MVHR: Is it all just hot air?

The light-hearted, but factual debate about which ventilation strategies are most appropriate for low energy buildings was a joint PHT & AECB event, kindly hosted by UBM. The Passivhaus standard requires Mechanical Ventilation with Heat Recovery (MVHR.), but many outside the Passivhaus community claim not to like it as an approach. This event aimed to explore the arguments for and against MVHR and to see if there was a preferred ventilation solution for all low-energy buildings.

The evening consisted of 4 presentations each 10 minutes long. All the presentations were informative rather than provocative, and all the speakers explained that achieving good ventilation was a complex task, so the event didn't generate quite as much controversy or differences of opinion as last year but seemed instead to reach some common conclusions. Presentations can be found below along with key points from each speaker:

Choosing passive, mechanical or hybrid ventilation	Making MVHR work
Peter King, Aereco	Sally Godber, WARM Low Energy Building Practice
• Demand controlled ventilation has the potential to provide a cheaper, efficient alternative to MVHR for comfortable buildings.	• Make it easier for the certifier & designer to know when the MVHR has been commissioned correctly • Make it easy for a commissioning engineer to declare a system ‘not fit for purpose’
Mechanical extract or MVHR: the human dimension Part 1.         Part 2.	Horses for courses: MVHR wins
Harry Paticas, Arboreal Architecture	Janet Cotterrell, Passivhaus Homes
Ventilation should be: • Joyful - connection to nature/experience external conditions/visible • Low energy - when possible should have ground cooling and heat recovery • Responsive - demand controlled, weather controlled, more anisotropic when desired	•  MVHR i s part of an integrated approach that can enables 80-90% uplift in energy efficiency •  It has a supporting community in Passivhaus Trust who can help promote and drive good practice • The MVHR approach has a context in which post-occupancy monitoring is encouraged – there are more built-in checks and balances.

Unlike last year, there was not a clear cut divide of opinion from the speakers, who seemed to share common denominators:

• Thought and care is required on any building ventilation strategies. One size does not fit all! Systems should be responsive to individual buildings. Ventilation strategies are never clear cut; even those employing MVHR systems usually allow natural ventilation (e.g. opening windows) in addition.
• The risks of inadequate ventilation and its impacts need to be considered and understood by all involved. Tests and checks after 1st fix would help identify potential problems
• Older buildings and renovations may require more sensitive ventilation strategies as part of a whole-house retrofit. Risks of any upgrades or alternations to existing building fabric need to be considered.MVHR, like other systems, is difficult to get right. Quality assurance at all stages from design, commissioning, installation, and maintenance is important. The Passivhaus approach helps with this, but further clear protocols would aid this.
• There is a skills gap in installing and commissioning any type of ventilation system. Currently any contractor can carry out installation. It should be treated as a specialised profession that requires training and qualifications.
• Competency: Roles and responsibilities should be clearly defined. Ideally commissioning engineers would work for the client rather than the main contractor.

 

The following questions were posed to delegates:

Q1. Quality: Can the industry deliver?	Yes	No	Maybe
Can the UK industry currently deliver MVHR systems that provide good indoor air quality in the majority of UK non-Passivhaus housing projects?	2	Clear Majority	3
Can the UK industry currently deliver MEV/other ventilation systems that provide good indoor air quality in the majority of UK non-Passivhaus housing projects?	13	Clear Majority	10
Using the Passivhaus Quality Assurance system, can the UK industry deliver MVHR systems that provide good indoor air quality in the majority of UK Passivhaus housing projects?	Clear Majority	1	7
Q2. Maintenance: Will occupants use and maintain MVHR?	Yes	No	Maybe
Can UK occupants learn to operate and maintain MVHR systems in their dwellings?	Clear Majority	3	6
Is it reasonable to expect occupants to learn to operate and maintain MVHR systems in their dwellings?	Clear Majority	1	0
Should maintenance of the MVHR system be undertaken by others where possible (for example as part of a service fee or in HA rental agreements)?	Clear Majority	3	4
Q3. MVHR or MEV/other ventilation?	Yes	No	Maybe
Given current UK building practices, should all new dwellings have MVHR?	24	25	8
Assuming that the UK industry could achieve the quality necessary, should we aim for all new dwellings in the future to have MVHR?	Clear Majority	7	-
Assuming that the UK industry could achieve the quality necessary, should we aim for all retrofit dwellings in the future to have MVHR?	30	25	8
Q4. Future quality	Yes	No	Maybe
Can we get the industry to achieve the quality necessary to deliver successful MVHR on a majority of new dwellings within the next ten years?

The last question was left for discussion with drinks, and the jury are still out! Thanks to UBM for hosting the event and Zehnder for providing the drinks. Thanks to all that attended and participate in the debate. We hope to see you next year.

27th January 2016

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