Integrated IEC+MVC air conditioning system for future sustainability

The global air conditioning (AC) demand have increased significantly, from a mere 800 TWh/yr in 2002 to 2200 TWh/yr in 2022, growing annually at a CAGR of 4.8%. Over this period, the increase in global warming effect is marked by a 16% increase in cooling-degree days (CDD) and almost 96 % increase in the European Union countries. The unusually high ambient temperatures recorded in many countries have affected the regional climatic weather patterns where severe draughts, stronger heatwaves and cyclones or hurricanes are increasingly occurring. In a business-as-usual (BAU) report on global cooling demand, it predicted by 2050 the AC electricity consumption could reach a massive 6300 TWh/yr or about 19% of global electricity production. Without major breakthrough in technology innovation and adequate green-house gases (GHG) emission guidelines from AC, the World Economic Forum predicted that the cooling industry alone could worsen the ambient temperatures rise by as much as 0.5-degree Celsius. In addition to the global warming effects from AC electricity, the continued usage and production of refrigerants for compressors, such as the hydro-chloro-fluorocarbon (HCFC) and hydro-fluorocarbons (HFC), have damaging effects on weather patterns from their high specific GWP potentials, typically 1500 times than CO2. However, the International Energy Agency (IEA) predicted a likely reduction of refrigerants use in AC and this reduction may lessen global warming gradually till then. The adoption of Montreal Protocol (1987) by all countries was an excellent example in limiting the production, consumption and trade of HCFCs and CFCs refrigerants. Similar concern in the continued production of HFC-32 and HFC-125 refrigerants for AC had similar bad effects to the environment, but the policy to curtailed their production could reduce emissions to the ambient by 50% and 100%, respectively. Despite the zero-ozone potential of HFCs, their usage as alternative to HCFCs could still harm the environment due to their high GWPs. The high energy consumption and GWP effect from AC refrigerants could be attributed partially to the low performance conventional chillers. We proposed innovative hybrid cooling system for future sustainability. In proposed system, indirect evaporative cooler (IEC) is hybridized with mechanical vapor compression (MVC) chiller to improve overall performance, effective temperature and humidity control and reduced water consumption. Hybrid IEC+MVC system is designed, fabricated and tested as assorted outdoor air conditions. In schematic, partial air from room return is utilized as a working air in IEC and accordingly outdoor air is introduced to makeup the cooling requirement. The IEC handles 33-45 of the total cooling load, and the energy consumption can be reduced by 20-40% as compared to conventional MVC. Moreover, the condensate collected from the evaporator can compensate for >75% of water consumption in IEC, making the system applicable in arid regions. We also proposed a simplified empirical model for hybrid system performance evaluation based on experimental results.