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

Wujek, S.S.; Hrnjak, P.S.

Permalink

https://hdl.handle.net/2142/12917 Copy

Description

Title

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

Author(s)

• Wujek, S.S.
• Hrnjak, P.S.

Issue Date

2006-12

Keyword(s)

evaporator systems

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 Name or Number

Air Conditioning and Refrigeration Center TR-257

Type of Resource

text

Language

en

Permalink

http://hdl.handle.net/2142/12917

Sponsor(s)/Grant Number(s)

Air Conditioning and Refrigeration Project 176

Owning Collections