High Performing Buildings - Winter 2008 - (Page 10)

proposals. On bid day, the contractor was required to base his proposal on the basis-of-design chiller and provide the amount to be added or deducted for substitution of each of the other two chillers that had been evaluated. One of the bid alternatives, a centrifugal compression chiller, was selected to be installed. Providing high-efﬁciency cooling, the centrifugal compression chiller uses HFC-134a. The refrigerant was required to be an HFC compound since the selection was made before the USGBC had revised its LEED® credit regarding the use of HCFC refrigerants to permit the use of HCFC-123. A variable primary pumping system was used. All chillers have limits to the amount of water that is allowed to be pumped through the evaporator and condenser. The low design ﬂow of building chilled water and the variable ﬂow system must be limited to provide at least the minimum ﬂow required by the chiller. A bypass valve was used to meet this minimum ﬂow requirement. The design ﬂow for the chiller is 300 gpm and the chiller minimum ﬂow requirement is 204 gpm. Thus, the smallest amount of water pumped when the chiller is operating must be 204 gpm. This limits the mass ﬂow savings in the pump energy equation, but not the savings due to the pressure reductions from the use of critical zone reset control. The pump energy savings are still high while keeping the chiller ﬂow within the manufacturer’s requirements. Plant efﬁciency is enhanced by use of a series ﬂow ﬂat-plate heat exchanger. The return water from the building either passes through the 10 HIGH PERFORMING An inverted heavy timber roof directs rainwater through an exposed collection system to a tower for reuse as gray water within the building. heat exchanger to reduce the load on the chiller or, if the heat exchanger cannot make a contribution to reducing the load, the water bypasses the heat exchanger. The space cooling energy saves 72.6% of the energy required for the Standard 90.1 budget building. Part of this is due to increased efﬁciency of the plant, but much of it is due to avoided load from the daylight harvesting and high-efﬁciency lighting system. Winter 2008 The cooling tower was selected to operate at a three-degree approach to entering wet bulb rather than the ﬁve-degree approach that is normally used. While this tower has a somewhat greater cost, it will improve efﬁciency over the life of the building. The cooling tower fans are also equipped with variable frequency drives. The three-degree approach and the variable frequency drives result in cooling tower energy use BUILDINGS Photo © Timothy Hursley

Table of Contents Feed for the Digital Edition of High Performing Buildings - Winter 2008

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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