In approach of optimization the HVAC system to make the system much more efficient and minimizing the initial and running cost, a lot of variables has to be considered during the system design, the building application, the project location and the end users specific requirements are the major concerns to be respected. This article focused in the large chilled water system application that might applicable in the mega projects such as the airports, the industrial hangers, the Holy Haram extensions, assembly areas and all the applications need the large amount of fresh air.

The amount of fresh air should meet the minimum requirements of the IAQ specified in ASHRAE standard 62.1-2010 or the latest published version. The larger the amount of the fresh air the great cooling capacity and electrical power consumption shall be expected.

In deed the fresh air load has the great impact in the thermal load and the cooling capacity of the HVAC system equipments.

In such buildings applications, the power consumption of the HVAC system represents at least 60% of the total connecting power input, the percentage shall increased in the hot climate zones. The water cooled central chilled water system is normally the suitable system for such applications when considering the higher COP of the centrifugal chillers. In hot dry climate zone in US western cities, such as lass Vegas, los angelus, Albuquerque, Tocson, the indirect / direct water evaporation system integrated with the traditional cooling coil is the most energy efficient air cooling system. The engineering technical analysis performed for the cities located in the Middle East such as Riyadh, Madinah in KSA and Aswan in Upper Egypt gives significant energy savings in both of the capital cost and interested benefits in the running savings.

At least 20% saving of the initial cooling capacity and 60% annual savings in the electrical power consumption as resulting from the technical engineering analysis, when considering to provide indirect – direct evaporation sections to the traditional full fresh air handling units, moreover the saving of the makeup water needed for the cooling towers due to the 20% saving in the chillers capacity shall used to the indirect – direct evaporation sections in the air handling units.

The technical analysis performed based on the ASHRAE handbook, fundamentals, system and equipments and code of practice referenced to the brand name manufacturer’s in this field.