Optimum green building label for an office building in Thailand

This article presents a study on evaluation of an optimum level of Thailand's green building label for an office building. The sample building was a 4-storey office building with a total floor area of 1,295.91 m
²
comprising 741.69-m
²
conditioned area and 554.22-m
²
unconditioned area. The air conditioning system was a central system using an air-cooled water chiller. The building as originally designed was treated as the base case. It was evaluated to obtain the scores according to the Thailand's green building standard (Thai's Rating of Energy and Environmental Sustainability for New Construction and Major Renovation, TREES-NC). The building energy consumption was assessed by using the EnergyPlus software. In order to earn more scores to achieve higher green building labels (i.e., certified, silver, gold, and platinum levels), all possible measures related to the 8 topics in TREES-NC were listed and relevant costs and benefits of each measure were estimated. The measures that required none or small investments were considered first, followed by the ones that required some investments and provided benefits in form of savings (e.g., electricity and water savings). The measures that needed investments but gave no financial benefits were considered last. Then, financial analysis was carried out to see which green building label would give optimum returns. The results showed that `gold label' was the optimum level. If the building could achieve the gold label, energy and water savings would be 30.20% and 66.70%, respectively, compared with the base case. The investment would be 4.18% higher and the payback period would be 4.16 years which were the lowest compared with the other labels. The net present value (NPV), the internal rate of return (IRR), and the benefit-to-cost ratio (BCR) at the gold label were found to be 938,662.28 Baht, 24.00%, and 2.006, respectively, which were the highest compared with the other labels. The IRR of the silver label was 11% lower than that of the gold label while the platinum label provided a negative NPV.