Page 14 - Zero Net Energy Case Study Buildings-Volume 1

ZERO NET ENERGY CASE STUDY BUILDINGS, VOL. 1 INTRODUCTION
Practical Barriers to ZNE and Related ZNE Issues
Even with the most energy-efficient design features, there are a number of reasons why some individual buildings will be unable to reach ZNE performance levels on their own by any of these metrics. These primarily involve a lack of access to renewable energy sources in one way or another. For example, practical restrictions such as the size and footprint of the building, the in- ability to provide enough physical space for on-site renewable energy systems, the lack of solar access at the site, or some combination of these–such as might happen in an urban environ- ment–are all potential barriers to ZNE performance.
There are a number of ways that these constraints for on-site renewable energy production can be addressed. All involve some form of gathering and accounting of renewable energy from off- site sources. The following are some conceptual examples of this approach:
• A building adjacent to the subject building with an excess of on-site renewable energy could supply renewables;
• A group of buildings within a defined geographic boundary could install sufficient renew- able energy capacity within that boundary to zero-out the energy usage by the group of buildings taken together;
• A building or group of buildings could directly purchase renewable energy from a non- adjacent site or agency;
• A building owner could purchase renewable energy credits (RECs) from a REC provider to offset usage.
There are, of course, significant code-related, commercial-practice-related and legal issues and barriers affecting each, depending upon the context. Generally, voluntary rating and certification programs provide latitude for significant creativity in handling the constraints. In contrast, legal compliance issues may be difficult to resolve with regard to mandatory compliance-based sys- tems for which such solutions may be adopted.
There are discussions among building professionals about other possible definitions of ZNE. One prominent concept is that of a “zero net emissions” building in which the greenhouse gas emissions attributable to the consumption and production of energy at the facility would equal zero16.
Other proposed definitions include the reductions in the embodied energy of the building, reduc- tions in water use that correspond to energy use, and reduction in the transportation energy burden established by a building because of its selected physical location for that purpose. All involve plausible arguments for crediting reduction in energy demand, but there is at the moment no single type of definition, metric or certification system that accounts for these within a ZNE framework17.
16 Of the three metrics discussed, such a system might most closely resemble the Source ZNE metric, as suggested above.
17 Only the Living Building Challenge (LBC) certification represents that a building is ZNE within an objective, verifiable system, but this certification system has additional requirements unrelated to energy use. Therefore, a building may perform at ZNE as determined using one of the three princi- pal ZNE metrics but fail LBC certification criteria. This particular certification is therefore inherently limited.
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Zero Net Energy Case Study Buildings: Volume 1