Fresh Air, Fresh Perspectives: Benefits of MVHR Systems

Allan Corfield Architect, Construction Methods, Construction Professionals, Eco Homes, Self Build 4 Comments

Mechanical Ventilation with Heat Recovery: A System You Can Rely On

With changes to energy regulations in house building scheduled for 2016, there are more and more Self Builders sounding out ways of making their homes as energy-efficient as possible. Whether they gain the official rating or not, many strive to emulate the PassiveHaus building standard – which is focussed on an extremely airtight, fabric-first and highly energy-efficient design. Having such an airtight structure requires a high-quality ventilation system, in order to create a healthy environment within your home.

Without a good ventilation system, your home can fall victim to a number of problems. Any moisture in the air can form condensation, encouraging the growth of mould. Subsequently, dust mites tend to flourish in damp conditions, and this can lead to an increase in dust-related allergies or asthma. Things you might not even think of can remain in circulation throughout your home without a sufficient ventilation system; paint, cleaning products, and carpets can all release harmful organic compounds. On top of all this, there are also everyday odours from cooking, toilets, tobacco, and pets floating around the home.

So what ventilation systems are available for your Self Build? There are a number of ventilation systems, but they tend to fall short if you are striving for energy efficiency in your home. Here are a few examples:

Extractor Fans – Extractor fan systems can be easily installed, and the pollutants found around the home can be removed quite quickly. However, they have a tendency to waste heat easily via trickle vents, they can be rather noisy, and can be prone to letting draughts in.

Passive Stack Ventilation – This system avoids using electric fans by employing a ‘stack’ effect, in order to draw warm air up from wet rooms through ducts. Despite being initially useful for lowering electricity use, the lack of pressure differences can affect air flow. This means some rooms will be warmer than others, and this can enhance the need to open a window, or add a central fan during warmer weather. Without an even distribution of heat, there is a similar wastage of heat to an Extractor Fan system.

Central Extract Ventilation – Using this system will remove contaminated air from wet rooms, and replace it with fresh air through trickle vents, together with the air leakage from habitable rooms. Like the Extractor Fan and Passive Stack systems, the Central Extract Ventilation system can waste heat, and can create draughts through the trickle vents.

MVHR
Mechanical Ventilation with Heat Recovery System (MVHR)

An alternative ventilation system to the ones mentioned above, is the Mechanical Ventilation with Heat Recovery System – or MVHR. This system provides an ideal ventilation solution, and the technology couldn’t be more straightforward. Stale air is taken away from ‘wet’ rooms in the home through a combination of hidden ducts. This air passes through a heat exchanger in the unit of the main system, which is installed discreetly in an attic, garage or cupboard. UK-based experts, ADM Systems, explain that the MVHR system works much in the same way our own bodies work:

Just as our lungs filter and transfer essential oxygen into our blood, before sending it around our bodies via our arteries – so a heat recovery ventilation unit brings fresh air into your home, distributing it through a series of ducts. As our bodies expel carbon dioxide from our lungs into our veins – the heat recovery ventilation system simultaneously draws polluted air out of the home through separate ducts, passing it through the main unit, before being released into the atmosphere.

The stale air is taken through the ducts from the ‘wet rooms’ in the house, such as kitchens and bathrooms. This air then passes through to the ventilation unit and over the heat exchanger – which can recover as much as 90% of the heat in this air that would typically be lost in traditional means of ventilation. At the same time, fresh air is continuously brought in from the atmosphere, filtered to remove the likes of pollen, carbon, and insects, before it passes over the heat exchanger and ducted through the rest of the house – providing a balanced ventilation system and clean air.

Heat recovery ventilation systems also work well with alternative central heating options, such as underfloor heating, wood burning stoves, and renewable energy sources, e.g. photo-voltaic panels and wind turbines. Introducing a ground-to-air heat exchanger further maximises efficiency by harnessing natural geo-thermal energy.”

The heat recovery products can help to reduce a building’s carbon emissions by reclaiming and redistributing the heat into the property which would have been wasted if a traditional system had been used instead. Unlike these traditional systems, such as trickle vents or extractor fans, little or no thermal bridging occurs from using a MVHR system. The energy saved using the MVHR contributes to a reduced Dwelling Emission Rate (DER) in the Standard Assessment Procedure (SAP). MVHR systems also offer huge benefits towards achieving building standards. Heat recovery uses just a few Watts of energy (<1W/l/s) to recover many kiloWatts of otherwise wasted heat from conventional ventilation systems. This results in lower energy bills and carbon emissions.

ADM Systems point out that, as part of the 2010 Building Regulations Approved Document L consultation workshop, it was highlighted that modern buildings can lose up to 25% of heat through uncontrolled ventilation and air leakage. The heat recovery technology in MVHR can recover upwards of 90% of this heat – confirming its status as a practical and energy efficient ventilation solution.

Brian Singleton, of ADM Systems, answered some of our key questions Self Builder’s might have about MVHR systems:

MVHR
MVHR

What is the average unit cost for a 4-bedroom family home?

There are many MVHR units on the market, currently over 200 in SAP Appendix Q and over 70 Passive House Accredited. Some units come with basic features through to more sophisticated, integrated controls. The range of prices for a typical 4 bed Self Build would be from £3500 to £4500 depending on the specification and size of the property. The running costs for a properly designed and installed system would be in the region of £50 to £70 annually.

What maintenance do the MVHR systems require?

The main maintenance is the cleaning and changing of filters twice a year. Most can be cleaned and used again 2 or 3 times before replacing. The filter costs vary from £30 to £60 depending on the manufacturer. The heat exchanger would also need inspection every 2 years or so. It is removable and washable, and all maintenance on MVHR systems is something that can be done by the homeowner.

Can Self Builders install the MVHR system themselves and get you to commission them?

Very much so, over 50% of our projects are self-install following the sweat equity route, either by clients themselves or one of their trades. We provide them with schematic layouts and installation instructions and technical support and site visits. The radial duct system is very attractive for Self Builders as it is easier, quicker, and more fail-safe for self-install.

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Who are the market leaders in the industry at the moment?

There are two distinct markets for MVHR Multi Site Applications: First, there is the main builder, covering the likes of social housing, or the Olympic Village type of projects, for example. These projects are very price-driven and manufacturer-led by companies such as VentAxia and Greenwood AirVac.

Then, there is the the Self Build market. Currently, there are around 15,000 Self Builds per annum – representing 14% of the total new homes built in the UK. This is set to rise to 25,000 new homes by 2020. Manufacturers are active in the Self Build market, however, this is not their core business – so companies such as ADM Systems offer bespoke solutions, and are better suited to the Self Build market.

What separates ADM Systems from the competition?

ADM are an independent company dealing with many manufacturers, so we can offer choice to suit the project. We have been in the marketplace since the early 90s, and have a wealth of experience. ADM Systems are not just suppliers of Heat Recovery Ventilation – we offer a full range of ‘buddy’ services for Self Builders installing their own heat recovery systems. We also offer Compliance advice, complete installation by BPEC approved engineers, and full ventilation system maintenance and aftercare packages. We also offer ground to air heat exchangers to enhance your MVHR system, and central vacuum systems.

What would be your top tips for new Self Builders?

Step 1: Think ‘Fabric First’ – consider a thermal strategy early and strive for airtightness from your Self Build

Step 2: Determine the level of heat required for your Self Build.

Step 3: You have to consider how to ventilate – ventilation can represent a huge percentage of the heat loss in a building, and this can have an impact on the first two steps. Think carefully about your system’s location – you may find planning regulations can dictate that certain conditions are met.

Controlled ventilation = Controlled heat loss (MVHR), whereas Uncontrolled Ventilation = Uncontrolled Heat Loss.

Therefore, ‘Build Airtight, Ventilate Right’ – remember this and you should be on course for a brilliant, energy-efficient Self Build.

What stage would you (ADM Systems) need to get involved in a Self Build project looking to utilise a MVHR system?

As early as possible. Initial sizing can be done from any architectural or planning drawings, before detailed design and liaison with the client, architect, kit supplier and structural engineers takes place. This liaison and cooperation helps to integrate the system into the structure smoothly, whilst maintaining the aesthetics of the internal finish.

Our special thanks go to Brian Singleton and ADM Systems for their help and contribution to this blog. Along with ACA, Brian offers his expert advice at Self Build Seminars – hosted by our friends at SIPS Industries throughout the year. For more information, or to sign up to the next seminar, click here.

Contact ACA

For more information on MVHR systems, and when to integrate them into your Self Build designs, contact ACA today! Alternatively, leave a comment below!

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  1. Does an MVHR mean that all rooms will be at the same temperature, regardless of where the heating source is?

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