High Performing Buildings - Winter 2008 - (Page 13)

No part of the floor is more than 30 ft from a window. Photo © Timothy Hursley the ventilation units is insufﬁcient, adequate or excessive. Based on the relative humidity measurements, the temperature of air leaving the ventilation unit is raised or lowered to maintain the design humidity level in the space. As the setpoint of the ventilation unit is changed, the required chilled water temperature is also changed, resulting in higher chiller efﬁciency as the required water temperature is raised. Energy Use Summary primary pumping system was designed for the chilled water system. The control of the variable speed chilled water pump uses critical zone reset to maintain the required ﬂow to all of the cooling coils. Critical zone reset is part of the prescriptive requirements of Standard 90.1 for the air side of VAV systems. It also can be used with water systems although this is not required by Standard 90.1. Critical zone reset reads the position of each control valve and adjusts the pressure so that at least one valve is 85% open and no valve is more than 95% open. Control valves add resistance in order to limit the ﬂow allowed through the valve. If the valve is more open, less pressure is required to deliver the needed ﬂow. The 95% value is chosen to allow for the lag of the system in changing pressure values so that no zone is lacking water needed to meet the load. The 85% is chosen to allow for a 10% acceptable range and to introduce additional stability into the control loop. The combination of reduced ﬂow and reduced pressure, while still meeting the load, signiﬁcantly reduces pumping costs for the project. Pumping energy calculated for this project saves 57.2% of the energy required by the Standard 90.1 budget building. The heated and cooled part of the building encompasses a little over 83,000 ft2 in four stories. The energy use is 44,816 Btu/ft2 per year. This compares to the Standard 90.1 budget building at 95,979 Btu/ft2 per year, for a savings of 56.1%. The LEED® savings of 53.6% is based on the estimated dollar value of projected utility bills. The largest single group of points in the LEED® system is directed to optimize energy performance with 10 points available. This project earned nine of those points. The success is a result of the team approach and the sustainable goals set forth by the building owner. As Heifer International continues to address the problems of hunger in the world, they demonstrate that green can be functional and attractive, as well as energy efﬁcient. They also act as good stewards of resources that are necessary for the fulﬁllment of their mission. • ABOUT THE AUTHORS Reese Rowland is a design principal at Polk Stanley Rowland Curzon Porter Architects, Ltd. Todd Kuhn, P is a .E., mechanical engineer and John Hodoway is a senior mechanical designer at Cromwell Architects Engineers, Inc. 13 Heating System Heating water is produced by two pulse-combustion high-efﬁciency boilers. Finned-tube heating convectors are located in recesses along the outside walls of the building to offset heat losses in winter. Heating water ﬂow is also variable, but the many small control valves made implementation of critical zone reset impractical. Therefore, a convention differential pressure control system was used for the hot water pumping system. Comfort Control Systems A direct digital control system was provided to control all of the building systems. Controls were carefully set up to prevent simultaneous use of heating and cooling in the same space. Furthermore, space sensors that include relative humidity are used at various locations in the building. These sensors determine if the dehumidiﬁcation provided by Winter 2008 HIGH PERFORMING BUILDINGS

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High Performance Buildings - Winter 2008 Passing On the Gift: Heifer International Headquarters Head of the Class: University of Florida’s Rinker Hall How Far Can You Go? Pearl River Tower The Proof Is Performance: How Does 4 Times Square Measure Up? Lighting the Way: Two Guilford County Schools Montreal’s Retail Example: Mountain Equipment Co-op® (MEC)

High Performing Buildings - Winter 2008

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