Investigating the Impact of OTTV on Indoor Thermal Conditions and Cooling Load Energy in Indonesia’s High-Rise Residential Building

Indonesia’s rapid population growth necessitates a sustainable balance between energy supply and consumption. Residential energy use increases by 6.5–7% annually, primarily driven by cooling demands. The New Capital Nusantara (IKN) state civil service (ASN)—defense and security (HanKam) Flats, a 47-tower, 59,000 m2 residential project in East Kalimantan, faces significant cooling challenges due to its hot-humid climate. This study assesses its thermal performance using the Overall Thermal Transfer Value (OTTV) standard (≤35 W/m2) from SNI 03–6389-2020, focusing on U-Value, SHGC, and WWR. With an ultraviolet index of 7, the region’s climate intensifies cooling loads, increasing operative temperatures and energy consumption. Thermal and energy simulations, conducted via OpenStudio integrated with EnergyPlus, analyze a representative residential unit. Results indicate that the current design nearly doubles the OTTV limit, leading to excessive cooling energy demand. An interzone infiltration rate of 0.000285 facilitates convection, causing temperature fluctuations between naturally ventilated and air-conditioned spaces. Given the project’s near-completion status, non-structural façade modifications are recommended to enhance thermal efficiency without major alterations.