Revealing the Impact to EER From Bypass Zone Systems

New Study Shows No Negative Impact to EER Using Bypass Zone Systems

ACHR News, January 25, 2016. Image credit: geralt

The Zone Control System Technology (ZCST) Product Section of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) has released the results of a field study that evaluated the impact on the energy efficiency ratio (EER) of a bypass-type single-stage cooling zone system. The results revealed a positive influence on the system’s EER, with no negative impact.

A Public Interest Energy Research (PIER) Program report, sponsored by the California Energy Commission and several utilities, raised questions about the efficiency of a common practice in zone systems that routes excess conditioned air back into the return duct in order to control duct system static pressure. The PIER report indicated that there was a reduction of the cooling system EER in HVAC systems with high percentages of bypass air volume. However, the report also indicated many other deficiencies, such as undersized ductwork and high or low refrigerant charge. As a result, the product section selected AHRI member company EWC Controls Inc. to investigate if the reduction in cooling system energy efficiency ratios was due to these deficiencies or to bypass airflow.

EWC Controls designed and managed the project of installing a new zone system into an independent test home in Rancho Cordova, California. The system complied with both ACCA Manual Zr and the Performance Zoning Standard in Title 24, 2013, which allows a bypass so long as 350 cfm/ton return airflow is confirmed by the Home Energy Rating System (HERS) rater. The contractor for the project replaced the entire duct system and installed a new zone control panel compatible with the existing single-stage HVAC system, but capable of multi-stage operation. The contractor also installed a new bypass system and new zone dampers.

A professional engineering firm tested the performance of the zoned cooling system after the completion of the project on July 17, 2013. The results showed no negative impact on the cooling system EER due to the bypass airflow volume, and in fact, revealed a positive influence to the cooling system’s EER during zoned operation. A second test was conducted by a separate engineering firm on July 29, 2013, and found the same results.

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