Modern Building Services

MODERN BUILDING SERVICES JUNE 2021 19 FEATURE VERTICAL FOCUS SCHOOLS AND HOSPITALS The resulting air management system for the Quadram Institute ensures that supply and extraction of air is optimised automatically in each laboratory to maintain safe working environments. Specific room pressure control capabilities are installed for the Containment Level 3 labs, and volume offset tracking controls for the Containment Level 2 spaces. The air management requirements for the Containment Level 3 suite were particularly challenging. For this critical zone, the air management system controls a pressure cascade, within which laboratories are controlled at larger negative pressures than the adjacent circulation spaces serving them, to ensure there can be no reversal of airflow under normal operational conditions. The suite also has an automated ventilation sequence that allows ventilation shut down, fumigation and purge of labs in a number of combinations to allowmaximum flexibility. This automated ventilation sequence works by switching the air management system between different flow rate set points and pressure set points to achieve the desired ventilation strategy. Tackling energy costs In addition to the needs for safety and flexibility, NHS Trusts must accommodate the demands placed on hospital laboratories against a backdrop of spiralling energy costs. The energy consumption of laboratories is often more than three or four times that of offices on a square metre basis. This can mean that laboratory buildings are responsible for between 50% and 80% of the total energy-related (non-residential) carbon emissions of research-intensive universities. Government research facilities, hospitals and private sector laboratories are similarly affected. The higher energy costs and carbon emissions of laboratories are typically associated with the air supply and extraction requirements of fume cupboards. When sashes of fume cupboards are open, the volumes of air required to maintain a safe working environment for laboratory personnel increase significantly. For example, a 900mm wide cupboard with a maximum sash height of 500mm and face velocity of 0.5 m/s would extract approximately 225 l/s of conditioned air from the room. By contrast, the minimum air volume for a variable air volume fume cupboard would only be around 55 l/s when the sash is closed, saving 170 l/s of conditioned air, whenever the sash is in the down position. Best practice is to install a room air management system to fully integrate fume cupboard air supply and extraction with the wider air management systems to prevent wastage. The roomair management systemmakes it possible for all input and extract air for the laboratory to be controlled automatically to ensure that the required ventilation strategy and levels of safety are maintained. With this design approach, the supply and extraction of the fume cupboards (or other technical air management devices) is automatically balanced and offset in line with changing requirements, reducing the total supply and extract volumes. For example, if the fume cupboards are open and extracting air, there is not the same requirement for the room system to carry out this process. By scaling down room exhaust air extraction in line with fume cupboard extraction, the room air management system is able to prevent over-supply and extraction of conditioned air from the space, improving energy efficiency significantly. See Figures 1 and 2. If hospital budgets do not currently permit the installation of a room air management system, there may still be energy reduction measures that you can retrofit to reduce consumption and cost in the short or medium term. Firstly, you could assess whether energy efficiency of the fume cupboards can be enhanced by retrofitting new control technology into the existing cabinets. Secondly, it could be possible to introduce devices to close the sashes of fume cupboards automatically when they are not in use. Automatic systems, based on presence detection, can prevent unnecessary wastage of conditioned air. Thirdly, it might be beneficial to install local cooling or extraction devices such as ventilated down flow tables, canopy hoods or fume exhaust ‘snorkels’. These are capable of reducing loading on the central air conditioning facilities for the site by taking heat away at source. As hospitals continue to perform their vital roles, effective air management of laboratory spaces can be an important factor in addressing the challenges they face. More information can be found at www.troxuk.co.uk