Net Zero Energy Buildings for Enhanced Operational Benefits

Net Zero Energy movement started in India with the launch of Net Zero Energy Building Rating system in 2018. IGBC’s Advancing Net Zero is also aligned with WorldGBC. World GBC’s ANZ states that by 2030 all new buildings shall operate at Net Zero carbon and by 2050 100% of buildings must operate Net Zero Carbon.

CII-Godrej GBC is the first Platinum certified Green Building in India. The building achieved Green building rating in 2003 and demonstrated advanced green features. In fact, the CII-GBC HQ building paved the path for green building movement in the country. Today, India has over 10,200+ registered green building projects with over 10.1 billion square feet of green footprint. It has been realized that the green buildings have now become a movement in the country hence, it has been decided to convert the CII-GBC into a “Net Zero Energy Building”, to further accelerate transformation in Indian building sector. Advanced technologies which are robust and affordable are available in the country which can enable buildings to achieve net zero energy performance.

Overview of CII-GBC

The built-up area of CII-GBC is 1858 sq.m, out of which 1115 sq.m is fully air-conditioned (centralized cooling system). The building is designed for day-time, 100 occupancy. Building envelope (wall, roof and glazing) is energy efficient and designed for maximum daylighting for all regularly occupied spaces. Glass has been installed considering right orientation, more glass has been provided in north – harnessing daylight without heat.

Strategies for Achieving Net Zero Energy Status:  

Energy efficiency has paramount importance for achieving Net Zero Energy performance. CII-GBC has been designed with energy efficient measures and has demonstrated more than 20% energy savings over the baseline defined in ECBC 2017 (latest Energy Conservation Building Code). Retrofitting strategy developed to further reduce energy demand and to increase use of renewable energy, following measures suggested for implementation:

• Retrofitting of lighting (interior and exterior) system
• Replacement of air-conditioning system (chiller plant)
• Commissioning of advanced BMS system for optimised building performance
• Increased capacity of on-site Renewable Energy generation

Energy end-use summary and load profile recorded, and deep analysis performed to understand hourly energy use. The peak load is 100 kW. Maximum demand occurs during the daytime, cooling system (chiller and Air Handling Unit) are main energy guzzlers.

Retrofitting of Lighting and Cooling system:

Completely automated CFL based (with dimming control, integrated with daylight and occupancy sensor) lighting fixtures installed in 2003. Globally, lighting has found complete transformation owing to introduction of LED based lighting system which in fact reduced lighting load in buildings, drastically. Lighting system retrofitted in 2018 and it cut down the load from 16.5 kW to 3.5 kW. LPD (Lighting Power Density) is less than 0.4 W/sq.ft). Through analysis (thermography carried out) performed before retrofitting the lighting system. Temperature of lighting fixture recorded as 51^oC in case of CFL based lighting whereas, the temperature of LED lighting fixture was 29 ^oC, this led reduction in cooling load by 4%.

The whole chiller plant retrofitted including chillers, pumps and cooling tower with the most advanced and energy efficient system. The system is integrated with the wind towers (passive cooling system) that consciously supply pre-cooled fresh air. Two water-cooled screw chillers (2x49TR, COP of chiller is 4.85, iKW/TR is 0.725 at 100% loading). Since, most of the time, building operates at part load hence chillers selected giving more emphasis on part load performance (IPLV is 6.58 and ikW/TR at part load is 0.534). High efficiency pumps (IE4 motor) are installed for chillers and cooling towers, integrated with VFD to optimize the performance.

Commissioning of advanced BMS system:

A sophisticated Building Management System (BMS) system commissioned to optimize energy performance. It is estimated that an integrated BMS system can save 8-10% energy in commercial buildings. Chiller plant, AHUs and indoor & outdoor environmental variables are continuous being monitored, Then, the recorded data are used to analyse the performance.

Increased on-site Renewable Energy generation:

Since inception, 2003, CII-GBC has been promoting the use of renewable energy sources. Earlier, the SPV capacity was 24 kWp that off-set grid energy use by 21%. For a Net Zero Energy Building, it is mandatory to off-set 100% grid energy use by renewable energy. Hence, it was decided to opt new technology that can enhance RE generation from the roof-top (1175 sq.m). Initially, a site assessment was carried out and potential RE technologies are studied. Bifacial Solar PV technology adopted which had promising efficiency (high electricity generation).

Bifacial solar PV is a transparent and frameless module and unlike regular solar modules that come with a singular face for absorption of light. Bifacial solar modules are equipped to allow passage of light from both the sides of solar cell and generate electricity from both sides (front and rear face of the module).

This helps in increasing the efficiency per cell, resulting in an increase in the total energy generation along with reduced construction costs. In fact, to increase the yield on the backside, roof surfaces are coated with high SRI (more than 95) paint that reflects the radiation on back side of the module. The SPV system installed at 1.5 m height from the roof, so that diffused radiation will fall on back side of the SPV modules. Total 130 kWp (efficiency of module is 22.3% which is higher than the conventional module-18.6% ) capacity of onsite bifacial SPV installed (over roof-top and wind towers) and 8 kWp of old SPV system commissioned (on utility rom). The total SPV system capacity is 138 kWp.

Till July 2020, the SPV system was off-grid connected, the unique feature ‘curtailment of power’ ensured energy generation only to meet the requirement. Grid connected net metering installed in July 2019 and since than the building only uses RE to fulfil energy usage and excess energy is fed to the grid. On an occasion, when RE generation is insufficient to meet the demand, power is drawn from grid.

Net Zero Buildings in India:

Net Zero Energy Buildings offer immense tangible benefits (reduce operational expenditure). Residential, Commercial and Industrial projects shall come forward to have their projects future ready for technology and performance. In case of new building projects, it is important to embed passive design features which optimize building design and then consider energy efficiency measures for implementation. In existing building projects, retrofitting would lead significant energy savings. Hence, primarily; energy efficiency should be focused to reduce energy demand and later Renewable Energy sources shall be deployed to off-set grid energy use by renewable (on-site or off-site RE). Net Zero Energy Buildings are the future!