Natural Ventilation: Greening a 25 year old commercial building

Submitted by: Brandon Abdinor, Tuesday, October 8, 2013

Natural ventilation is one of the basic tenets of green building. One of the primary benefits is the reduction in energy use by reducing the need for energy hungry mechanical Heating, Ventilation and Air Conditioning technology (HVAC) that is commonly used to provide air circulation and thermal comfort to users and occupants of buildings.

An additional benefit arising from natural ventilation is an improvement in the indoor air quality, facilitated by introducing fresh air into the building. Indoor air quality (also called Indoor Environment Quality) is another fundamental goal of green building and one of the measurable categories in many green building standards, including South Africa’s Green Star building rating system. This aspect has gained prominence in recent years, as many case studies on green buildings are proving that productivity and the wellbeing of occupants is one of the most financially beneficial results of going green. Indoor air quality is a direct contributor to this. 

The KwaZulu-Natal Master Builders Association building

A picture of the MBA building, prior to the refurbishment, showing the small, high windows which let in very little air (Image Source: Master Builders Association).

When the KwaZulu-Natal Master Builders Association (MBA) undertook a substantial refurbishment and “greening” of its headquarters in Westville in 2010, natural ventilation was identified early on as offering a significant opportunity to make environmentally beneficial gains. The 25 year-old four-story building was not catering for all of the evolving organisation’s needs, and the necessary refurbishment provided an opportunity for the builders’ association to demonstrate environmental responsibility.

The major focus of the project was the ground floor, into which MBA decided to expand its conference and retail activities. It had one door and small high fanlight windows that let in very little light or air, and the central ducted air-conditioning system was by and large the only way air circulated through space.

The building has an almost square overall footprint and has a central triple volume atrium. These features allowed for the implementation of two effective methods of ensuring adequate natural air-flow, namely cross-ventilation and stack ventilation.

The MBA refurbished building’s retrofitted green roof, as well as the internal atrium, an integral part of the natural ventilation system (Image Source: Master Builders Association).

Creating new openings for cross ventilation

Air moves effectively through a building when there are two or more openings on different sides of the building. Air flowing naturally outside the building (breezes and winds) can then enter through one of these, and exit through another, depending on where they are located. It is however, not ideal in most cases, to introduce stronger winds through the building, as this creates discomfort (blowing papers) and can also introduce dust and other particle matter into the building.

It was decided to make large openings, sealable with glass and aluminium sliding doors, on all four sides of the building which would allow specific combinations of doors to be opened to optimise airflow while avoiding wind inside. These openings with big glass doors were in any event desirable from the point of view of “day-lighting”, a principle whereby natural daylight is allowed into the building to reduce reliance on electrical lighting. The views over the valley also connect users to the outside, further creating a pleasant (and healthy) indoor environment.      

Diagram showing cross ventilation in a stronger wind (Image Source: Brandon Abdinor).

Diagram showing cross Ventilation in a light breeze (Image Source: Brandon Abdinor).

Making the most of the atrium using stack ventilation

Where there is sufficient space for warmed-up air to rise in, and then exit, a building, the stack effect comes into play. Air becomes heated in a building, rises, and then fresh cooler air is drawn into the building through openings at a lower level. The MBA  building had a clear perspex dome added to it, so turbine ventilators (“whirlies”) were retrofitted in order to help draw the hot air up and out, assisting the stack effect.  

Diagram showing stack ventilation using the pre-existing atrium (Image Source: Brandon Abdinor).

A reduction in the use of air-conditioning

Prior to the refurbishment, the ground floor required that the air-conditioning was switched on for each and every hour of occupation, throughout the year. After the interventions were undertaken, the building would be sealed and air-conditioned, only on those days where it was very hot and humid and there were no cooling breezes available to be harnessed. In the first year observed, the central air-conditioning was switched off for two thirds of operational time, a result that exceeded the expectations of the design team. Direct measurement of savings proved highly complicated in that the usage of the area was totally different post refurbishment, with highly increased activity and traffic in the conference and retail area.

The retrofitted turbine ventilators that draw warm stale air out of the top of the atrium (Image Source: Master Builders Association)

Challenges experienced

  • Durban has windy conditions and it was sometimes challenging to ensure sufficient cross – ventilation without unwelcome drafts disturbing users.
  • Dust and particles: This was not an overwhelming issue, but plants were planted outside some of the openings which would help trap particles and clean and cool the air coming in.
  • The Durban climate is very hot and humid, and it is challenging (but not impossible) to avoid air-conditioning in a building of this size all year round. The intervention described here would probably be even more effective in a climate such as Johannesburg’s.
  • Measurement of savings: Due to the considerable change in use, it was difficult to create an empirical before and after scenario. It was also difficult to source the necessary software and measurement equipment at that time.
  • The optimised ventilation set-up required that facilities personnel understand the system and also be constantly aware of weather conditions, to ensure that the correct configuration of open doors was always implemented.

The benefits of the design

  • Natural outside air is, in most cases, cleaner and healthier than the air inside a poorly ventilated building. Mould is a common issue for buildings, and where the air is not flushed, spores can accumulate, affecting occupants. People bring germs into buildings and these too can create a negative impact. There is a recognised phenomenon called SBS (sick building syndrome) which has been shown to create illness in occupants and make these buildings unhealthy and undesirable to be in.  Volatile organic compounds (VOCs) emanate from paint, carpets, furniture and equipment, and these too have a negative impact on people’s health. And finally, stale air often has lower oxygen levels as carbon dioxide builds up. Fresh air gives users and occupants vitality and keeps them happy and more productive.
  • Energy savings as a result of reduced HVAC use, save not only money, but also reduce a building’s carbon footprint. This mitigates against climate change and reduces our reliance on centralised electricity generation, predominantly coal based in South Africa.
  • Operating a building in harmony with the weather connects users to nature and natural rhythms, uplifting people and making them feel part of creating a greener lifestyle. The personnel generally took a keen interest in the green interventions at the MBA. 

Brandon Abdinor was the CEO of the KZN Master Builders Association from 2007 to the end of 2011. He initiated, oversaw and participated in the design and implementation of the refurbishment and greening activities described in this article. The KZNMBA is undergoing further operational adjustments and is exploring further necessary changes to the configuration of this building. As such, the interventions described in this article may not remain applicable in future. The KZNMBA regrets that it cannot demonstrate these features to visitors at this time.   

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Brandon Abdinor