Designing safe laboratories and research facilities: HVAC
Scott A. Bilan, PE, Principal, Peter Basso Associates, Troy, Mich.
Matt Edwards, PE, LEED AP BD+C, Mechanical Associate, ME Engineers, Golden, Colo.
Gordon Handziuk, PE, Peng, Vice President, WSP, Atlanta
Rick Hombsch, PE, LEED AP, Principal, Energy and Infrastructure Group, HGA Architects and Engineers, Milwaukee
Kent Locke, PE, NCEES, Associate Principal, Bailey Edward, Fox River Grove, Ill.
Christian Matthews, PE, PMP, CEM, LEED AP, Associate; Client Manager, Dewberry, Raleigh, N.C.
John C. Palasz, PE, HFDP, Mechanical Engineer, Primera Engineers Ltd., Chicago
Aaron Saggars, PE, LEED AP, Core Team Leader, CRB USA, Kansas City, Mo.
Jim Sharpe, PE, LEED AP, Principal, Affiliated Engineers Inc., San Francisco
CSE: What unique heating and cooling systems have you specified into such projects? Describe a difficult climate in which you designed an HVAC system.
Palasz: Although it varies by lab, a lab with a high sensible load may lead to an active chilled-beam design. Because the active chilled beam can be very energy efficient, and is typically constant-volume airflow, the lab HVAC system is able to maintain minimum air-change rates and can maintain differential pressures between specific rooms with fewer control costs and higher reliability. This also has the benefit of being a good heating and cooling method due to the radiant cooling effects, and as the lab cooling load increases, the effectiveness of the cooling inherently increases, so this system design approach is more forgiving to the lab designer and allows for flexibility in that capacity. The active chilled-beam design approach also often maintains a very uniform temperature in the space, which leads to improved occupant comfort.
Edwards: In our area of the country, altitude is a significant factor in the design of HVAC systems and often has the effect of requiring larger equipment. Most HVAC equipment is designed with elevations of 2,000 ft. above sea level in mind, so it’s imperative that equipment be sized appropriately to account for thinner air. System types at higher altitudes are very similar to their sea-level counterparts, but often the equipment (burners, motors, compressors, etc.) is sized larger to account for the effects of altitude.
Saggars: We designed the environmental control system at the University of Kansas, where the university archives its museum specimens. The facility is historic, and through this process, CRB assisted the researchers with a new space that maintained tight temperature and humidity requirements. We used a dedicated outdoor-air system (DOAS) with a variable refrigerant flow heating and cooling system. The new system is considerably more efficient, but more important, it has stabilized the historic specimens that are used in research and to display at the university.
Sharpe: What was once unique but is now standard design for our San Francisco office—but is still unique to most of the industry—is the use of compressor-less “free” heat recovery. The way this works is we turn off the chillers and heat-recovery chillers when outdoor-air temperatures are below about 55˚F. We then circulate chilled water to fan coil units serving telecom rooms, electrical rooms, freezer farms, and anywhere else with year-round cooling needs. The cooling-coil valves on 100% outside AHUs are modulated so heat is transferred from the year-round cooling rooms and into the outdoor airstream of the air handling units (AHUs). This provides “free” heat recovery with only minor pumping energy required. No additional equipment is needed, only control software programming.
Hombsch: Cold climates pose unique challenges to prevent freezing of coils, etc. However, cold climates can provide good opportunities for free cooling to serve base-cooling and process-cooling loads. Another unique challenge in cold climates is confirming the building thermal envelope is suitable for handling humidified spaces without condensing issues.
CSE: What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?
Hombsch: Desiccant dehumidifiers for providing normal 50% relative humidity (RH) to 10% RH for specialized labs handling unstable or reactive materials; sensible cooling loops and high turn-down control valves (>500:1) and dedicated PLCs to serve recirculating AHUs to provide highly stable room temperatures (+/-.15 ˚F); and dilution-type exhaust-fan systems to eliminate the need for air scrubbers on some toxic and flammable exhaust applications.
Sharpe: We often use chilled beams in laboratory spaces with high heat gains from laboratory equipment. They are also used in office spaces where there are high heat gains from window solar loads. Using the 100% outside AHUs for laboratory and office spaces eliminates the added cost and complexity of separate units. Office-space occupants are also assured that chemicals within the laboratories are not transferred into the office spaces and recirculated throughout the building.
Edwards: We often specify diffusers with high airflow capacity and a low-velocity profile to meet the high airflow needs of laboratory spaces, and we specify Venturi-type zone airflow valves to meet space-pressurization needs.
CSE: Have you specified a radiant heating or cooling system into a laboratory or research building? Describe the project.
Bilan: A recent lab renovation was located in the basement of a building that was more than 80 years old. The floor-to-floor height was 10 ft. Having less than 2 ft. above ceiling gave us the opportunity to implement active chilled beams. The minimum outside air-change rate was distributed via a central AHU to the chilled beams.
Hombsch: In cold climates, our company has successfully used radiant panel heating systems at building perimeters of laboratory spaces; however, this needs to be coordinated with the lab planning strategy—casework layouts, lighting, equipment, etc.
Sharpe: At the Veterans Administration Medical Center in San Francisco we used a radiant heating system in the atrium of their new medical research building. This is a large 4-story atrium, so heating from a radiant floor system made the most sense. Radiant cooling was not required with the foggy San Francisco summers, and this building sits on a bluff overlooking the Pacific Ocean with views of the Golden Gate Bridge. We have not found a need for using radiant heating or cooling in laboratory rooms due to high first cost and the slow response time to changes in lab equipment heat gain.
Saggars: We are currently integrating a radiant heating system into a quality control laboratory. The client really appreciates that type of heating system, but with a cooling ventilation system, it will be important to complement and control both correctly. We have feedback that some of the existing systems currently installed in some other spaces have a tendency to fight.
Palasz: One past project that I have worked on incorporated chilled beams in conjunction with an existing dual-duct system. This helped us to use the existing constant-volume dual-duct AHUs but allowed for the increased cooling required for the high sensible-cooling load of the lab. This project had many facets of open labs, closed labs, low-temperature freezers packed into small rooms, a vivarium, as well as many collaboration and other support spaces. This project was funded by an NIH grant, so it was mandatory to comply with NIH requirements.
CSE: What types of air balancing do you typically include in your designs? Describe an example.
Matthews: We typically include volumetric offset with directional “waterfall” to control chemical- or biological-contaminant movement from clean to dirty lab spaces. We additionally use secondary barriers, such as full-height walls that are pressure-sealed and anterooms with sliding doors, to create architectural barriers to enhance the lab airflow balance.
Hombsch: Generally, we use National Environmental Balancing Bureau and Associated Air Balance Council formats and procedures with enhanced requirements for simulation and measurement of the various systems throughout the operating ranges, with an emphasis on the extreme ends of the ranges to ensure stable operation. We also include enhanced critical system test and balance during transition periods, such as normal chiller, boiler, pump and exhaust fan staging, etc., as well as equipment failure (chillers, pumps, boilers, exhaust fans, etc.) to confirm recovery response time for backup equipment start-up and stabilization.
Saggars: We recently completed a project that included a research and development, quality control, and toxicology lab. The program and overall performance requirements for these types of lab spaces should require final review/assistance by the engineer of record. These types of facilities usually have pressure, redundancy, and unique hood performance requirements that all operate as a system. Having a balancing contractor with experience and an understanding of the engineers’ intent for these types of facilities is very important.
Edwards: In addition to a requirement for all branch ducts on all supply and exhaust systems to be provided with balancing dampers, we also require that each air inlet and outlet be tested and balanced for proper airflow. The intent for this is to ensure that the design airflow for each space can be met as well as to identify any underperforming areas so that leakage sources can be identified and corrected.
CSE: When working on these types of facilities, describe the HVAC ventilation system, which might include hoods, fire suppression systems, or other specialized ventilation systems.
Bilan: Variable-volume central air handlers are commonplace. Typical lab systems have pressure-independent supply-air terminal units and fast-acting pressure-independent exhaust-air terminal units. A common control strategy is airflow tracking and offsetting between the supply air and exhaust air in a space. Specialty systems also exist for systems, such as perchloric acid that includes a washdown system to dilute the highly corrosive acid.
Sharpe: One-hundred percent outside-air systems are common for laboratory buildings because the recirculation of laboratory air that may contain chemicals and biologics from research can cause health issues. Avoid the need to install sprinklers in the fume-exhaust ductwork by using calculated engineered minimum airflows to keep airborne chemical concentrations below the lower explosive limits. Radioactive material hoods and certain biosafety cabinets need independent exhaust systems to overcome high HEPA filter pressure drops.
Matthews: On a recent BSL-3 laboratory project used for testing tuberculosis, our ventilation design used a three-tiered approach. The primary ventilation begins with localized containment from exhausted biosafety cabinets; fast-acting valves are connected to a manifold hazardous exhaust system equipped with bag-in, bag-out HEPA filters and dual high-plume exhaust fans. The secondary component of the ventilation system is the volumetric offset airflow balance in conjunction with active pressure monitoring to guarantee the negative pressurization of the lab as compared with adjacent spaces. Lastly, we worked diligently with all trades to pressure seal the lab’s envelope by using an anteroom with sliding doors all the way down to using specialty electrical junction wall boxes that are sealed airtight.
Hombsch: Laboratories can be highly specialized, requiring HVAC systems to provide precision quantities of make-up air for exhaust devices, control individual room pressure, maintain minimum-space air quality, and provide critical space sensible and latent temperature and humidity control within specified allowable ranges and various levels of cleanliness. Exhaust systems can be highly specialized as well to serve fume hoods of various types and sizes, biological safety cabinets of various sizes and types, local exhaust enclosures, snorkels, canopy or slot hoods, glove boxes, washers, acid benches, scrubbers, etc. Key considerations are confirming viability/compatibility for groupings of similar devices, appropriate ducts material and pressure classification, exhaust fan types and features, whether there is a need for fire protection sprinklers or washdown sprinklers, system controls and alarms, systems discharge location, and velocity and redundancy needs.
CSE: How have you worked with HVAC system or equipment design to increase a laboratory or research building’s energy efficiency?
Locke: We just finished with a recommissioning project for a laboratory with supporting office spaces, which completed a multiphase, multiyear project with a controls upgrade, building addition, and deferred maintenance program. We found that we could not recommission to the original drawings and specifications because the laboratory has evolved over that period. New equipment was added to the labs and operation of the labs changed so much since they were designed that the air quantities were obsolete. The building engineers needed to make immediate adjustments to the building systems to adapt to this new equipment load. We redirected our efforts into a “calibration and as-built” project to establish a baseline for a future project to evaluate the laboratory themselves and reconfigure the HVAC systems to match the ever-evolving lab spaces.
Palasz: The research building’s energy efficiency is always secondary to code requirements and lab-safety requirements. Improvements in efficiency are often discussed during design and often involve the prospects of incorporating more controls, and energy-recovery devices when required, or when the situation indicates a suitable/ quick payback.
Hombsch: Nearly every laboratory will use multiple energy efficiency strategies, which will typically include for initial consideration: VAV fume hoods/exhaust/make-up air systems, environmental assessment (EA) energy recovery, high-efficiency energy-recovery chillers, high-efficiency boilers, variable-speed pumping, and free cooling for base, sensible, and process cooling.
Matthews: Fan arrays for AHUs are a fairly recent equipment design that we like to integrate into the majority of our designs. This technology has improved fan-energy performance for all variable airflow systems and has provided additional benefits, such as added redundancy, using a smaller footprint, fan motors that are easier to replace, and lower sound performance.
Sharpe: Many energy-efficient means are employed. A partial list is: reduced ductwork and piping system pressure drop by reducing fluid velocities; lower AHU face velocities of 300 to 400 fpm; wind tunnel testing so exhaust-stack velocities are reduced by the exhaust-fan variable-speed drives in real time per a lookup table of acceptable wind speeds and directions; VAV fume hoods in fume hood-driven spaces; chemical sniffers in labs to reduce air-change rates when chemicals are below thresholds; chilled beams in heat-gain-driven spaces; heat-recovery chillers; energy recovery with runaround coils; and ventilation reduction or shutoff using room-occupancy sensors.
CSE: Describe a project in which you specified a specialty piping, hydronic, or pumping system for such a facility.
Locke: We are working with a group that has been successful in the lab with carbon dioxide (CO2) concentrations, using this to create barriers to fish and applying this success in a setting outside the lab. The system pumps out large amounts of water, infuses CO2 into the water, and injects the mixture back into the control boundary.
Hombsch: Some specialized laboratory projects have included water for injection; 18-megohm DI water; high-pressure process cooling loops (50-psi DP); -26°F process cooling loops; ultra-high-purity gases including oxygen, nitrogen, hydrogen; toxic and pyrophoric gas distribution; and 3,200-psi N2.
CSE: What best practices should be followed to ensure an efficient HVAC system is designed for this type of building?
Sharpe: Performing a wind tunnel study is critical for these building types where dangerous chemicals can be emitted from fume-exhaust stacks and entrained into building outside-air intakes. A wind tunnel study in the schematic phase will inform the design for placement of AHU intakes and fume-exhaust stacks and determining minimum fume-exhaust stack velocities. Another best practice is do not exhaust fume hoods individually or by groups. Instead, combine the fume hood exhaust with the laboratory’s general exhaust into a large central exhaust system. Do this so any chemicals are diluted within the ductwork airstream (often avoiding expensive stainless- steel fume-exhaust ductwork). This also allows flexibility when a fume hood needs to be added in place of the room’s general exhaust. There are numerous other best practices, like reducing room air-change rates, diffuser placement to avoid turbulence at the fume hood face, VAV fume hoods, and ceiling-space zoning of MEP systems to avoid congestion.
Edwards: A best practice would be to stay engaged with the owner to understand the facility requirements. Most laboratory buildings share requirements, but each facility has a unique twist that needs attention in the design of the HVAC system. To achieve an efficient HVAC system, it’s necessary to look beyond what was done on the last project to find what is better for the new project.
Hombsch: A comprehensive understanding of the program requirements, user/owner expectations, project goals, and project budget.
Matthews: We like to practice a low-tech approach to designing HVAC systems for laboratories that involves three key steps:
- Eliminate the unknowns—understand the intended lab operations (schedules for occupancy, space design requirements, capacity and limitations of the existing infrastructure, etc.).
- Engage with others—maintenance, architects, and health and safety personnel at the start.
- KISS—We believe keeping it simple includes designing with a scalable or modular approach to avoid oversizing as well as providing redundancy; investing in technologies that have the most impact over the life of the equipment (i.e., easier-to-maintain systems like air-to-air energy recovery); and using straightforward controls sequences that can be successfully implemented, commissioned, and maintained.