Details on Previous PIER II Contract (PIER II #500-98-026)

This project is complete and is summarized below.

Introduction
Previous research suggests that heating, ventilation, and air conditioning (HVAC) thermal distribution systems in commercial buildings suffer from thermal losses, such as those caused by duct air leakage and poor duct location. Because of a lack of metrics and data about the potentially large energy savings from reducing these losses, the California building industry has mostly overlooked energy-efficiency improvements in this area.

Purpose
The purpose of this project was to obtain the technical knowledge needed to properly measure and understand the energy efficiency of thermal distribution systems in commercial buildings. This information was researched to assist the California building industry in designing better thermal distribution systems for new commercial buildings and in retrofitting existing systems to reduce their energy consumption and peak electrical demand.

Project Objectives
The specific technical objectives for this project were to:

1. Develop metrics and diagnostics ("yardsticks" and measurement techniques) for determining the efficiencies of commercial thermal distribution systems.
    
2. Develop information that the California building industry (e.g., HVAC system design engineers and installers) could use to design new thermal distribution systems, estimate energy efficiency, and prevent or reduce the incidence of problems in existing commercial thermal distribution systems.
    
3. In an existing large commercial building, determine the energy impacts associated with duct leakage airflows that could be mitigated by applying duct retrofit technologies.
    

Project Outcomes
Based on the project objectives, the project had three primary outcomes:

Metrics & Diagnostics
The most important metric that we defined characterizes the overall efficiency of the thermal distribution systems in large commercial buildings: transport energy (e.g., total energy used to transport air) per unit thermal energy delivered. This metric is useful for comparing the relative performance of various types of thermal distribution systems. We recommend that California's Title 24 compliance process for large commercial buildings include quantification of this metric.

Our field tests of diagnostics focused on measurements of duct leakage airflows, fan airflows, and fan power. Of the two duct leakage diagnostics that we tested, only one reliably determined duct leakage airflows: it involves accurately measuring airflows entering and exiting the duct system; the difference in these flows is the duct leakage. With further development and testing, we expect this diagnostic tool will be useful in developing a database that characterizes the distribution of duct leakage airflows in California's large commercial buildings.

Characterization
Because there had been very little characterization of the actual performance of thermal distribution systems in large commercial buildings, we characterized one of these systems in detail. The test building showed every indication of a "tight" thermal distribution system: good application of mastic, metal bands at joints, and overall high quality. To demonstrate duct leakage impacts, we installed temporary calibrated leaks and monitored their effects on the system energy consumption and demand.

Energy Impacts
The principal outcome from this project is that we determined that duct leakage airflows can have a significant energy impact in large commercial buildings. Our measurements indicate that adding 15% duct leakage at operating conditions leads to an increase in fan power of about 25 to 35%. These findings are consistent with the impacts of increased duct leakage airflows on fan power that were predicted by previous simulations.

Conclusions
The primary outcome from this project was the measured confirmation that duct leakage airflows can significantly increase fan energy consumption in large commercial buildings. In addition, we defined a new metric for distribution system efficiency, demonstrated a reliable test for determining duct leakage, and developed new techniques for duct sealing. A similar effort in the residential and small commercial sector took 10 years to move from a stage comparable to our progress in the current effort for commercial buildings to the point at which technology adoption as mature (e.g., commercialization and inclusion in standards). We conclude that a concerted effort will be necessary to make the same - or better - progress for the large commercial sector.

Recommendations
Based on the project findings, our recommendations for further work were:

• Further develop the duct leakage airflow diagnostic and submit it to the American Society for Testing and Materials (ASTM) for adoption as a standard test method.
   
• Work with California's Title 24 staff to introduce a requirement for quantifying and reporting the "overall efficiency of the distribution system" metric for new large commercial buildings. Once we have a good understanding of the range of duct system efficiencies from reported data, we could then use these data to set guidelines for minimum acceptable levels.
   
• Develop specifications for maximum allowable duct leakage airflows and for duct sealing in new construction.
   
• Continue collaborative work with the U.S. Department of Energy, University of California, and private sector (e.g., Carrier, Eley Associates, Taylor Engineering) to transfer information to the building industry.
   
• Evaluate the performance of the thermal distribution system at the demonstration building over a heating season, with and without the added duct leakage. The investment of time and equipment at the demonstration building makes it worthwhile to continue monitoring the system to determine energy savings throughout the year.
   
• Survey additional sites to start a database of duct leakage characteristics in large commercial buildings. This work is currently planned with funding from the U.S. Department of Energy and would benefit from co-funding by the CEC.

Benefits to California
We identified several benefits that resulted directly from this study or that were expected to accrue over time as necessary information and infrastructure develops further:

Benefits in electricity savings.
The primary benefits from having tight duct systems are electricity savings. We estimate that eliminating duct leakage airflows in half of California's existing large commercial buildings could save about 560 to 1,100 GWh annually (about $60-$110 million per year or the equivalent consumption of about 83,000 to 170,000 typical California houses), and about 100 to 200 MW in peak demand.

Benefits to future buildings.
The identification of a metric for characterizing distribution system performance allows us to recommend its inclusion in the next round of California's Title 24 as a way of characterizing the new building stock. Once we have a good database of new duct system characteristics, we can set reasonable targets for distribution system performance, which will ultimately lead to further energy savings in this sector.

Benefits to new buildings in the UC system.
As an outgrowth of our work on this project, we have been collaborating with members of the design team on duct specifications for the new University of California at Merced campus. In particular, we have reviewed the draft design documentation for the duct systems and recommended changes to the specifications. Although specific energy savings were not calculated for this work, the benefits were expected to extend to other UC campuses once others adopted the revised specifications.

Benefits in building operations and maintenance.
A willing partner in this work was Thomas Properties, a major manager of public and private buildings. Through this study, that company saw the benefits not only of improvements in duct diagnostics but also in feedback on HVAC system performance via an energy management and control system. By working closely with the private sector, we saw the transfer of knowledge and resulting improvements in building operation in a major public facility.

Benefits to future engineers.
A key element of our research team was the inclusion of numerous students who learned a number of important lessons about the performance of thermal distribution systems. Some of these future engineers are expected become leaders in this area, practicing both in and out of California.

Contact: Craig Wray, Lawrence Berkeley National Laboratory (LBNL), (510) 486-4021