Efficient Thermal Energy Distribution in Commercial Buildings

According to California Energy Commission (CEC, 1998a), California commercial buildings use approximately 86,593 GWh or 35% of statewide electricity consumption, and about 1,945 million therms or 15% of statewide gas consumption. Space conditioning in commercial buildings accounts for approximately 18% of their electricity consumption, and 42% of their natural gas consumption. An additional 10% of commercial-building electricity consumption is used for building ventilation, i.e., fans and pumps.

This project focuses on thermal energy distribution systems in commercial buildings, namely the fans, pumps, ducts and pipes used to transport heating and cooling, as well as ventilation air. The tasks of the report include: 1) to characterize the stocks of commercial buildings, thermal distribution systems and their energy consumption in California; 2) to conduct an industry survey of thermal energy distribution design practice; 3) to perform energy analyses of several distribution-system; and 4) to preliminarily identify savings opportunities and some of the efforts required to realize those opportunities.

To optimize the use of limited resources, the energy analyses and opportunity assessments were directed at a subset of the issues and technologies deemed as important by the stock characterization and survey results. These include thermal loss reduction for rooftop-packaged systems, fan energy reduction in thermally perfect systems and thermally imperfect systems. The energy analyses performed focus on: 1) improving the performance of small rooftop package units, 2) fan energy reduction in medium-to-large buildings by use of variable-air-volume systems in new and retrofit cases, and by expanded use of hydronic systems in new construction, and 3) the impacts of duct thermal losses on fan energy in larger commercial buildings.

The study identifies significant energy-saving opportunities for space conditioning and thermal energy distribution. These include, but not limited to, 1) reducing thermal losses induced by air leakage through system components (i.e., duct, equipment), 2) decreasing thermal losses induced by heat conduction, convection, and radiation, and 3) improving equipment efficiency and system design and control strategies.

The report consists of the following sections: 1) Introduction, 2) HVAC system descriptions, 3) Stock characterization, 4) Design practice surveys, 5) Energy analyses and assessments for the improvements to thermal energy distribution systems, 6) Energy-savings opportunity assessment for statewide thermal energy distribution systems, 7) Summary and conclusions, followed by the acknowledgement, references, and appendices (a-d).