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.

能源效率要求的提高导致住宅空气处理单元长度的显着增加，进而由于测试设施空间限制而阻止使用要求的进气管道系统进行评级测试。因此，ASHRAE 研究项目 1743 的主要目标是在风扇性能方面研究与 ASHRAE 标准入口管道相比长度更短的替代入口管道配置。此外，该项目还调查了可能影响设备测试可重复性的其他影响。研究的影响是滞后效应与通过被测单元调整外部静压相关，大气压力效应与一个位置的大气压力的每日波动相关，来自测试设施中的去层风机的侧流效应，

考虑的缩短长度的替代入口管道配置是 4 英寸入口管道、带和不带导叶的入口箱，以及非常规的减少替代入口管道。除了没有导叶的进风箱外，替代的进气管道配置将风扇性能保持在±5% 的风扇功率和±2.5% 的空气体积流量内。相对于标准入口管道，入口箱配置的长度减少了 38% 到 44%，而减少的替代入口管道配置的长度减少了 71% 和 73%。

对于推入式电子换向电机风扇单元，滞后效应显着，而在低空气流量下，对于推入式恒转矩电机风扇单元，滞后效应显着。大气压力仅显着影响电子换向电机风扇单元。在某些配置中，来自外部“去层化”风扇的侧流对推进装置有显着影响。在测试标准入口管道期间，地板距离对风扇性能的影响微不足道。