Effect of operational parameters and inlet duct design on ECM fan performance of a push-through residential air handling unit

Abstract

The current trend in HVAC industry is to use increased air flowrate to increase the air conditioners' efficiency compared to when testing standards were originally developed. Manufacturers tend to achieve this increased efficiency by increasing the coil surface area and thus increases the equipment size. While this has indeed reduced environmental footprint it also has led to issues for the testing of units. In particular, increased indoor air handling unit height leads to conflicts between dictated inlet and outlet duct lengths and actually available total height of legacy testing facilities.

The issue is, that the current standard (ASHRAE 37) has limited guideline about inlet ductwork design while testing an air handling unit. It does not mandate using one but just recommends using one if the space permits. As there is no specific length (only the minimum length) for the inlet ductwork is provided in the standard, testing of the air handlers at different inlet duct length could lead to change in measured performance of the fan, in extreme cases resulting in 'false testing failures'. This thesis work studies the experiments conducted to evaluate the effects of changes in inlet ductwork configuration to the fan performance and highlights some of the constraints applicable to units with up-to-date Electronically Commutated Fan (ECM).

The purpose of this study is to develop an inlet duct design guideline with reduced length while maintaining the reliability of AHRI and ASHRAE standards and also it will reduce the risk of false testing failures and will lead to higher integrity of the testing results at different laboratories. Here we studied the fan performance of a 3-ton ECM blow through fan coil unit for a number of parameters such as flow rate, inlet duct length, unit capacity, fan type and motor configuration. An additional objective of this work is to reduce the overall height of the testing setup (inlet duct + test unit + outlet duct) by reducing this inlet duct length while maintaining the equivalent fan performance as of the minimum inlet duct length (standard case) as per ASHRAE 37.