Internal leakage in air handling units

Internal air leakage in ventilation systems is wasteful and can also affect indoor air quality, so we must minimize leakage to maximize energy efficiency while also ensuring the best possible air quality.

Internal leakage occurs between the internal section dividing walls, while external leakage occurs between the inside and outside of the unit through the unit casing.

All types of air handling units have the potential to leak air past the filters, resulting in poor air quality and dirty ducting with higher cleaning costs.

There will be a high pressure on one side of the dividing wall where the fan is positioned and a low pressure on the other. Clearly, there is the possibility of air leakage from the fan exhaust to the intake. This leakage will result in increased energy consumption, fan speed, and noise levels.

There is a risk of air leakage past the heat exchanger where coils are inserted. There will be a heat or cooling power deficiency, but no actual energy loss. In the case of cooling coils, such leakage can result in condensation downstream.

Heat exchangers used for energy recovery can potentially cause leakage. Plate heat exchangers should have low leakage by themselves, but a poor installation in the air handling unit can result in significant leakage, resulting in energy losses and poor air quality. Plate heat exchangers with proper installation will have very little leakage.

Rotary heat exchangers provide the advantages of high efficiency, minimal footprint, and low defrosting requirements. However, because they rotate, it is more difficult to effectively seal them.

There are four types of leakage in rotary heat exchangers:

The first is leakage from the edges. Leakage around the rotor's periphery has a direct impact on the rotor's overall heating power. Because a large drop in temperature efficiency can occur, it is critical that the perimeter seal is functional.

The second type of leakage is from outside air to exhaust air. The pressure difference between the external air side of the rotor and the exhaust side is usually quite large. A leakage from the supply to the exhaust air side is caused by this pressure decrease. Leakage in that direction will have little effect on air quality, but it will increase energy usage.

When rotating heat exchangers carry extract air over to supply air, the third mode of internal leakage occurs. A purging sector can be used to effectively eliminate carryover leakage. Extract air is blocked from entering a small section of the rotor, and outdoor air is bled through the rotor in both directions to purge it of extract air. This purging function removes contaminants from the rotor and guarantees that the supply air is of excellent quality. A pressure differential, which must be established by the extract fan, is required to drive this purge flow. The purging flow must be added to the extract fan's flow rate.

On the room side of the rotor, the fourth mode of leakage is from extract to supply. This leakage is caused by a pressure difference between the extract and supply air, which can be eliminated by throttling the extract air so that the pressure difference is in the right direction if the fans are properly positioned. The exhaust fan must account for this additional pressure reduction.

To minimize leakage, the fans in the air handling unit must be in the proper position. The rotors must have a purging sector and a control system that can adjust the rotor speed to reduce rotor carry-over at low airflow rates, allowing for safe use of the highest possible energy recovery.

Trosten Industries located in Dubai, is one of the most reliable manufacturers of energy efficient centralized Air Conditioning and Kitchen Ventilation Equipment, having established a trusted name across the UAE when it comes to Double Skin Air Handling Units (AHU). Our air handling units are Eurovent certified and feature AMCA certified fans for superior performance as well as UL certified filters for higher dust holding capacity and lower pressure drop.

Trosten has the best and safest air handling units for all applications among the region's leading AHU unit manufacturers.