Effect of Inlet Duct Design on Fan Performance of Indoor Air Handling Units

摘要

ASHRAE RP-1743 investigates the impact of inlet duct design on the fan performance of indoor air handling units during equipment testing. The standard inlet duct specified in ASHRAE 37 can be problematic as the duct might increase the length of the testing setup to exceed the height of legacy testing facilities. Hence, several alternative inlet reduced-length duct configurations were tested to identify a configuration that achieves fan performance comparable to the ASHRAE 37 inlet duct. The considered inlet duct configurations were 4-inch (10.2-cm) straight inlet duct and two unconventional inlet duct configurations. The inlet duct configurations were tested on two 3-ton (10.55-kW) units, one had Electronic Commuted Motor (ECM) and the other had Constant Torque Motor (CTM). Testing of the units for each inlet duct configuration was under two nominal air flowrates, which were 350 CFM/ton (46.97 L/s-kW) and 450 CFM/ton (60.39 L/s-kW), and seven External Static Pressure (ESP) points. Also, testing of the units included investigating various effects, such as hysteresis and atmospheric pressure, that might affect the repeatability of tests of indoor air handling units.The results showed that the effects of hysteresis and atmospheric pressure were significant, as the change in power and air flowrate were more than the uncertainty of measurements, on the unit with an ECM fan, while they were not on the unit with a CTM fan. In terms of inlet duct configurations, fan performance was maintained within the suggested tolerance, which was 5% in power and 2.5% in air flowrate, while testing the two unconventional inlet duct configurations compared to the standard inlet duct. The reduction in the stack-height of the inlet duct was ranged from 60%-80% compared to the standard inlet duct. For 4-inch (10.2-cm) straight inlet duct, the test was conducted on the unit with the CTM fan, and the results showed that fan performance was maintained within the suggested tolerance, as well.