Net zero – we have all heard this phrase, but what does it really mean and how do we get there? According to the United Nations, net zero is cutting greenhouse gas emissions to as close to zero as possible, with any remaining emissions re-absorbed from the atmosphere. With the deadline for new building compliance on net-zero goals set for 2030 and existing buildings to achieve net zero by 2050, there is a lot of work to be done.  

Marloes Reinink, director of Solid Green Consulting, shares some practical knowledge on designing for net zero. 

According to Reinink, working with a client who has clear goals pushes the design to find new ways to achieve net zero. “They are more involved, including choosing décor and building materials that will help a project reach its net-zero goal.”  

Sustainability and net zero 

The concept of sustainability is far-reaching, including elements such as healthy air quality, proximity to transport hubs, selection and use of materials. “Net zero focusses on one aspect to achieve the best possible result within that focus area, i.e., energy efficiency for a net-zero energy trajectory,” explains Reinink. 

The Green Building Council of South Africa (GBCSA) defines a net-zero carbon building as one that is highly energy-efficient, where the remaining energy use is from renewable energy, preferably on site but also off site (where absolutely necessary), so that there are net-zero carbon emissions annually. 

Carbon certification levels 

The GBCSA’s net-zero carbon certification is divided into different levels: 

• Level 1: Building emissions 

Buildings that are in the design or construction phase. It covers the base building energy consumption, without tenant loads. 

• Level 2: Base building emissions and building occupant emissions 

The entire building consumption that accounts for tenant loads, either within the design or operation of the building. 

Net-zero certification is available in four categories: Carbon (energy), water, ecology and waste. This system evaluates the environmental performance of the design and construction of buildings on the journey towards net zero. 

Net-zero certifications are valid for three years, ensuring that new innovations can be included in optimising the building in operation and continually improving their carbon footprint into the future.  

Three strategies to achieve a net-zero building: 

Passive design (reduce demand) 

Most commercial buildings’ energy usage is driven by heating and cooling, which accounts for approximately 40% of their energy bills. Passive design focusses on how to deliver a comfortable building for at least 80% of the year, using outdoor air only. These interventions would include optimal orientation of the building, opening windows, natural ventilation and light to deliver a more energy-efficient design. 

Efficiency 

“Decoupling ventilation from cooling is a potential solution for energy efficiency (and increased resilience during loadshedding). This allows the building to be ventilated by fresh air and maintain the indoor air quality when outside air conditions are right, without having to use a mechanical cooling system,” says Reinink. 

Better design reduces the energy load through efficiency. Secondary interventions include using technology sensitively, via proper sizing and scope of heating, ventilation and air-conditioning (HVAC), energy-efficient LED lighting and more efficient products. 

Renewable energy 

After the energy demand has been reduced and energy efficiency has been optimised, the remaining required electricity can be generated through renewable sources, of which solar PV is the most common in South Africa. 

Carbon offsets 

When there is not enough space on the roof or carports to accommodate enough solar photovoltaic energy to achieve net zero for a building, there is the possibility to offset the additional consumption. This includes the purchase of carbon credits for the remainder of the energy, the percentage of which is noted on the net-zero certificate. 

Case studies 

Project name: Lapalala Wilderness School.
Location: Waterberg, Limpopo.
Green Star rating: Net zero – carbon level 2 (modelled).
Size: 5 500m².

Services: Two boreholes and a solar plant for electricity as well as a wastewater treatment system. Power is supplied by a 105KVA solar PV system with 240kWH of storage. Water is heated using a thermodynamic solar hot-water system. 

Passive design elements: All the dormitories face north-south, with skylights to maximise daylight. Windows ensure extra light and passive heating, together with insulated walls to prevent heat loss in the residential spaces. Rammed earth gable-end walls provide thermal mass, which coupled with cross-ventilation means no need for mechanical ventilation for cooling. 

Project name: Fuchs Lubricants.
Location: Isando, Johannesburg.
Green Star rating: Net zero – carbon level 2 (modelled).
Size: 2 774m².

Services: All equipment in the staff canteen was changed to electric from gas, eliminating scope 1 emissions, allowing only scope 2 indirect emissions. A comprehensive metering system was installed to ensure ongoing optimisation of the building’s energy performance during operations. 

Passive design elements: The building fabric was optimised, specifying a high-performance double glazing. Decoupled ventilation was designed into the cooling system, so the building can be cooled by fresh air without opening windows, when outdoor conditions allow. 

Project name: Redefine.
Locations: 2 Pybus and 90 Rivonia Roads in Rivonia, and Rosebank Link in Rosebank, Gauteng.
Green Star rating: Net zero – carbon level 2 (measured).
Existing buildings with Green Star ratings in the past, certified for net zero.

Process:  

• Improving energy efficiency in the buildings through assessment of twelve-month energy data and calculating the kWh/m²/annum. 
• Maximising renewable energy opportunities both on site and off site by deducting the solar energy generated by the solar panels installed on the buildings. 
• Carbon offsetting through the purchase of carbon credits for the remainder of the energy. These are noted on the net-zero certification: 2 Pybus Road 11,5%, 90 Rivonia Road 56,3% and Rosebank Link 32,9%. 

Full acknowledgement and thanks go to https://www.solidgreen.co.za/ for the information in this editorial. 

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