Wheeler, Grant Benson (2013-08). An Investigation of Alternative Methods for Measuring Static Pressure of Unitary Air Conditioners and Heat Pumps. Master's Thesis.
This project was created to address an important issue currently faced by test facilities measuring static pressure for air-conditioning and heat pumps. Specifically, ASHRAE Standard 37, the industry standard for test setup, requires an outlet duct of a certain length, based on the unit outlet geometry, and this ducting added to the unit height may result in a test apparatus height that exceeds psychometric test room dimensions. This project attempted to alter the outlet duct in a way that reduces the test apparatus height while maintaining the reliability of the ASHRAE Standard 37 testing setup. The investigation was done in two scenarios, the first, which altered the direction of the flow after the unit with an elbow and measured static pressure downstream of the elbow, and the second which inserted a passive resistive piece in the flow to decrease the required distance between the unit and the static pressure measurement. Three air handling units were used in Scenario 1 and Scenario 2 testing, with the two smallest units additionally being tested in Scenario 1 with an over-sized duct. The scenario tests were required to be within 5% power and 2.5% airflow of a baseline test following ASHRAE Standard 37.
he results for Scenario 1 have shown that ASHRAE Standard 37 can be modified to reduce testing height restrictions by using a square elbow with turning vanes, provided it is oriented in a specific way in relation to the blower. Furthermore, additional Scenario 1 testing on the over-sized outlet duct shows that possibilities exist for using a single over-sized duct to successfully meet ASHRAE Standard 37 testing conditions when testing a variety of units. Finally, the results of Scenario 2 have shown that the height constraints of the outlet duct can be reduced by installing a passive resistive device consisting of a mesh at the outlet; however, this approach applies only to those units with the heat exchanger located downstream of the blower. As a result of specific issues or problems that were encountered during the project that were beyond the scope, eleven case studies were presented and recommended for future work.