All-Air Central Air Conditioning in Digital Era

Central air conditioning consumes a lot of energy, especially in the hot climate of the Middle East. The demand for air conditioning has also increased recently in Europe and other parts of the world because of climate change. Moreover, the new regulations of ASHRAE for increasing the fresh air percentage, after the worldwide COVID pandemic, require reexamination of AHU processes for optimization. This paper discusses the utilization of digital control of a VAV (variable air volume box) in all-air central air conditioning systems with an AHU serving a multi-zone building. This paper shows the impact of changing the path of return zone air and the return of excess air from the VAV as well as the utilization of condensed water in reducing the coil cooling load of the AHU. This approach can be applied under different operating parameters such as outside ambient conditions and the percentage of fresh air required. Examination of various process scenarios will help in optimizing AHU performance while meeting the load of each zone.The preliminary calculations of AHU cooling processes on the Psychrometric chart resulted in different cooling coil capacities based on different scenarios. The present results should encourage the air conditioning equipment manufacturers to program different AHU operating scenarios into their systems with the aid of digital signal processing and digital control to achieve the optimum AHU operation as a function of the given data and measured parameters affecting each scenario.