Modern Building Services

26 MODERN BUILDING SERVICES FEBRUARY 2023 FEATURE INSTALLER’S VIEW L ast year saw one of the biggest updates to the Building Regulations in years. Namely, that was the change to the volume of outdoor air required within an office in Approved Document Part F, which covers ventilation. Now an occupiable room such as an office must receive at least one litre of outdoor air per second per m 2 of space, or 10 litres per second per person. This, combined with the increased risk of cold, flu and other airborne diseases that are spread during winter months, has underlined the significance of attaining optimum ventilation performance to provide good indoor air quality (IAQ). It’s not just legislation though that is driving change – people are taking more notice of the air that they breathe. 2,000 hybrid working employees were surveyed by Onepoll 1 , and the research found that there is an increasing concern about how healthy the work environment is during the winter season. Over half of those asked (53 percent) said that they were worried that poor ventilation and air quality will impact their general health. A further one in five were concerned about catching diseases such as COVID due to poor IAQ in their workplace. To alleviate these woes and ensure compliance, building services engineers need to ensure a building’s ventilation system is as effective as it can be, starting with the fan’s installation. Two common fan types used in commercial buildings are axial, offering straight-through airflow, and centrifugal, named from the centrifugal nature where energy is imparted on the air and the airflow is radial in direction. There are several details to consider when fitting the two types of fans to create optimum performance to meet expected IAQ levels. Four ‘Dos’ to creating optimised ventilation systems 1. Ensure evenly distributed air is entering the fan inlet (See Figure 1) A fan’s performance can be undermined by uneven or excessive airflow entering the unit’s inlet, and this performance loss can be by as much as 45 percent. While the main flow on one side is accelerated, turbulence and high intensity pressure fluctuations occur on the other. These fluctuations can cause resistance which then lessens the ventilation performance of the fan. When using an axial fan with a free air intake, uniform air intake can be created using inlet cones. Without the use of inlet cones, air enters the inlet abruptly, generating turbulence at the impeller. It can also cause the blade tips to be starved of air reducing pressure development capability and causing the fan to stall. For centrifugal fans, uniform air entering the inlet is equally as important and can be achieved using splitters and turning vanes on the approach to the inlet box to decrease air pressure and prevent air spin. Additionally, such inlet boxes should be adequately sized, as small inlet boxes will generate spinning air which can reduce fan performance by 25 percent. 2. Use assistive measures when bends are necessary within vents (See Figure 2) Under the updated Approved Document Part F of the Building Regulations it is a recommendation to minimise the number of bends required within ductwork. Understandably though, there are situations in which bends and turns will need to be incorporated. Here, steps can be taken to lower their impact on the functionality of the ventilation system. For example, when using axial fans, it’s important to use turning vanes in sharp elbow vanes when adjacent to the fan itself. These assist with the creation of uniform airflow if they aren’t used, and eccentric flow of air will cause part of the impeller to be starved of air and thus the fan will not operate well. In recent years events have shown just how important indoor air quality (IAQ) is to a building’s design. With effective ventilation systems crucial to maximising peoples’ wellbeing and preventing ill health, David Millward , Group Product Manager at Elta Group looks at ways to ensure these systems are working to their highest capability. A guide to maximising the performance of ventilation systems