Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.2

Inquiry

This inquiry concerns a proposed Exceptional Calculation Measure (ECM) we wish to employ in the calculation of building energy consumption for EA Cr1. We understand that ECMs should be submitted as a separate line item, apart from the base energy model. We plan to submit this ECM as explained in the LEED-NC Version 2.1 Reference Guide on pages 145 to 148. ECM - Central Plant Efficiencies ASHRAE 90.1 Section 11.2.3 says that annual costs shall be determined using rates for purchased energy. The LEED-NC Version 2.1 Reference Guide clarifies (p 143) that the modeler needs to use the same rates for both the budget and proposed energy design. Our building is attached to the campus central utility plant (CUP), which supplies chilled water, steam and electricity. Both LEED and ASHRAE 90.1 do not address this situation directly. Our building does not purchase any of these utilities; rather the CUP purchases natural gas, which it uses to generate the other utilities. The campus also purchases some electricity from the local utility, which is then distributed via the CUP. Our situation differs from the situation of a stand-alone building purchasing steam or chilled water from a central utility in three important ways: 1. Both the building and the CUP are owned by the same entity. 2. No utilities are purchased by the building, the point of purchase is at the CUP. 3. Our project has the opportunity to influence the design and operations of the CUP. LEED EA Prerequisite 3 requires that central plant equipment serving a building seeking LEED be CFC free (LEED-NC Version 2.1 Reference Guide, page 131). In part because of this requirement, the owner has plans in place to upgrade the CUP to eliminate these refrigerants. It seems only fair and logical that if we must upgrade the plant to meet one LEED Credit we should be able to take advantages of the improved energy efficiency of the same plant to meet another credit. We therefore propose the following ECM: We will calculate chilled water, steam and electricity consumption for both the base case and design case buildings using the standard LEED Energy Modelling Protocol (EMP). We will then run a second model, which converts these consumption rates to utility costs as follows: Base Case - a typical (i.e. ASHRAE 90.1 compliant) gas/electric heating cooling plant, with gas and electricity purchased from the local utilities at current billing rates. Design Case - an appropriate fraction of the actual CUP, with gas purchased from the local utilities at current billing rates. We will also assume an appropriate fraction of the electricity is purchased from the local utility (note that we will take average plant efficiencies. We are not assuming the newest, most efficient equipment is dedicated solely to our building) Centralized utility plants with cogeneration are a well recognized energy saving strategy. We believe that projects which use this strategy to achieve real energy savings should receive credit under LEED. We are want to include the effects of the central plant in our overall energy model, to better reflect the real energy consumption of the building. Is this approach acceptable? (I might add as an editorial comment that this sort of situation would be greatly simplified if future versions of LEED considered source energy consumption or emissions, rather than energy cost.)