Technical and Economical Evaluation of Low-E Coated Building Glazing Systems

Regarding the important role of glazing systems in the building facades as influential envelope elements, proper design and selection of glazing specifications and area ratios in each climate can reduce energy consumption in buildings, because the radiative heat transfer into the building as light and heat occur through transparent surfaces. The objective of this study is to investigate and compute the energy savings and economical evaluation of the low emissivity coated building glazing systems in comparison with clear glazing systems in two extreme climates in Iran. In this paper, the cost analysis of using these coatings is performed for Ardebil and Bandarabbas which represent two cities with cold and hot climates. The EnergyPlus simulation tool is used to simulate the annual building performance with and without low-e coated glazing systems. The cost analysis is done through the payback period (PBP) indicator which refers to the period of time required to recoup the funds expended in an investment. The drawback of PBP is that this indicator does not account the time value of money. But, in Iran, the PBP is suitable as an indicator of energy performance because the investment is provided only by the private sector and it is not owned by the government. In this case, only the lowest payback period provides incentive to save energy. The analyses show that the PBP of low-E glazing systems are affected strongly by their dependency on the climatic condition. It should be remarked that the energy carrier which is used for the selected climates are different. For Ardebil, CNG is the most common and appropriate energy source because of the high heating load and very low cooling load. Vice versa, electrical energy is used for Bandarabbas as the energy carrier for the high amount of cooling demand in this climate. In Iran, the price of CNG and electrical energy differs considerably and CNG price still remains at a very low level. In the hot climate (Bandarabbas), using double glazing unit with low-E coating significantly reduces energy consumption due to higher solar transmittance and lower solar reflectance of the low-e glazing system compared to the clear glazing system. In Ardebil, this coating has a minor impact on annual heating load. The reason originates from the great amount of thermal radiation, even in the cold season. These results have been completely described in the previous paper written by the same authors. On the other hand, by comparing the PBP of low-e glazing system in two selected cities, the results indicate a considerable payback period in Ardebil in all the orientations. So, using this type of coating in this climate does not have any economical justification. It should be metioned that this situation will have economic justification in Ardebil only when the cost of energy carrier increases. For the hot climate, the PBP has a considerable reduction comparing to Ardebil. In this climate, the lowest PBP refers to the east orientation with maximum 2.7 years for the highest price of gas.