Development of High Efficiency Window Air Conditioner and Compressor Using Propane (R-290)

Abstract

According to US EIA, 2009, there were 46.7 million window air conditioners (WAC) in the United States, accounting for 1.5% of the total US residential energy use or about 0.33 quads. Propane (R-290) is a very efficient refrigerant and promising for small packaged air conditioner and heat pump systems. It is a much less expensive, but more efficient refrigerants than R-22 and R-410A. Propane has negligible environmental impact. However, it is highly flammable, so, system charge must meet safety regulation. We started with an Energy Star WAC as the baseline, i.e. GE AEC12AV originally designed for R-410A. The unit uses a slinger wheel spraying condensate water on the condenser surface. It has a condenser using 5 mm tubes, an evaporator using 7 mm tubes with a rated cooling capacity of 12K Btu/hr, EER of 12.0. We modified the unit by replacing the compressor and expansion devices optimized for R-290. Shanghai Highly Electrical Appliances Co. Ltd, a business of Johnson Controls, is our CRADA partner, which developed a high efficiency propane rotary compressor, reaching outstanding efficiency at the target working conditions. Through experimental verification in our environmental chambers, the improved WAC can achieve the project goals, i.e. 1) Met 260 g charge limit proposed by EPA. 2) Achieved same rated cooling capacity as the baseline WAC, and 17% higher EER, i.e. 14.0 EER. 3) Operated up to 131°F ambient temperature, suitable for mid-east, high ambient conditions. In addition, we conducted system simulations using ORNL HPDM to investigate further potentials for charge reduction. With using microchannel heat exchangers to replace the fin-and-tube condenser and evaporator, the system charge can be decreased to 150 grams. Use of the microchannel heat exchangers causes capacity and efficiency degradation. However, it can still achieve a rated EER > 12.0 and cooling capacity > 10,000 Btu/hr at the AHRI A condition, i.e. meet the Energy Star criteria. It implies that the use of a high efficiency propane compressor makes up the loss due to reducing the heat exchanger volume, to meet the performance targets with satisfying the safety (system charge) regulation.