Tag: Green Building Store

HPH256 : What makes a well designed MVHR system? – with Tom Heywood

Tom Heywood from Green Building Store explains why we need mechanical ventilation with heat recovery in high performance homes and why it needs to be well designed.

Interview with Tom Heywood

Tom studied architectural technology at university and was disappointed not to have been taught anything there about efficient building. So when it came to doing his dissertation he wanted to do something different, and decided to write it on Passivhaus principles.

Tom is now the MVHR design manager at the Green Building Store.

Airtight buildings need mechanical ventilation

Natural ventilation tends to be unreliable. The supply levels might depend on how windy it is, with areas of the building in the path of the wind receiving more than elsewhere. There isn’t a way of delivering a particular amount according to the requirements of a specific area.

With the increased ability to make buildings more airtight, comes the reduction of natural ventilation through trickle vents and leaky building fabric. At this point mechanical ventilation is required to provide enough fresh air to keep CO₂ levels down and prevent dangerous build-ups of volatile organic compounds and other indoor pollutants.

With a properly commissioned MVHR and an airtight envelope, you can deliver the right amount of fresh air to different spaces, ie more for a double bedroom than a single. The MVHR unit will also extract as much heat as it can from the exhaust air which will in turn drive down the heating load.

Tom suggests that, as a rough guide, when you get to less than five air changes per hour, that’s when you should start introducing some form of mechanical ventilation, such as Mechanical Extract Ventilation (which is just extracting, not supplying or recovering any heat).

Once you get down to three air changes per hour an MVHR starts to make sense, because then there’s not as much cooling going on with natural ventilation coming in.

The MVHR supplies clean, fresh air

An MVHR unit has two fans – a supply and an extract, and a heat exchanger. Stale, moist air (such as is produced in bathrooms, kitchens and utility rooms) is extracted and goes back to the heat exchanger, which is where the fans are.

The heat is transferred to the incoming fresh air that is then supplied to the habitable rooms, such as the bedrooms and living areas. The air is also filtered, ensuring a clean, fresh air supply to the rooms.

Concentrate on getting the design right

“People often focus mainly on the specification of components, which is right, but at the same time you can spend as much money as you want on the specification of components; if it’s not designed right, they’re not going to work anyway. You’re going to have to turn it off because it will be too loud and it will be inefficient.“

Rather than someone who provides a schematic of some ducting on a piece of paper, you want someone who is going to design it around the structure to make sure when you get to site that it will work efficiently and that the air supply will actually make it all the way along the ducting route to the required rooms.

Tom says key information to ask from a designer at the design stage is for sound data and pressure loss data. Pressure loss is the resistance that the duct is providing to the airflow. If pressure loss is too high the fans will have to work harder to push the air through. And when the fans are working harder, it will increase energy consumption and the noise will be louder. Likewise, if you never change the filters, the fans will have to work harder to drive the air through.

Tom says it’s always good to oversize the unit so that it’s not running too hard.

He stresses how important it is to get the system designed early. Even as soon as the architects and engineers are doing their drawings you should be getting your plans submitted to a designer to get their opinion on unit location, duct sizing, where they need to run and what sized joists are needed to accommodate them.

There are branch and radial systems

Tom likes the branch systems (of rigid ducting) because it’s easier to get a low pressure loss with careful sizing of ducts.

“A lot of people think that the radial system saves space, but if it’s done properly, instead of having one one-hundred mill. duct to, say, a bedroom, you’d have two ninety mill. ducts. Because those ducts are carrying the same amount of air but they’re smaller, so there needs to be more of them to compensate for that.”

A radial system, also called an octopus system, has a main manifold at the start which is a box with lots of small spigots on it. The semi-rigid plastic radial ducting plugs into that and goes off to the rooms. Each room would have its own branch (or two or three), all the way from the manifold at the start to the air valve in the room. It is a good system for preventing any cross-talk sound travelling from room to room because the sound can’t make it all the way along the ducts.

Tom believes radial systems do have their uses, especially in retrofits where the rigid ducts of a branch system would just be too big to get in.

Whatever system is used, Tom stresses that the component parts should be on site when the joists are being put in place, so they can be installed as the joists are being erected.

Commissioning a system takes a lot of toing and froing!

Tom explains the method of commissioning a branch system. The unit is told what it is running at, eg 300m³ per hour on fan speed 2. If the supply to a master bedroom was to be 35m³ per hour then they would go into that bedroom and adjust the damper to allow more or less accordingly until it was at the required amount. An anemometer over the air valve measures how much air is coming out.

But as that valve is closed down it will drive the air into another air valve somewhere else. So the next room would need to be checked to see if it has been impacted and needs adjusting. Any changes to one mean going back and checking all the others again, as it’s all on one system.

Carefully consider external vent placement

Ideally you want the intake and exhaust ducts on the north elevation. That way they’ll be shaded from the sun in the peak summer heat. The system will work more efficiently because you’re bringing in cooler, shaded air.

You should also avoid placing them right next to a window or facing onto a neighbour’s garden, because they could be blowing quite hard and at audible levels.

Too close to the ground and they could drag up leaves, debris and animal hairs into the intake duct, which will block up the filters more quickly. Ideally they should be 1.5m above ground level.

If incoming smoke from neighbouring properties is a problem, then you can get active carbon filters which filter out the smell and smoke even better than the F7 pollen filters would.

The controls should rarely need using

The idea of the controls is to have them as simple as possible and generally left running on fan speed 2. They may only really need changing if you’re going to be away from the house for a long time, in which case you could drop it down to fan speed 1. And if you have a large gathering and are going to be doing lots of cooking, then hit the ‘party button’ which increases it to fan speed 3 for 45 minutes, before automatically dropping back down to fan speed 2.

Generally there would be one main controller which would usually be in the kitchen for convenience to boost it if required. Alternatively you could have the main controller somewhere else with just a remote boost switch in the kitchen. Tom doesn’t recommend having it in a bathroom as boosting the system while showering early in the morning and late at night could become audible in the bedrooms and disturb the occupants. The fan is designed anyway to remove enough moisture whilst showering without the need to boost.

Only a small amount of maintenance is required

There shouldn’t really be too much maintenance required, other than changing filters every three to six months (depending on indoor and outdoor air quality, and whether you have children and pets).

After five years it might be worth unscrewing the air valves in the bathroom and giving them a clean as they could collect dust and towel lint over time.

And depending on the MVHR unit specified, the extract fan may need very careful cleaning, preferably by someone who has done it before.

If the unit is turned off for more than two or three days there could be a risk of mould growth in the ducts. There shouldn’t however be any danger of that happening if the system is left on and each branch to each room has air flowing through it.

Find out more

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Transcript

Download a transcript of the interview with Tom Heywood.

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June 28, 2019
HPH247 : Two radical retrofits that use an internal wall insulation strategy – with Bill Butcher

Bill Butcher from Green Building Company, the construction division of Green Building Store, explains how they tackled two radical retrofit projects in West Yorkshire. Each took a ‘whole house’ fabric first approach in order to improve comfort levels and reduce the heating bills.

Having been Passivhaus pioneers in the UK with their Denby Dale project, the building team at Green Building Company has kept honing their approach.

There was Golcar new build project and Stirley Community Farm retrofit. Now we look at two of their radical retrofit projects, Cumberworth and Lower Royd, and how they embrace the same philosophy but still require bespoke solutions.

Cumberworth retrofit after the work was completed

Cumberworth radical retrofit

Initially this was part barn conversion and part 1990s extension, so there needed to be two different strategies for this project.

The existing property was hard to heat

The owners were spending £3,500 a year on LPG trying to keep this 150m2 property warm but they were still cold!

A whole house ‘fabric first’ strategy was adopted

In order to make the house more comfortable and reduce heating bills they embarked on a deep retrofit. This embraced the Passivhaus methodology of making the house draught free, increasing the levels of insulation, reducing thermal bridging and introducing mechanical ventilation with heat recovery.

The designs were modelled in the Passive House Planning Package (PHPP).

Insulating internally maintained the natural stone facade

While a lot of retrofits use external wall insulation, there are a few reasons why they didn’t. Cumberworth is at the top of the Pennines and it is exposed to a lot of moisture. The natural stone works well in these parts.

Bill continues: “To build in any other way is totally out of character for this region. And that’s what the customer wants.”

The three moisture risks had to be addressed

The moisture risk depends on the wall build-up. The ex-barn wall had two stone leaves which were filled with rubble! Being a Victorian barn it was also susceptible to rising damp because there was no damp proof course.

In this high exposure region on the Pennines rain driven damp through the porous stone was another risk.

The third moisture risk is interstitial condensation which is the condensation of internal moist air reaching the dew point where it turns to water as it meets a cold wall.

This section of the building was insulated was a product called TecTem, which is vapour open and breathes like the original building would have done.

WUFI was used to model the moisture risks

A German software package called WUFI was used to look at the moisture risks. To increase accuracy it requires a lot of information first.

Bills gives a few examples: “It takes into account where you are, the orientation of the wall – obviously a West wall up here is in more danger than the East wall because most of our rain comes from the West – the rising damp, the type of stone it is, which quarry it’s from, the mortar joints and so forth, and then obviously the insulation.”

Moisture sensors in the walls help monitor the situation and allow Bill to assess the accuracy of the program. “I might say that all of the buildings are performing fine.”

Insulating the extension was simpler

As the 1990s part of the Cumberworth project is a cavity wall construction it should be less susceptible to rain-driven damp. And it’s got a damp proof course which should deal with rising damp.

A ground source heat pump is the heat source

For a new build Passivhaus the energy demand would be so low that underfloor heating would not be appropriate. In a retrofit situation it becomes more relevant.

Also the clients had a field in front of the house which they were keen to use for a ground source heat pump.

Bill explains: “Air source and ground source heat pumps work most efficiently at delivering 35C water, hot water if you like, for your central heating system. And that suits underfloor heating more than radiators. That then informs how you do the floor. Because we don’t want to be heating up masses of concrete in a floor because of the slow cooling and heating – it doesn’t respond. “

So it’s only 75mm of heating screed on top of the insulation.

The insulation follows the line of the roof

As with most of Green Building Company’s retrofit projects they have gone for a cathedral roof. This means the insulation is within the structural timber roof and that the loft space is inside the thermal envelope.

Bill says: ” What we tend to end up doing is having a studwork parallel with our rafters. So we end up with insulation between the rafters, insulation again, and then within the studwork which is between the purlins more insulation. So, we would use more rigid bats between the rafters – a mineral wool in our case – and the studwork, and then just ordinary loft fibreglass insulation between.”

MVHR duct runs were down corridors

As this is a low energy retrofit a mechanical ventilation with heat recovery was specified. It goes without saying that these are fairly intrusive, requiring a plant room for the unit and ducting around the house.

While a new build Passivhaus might use posijoists in the intermediate floor, in a retrofit situation you have to come up with other solutions.

Bill explains that they ran the ducting down the corridor because this was an area where a lower ceiling is not so noticeable.

Vaccuum insulated panels were used around some window reveals

Green Building Store had already supplied outward-opening triple glazed windows to this property five years previously and hence they were keen to keep these!

One challenge they faced was in maintaining the continuity of insulation.

Bill explains: “If you do it [insulation] well in ninety percent of your building, for example, the ten percent becomes very vulnerable to condensation and cold bridging. So, the reveals between the very good wall insulation we were doing, in to the window frame, only allowed for a ten millimetre insulation.”

To maintain that u-value at this thickness they needed to use vacuum insulated panels, custom made to fit!

Lower Royd after retrofit work

Lower Royd radical retrofit

Much like Cumberworth, this project had two different parts. One was a virgin barn and the other was an existing farmhouse that hadn’t been touched since the 1960s. So it was ripe for a retrofit.

A connection to mains gas helped inform the project

Despite it’s fairly remote location Lower Royd had a mains gas connection.

The clients had envisaged using a ground source heat pump to heat the house, but in terms of economics, their money could be better spent on insulation!

Bill comments: “A ground source heat pump may cost you twenty-grand to get into the building as opposed to gas and the standard boiler – and we’re talking about the smallest condensing boiler, off the shelf from your local builder’s merchant – costing, installed, fifteen-hundred, two-grand. You’re better off with that saving of fifteen-grand, say, to be put into your fabric. The cheapest energy is the energy you save.“

And of course this doesn’t rule out changing the heating system to an air source or ground source heat pump further down the line.

A spray-on lime based insulation saved flattening the walls

On the Cumberworth project they used a rigid insulation called TecTem. However, they had to invest a lot of time in flattening the walls to be able to apply it properly. So they were keen to consider other alternatives at Lower Royd.

So they trialled a spray-on internal wall insulation from Italy called Diathonite Evolution.

Not only is it airtight, but it is vapour and capillary open to address any moisture issues.

And being a lime product, it naturally inhibits mould growth.

Airtightness is the most important factor for comfort

Having carried out a few deep retrofits, Bill believes that when it comes to energy and comfort, airtightness is the most important factor. Then insulation comes next.

In fact they may experiment with reducing the insulation levels a little on future projects and look at the impact.

Find out more

Visit the website of Green Building Store

Follow Green Building Store on Twitter

Follow Bill Butcher on Twitter

Transcript

Download a transcript of the interview with Bill Butcher.

Please connect with me

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April 24, 2019
HPH134 : A new build cavity wall Passivhaus – with Angie and Paul Dallas
Angie and Paul Dallas explain why they opted for a Passivhaus, and the benefits of getting involved with the build.

Interview with Angie and Paul Dallas

Angie and Paul had been looking to build a comfortable, energy efficient house that they could retire in. There was no issue with finding land as their existing house had enough land available, albeit with its own planning challenges.

It took 5 years to be granted planning permission

Angie says that the planners weren’t necessarily against their plans, but the Highways department had to consider the problem of access because of the limited number of houses that could be on their unadopted road. The house is in a conservation area so that presented its own challenges, and there were a number of trees in their garden which had preservation orders on them.

After initially having their application rejected, they won on appeal in London.

A planning consultant helped with the process but in hindsight they think they should have appointed him earlier and benefited from his expertise in areas where their architect was struggling.

The decision to build to Passivhaus standard was taken after planning permission had been granted

It was on a trip to look for triple glazed windows that Paul started chatting with one of the directors of the Green Building Store who explained the differences that Passivhaus had from normal building practices. Coming away from that meeting Paul was convinced that, even if they didn’t strive for the full Passivhaus standard, he wanted the building to at least use the principles of high design quality.

Deciding to pursue this approach meant some design changes to their original plans. The amount of glazing had to be adjusted together with the orientation, but the actual size and construction wasn’t altered.

Being involved in the construction had its benefits

It had always been important to Paul to be actively involved in the construction of his house, however once the decision had been made for Green Building Store to take on the project to Passivhaus standard he was unsure what his role would be because his knowledge of the area was limited.

Whether Paul would be able to assist with the labouring was a decision for the building team, and Paul was careful to take his time and show that he could muck in and not be a pushy owner. Eventually he was invited to join the team and he relished learning on the job and taking their instruction.

One of the greatest challenges that Paul found was working on the site throughout the British winter. If the roof could have gone on during the summer months it would have been a much easier build.

A key benefit of Paul being on site was that if a problem arose or a decision needed making, he understood what was going on and could make the choice straightaway.

Paul found the camaraderie of being on site extremely enjoyable and believes the pride in the house afterwards far outweighs the efforts of doing it.

“And to be honest I don’t think I’ve ever laughed as much during a job ever. I thought it was great fun.”

The comfort of the house has lived up to their expectations

The temperature of the house remains fairly constant and the mechanical ventilation heat recovery system means that the air quality is good everywhere. Angie also notes that it seems to stay cleaner and that since having pollen filters put in she has also seen health benefits compared with their old house.

Take time to appoint your design team

Their first architect, although designing a great scheme, didn’t have the time to take it from there. Paul and Angie wish they had taken time to research, interview and appoint a replacement architect but instead they appointed someone on recommendation, who professed to be an architect but actually wasn’t. He claimed that the original plans couldn’t be built, but it took Angie and Paul several months (and £6,000) to have the courage to dismiss him and get somebody else. Thankfully the next architect they appointed confirmed that they would be able to build to their original plans. Paul emphasises the importance of researching specialists and finding someone that you feel comfortable with.

“If you’re building a Passivhaus you want somebody with experience of Passivhaus or at least is willing to learn and look at the differences between that and a normal house and take those on board.”

Deciding to use the services of an interior designer they were fortunate to have them involved at an early stage to assist with the layout of the interior and pick up on areas, such as space for hanging curtains, which would have been difficult to rectify after the construction work had been completed.

Green Building Store provided them with knowledgeable and skilled builders who Angie and Paul both say were a pleasure to work with. They used their own electrician and were also happy with the services of the plumber.

Paul stresses that it’s important to take your time at the stage of getting your team together. They were thankful that their whole team worked well together and that they enjoyed working with them.

“And it’s people you can work with as well. It’s not just a good track record but if you’re not comfortable with those people then it’s going to be a problem down the line.”

Find out more

Visit the website of Green Building Store

Check out the shortlist for the 2016 UK Passivhaus Awards

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June 22, 2016
HPH103 : Is Building a Passivhaus Expensive? – with Geoff and Kate Tunstall
Geoff and Kate Tunstall explain how they were able to create a fantastic Passivhaus in Denby Dale with a budget of around £150,000.

Interview with Geoff and Kate Tunstall

When Geoff and Kate decided to self-build and downsize for their retirement, their first idea was to build a dormer bungalow with a conservatory. Following a conversation with Green Building Store, they were encouraged to explore Passivhaus as an option.

Back in 2008 there weren’t any examples of Passivhaus in the UK that they could visit, so they travelled to Austria. After visiting two properties there which had temperatures of 20/21 degrees, despite outside temperatures of -4 degrees, they made the decision that if they could afford it, this was how they wanted to build.

Paying a Ransom Strip Demand Used Up Their Contingency Budget

The plot for their build was at the bottom of the garden of their existing house. Unfortunately a builder had bought the plot of land behind this and, based on the value of the plot, demanded £30,000 for a six inch ransom strip that they needed to provide them with access from their building to the road behind. After a year of fighting this, and the builder realising that the money was their contingency so it was this or nothing, they eventually agreed to pay a total of £18,000, which used up their contingency before the build had even started.

During that year however, the designs for the house were all researched and finalised to the extent that as soon as the ransom strip issue had been resolved they were able to progress straight away with the build.

Making a 3D Model Helped Their Understanding of the Scale and Spaces

Originally they wanted to build a bungalow but the plot size didn’t make this feasible. Kate found it useful to create a 3D model out of balsa wood to get a better idea of how well furnishings would fit and how comfortable the spaces were likely to feel. They also found using the model was a helpful way of explaining their ideas to the building team throughout the process.

An Important Feature was to Have Light and Warmth Throughout the Fabric of the House

Particularly because their last property was a dark and draughty cottage, Geoff and Kate were keen to build a warm and contemporary home with lots of natural light. They had to abandon their original conservatory idea after running it through PHPP, but instead they remodelled it to feature a two-storey solar space which beams the light throughout the house.

Using Kate’s 3D model they realised that one of the bedroom windows seemed uncomfortably small. Again using PHPP the design could be changed to accommodate a larger window by adding higher performance floor insulation to compensate.

Keeping Within Budget was a Collaborative Process

From the outset, everyone knew the budget was only around £140,000. With regular meetings between themselves and the design team throughout the design process and the build, they were able to keep on top of what was happening, when, and how much things were going to cost.

Living on site was a help because they were able to spot any little details that needed changing before the build progressed too far and became too expensive to amend.

Geoff explains that on a Passivhaus there are certain non-negotiable things that need to be budgeted for and for which there are no short cuts, such as triple glazing and the ducting for the MVHR. Where they saved money was by spending time researching things like inexpensive lighting and kitchen units.

“But it was a good discipline for the Green Building Store and ourselves to actually work to a figure, a limited figure, because it proves that Passivhauses can be built to a reasonable budget. And the budget for our house isn’t a lot for what we’ve got.”

The Build Wasn’t Without its Challenges!

One of the biggest challenges they faced was building throughout one of the coldest winters in a generation. It was too cold to use the paint they had planned, mould spores started showing on the clay plaster and they had to put up a screen so they could continue working in the howling gales and snow.

A further challenge was the corner windows of the solar space, both from a Passivhaus point of view but also a structural one. They needed to make sure there wouldn’t be too much solar gain, and also ensure that the structural support would be inside the thermal envelope.

The House Exceeds Expectations

Geoff and Kate have been living in their house for around five years. They wanted a house that could be kept clean easily, that would provide warmth when needed, that would be energy efficient and not amass big fuel bills during their retirement. It has achieved all of these and something which Kate hadn’t focussed on before they started was how important it is to have a healthy house. She describes it as being a calm, tranquil and healthy place which will benefit them in their old age!

One of the Passivhaus buildings they visited in Austria had some underfloor heating so Geoff and Kate assumed they should put it in their kitchen and bathroom. In hindsight they didn’t need to as it’s actually never been used.

Geoff is adamant that anyone embarking on a self-build project should go and visit a Passivhaus. Once they’ve experienced it he’s quite sure that’s how they will then go on to build. He says that even if the initial outlay is a little more expensive, it will pay for itself within three or four years, and be future proofed against rising fuel prices.

Find Out More

Find out more about Denby Dale in the Green Building Store blog.

Transcript

Download a transcript of the interview with Geoff and Kate Tunstall.

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October 13, 2015
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.

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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
HPH014 : Low Energy Barn Conversions – with Bill Butcher from Green Building Store
Bill Butcher from Green Building Store shares his approach to creating a low energy barn conversion by building a box within a box. Stirley Community Farm will meet the EnerPHit standard.

Interview with Bill Butcher

Bill started out, aged 16, at the tech college in Exeter doing an HNC in building. From there he pursued the quantity surveying route, before becoming a builder. He has always had an interest in the environment and founded Green Building Store with two other colleagues in 1995. Green Building Store focusses on supplying the components and services around low energy and sustainable construction.

In 2007 They Realised The Potential of Passivhaus

Bill tells the story of how his business partner, Chris Herring, had been over to Bregenz for the Passivhaus International Conference and had come back convinced that their business should go down this route.

An Opportunity Presented Itself in Denby Dale

When Geoff and Kate Tunstall approached the Green Building Store about constructing a ‘green house’, which in their eyes was going to be a dormer bungalow with a low of renewables, it presented the perfect opportunity to construct their new home to Passivhaus standard. In 2009, they started building. You can read a comprehensive blog on the whole project.

To Keep The Price Reasonable, Builders Will Stay Within Their Comfort Zones

As Green Building Store had built with masonry and cavity wall in the past, this was the approach taken at Denby Dale. This meant that all the materials were available locally in Huddersfield, with the exception of triple-glazed windows with insulated frames, mechanical ventilation heat recovery (MVHR), and various tapes and membranes (all of which are now handily stocked by the Green Building Store!).

Passivhaus is Not Restricted to a Single Construction Methodology

Bill talks about other examples including John Williamson from JPW Construction building with timber frame and Bere Architects using a kit home imported from Austria for the Camden House.

Passivhaus is as Much About Comfort as Anything

Benefits of a fabric first approach not only include the performance of the building, but you also create an environment that is tranquil and comfortable. Even when it is -10°C outside there’ll be no internal surfaces less than 17°C. This drastically reduces convection. Bill explains with an analogy of standing in front of a fire on Bonfire Night, where you’re burning on the front side but freezing on your back! In a Passivhaus where you don’t have that convection of cold air falling you can keep the thermostat down to 18°C, whereas in a conventional build you might have to adjust the thermostat to 23°C to counteract that feeling.

Stirley Community Farm

These were three bankrupt dairy farms on the outskirts of Huddersfield (in quite an exposed location) that were owned by Kirklees Council. Yorkshire Wildlife Trust took them over, and recognising that wildlife and farming are intertwined, they are now running the farms quite traditionally with minimal fertilisers. In addition to rearing a herd of beef cattle, they are growing food, and also showing how this can then be prepared and cooked inside the new education centre.

The Building Was Structurally Unsound

After getting in the structural engineers, the existing buildings were found to be unstable. Therefore a lot of work had to be carried out on making the building stand up by underpinning the foundations. The foundations themselves were very minimal.

An artist’s impression of the new Stirley Community Farm, courtesy of Eco Arc

Insulation is Put Under The Floor

Bill explains the process of excavating down in order to insulate underneath the floor (200mm of polyurethane underneath a 6-inch concrete slab with the hard core). Alternate 1m by 1m concrete pads are also placed under the existing wall to stabilise it.

Creating a Box Within a Box

As a barn is just an open space, the pioneering approach on which they settled was to construct a timber frame building within the existing masonry. At the same time the existing masonry would be stabilised with the timber frame, and the envelope would be insulated and made airtight. The two structures will then be separated by a nominal cavity. Bill goes into more detail.

A Building With No Windows or Doors Would Be More Energy Efficient!

Bill explains to Ben that you can build a wall to a U value of 0.1 quite easily (which is currently 3 times better than building regulations in the UK). However when it comes to the windows and doors, even using the best components, you might get to a U value of 0.8. That’s 8 times worse than the wall next to it. Therefore how that’s installed in the wall is crucial. The frame must be wrapped with insulation from the walls or so that it’s continuing the insulation around the frames. They are a thermal bridge in their own right.

Thermal Performance as Important as Keeping The Rain Out

Bill believes we have to look at the concept right from the beginning in a different manner where thermal performance is as important as keeping the rain out. He stresses that you wouldn’t want steel balconies cantilevering out of your buildings because steel is one of the worst conductors of heat.

Construction Industry Has an Opportunity to Raise its Game

Buildings of this quality demand attention to detail, and skill and teamwork are more important than ever. This is not the last bastion of a school leaver. It is also an opportunity for the whole team, including the client, to gain a better understanding of what the project is about.

Putting Tenders Out to 10 Builders Will Never Lead to High Performance

Bill suggests a procurement method in which we put out tenders to 5 or 10 builders will never lead to high performance, because the builder hasn’t any ownership over the project. It’s far better to get a builder in partnership during the design stages so they can have their input into the design.

Sources of Moisture

The problem with moisture in buildings can come from several different angles. One is groundwater, which is why people use damp proof courses and so on, and tanking when below ground. There’s also moisture from wind-driven rain through a wall, through masonry because stone brick is porous and it has to be dealt with in one way or another.

A Well-Ventilated Cavity Will Avoid Solar Driven Moisture

Solar driven moisture is less well known. It can happen in the summertime and is a danger where you’ve got a radical construction. Once you’ve extremely well insulated internally, the external masonry wall will be colder and it becomes more like a garden wall (lime based mortars breathe, allowing moisture both in and out of the wall).

When you’ve put internal insulation in with a complete air tightness layer, what can happen in the summer when you have a heavy rainstorm is that the wall gets very wet. After that the sun comes out and the heat from the sun drives the moisture inwards. If you haven’t got a well ventilated cavity, that moisture could potentially soak the timber frame inside. There was an example in Belgium where this damage occurred because there was not enough attention to detail during the planning stages.

WUFI

A software program called WUFI allows you work out the minimum air change rate that should be acceptable (in the cavity in this case) in order for moisture to be taken away as vapour. The calculation for this project shows that it is only if the cavity goes below 8 air changes per hour that there is a danger that moisture could start building up in timber frame. In other words, it can be designed out.

Not Practical to Have Every Building With Moisture Sensors

Stirley Farm will have moisture sensors but Bill suggests that it would be impractical to do it on every new building.

Green Building Store’s Free Resources
- Denby Dale Passivhaus (completed blog)
- Stirley Community Farm (ongoing blog)
Transcript

Download a transcript of the interview with Bill Butcher.

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3 Videos on Energy-Efficient Homes

Ben has been filming with former podcast guest Martin Evans from the Malthouse Consultancy. There’ll be 3 informative videos coming soon.

Google+ Communities

If you’re reluctant to take on more social media, find out why Google+ is important. We have set up 3 communities – Eco Homes, Energy-Efficient Homes and Passivhaus – which we’d love you to join.

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January 29, 2013