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ABSTRACT
Accurate determination of air-to-fluid heat exchangers' capacity requires accurate measurement of the entering and leaving airstreams' temperature and humidity. The most reliable approach to determine average conditions is to first thoroughly mix incoming and leaving airstream and then sample air from numerous locations using an air sampling apparatus. Available research in open literature is focused on mixers for round ductwork with only very limited guidelines available for commonly utilized square ductwork and air samplers.
ASHRAE RP-1733 will provide updated design guidelines for mixers as applied to commonly used square ductwork as well as for air sampling using traditional sampling mechanisms or a combination of RTD grid and humidity sampling tubes connected to a chilled mirror hygrometer. This presentation will provide an update on current progress of mixer evaluation as part of RP-1733.
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INTRODUCTION AND BACKGROUND
Psychrometrie performance testing of HVAC&R equipment requires accurate measurement of air flowrate as well as the inlet and outlet air conditions. Tolerances on capacity and efficiency measurements relative to the published ratings are limited to 5% as mentioned for AHRI standards (210/240, 340/360, and 365) and in US federal regulations, 10 CFR (DOE, 2017). Manufacturers are required to use third party performance validation tests. However, differences in design of the air mixing and sampling apparatus may result in discrepancies that exceed the allowable tolerances lead to "false testing failures" and question our industries' credibility.
Complying with the 5% tolerance requires accurate measurement of the equipment capacity which is particularly challenging when measuring airside capacity for the following reasons:
* Comparatively small changes in temperature and humidity between air-inlet and outlet of unitary equipment, especially...