SPONSOR CPD PROGRAMME Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on the final page. Each successfully completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd Demand-controlled ventilation for comfort, wellbeing and resource efficiency This module looks at demand-controlled ventilation and the technologys potential application in providing energy-efficient solutions Demand-controlled ventilation (DCV) is a strategy that is able to reduce building energy consumption while delivering good levels of occupant comfort. Most buildings regularly operate at occupancies below the design maximum, and can benefit from the ventilation being controlled to supply reduced flows that satisfy heating and cooling loads as well as meeting outdoor air requirements. This CPD will reflect on the state of current DCV systems and illustrate the potential application of the technology to a case study multi-use building. The principles and controls that evolved to provide variable air volume (VAV) systems have been developed and refined to produce the modern DCV systems that not only control temperature (and humidity) but also optimise the supply air volumes particularly outdoor air so that appropriate levels of environmental quality ensure wellbeing while minimising energy costs. The resulting installations can provide significant energy savings (compared with constant air volume [CAV] systems) because of reduced fan power and reductions in heating and cooling of the ventilation air. Digital control, and increasingly wirelessly connected components, use distributed sensors and motorised air volume control dampers with linked optimising controllers to provide environments that account for the presence of occupants as well as meeting the individual zonal comfort requirements. Many applications, including offices or schools, are almost never fully occupied, and it is unlikely that the peak design occupancy occurs simultaneously in those occupied rooms. Studies1 have shown that, in cellular offices, typically fewer than 50%-65% of rooms in an office block are occupied concurrently and the normal peak may only reach 75%-84% of all offices. With a CAV system the airflow rate is kept constant, while with a DCV system it is modulated to meet the actual demand. The energy saving potential of a DCV system will depend on: The variation in, and periods of, occupancy and use of the rooms The minimum flowrate required and its relation to the design airflow rate of the system. This will depend, for example, on the number of rooms, the base ventilation rate in these rooms and the minimum airflow rate (the turndown) possible with the airflow control devices The chosen indicator for indoor air quality control. For example, if airflow rates are controlled by simple occupation (or building use) sensors, then the airflow rate in the room is likely to vary in just two steps: minimum and maximum, resulting Figure 1: Engelsons retail store, offices, warehouse and dispatch area, Falkenberg, Sweden (Source: Engelsons, www.engelsons.se) www.cibsejournal.com June 2019 31 CIBSE Jun19 pp31-34 CPD 148 Supp v2.indd 31 24/05/2019 14:54