In a way, modern lifestyle forces us to spend a lot of time indoors. Office work, access to an increasing number of electronic devices and, consequently, a change in the model of leisure, are just some of the factors that contribute to this. Probably not everyone is aware of this, but currently, the average person spends up to 90% of their life indoors! This figure is imposing, and best illustrates how important it is to provide comfortable and healthy working and living conditions. The system, which has now become almost a necessity in modern construction, is recuperation, that is mechanical ventilation with heat recovery. We describe its operation and answer the question of why it is so important.

Traditional gravitational ventilation and recuperation

To realise all the advantages of recuperation, it is first necessary to learn about the principles of traditional gravity ventilation. Its operation is determined by the pressure difference between the air inside buildings and the air outside. In simple terms, it can also be said that the greater the temperature difference, the more intensive the gravity ventilation works (at the equalised temperature it is inefficient, while at the enormous difference it exceeds the needs). What is important, the operation of natural ventilation takes place at the cost of colossal heat losses, especially in winter. In modern buildings, this type of ventilation is the main “culprit” of their cooling – it constitutes from 30% to even 60% of all heat losses! For comparison, windows are responsible for 15-25%, walls for 20-30%, the roof for 10-25% and the floor on the ground for 15-25% of losses. As you can see, the difference is significant. Heat losses caused by ventilation of the old type are, in turn, a necessity to increase the intensity of heating, which not only involves an increase in expenses but also hurts the environment (higher fuel consumption = higher level of environmental pollution).

Mechanical ventilation with heat recovery – how does it work?

In modern construction, which is subject to strict standards in terms of, among others, energy efficiency, there is no room for inefficient solutions anymore. Therefore traditional ventilation of the old type (gravity) is replaced by a much more effective system, which is mechanical supply and exhaust ventilation with heat recovery. It works regardless of weather conditions or season, guaranteeing the removal of used air from rooms and pool of fresh, additionally filtered air from outside. What is essential, the whole process, thanks to the heat exchanger, allows reducing energy consumption and heat losses! How does it work? Mechanical ventilation consists of a system of exhaust and supplies air ducts and haemostats, which would enable to remove used air from the rooms and provide them with fresh – and also thanks to appropriate filters – immaculate air from outside. The heart of the whole system is the air handling unit with fans, which is responsible for the optimal air circulation for a given building (of course, it can be freely controlled, adjusting it to your needs). One of the critical elements of the system is a heat exchanger, which allows for energy recovery through the exchange of heat between exhaust and supply air streams. The heat of the air removed from the house is transferred to the supply air stream, which allows reducing its losses with the efficiency reaching 95% effectively! The air streams do not mix, so you can always enjoy clean air at home, saving money on heating expenses and protecting the environment.

Recovery from the design stage of the building

When deciding on the recovery, it should be remembered that this system is much easier to install in buildings that are just being built than in those that have already been finished. This is because it is necessary to provide all the rooms in the house or flat with ducts which are used for supply and exhaust air. Due to the need to ensure optimal operation of the whole system, the ducts above must have a reasonably large diameter (at least a dozen or so centimetres). Therefore their concealment would be difficult. The exposed ducts, in order not to spoil the aesthetics of the interiors, would have to be built in, which would mean the necessity to carry out further works and in practice, renovate the rooms. The decision to carry out the recovery already at the stage of building design has much more advantages. It allows not only to choose the right place for the recuperator but also to optimise the route of the installation. When planning the entire investment, there will also be no need to make chimneys for gravity ventilation, apart from that, collisions with other installations will be avoided. A significant advantage is also the earlier execution of culverts through ceilings, thanks to which there is no need to create additional holes and piercings. Including recuperation in the project is also the comfort of starting work at the right time, according to the work schedule, thanks to which different teams will simply not bother.

Recuperator – what parameters to pay attention to?

As we mentioned earlier, the heart of mechanical ventilation with heat recovery is the recuperator (air handling unit). Suppose most probably we will not choose a specific model of the device by ourselves and we will rely on the executive team (that is why it is so important to find appropriate specialists). In that case, it is worth to have at least basic knowledge on this subject. The main thing to pay attention to is the efficiency of heat recovery. Models with counter-current heat exchanger achieve the highest value of this parameter.

Devices equipped with cross-flow heat exchangers deal with this issue less well. The efficiency of an air handling unit is also affected by such factors as energy consumption of the fans used in it, protection against condensation, air filter parameters and control system capabilities. The energy label (its placement is currently mandatory) is excellent facilitation, which allows for a quick overview of the technical data of the unit. From the information contained there, you can find out, among others, what is the energy efficiency class of the air handling unit. It is determined, based on unit energy consumption (RES). This value tells us what energy savings can be achieved annually (per square meter). The best models that can be found on the market belong to class A+. The label also contains information about the efficiency of the air handling unit. Thanks to this, having a ventilation system design, you can immediately see if the recuperator will be suitable for your building. The level of noise generated by the air handling unit is also an essential element when selecting the air handling company. This is particularly important when the recuperator will be located close to frequently used rooms, especially bedrooms. Of course, there is no need to demonise the noise generated by the air handling unit, as the vast majority of devices are quiet. Higher noise intensity is generated by air flowing in ventilation ducts. Therefore it is necessary to bear this in mind. It is worth knowing that recuperator fans can operate at different speeds.

The recommended efficiency should be achieved by operating in the middle gear. Recuperation is an exciting and complex subject, but we have tried to raise the most critical issues related to it for you. From the content of this article, you can easily deduce that mechanical ventilation with heat recovery is almost exclusively beneficial. Yes, you have to pay for the installation at first, but this is an investment for years that pays for itself quickly due to the reduction in heating costs. Recuperation ensures energy recovery with an efficiency of up to 95%. A properly executed system enables comfortable control of the air stream and its parameters. Mechanical ventilation with heat recovery allows air to be treated, i.e. properly filtered, heated and humidified. Recuperation also reduces the problem of wall moisture, which could cause the appearance of harmful microorganisms such as mould, algae, etc.