The importance of good ventilation in classrooms has been recognised since Victorian times, but many of today's schools fail to reach even basic levels of indoor air quality. Ewen Rose reports on a growing health crisis.
Two decades of heavy focus on making buildings more energy efficient may be responsible, at least in part, for a legacy of poor indoor air quality (IAQ). The fact that the problem seems most acute in schools is giving rise to serious concern about the long-term health implications for children. There is even growing evidence of a link between outbreaks of winter flu and poor classroom IAQ.
The increase in respiratory diseases linked to sealed buildings and condensation is becoming better understood, but the range of factors involved in measuring IAQ levels remains confusing- particularly for end users.
For good health and productivity, the rule of thumb suggests temperature needs to be 20-24°(, with relative humidity between 40% and 60%. The ventilation system needs to dilute C02 levels and replace oxygen. CIBSE guidance calls for an air-change rate of between six and eight litres per second (l/s) per person, but striking the right balance seems increasingly hard when most establishments are heavily focused on energy.
Airtight building envelopes are effective at keeping out external pollutants, but the use of open able windows as part of passive or 'natural' ventilation strategies is a concern because of rising levels of harmful diesel particulates in urban areas. This is a particular problem for schools situated close to major roads.
While it is now common practice to monitor energy consumption, IAQ is all but ignored. This means there is a growing temptation among building operators to sacrifice ventilation in order to reduce energy use. The situation in schools is of particular concern because of the potential impact of increased concentrations of harmful particulates on growing bodies and pupils' ability to concentrate and, therefore, learn.
A large body of research shows that poor air quality has a much more serious impact on 'cognitive performance' than high temperatures. 'There are a lot of people turning off the plant to save energy without thinking of the implications,' says Peter Dyment, air quality consultant at Camfil Farr. 'If you turn things off, then you have to monitor particulate levels in the air.'
Dyment believes 'cost engineering' has much to answer for. 'People who should know better often don't provide the right advice and simply look for an easy saving.'
Studies carried out by the University of Exeter show that C02 levels exceeding i ,500 ppm can lead to a 5% reduction in 'power of attention', and further research from Denmark has shown there is an improvement in school performance when classroom ventilation is increased from around three litres per second per person to 8.5 litres'.
IAQ takes its toll
Air pollution causes up to 360,000 premature deaths per year in the EU, according to research from the European Commission’s environment committee. However, there is concern that this number could rise because the indoor threat has been exacerbated by the drive to improve the energy efficiency of buildings.
The Healthvent EU research project reported last year that almost two-thirds of the burden of disease caused by IAQ were from pollutants coming into the building. Pollution experts suggest this threat continues to grow because government policy is focused on reducing CO2 emissions and has led to the promotion of diesel vehicles. The World Health Organisation has declared diesel particulates as a Class 1 carcinogen.
Restricting C02 levels to between 400 and 1,000 ppm is considered optimal for learning. At between 1,200 and 2,000 ppm, fatigue and impairment of concentration increases; 2,000 to 5,000 ppm leads to fatigue, headaches, increasing the loss of concentration: and beyond 5,000 ppm we are into the very serious territory, where lack of oxygen causes faintness.
SE Controls measured C02 levels and temperature in 28 classrooms in six schools around England for between three and 20 months. This revealed that 'excessively high' C02 concentrations of more than 4,000 ppm are not uncommon in classrooms where the principle ventilation is via manually operated windows.
'IAQ tends to be better during the summer, when occupants are more likely to open vents for thermal comfort, compared to winter. During November to December 2013, 85% of monitored, manually ventilated classrooms failed to deliver average occupied C02 concentrations of less than 1.500 ppm,' the SE Controls report says.
SE's design manager Chris Iadon adds that IAQ 'doesn't appear to be high up on the agenda of the education sector, perhaps because the effects of poor IAQ on health and performance are not well understood'. He says there were no 'drivers to incentivise the use of limited maintenance budgets on remediating IAQ problems', plus a general reluctance to pay for post-occupancy evaluations needed to assess the issue.
'Airflow rates for classrooms are actually quite large because these spaces are heavily occupied,' says Iadon. 'The main practical challenge is to deliver these rates in a manner that does not impact on occupant discomfort by producing cold draughts during the heating season, for example. Just opening the windows may not always be an appropriate solution.'
Open able windows are one means of providing ventilation to satisfy an allowable ventilation solution under Part F of the Building Regulations, despite the fact they are likely to remain firmly closed during the heating season. However, there are a growing number of consulting engineers who believe the best approach is mechanical ventilation with heat recovery (MVHR), despite some highly publicised problems caused by installation mistakes.
If installed and run correctly, Lars Fabricius, of SAV Systems, believes MVHR is the most appropriate solution because it solves a number of practical problems specific to schools, and can be set up to avoid wasteful continuous ventilation of spaces that are empty or partially occupied.
'The common alternative, opening windows, offers no opportunity to recover heat from the outgoing air,' says Fabricius. 'School staff also tend to open windows in response to rising temperatures rather than "stuffiness" caused by elevated C02 levels. There are also issues of security, air pollution and noise ingress associated with opening windows [in urban areas].'
Fabricius suggests MVHR units could be mounted in each space with direct connections to the outside through the wall or roof. 'Such units are easily retrofitted to existing classrooms and can be configured to provide true demand controlled ventilation by modifying the ventilation rate in relation to the key IAQ parameters of C02 concentration or relative humidity,' he says.
Control can also be arranged via PIR movement sensors and timers, or through an interface with a BMS, according to Fabricius, who recommends a combination of the automatic bypass, fan speed differentials, night cooling and optional cooling modules to improve temperature control.
Success depends on the installation and commissioning process, backed up by planned maintenance strategies. The new BS EN 15780 Ventilation for buildings. Ductwork. Cleanliness of ventilation systems standard includes recommended inspection time periods for air systems, to ensure they are properly monitored and remedial action taken if air quality conditions worsen. The newly revised Guide to good practice for ventilation system hygiene (TR/19) from the Building & Engineering Services Association underpins the standard, with practical guidance for contractors engaged in ventilation installation and maintenance. A new version of CIBSE GuideB: Heating, Ventilation, Air Conditioning, and Refrigeration will also be available in the summer.
However, Kevin Munson, managing director of Ruskin Air Management, believes some project teams are building IAQ issues into buildings from the moment their project starts. 'We need to impress upon specifiers and clients that IAQ considerations need to be part of the complete solution,' he says. 'If your envelope is not airtight, you are building in problems.'
“The situation in schools is of particular concern because of the potential impact of increased concentrations of harmful particulates on growing bodies”
Supply chain problem
The Building& Engineering Services Association (B&ES) has launched an initiative seeking to unite the construction supply chain so that IAQ is addressed as a fundamental part of the project process.
'IAQ is very much in our sights,' says B&ES head of technical and safety, Bob Towse. 'We think this is as much about the way the supply chain functions as equipment selection. There are plenty of good-quality solutions around, but it is a wide and complex subject, which is poorly understood by contractors, consultants and clients alike. We will be seeking to raise the profile of this whole topic so that it becomes a clearly defined part of any building specification.'
Munson points out that the people responsible for specifying the solutions are often under pressure to buy at the cheapest price. 'IAQ needs to be part of the commissioning process, but that is often left out.' he says.
'lf we could make it part of the handover, then we would have a value at the outset that we could monitor during maintenance to show that our IAQ measures are working. It would also show the client why good ventilation is worth paying for.
Many planned maintenance programs omit regular checks on air handling unit performance and ductwork hygiene, so undermine efforts to keep particulate levels under control, claims Dyment, who called for closer attention to be paid to the quality of air filters.
'Standard G3 filters does not deliver the level of clean air quality required; the only things available at the moment that also provide improvements at low energy are F7 filters.' He says. However, he warns that even good filters can be compromised if they are inserted in side-withdrawal mounting rails, which allow the air to bypass the filter.
'Second-stage filters are designed to remove smaller particles, and they must be in properly engineered, front-withdrawal mountings to ensure they can be fully sealed so air bypass does not compromise the design.' says Dyment.
On the plus side, sales of energy saving filters are growing by 20-30% per year because of pressure on FMs to cut running costs. Users get the added benefit that these products will last two or three times as long as commodity filters. So the major elements that contribute to IAQ are understood and a large body of research work exists, but the complete picture is missing, according to James Griffiths, regional operational marketing manager for Flakt Woods.
'We have regulations covering design, construction, installation, commissioning and provision of information, but compliance is very weak, and the information rarely reaches those who maintain and operate the school,' he says.
At the same time, a panic-stricken rush into purely mechanical solutions could be counterproductive, according to many observers.
'Natural ventilation still has a big role to play in schools,' says Rob Davies, director of smoke ventilation specialist Adexsi UK. 'There has been a backlash against this type of solution because of some high-profile failures, but it is too simplistic to suggest that only mechanical systems will deliver the right number of air changes.
'It is correct to say that natural ventilation is not the right solution in every application, but – given the appropriate design conditions - it can provide adequate air quality at the lowest possible energy penalty, and should certainly be on the table in early design meetings.'
However, Davies emphasizes the importance of addressing the issue of user training and occupant behavior. 'You cannot simply hand over a naturally ventilated school and expect teachers and non-specialist staff to know how it works. The industry has to get better at communicating design intent to its customers, and ensuring they are properly trained to ensure the system continues to operate and is not undermined by changes to the building use, or during service and maintenance.'
While we often look to Scandinavia for inspiration in many building quality issues, they have had similar issues to ours in their schools. The big difference is that IAQ has become a high priority for them, according to Jesper Sondersby Laursen, from Danish duct system supplier Lindab.
‘Many schools in Scandinavia also have poor IAQ, but in the last few years it has been taken seriously here, and we see more and more investment in tackling the problem. VAV (variable air volume) solutions are used in almost all of these renovation projects,’ says Laursen.
‘Standards that prescribe six to eight l/s per person are not being met in schools, and that affects health and productivity.’ He believes ‘simplified’ VAV systems could hold the answers for the UK market too.
Rose, E. (2014) ‘Failing the IAQ test’, CIBSE Journal, April 2014, pp. 12-18