For many reasons, the performance of thermal distribution systems (TDS) in some California commercial buildings is suboptimal. LBNL, supported in part by the California Energy Commission (CEC) through the Public Interest Energy Research (PIER) II program, has been working to improve TDS efficiency. This work follows a similar pathway to that of work previously undertaken for residential duct systems, which culminated in 1999 duct performance credits within Title-24.

The PIER II work (PIER II #500-98-026) built upon earlier "transition" work funded by the CEC through the California Institute for Energy Efficiency (CIEE), and focused on several aspects of the TDS problem. These efforts included developing metrics and diagnostics for determining TDS efficiencies, developing design and retrofit information that the building industry can use to improve TDS, and determining the energy impacts associated with duct leakage airflows. Of particular note, our measurements in an existing large commercial building have confirmed earlier elementary predictions that duct leakage can significantly increase heating, ventilation, and air conditioning (HVAC) system energy consumption: adding 15% duct leakage at operating conditions leads to an increase in fan power of about 25 to 35%.

The work in the Efficient Distribution Systems project involves creating a whole-building energy simulation approach for analyzing duct performance (leakage and insulation) in large commercial buildings and using the tool to develop recommendations for addressing duct performance in the 2008 update of the Title 24 Energy Efficiency Standards for Non-Residential Buildings.

Tasks:

Examine recent work on whole-building modeling of duct leakage and insulation energy impacts in light and large commercial buildings and determine which aspects we can carry over to Title 24 compliance processes for large commercial buildings. Based on this review, develop a duct analysis methodology to be used for benefits analyses in support of the 2008 Title 24 Standards (with recommendations on how to proceed over the long term using EnergyPlus or DOE-2).

Using the simulation approach identified in Task 2.2.1, assess the benefits of duct leakage and insulation improvements in support of the 2008 Title 24 Standards.

Recommend a set of changes for the 2008 Title 24 Standards to incorporate duct efficiency metrics and make use of the new duct modeling capabilities.

Develop a proposal to revise the Alternative Calculation Method (ACM) to include an overall metric for distribution system efficiency in the reporting requirements of the 2005 Title 24 Standards. The proposed metric is the ratio between the energy expended to transport heating, cooling, and ventilation throughout a building and the total thermal energy delivered to the conditioned zones in the building.

Project Team:

Craig Wray, Nance Matson, and Mark Modera (Lawrence Berkeley National Laboratory)