacent labs will also change the measured offset between a lab and corridor especially when door sweeps are used.
Laboratories that deal with hazardous biological agents pose many commissioning challenges. For instance, the supply and exhaust systems for biosafety Level 3 and 4 labs should be interlocked to ensure that they are not positively pressurized with respect to their surrounding environments. This can be a difficult task especially if the containment zone does not have an independent supply air system. A Level 3 lab that was not interlocked and that was served by a supply air system that fed many other labs was being commissioned to conform to the relevant guidelines. An initial stage in the sequences was to be written to shut off the supply-air valve that fed the containment zone, which was to be accomplished by adding a solenoid valve to bleed main air to the normally closed supply valve. If this sounds confusing to you, it's no wonder it did to the temperature control technician who was making the programming changes as well. This technician was performing the work after hours and happened to be the fourth person his company had sent to the site in a six-week period. When he was instructed to program the supply valve in a closed position, he actually programmed the solenoid valve closed, which kept the supply valve open. Needless to say, testing failed and the lab went positive in pressure. This valve terminology misunderstanding was finally discovered and the programming was changed.
The creation of construction dust can have a significant impact on the operation of biosafety labs as was evidenced recently during retro -commissioning of a large laboratory complex. The client wanted to monitor the pressure differential of each individual lab with respect to the corridor and consequently was having sensors and displays installed after hours by the temperature control contractor. We had been in the facility a couple of weeks when we started noticing low-flow alarms on the biological safety cabinets in some of the labs. The problem seemed to get worse, spreading from lab to lab. We measured the differential pressure across some of the HEPA filters in the cabinets and noticed that they were loaded. It is then that we came to the conclusion that the control contractor was being sloppy when drilling into the drywall to install the pressure sensors. The client ended up paying to have all of the HEPA filters quickly replaced after the controls contractor completed work.
High-powered HVAC systems used to contain biological agents in biosafety labs can wreak havoc if not designed and installed properly. If the supply system goes down and the exhaust system continues to operate—which it should—a dangerous under-pressurization of the space can occur causing ceilings to collapse. Both the supply and exhaust systems should be powered from an emergency system and since biosafety labs should be designed so that they never achieve positive pressure with respect to the outdoors, the exhaust systems should be fed through an uninterruptible power supply. This common arrangement will cause the exhaust system to operate for up to 10 seconds without the supply system until the generator starts and begins to deliver power. To counteract the potential damage, quick-acting bypass dampers can be installed in the exhaust system to limit the negative pressurization. Another, more expensive solution is to provide UPS power to the supply fan as well.
The impact of HVAC system dynamics is not limited to collapsing ceilings— problems can surface in the plumbing systems as well. An animal biosafety lab had two separate waste systems inside the containment zone. One served labs and holding rooms that drained by gravity to a liquid waste decontamination system and was vented through a HEPA filtration system. The other served toilets located in two separate restrooms and was vented through the roof. Water and toilet paper were found on the ceiling of one of the restrooms after the emergency power system was tested. It turns out that when the supply system went down along with normal power during the test, its outside air damper slammed shut. This abrupt action caused all of the air that was coming into the building through this system to attempt to enter through a 3-in. vent at the roof forcing the toilet to erupt. The control loop for the outside air damper on the supply system was modified to cause it to close more slowly.
Laboratory pressurization can also affect the general trades work as happened on a fast-track animal laboratory project. This case involved an expensive, seamless floor system that had to be installed in a short time frame. The construction manager had given approval on an alternative floor adhesive system without consulting the architect. This change went undetected until the ventilation systems were started and the floor began to bubble. These were not bubbles the size of quarters or even grapefruit, but the kind of bubbles that could entertain kids at a carnival.
Laboratory ventilation systems are complex and have the potential of interacting with other systems in unanticipated ways. Consequently, commissioning should be a part of the laboratory building project. Retro-commissioning older facilities can also uncover defects and help build peace of mind for laboratory personnel knowing their facility functions as intended and meets industry guidelines. Because laboratory ventilation systems consume large amounts of energy, re-commissioning has the potential of substantially cutting operational costs.
Commissioning Checklist for Lab Facilities
The commissioning effort required to ensure a safe laboratory requires cooperation and coordination between owner, designer, builder and commissioning agents. And naturally, cooperation with the owner's operations and maintenance staff is essential. However, because of the importance of safety, lab commissioning must go a step further and include the owner's environmental health and safety (EH&S) group.
The EH&S staff members know the habits and capabilities of the people who use and maintain the lab, as well as the agents and chemicals being used. They are also responsible for establishing and enforcing the standard operating procedures (SOPs) that govern laboratory use and maintenance. Both design professionals and the commissioning agent should consult EH&S in regards to the containment goals for fume hoods and bio-safety cabinets, to gain an understanding of their campus primary and secondary barrier concepts and to gain an understanding of the facility SOPs.
The design intent contains the metrics that will be used to define and judge the laboratory; it therefore must be as comprehensive as possible and presented in verifiable terms. The integration of commissioning into the design process begins with the development of an in-depth design intent document that describes the project goals both qualitatively and quantitatively. Quantitative criteria used to describe the laboratory with regards to safety generally starts with:
Minimum and maximum room differential pressures.
Maximum recovery time following system or equipment failure.
Maximum recovery time following system intervention.
Time limit for loss of pressurization during system or equipment failure.
Allowable sensor error.
Qualitative parameters for the laboratory systems include:
Space pressure reference points (a known and stable location.
Specific details surrounding "hand" operation of equipment.
Primary and secondary boundaries.
It is no accident that functional performance testing is synonymous with commissioning, the success of which depends on the effectiveness of the testing process. It is therefore essential that test documentation be well designed.