Comparative Assessment of the Energy Performance of an Office Building Based on Chapter 19 with ESGB and Green Mark

Introduction:
The building sector is a major contributor to global energy consumption and energy-related carbon emissions, making the improvement of building energy performance an important component of climate and sustainability policies. In Iran, Chapter 19 of the National Building Regulations (2020 edition) provides the principal regulatory framework for reducing building energy demand and improving the thermal and energy performance of buildings. However, its scope is mainly focused on minimum requirements for the building envelope and technical systems, while several aspects addressed by contemporary green building assessment systems, including renewable energy, air infiltration, mechanical ventilation, and operational energy management, receive limited attention. This issue is particularly relevant in hot-arid cities such as Kashan, where high cooling loads, solar radiation, envelope characteristics, and the potential for solar energy generation simultaneously influence building energy performance. International assessment systems such as China's ESGB and Singapore's Green Mark consider a broader range of energy and environmental criteria and establish different levels of performance. Despite numerous studies comparing green building assessment systems, limited research has directly evaluated the performance of an office building designed according to Iran's Chapter 19 against both ESGB and Green Mark within the climatic context of Iran. The present study addresses this gap by linking the requirements of the Iranian regulation to quantitative building-energy performance indicators and comparable criteria within two Asian assessment frameworks.
The Purpose of the Research:
The study aims to comparatively evaluate the energy performance of a representative office building in Kashan according to Chapter 19 and examine its alignment with the relevant requirements of China's ESGB and Singapore's Green Mark 2021. The research also evaluates the contribution of a photovoltaic system to reducing energy consumption and electricity purchased from the grid. Accordingly, the study seeks to determine the effectiveness of Chapter 19 as a basis for energy reduction and identify the regulatory areas that require further development to approach the broader scope of international green building assessment systems.
Methodology:
The research follows a quantitative approach and is applied in purpose, with a descriptive-analytical method based on building energy modeling and simulation. A two-story office building with a total useful floor area of 480 m², located in Kashan's hot-arid climate, was selected as the case study. A three-dimensional model was developed in SketchUp and transferred through OpenStudio to EnergyPlus version 23.2. Annual energy simulations were performed using a six-minute time step and considering climatic conditions, envelope properties, occupancy schedules, internal loads, lighting, equipment, and HVAC systems. Three simulation scenarios were developed. The Base Case represented the building without energy optimization measures and included uninsulated walls and roof, single-glazed windows, a conventional heating system, conventional cooling equipment, and higher air-infiltration rates. The Optimized Scenario incorporated the requirements of Chapter 19, including a 15-degree adjustment in building orientation, improved thermal insulation, Low-E windows, more efficient heating and cooling systems, reduced air infiltration, and horizontal shading. The third scenario combined the optimized building with a 40 kWp photovoltaic system consisting of 114 polycrystalline 350 W panels with a total area of 228 m².
Because measured operational data were not available, model verification was performed using three complementary procedures: annual energy-balance checking, sensitivity analysis of key parameters, and comparison of the resulting energy-use intensity with values reported for comparable office buildings in hot-arid climates. The simulated energy indicators were subsequently compared with relevant ESGB and Green Mark criteria. A sequential parametric analysis was also used to determine the relative contribution of individual optimization measures to the reduction in annual energy consumption.
Findings and Discussion:
The annual simulation results showed that energy consumption decreased from 75,823 kWh in the Base Case to 58,301 kWh in the Chapter 19-compliant Optimized Scenario, corresponding to a 23.11% reduction. The largest individual contributions to this reduction were associated with optimal building orientation (7.03%) and continuous thermal insulation of the envelope (5.08%), followed by improved heating and cooling systems (4.52%), Low-E windows (3.36%), and horizontal shading (3.12%). These results indicate that reducing the building's energy demand through coordinated envelope and system improvements is more influential than relying solely on renewable energy generation. The integration of the 40 kWp photovoltaic system produced approximately 40,500 kWh annually and reduced electricity purchased from the grid to 17,850 kWh per year. The resulting net energy use intensity reached 37.19 kWh/m²/year. Nevertheless, photovoltaic generation was insufficient to fully offset the building's annual energy demand; therefore, the building did not achieve a true near-zero-energy condition.
The comparative assessment revealed that the building performed relatively well against the energy-saving requirements of ESGB. It achieved the required energy-saving improvement, complied with the assessed envelope and window-to-wall-ratio criteria, and satisfied the requirement for energy simulation. However, deficiencies remained in air-infiltration testing, operational energy management and monitoring, mechanical ventilation with heat recovery, and the extent of renewable-energy integration. Based on the eight shared criteria considered in the study, the project's alignment with ESGB was 50%. The comparison with Green Mark 2021 revealed a more substantial gap. The calculated Envelope Thermal Transfer Value remained below the 50 W/m² limit for non-residential buildings, indicating acceptable overall envelope performance according to this indicator. However, the project did not satisfy the prescribed U-value requirements for individual envelope components and lacked several measures associated with advanced building performance, including mechanical ventilation with heat recovery, air-infiltration testing, continuous energy management, and sufficient renewable-energy contribution. The resulting alignment index with Green Mark was only 12.5% (1 of 8 criteria). These findings indicate that the principal difference between Chapter 19 and the two international systems is not limited to the stringency of thermal requirements. More importantly, the international systems cover a broader range of operational and environmental performance dimensions. Chapter 19 can therefore provide an effective regulatory basis for reducing operational energy consumption, but compliance with its requirements alone does not ensure comprehensive green-building performance or near-zero-energy operation.
Conclusion:
The study demonstrates that applying the energy-efficiency measures of Chapter 19 can substantially improve the performance of office buildings in hot-arid climates. In the case study, the optimized configuration reduced annual energy consumption by 23.11%, while the photovoltaic system further reduced dependence on grid electricity. However, the building remained above the near-zero-energy threshold because renewable generation did not completely offset annual demand. The comparative assessment also shows that the main limitation of Chapter 19 is not simply insufficiently stringent thermal requirements, but its narrower scope compared with comprehensive green building assessment systems. Greater alignment with ESGB and Green Mark would require further development of requirements for envelope performance, air-infiltration control and testing, mechanical ventilation with heat recovery, renewable-energy integration, and operational energy monitoring and management. The findings are limited to a single office building in the hot-arid climate of Kashan and rely on simulation-based verification rather than measured operational data. Future studies should therefore examine additional building typologies and Iranian climate zones and incorporate field measurements, air-infiltration testing, and long-term operational monitoring. Developing a locally adapted green building assessment framework that integrates energy performance, renewable energy, indoor environmental quality, operational management, life-cycle carbon, and Iran's climatic conditions could also provide a basis for future revisions of national building regulations.