Tag: mechanical ventilation with heat recovery

HPH280 : A beginner’s guide to the Passivhaus Standard – with Jon Bootland

Chief Executive of the Passivhaus Trust, Jon Bootland, explains the processes and benefits of building your house to the Passivhaus Standard.

Interview with Jon Bootland

When Jon Bootland finished his university degree he began his employment first as a building services designer, and later working on good practice for sustainable low energy buildings, now with nearly 30 years experience. He has also been involved with the Passivhaus Trust since it was formed back in 2010. With initially very slow progress since the first Passivhaus was completed in the UK in 2010, numbers are now increasing rapidly at around 1,200 completed buildings (of which around 200 are individual owner-occupied homes), with another thousand already in the pipeline.

Carrowbreck Meadow – Image copyright Jefferson Smith

There’s nothing hugely complicated about Passivhaus

The origins of Passivhaus come from Germany, where the physicist Wolfgang Feist wanted to find a way of making sure that high performance buildings actually delivered on their claims, and performed the way that they were designed to do.

“It’s all about building physics. There’s nothing hugely complicated about it. It’s just what do we need to do to actually make it work and do what we said it was going to do.”

High in comfort levels, low in energy use

The fundamentals of a Passivhaus are:

Insulation – This is an important part of reducing the energy required to heat the building. A typical Passivhaus might have up to 30cm of insulation, meaning that the walls will be very thick.

The building fabric and airtightness – The other parts of the building will also need to have a very high performance. Windows for example will need to be triple glazed with good quality frames and careful detailing about how they fix together. The airtightness of the building is important with the aim being to stop draughts coming in and heat leaking out.

Ventilation – Because the building is now free of draughts, attention then needs to be paid to how to ventilate it. A mechanical ventilation system is used (MVHR) to bring fresh air into the building, while recovering the heat from the outgoing air.

As well as dealing with keeping the house warm in winter, Passivhaus formulae also look at the sun and other heat sources coming into the building and how the ventilation and insulation can work to keep it cool in the summer.

Old Holloway – Image copyright Juraj Mikurcik

Have a Passivhaus expert in your team

Jon says that building a Passivhaus is harder to do than a normal house, but that doesn’t necessarily mean you have to employ a team of specialists. He would however recommend having someone in your team that does have Passivhaus training, and preferably experience. It doesn’t have to be the builder, but could be the architect or a consultant.

The Passivhaus Planning Package does the calculations

You will need someone who knows what they’re doing to fill in the Passivhaus Planning Package (PHPP) and work out the answers to the calculations with you. It is a tool that takes a holistic approach to making all the elements work together, to make sure you end up with a building that has the performance and comfort that you are looking for.

There are benefits to having certification

PHPP should be used right from the beginning to look at the size and shape of the building, the window locations, balconies or anything else that might penetrate into the building etc. A certifier is able to check what is being put forward and advise on whether what you’re suggesting is actually going to work in the way it is intended.

Without having a certifier on board you will not be able to call it a certified Passivhaus, which does have some value in being able to sell the project. Certification is the best way of ensuring that your building will meet the required standards and provide the comfort and energy performance that you are looking for. If you’re not planning to use a certifier, then Jon recommends ensuring your team of architect, builder and consultants have plenty of Passivhaus experience between them to give you confidence it will perform as intended.

There are health and cost benefits

Jon outlines some of the key benefits of a Passivhaus:

Lower energy bills – The extra insulation and airtightness means less heat is escaping from the house, and therefore less energy is needed to heat it. Typical heating bills for a standard sized Passivhaus might be around £100, compared to several hundred for a non-Passivhaus equivalent.

Health benefits – Jon says there are research projects planned in the next few years looking into this, but there is still plenty of anecdotal evidence from occupants talking about the health benefits of living in a Passivhaus. As well as thermal comfort, the air that comes in can filter out air pollution and pollen, and people have reported improvements in asthma conditions. The mechanical ventilation also reduces moisture levels in the building which prevents condensation and mould.

Some construction methods will be harder than others

Jon says that although you could achieve Passivhaus with any construction type, it will be harder to achieve with brick and block for example than with timber panels. Although it’s possible to do, it will just need to be approached differently.

The extra outlay is money well spent

Jon uses social housing to get comparable benchmarks for how much more a Passivhaus will cost to build over a standard form of construction. Typically the additional cost of building a Passivhaus will be around 4-8% higher. Jon says that probably half of that is just on better quality building, which actually should be applied to all new buildings anyway, regardless of whether they’re Passivhaus.

So on a £200,000 – £400,000 build cost, that’s likely to add on just £8,000 – £16,000 extra.

“So, say you’re going to get a much better quality building that will make you more comfortable, more healthy and will perform better for 50, 100 years or more, it’s a very small amount of money in my book and it’s a much better way to spend your money than on a super flashy designer kitchen.”

There are ways to keep costs down

The shape and form of your building is crucial in keeping the costs down. Adding on multiple wings, outlying parts, differing floor levels, balconies additional roofs, lots of corners and odd shapes, will all make it more difficult to make a Passivhaus work, and will be more costly.

Jon wouldn’t recommend everyone try and build a square box as being the answer, but the closer you aim to a square box shape the easier it is to achieve Passivhaus.

Another way to keep costs down is to bring in your Passivhaus expert as early as possible. Don’t wait for the design to be finished and then call them in to do the calculations, but involve them at the design stages to help develop the building shape, window sizes and locations etc.

Multiple heating sources are not needed!

Jon explains that it can be challenging mentally to think of a house not needing multiple heat sources in it, but really they’re not needed.

Commonly though, people might put a radiator by the front door so that as you walk in there is a perception of extra warmth, while your body adjusts from the cold outside to the comfortable 20-21 degrees inside. A heated towel rail in a bathroom is also quite popular.

The design needs to minimise overheating risk

With homes becoming more energy efficient, the risk of overheating in the summer is becoming more significant and has to be planned for.

The main source of heat coming into the house in the summer will be from the sun, mostly in the late afternoon and evening. To stop the heat coming in without losing the views, Passivhaus buildings will often have some kind of shading or overhang on the west or south facing walls which keeps out the heat until later in the evening when the temperature drops.

There are also other heat sources to take into account such as the occupants and appliances, which heat the house slowly during the day. This data also feeds into PHPP to calculate how much heat will need to be taken out of the building to keep it cool. This can be done using the mechanical ventilation, or by opening the windows, particularly overnight. The temperature fluctuation in a Passivhaus will only be a few degrees, compared to 10-15 degrees in other houses.

“But the extra insulation and the extra performance of the windows, the doors and so on helps in the summer. Just as much as it helps in winter in keeping the heat in, in the summer it keeps the hot air out.”

The Passivhaus Trust oversees the standard in the UK

The standard was invented and developed in Germany, but in the UK it is looked after by the Passivhaus Trust. Their job is to look at how to apply and make the Passivhaus work in the UK, with our differing weather patterns and culture. Jon gives an example of these different considerations being parts of Scotland, where people don’t want to open their windows for night-time cooling because of midges coming in, so different approaches have to be developed.

The second aspect to their work is promote the adoption of the standard, by engaging with central government, local authorities and trying to get people on board.

Jon accepts that while it’s a great standard it’s not perfect, so the third part of their work is carrying out research on specific aspects that can be changed and improved over time.

There are different levels of Passivhaus standard

There are two main standards: Passivhaus Classic for new build and EnerPHit for refurbishment. The criteria for achieving EnerPHit are slightly less stringent because it is that much trickier to do a retrofit. Certain aspects of the building are fixed and can’t be changed, so an allowance is made that if you can’t change those things you can still get Passivhaus.

The Barrel Store – an EnerPHit Standard youth hostel. Image copyright Mac McClure

In addition there are also two new standards: Passivhaus Plus and Passivhaus Premium, which are effectively the Passivhaus Classic but with renewables. Passivhaus Plus is where the energy generated by the renewables will exceed the energy demand of the house and reach zero carbon. So the energy generated will be equal to or more than your energy used during the year.

Passivhaus Premium takes that a step further with enough renewables to create an energy positive house, so you’re generating more than you need and reclaiming money back from the grid.

PHPP can be used to calculate embodied energy

Within the planning tool they are now looking at add-ons which consider the embodied energy of the materials that you use and form part of the Passivhaus calculations. This will benefit people who are keen to use natural materials or who are just interested in understanding how much embodied energy there is. Jon stresses it is not a requirement for achieving the standard, it’s just developing the capacity to do it for those that would like it.

Find out more

Visit the Passivhaus Trust website, and learn more about their Passivhaus goes Personal campaign

Transcript

Download a transcript of the interview with Jon Bootland.

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March 4, 2020
HPH181 : Improving acoustics, noise control and soundproofing – with Jack Harvie-Clark
Jack Harvie-Clark from Apex Acoustics provides an overview of acoustics in the home. He also explains how we might go about controlling noises and soundproofing.

Photograph by Martin Neeves Photography

Interview with Jack Harvie-Clark

Jack Harvie-Clark’s background is in engineering. His work in acoustics started when working for mechanical engineers in the power generation industry. A change to Building Regulations in 2003 meant a growth in acoustics in the construction sector and Jack set up Apex Acoustics in 2006. His work is concerned with the acoustics of buildings and how noise affects people’s health.

Acoustics is about how sound travels

Sound travels through structures as vibrations, and acoustics distinguishes between two concepts: sound insulation is how you stop the sound transmitting from one room to another; sound absorption is about how quickly the sound within a room gets absorbed.

Jack explains that your ears know immediately when you’re in an enclosed space like a room, rather than outside, because you hear many reflections. Some reflection is very useful because it adds volume to your voice, but too much can be uncomfortable. Jack says that someone building a home should consider the room acoustics and how good they want it to be.

There are restrictions for sound levels between attached dwellings

Jack provides assistance for projects that need to comply with Building Regulations. People rarely call him just to make the acoustics better on their build; rather they want a competent specialist to help them meet the required standards.

Building Regulations are mostly concerned with sound insulation between attached dwellings; so much of Jack’s work is on the airborne sounds through walls and floors and impact sounds through floors between flats.

Reducing noise from neighbours may require sacrificing space

If a client has a noisy neighbour, Jack will firstly find out whether there’s a problem with the wall that can be rectified. Then he has to interpret the client’s needs, to balance noise reduction with space lost and money spent. Jack explains, “You might think maybe they want it to be 10 dB quieter or 20 dB quieter. And then we’ll suggest the sorts of things they would need to build to achieve that.”

Noise levels shouldn’t interfere with sleep or cause any annoyance

Jack often advises homebuilders on how to keep out external environmental noise in order to comply with planning conditions. By considering the building plans and measuring the noise level outside they can recommend the required type of glass for the given window sizes and any appropriate treatment for the ventilation system.

Whether or not there are planning conditions, noise levels outside might make you reluctant to open your windows. So Jack says good design should account for this.

Rules on sound insulation between rooms aren’t very demanding

Noise between internal walls is covered in a small way by Building Regulations. However, they don’t ensure any particular level of sound insulation to rooms that might be sensitive from other rooms within your house. Jack’s advice is to be sure to consider the issue of noise through floors and walls between rooms.

There are ways to reduce noise between and within rooms

In the design of a room the door will be the weak spot for sound transmission, including the gap at the bottom. Acoustic doors and an acoustic seal on the bottom will improve performance.

In a house with ventilation, noise can sometimes travel from one room to another through ducts. You can improve sound insulation by including crosstalk attenuators in the vents, which let the air through but not the sound.

Rooms designed for recording sound need to have minimal reverberation. Sound absorption can be achieved by putting carpet on the walls and similar use of soft furnishings.

Large and high spaces need more sound absorption

Rooms with higher ceilings or larger volumes are naturally more reverberant and can feel noisy and echoey. The noise level will increase dramatically when more people are in there, says Jack, especially if you have children! The more sound absorption you put in, the more comfortable it will be.

The earlier the better where acoustic advice is concerned

Jack says that acoustic consultants always get brought in too late, or only asked to look at very small bits of very big projects. He understands this, as you don’t want to build your whole house around the acoustics, but says if it were his house, he would want someone like him to look in more detail.

Some audiophile clients might require advice about how rooms respond to sound. Jack can advise on the shape of the room, and recommends that wires for the sound system are planned as part of the electrical works, to avoid more holes in the walls later.

Ventilation systems are designed to deliver and extract air, not to limit noise

As most people will have some kind of ventilation system, Jack says that attention should be paid to getting the acoustics right. This could start with a specification for noise that the builder or the designer has to achieve, so that it will get taken care of in the design. In a Passivhaus, noise levels must not exceed 25 dB(A) in living spaces and 35 dB(A) in bathrooms; noise levels that are very unlikely to annoy.

For other houses, the Building Regulations are less stringent and their legal requirement is even debatable, so they’re not being enforced. Many new houses have some form of mechanical extract, but Jack says that nobody is checking or designing the noise levels for these systems. This presents a big problem: people turn the fan down to reduce the noise, but that then means that they’re not getting enough air.

Racecourse Passivhaus project – measuring the noise levels from the MVHR

Mechanical ventilation systems need to be designed and maintained properly

Absence of design, poor procurement and bad installation can be typical of ventilation systems in current mainstream housing. According to Jack, problems include:
- houses handed over with dirty filters
- residents not knowing they’re supposed to change the filters
- residents not even knowing they have a ventilation system running
Inadequate ventilation in airtight houses can lead to health problems

Mechanical ventilation systems have become more common in new houses as a more efficient way to meet energy performance requirements. However, recent research has suggested that people prefer to control their internal environment by opening windows. Jack warns that if ventilation systems get turned off in very airtight modern houses, you can get health-related issues such as poor air quality and mould growth.

Furthermore, opening windows to provide additional ventilation is the default method to mitigate overheating. However, there is no current assessment for resultant noise so if you’re building in a noisy place, Jack advises bearing in mind both how you provide the ventilation and how you control overheating.

Award-winning double height open plan house – gaps between the timber laths provide the sound absorption with acoustic absorbent material behind

Find out more

Visit the website of Apex Acoustics

Follow Apex Acoustics on Twitter

Transcript

Download a transcript of the interview with Jack Harvie-Clark

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June 15, 2017
HPH059 : What Qualities Should an MVHR System Bring to a Low Energy Building? – with Andrew Farr from Green Building Store
Andrew Farr from Green Building Store explains what qualities mechanical ventilation with heat recovery (MVHR) should bring to a house. He also shares how to make sure you get a system that is properly designed, installed and commissioned.

Interview with Andrew Farr

Andrew Farr’s background is a mixture of mechanical engineering and building work, having done multi-material fabrication for a number of years. When Chris Herring, the founder of the Green Building Store, was developing their Mechanical Ventilation Heat Recovery Department he invited Andrew to join them as they had previously worked together on various building projects and as Andrew is a fluent German speaker.

HRV and MVHR are the Same Thing

HRV (Heat Recovery Ventilation) and MVHR (Mechanical Ventilation with Heat Recovery) refer to one and the same thing. Andrew clarifies that there are various other acronyms out there, but the broad idea is that you are ventilating and recovering the heat energy out of the ventilation air.

In a Balanced Ventilation System the Same Quantity of Air is Supplied as is Extracted

An MVHR system can be a pragmatic way of delivering very good air quality into a building. The Air Handling Unit (AHU) or the Mechanical Heat Recovery device of the MVHR system draws air into the building from the outside, filters it, takes it through a heat exchanger and supplies the clean air into the habitable spaces of the house, usually bedrooms, living rooms, studies etc. A completely separate ducting system extracts air out of the foul air rooms (toilets, bathrooms, kitchens etc.) through the other side of the same heat exchanger and exhausts it out of the building. This enables a balanced ventilation system where you are supplying exactly the same quantity of air into the building as you are extracting out of it.

MVHR systems may not be essential for every project, however, they are recommended for very airtight buildings with an airtightness of 3ach @50pascals or lower. For an MVHR system to be energy and cost effective, the airtightness of the house should be below 1ach.

Getting the Design of the MVHR System Right – Sound Thresholds and Air Flow Rates

The criteria set out for MVHR design by Building Regulations and Code for Sustainable Homes in the UK are primarily intended to create an energy efficient system. This has led to a common occurrence of noisy MVHR systems in the mainstream building industry owing to their poor design.

Andrew argues that in the case of a house, the primary criteria should be comfort and good air quality. A well designed MVHR System does not impact on the consciousness of the people who are living in that building. It should not be the first thing you notice when you walk in, nor the last thing that you notice when you’re going to sleep.

To achieve this, the main criteria of the design should be to deliver an inaudible – in everyday activity – ventilation system which generates less than 24 dBA of sound at a distance of more than one meter away from the air valve (The human threshold of hearing is somewhere around 24 to 27 dBA). With the amount of noise that the ventilation unit is going to create, the location of the MVHR unit itself is also crucial. Positioning the MVHR unit close to the kitchens and bathrooms, where people are used to hearing noise, is more suitable than locating it close to a bedroom.

Another important criteria is to deliver exactly the right amount of air into the building. Over ventilating will tend to dehumidify the air in winter and also use excess energy. While under ventilating will result in unpleasant odours and humidity remaining in the building.

The Traits of a Good MVHR Unit

Green Building Store has the franchise for selling PAUL Ventilation units (PAUL is a German company) which they believe are some of the very best on the market as they are very well manufactured. The ventilation unit itself emits a relatively low frequency which doesn’t travel as well through walls, as compared with other units. The fan has a constant volume function to continually deliver exactly the same amount of air through both sides of the heat exchanger – as set up at the time of commissioning. This is extremely important, as during the yearly cycle of a ventilation unit there are various things that happen which change the resistance to the air moving through both the intake and the exhaust ducting systems.

One of the major influences on the performance of the MVHR system are the filters on the ventilation unit. A filter on the intake prior to the heat exchanger protects the heat exchanger from the very fine debris that can be drawn into the air stream. There is also a filter on the extract prior to the heat exchanger. These filters will get dirty and provide resistance to the air-flow at different rates depending on what the pollution load is. In the case of a house being situated close to a main road, carbon particulates will block up the very fine filters resulting in the intake filter becoming dirtier sooner than the extract filter. To maintain a balance between both air-flows, the fans will increase their effort against the filter resistance in order to maintain the same volumes of air. Thus having a fan with a constant volume function is very crucial to maintaining the heat recovery efficiency of the ventilation unit.

Maintaining the Efficiency of the MVHR System

Modern ventilation units are very similar in their tested performance (the one against which they will be certified). However, there is a very real difference between the unit’s individual tested performance and that of its performance embedded in the building. The efficiency of the MVHR system depends on two important factors:
1. maintaining the balance between the two air flows, and
2. the design of the ducting associated with the MVHR system
If the resistance to the air moving through the ducting system is high, then the fans will have to exert a lot of effort in order to move the air. Consequently they will make more noise and use more energy, which in turn will cost more. The energy efficiency of the MVHR system is the efficiency of the whole system, including the ducting and everything associated with it, and not just on the efficiency of the MVHR unit alone.

Round and Rigid Ducting Works Best

The most important criteria when considering what type of ducting to use is which type of ducting will allow the air to move through most easily and offer the least resistance. Round ducting is the most efficient in this case, as it offers the best surface area to volume ratio – the surface area is smaller than the volume of air. Rigid ducting is sealed by design, not by the addition of mastics and tapes as in the case of flexible ducting and is less likely to fail.

Invest in a Well-designed MVHR System from the Get Go

The design of the ducting system should be of paramount importance in order to deliver a ducting system that you will want to live with. Ducting systems should be designed to reduce pressure loss and to attenuate the associated sound. If it is not designed properly and especially in larger houses, some air valves could end up being very noisy because they’ve got too much pressure on them, and in other rooms the air valves are not getting sufficient air out of them. A well designed system with rigid ducting and appropriate sound attenuation however will come at a premium cost. Rather than going for a cheaper poorly designed system, Andrew’s advice is to invest in a well-designed system from the outset that won’t have to be replaced after a year.

Quality of MVHR Design Currently in the UK

Up until now the industry has seen experienced commercial mechanical and electrical installers bringing their knowledge from commercial spaces into domestic MVHR installations, where the requirements for sound are not the same.

In an office, you probably won’t notice a bit of fan noise in the room because you’re busy, there are computers on or you are talking to people. But when you’re at home and you’re working on your desktop PC, the running fans and hard drive generate such a constant background noise, that when you turn it off, you realise the blissful peace that follows.

According to Andrew, an MVHR system should be giving you this blissful peace all the time despite the fact that it’s running, and if it’s not, then it’s not designed to quality. Andrew believes that in the next few years the quality of delivery of MVHR systems in the UK will improve and that more people are now beginning to understand what the appropriate criteria for MVHR design in domestic buildings is.

Find Out More

Green Building Store

Follow Andrew Farr on Twitter

Transcript

Download a transcript of the interview with Andrew Farr.

Passivhaus in Plain English

We are very excited about the fact that Elrond Burrell has launched his own blog! And we expect big things from it. Titled ‘Passivhaus in Plain English & More‘ it has already been noticed by Lloyd Alter from Treehugger.

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June 25, 2014
HPH020 : An Introduction to Ventilation in The Home – with Andy Simmonds from Simmonds Mills Architects
Andy Simmonds from Simmonds Mills Architects explains ventilation in the home, why it’s important and what the options are if you’re looking to retrofit a property for energy efficiency.

Interview with Andy Simmonds

Aged 12, Andy got his first taste of sustainable construction taking a few courses at the Centre for Alternative Technology. After attending architecture college, Andy worked with engineer Chris Wallis, son of Barnes Wallis, on numerous interesting projects including stonework, timber frame construction, repairing windmills, etc. With a love of nature and the countryside, he developed an awareness of the importance of ecology when designing and building. As well as running Simmonds Mills Architects he is part time Chief Executive of the AECB (the sustainable building association).

The AECB is a Network of People with a Common Aim of Promoting Sustainable Building

Andy gives some background about the AECB. It was set up by a builder and his wife in 1989, focussing on construction but with an awareness of ecology and the environment. It’s got a very broad mix of members and there are many resources, such as the low energy buildings database, the technical discussion forums, the annual conference, local groups and so on. With about 1500 members, this vibrant group of people share their practical experience and expertise with each other. Andy says it’s a very fast way of learning, getting to grips with things and improving your business as well.

Ventilation is Necessary to Get The Air to Breathe, But Also to Remove The Pollutants

Andy uses an example of the International Space Station to illustrate the fundamentals of ventilation. They are in a sealed unit (although not completely airtight) and need air to breathe, but also a way to flush away pollutants. These could be carbon dioxide or other gases created by equipment, etc.

Early Buildings Just Let The Wind Blow Through

Although early buildings had a lot of natural ventilation, some stone and brick buildings with solid floors were actually pretty airtight. As people found new ways of building, some constructions (from 60s, 70s and 80s, for example) were potentially leakier and more open to the elements than some of the older buildings. Draught proofing without thinking of ventilation can create quite unhealthy environments.

Over Ventilating and Under Ventilating Are The Two Extremes

A house with all its windows open could be an example of over ventilating. This might be useful to clear a fug but if it’s cold outside, a lot of heat energy from the house will be wasted during ventilation. The reverse situation could be keeping all the windows shut and draught proofing well, so any pollutants from off-gassing carpets (for example) or from cooking with gas hob, etc., cannot escape. In the heating season neither of these extremes is an effective way of ventilating a house and getting good air quality.

In a Retrofit, Mechanical Ventilation Lets You Control The Situation

Mechanical ventilation is an approach that’s becoming used much more often. Two systems worth considering at are extract-only or mechanical ventilation with heat recovery (MVHR).

Extract-only Mechanical Ventilation

This approach extracts air from wet rooms, kitchens, bathrooms and so on, and then the fresh air is drawn in through trickle vents in the windows. These are slots in the windows, which will provide a background level of fresh air coming into the house. However, with the extract ventilation system, which is basically a box with a fan in it, the air is continually pulled through at a very low level. Even with a peak load during cooking, for example, this background ventilation can cope without turning up the fan.

Incoming Air From Trickle Vents Will be at The Outdoor Temperature

Andy explains that on a cold winter’s day, you might feel that incoming air as a cold draught if you’re sitting near the window. This is why radiators have often been positioned underneath the windows, so as the cold air comes in it falls down and to some extent warms up. Andy outlines a good approach used in Scandinavia, where they put an air inlet through the wall, maybe behind the radiator, so as you pull in air from outside it comes and warms itself on the radiator and doesn’t feel like chilled air.

Mechanical Ventilation with Heat Recovery Provides Fresh Air and Keeps The Heat

Mechanical ventilation with heat recovery both extracts the air from the wet rooms (kitchens, bathrooms and so on) but also puts it back in via ducts and air terminals throughout the house. This is therefore a balanced system. Although the heat is taken out of the outgoing air and put back into the incoming air, the air itself doesn’t mix. The heat is transferred as the air crosses through a matrix, a plastic honeycomb for example. So just the heat is transferred. The warmed incoming air is fresh.

In a Low Energy Retrofit, Ventilation Air and Air Leakage are Considered Separate Issues

Andy points out that until recently ‘ventilation air’ and ‘air leakage’ (the air that finds its way in through cracks, gaps and holes in the building) were much the same thing. However, in a low energy retrofit where the objective is to make the building as airtight as possible, the issues are considered separately. Creating and designing a system specifically for ventilation is vital.

Think About Ventilation From The Outset

Your ventilation strategy will depend a lot on the building you’re hoping to retrofit. Once you have a professional assessment of how airtight you can make the building, then you can make an appropriate strategy. British houses from the 1970s and 1980s can be difficult to make airtight, whereas solid-walled properties with solid floors are often much easier. This year the AECB aims to release a retrofit guidance programme to help in this process.

Grove Cottage meets the EnerPHit standard

Larger MVHR Units Are More Efficient

Andy talks through the MVHR unit he has at Grove Cottage, which has two low voltage, low wattage fans, one for extracting air from the house and one for pulling air into the house. The largest part of the box is the heat exchanger. Andy’s unit is situated behind cupboard doors in a utility room. While it does take up a fair amount of space, Andy points out that the larger the unit, the more efficient. This is because the more space the air has to move through, the less work the fans have to do, so very small units tend to be much less efficient than Passivhaus certified units.

Mechanical Ventilation Only Makes Sense With Certain Levels of Airtightness

Andy generally only recommends mechanical ventilation with heat recovery when the air change rate for the house is less than 1.5 air changes per hour. This is because the savings must warrant the investment in electrical energy. However, for the extract-only system an air change rate of 3 would be acceptable. Part of the difficulty is in planning for the air change rate when you’re deciding what sort of ventilation system to have, because after construction you may not have achieved the level of airtightness you had hoped for!

Externally Insulating Grove Cottage Was an Easy Route

Andy explains his approach to retrofitting Grove Cottage, which is a solid brick house. As the brickwork was of no particular architectural quality – it was painted white – externally insulating was the easier option (compared to internally insulating). The starting point was to mark on the plans in a red pen where the continuous air tightness plane goes, forming a strategy of how to deal with weak points. Andy describes how he sealed the brickwork to the roof membrane (which is basically a plastic sheet) with bitumen tape, which proved to be very successful. He emphasises the importance of a clear strategy and not leaving it to the last minute.

The Right Advice Can Save You Money

It is essential to spend time early on thinking through the detail of the retrofit. This could stop all sorts of problems arising on site and prevent a poor result at the end of the job. Andy reflects on how people can be reluctant to spend money on these services, preferring to invest in the measures instead. However, this upfront thinking could actually save a lot of money.

Maintaining a Ventilation System is Not Onerous

Andy’s MVHR unit runs throughout the year and supplies fresh air which is slightly warmed by the outgoing air (although it’s not a heating system) to about 21 degrees. The system has been set so that the fans go up to a higher speed around mealtimes, etc. While you can adjust it manually on the control panel as required, most of the time no intervention is necessary. The one exception to this is when the cardboard and fleece filters need changing. A light on the unit may even indicate when to do this.

Make Sure You Have Easy Access to Your Ventilation Unit

Think carefully about where the ventilation system is located. If it’s positioned in the loft or screwed down behind a panel, this will make the simple maintenance jobs more of a pain. Equally, in a retrofitted house like Grove Cottage (that has been well-insulated and has triple glazing, etc.) and is therefore peaceful, you want to locate the ventilation units away from quiet spaces. There will be a slight hum, so keep it away from sleeping areas, for example.

Ventilation Systems Must be Properly Commissioned and Balanced

When these systems are put in, it’s very important that they are commissioned and balanced properly. There’s a number of reasons for that, but in terms of comfort, over ventilation could mean that you start to notice draughts!

Not Considering Ventilation Could be a Health Risk

Andy outlines his concerns about the choices some people are making with their homes. He gives an example of putting in a wood stove. Leaving aside the combustion products and air pollution, Andy suggests that without an external air supply vent for the wood stove, you will be pulling in cold air up through your basement, through the floorboards and cracks and gaps. This will create cold draughts, which will add to discomfort, but the whole reason the stove was installed was to be more comfortable!

MVHR Systems For Retrofit Likely to be a Small Niche

Andy believes that we need to be much more conscious of ventilation because air quality is very important. He sees mechanical ventilation with heat recovery as being a relatively small niche for retrofit, but that extract-only ventilation could have a bigger role to play.

Useful Links

Download a PDF About Retrofitting Grove Cottage

Simmonds Mills Architects

Follow Andy Simmonds on Twitter

Transcript

Download a transcript of the interview with Andy Simmonds.

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April 10, 2013