Experimental Investigation of an Environmental Control Unit Utilizing Carbon Dioxide for Heating and Cooling

摘要

This report details the tests performed on R22 box and R744 breadboard versions of the US ArmyEnvironmental Control Unit (ECU) with a nominal cooling capacity of 9,000 BTU/hr (0.75 Tons or 2.64 kW). AnR22 ECU box currently used by the Army was tested and used as the baseline for comparison with the later R744testing. This baseline system is generally used where portable air conditioning is needed in the field; the box is alsoequipped with electric resistance heaters. The baseline box was found to outperform its rated capacity. An R744system was tested in a breadboard format, this system was comprised of components similar to what would be usedin an ECU box if it were converted from R22. This breadboard system was capable of operating as both an airconditioner and as a heat pump. A cooling COP approximately equal to the box system was attained with thebreadboard. The breadboard did provide a HPF greater than unity for all heat pump tests, making it is more efficientthan the electric resistance heaters found in the box system. Detailed comparisons were made between several R744heat exchangers in different orientations under varying operating conditions. Evaporators were tested in horizontaland vertical tube orientations. The flat top fin evaporator was found to work well in both horizontal and verticalorientations. The round top fin evaporator, which may have contained a manufacturing defect, performed muchbetter with the tubes vertical, than with the tubes horizontal. Overall the best heat exchanger was the round top finevaporator with the tubes vertical; however this heat exchanger performed the worst with the tubes horizontal. In airconditioning mode, both gas coolers performed similarly. In heat pump mode, the six-port tube heat gas coolerperformed better in almost every regard in comparison to the four-port tube with the only exception being the airside pressure drop.