16.01.2025
FAQ: Centralized AHU's
Answers to some of the questions that may arise when considering the acquisition of a centralized heat recovery unit:
Q: What is a centralised heat recovery system?
A: As the name suggests, a centralised heat recovery system is used to exchange air and maintain its quality throughout a building, unlike a wall-mounted recuperator, which can only do this in the room where it is installed, and unlike which the air exchange in the room can be adjusted depending on its size and the expected number of occupants.
Q: What does a centralised heat recovery system consist of?
A: Unlike a wall-mounted recuperator, where the installation includes all the elements necessary for air exchange, a centralised recuperation system is much more extensive and includes individual elements for air exchange in the building:
- Diffuser with diffuser box (if required): An element that is mounted in the ceiling and serves as an opening for exhaust and return air. Depending on its type, it may be mounted separately or may need to be combined with a diffuser box mounted above it. With the exception of bathrooms, where only the extract is provided, there are normally no fewer than two diffusers per room, supply and extract (note that exceptions may occur depending on the design of the ventilation system);
- Ducts: Pipes used for supply air and extract air. It is possible to use plastic pipes, which are then discharged from the distributor to the rooms, or to prepare the whole system with galvanised tin pipes;
- Silencers: Used to reduce noise from airflow and AHU equipment entering the room, increasing user comfort;
- Safety valves: a fire safety valve that blocks the air exchange and exhaust in the room in the event of a fire. The amount of air supplied to the room itself is regulated by a valve already integrated in the diffuser;
- Centralised heat recovery unit: the heart of a centralised heat recovery system, it provides the supply air while controlling humidity levels and temperature changes.
Other elements of a centralised heat recovery system can also be found, such as additional humidity or CO2 sensors, electric or water heaters/coolers, separate shut-off valves for each diffuser and, of course, the control panel.
Q: What types of centralised heat recovery units are available on the market?
A: Centralised heat recovery units will mainly differ in the way they can be deployed - under ceiling, floor, vertical - as well as in the heat exchangers they contain. Most commonly, centralised heat recovery systems are designed with two types of heat exchangers: a plate heat exchanger and a rotary heat exchanger. Of course, it is necessary to take into account the type of building for which the centralised heat recovery unit is intended - a heat recovery unit designed for a commercial building will not be suitable for use in private homes.
There are also other differences between the models of centralised heat recovery units, related to their controllability or quality of manufacture (depending on whether a budget or high-end unit is chosen). But these features ultimately do not change the operating principle of the unit.
Q: What is the difference between a rotary heat exchanger and a plate heat exchanger?
- A plate heat exchanger is a more budget-friendly solution, but is more suitable for warm climates - at low temperatures, icing is possible and the efficiency of the heat exchanger is reduced.
- Rotary heat exchangers will generally be more expensive, but will also operate more efficiently at low temperatures - suitable for Baltic and Scandinavian climates. Unlike plate heat exchangers, this type of unit will also not require a condensate drain.
Note that there may also be differences between different plate or rotary heat exchangers. For example, Komfovent offers units with standard condensing heat exchangers as well as heat exchangers that are able to better control humidity levels, temperature output and consequently increase the air and living quality in the building.
Q: Where is the best place to locate centralised heat recovery units?
A: Although there are no restrictions on their location, given that centralised heat recovery units are (relatively) loud, it is recommended that they are installed in an insulated technical room. Underfloor or underfloor centralised units can also be installed in the attic of the building, but the attic must also be insulated. Otherwise, the supply air temperature may be affected (if the pipes are not insulated) and, more importantly, the amount of humidity in the system will reduce comfort and offer prime conditions for mold and condensation to appear.
Q: How do I know which type of heat recovery unit I need and how powerful should it be?
A: Although it is possible to make rough assumptions just by looking at the building plan ( sufficient if you just need to know, what kind of unit to install), the most useful way to get this information is to draw up a ventilation system project. This not only allows the calculation of the ventilation system to determine the exact amount of air exchange and the choice of equipment, but also provides an accurate estimate of the installation materials and labour costs.
Q: How will I be able to manage a centralised heat recovery system?
A: Almost all centralised heat recovery systems come with (or offer as an option) a control panel, which is installed in a utility or living space, through which the heat recovery system can be controlled. In addition, most of the centralised heat recovery units on the market have the possibility to be controlled remotely via a mobile app or a website on a PC.
Q: What are the approximate costs I need to consider when choosing a centralised heat recovery system?
A: It all depends on the size of the home, the amount of air exchange required and the complexity of the installation. Assuming that a centralised heat recovery system needs to be installed for a medium-sized private house (~120m2), providing it with triple the air exchange with the appropriate Komfovent equipment, the cost of the equipment starts from 2270.00€ + 300.00€, while the cost of other materials can be calculated from 30.00€/m2 (for new buildings or existing buildings with free access for piping and equipment placement) to 60.00€/m2 (in cases where more extensive changes are required for a centralised system), plus VAT on the final installation price. Total amount: 2123.97 € + 3600.00 € + VAT (21%).
Please note that the installation costs assumed here are broadly useful for budgeting purposes only - the best way to determine the costs of installation work and materials is through drawing up a project for the ventilation system. This will identify the works and materials required and will lead to a specific cost (which will in most cases be lower than the estimate, even taking the project costs into account).
We hope that the information in this article will help to clarify the choice and installation of a heat recovery system.
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