Engineered Systems - December 2008 - (Page 33)

Lakefront Library Planning on going green? FIGURE 5. An airside graphic. Qc = 0.31 [tp-ta]^0.31 (tp-ta) Where Qc = natural convection from a cooled ceiling, Btuh/sq ft ta = AUST for ceiling cooled spaces with large proportions of exposed fenestration, °R Lower distribution energy. Due to the excellent thermal properties of water, the transport energy associated with a radiant system (pump energy) is significantly lower than the equivalent transport energy for an air system (fan energy). Some of the challenges associated with radiant systems include: • Controlling the indoor dewpoint in the cooling mode to avoid condensation on the surface of the radiant panels • The slow response to step loads typical of massive radiant systems At Klarchek Information Commons, the decision was made to use cross-linked polypropylene (PEX) tubing imbedded in the precast concrete ceiling panels. The 5/8-in. PEX tubing was placed a few inches above the surface at 6-in. centers. Due to the contour of the coffered ceiling, care had to be taken to avoid air traps. A spiral pattern of the tubing was incorporated to minimize temperature gradients across the slab. The manifolds were placed underneath the structural raised floor, which was used throughout the building. The ceiling system was designed to meet 60% of the design sensible cooling load, with approximately 4 W/sq ft of cooling power at 80% ceiling coverage. An underfloor air system (UFAS) was designed to provide ventilation air and supplement the radiant cooling systems on design days. To improve overall dehumidification and lower indoor dewpoint temperatures, the air handlers that supplied air to the UFAS were custom designed. In heating mode, the air handlers operate as a variable DOAS with heat recovery (Figure 4). There are individual VAV boxes, which in heating mode respond to measured CO2 levels in the space. In cooling mode, a runaround coil was designed to enhance the latent heat/moisture removal of the outside air. A separate return air path was used to further dehumidify the space. The return air path uses a stacked coil arrangement allowing part of the air to be cooled low enough to effectively dehumidify the air. The temperature of the conditioned outside air path and the conditioned return path were set as equal and mixed at the blower. Since these air handlers supply the open areas of the library, the space is treated as one large zone from a CO2 standpoint. The delivered volume of outside air is controlled by the highest measured CO2 in the space. The individual boxes in cooling are controlled by measured CO2 levels with a temperature override. The AERCO helps facilities become LEED certified. At AERCO, we recognize the importance of the LEED certification system and green building design and operation. In fact, as an industry leader and member of the US Green Building Council, we have written a white paper to help engineers and facility managers understand how AERCO products complement LEED-NC projects. For your FREE copy of our white paper and more details, visit www.aerco.com/leed3 Heat You Can Bank On Copyright 2008 AERCO International, Inc. Input 72 at www.esmagazine.com/instantproductinfo w w w. esmag a zin e. c o m 33 http://www.aerco.com/leed3 http://www.aerco.com/leed3 http://www.esmagazine.com/instantproductinfo http://www.esmagazine.com

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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