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Oklahoma State University

ASHRAE Projects Awarded - Graduate Research Assistantships Available at the MS-level within the Thermal Energy Systems Field - 02-2017


Christian K. Bach (, Craig R. Bradshaw (, Omer San (


Buildings, residential and commercial, consume roughly 40% of all primary energy annually in the U.S. with cooling and refrigeration systems consuming 22% of the building energy.  Component and system optimization leads to improvement of the overall cooling equipment efficiency.

The PIs are currently looking for students interested to start at OSU’s master’s program in funded research projects. See separate announcement for the currently open PhD position.


Position 1 (MS Level, ASHRAE RP-1785, starting ASAP):

ASHRAE RP-1785, recently awarded to Drs. Bach and Bradshaw will provide accurate charge measurement data for the HVAC industry. Your job as the student will be to build and operate the required experimental setups, operate the setups together with the OSU psychrometric facilities, and to analyze the data and prepare it for presentation of the sponsoring ASHRAE technical committee.

Background: For single evaporator air conditioning systems, charge can often be tuned for reasonable performance without the need for additional refrigerant storage volumes. However, this is not the case for reversible heat pump systems, especially if the same outdoor unit is combined with different indoor heat exchanger coils. In practice, suction side accumulators are used on split system heat pumps for the US market. However, refrigerant charge is only part of the issue, since oil charge migration needs to additionally be addressed. For variable speed systems at low ambient temperatures, increased oil viscosity and oil retention in the outdoor coil might cause oil starvation of the compressor. Prediction of the location of the oil will support manufacturers in their coil and system design process.

The goal of this project is to provide high quality data for oil retention and refrigerant charge in fin-tube heat exchangers.


Position 2 (MS Level, ASHRAE RP-1743, starting ASAP):

Air conditioning units’ performance is tested according to ASHRAE and AHRI standards. These standards serve to determine the units’ efficiency in order to comply with governmental efficiency requirements and to inform customer purchasing decisions. However, currently some of these standards do not clearly define the inlet ductwork to the equipment and also do not define any guidelines on how to conduct CFD simulations to select inlet ductwork.

ASHRAE RP-1743, recently awarded to Drs. Bach and San will provide overdue recommendations for the design of the inlet ductwork used during equipment rating tests. Your job as the experimental student of the project will be to build a test setup to investigate the inlet airflow under different inlet duct configurations. A second student that was already determined will conduct the accompanying CFD studies.

Background: ASHRAE 1743-TRP identified a lack of detail in the ASHRAE 116 and AHRI 210/240 test methods and testing standards: While ASHRAE standard 37, incorporated by reference into AHRI 210/240, specifies the location of pressure taps, none of the applicable standards specify the geometry, dimensions of the inlet ductwork and opening/closing rates of the required damper in detail. The sponsoring committee, TC 8.11, identified this to be an issue for repeatability of test results and referred to ASHRAE project 1581-RP where it was shown that inlet duct design changes fan load. TC 8.11 rightfully pointed out that the integrity of the test results is vital for consumers, and equipment re-ratings will reflect negatively on our HVAC&R industry.

As a brief technical background: Several possible configurations for the test setup are acceptable, see Appendix D of AHRI 210/240 for details. Room air enthalpy method and tunnel air enthalpy method use a straight duct leading to the indoor unit or indoor coil, without specifying minimum distances to adjacent ductwork or walls at the inlet and without guidelines for allowable flow perpendicular to the inlet surface area of the duct. However, an even larger problem can be seen for the loop air enthalpy method, the example ductwork chosen in the standard has two 90 degree elbows very close to each other, leading to uneven airflow at the inlet to the test unit.

Moreover, section 2.6 of AHRI 210/240 specifically states that >>>Instead of following one of these examples, an alternative set-up may be used to handle the air leaving the airflow measuring apparatus and to supply properly conditioned air to the test unit's inlet.<<<. This statement allows a plethora of other possible configurations that will affect equipment performance to an unknown extent.

This project will result in specific guidelines for the design of the inlet ductwork to reduce the design space towards inlet duct designs that are known to have little effect onto the equipment performance, as shown by comparable outlet flow profiles obtained from a validated CFD method and experiments.