Using High Induction Diffusers to Improve Air Quality

USING HIGH INDUCTION DIFFUSERS TO IMPROVE AIR QUALITY

In ceiling-type air distribution systems operating in heating mode, improving ventilation performance is often challenging. The primary reason for this is that warm supply air struggles to spread downwards due to its positive buoyancy. Furthermore, heating in mixed air distribution systems is typically designed to operate with lower airflows and supply air temperatures approximately 10°C higher than the ambient temperature, compared to cooling. This situation often leads to undesirable thermal stratification and inadequate air distribution, especially during winter months.

According to ASHRAE Standard 62.1, the efficiency of a ventilation system is measured by how effectively clean air is delivered to the occupied zone. From this perspective, systems with low air distribution effectiveness reduce comfort and lead to energy inefficiency.

While many solutions exist for these problems, the use of high induction swirl diffusers stands out due to their easy integration with existing systems and cost-effectiveness.

High induction diffusers introduce air into the space with a swirling motion parallel to the ceiling. Thanks to this circulation, the throw distance is shorter compared to traditional diffusers, while more room air is induced in the region near the ceiling. This results in more homogeneous air mixing in the living area, reduced thermal stratification, and increased air distribution effectiveness.

The field performance of these diffusers was tested by the Predict engineering team of Price Industries, whose representation we hold, in a new elementary school project built in Quebec. The team conducted a detailed computational fluid dynamics (CFD) analysis for a typical 567 square meter classroom in the school to evaluate the performance of the air distribution system in heating mode.

In the initial design (Figure 1), in addition to low-induction slot diffusers placed in front of the windows, two swirl diffusers were positioned in the center of the classroom. This arrangement aimed to achieve a more homogeneous temperature distribution indoors and more effective fresh air delivery to the occupied zone.

Figure 1. CFD model of the initial design

CFD results for the initial design showed high thermal stratification in the room (as shown in Figure 2) and low air distribution effectiveness in the occupied (breathing) zone.

Figure 2. Temperature profile of the initial design with superimposed velocity vectors

Looking at the air patterns in Figure 3, we can see that although the system creates air movement towards the occupied zone, it is not sufficient to adequately mix the warm supply air into the occupied zone.

Figure 3. Velocity profile of the initial design with superimposed velocity vectors

In the team's final design, the slot diffusers were removed from the system, and the entire airflow was distributed into the space through repositioned swirl diffusers to optimize air mixing.

As a result of this optimized placement, a more homogeneous temperature distribution within the classroom (Figure 4), significantly reduced thermal stratification, and a meaningfully increased regional air distribution effectiveness were achieved. This led to a noticeable improvement in user comfort.

Figure 4. Temperature profile of the optimized design with superimposed velocity vectors

If we compare Figure 5 with Figure 3, we can understand why this is the case. In the optimized design, the placement of diffusers, along with extra airflow, creates more air movement and allows the supply air to penetrate deeper into the occupied zone.

Figure 5. Velocity profile of the optimized design with superimposed velocity vectors

This study demonstrates not only the effectiveness of swirl diffusers in heating regimes but also:

• The positive/negative effects of designing diffusers within the correct flow rate ranges on air distribution,
• The advantages of using high induction equipment, whether slot diffusers or any other type of diffuser,
• How beneficial CFD analyses are in completely simulating differently designed systems to select the most effective air distribution system.

As STEKON, we determine the most suitable diffuser system for your scenario from hundreds of different diffuser systems we supply and produce for air distribution solutions, and we price them accordingly.

Source: Price Industries