System selection guide

How to select a ventilation solution for multi-apartment buildings?

Centralised ventilation with heat recovery

In centrally placed ventilation system one air handling unit serves supply and extract air for multiple apartments via a duct network. The heat recovery exchanger transfers energy from exhaust air to incoming fresh air. System can consist of one air handling unit covering all the apartments in a building or several units each serving several apartments in the same floor/corridor.

Advantages

High energy efficiency
Often most cost efficient installation in large buildings
Easy to maintain in one location and therefore creates less maintenance costs over lifetime
Quiet operation when designed correctly

To consider

Requires significant duct space
Higher installation complexity
Not as indivually adjustable - adjustments affect multiple apartments if not zoned properly
Requires fire sections
Risk of odor transferral between flats

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CENTRAL SYSTEMS

Apartment-specific ventilation with heat recovery

In apartment-specific ventilation system each apartment has it's own individual air handling unit that serves supply and extract for that specific apartment via a duct network. The heat recovery exchanger transfers energy from exhaust air to incoming fresh air. The air handling unit can be installed in the bathroom, storage room, or kitchen area or in suspended ceiling.

Advantages

High energy efficiency
Each apartment controls their own indoor climate
Individual adjustable to each residents needs
No risk of transferal odors
Less vertical and horisontal shafts required
With wall outlets/inlets for fresh and exhaust air even less ducting required
Minimum or no fire blocks depending on design

To consider

More units to maintain
Space for the unit needed inside each apartment
Service access inside apartments

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APARTMENT-SPECIFIC SYSTEMS

Centrally placed apartment-specific ventilation with heat recovery

A unique residential solution that combines the best qualities of central and apartment-specific ventilation. Each apartment has it's own individual air handling unit that serves supply and extract for that specific apartment with all the units located outside the apartment in the roof and connected to the apartments via a duct network. The heat recovery exchanger transfers energy from exhaust air to incoming fresh air.

Advantages

A gapless continuous isolation of building and heat exchangers
Higher energy efficiency for the building
Roof placed unit saves space in the living area
Maintenance and repair is possible without entering the apartment
Quick installation
Lower investment costs due to quick mounting and less ducting compared to centralised systems.

Disadvantages

Optimal for lower buildings (up to 5 stories) ang bigger apartments per floor
Shafts and installation needs to be taken into consideration early in the building design

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APARTMENT-SPECIFIC ROOF PLACED SYSTEM

Wall placed ductless ventilation with heat recovery

These compact heat recovery ventilation units are installed directly through external walls. Therefore they don't require any ducting for suply air, but a separate extract duct from bathroom can be connected. Simple ductless installation makes these units ideal for renovation.

Advantages

Minimises needed ductwork
Simplified planning and minumun disturbace with installation
Suitable for renovations
Serves multiple rooms with transfer air unit (freeAir+ as accessory)

To consider

Potential for increased noise
Limited airflow performance
Larger apartments may require several units to meet airlow requiremenets

Exhaust only

Exhaust ventilation is a traditional ventilation method that is used in many older buildings. In exhaust ventilation used indoor air is being extracted with a fan unit and fresh replacement air enters through inlets in the wall.

Pros

Simple and affordable

Cons

No heat recovery results to significant energy loss
Increased heating costs and carbon footprint
Draft risk (cold supply air)
Less control of incoming air quality

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Roof fans

Exhaust ventilation can be upgraded to mechanical heat recovery ventilation to improve energy efficiency and indoor air quality. For examples lear more about our renovation solutions.

How to choose a system?

The choice of ventilation system is essentially based on three key factors:

Comfort
Energy efficiency
Investment cost

In practice, achieving the highest level of performance and comfort is rarely possible with the lowest investment. Therefore, the final selection is usually a balance between these factors, depending on the specific requirements of the project and the building.

Every project is unique, and numerous factors influence the choice of the most suitable ventilation system for a residential building.

Below are the key considerations to take into account when selecting a ventilation system.

Key factors to consider

1. Building size and layout

Size, shape and layout of the building has a major influence on which system is the most feasible to build.

How many apartments?
How many storeys?
Are air shafts feasible?
Is there space for central units / for apartment-specific units?
The amount of different design variations will increase complexity and costs.
Consider potential for module building
In apartment-specific solution consider the benefits of using wall inlet/outlets

2. Local regulations and standards

Ventilation requirements vary between countries, but typically specify:

Minimum airflow per apartment/home and minimum supply air volume per person
Minimum extract rates for kitchens/bathrooms
Pressure balance guidelines
Correct direction for airflow (from clean areas to bathroom/toilet/kitchen)
Regulations for kitchen ventilation (boosting during cooking and requirements for balancing airflows)

3. Energy efficiency

Ventilation can account for up to 50% of heating energy losses if heat recovery is not used.
Efficient heat recovery (HRV/ERV) significantly reduces heating and cooling demand.

Heat recovery efficiency % illustrates how much heat energy can be recycled
Defrosting ensures continuous heat recovery in cold climates
Demand control can furher decrease energy consumption by 10-30%
Humidity optimisation can decrease energy consumpition especially during cooling period

4. Installation constraints

5. Noise requirements

Ventilation noise is one of the top complaint sources in apartments. System choice and component quality matter greatly. Factors influencing noice level:

The placement and installation of the air handling unit affect the noise levels in the surrounding area.
Ductwork should be designed to minimise pressure losses and be properly insulated.
The use of sound attenuators, particularly longer ones, effectively reduces low-frequency noise.
It is essential that the ventilation unit can be easily commissioned together with the entire system (e.g. using a commissioning wizard).
Select high-quality diffusers that are suitable for their intended application.
Commission the system with minimal pressure reductions across the diffusers, in coordination with the ventilation unit and the overall system.
When selecting a cooker hood, pay attention to its odour catching capacity and sound level at the designed airflow rate.

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With extensive experience from delivering solutions to millions of apartments, we can help you choose the ideal system for each unique project and requirement.

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