14.01.2025
FAQ: Decentralized AHU units
Answers to some of the questions that may arise when considering a wall-mounted AHU:
How does a wall-mounted AHU work?
A wall-mounted AHU is used for air exchange - the air in the room is exhausted outside and replaced by fresh outdoor air. This is achieved by using a fan integrated in the recuperator, which is able to reverse the direction of operation (exhausting air for a certain period of time, then switching to supply air). Wall-mounted recuperators are most often made with a single tube containing the elements - motor, fan, filter, heat exchanger - but variants are also available which, like centralised recuperators, have their own tube for air intake and exhaust (e.g. Mitsubishi Lossnay VL-100). The heat exchanger is designed for heat retention - unlike a bathroom extract fan, it at least partially maintains the room temperature (without heating the room in summer and without freezing it in winter). It should be noted that a heat exchanger does not provide heating by itself, nor can it prevent 100% of the temperature changes.
Is it possible to use the recuperator only for supply or extract air?
Yes - wall-mounted recuperators are also capable of only supplying or exhausting air. Depending on the type of controller, this is done by pressing a key on the remote control or by selecting one-way operation during installation. This functionality is particularly important if the wall-mounted recuperator is designed for a larger room (or a room with a larger number of occupants) where one is set to operate only for air intake and the other for exhaust, with a similar operating effect to a centralised air exchange system.
How efficient are wall-mounted AHU's?
Although a wall-mounted recuperator will not be as efficient as a centralised recuperator, if an appropriate recuperator is chosen for the room, it will still be able to exchange air efficiently and maintain an acceptable level of humidity and comfort in the room.
Can an wall-mounted recuperator be used as a bathroom fan?
No. In bathrooms we recommend installing an extractor fan with a valve that closes when the fan is not running. Using a AHU unit will ensure that the humidity level in the bathroom will be constantly high and that it will not be able to completely remove any odours from the bathroom.
What control options do recuperators have?
Wall-mounted recuperators offer a variety of control options depending on the manufacturer and model of the unit chosen, often offering simplified control options that would not be possible in a central recuperation system:
- Switch: the simplest option, a two- or three-button switch connected to the recuperator, which is no different in functionality from a normal light switch. For some recuperators, such as the Mitsubishi Lossnay, the switch is controlled by a cord embedded in the unit - similar to an older luminaire;
- Remote control: one of the most popular control solutions is by remote control, as it is not dependent on an internet connection or hard-wired electrical installations. This may differ from the recuperator, for example the remote for the Mitsubishi Lossnay VL50 mentioned above is simple, designed for easy speed changes, whereas the Aerauliqa Quantum Next remote control gives extended options, such as changing its direction of operation, setting the ECO mode, or setting its operation using an already integrated humidity sensor (see below);
- WiFi: more and more recuperators can be controlled remotely via an integrated WiFi sensor and a mobile app. This can also provide additional functionality to the recuperator (e.g. two Lotus recuperators can be set up as separate supply-exhaust units in the same room, a process that recuperators with simpler controls would have to perform during the set-up of the electrical installation);
- Humidity sensor: some of the recuperators incorporating a humidity sensor can be set to be controlled by the humidity sensor, by varying the operating speed of the recuperator depending on the humidity level in the room;
- About CO2 sensors: the control of a recuperator using an integrated CO2 sensor is often asked about. While this seems like a good idea in theory (the recuperator is able to operate based on the amount of air in the room), it should be noted that CO2 sensors have an average working life of ~1 year, after which they need to be replaced - a measure that is not financially viable for wall-mounted recuperators. For this reason, we only offer this solution on request.
How thick the wall must be for a wall-mounted AHU?
This depends on the type and model of the recuperator you choose. For example, Mitsubishi Lossnay series recuperators can be installed on thinner walls as the elements required for the operation of the unit are not located in the supply/exhaust duct, whereas Aerauliqa recuperators have a minimum wall thickness of ~300mm (for models with 150mm diameter). In case the wall is too thick, it is possible to purchase or design an extension to it.
Is it possible to install a wall-mounted recuperator by myself?
Yes! Installation of wall-mounted recuperators, unlike centralised systems, is relatively straightforward - you need to prepare a hole of the appropriate size (according to the product installation instructions, usually about ~10mm larger than the diameter of the pipe of the unit itself) and then insert (and insulate), attach and connect the recuperator to the nearest power supply, a process which will be detailed in the product instructions (click on this link to see the Aerauliqa Quantum Next installation instructions as an example). Unlike more complex appliances such as heat pumps, if you have installed the recuperator yourself according to the instructions, then its warranty will remain valid.
We hope that this small insight has brought some clarity to the operation, control and use of wall-mounted heat recovery units.
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