Excerpted from LEED 2009 for Neighborhood Development
To encourage the development of energy-efficient neighborhoods by employing district heating and cooling strategies that reduce energy use and adverse energy-related environmental effects.
Incorporate a district heating and/or cooling system for space conditioning and/or water heating of new buildings (at least two buildings total) such that at least 80% of the project’s annual heating and/or cooling consumption is provided by the district plant. Single-family residential buildings and existing buildings of any type may be excluded from the calculation.
Each system component that is addressed by ANSI/ASHRAE/IESNA Standard 90.1–2007 (or a USGBC approved equivalent standard for projects outside of the U.S.) must have an overall efficiency performance at least 10% better than that specified by the standard’s prescriptive requirements. Additionally, annual district pumping energy consumption that exceeds 2.5% of the annual thermal energy output of the heating and cooling plant (with 1 kWhA kilowatt-hour is a unit of work or energy, measured as 1 kilowatt (1,000 watts) of power expended for 1 hour. One kWh is equivalent to 3,412 Btu. of electricity equal to 3,413 Btus) must be offset by increases in the component’s efficiency beyond the specified 10% improvement. Combined heat and power An integrated system that captures the heat, otherwise unused, generated by a single fuel source in the production of electrical power. Also known as cogeneration. (Adapted from U.S. Environmental Protection Agency)(CHPCombined heat and power (CHP), or cogeneration, generates both electrical power and thermal energy from a single fuel source.) district systems can achieve this credit by demonstrating equivalent performance.
The project I am working on is a mixed-use (mostly residential) neighborhood. There will be solar PV on every home as well as ground source heat pumps. The client and achitects are aiming for net-zero. They seem very confident that all exemplary performanceIn LEED, certain credits have established thresholds beyond basic credit achievement. Meeting these thresholds can earn additional points through Innovation in Design (ID) or Innovation in Operations (IO) points. As a general rule of thumb, ID credits for exemplary performance are awarded for doubling the credit requirements and/or achieving the next incremental percentage threshold. However, this rule varies on a case by case basis, so check the credit requirements. points dealing with energy will be achieved.
However, they also plan on having a district heating and cooling system. The on-site renewables and ground source pumps will acount for much of the energy and heat needed. Where does this leave the points for GIBc12? The credit language states that district heating and cooling must account for 80% of the project's annual heating and cooling. If the majority of that is already accounted for through other measures, and it is not necessary that the district heating and cooling system supply 80%, does that mean that the credits are rendered unachievable?
Thanks in advance!
Colin, you raise an interesting point. First, the project's thermal demand should be calculated after GIBp2 and c2 have been taken into account. The solar PV isn't relevant to thermal supplies, so you're left with determining how much of the thermal load will be met by the ground-source heat pumps. If that share exceeds 20%, you've got a problem meeting the required DHC 80%. But you might have a good argument for a CIRCredit Interpretation Ruling. Used by design team members experiencing difficulties in the application of a LEED prerequisite or credit to a project. Typically, difficulties arise when specific issues are not directly addressed by LEED information/guide if a lesser DHC share is being offset by an equal or better efficiency alternative. The bottom line for GIBc12 is delivering thermal Btus more efficiently that baseline conditions.
Great, thanks Eliot. That makes a good deal of sense and confirms what my thinking has been about this issue. You say the PV isn't rlevent to thermal supplies, which I do understand, but what if the PV is linked to HVAC systems?
Power for HVAC fans/controls falls outside of the credit's thermal production scope that's limited to "heating and/or cooling consumption." So it's the production of the thermal BtuA unit of energy consumed by or delivered to a building. A Btu is an acronym for British thermal unit and is defined as the amount of energy required to increase the temperature of 1 pound of water by 1 degree Fahrenheit, at normal atmospheric pressure. Energy consumption is expressed in Btu to allow for consumption comparisons among fuels that are measured in different units., not ancillary power to distribute it.
Crytal clear, thanks Eliot!
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