Designing laboratory controls
Labs have unique building automation and HVAC control requirements. Here’s a look at two examples of university research labs.
Raj Vora, PE; Peter Pobjoy, PE; Mark Crawford, PE; and Michael Phillips
Laboratory facility engineers face significant design challenges in meeting the criteria of laboratory functionality, energy efficiency, sustainable design, health and safety codes, reliability, and long-term system flexibility. Conflicts among requirements, code updates, and code interpretations add to the complexity of many lab projects and result in many unique solutions. HVAC system design and corresponding building automation systems (BAS) are likewise becoming increasingly complicated.
In this article, we will explore the trends associated with a standard BSL-2 compliant large university research lab from both a BAS standpoint and from the update and interrelationship among codes, standards, guidelines, and local authorities having jurisdiction (AHJ) approvals. BSL-2 compliance refers to the lab’s BioSafety Level (BSL). In this case, BSL-2 means that the lab environment contains bacteria and viruses (Lyme disease; hepatitis A, B, and C) that are known to cause mild illness in humans, and standard personal protective equipment (PPE) is limited to gloves and safety glasses.
Developments in lab criteria
Typical laboratory design is complex due to the number of criteria to meet. Common factors are:
- Occupant comfort
- Air change rates (air changes per hour, ACH)
- Room airflow direction and speed
- Pressure relationship between spaces
- Filtration: supply and exhaust
- Hood HVAC requirements
- Redundancy and emergency backup requirements
- Modes of operation: normal, emergency, setback
- Fire and life safety requirements
- Equipment and space criteria monitoring and alarms
- Energy efficiency
- Energy/utility metering.
The trend toward green building has made a significant impact on laboratory design, including "energy efficiency" and "energy/utility metering" from the list above. Federal regulations have increased the number of requirements to reduce energy use in all government facilities. The Energy Policy Act of 2005 (EPACT 2005) and the Energy Independence Securities Act of 2007 (EISA) have significantly increased the number of requirements for energy efficiency and sustainable design. Requirements for federal buildings include 30% energy savings, reductions in fossil fuel use, and consideration of solar water heating. While laboratories, due to their critical nature, are sometimes exempted from these requirements, often these standards must be met in addition to the usual laboratory requirements.
Local code adoption of green building codes and standards such as U.S. Green Building Council LEED and Green Globes has done the same for both public and private sector buildings. ASHRAE 189, Standard for the Design of High-Performance Green Buildings, is poised for adoption by local jurisdictions to incorporate green building standards, which should expand the jurisdictions’ green building regulations. Typically, these codes reference ASHRAE 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings (this is technically a standard often adopted as code), which becomes stricter and more complicated with each update. Versions 2004, 2007, and upcoming 2010 have all made significant increases in required energy savings as well as mandated certain energy-saving features such as variable speed control of most motors. In addition, owners are adopting LEED building targets for buildings that exceed code requirements by selecting performance standards higher than code using approaches such as LEED and/or Energy Star.
On public-sector projects, it is our experience that projects often require meeting several "competing codes" that overlap in regulation. Public sector projects have several more governing bodies: AHJs, federal codes/mandates, and federal requirements like Unified Facilities Criteria and GSA’s PBS-P-100. The private sector projects are usually limited to local and state codes and local AHJs. This creates unique criteria for a project based on the compilation of various codes such as National Fire Protection Assn., International Mechanical Code, and others.
The changes detailed above result in new mandates that require new interpretations by and agreements between the local code officials and the engineers. Strong communication between design team members is critical to keeping abreast of changes in laboratory design criteria. Early involvement in the design process by local AHJs and by key subcontractors has been proven to aid the project in reaching affordable, constructible, controllable, and on-time design. The case studies include examples that demonstrate success due to early design involvement by the right parties. As changes in criteria become increasingly common and requirement complexity grows, project delivery with integrated project teams should be a growing trend in laboratory work.
To achieve the controls strategies needed to make these lab projects compliant, it is important not only that the BAS provider be involved early in the process—even before the design phase--==—but that the provider understands the design build process and collaborates as a “partner” to the process and not just another subcontractor. Some of the elements that the controls design team must understand early in the project include:
- The complete expectations of the customer and design engineer of record
- Redundancy requirements
- Fume hood controls, room pressure controls, and expected control response times
- Control and/or monitoring of life safety functions and the various codes and standards that need to be met as listed above
- The importance and level of monitoring for alarms, energy usage, and validation.
The teaming and partnering approach can be a challenge for some building automation providers who are more used to the plan-and-spec bid contracting delivery. In fact, in some delivery methods the controls contractor has not been involved until very late in the process, sometimes after the construction is well under way.
Both building automation providers and laboratory control providers have a wide array of technologies to bring to the table to solve the many lab controls challenges. For starters, many one-time extras or costly additions to BAS are now standard features, making it easier for customers to select more cost-effective commercial control systems. Examples include the following:
- Communicating room sensors now come with not just temperature and humidity inputs but CO2 and occupancy sensors built in. This saves installation costs and can streamline implementing energy-saving strategies such as demand control ventilation (DCV) or lab use occupancy controls. It is important to note that these are typically third-party products and the native capability of BAS vendors’ products may be lost if these integrated devices are used.
- Newer commercial-grade control systems are becoming more programmable logic control-like, featuring much higher processor speeds and high-density input/output.
- Systems are now almost entirely Ethernet-based at the master panel level, allowing for much faster data collection and quicker response times.
- Most systems offer permanent data trend archiving of several years as standard options and advanced reporting features for energy monitoring and verification. Dashboards, while an overused buzzword, can be extremely useful in evaluating a facility’s energy use and performance when properly set up to do so.
- Standard communication protocols make it easier to integrate different systems within a lab building and therefore centralize monitoring, reporting, and data tracking
- Advanced cost-effective sub-metering can be used to meet the requirements of many of the new codes and standards being implemented, such as ASHRAE 189.1.
- Direct digital control systems, similar to older pneumatic systems, can be designed to operate in “fail-safe” modes, ensuring critical functions are maintained during power failures or building events such as fire or earthquake.
Modern lab control and fume hood systems also offer advanced features that maintain safety while assisting with energy conservation measures:
- Variable air volume (VAV) fume hoods with sidewall sensing controls. Fume hoods with sidewall sensors actually measure the average fume hood face velocity. Controls quickly adjust face velocity based on competing airflows and sash movements. These VAV fume hood controls therefore maximize safety by detecting any change to face velocity. Although sidewall sensing technology has been around for more than 20 years, the debate continues on how which control scheme is the best and which device technology improvements can provide the most impact.
- Low-flow fume hoods that operate efficiently at face velocities of 60 or less fpm. (Many local codes require minimum face velocities of 100 fpm, so a variance may be required.) It should be noted here that most low-flow (high-performance) hoods can be operated in a VAV mode.
- State-of-the-art pressure monitors or offset tracking systems with higher resolution and faster response times allow for more reliable flow tracking.
- Integration of fume hood controls and BAS monitoring and alarming. For example, to take advantage of additional energy savings by using VAV fume hoods, an alarm is generated on the BAS if a fume hood sash is left open and the room sensor indicates that the room is unoccupied.
- Laboratory exhaust fans have evolved past the outside air bypass approach, and the use of either variable exhaust velocity or variable geometry (thus controlling volume) systems
University of California
University of California San Francisco (UCSF) Cardiovascular Research Building (CVRB) is a recently completed 232,000-sq-ft research facility located in the Mission Bay campus. This design-build project includes wet chemistry and biology labs on floors two through four, a 30,000-sq-ft vivarium on the fifth floor, and an outpatient clinic on the first floor. The labs are served by dedicated 100% outside air units and dedicated exhaust.
Several unique control challenges arose during the design of this project, challenging the engineering firm to deliver a system that met the client’s requirements and local codes and regulations.
One of the initial challenges was a fire/life safety control issue with the labs on floors two through four. The local fire marshal required that the laboratory fume hood exhaust fans remain running at all times, even upon the loss of airflow of one or more makeup air handlers. This requirement was not based on any specific code or standard; the fire marshal did not want a potentially hazardous situation created if the fume hoods were shut down. The dilemma: If the make-up air units were off, the exhaust system would create a negative pressure in the space exceeding the local building code mandated maximum door-opening force. Southland Industries’ solution was to provide the laboratory spaces with operable windows, which would be controlled by the BAS. In normal operation, the window closures are energized closed. When the BAS receives information of an air handler or fire-smoke damper shutdown, the system communicates with the associated window closures to be de-energized, allowing makeup air into the space. By implementing this control strategy, both the fire/life safety and exiting code requirements were met. As the operable windows are used for emergency or test conditions only, insect- or vermin-proofing was not considered at the time of design.
One of the major design challenges was for the building to have the chilled water (CHW) system separated into two subsystems, critical and noncritical. The critical chilled water system served the vivarium, lab equipment corridors, data closets, and the main server room. The noncritical system served the rest of the building. The critical system was decoupled from the plant chilled water via a heat exchanger, which was connected to a backup chiller. The backup chiller was connected on the secondary side of the heat exchanger to provide emergency cooling to the critical system in the event of loss of plant CHW. The backup chiller is energized only on a communicated loss of supply water temperature setpoint on the secondary side of the heat exchanger. The backup chiller is enabled if temperature in the critical CHW loop is over setpoint for more than 15 min and the condition of the CHW valve from the campus plant is fully open while the pump is in operation. The pump and valve on the primary side of the heat exchanger are closed, and the sequence calls for the backup chiller and pump to energize accordingly.
Another challenge was to meet LEED Energy and Atmosphere requirements for optimizing energy efficiency on the mechanical systems. This was done by implementing several energy control measures. One such measure included a controls strategy to maintain minimum CHW temperature returning to the campus plant. Another strategy was to use waste heat from the server room CHW coil to preheat the noncritical air handlers during cold winter days.
The intent behind the return CHW control was to maximize the CHW temperature differential across the building and to minimize campus plant usage during partial load conditions. This was achieved by modulating the campus CHW valve based on building return water temperature.
The intent of the CHW return temperature control was to minimize the campus plant energy usage by sending design return water temperature from the building back to the plant to maintain a 16 F delta (triangle) T. The building CHW was designed for a 16 F delta (triangle) T. If the return water temperature is colder than 61 F, then the CHW valve feeding water from the campus plant has to modulate to maintain a minimum of 61 F return water temperature with the some of the colder return water recirculating back to the building.
The energy recovery strategy using the server room coils was the most challenging. It required the use of isolation valves and diverting valves, which had to be controlled based on a combination of CHW flow and temperature. These parameters were measured at the servers and compared to the outdoor ambient temperature. Several criteria had to be maintained to successfully implement this strategy:
- The minimum supply water temperature needed to be maintained at the server racks during the energy recovery cycle to ensure the server rack cooling units functioned properly.
- As the CHW system was being converted into a preheat system, the outdoor air temperature had to be cold enough to warrant a switchover to preheat.
- Switchover from normal operating mode to energy recovery was complex as the noncritical CHW pumps had to be de-energized and multiple isolation valves and a diverting valve had to be sequenced before the system could be switched over to the energy recovery loop. See Figure 1 for the CHW riser flow diagram.
The UCSF-CVRB project was complex, with many operational parameters to be met. A thorough understanding of these requirements, and due diligence, enabled the design team to overcome these challenges.
Los Angeles Mission Community College
The New Educational and Laboratory Building (NELB) at Los Angeles Mission Community College in Sylmar, Calif., is a three-story building of about 98,000 sq ft. The building consists of two wings connected by a three-story atrium. Once built, the west wing of the building will be primarily used for classrooms and offices, while the east wing will be used for wet and dry laboratories. These spaces include chemistry and biology wet labs and physics and geography dry labs. The building is currently being constructed while employing a number of strategies to meet the owner's project requirements (OPR), codes and standards, and energy-savings goals.
The OPR dictates several specific design conditions along with referencing ASHRAE, NFPA, and OSHA. The lab minimum ventilation rates are 6 ACH for occupied mode and 4 ACH for unoccupied mode. The lab space temperatures are specified as 75 F cooling and 70 F heating for the occupied mode, and 78 F cooling and 68 F heating for the unoccupied mode. In addition, the lab controls are addressed in the OPR and propose the use of VAV fume hoods with proximity sensors.
The design challenge is to meet the air change rates called for in the OPR while using VAV fume hoods and maintaining space pressure relationships. This has to occur while keeping the space comfortable. Southland’s strategy is to use sophisticated lab controls capable of maintaining a minimum volume of ventilation air. As each fume hood sash is raised or lowered, the sash sensor changes the exhaust volume proportionally, maintaining a constant average face velocity of 100 fpm at each hood opening. The lab controls then adjust the makeup air volume to maintain the room pressurization. When the minimum volume of ventilation air is being delivered to an individual laboratory and the fume hood exhaust valve is exhausting less than this minimum volume, the laboratory’s general exhaust volume is increased. If there is a need for cooling, the lab controls will reset the minimum ventilation signal from the scheduled supply flow minimum to the flow required to maintain the temperature setpoint.
When a control zone occupancy proximity sensor indicates that the zone is unoccupied, the lab control system will reset the fume hood face velocity as well as the minimum ventilation air volume to the unoccupied zone setpoint. If the BAS signal is lost due to a change in operating mode or a failed sensor, the control zone minimum ventilation air volume will reset to the scheduled value corresponding to the operating mode.
In addition to ventilation and space temperature requirements, the OPR includes specific energy-saving goals. The project has a requirement to exceed the California Title 24 energy code by 20% while achieving a goal of LEED Platinum. Several energy-saving features have been designed into the lab HVAC system. These include selection of high-efficiency equipment, heat recovery, and low-pressure-drop duct sizing.
The lab exhaust system has variable speed drives and will use three fans connected to a common plenum. This will allow for the turn-down required for different modes while maintaining the plume discharge height and simultaneously reducing fan energy. The goal of the lab exhaust system is to efficiently remove and dilute large volumes of laboratory exhaust air high above the surrounding campus and neighborhood. Mixed-flow high-plume dilution blowers have been selected and installed to meet this requirement. The lab exhaust system consists of three fans connected to variable speed drives, connecting to a common plenum. The multiple fans allow for the turn-down required for the unoccupied mode while maintaining the plume discharge height and reducing fan energy. Turing off one exhaust fan reduces the operating horsepower by 1/3 while the plume height discharge remains the same. The lab exhaust system also uses a run-around coil loop to safely remove energy from the contaminated exhaust airstream and transfer the energy to the supply air system.
The air handlers will include coils for heating, cooling, and heat recovery. The system will incorporate a bypass scheme to further reduce fan horsepower (energy) when the coils aren’t being used.
The heat recovery coil, a run-around loop system, will use finned tube water coils in the supply and exhaust airstreams of the lab ventilation systems. The coils will be connected in a closed loop via counter-flow piping through which water will be pumped. This system will operate for sensible heat recovery only, and the energy transfer is seasonally reversible—the supply air will be preheated when the outdoor air is cooler than the exhaust air and precooled when the outdoor air is warmer.
Vora is director of life sciences, Pobjoy is chief design officer, Crawford is principal engineer, and Phillips is senior controls engineer with Southland Industries.