U.S. Department of Energy - Energy Efficiency and Renewable Energy
Federal Energy Management Program
New Best Practice Guides for Laboratories Now Available
August 28, 2007
The Laboratories for the 21st Century program (Labs21) has published several new best practice guides on specific technologies that contribute to energy efficiency and sustainability in laboratories. The guides were developed by the Labs21 technical team, with significant participation from industry experts. Each guide was also peer reviewed for technical accuracy. Each includes a description of the technology and provides specific best-practice strategies along with performance metrics and implementation examples. Since a full description of each guide is beyond the scope of this article, we encourage the reader to download them from the Web site for more detailed information.
Modeling Exhaust Dispersion
The standard practice for designing exhaust stacks in laboratories involves the use of prescriptive guidelines, which may oversize the system while not necessarily meeting performance requirements. The practice strategies described in the guide include ASHRAE and Environmental Protection Agency (EPA) calculation and graphical methods, plume dispersion calculations, computational fluid dynamics, and wind tunnel modeling. These methods provide a more accurate assessment of exhaust dispersion. They can be used to produce exhaust/intake designs optimized for energy consumption, taking into account stack height, volume flow rate, exit velocity, expected pollutant emission rates, and concentration levels at sensitive locations.
Water Efficiency in Laboratories
Laboratories offer significant opportunities for water savings. Some of these opportunities, such as increasing the concentration ratio for cooling tower water, rainwater harvesting, etc., are common to other commercial buildings. However, this guide focuses on strategies that are unique to laboratories, such as:
- Elimination of single-pass equipment cooling, which typically consumes more water than any other cooling method in laboratories;
- Use of counter-current rinsing to minimize water used for glass-washing;
- Flow control by using a control or solenoid valve that allows water to flow through a piece of equipment only when it is actually being used;
- Use of reverse-osmosis reject water for non-potable domestic uses; and
- Use of water efficient equipment for sterilization, photography, vacuum systems, dishwashers, and vivariums.
Labs21 Best Practice Guides
- On-Site Power Systems
- Energy Recovery
- Low-Pressure Drop HVAC Design
- Modeling Exhaust Dispersion
- Water Efficiency
- Minimizing Reheat Energy Use
- Right-Sizing Laboratory Equipment Loads
- Optimizing Ventilation Rates
Right-Sizing Laboratory Equipment Loads
Peak equipment loads in laboratories are frequently overestimated because designers often use estimates based on "nameplate" rated data, or design assumptions from prior projects. These estimates result in oversized heating, ventilation, and air conditioning HVAC systems, increased initial construction costs, and increased energy use due to inefficiencies at low part-load operation. This best-practice guide presents a case study of over-sizing, and then describes best practice strategies to obtain better estimates of equipment loads and right-sized HVAC systems. Some of these strategies include:
- Measuring equipment loads in a comparable laboratory during peak activity, and then sizing HVAC and electrical systems based on this data;
- Use of a probability-based "bottom-up" approach to more accurately assess load diversity in a structured, methodical manner;
- onfiguring equipment for high part-load efficiency; and
- Negotiating risk management between owners and designers.
Minimizing Reheat in Laboratories
Load variation across different laboratory spaces can significantly increase simultaneous heating and cooling, particularly for systems that use zone reheat for temperature control. This best practice guide describes the problem of simultaneous heating and cooling resulting from load variations, and presents several technological and design process strategies to minimize it:
- Properly assess load variation during the design process and design HVAC systems taking these variations into account — do not assume uniform loads across the labs.
- Consider alternative HVAC systems that can mitigate reheat energy use by separating the thermal and ventilation systems. For example, a dedicated ventilation air stream can provide tempered air while thermal conditioning is done in the zone with fan coils or radiant panels.
- Continuous commissioning and diagnostics can help to identify zones with excessive reheat and adjust system control and operation accordingly.
Optimizing Laboratory Ventilation Rates
Ventilation is often the largest component of energy use in a laboratory. Various codes and standards recommend a wide range of minimum ventilation rates — from 4 to 12 air changes per hour. In many laboratories, these minimum ventilation rates are set at excessively high levels even though more air changes do not necessarily improve safety. The challenge is to determine an optimal ventilation rate that handles both the worst scenario (possible) safely and manages routine scenarios (probable) efficiently. This guide describes a detailed deliberate decision-making process to optimize ventilation rates, with techniques such as:
- Controlling banding, i.e. classifying hazards in each lab and customizing the ventilation rate accordingly;
- Using lower ventilation rates during unoccupied periods;
- Using emergency overrides with higher ventilation rates during a spill, but reduced ventilation rates during normal operation; and
- Using computational fluid dynamics (CFD) modeling or tracer gas evaluations to optimize the configuration of the ventilation system components.
Labs21 will continue to develop best practice guides on various efficiency opportunities in laboratories, and welcomes input from interested stakeholders for developing these guides.
For more information, please contact Otto Van Geet of the National Renewable Energy Laboratory, 303-384-7369.