Energy Efficiency Enhancement of Air Conditioners Operating Under High Ambient Temperatures Through Standards and Energy Storage Systems

The demand for air conditioning systems is increasing in high ambient temperature (HAT) regions, presenting a challenge of higher cooling loads, lower unit efficiency, higher energy consumption, and higher loads on electrical grids. This study first explores improvements for residential air conditioners in HAT regions and provides a definition for HAT — 40oC and above — as it was not provided in the literature. The improvements include vapor compression cycle components: condenser, compressor, evaporator, and alternative refrigerants. Challenges, possible design modifications, and limitations of air conditioners operating under HAT are also explored.The minimum energy performance standards (MEPS) of HAT countries are then discussed with a focus on Kuwait. The rating temperatures of HAT countries, T3(46oC) and T4(48oC), are compared in terms of cooling capacity, electricity consumption, and greenhouse gas (GHG) emissions. Moreover, the inclusion of the seasonal energy efficiency ratio (SEER) in Kuwait’s energy code is also discussed. By adopting a 1% design temperature of 47.1oC and rating units at T3, rather than at T4, annual energy savings of 37 kWh per ton can be achieved, with negligible cooling shortages at extreme outdoor conditions. Additionally, shifting from SEER 10 to SEER 12 saves about 504 kWh per ton annually.
As thermal energy storage (TES) systems offer promising potential for enhancing air conditioners during peak loads, two novel concepts are discussed in this study. The first TES method involves a cold refrigerant storage system, which is utilized during peak load hours to further subcool the refrigerant at the inlet of the thermal expansion valve (TXV). The second TES system utilizes a phase change material (PCM) integrated with the condenser, which stores cold energy and allows the condenser to utilize it during peak load hours. Each TES system showed promising potential for air conditioner enhancement during peak HAT hours where the maximum savings occur at maximum outdoor temperatures, making them suitable candidates for enhancing air conditioners under HAT.