Not too long ago, nearly all buildings were ventilated naturally.  Over time, these buildings were adapted and changed, with partition walls and reconfigured internal structures.  Mechanical ventilation systems were introduced and became widespread.  

Today, as energy costs continue to rise and we focus more on the environmental impacts of energy use, passive ventilation is once again being seen as an attractive option.  But it’s not as simple as it might seem upon first glance.  Getting the design right will lead to real advantages but get it wrong and it’ll be wholly ineffective.  In the worst case scenario, it can be dangerous (for example, some historic designs would use stairways as an exhaust stack).

Defining Passive Ventilation 

Passive ventilation (or natural ventilation) uses the natural forces of wind and thermal buoyancy to deliver fresh air into buildings.  The introduction of fresh air is important for thermal comfort, alleviating odours and contaminantes, providing fresh oxygen and generally making the indoor space a nicer place to be and work (turn the temperature up too much in a building and you’ll notice the drop in productivity).  

Buoyancy driven passive ventilation works by harnessing the forces resulting from the temperature difference between the interior and exterior of a building.  It does this because the warmer air in a building will rise to the top, being less dense than the cooler air which stays at the bottom.  An opening in the roof is a natural place for the warm air to escape.  It’s like when you remove the lid from a takeaway coffee and can feel the warm air rise upwards.  

If there is an opening lower down, as the warm air escapes it will suck in the cooler air through that opening.  The warmer the air is, the quicker it will rise and faster it will suck in cooler air from outside.  That is, when designed correctly, passive ventilation systems can be self-regulating and adjust to the conditions.  

Wind driven passive ventilation achieves the same effect by using the different pressures created by winds around a building.  Where there is a positive pressure on the windward side, there will be a negative pressure on the leeward side.  These pressures are used to drive the fresh air through the building.  

Advantages of Passive Ventilation

One of the most obvious (and important) advantages of passive ventilation is its ability to reduce a building's energy use and carbon footprint.  For any building with aspirations of being considered green, the use of passive ventilation should be considered a must.

Closely related to the reduced environmental cost is the reduced energy cost.  Where passive ventilation is used instead of a mechanised solution, it might reduce the total energy consumption by up to 30%.  Further savings can then be accrued from reduced service and maintenance costs.  There is simply less to go wrong.  

Not all of the benefits are financial and in a time when wellbeing is a greater focus than ever before, a passive ventilation system offers a low noise solution that reduces the noise burden on occupants.  In turn, this helps lower the general stress levels of your workforce.

With clean air flowing throughout your building at all times, the air quality is much improved.  This is known to improve the general health of occupants, increase productivity and concentration levels.  It is especially important given the heightened need for well ventilated spaces in the post-pandemic world.  

A final advantage of passive ventilation is the continuity.  It’s always on, supplying the indoor space with fresh air and helping maintain a pleasant, constant temperature.  There is no need for constant adjustments or waiting for the ‘system’ to kick in when the first person through the factory door fires everything up on an early Monday morning or after a period of closure.  

Using Louvres and Turbine Vents in Passive Ventilation

When designed correctly, the use of Ventilation Louvres in conjunction with Turbine Vents will achieve all of the advantages of passive ventilation as outlined above.  

Ventilation louvres work by allowing air in and out whilst providing protection against wind driven rain.  There are many different options available and matching the right type of louvre with the climatic conditions of the location is important.  For example, the Ventuer VL-3SD system is a highly efficient three stage ventilation louvre for use in exposed locations where high wind speeds and levels of rainfall can be expected.  In more sheltered locations, the Ventuer VL-104D will likely be efficient in providing enough weather protection whilst still allowing for that all important air intake.

On the roof of your industrial or warehouse building, a turbine vent such as the Ventuer SVV Series is needed to provide that buoyancy driven pull through.  Sitting near the ridgeline of the roof, it allows the heated air to escape whilst sucking in that cooler air through the ventilation louvres below. Turbine Vents also capitalise on the wind blowing over the roof, as it hits the vanes of the turbine ventilators and causes them to spin.  This spinning motion creates an area of low pressure both within the ventilator and to the side opposite the direction the wind is coming from.  These low pressure areas create a suction force which assists with drawing the air from within the building.

As with all things, it’s not quite as simple as identifying the right product and installing them where you think they might work though.  The solution must be designed to take into account the geographical considerations, the internal layout and a myriad of other influencing factors.  In fact, just trying to express the airflow induced by the stack effect from buoyancy ventilations looks like this:

Qstack = Cd*A*[2gh(Ti-To)/Ti]^1/2, where

Qstack = volume of ventilation rate (m3/s)

Cd = 0.65, a discharge coefficient.

A = free area of inlet opening (m2), which equals area of outlet opening.

g =9.8 (m/s2). the acceleration due to gravity

h = vertical distance between inlet and outlet midpoints (m)

Ti = average temperature of indoor air (K), note that 27°C = 300 K.

To = average temperature of outdoor air (K)

In other words, it can get complicated.  If you want a guaranteed outcome that best exhibits all of the positive characteristics of passive ventilation it will always be beneficial to consult with the experts.

If you’d like to find out more about passive ventilation then please do contact us.  We’re here to help.