Engineered Systems - December 2008 - (Page 34)

Lakefront Library fan speeds are controlled by static pressure. To further enhance dehumidification in the space, the bookend seminar/classrooms are conditioned by a traditional VAV ceiling supply system to respond to the anticipated step cooling loads. The supply of the air to those spaces was designed at 51.5° to provide good de-humidification. Since there is no significant vapor barrier between the bookends and the open areas this lowers the overall humidity in the building. Sensors are embedded in the ceiling to monitor the actual ceiling surface temperature. The BAS maintains the ceiling temperature in cooling between 62° to 67° as required for cooling, or 3° higher than the measured indoor dewpoint. In cooling mode, the space temperature is trimmed with the UFAS. Improved plant efficiency. Since the ceiling is maintained between 62° to 67° in cooling, 56° to 58° return water to the central plant is used to chill the ceilings. This increases the return water temperature to the central chilled water plant and increases the overall efficiency of the chillers. Another benefit is that no additional primary chilled water is used and the additional hydronic pressure drop of the chillers and associated auxiliaries is avoided. In heating mode, this same dualtemperature loop supplies warm water from the central plant for the radiant ceiling and the other systems requiring hot water. Daylighting. An automatic digitally controlled dimming system harvests natural daylight and reduces required artificial light energy. Demand controlled ventilation. CO2 sensors were installed throughout the space to control the volume of outside air required while maintaining the space IAQ. Heat recovery. The system recovers approximately 45% of the available energy from the exhaust air to precondition the outside air needed for ventilation (Figure 4). External/internal shading. The west-side façade has motorized Venetian blinds that are controlled by the BAS. The blinds are only deployed when both the celestial calculations of the sun position and the ambient external light sensor determine that external shading is required. When required, the blinds are lowered and the angle of the 4-in. slats is adjusted based on the angle of the sun’s rays. On the east façade, there are motorized rollup shades that are controlled in a similar manner except that there is only one degree of motion. Hybrid mode. To further reduce cooling and fan energy, the building has a hybrid mode where the system is in natural ventilation (all the fans are off and the windows are open) and the radiant chilled ceiling is activated. In this mode, the outdoor dewpoint is equal to the indoor dewpoint, requiring additional precautions to avoid condensation. The ceiling temperature is kept 5° above the outdoor/indoor dewpoint in this mode. Intelligent control. It was imperative that all these dynamic systems be integrated into the BAS. BACnet® was used as the backbone to integrate standalone system protocols. The BAS was integrated into the campus-wide network to allow the monitoring and operation of the building. Electric submeters and Btu meters were installed and connected to the BAS to provide real-time monitoring of the energy usage and long-term trending. Energy model and actual results. The design model predicted 52% less energy usage than an ASHRAE 90.1-base building, excluding computer/plug loads. Figure 3 provides a summary of the design energy model with computer/plug loads based on 24/7 operation. Chilled water is supplied from a central plant with a measured average efficiency of 0.6 kW/ton, including the tower fans and pump energy. Heating is supplied via the central steam plant, with an average measured steam to fuel efficiency of 82.5%. During a 30-day period in July/August, the system was in natural or hybrid mode approximately 37% of the time. During one 84° day, it was observed that the building was being cooled with only 32 tons of cooling. It was further observed that the base plug-load energy was higher than anticipated. Field measurements showed that over 50% of the total electric usage (including space cooling) was attributed to computers (over 300 PCs) and plug loads. Currently, the university IT department keeps the computers in ready mode at all times. This has resulted in an average computer plug load of 1 W/sq ft. Even with higher-than-anticipated computer usage, the total building performance is as expected. LESSONS LEARNED The natural ventilation system was the most challenging to commission. Loyola’s project management team is still working through some issues with unreliable window actuators and insect screens on the east facade. Despited these issues, the building has performed better than expected in natural-ventilation mode. Typically, the system is operating in either natural or hybrid when outside air temperatures are between 55° and 75°. The indoor temperature can generally be maintained within 1°F of the outside temperature. This translates to approximately 5 cfm/sq ft of outside air. Further, the audible experience of the rhythm of the waves on Lake Michigan adds to the aesthetic appeal of the facility. Although we are still optimizing the systems and expect to further improve the facility’s energy efficiency, feedback from students and staff has been incredible. The goal of the university was to create an environment that meets the three C’s: Collaboration, Connectivity, and Community. All the current feedback suggests that these goals are being met. ES McLauchlan is principal of Elara Energy Services, Inc.. He brings over 30 years of experience in MEP design, construction, and commissioning and has received nine first place Illinois ASHRAE excellence in engineering awards. He is a licensed professional engineer, certified energy manager and LEED® AP. He has authored several technical articles for trade journals and has been a speaker at numerous industry conferences. He holds a bachelor of science degree in mechanical engineering (BSME) from University of Illinois at Chicago. Lavan is a senior engineer with Elara Energy Services. In addition to his experience in MEP design, he has lectured in the mechanical engineering department at the University of Illinois at Chicago. He has received three first place Illinois ASHRAE excellence in engineering awards. He holds a bachelor of science degree in mechanical engineering from Illinois Institute of Technology, a bachelor of science degree in physics from Northeastern Illinois University and a masters of science degree in mechanical engineering from University of Illinois at Chicago. 34 En g i neer ed Sy stem s December 2008

Table of Contents Feed for the Digital Edition of Engineered Systems - December 2008

Engineered Systems - December 2008 Contents Editor's Note HVAC Challenge Back2Basics Case In Point Commissioning Building Automation HVACR Designer Tips Applications Checklist Lakefront Library: Radiant Systems Meet Natural Ventilation Before (And After) The Flood Basics For Refrigerant Chillers Wire-To-Shaft Efficiency For HVAC Pumps Products Glossary Classifieds Advertiser Index Tomorrow’s Environment

Engineered Systems - December 2008

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