Fans for Heat Recovery Units

Balanced Airflow in Heat Recovery Systems with Constant Volume Fans

High-cost savings and better indoor air quality are just a few of the key advantages of energy efficient fan refurbishments in HVRs and also when designing new builds using controlled ventilation with heat recovery.

A ventilation system with heat recovery should always be operated in a balanced way. This is the only way to ensure long-term heat recovery efficiency of the ventilation unit, achieving energy savings compared with exhaust-only systems. Devices, such as industrial centrifugal fans with automatically balanced and pre-set volume flow rates can secure a balanced operation on a permanent basis, reducing the ventilation heat losses and preventing structural damage through condensation because of trapped humid indoor air penetrating the thermal building envelope. Older buildings have a much higher risk of structural damage than new constructions. With existing buildings, it can be difficult to achieve a consistently airtight building that is effective all over due to their original features such as wooden beams and ceilings. These weak points can be compensated with the use of a balanced design of constant flow ventilation using constant volume fans as part of the overall system.


K39-A7 For Heat Recovery

The first image shows how a simple mechanical ventilation with heat recovery system facilitates effective ventilation in a domestic unit.


Understanding the role of the Industrial Fan in MVHR Systems

The fan is the core of most air movement systems, it’s the work horse that moves air through duct work, filters and allows clean, warm, or fresh air to circulate effectively within the heat recovery process. Ventilation systems are built for both domestic and commercial properties so the fan speed can be set depending on the needs of each building. Learn more about the difference between basic and quality MVHR systems here.

A slow to medium fan speed may be adequate for a domestic property but may need to run faster for busier commercial properties. Large ventilation systems can be equipped with a constant volume system which determines the volume flow rate by means of a measurement of the effective pressure at the fans inlet. With this method, a high rate of accuracy can be achieved. Constant volume fans with energy efficient motors and integrated electronics and alarm signals, utilise the relationship between Speed (RPM) and the power consumption of the fans and the volume flow rate. Each building, whether new or existing, will be different, with the geometry and length of the duct work varying resulting in very different pressure losses on each installation. On forward curved centrifugal fans such as those from Ecofit, the air flow rate can be clearly determined from their performance curves only, based on the rotational frequency and the power consumption. By comparing the actual and set values and the corresponding re-adjustment by the fan control, the flow rate can be kept constant regardless of the changing pressure drop in the duct work. Double inlet forward curved fans will provide even higher air volumes and system performance, resulting in an even more cost effective and energy saving system.

This additional constant volume feature may not be a consideration to some in the marketplace who are price conscious, but with legislation and a demand for heat recovery products, as an aid to more energy efficient buildings, increasing continuously, the benefits outweigh the additional costs, and devices with built in systems should be used. These include the prevention of structural damage by minimising leakage, reduce ventilation heat losses lowering running costs; a constant flow system ensures long term heat recovery efficiency. Constant flow fans reduce maintenance costs by enabling the system to automatically adjust flow rates – therefore system readjustment is not needed regularly. During assembly of the heat recovery unit the fan can be present to deliver the specified air volume at that point.

The higher the heat recovery efficiency of the ventilation systems and the better air tightness of the building, the higher the savings will be. For more information on energy efficient constant volume fans see Axair Fans website.


Many systems feature two fans, one to take out stale air and one to bring in fresh air. The incoming and outgoing air stream runs over the heat exchanger allowing the outgoing air to pass thermal energy to the incoming air without the two air streams actually mixing together. This is shown in the second image, located above. 


EC Constant Volume Fans
  • The Axair GRE range of EC single inlet centrifugal fans, as shown in the third image, are designed with built in constant volume software enabling it to regulate its impeller speed to maintain its pre-set volume against variable pressure.
  • With constant volume software on board, the Axair fan can be pre-set during assembly of the MVHR to deliver the specified volume required on site. The install team then provide power and the MVHR will automatically provide the desired airflow.

K39-A7 Curve Heat Recovery

The same constant volume software is available for larger domestic applications using the GDS range of double inlet centrifugal fans, the RRE range of backward curved impellers or the GKHM range of energy efficient plug fans, enabling higher air volumes and system performance, resulting in a cost effective and energy saving device.
Replacing the Fan in a Mechanical Ventilation and Heat Recovery System

A poorly designed heat recovery system or one that has not been designed with the right fan components to achieve the duty, will be inefficient and result in poor ventilation. The fan in the system must supply the correct air volume enabling the system to provide the correct levels of ventilation throughout the building. Incorrect fan integration can also result in a noisy system. Fan replacement will be required where the airflow calculations are incorrect or there are signs of inefficient ventilation. Failure to repair an ineffective ventilation system can result in moist air and a build-up of mould which poses a health risk.


Request A Quote - EC Constant Volume Fans

Product CodeVoltage
Input Power
Speed Rotation
Request a Quote
2GRE15230730.32 2.0240201557
4RRE25 225x63R230500,231,5740140055
2RRE15 192x40R230620,282,0575251061
4RRE15 192x40R230330,151,5305139055

How Can Axair Fans Help?


We have a wealth of technical expertise and can assist with fan selection for a wide array of applications in the industrial and OEM market.

Contact us or visit our website for more information on how Axair can assist with Heat Recovery application, increase energy efficiency or any other project on 01782 349430

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