Energy-Efficient Laboratory Design

Transcription

1 2005, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ( Reprinted by permission from ASHRAE Journal, (Vol. 47, No. 5, May 2005). This article may not be copied nor distributed in either paper or digital form without ASHRAE s permission. School HVAC Energy-Efficient Laboratory Design By Nicolas Lemire, Eng., Member ASHRAE, and Roland Charneux, Eng., Fellow ASHRAE Located on the Loyola Campus in Montreal, the Concordia University Science Complex (Richard J. Renaud Pavilion) is a 345,000 ft 2 ( m 2 ) L-shaped building consisting of two subbasements and up to six aboveground fl oors. This facility houses academic and research laboratories, classrooms and offi ces. It serves 2,300 students, researchers and staff. The main activities are teaching and research in fi elds such as biology, chemistry, biochemistry, psychology and physical education. It is also home of the Science College and the Centre for Structural and Functional Genomics. About 45% of the building is teaching, research and development, or wet laboratories, including about 250 fume hoods. Modularity and Distribution: For obvious reasons, fitting a 480,000 cfm ( L/s) HVAC system in a mechanical room and distributing air to an L-shaped building is no easy task. Furthermore, redundancy was mandatory for several reasons. Four 80,000 cfm ( L/s) systems were installed in the A wing supplying air to the eight-story North wing, while two identical systems were installed in the C wing supplying air to the four-story B and C wings. Two dedicated 25,000 cfm ( L/s) systems also are installed to supply 100% fresh air to the animal quarters located in the lowest basement. Energy Efficiency Energy efficiency was a primary goal when designing the pavilion. Early on, Concordia University decided to remain the most efficient university campus in the province of Quebec even with a laboratory building housing 250 fume hoods. This project was registered with Natural Resources Canada s (NRCan s) Office of Energy Efficiency s Commercial Building Incentive Program (CBIP). The main objective of the CBIP is to design a building with an energy consumption of at least 25% lower than the reference building designed About the Authors Nicolas Lemire, Eng., is associate and design engineer at Pageau Morel and Associates in Montreal. Roland Charneux, Eng., is associate, senior design engineer, COO and operations vice president at Pageau Morel and Associates in Montreal. Lemire won a 2005 ASHRAE Technology Award (1st Place Institutional Buildings [New]). 5 8 A S H R A E J o u r n a l a s h r a e. o r g M a y

2 Lemire won a 2005 ASHRAE Technology Award (1st Place Institutional Buildings [New]) for Concordia University Science Complex. to strictly comply with the Model National Energy Code of Canada for Buildings (MNECB). At Concordia s Science Complex, those objectives are met and exceeded, as the complex is about 50% more efficient than the MNECB. Comparisons with the ANSI/ASHRAE/IESNA Standard , Energy Standard for Buildings Except Low-Rise Residential Buildings, reference building were not done. However, LEED Canada-NC 1.0 documentation gives an equivalent Standard efficiency of 44% compared to its reference building. Motion detectors were installed in all rooms to directly shut off lights after an adjustable delay. While doing so, a signal also is sent to the building automation system (BAS) to reduce ventilation rates. In labs, 10 air changes per hour (ACH) are maintained at all times when the lab is occupied. However, this ventilation rate falls to 6 ACH when motion detectors don t detect any occupants during the day. At night, it even falls deeper at 3 ACH giving a total strategy for labs of 10/6/3. If occupants are detected at night, the ventilation rate climbs back to its secure position at 10 ACH. This strategy also is applicable for non-lab usage where the rates are slightly modified to 6/3/0. Concordia University Science Complex. The manifolding laboratory exhaust system presents several advantages. The most significant are probably energy savings and lower capital costs and are directly linked to diversity. Since not all fume hoods are operating at maximum capacity at the same time, a diversity factor was agreed with Concordia, allowing for smaller systems. Flow tracking is done on each lab unit totalling air supplied, exhausted and returned to ensure continuous balancing of lab units, departments and floors. Each floor is maintained at neutral pressure by modulating the general return boxes located in public corridors. Airflow tracking also is done at the system level on the supply and return fans. Heat recovery is used on fresh air and exhaust using a runaround glycol loop. Coils and filters in main systems are selected at 400 fpm (2.03 m/s) to reduce static pressure loss. Variable frequency drives (VFD) are installed on all fans, and motors are direct coupled to avoid belt losses and minimize maintenance. A closed loop steam system is implemented in the new facility to prevent flash steam. A low temperature (85 F to 105 F [29.4 C to 40.6 C]) water heating loop also is used to recover heat from various equipment such as M a y A S H R A E J o u r n a l 5 9

3 boiler stack with direct contact heat recovery boiler, chiller condensing water (summer) and heat recovery chiller (winter) condensing water. This chiller is mounted directly between the chilled water loop and the low-temperature water heating loop. It basically is used to recover all internal heat from cold room compressors, growth chambers, freezer rooms, electrical substation, electrical and telecom rooms, computer rooms, etc. The low temperature water heating loop is used for heating and reheating purposes. Summer chillers have been selected to operate at maximum of 0.6 kw/tons (0.17 kw/kw) at full load and cooling towers are equipped with direct-drive low power axial fans coupled with VFD. A summary of energy consumptions for both reference and simulated buildings is shown in Table 1, while Table 2 shows an energy comparison for the reference, simulated and actual building and the related costs. By reviewing literature on existing laboratories, it was possible to estimate that energy consumption averages 94 kwh/ft 2 (1012 kwh/m 2 ) for five very efficient similar laboratory installations as published by Labs 21, a program sponsored by the U.S. Environmental Protection Agency and the U.S. Department of Energy. Table 2 shows that the new pavilion is competitive with its total energy consumption of kwh/ft 2 (623 kwh/m 2 ) (62.59 kwh/ft 2 [674 kwh/m 2 ] simulated), proving the efficiency of all measures detailed during design phases and implemented during construction. Concordia and the design engineers insisted on having a commissioning program to ensure the performance and fine-tuning of all mechanical equipments. Commissioning was done particularly on Energy (kwh/ft 2 ) Reference Building Simulated Building DHW Process Lights Equipment Heating Cooling Pumps Fans Total Table 1: Energy consumption. Case Building Natural Gas (ft 3 ) Electricity (kwh) Total (kwh eq.) Reference 86,698,220 13,496,400 38,898,750 Simulation 44,921,050 8,431,800 21,593,550 Actual 40,572,200 8,083,350 19,978,300 Natural Gas Electricity Total (kwh eq./ft 2 ) (kwh eq./ft 2 ) (kwh eq./ft 2 ) Reference Simulation Actual Natural Gas (CDN $) Electricity (CDN $) Total (CDN $) Reference 1,041, ,050 1,790,546 Simulation 539, ,965 1,007,597 Actual 487, , ,921 Annual Savings $854,625 (CDN $) 1CDN$ equals $0.80 U.S. the BAS to comply with ASHRAE Guideline 1, The HVAC Commissioning Process. This helped to improve energy efficiency. Indoor Air Quality Ventilation Strategies: The ventilation rate procedure of ANSI/ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality, was used to determine required outdoor air quantities based on occupancy information provided in the functional program of Concordia. As discussed earlier, motion detectors were installed to save energy. However, the detectors also are Table 2: Energy consumption (building comparison) & related costs. used for ventilation rate strategies, making sure air change rates are adequate when people are present in labs, whatever the time of day. As shown in Figures 1 and 2, a physical segregation is present between lab units and offices as another way to prevent contaminants from migrating from lab spaces to common areas. As shown, the service corridor, only accessible by authorized personnel, is adjacent to lab units only. That kind of installation was designed based primarily on containment level. Thus, the fume hood, being under negative pressure relative to its environment, represents the first level of containment. Since the lab unit also is under negative pressure relative to its environment, it represents a second level of containment. Finally, the service corridor is maintained under negative pressure relative to the common area but under positive pressure relative to the lab units, giving a third level of containment. Combining both lab and non-lab functions on the same system provides better than minimum prescribed amounts of outside air to all areas while reducing the total amount of outside air (since 100% outside air would have been required for labs and 20% outside air for other purposes). Thermal Comfort: The special VAV system with predetermined air change rate and terminal reheat efficiently provides effective temperature control with no risk of complaints. All zones in the building can maintain effective temperature within the ASHRAE comfort zone as defined in ANSI/ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy (average occupant activity level: 1.2 met, clothing: 1 clo). Light primarily sedentary activity and typical indoor clothing is the general design condition. A maximum of 60% RH is allowed during summer while a minimum of 30% is maintained during winter using steam humidifiers installed in main air-handling units. Mechanical Systems and Equipment: Ventilation ducts and plenums are constructed to comply with the Sheet Metal and Air Conditioning Contractors National Association (SMACNA) Standards, the National Building Code of Canada and the National Fire Protection Association (NFPA), thus reducing opportunity for growth and dissemination of microorganisms. 6 0 A S H R A E J o u r n a l M a y

4 Acoustical insulation was allowed only from terminal boxes to diffusers on the supply network, and from return grilles to control boxes on the return network. Thermal insulation is installed on supply ductwork and media-less silencers are installed on the exhaust network to meet the acoustical level required in labs. Draw-through type systems are used, reheating the saturated dehumidified air just enough to lower the relative humidity to safer levels, at which microbial growth is less likely to occur. Those systems use at least two stages of filtration: 30% pre-filters and 85% bag filters. Efficiencies rating the filtering media are according to ASHRAE Standard , Gravimetric and Dust-Spot Procedures for Testing Air- Cleaning Devices Used in General Ventilation for Removing Particulate Matter. All equipment where condensation is likely to occur are equipped with accessible pans designed for self-drainage, precluding buildup of microbial slime. Coils also have been placed in systems and selected to allow easy access and facilitate cleaning. Laboratory Exhaust Contaminants and Acoustics: Concerns were raised during the design period about lab exhaust re-entrainments and impacts on other buildings in the neighborhood. Concordia University asked for a study of the proposed design in a wind tunnel. However, Concordia s researchers in the field were able to perform that study to assess all concerns. It confirmed that, with minor stack height adjustments, dilution and dispersion of contaminants will not be of any harm for any wind velocity or direction. Acoustical concerns also were raised. Therefore, the exhaust stacks, as well as the air intake and air exhaust, were treated to avoid noise impact to the neighborhood (residential housing). Innovation Considering the two major types of activity occurring in the building, two basic options were analyzed: dedicated systems vs. centralized. The use of dedicated systems would have required a 100% outside air system for the laboratory and at least a 20% outside air system for other functions in the building. By combining both systems into a centralized one, we obtain a 480,000 cfm ( L/s) system with about 65% of outside air. This resulted in a reduction of total quantity of outside air entered and an increase of the outside air ratio in systems, improving air quality in classrooms and elsewhere in the building. The centralized system enabled the reuse of quality air (from offices) that normally would have been exhausted. As mentioned earlier, the 480,000 cfm ( L/s) system was split in six modules of 80,000 cfm ( L/s). This strategy allowed this system to be built at a reasonable cost. It has the additional advantages of redundancy and easier maintenance of smaller systems, even during occupied periods, by isolating one module at a time. Flexibility of mechanical systems (with Accessible Service Shafts for Labs (Typical) Wet Labs Offi ces Occupancy Sensor (Typical) Lab Bench General Return Shafts Service Corridor Public Corridor (Natural Lighting) Main Supply Shafts General Return Shafts Figure 1: Lab units vs. offices & common areas in the north wing. Exhaust to Common Collector In Penthouse Horizontal Exhaust Collector Tel/Data Cabling To Labs Service Corridor Vertical Plumbing Labs Services Figure 2: Cross section of lab units with service corridor. Lab General Exhaust Variable Air Volume Fume Hood the service corridor) allows the retrofit of labs without disturbing any adjacent modules, which helps to maintain safety and security at all times. A bypass opens around heat recovery coils to reduce static pressure when heat recovery is not needed. Combining efficient window glazing with linear floor grilles on perimeter maintains comfort in rooms without downdrafts, even at low outside temperatures. Installing small dedicated exhaust chimneys in the central core of a high flow general exhaust helped provide good velocity and dilution of that particular exhaust. It also was an efficient way of maintaining a lower amount of apparent chimneys. Operation and Maintenance Accessibility of Equipment: Air-handling units, exhaust units and mechanical components are centrally grouped in two large mechanical rooms located on top of both A and C wings. They are accessible by service elevators. Replacement equipment can travel easily from the truck dock to the penthouses. All major equipment is located high above floor level and is accessible through permanent ladders, stairs and catwalks. Maintenance can 6 2 A S H R A E J o u r n a l a s h r a e. o r g M a y

5 CDN $ CDN $/m² CDN $/m² Mechanical 20,900, Electrical 6,400, Building 59,500, , CDN $ equals $0.80 U.S. Table 3: Construction costs. Summer Boiler $60,000 Airfl ow Reduction During Unoccupied Periods $560,000 Motion Detectors $114,300 Glycol Heat Recovery $494,000 Static Pressure Reduction $376,560 Direct Contact Heat Recovery Boiler $90,000 Low Temperature Heating Water Loop And Peripheral Forced Air Heating ($339,000) Total $1,355,860 1 CDN $ = $0.80 US Table 4: Additional construction costs. Additional Costs (Table 4) $1,355,860 Annual Savings (Table 2) $854,625 Payback 1 CDN $ = $0.80 U.S. Table 5: Simple payback Year (19 Months) be performed on each air-handling unit without disturbing occupants. Builtup plenums and air-handling units have large access doors, inspection windows and are well lit. Walk-in access sections are provided between all components of the air-handling units. Control and Monitoring: A centralized BAS links all mechanical components through a centralized direct digital control network. Building operators have access to that network using a computer interface to view remote monitoring of component status, operating conditions, measuring stations, alarms and preselected trend logs. Operators also can modify sequences, setpoints, schedules or issue live commands. Flexibility of Design: As shown earlier in Figure 1 and demonstrated in Figure 2, laboratory units are adjacent to the service corridors, giving easy access to special laboratory services such as compressed air, special gases, DI water, laboratory drainage, telecom, electrical panels, etc. It also gives easy access to the manifold exhaust system located in the ceiling of the service corridor. All this accessibility is useful when modifications or retrofit occur. Modifications can be performed on a lab unit without interrupting activities occurring in neighboring units. Furthermore, mechanical equipment has been designed to accept increase in supply and exhaust capacities for laboratory units. Diversity in the use of HVAC-dependent equipment (fume hoods, capture arms, etc.) can influence directly the remaining capacity of the installations. Commissioning: As mentioned earlier, commissioning of the building was performed placing emphasis on performances of primary air-handling Advertisement formerly in this space. M a y A S H R A E J o u r n a l 6 3

6 units, fume hoods, exhaust network and ventilation strategies. The fume hoods were tested under ANSI/ ASHRAE Standard , Method of Testing Performance of Laboratory Fume Hoods, procedures. Cost Effectiveness Tables 3 and 4 show the project cost breakdown, while Table 5 indicates the simple paybacks for the energy efficiency measures. Costs were controlled by choosing simple systems that rely on well-established low-cost technologies, and by optimizing equipment selection for dependability, low maintenance and maximum efficiency. A major advantage of the VAV systems with terminal reheat is that, despite different load requirements, a comfortable environment can be maintained in all rooms. This, in turn, makes the systems flexible enough to adapt to new layouts. Optimizing selection meant performing computer models that detailed heating/cooling load calculations, duct and piping loss calculations and dynamic systems simulation, to help avoid oversizing equipment. An example of simple reliable systems include local thermostats and actuators regulating flow through terminal boxes for room controls, centrifugal chillers and axial flow cooling towers, direct contact heat recovery boiler, VFD on fan motors for flow modulation equipped with direct drives whenever possible. These efforts to control capital costs throughout the design stage resulted in an on-time project. Life-cycle cost analysis was used as a decision-making tool throughout the design process. Designing complex systems does not always guarantee energy efficiency. In fact, the guiding principle is that the simpler the systems are (as long as energy efficiency is not compromised) the better the maintenance personnel will understand the systems. This saves on operation costs. The A-wing of the Concordia University Science Complex. To integrate the new complex on the Loyola Campus, it was decided to use the existing installations as much as possible. Thus, the central heating plant was analyzed and a direct contact heat recovery boiler was installed on existing boilers exhaust flue gas for the heating requirements of the new complex. It resulted in no net increase of the heating capacity of the central plant. Almost 60% of the area of the existing central heating plant was renovated, eliminating former nonoperating equipment, which was replaced over time to install mechanical equipments for the new complex (heat exchanger, expansion tanks, pumps, chillers, etc.). A neutralization tank is installed to ensure all lab effluents will not damage the environment when leaving the building. Natural ventilation in staircases also is implemented to reduce energy consumption and increase indoor environmental quality (IEQ). Environmental Impact Reducing environmental impacts when creating new buildings doesn t only mean reducing energy use. Environmental impact must be considered as a whole, including factors such as site, energy, materials and resources. On this project, an existing four-story building was present on the site of construction: the Bryan building. Built in the 1970s, this pavilion was used for offices and classrooms. Instead of demolishing it from the site before constructing the new complex, it was decided to integrate the existing building in the design. Of course, this old building wasn t perfectly suited for wet laboratories. However, several square feet of teaching labs were required in the complex. The two new wings (A and C) were annexed to it, creating the L-shape. Those wings basically were used for wet labs while the decision was made to concentrate the use of the Bryan building (B wing) for dry labs and offices. Conclusion Occupant safety, energy efficiency, sustainability, low capital costs and flexibility were primary concerns addressed by the mechanical systems while ensuring high IEQ and considering sustainability. The use of innovative air systems serving laboratory and nonlaboratory areas allowed the building outside air requirements to be kept at a minimum while increasing fresh air quantity over requirements in the offices. Laboratory exhaust is provided by a manifolded system taking full advantage of diversity to reduce energy and capital costs. Well-located service corridors in relation to lab units result in maximum flexibility for future retrofits since all services (ventilation, piping, plumbing) are easily accessible. Sustainability issues and energy efficiency measures resulted in a 46,000 ft 2 (4300 m 2 ) of building salvation and energy savings equivalent to approximately 2,250 tons (2040 Mg) of CO A S H R A E J o u r n a l M a y