|Title:||Experimental Investigation of an Environmental Control Unit Utilizing Carbon Dioxide for Heating and Cooling
|Author(s):||Wujek, S.S.; Hrnjak, P.S.
|Abstract:||This report details the tests performed on R22 box and R744 breadboard versions of the US Army
Environmental Control Unit (ECU) with a nominal cooling capacity of 9,000 BTU/hr (0.75 Tons or 2.64 kW). An
R22 ECU box currently used by the Army was tested and used as the baseline for comparison with the later R744
testing. This baseline system is generally used where portable air conditioning is needed in the field; the box is also
equipped with electric resistance heaters. The baseline box was found to outperform its rated capacity. An R744
system was tested in a breadboard format, this system was comprised of components similar to what would be used
in an ECU box if it were converted from R22. This breadboard system was capable of operating as both an air
conditioner and as a heat pump. A cooling COP approximately equal to the box system was attained with the
breadboard. The breadboard did provide a HPF greater than unity for all heat pump tests, making it is more efficient
than the electric resistance heaters found in the box system. Detailed comparisons were made between several R744
heat exchangers in different orientations under varying operating conditions. Evaporators were tested in horizontal
and vertical tube orientations. The flat top fin evaporator was found to work well in both horizontal and vertical
orientations. The round top fin evaporator, which may have contained a manufacturing defect, performed much
better with the tubes vertical, than with the tubes horizontal. Overall the best heat exchanger was the round top fin
evaporator with the tubes vertical; however this heat exchanger performed the worst with the tubes horizontal. In air
conditioning mode, both gas coolers performed similarly. In heat pump mode, the six-port tube heat gas cooler
performed better in almost every regard in comparison to the four-port tube with the only exception being the air
side pressure drop.
|Publisher:||Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
|Series/Report:||Air Conditioning and Refrigeration Center TR-257
|Sponsor:||Air Conditioning and Refrigeration Project 176
|Date Available in IDEALS:||2009-06-24