HVAC System Technologies

Measuring condensing unit entering air temperatures

Fan efficiency contour map

Air-handling system leakage flow characterization

Although the energy efficiency of many HVAC components has substantially improved over the past 40 years, there is still a need to make systems as a whole more efficient and to use much less energy. For example, data suggest that air leakage from thermal distribution systems in commercial buildings is common and increases HVAC energy consumption by 10 to 40%. Ducts and piping located in unconditioned spaces, excessive flow resistance at fittings, poorly configured and improperly sized fans and pumps, unnecessarily high system static-pressure set-points, and inefficient terminal units further reduce system efficiency, and in turn increase energy consumption even more.

There is no single cause for system deficiencies. One is that the building industry generally is unaware of existing performance problems and opportunities for improvement. Others include a lack of reliable diagnostic tools and procedures for commissioning as-built systems, as well as a lack of suitable analysis tools and guidance. To address these issues, our research focuses on system analyses and commissioning for both new and existing buildings, as well as developing new technologies and related codes and standards, with a particular emphasis on thermal distribution system performance. These efforts include laboratory and field studies to characterize system performance and demonstrate the benefits of good practice so that the design, installation, and commissioning of low-energy effective systems becomes the norm.

More specifically, our program of HVAC system research addresses the following key needs for new and existing buildings:

  • System Diagnostics: Several steps are needed to achieve reasonably accurate, cost-effective diagnostics in areas such as determining system airflows, leakage, and the potential for combustion gas spillage, and for evaluating the performance of system configurations that are gaining popularity (e.g., under-floor supply air distribution). One step is to evaluate the applicability and reliability of existing diagnostics and to develop new ones where needed. A second is to assess the applicability and acceptance of diagnostics as training and quality control aids for the building industry. A third is to initiate their commercialization and standardization. The spectrum ranges from diagnostics as research benchmarks to those for rapid screening in building audits.

  • System Analysis Tools: To support analytical tool use in new construction, retrofit, and research applications, improved physics-based component models that address system energy and indoor environmental quality issues together need to be developed and tested. Simplified calculation methods for use in related codes and standards also need to be developed. The models and methods need to be driven by the availability of measured data whenever possible.

  • System Characterization and Guidelines: More research-grade data need to be collected about the physical characteristics of HVAC systems in the existing building stock and the performance gains that can actually be obtained by system improvements. Analyses of system impacts on energy use and IEQ are needed to establish baselines and technical targets for codes and standards that are technologically feasible and economically justified over the life of the system, and to verify over time that targets are being achieved. Design, retrofit, and commissioning guidelines that identify packages of appropriate technologies, metrics, diagnostic, and norms also need to be developed.

  • Advanced Technologies: To reach aggressive targets such as 70% reductions in energy use, new technologies that allow life-cycle-cost-effective reduction in energy use while meeting IEQ requirements are needed. For example, system aerodynamics need improvement to address fan efficiency losses during part-load operation. Proof-of-concept prototypes need to be built in collaboration with equipment manufacturers, and then tested in the laboratory and field to demonstrate performance improvements.