How to achieve excellent Indoor Air Quality (IAQ) on Refurbishment Projects

Many refurbishment projects include a requirement to improve Indoor Air Quality (IAQ) to ensure compliance with Part F (Ventilation) of the Building Regulations. Yet the need to provide healthy IAQ in existing buildings – especially those with improved ‘airtightness’ – can present awkward challenges for building services engineers.

Direct, heat recovery air handling units can provide the answer.

The engineering challenge


When it’s no longer possible to open the windows, and there are limits to adding load to an existing central ventilation system, how do you meet the requirements of Part F of the Building Regulations?

How is this achieved while also maintaining compliance with Part L (Conservation of Fuel & Power)?

At the same time, how do you address the specific requirements for low noise in areas such as teaching areas and offices?

The engineering solution


One solution now gaining acceptance is based on localised, zone-specific mechanical ventilation with heat recovery. Not only does this approach deliver fresh air with low noise operation and recover heat from exhaust air, it also dampens the ingress of external noise.

AirMaster AHUs can deal with windowless ‘landlocked’ rooms within a natural ventilation cluster, or serve rooms not connected to an existing centralised system. They can also bolster IAQ in areas where existing ventilation should be doing betnd ventilate rooms adjacent to roads, where windows must remain shut.
By helping to improve indoor air quality, direct ventilation units ensure that room occupants remain alert, more productive and can maintain good concentration through the working day.

Restoring control of IAQ

Poor indoor IAQ in existing buildings has a significant impact on the comfort, wellbeing and productivity of occupants. Elevated CO2 levels create a stuffy environment but may also cause drowsiness and lack of concentration. Poor temperature control is often another important issue.

Refurbishment projects that improve a building’s air tightness also limit the ingress of fresh air through ‘natural leakage’, posing a threat to good IAQ unless additional ventilation measures are introduced.


However, in existing buildings such remedial action to improve IAQ is rarely straightforward. Conventional methods may entail haphazard control of CO2 levels, draughts, noise ingress and a window-opening strategy governed by temperature rather than CO2 level. On the other hand, extensions to centralised ductwork can be expensive and may easily run up against capacity constraints.

The alternative

Solutions based on AirMaster direct, zone-specific, heat recovery air handling units (AHUs) overcome such issues. They are installed within each space to be ventilated; mounted at high wall or floor level and connected directly to the outside through an external wall or roof so there is no requirement for supply or extra ductwork.

How can AirMaster ventilation contribute to refurbishment / upgrade projects?

  • Choice of attachment enables easy retrofits
  • No distribution or return ductwork required
  • Demand control of CO2 level or humidity
  • High efficiency heat recovery
  • Free cooling to help with temperature control
  • Quiet operation, with attenuation of external noise
  • Range of sizes, for individual offices to seminar rooms

AirMaster Ventilation – The benefits:

1. Ease of Installation. With no requirements for distribution or return ductwork, AirMaster MVHR units can be installed with minimal fuss.


Typical installation time = 3 ½ hours.newsletter44-pic4

2. Demand Controlled Ventilation. Fan speed can be linked to CO2 levels for classrooms and offices. This means that IAQ can be maintained at the required level (eg, 1,000 ppm), regardless of changes in occupancy. Reduced occupancy produces lower fan speeds, thus helping to save energy.


3. Low Noise. The last thing the users of a retrofit project want to have is an increase in noise. Noise levels from AirMaster units are just 35dB(A) @ 1m at full throughput, falling to 30dB(A) at 80% throughput, making them ideal for noise-sensitive applications. Noise from outside is strongly attenuated.

newsletter44-pic54. Energy Efficiency. Counter-flow heat exchangers recover 92% (84% on dry bulb) of the energy contained in extracted air. Once a room is up to temperature in the mornings, radiators can be shut down for the rest of the day – AirMasters have the technology to look after temperature control.


5. Free Cooling. An automatic bypass enables external air to be brought in clear of the heat exchanger, thus producing a ‘free cooling’ effect (assuming that external temperature is low enough).

6. During night cooling, Printthe bypass is set to 100% open, so that unit fans deliver external air at the lowest daily ambient temperature. This helps to deal with overheating risk.

7. IAQ Protection. Efficient M5 class filtration keeps pollutants at bay. Not only does this safeguard IAQ, it also ensures that the heat exchanger surfaces stay clean.



8. Long life.

newsletter44-pic7Aluminium heat exchangers are resistant to condensate attack and can easily achieve a 15-year lifespan. Robust M5 filters are an essential part of protection against fouling.

Optimum application

SAV provide a design support service, to ensure that AirMaster units deliver maximum performance, cost and energy benefits over at least a 15 year life span. Our objective is that every AirMaster installation should reflect well on the specifying consultancy. For those designers coming to AirMasters for the first time, SAV offer a 1-hour CPD seminar at the premises of your choice.

For further information, please call 01483 771910 or e-mail at


Recessed AML 500 unit in meeting room with PIR controller in top corner


Refurbishment of council offices in progress, using AML 500 units


Test rig at Airmaster R & D centre, noise testing underway


AMP 900 MVHR unit, mixing type