A Performance-Based Approach to Laboratory Design
By Nathan Ho, PE – Market Leader, Laboratory Environments
Following up on our previous article covering design trends in the laboratory industry, this article will build on the concept of designing laboratories for top-tier performance. As construction, utility, and operation costs continue to escalate, both owners and users have a growing stake in laboratory facility performance. These costs diminish the funds available for research and investment, thereby impacting the capacity and quality of laboratory output.
At the core of the laboratory optimization process is close collaboration among facility stakeholders – chief scientists, environmental health and safety (EH&S) professionals, owner / operators, and the design team – all of whom play an important role in identifying key performance metrics and exploring options to achieve them. These metrics define the parameters that bound the optimization process and drive all design decisions that follow.
Life-Cycle Cost (LCC) effective HVAC design is the basis for optimizing laboratory facility performance. Utilizing the LCC method involves evaluating multiple design concepts to identify the best approach for the project.
A holistic approach is required to effectively apply LCC champion designs in laboratory and facility applications. Thermal and ventilation loads, as well as environmental conditions, can drastically alter the outcome of LCC design analysis. For example, a favorable design for a thermal load-driven laboratory may be completely different from an optimum design for a ventilation-driven laboratory. Therefore, it is imperative that the above described collaboration takes place to define the critical parameters for laboratory design.
Prescriptive vs. Performance-Based Approach: What’s the difference?
When working in any engineering environment, there are two approaches one can take: prescriptive or performance-based. In mission-critical systems, such as laboratory facilities, the performance-based approach will often lead to better outcomes when LCC studies are taken into consideration.
Over 100,000 decisions are made during the design process. Below are three examples of ways in which the performance-based approach yields superior results.
- Fume Hoods – The latest version of NFPA 45 provides new performance criteria to determine minimum fume hood exhaust rates based on percentage of LFL (Lower Flammability Limit) of chemicals within the hood. The previous requirement, and common industry practice, is a prescriptive 25 CFM per square foot of interior hood space. The new performance-based approach allows for up to approximately 60% reduction in the minimum required airflow rate.
- Laboratory Exhaust Systems – The purpose of the laboratory exhaust system is to safely disperse harmful contaminants from the lab facility. For many years, and still common industry practice, the prescriptive approach has been to design lab exhaust stacks to achieve a discharge velocity of 3,000 FPM. However, this approach is lacking in that it does not take into account all of the factors that determine exhaust plume performance. Exhaust plume performance is essentially a function of momentum, which includes air mass as well as velocity.
Conducting a wind study using local wind and topographical conditions can assist the design process by modeling dispersion performance. Constructing a scale model and performing wind tunnel analysis can validate the computational model and provide insight into the unique performance operating parameters required for the project. We have found that large centralized lab exhaust systems can often operate safely at velocities lower than the prescriptive option of 3,000 FPM, which can yield significant fan energy savings.
- Vivarium Ventilation Rates – The Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC) suggests a typical acceptable range for room air change rates. However, the guide does not specify for which space types or uses these broad ventilation rate guidelines are appropriate. Therefore, many designers tend to assume that the highest rates apply to all spaces.
Our approach differs in that we collaborate with stakeholders such as the chief scientists and lab managers to understand the intended space uses and confirm ventilation requirements. Often times, lower ventilation rates are sufficient depending on space use and application. For example, if animal holding rooms utilize ventilated cage racks, then lower ventilation rates from the central HVAC system may be sufficient to achieve proper room conditions. This requires close coordination with the lab users, as well as the lab equipment specialist, but can lead to leaner designs that deliver superior efficiency in terms of energy and cost savings to the owner.
Designing for Existing Laboratory Facilities
Laboratory optimization is not exclusive to new construction. This approach can be applied to existing laboratories with great success. Our experience has shown potential annual energy cost savings in the range of approximately $3 to $5 per cubic feet of air (CFM) in turn-down achieved for our laboratory variable-air-volume (VAV) conversion projects in coastal California. Deeper savings are possible in more extreme climates. Typical laboratory facilities are often able to achieve approximately $1,500 to $2,500 per laboratory space in annual energy cost reduction when converted from constant-air-volume (CAV) to VAV operation in California.
We have found existing vivarium and Biological Safety Laboratories (BSL) facilities to be especially attractive candidates for optimization due to the generally lower mechanical equipment costs when compared to fume hood laboratory retrofits. Combine the above observations in energy savings with the reduced capital expenditure to retrofit mechanical systems for vivarium and BSL facilities and the simple payback comparison is usually better than the already excellent paybacks achieved at similar fume-hood laboratory applications.
Popular Retrofit Opportunities for Existing Laboratory Facilities
- CAV to VAV Conversion – Save energy and improve operational flexibility
- Laboratory Exhaust Fan Consolidation – Reduce ongoing maintenance while improving IAQ and operational flexibility
- Laboratory Exhaust Fan Optimization – Reduce or eliminate the need for bypass air
- Glass and Cage Wash Controls Upgrade – Allow smart operational scheduling
- Fume Hood Sash Management – Monitor and manage use
- Flexibility Upgrades – Capability to convert from 100% outside air to local-conditioning for labs that are repurposed from wet-chemistry to non-chemical use
- Ventilated Cage Racks – Reduce ventilation energy consumption and bedding replacement costs
At P2S, we’re committed to pursuing the performance-based approach for our projects, no matter the industry, as it will lead to better, more efficient, cost-saving outcomes for our clients.