Abstract
Increasing energy efficiency requirements lead to substantial increases in residential air handler unit’s length, in turn preventing usage of requiring inlet ductwork for rating tests due to testing facilities space constraints. Therefore, the main goal of ASHRAE Research Project 1743 was to investigate reduced-length alternative inlet duct configurations as compared to ASHRAE Standard inlet duct in terms of fan performance. Additionally, the project investigated other effects that might affect the repeatability of equipment testing. The investigated effects were hysteresis effect associating with adjusting external static pressure through unit under test, atmospheric pressure effect associating with daily fluctuations of atmospheric pressure in a location, side flow effect from a destratification fan in the testing facility, and floor distance effect on ASHRAE Standard 37 inlet duct. The reduced-length alternative inlet duct configurations considered were 4-inch inlet duct, inlet box with and without guide vanes, and nonconventional reduced alternative inlet duct. The alternative inlet duct configurations maintained fan performance within ±5% for fan power and ±2.5% for air volumetric flowrate except for the inlet box without guide vanes. The reduction in length relative to the standard inlet duct was between 38% and 44% for the inlet box configuration up to 71% and 73% for the reduced alternative inlet duct configuration. The hysteresis effect was significant for the push-through electronically-commutated-motor fan unit and was noticeable for the pull-through constant-torque-motor fan unit at a low air flowrate. Atmospheric pressure affected only the electronically-commutated-motor fan units significantly. Side flow from external ‘destratification’-fans had a significant effect on the push-through units in some of the configurations. Floor distance had an insignificant effect on fan performance during testing the standard inlet duct.
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