The science behind laboratory and research facility projects: HVAC and sustainability/energy efficiency
- Steven Graff, PE, Senior Mechanical Engineer, Kupper Engineering Inc., Ambler, Pa.
- Mike Lawless, PE, FPE, LEED AP, Client Executive, IMEG Corp., St. Louis
- Gerry Williams, PE, LEED AP, CxA , Senior Mechanical Engineer, CRB, St. Louis
- Robert Zamudio, PE, LEED AP, Senior Design Engineer, Southland Engineering, Union City, Calif.
CSE: What unique HVAC requirements do lab and research facilities have that you wouldn’t encounter in other buildings?
Gerry Williams: Many facilities, such as dry labs, electronics labs, clean rooms and pharmaceutical labs, require high amounts of airflow or filtered air to maintain sterility, but have very low amounts of latent load. They also are often kept at a lower room setpoint temperature—between 64° and 68° F—to keep from overheating occupants who often must wear lab coats or Tyvek covers. These facilities also can have critical high and low relative-humidity requirements; however, due to the high air-change rate, they do not require the 55°F supply-air temperature that is more common in traditional facilities. These spaces only need supply air at 60°F or higher to control the relatively small sensible load. Due to the psychrometric requirements to maintain 50°F relative humidity in the space at 66°F, the supply air would be cooled down to 47°F to wring out the moisture in the air (introduced by outside air). Then the 47°F air would need to be reheated back up to 60°F to keep it from overcooling the rooms. Or, a dedicated outside-air system can be used.
Graff: Specialty lab equipment with high heat loads or unique installation requirements. One project had an existing high-performance electron microscope that was being relocated. We needed to consider acoustic noise and vibration as well as HVAC requirements. The microscope needed to be mounted on a thick concrete pad and was located in a separate room from the ancillary equipment to reduce heat loads and vibration issues. The air-handling system had to be designed to maintain a tighter temperature tolerance than usual, to not affect the specimen being studied. Other types of equipment we run into quite frequently are high-performance liquid chromatographs and gas chromatographs. These are also highly sensitive instruments that have significant heat loads and have precise HVAC requirements that need to be considered during the design of these labs.
Zamudio: Once-through air systems (non-recircuiting), exhaust valves, minimum air changes per hour (ACH), low-velocity diffusers, high filtration levels, 24/7 operation. Additionally, there is a variety of lab equipment requiring direct exhaust, such as fume hoods and vacuum-pump cabinets.
Lawless: The primary HVAC requirement that drives lab design is the requirement to exhaust labs and provide for a minimum number of outside-air changes in every lab. This outside-air requirement drives the entire design, from system capacity to air distribution, to minimize occupant exposure to contaminants. The goal is to first minimize the amount of outside air that is required, then set out to minimize the amount of energy you use to treat the outside air. In very simple terms, that is the path for effective HVAC design in a lab.
CSE: Have you specified distinctive HVAC systems on any such facilities? What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs? This may include fume hoods, pressurized rooms, or other specialized products and systems.
Graff: I wouldn’t consider them infrequently specified, but we use a lot of Venturi-type airflow valves in lieu of the standard butterfly-type VAV boxes that you would typically find in an office HVAC system. The Venturi-type airflow valves are used to actively control and maintain pressurization schemes within the labs. The control of these valves is often tied into the fume hoods to maintain the proper airflows at different sash positions and reduce energy consumption.
Lawless: Sometimes simple solutions can seem innovative to others. On the Jarvis Hall project at the University of Wisconsin-Stout, we asked a simple question of the faculty: How much do you use each hood? The faculty estimated that each hood was used an average of 5% of the year. We then collaborated with the team to provide solutions for storage of chemicals or other uses that might cause a hood to need to remain on. We then provided a switch on each fume hood so it could be turned off, closing the air valve. The most energy-efficient fume hood is one that is off. I think this is a great example of a university evaluating how they use a space and spending their resources efficiently.
CSE: Have you specified variable refrigerant flow (VRF) systems, chilled beams, or other types of HVAC systems into one of these structures? If so, describe its challenges and solutions.
Zamudio: We have explored chilled beams and displacement ventilation, but due to a large amount of economizer hours in the San Francisco Bay Area, the energy savings did not result in viable payback periods. Other than first costs, ceiling space and maintenance (coil cleaning) is a challenge with chilled beams, while wall space or millwork integration is a challenge with displacement ventilation.
CSE: What types of waste-heat recovery, combined heat and power, or other systems have you designed for such a project? Please describe the challenges and solutions.
Graff: We have done waste-heat recovery on exhaust airstreams with a glycol runaround loop to preheat incoming outdoor air.
CSE: What types of dedicated outside-air systems (DOAS) are owners and facility managers requesting to keep their facility air fresh?
Williams: These types of facilities are ideal for DOAS. By using a DOAS, sensible-cooling-only AHUs can provide the required air changes to the rooms with cooling coils that modulate to remove the sensible load from motors, lights, and people in rooms. These systems cool down the air from a room condition of 66°F to supply 60°F air, or as needed, to maintain room temperature. The DOAS unit would cool the air to 47° (or colder) to remove the moisture from the air and provide preconditioned, dry make-up air to the sensible-cooling units. The dry make-up air absorbs the small amount of latent moisture generated in the space. Significant energy savings can be achieved as a result. Cooling the make-up air—which can be as low as 10% to 15% of the total airflow—to a low dew point temperature and using the AHUs to sensibly cool the air to the supply-air temperature that is needed eliminates the use of reheat coils.
CSE: What types of air balancing or environmental balancing do you include in your design? Describe the project.
Williams: Air balancing and rebalancing are critical to the proper operation and longevity of environmental controls systems. Provide access to the air balancing and controls device so that service technicians and maintenance staff can work on those devices without disturbing the building’s occupants. Ideally, this is a consideration during the design phase of the building. For example, wide corridors allow for VAV boxes and balancing dampers to be accessed from the hallways. In critical-control facilities, such as pharmaceutical facilities, the HVAC system needs to be rebalanced annually or even semiannually. HVAC equipment, VAV boxes, reheat coils, filters, and balancing dampers should be in mechanical mezzanines or interstitial floors above the spaces they serve. Well-lit, defined walkways that have adequate clearance height for maintenance personnel should also be included. This can be the difference between a well-maintained, properly working system and one that is not.
Graff: We specify air balancing on all our projects to verify that the installed and operating condition meets our design. For lab and pharma projects, we calculate door leakage or transfer air into and out of spaces to create pressure differentials. We then require a certified air balancer to come in and verify that the specified pressure differentials are being met and maintained.
CSE: What unusual systems are owners requesting that help save energy and/or electricity when a space is unoccupied?
Zamudio: Proactive owners are using occupancy sensors to reset air-change requirements when zones are unoccupied. This strategy generally requires environmental, health, and safety approval.
CSE: Energy efficiency and sustainability are frequent requests from building owners. What net zero energy and/or high-performance systems have you recently specified in such facilities (either an existing building or new construction)?
Zamudio: HVAC loads in laboratories are typically process-driven, and there is little flexibility for temperature setback. This imposes severe constraints on achieving net zero, short of a massive photovoltaic array. That said, there is still significant room for energy reduction. Low-hanging fruit includes optimized control strategies as well as energy-conscious lab protocols. It’s common to walk into a lab and see every fume hood wide open and only a few in use.
Graff: Unfortunately, we have not done any net zero energy projects to date, but it is a hot topic.
CSE: What are some of the challenges or issues when designing for water use in such facilities? What types of low-flow fixtures, water reuse, or other techniques have you designed?
Zamudio: Traditionally, glass wash and autoclave discharge are tempered with potable water prior to entering the waste-drainage system. Alternatively, we have discharged through a heat exchanger cooled by the chilled-water system. We also have evaluated reuse of RO-reject water for the cooling tower make-up.
CSE: How has the demand for energy-recovery technology influenced the design for these facilities?
Zamudio: A large institutional client requires new projects to exceed California Title 24 efficiencies by 20%. To achieve this, we used runaround heat-recovery coil loops at the air handlers to recover waste heat from the lab exhaust.