Tag: Building Performance Evaluation

HPH308 : Testing the thermal performance of a house – with Tom Fenton from Veritherm

Tom Fenton from Veritherm explains how to test the thermal performance of a home, what this data can reveal and how it can then be used.

Interview with Tom Fenton

Tom Fenton began his career working in the family’s design consultancy that focused on the envelopes and facades of commercial and industrial buildings. From this unique vantage point they were able to see the pitfalls in the design and construction process that impact on the performance of the building fabric, which led them to develop Veritherm’s test of thermal performance.

Thermal performance measurement should be affordable and scalable

In general, the construction industry’s understanding of thermal performance has been based on theoretical design assumptions and desktop modelling. Academic approaches to measuring thermal performance are lengthy, costly and complex, and only really used at a research level. Veritherm’s aim was to develop a solution that would be simple to use while being affordable and quick enough that it could be implemented at scale into a range of projects.

Heat will find the weakest point

Even in properties with high-performing materials and quality specifications like a Passivhaus, if the build quality or detailing isn’t quite right, then it will be sub-standard compared to its design predictions. Heat is like water and will always find the weakest point, which is where the energy will be lost.

A phased testing approach can be beneficial

The assumption is generally that testing would be carried out on completion of a new build home, but Tom says that actually, the retrofit market is accounting for around half of their business. Using a phased approach, an initial test will give a baseline measurement of the existing home and how it is performing. That information can be fed back to the design team to consider the most suitable fabric upgrades for the property, rather than relying on design assumptions. Further testing can then be used at other stages as new elements are introduced, to quantify the difference that eg, replacement windows or external wall insulation have made. A final test can determine whether the project goals have been achieved.

A phased approach can also be useful on a new build, with measurements being taken before linings are installed. Together with further diagnostics, this can help to identify the possibility of any errors in the external envelope and allow them to be rectified before being sealed up.

There are three phases to a Veritherm test

The Veritherm test is carried out overnight and is broken down into three stages.

The first step is to retrieve relevant design information for the property, such as its thermal specification and basic dimensional information, which is entered onto the Veritherm dashboard.

Also in this preparation stage, the equipment is deployed in the property which includes temperature sensors in each of the habitable rooms, along with fans and heaters.

During the measurement stage, the Veritherm platform activates the equipment remotely and a controlled and measured heat load is applied to the property, using the fans to ensure temperatures are rising uniformly throughout. It is heated for the first half of the night before then being left to cool passively for the remainder of the time. All of the heat load and temperature data is sent throughout the night to the cloud-based software platform, which uses its integrated algorithms to generate the results.

On completion of the test the following morning the results are instantly available in a full report. This quantifies the rate of energy loss from a building per degree of temperature difference, expressed in units of watts per kelvin. The report also breaks down the data from the individual temperature loggers to give a better understanding of what is happening, and where, in the building.

A Veritherm test is quite often carried out alongside other diagnostic tools, such as an airtightness test, so that you can understand what losses are attributable to air infiltration through gaps, and what losses are attributable to the fabric.

Thermal imaging can pinpoint problems

Veritherm’s test quantifies the rate of heat transfer, giving the average U-value for the building as a whole. However, if the test flags up any areas of concern, further diagnostics such as thermal imaging could be carried out to pinpoint anomalies.

The performance gap can be quantified

The Veritherm report compares the ‘measured’ data from the test, with the ‘designed’ data that was entered into the system in the preparation stage. This gives you a quantification of what that difference is between the designed and as-built performance, ie the performance gap. That information can for example be fed back to the architect to help them improve their design processes. If there’s a 400% gap in performance it might mean that the self-builder needs to look at considerably improving their envelope, but if it’s only 5% then that’s not going to make a significant difference on their fuel bills post-completion.

The data that is produced can also be fed back into energy modelling software to communicate to clients what the longer-term impact will be on emissions and heating demand. This is particularly useful when it comes to designing heating systems to be correctly sized for the property. A new build property that doesn’t perform to its designed intent, means that the heating system may not be suitable or efficient. And conversely, many existing buildings have heating systems that are oversized in order to compensate for the unknown, which means there are many capital and operational savings to be had by getting it right and installing the correct system based on the particular property’s requirements.

Also in the Veritherm report is a thermal efficiency rating, which is where the rate of energy loss is divided by the usable floor area. Using this traffic light style rating means you can compare for example a 5 bedroom house with a 1 bedroom bungalow, and identify where your property sits on that scale.

The ‘designed’ and ‘measured’ data almost never tally!

With the experience of carrying out these tests comes the knowledge that there is nearly always a difference between the designed and measured values. In general, new builds will tend to underperform against their designs. Existing buildings that use EPCs or reduced data standard assessment procedure (rdSAP) will pluck thermal values from standardised tables based on the building’s construction type and year of construction, to come up with basic thermal specifications for that property. Once measured, these properties will often outperform what was expected of them and the client can actually have a cost-saving on their planned improvement works. With upgrades being rolled out to millions of homes across the UK, Tom says that there is serious value and savings to be had by using a measured approach to retrofit.

The goal is to have thermal performance testing in legislation

Even testing identical properties on a development can throw up variable results and identify pitfalls in the construction process, in much the same way as when air tests were first introduced, showing why it’s so important for testing to be carried out.

Tom is keen therefore for thermal performance testing to be included in Part L of the Building Regulations, and with the introduction of the Future Homes Standard which has a requirement for photographic evidence of insulation, he suggests that using a measured approach is actually of far greater value and a better way forward.

Find out more

Visit the website of Veritherm UK

Follow Veritherm on Twitter

Follow Veritherm on Instagram

Find out more about Veritherm’s thermal performance test

Transcript

Download a transcript of the interview with Tom Fenton.

Building Performance Interactive

Ben Adam-Smith is taking part in a new series for Passive House Accelerator which aims to share lessons and best practice from low energy projects across the UK and Ireland. Hugh Whiriskey of Partel has devised the hour long format and is hosting alongside Ben and Mike Jacob of KISS House. The Building Performance Interactive is held monthly and everyone is welcome.

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November 4, 2021
HPH277 : The importance of building performance evaluation – with Professor Fionn Stevenson

Professor Fionn Stevenson explains why building performance monitoring and post-occupancy evaluation should be mandatory on new homes.

Interview with Fionn Stevenson

Having spent eight years in practice as a chartered architect, Fionn was finding that the housing wasn’t performing as well as she had designed it to do. This led to her interest in building performance and eventually she became a researcher and academic in the subject, as Professor at University of Sheffield – School of Architecture. She has now been involved in building performance for over 20 years.

Six simple action points in a light touch review

A light touch post-occupancy evaluation involves going into a home to check how well it’s performing against its design intentions.

The first step is for the expert to spend around half a day studying the original drawings and specifications for the project, as these are what will be checked against during a tour of the home. They provide the baseline of what is supposed to have been done.

This is followed by a half day tour of the home with the occupants, plus the designer and contractor. The occupants will explain about living in the house for the evaluator to see what’s going on and check that against the original design intentions.

The occupants will also complete a simple two-page survey which provides a lot of further information.

A half day thermographic imaging survey is then carried out to see how the fabric of the building is really working.

Next is looking at how the building is performing in terms of energy used and water consumption. This can be done at the simplest level of looking at utility bills, or recorded through smart metres.

And finally, there will be a spot check where, during the half day tour, the evaluator will use a hand-held 4-in-1 metre to check on the room temperatures, plus levels of light, sound and humidity.

UK housing doesn’t perform as it should

Given the nature of unique sites and being very contextual, Fionn says UK housing does not perform as it is expected to do. She says that research shows that on average new homes in the UK use at least twice the amount of energy they’re supposed to use. That can be down to the design but also the quality of construction.

Another concern is the indoor air quality results, with high levels of carbon dioxide build-up, low-level toxins from off-gassing of new materials, and air fresheners which are supposed to make the air quality better but can actually make it worse. New homes need to have good ventilation strategies, but often they have been poorly designed, constructed or commissioned.

Building evaluation should be mandatory

As well as post-occupancy evaluation, there can also be building performance evaluation. This involves starting the evaluation process from as early as developing the brief, and right through the complete cycle of the project.

Fionn says it’s amazing that there is no mandatory requirement to carry out post-occupancy or building performance evaluations, and that is something she is lobbying to get changed. The RIBA is now producing new guidance and in the future is looking to mandate its practitioners to make it a part of their service. But there’s no mandatory requirement to carry it out as currently it requires consent from the client.

“If it was mandatory there would be an automatic performance feedback loop because people would have to automatically report what is actually going on in the housing. That reporting would then go into databases and everyone could see what was going on.”

Fionn has worked with a number of volume housebuilders, and says that although they carry out extensive customer satisfaction surveys to see how well their buildings are performing, they are not asking the right questions. They don’t drill down into why the house is or isn’t working for them, and this is because they haven’t had to be accountable for the performance in mandatory terms.

“What they’re interested in is selling the home. They’re not as interested in how well the home is performing once they’ve sold it. They just want to make sure the customer is happy, they want to make sure that they get their NHBC scorecard with the highest number of stars, and that’s all about reputation. And their reputation rests on the initial customer satisfaction survey, not the overall performance of their homes.”

There needs to be databases of results

Fionn mentions the Building Performance Network as being a group of organisations and experts who are spearheading the drive to make building performance evaluation and post-occupancy evaluation routine. They are collecting data and setting up a UK database.

And Fionn says that this is what needs to be happening. She says there should be two databases: one a private one where people can access their own data, and the other a public one with anonymised results to give a national picture of how everyone is doing and enable people to benchmark and compare against others.

A culture shift is required

Fionn explains that at the moment the process for architects and clients is “let’s design a home.” In fact what it should be, is “let’s design and evaluate the performance of a home.” The majority of architects don’t go back to really evaluate how well their buildings are performing. Fionn says the key message she is trying to get across in her book is that this should be routine.

Be energy sufficient, not just energy efficient

Fionn is in the process of starting her own self build project. But rather than design it herself, as she has been out of practice working as an academic for so long now, she is using the networks she has built up to find the best team to deliver her project.

She has prepared her brief and will be looking for people that will champion her wants, needs and follow the details of the brief throughout.

A fabric first approach will be used to make sure the house is properly insulated, airtight and ventilated. With that is the importance of getting the size of the home right. She explains that it’s not enough just to be energy efficient, but we need to think about whether we are being energy sufficient. In other words, having the house optimally sized and not any larger than it needs to be.

“There’s a bit of a misnomer about zero-carbon because of course you can make your home automatically zero-carbon if you go onto a renewable energy supplier. But that doesn’t mean your home is actually being very good for the environment. We’ve got very large self-built homes that are claiming to be exceptionally low energy or carbon zero but actually the embodied energy, the amount of materials that are being used in them is huge.”

Keep the buildings simple

Fionn says that there is a temptation with self build to have the house of your dreams and put in a lot of unnecessary kit. Her own research has found that often in homes that were using heat pumps together with PV and solar-thermal, often they were contradicting each other as they weren’t designed to work together. Also, solar renewable energy installations hadn’t been installed correctly or on the wrong orientation, meaning they weren’t performing as they had been designed to do.

Another thing the post-occupancy evaluations have thrown up, is how important it is for any mechanical ventilation system to be well designed, brilliantly constructed and have the minimum duct runs possible. It must have vents perfectly positioned and be ergonomically designed in a way that is accessible for the occupant to interact with it.

There isn’t enough data to help self-builders with decision-making

Fionn explains that we’re still flying blind with a lot of modern building systems as there just isn’t enough data from post-occupancy evaluations to see how well they perform. Being laboratory tested can only do so much.

“Who is going out there, outside of the laboratories, into the homes with the thermal imaging camera, doing the walkaround, seeing the little bits of mould that are appearing in the corners? If we move on to service systems, we’ve got loads of mechanical ventilation heat recovery systems. But who went out there and actually asked the occupants whether they can use them? That’s been the issue, that it is difficult for self-builders to choose systems and know that those systems have been not just rigorously tested in the laboratory where the products are developed but that they’d been systematically tested around the country in every city, in every town, as a routine part of post-occupancy evaluation which is then fed back into the industry. This is exactly why the housing industry performs so badly.”

An investment worth making

Fionn stresses that you should be alert throughout the whole design, build and occupancy process, but there are key points where attention particularly should be paid.

The first is at the outset of the project, where post-occupancy evaluation is included in the brief, and budget allocated for it. Typically it might cost around £5,000 for a light touch post-occupancy evaluation, but it could be saving you tens of thousands in identifying hidden risks and defects.

Other benefits are that you’re also future-proofing for climate changes, ensuring there won’t be overheating as UK summers continue to get hotter, and also improving health issues with better air quality.

The second critical stage is the commissioning of the home. When the services, heating and ventilation systems are commissioned is a crucial time for there to be an independent evaluator checking whether they have been set up properly, to avoid a lot of problems down the line.

Find out more

Follow Fionn Stevenson on Twitter

Check out Fionn’s book:

Transcript

Download a transcript of the interview with Fionn Stevenson.

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February 12, 2020
HPH128 : Closing the performance gap – with Helen Brown from Encraft
Helen Brown from Encraft explains the ‘performance gap’ – what it is, why it happens and how we can avoid it on our projects.

Interview with Helen Brown

Helen has been working at Encraft for nearly 9 years and is currently head of their building physics department. When she started she was interested in renewable energy and micro generation, but she gradually became drawn to low energy construction in new build housing, with Passivhaus being a particular focus.

Encraft are renowned for their research projects

Previous research projects have included:

Warwick Wind Trials – Funded by Pilkington Energy Efficiency Trust and BRE Trust, this looked at the performance of building-mounted micro wind turbines.

Retrofit for the Future – The programme announced by Technology Strategy Board (now Innovate UK) aimed to achieve deep cuts in carbon emissions by retrofitting existing homes.

OWLs – A project using Beattie Passive TCosy system to refurbish a block of 6 flats.

I-LIFE – A current project funded by Innovate UK, to develop an insurance product that would guarantee a home’s energy performance.

A possible future research project, likely to take several years in order to obtain a meaningful and large enough dataset, would be looking at the indoor air quality in homes by considering the effectiveness of different ventilation systems.

‘Performance gap’ is the difference in actual energy consumption compared to the designed intent

The range can be from as little as zero gap, which means the house is performing exactly as intended, to as much as 200% where the house is actually consuming double the energy that was expected.

The main performance gap causes:

As identified by Zero Carbon Hub –
- Quality of workmanship on site
- Quality in the design stages
- Lack of skills, knowledge or understanding either in the design stages or during construction
- Using the wrong materials and products, not following the specification or not having a clear enough specification from the outset
Effective monitoring is required to assess how well a building is performing

Most new buildings aren’t properly monitored to see how well they’re performing, so clients aren’t well informed about how the in-use performance relates back to the design stage targets.

If monitoring is to be performed effectively, it requires someone to review the data and feed the results back to the occupants, builders and designers.

In the case of Encraft’s insurance product idea which sets out to guarantee a home’s energy performance, monitoring would be required in order to verify that the performance targets are being met.

An airtightness test is an easy way to see if a building is performing according to its design intentions

All buildings will have an airtightness target, though not all homes are required to have an airtightness test. In large developments it may be only 10% of them that are tested.

Encraft have found that there is a correlation between airtightness and construction type. In situ concrete is an inherently airtight construction method which seems to consistently meet or exceed its airtightness targets, whereas masonry construction is much more likely to fail the airtightness targets that have been set.

In situ U-value measurements can be compared to performance targets

Testing whether insulation has been well installed can be achieved by measuring the temperature gradient across a wall and calculating its U-value.

Encraft have been looking at this data from the Building Performance Evaluation programme which shows a clear performance gap between the target U-value and the actual measured U-value in the houses that it studied. Their data included Passivhaus and non-Passivhaus developments and found that the performance gap within the Passivhaus subset was much smaller than the performance gap measured across the wider dataset.

‘People factor’ affects the correlation between airtightness and total energy consumption

Encraft have found that when they’ve tried to map airtightness with total energy consumption they’ve found no correlation, which seems like it should be wrong because in terms of building physics there should be a direct correlation.

The reason why there is no correlation is purely down to the building occupants, which drives the variation from home to home in terms of energy use. Encraft would like to be able to somehow normalise the data to eliminate the affects of occupancy, because the people factor is the most complex and difficult to account for, while having the biggest influence on total energy consumption.

Transcript

Download the transcript of the interview with Helen Brown.

Find out more

Visit the website of Encraft

Follow Helen Brown on Twitter

The Hub Update

Something new that we’re going to be offering our members is a quarterly progress call. This will be a private conference call for any members that want to be involved, to provide encouragement, share and resolve challenges, and perhaps even bring in a guest or two to give us some extra inspiration.

The progress call will join our existing offerings, which include our video case study of Long Barrow, monthly modules – the latest of which is about sweat equity – and access to our Facebook group.

The price is just £99 for the year and this is a lock-in price for as long as you stay a member. Find out more.

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May 11, 2016