The Benefits Of Correct Ventilation Installation: Maximising Health And Comfort

Following the events of the pandemic, indoor air quality (IAQ) is now acknowledged as a key component of building design, with effective ventilation systems becoming crucial to reducing any negative health impacts. David Millward, Group Product Manager at Elta Group discusses the steps that can be taken during installation to ensure that ventilation units are working to their maximum capability.

In June 2022, Approved Document F of the Building Regulations, which covers ventilation, saw the volume of outdoor air required within an office updated. An occupiable room such as an office must receive at least one litre of outdoor air per second per m² of space, or 10 litres per second per person. This, paired with the increased risk of cold and flu spread during winter months, has highlighted the importance of achieving optimum ventilation performance to provide good indoor air quality (IAQ).

A survey of 2,000 hybrid working employees conducted by Onepoll[1] found that there is an increasing concern about how healthy the work environment is during the winter season. Fifty-three per cent of those asked 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 indoor air quality in their workplace.

Ensuring effective ventilation within a building should start at the installation of the fan. Two common fan types used in commercial buildings are axial, offering straight-through air flow, and centrifugal, named from the centrifugal nature where energy is imparted on the air and the airflow is radial in direction. There are multiple installation details to consider when fitting the two types of fans to create optimum performance to meet expected IAQ levels.

Creating optimum fan performance

• Do ensure evenly distributed air is entering the fan inlet

Uneven or excessive airflow entering a fan’s inlet can deteriorate its performance by up to 45%. While the main flow one side is accelerated, turbulence and high intensity pressure fluctuations occur on the other. These fluctuations can cause resistance which in turn reduce the ventilation performance of the fan.

When using an Axial Fan with a free air intake, uniform air intake can be created through the use of inlet cones. Without the use inlet cones, air enters the inlet abruptly which generates 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 reduce air pressure and prevent air spin. Additionally, such inlet boxes should be amply sized, as small inlet boxes will generate spinning air which can reduce fan performance by 25%.

• Do use assistive measures when bends are necessary within vents

Under the updated Approved Document Part F of the Building Regulations it is a recommendation to minimise the number of bends required within ductwork. However, there are situations in which bends and turns will need to be used but steps can be taken to reduce 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 satisfactorily.

When bends occur in the ductwork near Centrifugal Fans, it’s important to ensure that the bend ‘rotates’ in the same direction as the impeller.  The use of splitters within the bend can help prevent spinning in the air flow.

• Do look for pressure recovery at fan outlets

The fan system’s total pressure can be reduced by using a correctly designed discharge diffuser adjacent to an Axial or Centrifugal fan’s outlet, when used in a non-ducted outlet system,  at a 15 degree or less angle. This arrangement can also reduce discharge losses by up to 75% for both fans, increasing the IAQ level.

• Do not block fan inlets or outlets

You should allow a gap that is at least equal to one fan diameter between the fan’s intake and any near obstructions, however, it should be noted that even doing this can make the fan’s performance less than rated. When an inlet is obstructed, the impeller can be starved of air, which in turn increases the system’s resistance and reduces air flow being handled by the fan. This applies to all fan types. Additionally, you should always fit an inlet cone on open Axial Fan inlets.

When placing a fan, you should allow a gap of at least one fan diameter between fan outlet and any obstruction and fit a diffuser on the discharge. When the discharge is too close to a wall the obstruction can generate noise and increase discharge losses.

Ensuring correct insulation for efficient ventilation

In this period of heightened concern for improved IAQ, it is essential that all measures are taken to guarantee the highest level of efficiency in ventilation systems. To support installers in achieving good IAQ levels, we have collated a comprehensive ventilation dos and don’ts guide titled ‘Give a Fan a Chance’. Broken down into five sections, the guide details installation tips for Axial, Centrifugal and Roof Fans before delving into the topics of noise and vibration reduction.

To read the full Elta ‘Give a Fan a Chance’ guide click here.

[1] Poor indoor air quality is a threat to health, say people coming into the office – Workplace Insight