ARLINGTON, Va. — 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.

“The data from this study will be valuable for manufacturers and contractors, and we are proud to have taken the lead on this important project,” said Richard Foster, president of Trolex Corp. and chairman of the ZCST Product Section.

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.

In summary, the research found that a zone system designed to comply with Manual Zr and California Title 24, 2013, installed on a properly designed HVAC system, has no negative effect on a single-speed direct expansion cooling system’s EER. Thus, it is possible to achieve a positive effect on a single-speed direct expansion cooling system’s EER when utilizing the same zone system design specified in the study. The full study is available online here.

Publication date: 1/25/2016

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