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Natural Ventilation Isn't the Most Efficient Solution in All Cases

Natural Ventilation Isn't the Most Efficient Solution in All Cases

Ventilation serves two main purposes in a room: first, to remove pollutants and provide clean air; second, to meet the metabolic needs of the occupants, providing pleasant temperatures (weather permitting). It is well known that environments with inadequate ventilation can bring serious harm to the health of the occupants and, especially in hot climates, thermal discomfort. A Harvard University study demonstrated that in buildings with good ventilation and better air quality (with lower rates of carbon dioxide), occupants showed better performance of cognitive functions, faster responses to extreme situations, and better reasoning in strategic activities.

It is not difficult to see that ventilation plays a vital role in ensuring adequate air quality and thermal comfort in buildings. We have all felt it. But when we talk about ventilation, a light breeze from the window might come to mind, shifting through our hair and bringing a pleasant aroma and cooling temperature that brings fresh air and comfort. In mild climates, this experience can even be a reality on many days of the year. In harsh climates or polluted spaces, it could be quite different.

Gimnasio de la Escuela secundaria Blaise Pascal / Koffi & Diabaté Architectes. Image © François-Xavier Gbré
Gimnasio de la Escuela secundaria Blaise Pascal / Koffi & Diabaté Architectes. Image © François-Xavier Gbré

Air must enter and exit through openings such as windows, doors, solar chimneys, or wind towers. The efficiency of the ventilation will also depend on the local climate, the geometry of the building, and even human behavior (opening or closing a window will affect ventilation). Natural ventilation is a passive strategy that uses winds (cross ventilation) and differences in density and air temperature (the chimney effect) to circulate the air inside. When well designed and located in milder climates, it can be an excellent solution. João Filgueiras Lima, Lelé, through refined technical knowledge, developed passive ventilation solutions for SARAH Network hospitals in Brazil; this strategy significantly reduced maintenance costs and rates of patient infection from bacteria.

However, designing good ventilation in a project is not a simple task, especially when the building has not yet been occupied and its particularities are not well known. There are internal and external sources of heat and pollution, as well as physical barriers, prevailing winds, and other unexpected elements that may arise with the occupation of the site. Yet passive solutions should take priority whenever possible, as they reduce energy consumption in the building, construction and maintenance costs, and, mainly, because they work practically alone.

Hospital Sarah Kubitschek Salvador / João Filgueiras Lima (Lelé). Image © Nelson Kon
Hospital Sarah Kubitschek Salvador / João Filgueiras Lima (Lelé). Image © Nelson Kon

In small projects, the concern for lack of control and possible discomfort can be reduced further, since small changes can be made to improve the thermal comfort and ventilation of smaller environments. But in large-scale projects, such as airports, hospitals, office buildings, and others, relying only on natural ventilation is almost always unfeasible. When we depend entirely on natural conditions, it is very difficult to have total control over the ventilation rate in the building, which can lead to problems with indoor air quality, excessive heat gains and loss, and consequent waste of energy. There are several other factors that can weigh in the decision to include mechanical ventilation devices in the project:

  • The climate is very severe;
  • The outside air is not of good quality;
  • There is a lot of noise outside;
  • The building's geometry or even the influence of neighboring buildings do not allow all interior spaces to receive natural ventilation;
  • The activities carried out in the interior do not allow the windows and doors to remain open, or for an exchange of air between environments.

Passenger Terminal Complex Suvarnabhumi Airport / Jahn. Image © Rainer Viertlboeck
Passenger Terminal Complex Suvarnabhumi Airport / Jahn. Image © Rainer Viertlboeck

Many of the deficiencies of natural ventilation can be overcome by mechanical ventilation. Its use can provide greater control of the system and even complement or regulate the naturally conducted flow. That is, it is possible for mechanical ventilation to enhance and make passive ventilation more efficient. Such systems are able to provide a controlled rate of air exchange, accommodate the different needs of occupants, and respond to polluting loads regardless of climatic variations. Like passive systems, the type of mechanical ventilation will depend on the climate and the activities carried out inside the building. Hot and dry climates necessitate very different solutions from cold climates, for example, to ensure good energy efficiency. As it is an extremely complex subject, mechanical ventilation systems must always be conducted by specialized professionals, who can evaluate and dimension the ventilation systems more efficiently.

Casa en Himeji / FujiwaraMuro Architects. Image © Katsuya. Taira
Casa en Himeji / FujiwaraMuro Architects. Image © Katsuya. Taira
Oficina para Communique Marketing Solutions / groupDCA. Image © Andre J. Fanthome
Oficina para Communique Marketing Solutions / groupDCA. Image © Andre J. Fanthome

According to Martin W Liddament, in the book A Guide to Energy Efficient Ventilation [1], “Many systems operate in 'blending' mode to dilute pollutants, while others operate in 'displacement' mode to remove pollutants without mixing. Some systems incorporate heat recovery techniques from the exhaust air to reduce heat loss from ventilation. Well-designed systems installed in good quality buildings cannot be affected by the driving forces of the climate. The benefits must be balanced against operating and capital costs, needs for ongoing maintenance and eventual replacement. It is often this balance between cost and performance benefit that dictates the ventilation approach. Mechanical systems need to be designed to meet the specific needs of the building in which you are going to operate. An integrated design philosophy guarantees optimal performance combined with maximum energy efficiency.”

Even though mechanical ventilation systems will always require some supply of electricity, it is always possible to improve their efficiency and reduce the environmental impact of the materials used. In general, the air is conducted through ducts, traditionally rectangular metal tubes with thermal insulation. CLIMAVER®, for example, is a self-supporting duct for air conditioning, ventilation, and heating systems. It was designed to offer good thermal, acoustic, and watertight-ness levels, as well as good fire safety, making the system energy efficient and reducing noise levels generated by fans and air conditioning units. The main difference is that the system arrives on the job in light sheets, which are properly folded into the desired sections for each duct and attached to the ceiling through very simple installations. This makes transportation simpler and the system cheaper. Made with up to 80% recycled glass wool, it also reduces the need for sand extracted from quarries and helps to protect biodiversity. As a point of comparison, using 1000 m2 of the product in place of traditional metal ducts saves the equivalent of more than 3 tons of steel across installation, insulation, and disassembly. Therefore, it is vital to think about all the elements of the project, the possible passive solutions, the possible mechanical solutions, and all the materials that will constitute the system.

Pabellón polideportivo de Villacelama / QUIRÓS PRESA. Image © Imagen Subliminal
Pabellón polideportivo de Villacelama / QUIRÓS PRESA. Image © Imagen Subliminal

Since we spend about 90% of our time indoors, thinking about air quality is also vital. The pollutants most often found in work and home environments are so-called VOCs, or "volatile organic compounds." They are naturally emitted by people, pets, and cleaning products, as well as furniture, carpets, paints, and varnishes. After long periods indoors, people often complain of symptoms such as headaches, nausea, lack of concentration, eye irritation, fatigue, and even breathing problems.

Instituto Biodesign C de la Universidad Estatal de Arizona / ZGF Architects. Image © Nick Merrick © Hall+Merrick
Instituto Biodesign C de la Universidad Estatal de Arizona / ZGF Architects. Image © Nick Merrick © Hall+Merrick
Holland Boulevard y Rijksmuseum Schiphol / NEXT architects. Image © Thijs Wolzak
Holland Boulevard y Rijksmuseum Schiphol / NEXT architects. Image © Thijs Wolzak

In conjunction with natural or mechanical ventilation, it is possible to incorporate other systems and products that can contribute to improving indoor air quality. Activ'Air® was specifically designed to break down formaldehyde emissions into non-harmful inert compounds, thus eliminating the risk of re-emission. The technology can be incorporated anywhere from plasterboard to acoustic ceilings, and several tests in schools and hospitals have shown that it significantly reduces formaldehyde concentration, improving indoor air quality and reducing the chances of occupants feeling unwell.

At the same time that air conditioning provided new possibilities for architecture, it also caused issues in many cases. The idea that any building could have adequate air conditioning with any materials, shapes, or solar exposures contributed a lot to the energy crisis that the world has been going through. In fact, it is known that a significant portion of a building's maintenance costs are spent on air conditioning. But air conditioning systems in themselves are not the bad guys. The big problem is when they are used indiscriminately, without even considering complementary passive solutions or design strategies that could mitigate many of the environmental problems. In challenging contexts or environments that require strict control of climatic conditions, relying solely on natural ventilation is practically impossible. In this sense, developing a project in which the project teams and HVAC installation specialists are well integrated is essential to achieve sustainable results, good indoor air quality, and thermal comfort for the building's occupants.

Note
[1] Liddament, Martin W. A Guide to Energy Efficient Ventilation. 1996. Available at this link.

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Cite: Souza, Eduardo. "Natural Ventilation Isn't the Most Efficient Solution in All Cases" [A ventilação natural não é a solução mais eficiente em todos os casos] 15 Apr 2021. ArchDaily. Accessed . <https://www.archdaily.com/958430/natural-ventilation-isnt-the-most-efficient-solution-in-all-cases> ISSN 0719-8884

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