Compliance with the document, Required Treatment of District Thermal Energy System, version 1.0, requires projects served by a central plant to demonstrate achievement of the EAc1 2 credit prerequisite performance threshold as a "stand-alone" building. In the stand-alone scenario, the loads served by the central plant are included in the energy model, but maintained as cost-neutral between the base case and design case. The assumed intent of this policy is to ensure that buildings served by a central plant are efficient on their own and not simply inefficient appendages of an efficient plant. However, for the circumstance where several building projects are developed in conjunction with a central plant, this requirement penalizes the addition of appropriate loads from the buildings to the central plant by making it increasingly difficult for each building project to meet the EAc1 2 credit prerequisite. With each load transferred, the opportunities to improve the development's overall energy performance increases, while the opportunities for efficiency improvements in each building become increasingly limited. Ultimately, it becomes impossible to achieve the EAc1 2 credit prerequisite as a "stand-alone" building. We respectfully request an alternative compliance path for building projects that are tied to a central plant that is designed and constructed specifically for those buildings. Without an alternative compliance path, this policy discourages neighborhood developments from employing central plants to their full capacity. The Project The developer is constructing a neighborhood in climate zone 7 that includes 9 anticipated LEED-rated buildings and a central plant. The plant will serve each building with hot and chilled water for space conditioning, domestic water heating, and snow melt. The plant will generate hot water with 96% efficient condensing boilers and chilled water with a premium efficiency chiller with water-side economizer. The plant serves loads to each building that constitute 80-90% of their total energy use. In effect, the District Thermal Energy document requires each of the development's buildings to individually surpass the ASHRAE 90.1-2004 baseline by 14% by improving loads that constitute just 10-20% of their total energy use. These loads reflect contributions from the building envelope, lighting power density, controls and exhaust for corridor supply systems, and fan coil units (baseline). A baseline energy model for a building within the project has demonstrated that the central plant loads account for 90% of building energy use: space heating and cooling for 21%, domestic hot water for 54%, and snowmelt for 15%. The 10% that remains is for lighting and the base process load, each accounting for 5%. Modeling of reasonable improvements including R-20 walls, R-50 roof, U=0.3 windows, a 20% lighting power density reduction, and reduced fan-power on each fan-coil unit would only yield a 4% improvement over ASHRAE 90.1-2004. Further energy modeling demonstrated that with R-30 walls, R-60 roof, U=0.2 windows, 0.0 LPD, (no lights at all), and minimized fan-power the building would reach just 11%. Given these results the design team has concluded that achieving the 14% threshold is impossible with such limited opportunities for improvement. REQUIREMENTS AND SUBMITTALS: The project team proposes amendment of the District Thermal Energy stand-alone modeling requirement by one of the following paths: 1. Exempt building projects from the stand-alone modeling requirement that are built along with a central plant as part of an overall master planned development. 2. Exempt building projects from the stand-alone modeling requirement that have a central plant built as part of the overall master planned development - and where that central plant provides more than 40% of the building project's annual energy cost (assumed space conditioning load plus 10%). This exemption would incentivize the expanded use of central plants in development projects beyond space conditioning loads.
The applicant is requesting exemption from the stand-alone modeling requirements specified in the Required Treatment of District Thermal Energy document (http://www.usgbc.org/ShowFile.aspx?DocumentID=4176). While it is clear that the central plant and proposed buildings have been included in a development master plan, the project may not be exempted from the 14% energy cost savings requirement (i.e., two points for EAc1) for each stand-alone building. The District Thermal Energy document specifically states that projects must demonstrate that buildings be able to achieve two points for EAc1 without savings projected for the District Energy Supply (DES) system. The applicant has indicated that the DES system constitutes 80-90% of the total energy load of each building. Preliminary simulation runs appear to indicate that achievement of 14% energy cost savings by increasing envelope performance and lighting design is not possible. It is not clear why the loads associated with the envelope and lighting parameters (i.e., heating load, cooling load, and interior lighting loads) are represent such a small part of the total building load. The project appears to be located in Climate Zone 7, a substantially heating load dominated climate; heating loads should represent one of the largest end use consumptions. The project team should verify that the schedules, temperature setpoints, glazing percentages, and envelope parameters have been selected correctly for the baseline and proposed cases. The required minimum stand-alone building energy costs savings should be achievable through envelope efficiency increases. Applicable Internationally.
Related Addenda (Corrections & Interpretations)