Hot/Dry Air Conditioner

Evaluate the performance of standard and high efficiency A/C units at hot and dry conditions. The assessment involved testing pairs of 3-ton split and 5-ton RTUs. Each pair consisted of standard and high efficiency units.

The residential and commercial unitary air-conditioners (A/Cs) are the primary cause of the growing peak power demand in California. For instance, 24% of the peak power demand in 2006 was due to the residential A/Cs. Past laboratory evaluation has demonstrated that the performance of A/Cs degrades at ambient dry-bulb temperatures (DBTs) above 95 degrees Fahrenheit (°F). Since the ambient DBTs in the inland valley and desert regions of California during summer peak periods are well above 95°F, the need for the high-performing A/Cs at ambient DBTs above 95°F becomes essential. Subsequent research has proposed performance criteria in terms of the sensible cooling and efficiency for A/Cs more appropriate in the hot and dry climatic regions. From this work, the notion of hot and dry climate A/C (HDAC) emerged. The hot and dry conditions were defined as the ambient DBT of 115°F, indoor DBT of 80°F, and indoor wet-bulb temperature (WBT) of 67°F (115/80/67) and 63°F (115/80/63). The HDAC units were largely composed of the optimized commercially available energy efficient and high performing components. Hence, the HDACs were essentially comparable to commercially available high efficiency A/Cs. As part of the research cited above, a field test was carried out to measure and compare the performance of the HDACs against the specifications developed from laboratory tests. Using the manufacturers published performance data, the A/Cs that met or approached the HDAC specifications were selected for the field test. The performance of the selected units was not verified in the laboratory. Field test reported the power and energy reductions anticipated with the HDACs for five out of seven test sites. About half of the reductions attributed to the use of a more efficient electronically commutated motor (ECM) as opposed to permanent split capacitor (PSC) motor for the circulating or evaporator fan. Notable, the manufacturers do not certify the performance of the A/Cs at hot and dry conditions, and generally do not publish the evaporator fan motors power demand. Most of them, however, supply extended application rating tables for estimating the performance under hot and dry conditions. Therefore, this laboratory assessment project was initiated to substantiate the performance of commercially available standard and high efficiency A/Cs at hot and dry conditions. The assessment included investigating the impact of using energy efficient evaporator fan motor type, ECM, on the performance. The key performance parameters encompassed the power demand, cooling capacities, and energy efficiency ratios. The objectives were achieved by testing four A/Cs in the laboratory setting. The tested A/Cs was a pair of nominal 3-ton split units, and a pair of nominal 5-ton packaged rooftop units (RTUs). The rated seasonal energy efficiency ratio (SEER) for the 3-ton standard efficiency was 13 and 16 for the high efficiency in British thermal unit (Btu) per watt-hour (W-hr). The standard efficiency unit was equipped with a PSC type evaporator fan motor while the high efficiency unit with an ECM. The high efficiency unit had a slightly larger evaporator coil and a larger horsepower condenser fan motor. The rated SEER for the 5-ton standard efficiency was 13 and 14 Btu/W-hr for the high efficiency unit. Both 5-ton RTUs used ECM evaporator fans. The high efficiency RTU had a larger condenser coil. All units used refrigerant 410-A.