TOP MARKS FOR AIR QUALITY - Nuaire reports on the latest ventilation needs in Britain's schools

Education policy, high profile government initiatives and increased media attention have forced the issue of good indoor air quality in schools to the foreground in recent years. Our awareness of the spaces occupied by children has never been greater as our concerns about air-born pollutants, CO2 levels, temperature and noise are focused on the classroom.

Whether an existing school is being refurbished or a brand new school is being built, the importance of creating a healthy and comfortable learning environment for pupils, teachers and staff cannot be underestimated.

However, compared to most other types of buildings, schools, universities and academies are extreme environments which service high and sporadic occupancy levels and house many competing activities and functions, from classrooms, halls and canteens to commercial kitchens, laboratories, offices and even accommodation.

The government Building Bulletin 101 guidelines provide building designers with a blueprint for ventilation in schools, issuing stringent requirements for the acceptable level of carbon dioxide, required air changes per second per person, and optimum temperatures, whilst also stipulating a reduction in carbon emissions and energy usage in the ventilation design for new schools and refurbished schools.  At the same time, research into the impacts of inadequate ventilation on pupil performance and learning outcomes has put pressure on school designers and local education authorities, shining an even brighter spotlight on the importance of ventilation.

In several studies, researchers at Exeter University (Coley and Greeves 2004) have revealed that many schools are still not meeting recommended ventilation rates. Using standardised, computerised tests of cognitive function, they demonstrated that the attention of school children was significantly slower when the level of CO2 in classrooms is high, with pupils likely to be less attentive and concentrate less well on what the teacher is saying, which over time can lead to lower learning achievements.

Research backs up the need to not only provide adequate ventilation in schools – for the UK a background fresh air supply rate of 3 litres per second per pupil with the capacity to supply 8 litres per second per pupil when required – but to ensure that CO2 levels should never exceed 1000ppm, however long a space is occupied.  

There are several ventilation strategies that could be employed to meet these requirements, but as with all public funded building initiatives, external forces are at play. With the UK population predicted to rise by 4.9 million to 67.2 million by 2020, a chief concern for those who design and maintain schools is how their buildings and facilities will cope with extra capacity against a backdrop of increasing budget cuts and ever stricter environmental targets.  Schools are being asked to serve more for much less.

The situation is exacerbated when the current economic climate drives costs savings at such a rate that contractors are looking for any way possible to trim build costs and claw back profits on tight bids to keep their margins.  Even today schools, classrooms and buildings are often redesigned after initial planning forcing contractors and consultants to meet the specification as effectively as they can.

This autumn, the government announced news of £2.5bn of contracts on new school buildings with plans to replace 261 primary and secondary schools it has deemed to be in the worst condition as part of a five-year programme.  The bad news for architects and designers is that these new schools will be 15% smaller than those built under the previous government, in a bid to cut costs by 30% and save up to £6m per school compared to schools built under the Building Schools for the Future project.  

The size of classrooms, staffrooms, sports and art facilities are expected to be maintained, and the need for simple maintenance and energy-efficiency will be essential.  This no-frills approach will put strain on the available space for ventilation and ductwork, and may encourage some schools to take shortcuts in their ventilation strategies in order to save on installation, running costs and space.

Advances in technology

So with the need to do more for less, how do we actually achieve it? For ventilation there are many strategies that can be employed in schools from natural ventilation through to localised control and heat recovery.  A crucial issue is to ensure that the final building design is achieved with no gap between concept and realisation.  All too often people forget that the IT room requires additional cooling; the chemistry labs require certain fume extract and that many rooms won’t have openable windows.

The move towards 'Heat Recovery'

Every person in a classroom can be expected to give off 0.1kw of total heat while inactive, rising to 0.4kw with athletic activity.  A typical classroom will have heat output from lighting, projectors, computers, and central heating.  Combined with their high capacity and mixed functions, schools are well-suited to heat recovery ventilation where the additional heat from facilities and bodies is utilised to temper the incoming fresh air

Another consideration is that an average school child can lose up to 2 pints of sweat per day, with ½ pint of this moisture present in the air. This, plus other contaminants must be removed to maintain good indoor air quality. Heat recovery ventilation will dissipate the heat from the building’s occupants and will balance the heat loads with heat losses. More importantly, it is designed to provide the fresh air required for good indoor air quality. In the summer, the use of night time purge facilities can offset the need for mechanical cooling.  Similarly, energy savings can be found in the winter months when the heat recovery system will turn the fans on in the early hours of the morning, before the pupils and teachers arrive, starting the warming process.  Where typical supply and extract systems are now under regulation to have lower specific fan powers with a drive towards a true reduction in energy costs, there needs to be consideration for how the heating is designed and making sure this heat is not wasted.

Many companies have designed heat recovery ventilation for UK schools during the BSF programmes.  It quickly became clear that as much as designers and builders were looking to standardise products and solutions, each school presents a difference in shape, size, load requirements and, more importantly, budget, so often a standardised design is a goal rather than a reality.

Nuaire developed the XB55 heat recovery system as a solution to this common problem.  The system   is specifically designed for a 30 seater classroom, which has been the most common format seen during the BSF developments.  It features a mixing box which, rather than taking the cold air from outside which would take more energy to heat, utilises the warmer air already inside the building which it  filters, recirculates and warms using a heating coil.  As soon as the CO2 levels rise, the mixing box shuts off and fresh air from outside is brought in. Offered as a standardised build, this is an ideal solution for repeat format designs.

A properly designed heat recovery system will benefit pupils and teachers by creating the optimum working environment. When it comes to reducing energy and saving money, however, the real technology lies in the use of intelligent controls.  Effective controls and control systems are key to obtaining the lowest levels of energy use in a ventilation system. 

A move towards Demand Control

Schools may have a building management system, such as TrendTM controlled via BACnetTM, and may integrate all elements of the design. In these cases manufacturers not only need to provide ventilation products but also BMS compatible solutions.  Nuaire saw the trend in these control systems many years ago and have offered Ecosmart TM controls as standard.

Ecosmart controls embody the concept of energy saving, intelligent, fully integrated fan controls, managed by a range of easily selectable enabling sensors, controlling sensors and signalling devices.  It offers a flexible Demand Controlled ventilation control system, with full BMS interface.

Nuaire also offer TRENDTM and BACnetTM compatible solutions for fans, heat recovery units and AHUs and as schools designers and builders continue to consider both initial build costs and whole life and running costs, manufacturers need to be able to offer more.  Another key consideration that cannot be overlooked when considering ventilation in schools is that of noise.  With strict criteria for noise in schools outlined in BB93 each manufacturer needs to ensure that the system will meet noise criteria. Often manufacturers provide noise data for fans and heat recovery units while silencers and ducting are purchased from other suppliers.  It is vital that the noise requirements are met and that component choices are compatible, installation is correctly carried out and detailed commissioning is undertaken to prove that the design works as a system.

Acoustic guidelines for ventilation have been tightened up in recent years to reflect the general recognition that poor acoustic conditions in the classroom are detrimental to learning and teaching.  It’s a common misconception that natural ventilation is always a self-contained low-noise solution, but in reality many natural ventilation systems require at least partial assistance from mechanical ventilation, and are particularly vulnerable to external noise sources.

As a manufacturer, Nuaire have addressed this issue by providing matched, close coupled inline attenuation and have optimised the acoustic treatment of the equipment enclosures so noise levels can be guaranteed to meet consultant and customer specifications. 

What is clear is that with many options for ventilation strategies, the emphasis is not only on compliance with air change, co2 levels and temperature control, but now also on noise, ease of control and running costs.  Building or refurbishing a school is a long-term commitment so the emphasis in the future has to be on the client understanding the true running costs of the ventilation systems installed rather than the initial build and installation costs. On-demand ventilation offers far greater financial savings in the long-term, critical for shrinking school budgets.  Choosing a bespoke ventilation solution with controls is a sound financial investment for the future of energy-efficient and sustainable schools rather than settling for cheaper up-front alternatives.

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