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Further, if electricity is separated from all other fuels, the operation of buildings consumed 76% of the total power generated in the US in 2000[2]. A closer look at the energy consumption by most buildings reveals that heating, air conditioning, and ventilation top the list, followed by ancillary lighting and appliance power. The propensity of engineers and architects has been to seek energy savings through the easiest possible methods, or the proverbial "low hanging fruit."
Many believe that the green movement starting in the late 1990's has become the modern-day industrial revolution. The green movement is now well-engrained in politics through new laws, executive orders[3] and energy guidelines, as well as in the disciplines of engineering and architecture. This is best demonstrated, for example, through new and evolving ASHRAE guidelines, private sector groups such as the Green Building Council (LEED® program), and through new academic training; both collegiate and professional engineering.
The focus of this article is on energy efficiency in lab animal facilities. These buildings tend to be high consumers of resources due to the unique constraints under which they operate. Because of the expense of many species of lab animals, it encourages facility owners to use more energy to provide the safest and most stress-free environment available for the animals.
Many other constraints also contribute to the demand for higher energy consumption in this industry such as stringent government requirements for ethical treatment of animals, a certain degree of barrier protection from outside pathogens, a prescribed amount of housing space, and a reasonable indoor air quality (IAQ) for both animals and their caregivers. Other constraints may include the provision of comfortable working environments, the need for sufficient lighting and the requirement for power-intensive equipment necessary in research. When these constraints are compared to the demand for energy efficiency, the job of engineers and architects becomes much less tenable than in previous years.
One More Energy Saving Opportunity
In many cases, the majority of the "low hanging fruit" such as energy-efficient lighting, occupancy sensor driven Variable Air Volume (VAV) ventilation, and highly efficient appliances have already been identified. The next easiest energy-saving item is the design of efficient room ventilation distribution.
Finding the Ventilation Sweet Spot
A plethora of engineering techniques exist to reduce the cost of operation and make the facility “greener” overall. These techniques include recovery of waste heat from exhaust air as a means of preconditioning for the supply air; premium efficiency motors driven by variable speed drives; low static pressure air distribution; supply air temperature reset to reduce simultaneous heating and cooling; and ultrasonic humidification. However, one of the most significant efficiency improvements that a designer can achieve is through the optimisation of air distribution in the holding rooms. All of the other efficiency improvements listed to this point are upstream and are related to the actual mechanical operation of the ventilation system itself.
Optimisation of air distribution is the most commonly overlooked efficiency improvement in lab animal facilities, both currently and historically. It is often dismissed as trivial in the overall scheme of things, where engineers have traditionally relied upon antiquated or unreliable hand calculations using often invalid assumptions to arrive at their conclusions. For instance, many calculations make erroneous assumptions about perfect mixing of gases (odors) or heat, assume no temperature stratification and presume some ideal flow path of air in the room. Also, hand calculations can neither differentiate between low or high exhausts, nor use point-source locations of odour and heat sources.
The analysis technique we use to help identify the best air flow distribution in a holding room is known as Computational Fluid Dynamics (CFD). CFD is a computer software tool that considers a virtual replica of the space, and using the laws of physics, predicts the dynamics of ventilation air - flow path, temperatures, odour and particulate accumulation.
CFD is the most accurate and visually intuitive way of assessing IAQ and ventilation performance available today. Many facility owners, architects and engineers still don't rely on CFD, but the concept is rapidly building popularity as the green revolution demands greater energy efficiency in buildings.
The Guide for the Care and Use of Laboratory Animals[4] has recommended the use of CFD since 1996, and many of the mainstream engineering organizations are now recommending this type of analysis as well. Further, the US Green Building Council is offering potential award points toward the LEED program for using CFD[5].
Understanding How Typical Ventilation Behaves
Past observations on room air contamination revealed that the levels can be increasingly controlled with higher fresh air flow rates - not surprisingly. The difference between efficiently ventilated rooms and poorly-ventilated rooms, however, is to what degree lower flow rates impact those concentrations. The behaviour of poorly ventilated rooms exhibit high concentrations at static or low air change rates. These concentrations usually remain fairly constant through the 15 Air Changes per Hour (ACH) range, falling precipitously in the 20 ACH range, followed by diminishing returns after approximately 25 ACH. Optimal ventilation, on the other hand, typically shows the best ventilation efficiency between 10 and 15 ACH (Figure 1.). The net result for most rooms is a drop in the airflow rate from around 20 ACH to less than 15 ACH, or a 25% to 40% reduction in flow.
Figure 1. Optimal ventilation window.
By efficiently lowering the air flow rates 25% in a facility, a non-linear initial cost reduction of 40 to 60% may be achieved, depending if building is new or renovated. Most of the savings are due to the downsizing of HVAC equipment. Further, the annual operating cost would be decreased by 50% to 55% due to smaller chillers and more efficient air handling[6]. Other non-mechanical savings may also present themselves such as smaller infrastructure and shorter floor-to-floor heights in the building.
Optimal Air Distribution Case Studies
Through three actual case studies, we teach a methodology of evaluating and identifying ventilation designs that can significantly reduce energy while simultaneously improving IAQ. These case studies involve two new lab animal facility room designs, and one older renovated design. The primary species utilized in the three rooms include rabbits, but also consider non-human primates and dogs. The dog kennels are intended to be multi-species designs where small adjustments to the ventilation system can be made and new caged animals could be relocated into the space.
The strategy for all three room types was to benchmark the initial ventilation designs using CFD, then systematically "tune" the ventilation system for optimal performance. The tuning is accomplished by (1) evaluating locations and quantities of exhausts grilles, (2) evaluating flow paths between the supplies and exhausts that effectively “wash” the contamination sources, (3) making use of available thermal buoyancy to help move the air, and (4) reducing the supply air while achieving the best IAQ performance.
Case 1 - A New Rabbit Room
The first case study involves a rabbit holding room with open metal caging as the preferred housing rather than ventilated racks.
The room is setup as a symmetrical arrangement of 3-tiered, double-wide rabbit racks with supplies and exhausts located on a central soffit on the ceiling. The soffit is a well-proven design that works best for caged animals where significant metabolic heat is densely packed into small areas. The function of this ventilation technique is based on a flow pattern that spreads to the floor, bifurcates toward the walls and cages, rises upward along the walls carrying away contamination, then at the ceiling becomes redirected toward the soffit exhausts.
The success of each design is judged on the airborne ammonia concentrations coupled with temperature uniformity and air movement through the racks. When comparing to conventional room designs, the soffit will use at least 25% less air to achieve better IAQ in the same space.
Figure 2 shows a photograph of the finished room design, figure 3 depicts a typical cross-section of ammonia concentration at 15 ACH, and Figure 4 shows isosurfaces of a barely detectable ammonia concentration of 7 parts per million (ppm). The flow rate could arguably be lowered even further if slightly higher ammonia concentrations and temperature gradients are deemed acceptable.
Figure 2. Photo of new rabbit room.
Figure 3. Ammonia contours on a cross-section.
Figure 4. 7ppm Isosurfaces of ammonia.
Case 2 - Renovated Rabbit Room
The second case involves an existing rabbit room with known deficiencies in its ventilation. Caregivers working in this room often remarked about the potency of the odours and its stuffiness. The space is densely packed with eleven 3-tiered, double wide rabbit racks, two conventional ceiling supplies and one low corner exhaust. The flow delivered to the room is in excess of 20 ACH.
A benchmark evaluation was first performed to quantify the room temperatures and airborne ammonia concentrations compared to observation. Consistent with physical observations, Figure 5 shows relatively high ammonia concentrations at 5 feet above the floor, and Figure 6 shows pervasive 15 ppm isosurfaces.
Figure 5. Ammonia concentration at 5 ft from floor (Before optimisation).
Figure 6. 15ppm Isosurfaces of ammonia (Before optimisation).
In this particular case, the existing building construction prohibited the use of a soffit configuration, so other avenues were pursued to solve the ventilation issues. An optimisation study followed the benchmark study that systematically replaced existing diffusers with radial diffusers and changed the location and quantity of exhausts.
The final design uses three square radial diffusers with two sets of high/low exhausts at diagonal corners of the room. Figure 7 shows improved ammonia concentrations at 15 ACH, and Figure 8 depicts sparse 15 ppm isosurfaces. Using an Optimised air distribution in this case permitted designers to achieve superior contamination control at significantly lower air flow rates.
Figure 7. Ammonia concentration at 5 ft from floor (Optimised).
Figure 8. 15ppm Isosurfaces of ammonia (Optimised).
Case 3 - A New Hybrid Multi-species Room
The final case evaluated in this study involves a kennel with the capability of being easily converted for smaller caged animals. The design uses a central soffit as described in case 1, but also has low exhausts on one long side of the room. Multiple low exhausts tend to extract contamination better for larger animals where heat is not concentrated and the odour sources are on the floor. When operating in the kennel-mode, the soffit exhausts are closed. If smaller caged animals are used, the low exhausts are shut off and the soffit exhausts are turned on. A similar success in distribution efficiency was achieved in this design as compared to other cases examined.
Figure 9 is a photograph of the final design without dog runs or other caging. At 15 ACH, this room performed with superior function as either a kennel or a room with smaller caged animals.
Figure 9.Photograph of final design: Multi-species room
The Operating Cost Benefit
An operating cost-benefit analysis was performed for this 40,000 GSF multi-species vivarium based on three different US cities; Boston, Dallas (near the actual installation), and San Francisco. Factors included in the energy study are the fan energy, chiller plant, and boiler plant, the facility geographic location and the cost of energy in the respective region. By employing the simple optimum air distribution techniques outlined in this article at 2007 energy costs, yearly operation savings would be $185,726 in Boston, $218,878 in Dallas, and $123,179 in San Francisco7. Additionally, the carbon footprint is reduced by well over one million pounds of CO2.
Conclusion
The continual increase in the cost of energy and the impact that buildings place on our global environment has forced everyone to more closely scrutinize energy consumption of their facilities. Engineers and architects have already discovered many efficiency improvements with mechanical equipment and appliances used in lab animal buildings, but have largely overlooked a substantial and easily-obtained energy savings.
The use of advanced analysis tools, such as CFD, can lead to optimal ventilation distribution design, improvement of indoor air quality, and at least a 25% reduction in operating cost. Additional savings are available through capital cost reductions for smaller HVAC equipment and potential savings through reduced building infrastructure. Air distribution optimisation, when combined with other sustainable design strategies, begin to steer our buildings toward the goal of a zero carbon footprint.
Scott Reynolds, MS, PE is the founder and manager of the CAES Group of M/E Engineering, PC. He has been in the field of CFD since 1988 and has modeled over 500 projects worldwide in that timeframe. The CAES Group, M/E Engineering PC., 441 S. Salina St, Suite 702, Syracuse NY 13202; (315) 218-9569; sdreynolds@meengineering.com; www.meengineering.com/CAES.asp
Eric Joesten, PE, LEED AP, is the Director of Mechanical Engineering for the Architectural/Engineering Firm EwingCole, specializing in mechanical systems for animal research facilities. He has designed the HVAC systems serving over 1 million sq.ft of vivarium space for a variety of private and government sector clients. EwingCole, Architects, Engineers, Planners, 100 North 6th Street, Philadelphia, PA, 19106; (215) 625-4491; ejoesten@ewingcole.com; www.ewingcole.com
References
- US Energy Information Administration. (n.d.). Energy Information Administration. Retrieved 10 30, 2008, from Official Energy Statistics from the U.S. Government: http://www.eia.doe.gov/
- NYS OGS. (2005, 5 12). Executive Order 111 Directing State Agencies To Be More Energy Efficient And Environmentally Aware. Retrieved 10 30, 2008, from NYS OGS: http://www.ogs.state.ny.us/purchase/spg/pdfdocs/EO111.pdf
- Institute of Laboratory Animal Resources, Commission on Life Sciences, National Research Council. (1996). Guide for the Care and Use of Laboratory Animals. (N. Grossblatt, Ed.) Washington DC: National Academy Press.
- Architecture 2030. (n.d.). The Building Sector: A Hidden Culprit. Retrieved 10 30, 2008, from Architecture 2030: http://www.architecture2030.org/current_situation/building_sector.html
- USGBC. (n.d.). Retrieved 10 30, 2008, from US Green Building Council: http://www.usgbc.org/
- Reynolds, S; Joesten, E. (2007, 4 11). How to Improve Holding Room Ventilation While Saving Energy. 2007 Turnkey Conference . Boston, MA, USA: Animal Lab News.
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