How to use natural and hybrid ventilation to deliver good Indoor air quality

By 2020 local authorities are projecting there will be an extra 366,000 primary school pupils and an extra 362,000 secondary school pupils. As a result of this there is a focus on an accelerated school building programme. Cost-efficiency remains a priority and the construction industry is invested in looking at innovative ways to achieve sustainability requirements within these guidelines.

In spring last year a study from RIBA found that 1 in 5 teachers have considered quitting because of the condition of the school buildings they have to teach in, whilst over 90% of teachers believe well-built and designed schools improve educational outcomes and pupil behaviour.

Ventilation is a critical element of new school design and existing school re-design. There is a regulatory need to ensure that education spaces provide well ventilated space for staff and students.  Air quality within the classroom should be optimal to allow pupils to keep their concentration levels and focus. There is also a need to remove stale air.  This can impact learning by causing an increase in allergies such as asthma and other respiratory conditions.

Appropriate planning needs to be carried out in advance of implementation, when building simulation tools play an important role.  This allows planners to consider the size of the room and occupancy rates.  A suitable control strategy is also important with a variety of potential users operating the system, from building and facility managers through to teachers and students themselves.

The Facility Output Specification is the document which forms the basis for the design of new and renovated schools.  To meet the required ventilation levels, whenever spaces are occupied, purpose provided ventilation should provide external air supply to all teaching and learning spaces of:

  1. A minimum of 3 l/s per person (90 l/s)
  2. A minimum daily average of 5 l/s per person at any occupied time
  3. Provide capacity to achieve 8 l/s per person for night time purge during summer
  4. Meet the acoustic requirements for BB93.  35 dB(A)  (mechanical ventilation noise plus an extra 5dB(A) allowance for noise breakthrough from outside)

There are three main approaches to ventilation in education in the UK currently.

Natural ventilation: Suitable for many types of buildings located in mild or moderate climates.  This would typically mean an “open window” environment.  There is no fan or system noise and minimum maintenance but short periods of discomfort during warm weather is to be expected, as has been seen in recent weeks in the UK.

The BB101 guide for schools outlines a significant need for natural ventilation and where appropriate, simple, responsive mechanical ventilation to maintain air quality.

Thermal comfort and control is more important than temperature. Thermal controls should be easy to use and quick to adapt to changing uses of space.  Lastly, but of equal importance, good acoustics are essential.  These aid effective learning, pupil engagement, and wellbeing.

Mechanical ventilation can ensure that the quality of air is controlled, exhaust moisture & odours out of rooms.  There is potentially less ductwork compared to balanced ventilation with the possibility of individual controls per room. This can be a good solution in areas of high pollution.

Analysis of the severity of health problems caused, and the number of people affected by air pollution was carried out for the Department for Communities and Local Government in 2008.  One of the most serious indoor air quality risks identified is one over which building designers and occupants have limited control.   Particles - predominantly products of combustion - increase the risk, and the severity, of heart disease and respiratory illnesses. The main source of particulate pollution is traffic, especially in UK cities.  London, along with 11 other UK cities, has frequently seen spikes in air pollution already in 2017. 

In addition to polluted air being brought inside, poor indoor air quality can also be attributed to many problems inside a building.  Excess humidity causes dampness, rot and mould, whilst pollutants are known to be a major cause of health issues such as asthma and eczema. Stale air is also believed to lead to a loss in productivity and low morale.

One way to counteract outdoor air-pollution in schools near busy roads, is to use a fully ducted ventilation system with extra fine filters fitted.

Lastly, a hybrid ventilation system allows the controlled introduction of outdoor air ventilation into a building by both mechanical and passive means.  It has built-in controls to allow the mechanical and passive systems to work in conjunction with one another. This should avoid additional ventilation loads compared to using mechanical ventilation alone.  Controls play an important role in hybrid ventilation, allowing the system to switch between mechanical and passive ventilation seasonally, diurnally or based on a measured parameter.

Hybrid ventilation can support the current trend to build schools and classrooms with a modular or standardised approach as seen with the Priority Schools Building Programme (PSBP).  

Hybrid Ventilation is an innovative and energy-efficient way to provide outdoor air ventilation to buildings, and in some conditions, to cool them, thus reducing energy otherwise required from conventional sources.

It can lead to a lower building life-cycle cost and create a healthier environment for building occupants.  There can be a greater sense of occupant satisfaction due to the increased ability to exercise control over the ventilation provided.  The lifecycle of the product can be extended and there is a strong ROI as there is less use of the mechanical elements and therefore lower maintenance required.

A review by the German research institute, Fraunhofer Institute for Building Physics and published by Velux, revealed that many children are frequently working in classrooms with excessive levels of CO2, above the recommended range of 1,000 – 2,000 ppm.  The researchers found that improving ventilation rates, reducing CO2 concentration and increasing access to daylight in classrooms, improves pupils’ performance in terms of higher levels of attention and concentration and lower rates of absenteeism. 

In the US, a study published in the Journal of Environmental Economics and Management, showed that improved indoor air quality in schools positively impacts student performance.  A renovation project for ventilation had a positive effect on test scores, comparable to reducing class sizes. The study focused on 65 primary schools which all underwent substantial repairs within a 5 year period meaning that there was an opportunity to compare schools before and after the renovations.

It is possible to use a touchscreen controller to provide a graphical insight into the operation of the ventilation system. Through the touchscreen interface, a user can explore how the systems work, adjust settings, and find out information on the system in order to maintain a comfortable environment with minimal energy use.

Using the latest controls available, the building manager can ensure that the system is operating as it should and end-users can be given guidance as to the correct action to take for optimum performance.

There are many benefits from using a more natural approach to ventilating a school building, from both the perspective of improving learning outcomes, health and concentration and also the opportunity to reduce energy costs for schools and local authorities through using less mechanical approaches.

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