Economic comparison of an air-conditioner and a desert cooler for residences in arid areas

The paper compares two domestic cooling systems, namely the air-conditioner and the direct evaporative (desert) cooler, using a life cycle costing approach. Both systems are capable of providing a certain degree of cooling relief during the hot and dry conditions typical for the summer in arid regions, such as the city of Eilath, Israel. Each, however, utilizes a different thermodynamic principle, thus possessing different features that affect the expenses involved in cooling the residential apartment. The criterion for the economic evaluation is the system's Annual Equivalent Cost. This parameter represents a common denominator of annual cost involving purchase, installation, operation, and maintenance of each system. The evaluation of operating costs considers the hourly variations in the cooling load as a function of the changing outdoor conditions, the thermal properties of the enclosure and the cooling pattern of the building. For the air-conditioner, the analysis accounts for the relationship between both outdoor and indoor thermal conditions and its electric energy consumption. For the direct evaporative cooler, the operating costs originate from electric energy consumed and from the cost of the water evaporated and drained to carry on the evaporative cooling process. The comparison is performed in middle-class apartments and is limited to comfort level achievable by the desert cooler. The economic model is simple yet detailed, and it has been derived in a manner that most conveniently accommodates small energy consuming systems in buildings. Such systems typically consist of one principal part - the mechanical system - and several auxiliary sub-systems (piping, wiring, etc.), the separate operating and maintenance costs of which are hard to determine. The analysis shows that for the prevalent conditions in Eilath, the desert cooler is significantly more economical to own and operate than the conventional air-conditioner. Analysis demonstrates that this superiority remains for a range of realistic changes in both economic and thermodynamic parameters. In spite of a slightly higher initial cost, the desert cooler proves to be more economical, mainly due to its significantly lower operating cost.