Restoring the Balance: Energy Saving vs Indoor Air Quality in Schools
David Millward, Group Product Manager at Elta Group, discusses how schools must re-assess energy saving priorities and introduce quality-designed mechanical ventilation systems into these crucial buildings.
Good indoor air quality is a key pillar not just for better learning, but also general wellbeing.
With the effects of the pandemic placing greater emphasis on ventilation, the high levels of CO2 across school building stock have become a prevalent concern. Yet, at the same time, saving energy remains a top priority in line with sustainability agendas. With these two matters in mind, schools have historically relied on natural ventilation methods such as opening windows to maintain low energy usage. However, this approach does not guarantee good quality air. Many schools are located in suburban or heavily urbanised areas where a high count of nitrogen dioxide is in the air, along with harmful particulates such as car brake pad dust, fumes, sulphur dioxide and other pollutants. As such, ventilation is one of the building services that should be high on the priority list.
Proper ventilation aims to create a comfortable living environment while minimising energy usage. A well-designed and well-maintained ventilation system can help regulate indoor temperatures, reduce the need for excessive heating or cooling, and ultimately lower energy bills. While conserving energy is important, this should not take precedence over peoples’ wellbeing; especially as the young are more vulnerable.
Furthermore, numerous scientific studies have highlighted that CO2 and harmful particulates directly hinder pupil’s learning and concentration. Coinciding with the introduction of the school rebuilding programme, now is the time for indoor air quality to be treated with greater importance through adequate ventilation.
The legislative landscape
While the Building Bulletin (BB101) is in place as a framework for ensuring effective ventilation, the changes to Building Regulations reflect growing concerns around management of indoor air quality. With updates to Part F, there is now a firmer guidance to adhere to. Namely that buildings must provide sufficient ventilation to keep CO2 levels below 800ppm (parts per million).
These regulatory measures highlight the need for measuring and controlling CO2 as part of ventilation strategy – placing further onus on schools to implement appropriate solutions.
Clearing the air
Alongside acknowledgement of regulatory guidance, there must also be an understanding of what good quality or ‘fresh’ air is. As outlined, good quality air isn’t simply air brought in from the outside. Many harmful compounds can be present that affect both health and concentration levels in pupils.
Evidenced by the rising popularity of air purifiers, another misconception is that continuous recirculation and purification constitutes fresh air. In actual fact, this air becomes stale, allowing for CO2 and VOC (volatile organic compound) levels to increase and subsequently be inhaled. While air purifiers do have their place in a ventilation system, they should not be treated as a comprehensive solution. Such applications will remove pollutants but have no impact on CO2 levels. As such, a good quality ventilation system is one that extracts all pollutants, brings air in from the outside and filtrates it before reaching the classroom.
To ensure adequate ventilation, CO2 should be considered as a proxy for air quality. The CO2 level rises as a result of building occupants exhaling, while increasing the ventilation rate reduces it. On this basis, measuring CO2 can allow for effective control of both air quality and energy usage.
Building ventilation systems often operate at constant or pre-determined ventilation rates regardless of the occupancy level of the building. Ventilation rates are normally based on maximum occupancy levels, resulting in consequent energy wastage. This is not only due to the fan operation, but also includes the energy used to condition the air for both heating and cooling modes.
Through MVHR (Mechanical Ventilation with Heat Recovery) solutions such as Elta Fans’ energy recovery units, the amount of airflow can instead be controlled to suit occupancy levels and delivered through demand-controlled ventilation (DCV). DCV is recognised as a reliable method of ensuring a building is ventilated cost effectively, while maximising indoor air quality.
Closed loop speed control for both EC and AC motor options provides major energy savings as the fan power is proportional to the speed cubed. CO2 or temperature sensors are used to continuously measure and monitor ambient conditions in the conditioned space and provide real time feed back to the zone controller. From here, fan speed is adjusted – modulating the ventilation rate to match the specific use and occupancy of the building. Significant energy savings are made by effective DCV, which ensures that the ventilation rate continuously matches the current occupancy rate and varying ambient conditions.
Efficient energy conversion and recovery
With all ventilation solutions, it’s important to consider the design properties of the ventilation system itself prior to making a decision. This is where small yet significant long term energy gains, and subsequently cost savings, can be made.
As an example, energy recovery units have a free running, backward curved impeller and special three-dimensional blade geometry that provides reduced rotational tone, which provides greater energy savings through higher performance. Attention should also be paid to how much thermal energy can be recuperated. With energy recovery units, the thermal energy exchange is enhanced by the large surface area of the heat exchanger resulting in as much as 92% of thermal energy being recovered.
When designing and specifying a mechanical ventilation system, it’s important to always consult with the manufacturers as quite often they can offer best practice and guidance to achieve the desired performance. For schools, there should be a particular focus on specifying high-quality filtration methods to restrict external pollutants. As an example; in line with requirements, all ventilation systems from Elta Fans come with ePM1 Filters that offer high filtration levels and follows the ISO 16890 Standard.
When specifying mechanical ventilation systems, it must be ensured that the fan has enough power output to overcome any pressure development drop due to the filtration solution. Layout and length of the ducting, as well as any other ancillaries involved in the design will also need to be considered.
Post-installation, any solution must also be well maintained and serviced to ensure they are operating efficiently. Here, consulting with a manufacturer can ensure the right maintenance schedule is created and followed.
The future learning environment
As the school rebuilding programme comes into effect, it’s clear that ventilation and air quality must not be left behind as an afterthought.
Schools must have a well- engineered system for ventilation (whether it is mechanical or hybrid) and receive the necessary support to realise such solutions. From designers to contractors, consultants to installers and beyond, the entire supply chain must consider how to deliver good indoor air quality and follow through to enable better learning environments for years to come.