©2014 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 56, no. 7, July 2014.
By Charles E. Gulledge III, P.E., HBDP, Member ASHRAE; Rich S. Conyers, Member ASHRAE; Bradley M. Poe; Charles M. Kibby
About the Authors
Charles E. Gulledge III, P.E., is senior mechanical engineer, Rich S. Conyers is senior mechanical designer, Bradley M. Poe is mechanical estimator, and Charles M. Kibby is CAD/BIM manager and senior designer at AC Corporation in Greensboro, N.C..
The Caterpillar Axle Manufacturing Plant is a new 874,700 ft2 (81 262 m2), state-of the-art, heavy manufacturing complex that machines, fabricates, tests, assembles, and paints truck axles for large mining equipment. The complex is located on a 102 acre (41 ha) site in Winston-Salem, N.C., and opened in December 2011. The project was completed via a design build model and fast track delivery, which required early release of major equipment. Therefore, iterative solution development occurred prior to, and parallel to, construction activities.
Energy efficiency was a fundamental project parameter. The relatively large process energy load component required the project team to explore and implement creative interdependent solutions to realize a reduction in overall facility energy usage. The Appendix G Energy Model (ASHRAE Standard 90.1-2007) projected a 10% (energy) annual savings, compared to a baseline facility. The design annual energy use was projected at 213 million kBtu compared to a baseline energy usage of 239 million kBtu. The model projected an energy use intensity (EUI) reduction from 267.51 kBtu/ft2•yr to 238.8 kBtu/ft2•yr (843 kWh/m2•yr to 754 kWh/m2•yr). Tables 1 and 2 show the proposed and actual energy usage comparisons for electricity and natural gas use.
Realizing these energy use reductions required the optimization of multiple component and system solutions. Iterative analysis was used to determine project responsive configurations.
The building envelope was improved above energy code minimum to reduce cooling load at the source. The expansive roof has an insulation value of R-25.0 (c.i.), exceeding R-20.0 (c.i.). The roof membrane offers a Solar Reflectance Index (SRI) of 102. All fenestration assemblies use 1 in. (25 mm) minimum reveals. The main office and employee services envelope construction incorporates south orientation fenestration overhangs and side fins (building faces).
The main office and employee services areas use dedicated outdoor air systems (DOAS) and decoupled ground source heat pumps (GSHP) connected to a geothermal well field. Terminal units are single-stage and dual-stage, depending on the zoning. Cooling efficiencies range from EERs of 14.2 to 23.2, exceeding 13.4 EER. Heating efficiencies range from COPs of 3.1 to 4.4, equaling or exceeding 3.1 COP. The DOAS units use digital scroll compressors for load response matching and modulating waste refrigerant gas heat to provide dehumidification reheat. DOAS unit efficiencies are 11.7 and 11.2 EER, exceeding 11.0 and 9.8 EER.
Solar hot water energy recovery and storage is used for the employee services shower and locker rooms.
The 4,000 ton (14,000 kW) HVAC chilled water plant uses dual compressor technology water-cooled chillers, variable primary flow chilled water pumping, and induced draft cooling towers. Chiller efficiencies are 5.92 COP and 0.43 non-standard part-load value (NPLV), bettering non-standard values of 5.86 COP and 0.616 NPLV stipulated for 42°F (5.5°C) chilled water, 85°F (29°C) condenser water, and 3 gpm/ton (0.05 L/[s•kW]) condenser flow rate. Cooling tower efficiency is 40.5 gpm/hp (3.42 L/[s•kW]), exceeding 38.2 gpm/hp (0.68 L/[s•kW]).
Makeup air for plant exhaust systems and building pressurization is delivered through energy recovery makeup air units. Total energy recovery effectiveness equates to greater than or equal to 68%.
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