From System Efficiency Improvements in
Iowa’s HVAC SAVE Program
Building Technologies Program
Office of Energy Efficiency and Renewable Energy
U.S. Department of Energy
S. Yee, J. Baker, L. Brand, J. Wells
Partnership for Advanced Residential Retrofit
Midwest Energy Efficiency Alliance (MEEA)
20 N. Wacker Dr. Suite 1301
Chicago, IL 60606
NREL Technical Monitor: Stacey Rothgeb
Prepared Under Subcontract No. KNDJ
The objective of the Iowa HVAC System Adjusted and Verified Efficiency (SAVE) program is to train contractors to measure installed system efficiency as a diagnostic tool that can then be used to reduce space heating and cooling energy consumption. For heating system performance, SAVE provides training in energy measurement tools, techniques used to tune furnaces, and procedures to reduce losses from duct distribution systems. Through a system efficiency approach, the program ensures that the homeowner achieves the energy reduction target for the home rather than simply performing a tune-up on the furnace or having a replacement furnace added to a leaky system. This report uses pre- and post-system upgrade data to analyze the energy savings associated with Iowa’s HVAC SAVE program for space heating.
The research conducted here first examined baseline energy usage from a sample of 48 existing homes, before any repairs or adjustments were made, to calculate an average energy savings potential and to determine which system deficiencies were prevalent.
Test procedures used in the SAVE program consisted of measuring airflow, static pressure, and temperature across several components and the whole system to determine how well the furnace was performing compared to the manufacturer’s specifications and where the losses were occurring
After an initial assessment, duct distribution systems were sealed and insulated and in some cases additional drops were added from the return duct to the furnace to improve airflow.
The results of the baseline study of 48 homes found that on average about 10% of the space heating energy available from the furnace was not reaching the conditioned space.
Thirty-one of the 48 homes were identified as having a return duct that was too small to meet the required airflow across the heat exchanger, while 43 of the 48 showed that the static pressure across the filter significantly reduced the airf low due to face area, blockage, or improper selection.
In the second part of the project, the team examined a sample of 10 homes that had completed the initial evaluation for more in-depth study. In these homes, the furnaces were tuned or replaced and duct systems were modified. Four homes had equipment replacement and duct upgrades, and six homes had system tune-ups for both furnaces and ducts.
For these 10 homes, the diagnostic data show that it is possible to deliver up to 23% more energy from the furnace to the conditioned space by doing system tune-ups (furnaces and ducts) with or without upgrading the furnace.
The increase in system efficiency from this study also varied significantly, but it appears from the results that it is possible to deliver 80%–90% of the heat generated by the furnace to the conditioned space. Replacing the furnace provides additional energy reduction. The findings of this study indicate that residential heating and cooling equipment should be tested and improved as a system rather than as a collection of individual components.
The full study can be found here.