The world is increasingly focused on saving energy. Not only because of the rising cost of maintaining buildings, but also because of climate change. A heat recovery system makes use of what is already there and reduces our collective impact on the environment, including the amount of heat we lose every day. The growing awareness of investors and the increase in materials available to improve energy efficiency means that ventilation based on natural air flow is no longer sufficient to provide the right level of air exchange. In such cases, gravity ventilation is not very effective and an advanced HRV system should be a consideration. Heat recuperation works by taking the valuable warm air and using it in a positive way. How heat recovery units works and what types of heat exchangers are currently available?
You have probably heard of ventilation with heat recovery - what is it exactly? The definition of it is related to the recovery of heat for further use. This makes it possible to limit heat loss through the ventilation system. In general, the main reasons for using HRU’s are to save energy and to provide fresh and clean air. A heat recovery unit is basically composed of a directly driven fan, an exhauster and a heat exchanger, all perfectly assembled and joined inside a thermal and noise insulated structure. Ventilation by means of heat exchangers allows a high percentage of the energy used to acclimatise the room to be recovered, which would otherwise be wasted.
A heat recovery ventilation system recovers thermal energy and removes old and polluted air from the indoor environment, while at the same time collecting, filtering and supplying new, fresh air. With the use of appropriate filters, the amount of dust, dirt and various allergens that have a negative impact on human health is reduced. A heat recovery system can also include an ionising device for additional air treatment. For those suffering from allergies, this is a very useful solution. What is a heat recovery unit and how it works?
The heat exchange between the flue gases and the air takes place in a recuperator through walls made of metal or ceramic. Ducts or tubes bring in the combustion air to be preheated, while the other side contains the waste heat stream. The internal exhaust air circuit passes through the exchanger without mixing with the external driven air circuit.
The thermal efficiency of the heat recovery process depends, among other things, on the type of exchanger and the materials from which it is made. The efficiency of a heat recovery unit is directly related to the exchanger. The most common are:
The technical characteristics of the fans are calculated according to the volume of air to be moved and the number of daily cycles. The amount of fresh air required is the basic factor for choosing the right type of recuperator. This quantity will correspond to the capacity of the unit to provide an adequate number of air changes. The assumption is that there should be one complete air change per hour in the room with the unit in operation.
Understanding how ventilation works from different perspectives is critical to making informed decisions. By learning about the different types of heat recovery units available, their benefits and limitations, you can tailor your choice to specific operational requirements. Whether it's the efficiency of a shell-and-tube heat exchanger, the compact design of a plate heat exchanger or the specialised applications of finned tube heat exchangers, a comprehensive knowledge base will ensure you make the best choice and achieve peak performance.
For this reason, designers are often forced to use mechanical ventilation systems where the airflow is driven by fans, for example. However, we see in practice that even with a proper thermal refurbishment of the building, almost 50% of the energy consumed is used to heat or cool the air supplied from outside. A good heat recovery system therefore provides fresh, filtered air even when the windows are closed. This is particularly important in winter, when every time you open a window to ventilate a room, you have to heat it again.
The choice of the right HRU will greatly influence the correct operation of the whole ventilation system. If it's not the right type for your installation, even the best class of HRU won't meet your requirements. The result will be a reduction in comfort and an increase in running costs. The design of heat exchangers ensures that the substances involved do not mix, while optimising heat transfer, making them ideal for use in a wide range of applications. Which recuperator to choose?
Heat Recovery Units with cross-flow exchangers have a simple design with no moving parts and provide up to 75% heat recovery. In counterflow exchangers, the air flows laterally in opposite directions. The air flow channels have a triangular cross-section. This design means that the surface area of contact is larger, which in turn improves the efficiency of the recovery. They also have a simple design with no moving parts, which allows heat recovery of up to 80% and no freezing of the installation or obstruction of flow. Importantly, both heat exchange types are made from a material with an antibacterial coating that kills various types of bacteria and prevents the spread of fungi inside the heat exchanger.
Heat recovery is often more effective than conventional gravity ventilation in terms of providing efficient air exchange. Regardless of the weather outside, this increased performance has a direct impact on the comfort of the building's occupants. A heat recovery ventilation system filters the air 24 hours a day, maintaining an appropriate humidity level, which also improves occupant comfort. They also have a positive effect on the condition of walls, floors and furniture by helping to eliminate mould and mildew.
With the installation of a heat recovery system, it will extract the damp, stale air from all the wet rooms in your home and replace it with clean, filtered, fresh, warm air in all your habitable rooms and bedrooms without letting the heat escape. Your home will be fully ventilated all year round, with up to 95% of normally wasted heat recovered, giving you significant energy savings. A healthier, cleaner and quieter environment is achieved by installing a heat recovery unit as your home remains airtight with no need for window vents or bathroom extractors.