AHRI Study: Impact of Bypass Zone Systems.

ARLINGTON, VA-Bypass-type single-stage cooling zone systems have a positive influence on the EER of single-stage cooling zone systems, according to research released in January by the Zone Control System Technology (ZCST) Product Section of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI).

An earlier 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 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. The ZCST research project consisted of installing a new zone system into an independent test home in Rancho Cordova, Calif.

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.