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Indoor air quality has been in the news a lot lately so ventilation specialist, Janvi Patel looks at the key aspects of air handling units that need to be taken into account.

Over the past few months, the news has been full of reports on the damage that pollution and particulates can cause to health, with a recent item on the BBC reporting that school pollution levels in London could be breaking World Health Organisation guidelines – This is INSIDE the classroom, where our children should expect to be protected.

Within the construction industry, another related issue that has received widespread publicity is the introduction of the WELL standard, which looks the well-being of staff inside a building, with a major focus on comfort and air quality.

We know that there are several different ways to heat, cool and ventilate a building, whether that is with a Variable Refrigerant Flow (VRF) air conditioning system, a more traditional chiller and heater combination, or a ventilation system with inbuilt heat recovery and I’m going to focus predominantly on the Air Handling Unit (AHU) sector, which has been a fast growing part of the UK market over recent years.

So, what are the key things to look out for when choosing an AHU?

Janvi Patel Janvi Patel Ventilation expert at Mitsubishi Electric

Key focuses

There are several types of units available and numerous manufacturers selling them, so what are the key things to look out for when choosing an AHU?

In its most basic form, an AHU brings in outside air, conditions it and then supplies it as fresh air to a building, through a series of connected ductwork and ceiling grilles.

All the stale, indoor air is removed and depending on the required temperature of the conditioned incoming air, it is either heated or cooled using water, refrigerant or direct electric heaters.

Adding a heat recovery element gives the added bonus of helping to heat or cool the incoming fresh air.

The units are available in all shapes and sizes for almost any building and can provide a much more cost effective ventilation system than many other building services. 

They can also work in conjunction with VRF air conditioning or Chillers to provide a comfortable, energy efficient environment within the building.

However, the size, filtration, power requirements and efficiency of the unit can make a significant difference to both comfort levels and running costs.


Legislation such as Minimum Energy Efficiency Standards (MEES) is placing increasing demands on the efficiency of commercial buildings, so the equipment used to heat, cool and ventilate these buildings needs to ensure it is minimising energy consumption.

The best AHUs include heat recovery elements which capture heat energy thus heating the incoming air to help reduce the amount of energy needed to bring the new, fresh air up to the required set point temperature.


In the past, we would simply open a window to bring in fresh air but this is no longer an option for three main reasons: Firstly, bringing in unfiltered outdoor air can also bring in pollutants from outside, secondly; this also allows any noise from outside to enter the space, and thirdly, any energy used to heat or cool the indoor air is simply ‘thrown’ out and more energy needs to be spent bringing the outdoor air up to the required temperature.

Because AHUs filter the air and circulate it around a building using ductwork, it can keep the indoors comfortable without letting in the noise from the outside, and with the ability to recover heat energy, AHUs can seriously reduce energy wastage and help lower emissions levels.

In addition to this, a lot of modern buildings no longer have windows that can be opened so finding other, efficient ways of bringing in fresh air is now an essential requirement.

Coupled with this is the increasing congestion of our inner city areas, which makes choosing an AHU with low noise levels even more important so that the outdoor unit is not causing its own noise pollution and annoying the neighbours.


In the same way as noise pollution, the best AHUs will include a filtration system which can block out nasty particulates, pollution, dirt, smells and other undesirable outdoor elements, whilst keeping the indoor areas fresh and comfortable. 

In particularly dry areas of the world, humidifiers can also be added to the AHU if necessary to avoid dryness and any build-up of static, although this is not often an issue here in the UK.


In today’s congested urban centres, plant space is at a premium, so any AHU must be sized to ‘do the job’, in the smallest box available. 

This places an increased performance on the specification right at the start of a project and the best systems will include full support from the manufacturer to ensure that the smallest and most flexible system can be achieved.

Ease of maintenance

Any system will be expected to work effectively for years to come and this will also demand regular maintenance so ease of access to all of the elements of an AHU are essential.

Balancing all of the choices available relating to performance, available space, efficiency levels and ease of maintenance, will enable any designer to come up with the ideal solution for any building, large or small.

A wizard of an idea

And this is where we believe our new Wizard AHU's can really help to make a difference

We have taken all of the best bits from the Climaventa brand we purchased last year, such as the highly efficient thermal wheel heat recovery technology, and incorporated our most popular Mr Slim Power Inverter heat pump technology, packaged with an integrated controls system to deliver highly advanced, flexible and efficient units that are suitable for almost any building.

All of the customisable units are Ecodesign 2018 compliant and offer air volumes from 0.56 m3/s to 5.56 m3/s, with heat recovery efficiency compliant to and in most cases exceeding Ecodesign 2018 requirements.

Presented as a ready-to-use unit, with all the control, regulation, and safety components already installed inside the unit and tested in production, we believe these new AHU will quickly stand out for their cutting-edge technical and construction features and the attention to detail of the base unit and each individual accessory.

Janvi Patel is ventilation specialist at Mitsubishi Electric