Looking after your MVHR

Changing MVHR filters I Regular servicing I Housing Providers

Mechanical ventilation with heat recovery systems (MVHR) are a crucial component in Passivhaus buildings. It is common to get our cars & gas boilers regularly serviced; Ventilation units should be treated the same! If well-designed and installed correctly, they should only require minimal maintenance. Here we outline a few critical steps and top tips for ensuring optimal performance.

Commissioning

Properly setting up the MVHR system to ensure its optimal performance is known as commissioning. This crucial step can only take place once the construction work is complete, and the building is clean. Commissioning is typically carried out by a knowledgeable Passivhaus specialist before a Passivhaus building certificate can be issued.

MVHR Commissioning. Alan Clarke & Nick Grant

In addition to flow rate adjustments, commissioning will also involve verifying the correct operation of controls and confirming that the system meets the specific criteria and performance targets outlined by the Passivhaus standard.

Traditional branched MVHR systems: it is necessary to adjust the flow rate for each room at the terminal. Ideally, a well-designed ductwork system should provide the required flow rate settings (in millimeters) for each room.
Semi-rigid MVHR systems: may come with specific flow regulating inserts designed for the ducts leading to each room. However, it is still important to check and verify the flow rate at each terminal to ensure accurate and efficient operation.

Further details can be found in chapter 8, Building Services (pg 54), of the Trust's How to build a Passivhaus: Good practice guide.

Handover

Your MVHR system can maintain fresh clean air while conserving energy. Do you know how to operate it, and how many times the filters need changing? By obtaining the following comprehensive information at the start, occupants should be equipped with the knowledge and tools necessary to effectively maintain their Passivhaus ventilation system:

CONTROLS: During induction/ handover, as a new Passivhaus occupant, you should be provided with a thorough understanding of the MVHR system. This should include a clear description of the system, specific features & benefits, and a demonstration of how to operate the controls effectively.
FILTERS: A key component of MVHR maintenance is the regular replacement of filters to ensure optimal performance. As part of the induction process, the importance of filter maintenance should be highlighted. Where possible, occupants should be provided with written and illustrated instructions on how to change the filters. The recommended frequency for filter replacement is typically every 3 to 6 months.
OBTAINING REPLACEMENTS: Occupants should also be informed about where to obtain replacement filters. This can include providing contact information or reliable suppliers where the appropriate filters for the specific MVHR system can easily be purchased.

Housing providers

While the maintenance team have no legal obligation, like boilers, to change filters, housing providers and landlords have a crucial role in ensuring the well-being and comfort of residents in Passivhaus buildings. As well as the above, housing providers should also consider:

Informing residents how the housing provider will manage the ventilation system & regular filter changes.
It is important not only to inform residents about the ventilation system during their initial orientation but also to repeat this information during all future change-overs.
A ventilation system services plan should be set up at the start of any maintenance programme, and ventilation faults should be treated as urgent.
Involvement of maintenance expertise at design and specification stages is strongly recommended.

Learn more in chapter 10, Handover, soft landings, & POE (pg 72), of the Trust's How to build a Passivhaus: Good practice guide.

Filter replacements (& how often)

The primary maintenance requirement for an MVHR system is changing filters, including any extra on the kitchen grille. Regular filter changes are important. If you look after them, they will look after you! Some ventilation units maintain a constant airflow rate when filters get clogged, but in so doing the fans get noisier. Older or cheaper systems just supply less air. Write the date of installation on the filter. Most control units have a filter-change indicator, but this is based on number of days since the last filter change.

It is an advantage if occupants can periodically check the system: some systems are so quiet that occupants may not notice if the fans stop running. The recommended frequency for filter replacement is typically every 3 to 6 months but check with your manufacturer. Other factors such as local pollution levels, dust load, & use of the system will also have an impact.

MVHR Filters. Before & after. Harry Paticas

MVHR filters before & after. Juraj Mikurcik

Before & after MVHR filters

Cleaning air valves

Over a few years, dust builds up on extract valves. These can be removed and cleaned, being careful not to change airflow settings or mix valves between rooms. Terminals should be removed for redecoration but must be labelled by room if more than one is removed.

Respond to error messages & faults

Any MVHR error messages and faults should be reported and addressed straight away. An MVHR failure is as much an emergency as a heating system breakdown!

Servicing

The MVHR system should be fully serviced every four to five years. This should be done by a professional who is knowledgeable in Passivhaus.

Servicing checklist

Open MVHR unit, take out heat exchanger & inspect - clean if necessary.
Replace dirty filters and clean around filter housings.
Check fans for dirt and damage and clean if necessary.
Check bypass valve.
Check preheater and clean if necessary.
Take out condensate trap and wash through, then check condensate is draining properly.
Confirm airflow rates are as design - either from MVHR controls or measurement at terminals.