Ventilation for people, not spaces
Ventilate when you need to — Nygel Humphrey.
Part of the Building Schools for the Future programme is the provision of adequate ventilation. Nygel Humphrey discusses how ventilation can be provided effectively and efficiently in schools - and other buildings.Through its Building Schools for the Future (BSF) initiative, the Government has earmarked over £2 billion for local authorities and schools to spend on maintaining and improving all secondary school buildings in England. Under the scheme, every child will be educated in a 21st century environment within the next 10 to 15 years.
Already, 38 BSF schools have opened, with over a thousand secondary schools engaged in the programme, between design and delivery. This investment programme is underpinned by Building Bulletin 101 which provides the regulatory framework in support of the Building Regulations for the adequate provision of ventilation in schools. It deals with the design of school buildings to meet the ventilation requirements of both The School Premises Regulations and the Building Regulations Part F (Ventilation).
With this focus on improvement and renovation to create a healthy learning environment, the local partnership teams created to manage and deliver the BSF programme have a responsibility to identify and prevent indoor air quality problems, and improve it where they can by removing moisture, CO2 and external fumes. In fact, Building Bulletin 101 specifies limiting CO2 levels within teaching and learning spaces to 1500 parts per million. However, fresh-air supply rates per person in schools are often so low that CO2 levels are well above this recommended level, leading to adverse health effects and also impacting on the learning performance of pupils. In a recent Government study which involved research across eight English schools, more than half of the ventilation rates measured came below the minimum recommended levels.
Poor indoor air quality puts pupils and staff at an increased risk from health problems, such as fatigue, nausea and asthma. In a study carried out by the San Francisco Health Department, two pilot schools saw a 50% drop in student use of asthma inhalers following improvements to indoor air quality. This is especially significant when asthma-related illness is one of the most common causes of school absences in the UK.
During a European study in the late 1990s, 800 students completed health-symptom questionnaires, while a computer-based programme scored their ability to concentrate and at the same time measured CO2 levels in the classrooms. The study found that high CO2 levels were strongly related to student health symptoms and performance. This research is further supported by the Technical University of Denmark, which in 2005 found that improving classroom ventilation in a Danish school led to a substantial improvement in the performance of school work by children.
Increasing fresh-air ventilation to prescribed levels is the solution. However, with the Energy Performance in Buildings Directive (EPBD) in mind, partnership teams must be sure that they opt for the most energy-efficient solution possible. Here the answer is, unequivocally, on-demand ventilation. The latest on-demand energy-recovery ventilation systems, such as our Sentinel Totus D-ERV can recover 90% of the energy that would otherwise be wasted.
In comparison, many fixed-volume ventilation systems provide coarse and rudimentary system control at best. The system is either on or off, with fan speed set at minimum, medium or maximum. The result is that rooms are often over ventilated, or ventilated when empty or occupied by just one or two people, wasting energy and money. Under-ventilation is also a probability, creating an inefficient and unproductive working environment.
On-demand systems respond to the exact ventilation requirements of a room at any one time providing the right level of supply and extract airflow only when required. Energy-recovery systems recover energy from the extracted air (both heating in winter and cooling in the summer) and transfer it into the fresh supply air via an integral heat exchanger.
Sensors, such as CO2, PIR occupancy detection, humidity or temperature, determine the occupancy of the rooms and manage ventilation rates accordingly. They communicate with the main unit which, in turn, drives the fan to the required speed to deliver the airflow and respond precisely to room conditions. Sensors can be combined to generate a hierarchy of control for the ventilation system to link to a building-management system for full control and monitoring, if required.
This type of system also offers further energy-saving potential. Automatic air-conditioning and heating interlocks enable the system to optimise energy-recovery performance and provide free cooling during summer through bypass optimisation. A night-time purge facility reduces start-up loads for any air-conditioning plant and helps reduce over-heating in summer if there is no air conditioning.
In short, on-demand ventilation incorporating energy recovery avoids ventilating rooms that are not in use or over-ventilating rooms with only one or two occupants — overcoming many of the issues encountered with a traditional fixed-volume ventilation system. Required airflow rates can be comfortably achieved in classrooms, lecture theatres or open-plan areas, bringing added value in terms of quantifiable air quality, health and productivity benefits.
On-demand ventilation using heat recovery meets the requirements of Building Regulations Part L2A and L2B, achieving a specific fan power at 25% of design flow rate, no greater than that achieved at 100% design flow rate. It will also help ensure that education buildings meet EU demands to the 20% cut in energy consumption by 2010 targeted by the EPBD.
With regulatory pressures signalling a big shift towards energy-efficient, well-ventilated schools, on-demand energy-recovery systems can improve air quality, keeping CO2 levels within prescribed regulatory limits and help to create a productive and energy-efficient academic environment.
Nygel Humphrey is product manager — industrial with Vent-Axia.