Building some Rising Stars in the housing sector

Big Things are happening in Purrmetrix land – we are a regional winner of Tech Nation’s Rising Star programme.

This is incredibly exciting for two reasons:

1) Rising Star is a well respected programme with a long track record of identifying exciting seed businesses, but *also*,

2) It underlines that the business of making housing net zero makes commercial sense, even to those outside the sector.

So if you’re in the housing sustainability sector – especially if you’re working with data – let’s talk! There’s so much to do if we’re going to build the solutions that housing is going to need to deliver retrofit at scale, and the opportunities are definitely there: Tech Nation think so 😉

Team Purr looking forward to being Rising Stars

Monitoring for retrofit at London Borough of Havering

If you’re delivering retrofit, how do you understand which homes are going to benefit the most and what should be done? Measuring the true heat loss of a home is an important benchmark for defining potential savings and designing the upgrades needed. At the same time, project managers, designers and contractors have questions about which homes show the worst internal conditions, which have high levels of condensation and where ventilation may be an issue.

Flexible monitoring and heat loss testing

Based on our years of experience in delivering measurement of building performance, Purrmetrix have built a monitoring solution that can be deployed quickly and flexibly in housing to deliver measurements after a few weeks of testing. Warmscore is a toolset of sensors and web based software that can be installed in any house in 30 minutes to give measurements of:

–  heatloss

– condensation risk profile

– ventilation rate (air changes)

– comfort level

Testing combines energy and environmental data from each home, taken either from a smart meter or meter reads. Results are available after less than a month of monitoring, or the toolset can be left in the home for longer term tests to understand how performance varies across the season and with different resident behaviour. 

Measuring building performance in retrofit projects

For many retrofit projects testing is helpful at multiple stages – including stock selection, site survey and after delivery. Portable testing kits reduce cost per test and give you more flexibility in your monitoring plans; if one home has to be excluded from the test sample it is straightforward to retrieve the kit and deploy it elsewhere.

Our project with London Borough of Havering in the first wave of SHDF is a great example of how this works

Delivering measurements for London Borough of Havering

London Borough of Havering have been testing with Purrmetrix during the first wave of SHDF, to augment their EPC data and survey work with additional data on the archetypes. Funding was confirmed late in the heating season, being able to quickly deploy test systems was useful.

Working with LBH’s contractors, Purrmetrix provided heat loss for 10% of the homes to be upgraded, with measurements of ventilation rate and condensation risk for 20% of stock. The data identified homes with high heat loss and ventilation rates and gave confidence for models being used to design upgrades. Post works it will be used to verify improvements and confirm that tenants have more affordable comfort.

“The data provided by Warmscore is really helpful in developing our understanding of what is happening in our homes. We’re looking forward to getting additional measurements post works to confirm all is working correctly’” Robert Ditsell, Project Manager

Support for your monitoring

Warmscore’s measurement toolkit is valuable in any situation where you need better understanding of your building stock; building the business case for retrofit, identifying stock for grant applications, even finding causes of disrepair.

We can help you figure out what monitoring is needed for each project and how you can go about collecting the data you need. Contact us if you would like to learn how we might support your projects – there’s always a human on the end of this form, we promise!

Monitoring for retrofit – flexibility is key

Across the country, a hum of data crunching and form filling is growing, as applications for SHDF and HUG 2 are maturing. Many of these applications are including an allowance for digitalisation, and if that is you we wanted to share a few thoughts on retrofit monitoring as an important piece of the digitalisation strategy.

Why does retrofit monitoring matter?

Accurate performance measurement using real data means you get better targeting of retrofit measures on homes that need it, quality assurance on work done, and an understanding of how tenants are reacting to new systems in their homes. It adds depth and insight to EPC data revealing which homes are losing the most heat, where condensation problems are acute, and where tenants are unacceptably cold (or hot) in their homes.

When and where should you monitor in a retrofit project?

From talking to landlords it seems that data gathering is particularly relevant at three points in retrofit projects. 

Firstly when as you finalise stock selection and start to move into detailed design for each archetype. At this stage there are often question marks over which homes should be provided, whether EPC data really reflects the state of the home, and what measures should be applied.

Monitoring and measurement can help confirm that the right homes are in the pipeline, spot issues – like condensation – that should be addressed as part of the project, and anchor models used to calculate improvements in performance with real data.

Next at the snagging stage when the works are completed. Measurement will give an early indication of how successful these have been and how close to the modelled outcomes the home might get. It allows for quick mitigation if problems are persisting.

And finally as tenants adapt to upgraded homes and new heating systems. Monitoring the performance of the home in the longer term helps understand how householders adapt to new systems and supports them in making sure that heating and ventilation can be optimised to suit their lifestyles.

Rapid results are important in complex retrofit projects so landlords are often trying to understand performance at an archetype level. However, even within archetypes issues such as heat loss can vary quite widely, so testing a number of home in each archetype is useful to give an understanding of the potential range of performance. Adding data collection tools to the survey stage provides a convenient way to get around a wide range of homes and quickly build up a picture of the true performance of each archetype.

How can you capture this data?

These situations call for monitoring that can be deployed quickly, is flexible to cover different styles of property and will deliver fast, high quality results.

Warmscore is a portable set of IOT sensors that can be fitted into nearly any home in less than 30 minutes, without any specialist qualifications. Data on temperature, humidity and CO2 is fed to a web based platform and used for measurements of heat loss, condensation risk, ventilation rates and comfort levels. The toolset can deliver early results after three weeks of data collection or it can remain in the home for longer to pick up longer term patterns of use. 

Why move now?

The most important testing season is September to April, so for funding rounds announced in February, a wave of testing should be possible in spring 2023. If you want to discuss the design of your monitoring project or how else Purrmetrix might support you in bidding for retrofit funding then please do get in touch. There’s always a real live human on the end of our contact form.

Interning – from both sides of the desk

One of the highlights of our summer has been working with some very good interns who have been polishing their technical and commercial skills on our real world projects. We asked one – Dulcie – to write up her summer for the blog, but we also cheated by adding our ideas and tips for any student looking for a technical intern role, completely messing up her lovely post (sorrynotsorry, Dulcie!)

‘My name’s Dulcie and I’m an incoming third year Engineering student at the University of Cambridge. Over the summer, I’ve been interning at Purrmetrix. So, for the past 10 weeks, I’ve been working on web development for the internal site, improving older features and adding new ones.’

What Dulcie isn’t saying here is that she was very proactive – reaching out to us in January. This gives us plenty of time to ring fence appropriate / interesting projects. Don’t be put off if you aren’t able to contact us early – we’re always interested in hearing from interns at any time of year, but we’ll have more confidence in what we can offer with some advance notice!

‘What have I been working on? Well, most of my time this summer has been spent developing tools to help users to calculate the overall heat losses from their buildings. I needed to find a way to let users combine data from their sensors and their energy meters in the Purrmetrix account, which involved coding up a whole new view (a calculation box in account).’

I’ve also been working on improved ways for users to access energy data. In account I’ve written several new ways of integrating energy data. Depending on your energy provider and type of meter, you can now save meter readings, import smartmeter data, or even have the data fetched automatically from your smartmeter.

One of the great things about interning in smaller businesses is that you can work on projects that will have impact quickly, and maybe even see your work in customer’s hands. This project will give Purrmetrix more options on the way we deliver heat loss calculations, which are an important tool in understanding the energy efficiency of buildings.

In my time here at Purrmetrix, I’ve learnt a lot! To start with, I’ve improved my technical skills and I now feel much more confident as a developer in a company environment. Purrmetrix has a small team, and this means I’ve been able to learn about what goes on in all parts of the business. It’s an interesting place to work because of this – I’ve really enjoyed the freedom and variety of the job.

Many interns aren’t confident in their technical skills initially, but a good internship should offer you a range of projects and support to get started. Dulcie hit the ground running so we ended up giving her a whole heap of extension work, but there should be a team to back you up and challenge / extend  the results of your work.

I’ve also picked up a lot about building monitoring in the past few weeks. It’s something that I never thought I’d be working in, but I’ve discovered that there’s a lot of interesting things going on in the field. I’ve gained an understanding of the challenges involved in performing analyses like heat loss, and also how valuable it is as a metric for understanding buildings. As someone interested in environmental issues, I’ve thoroughly enjoyed learning about how these (often underappreciated) methods can be used to increase efficiency and reduce emissions.

Interning is a great opportunity to try out a wide range of industries and corporate cultures to find out what really delivers job satisfaction – is it the work, the team, the purpose of the company? We definitely have a purpose at Purrmetrix and we’re really pleased to be able to infect share it with Dulcie. We hope  that, as much as the technical experience, that’s something that she can build on for her future career.

Overall, I’ve had a wonderful experience this summer. I’ve been able to improve my development skills and get a good insight into how Purrmetrix works. Building monitoring is an interesting field that allows great opportunities for decarbonisation and saving energy, and I’m glad to have been able to help. 

Thanks for helping Dulcie, it’s been a pleasure working with you!

If you’re an intern reading this and want to know what we currently have on offer, please do get in touch: there’s always a human on the end of this form.

Digitalisation for SHDF – a cheat sheet

If you are a housing provider it’s been hard to miss the launch of the next wave of the Social Housing Decarbonisation Fund. Funding applications open shortly, and need to be submitted before November (dates are not fixed at the time of publishing this blog).

A shiny new feature in this round is a line of funding for digitalisation projects, alongside the funding for decarbonisation of homes. Since this is our bread and butter we have put together a 1 page cheat sheet (HT to Jon Daley at Magenta Living for the concept!) covering what digitalisation is, for the purposes of this bid, the conditions on bidding for this funding and the benefits you might want to call out in an application.

Download the cheat sheet below – and of course if you want to discuss how Purrmetrix can support you in bidding for the Digitalisation Funding then please do get in touch. There’s always a real live human on the end of our contact form.

Happy New Year!

Yes, obviously not the calendar year. For historic reasons (I think our CFO wanted a holiday) Purrmetrix official year end falls in the summer holidays. So we’ve had an opportunity to pause and take stock of what we’ve done in the past 12 months. Turns out it’s quite a bit;

  • we’ve doubled our revenue (and broken even)
  • expanded our team of colleagues and contractors by 4
  • secured 2 new research grants for building better building performance tools
  • proudly graduated our first accelerator programme with Cambridge Institute for Sustainability Leadership
  • put more than 200 homes – from Jersey to Teeside – onto a platform that already hosts hundreds of schools and office buildings
  • installed monitoring in the bulk of Coventry City Council’s facilities
  • started working with our first dozen housing providers
  • now logging more than 1 billion data points per year, so invested heavily in our server and database infrastructure
  • data which are being put through our new integrations analysing heat loss (thanks to Build Test Solutions) condensation risk, comfort levels and air changes / ventilation rates

For a tiny, bootstrapped, team we are quite proud of ourselves. And we’re hugely excited about the year coming and the chance to deliver on many of the dozens of interesting projects in the pipeline. But, in the interests of balance* we should also look at the less fun things (aka ‘learning experiences’) from the year.

  • The emotional toll of running a small business you care about. Oh man the bad days….
  • The struggle of running a hardware business in a supply chain crunch (goodbye margin, it was nice knowing you)
  • That under no circumstances should you rely on a business plan based on policy announcements. If it arrives, it’s jam, but your business case has to make sense on its own.

Whatever the ups and downs of our business, we’re facing a winter where energy efficient housing has never been more important to people’s health and welfare. Now, more than ever, we believe it’s important to measure building performance; to make sure that the right measures are going to the right homes and the people that need it most.

If you agree, or have ideas to help us build, please get in touch. There’s always a human on the end of the form.

Happy 2022!

*There’s a particular brand of LinkedIn bragging posts which make me want to curl up because of their hysterical insistence that everything is awesome. Life’s not that simple…

Putting data into the contractors toolbox

Maybe its confirmation bias on my part, but it looks like 2022 has seen a big uptick in activity on home energy efficiency. The first phase of SHDF is underway, the FT is reporting record interest in energy efficiency from home owners and a Travis Perkins survey confirms that tradespeople of all types are seeing increased demand for energy efficiency projects.

The colossal increases in energy costs have focussed minds on some very difficult questions: how do I know how much energy I will save from an efficiency project? Are we upgrading the right homes? Is the upgrade we’re investing in actually performing?

Taking the guesswork out of retrofit

To answer these questions a whole new generation of monitoring and diagnostic tools are just hitting the market. Using IoT sensors to collect environmental and energy data from homes these tools measure important factors such as heat loss, condensation risk and heating comfort, so that the real performance for each home can be assessed, before and after upgrade projects.  With actual measurements of conditions in the home hidden defects no longer go uncounted. Detailed questions can be asked about the performance of each measure. Calculations of potential energy savings can be made specific to each home.

For the past year, Purrmetrix have been helping landlords across the UK – from Stockton to Devon – with their retrofit programmes, helping them monitor and benchmark housing performance with our sensors and software platform. We’re seeing first hand how heat loss calculations and data on comfort in homes can underpin decisions on which homes are upgraded and what should be done to them. In the next year we expect to spend a lot of our time checking that insulation and heat pumps are delivering the promised improvements.

Most asset managers in the social housing sector have limited or no insight into conditions and energy efficiency for each of their homes. For retrofit projects one immediately useful thing we can do is produce rapid benchmarks of performance for as many homes as possible to enhance EPC data and help landlords distinguish which homes in their portfolio will benefit most from insulation or heat pumps. This needs a simple toolset suitable for nearly any home that can produce information on heat loss, comfort and other metrics within a month, without disturbing tenants or requiring any disruptive installation.

Installing the future with confidence

Alongside this a new trend has emerged: we’re now having more conversations around retrofit with the supply chain than directly with landlords. As the supply chain is getting busier and busier the pressure is on to do more with less, so using data to speed up and improve design and specification is attractive. The businesses with a critical role in delivering good quality projects – such as electricians, heating engineers, EWI specialists, general builders – all have interests in using data and software to demonstrate the improvements they’re delivering. The scale of the decarbonisation challenge and the new technologies that contractors are working with also means it is very important to get speedy feedback on what really works and what doesn’t to improve product selection and processes.

We’re learning that contractors have some particular requirements when collecting data in their projects  – sensor sets that are easy to work with and don’t disturb householders. Software that delivers robust, high quality results that are easy to interpret. Tools that can be redeployed across a large number of homes. Alongside this there’s a whole new set of skills for the supply chain to engage with – in collecting, using and presenting data as well as working with new software and calculations. 

Monitoring – the contractors’ new friend

There’s an army of contractors needed for improving energy efficiency in homes and they will come from all types of business; one man shows to nationwide businesses. Not all will want to get involved with monitoring and measurement in housing but there is a lot of potential for those that do to add value to their projects and develop long term relationships with their customers. It will also ‘future proof’ these businesses. In the longer term, using real performance data from homes may become the norm for quality processes such as Building Regs inspection, PAS2035 and for funding applications, so many in the industry will become used to incorporating it into their day to day work.

Right now there is a world of opportunity for contractors of all types to influence the development of the right tools for the job and help develop something that will become as familiar a tool as your phone. We know the industry doesn’t speak with one voice – no trade union and a range of interested associations – so we’re learning most from one to one conversations with those in the supply chain. And we’re keen to share what we have learned so far about how measuring the performance of homes can improve energy efficiency projects; get in touch to learn more about the series of webinars we are lining up for the second half of this year to provide basic training on what data from homes can tell you and how to make sense of it.

Find out more about monitoring

The energy efficiency supply chain of the future will have a whole new range of data tools at their disposal – to produce reports their customers are interested in. As contractors learn how monitoring data adds value to their business (and it is incorporated into regulations), they will be able to provide more and better design and installations. All of which are urgently needed if we are to have a hope of decarbonising housing in a timely way.

Purrmetrix will be at the Installer Show (NEC, 21-23rd June) talking to contractors about the next generation of monitoring toolsets. Find us in Wates Innovation Zone (stand H191). Or get in touch if you would like to be added to the list for our training webinars later in the year.

News from account. Working with data

Getting more from your data.

Everyone wants data from buildings these days. Most people don’t want to spend all day (or even an afternoon) trying to make sense of it. 

With that in mind we built the Purrmetrix account to provide tools for quickly making sense of your environmental data and processes to automate the results. Tools in account can be used to produce simple performance metrics, or they can help visualise data for a deeper dive into a building’s performance to understand where things might be going wrong.

With our account overhaul nearly complete, now seems like a good time to revisit some of the most popular tools and give some real world examples of how they can be used.

Building Performance Metrics

Heat loss – measuring HTC for retrofit

A lot of our work at Purrmetrix is digesting a lot of data to deliver single figures of performance. We looked at condensation risk and ventilation rate in our last blog post – another very important attribute for building performance is heat loss, and we deliver HTC SMETER calculations for housing, with our partners City Science and Build Test Solutions. In situ heat loss testing is extremely helpful to cut through the confusion when trying to manage retrofit projects: it helps identify the right homes for funding and improvements and validate that these projects are successful. 

Heat Loss calculation generated with Smart HTC

An accurate heat loss figure is the critical building block for determining the heating thermal energy requirement (kWh/m3). It helps refine EPC and archetype data to better understand the real world performance of homes and to inform design decisions. We use smart or conventional meter reads combined with temperature data to deliver HTC reports for each home. This is a delivered as a standalone report at present, with plans to deliver HTC in account in future versions.

Goldilocks – a universal building performance benchmark

For benchmarking performance, Goldilocks sets the targets for performance and then tells you how much time has been spent in compliance. It’s a handy way to compare large numbers of buildings or to compare performance across time.

There are lots of uses, depending on the environmental metric you are using. For example in housing it can be to compare homes to see which homes are persistently cold, identifying possible fuel poverty issues.

It can also be used as a rough guide to homes at risk of condensation issues. In offices or schools it can be used to compare CO2 in meeting rooms or classrooms to show where extra ventilation is needed.  

While we’re talking about general tools, there are also views to calculate comfort metrics, averages and max min for any data stream. These are most typically used when benchmarking performance and comparing it over time, before and after improvements to a space.

Visualisations – making sense of building complexity

Sometimes it’s important for technical specialists to get deeper into the data and see what clues it can give about problems in buildings. For these situations, visualisations can be incredibly powerful, making it easier to digest and make sense of a lot of data. Graphing and bar charts are a standard way of visualising data, and we provide these, but other views go deeper:


Our heat map tool allows the data to be accurately positioned on a building plan and replayed to examine the behaviour over time – can you see solar gain moving around an office building? Is high humidity in the kitchen also affecting the living room?

heatmap of housing with temperature data


Each line of a waterfall visualisation heat maps a metric across a complete day. This is a fantastic visualisation for spotting recurring patterns of behaviour; whether it is identifying if heating systems are turning on and off at the right time, or finding a damp problem that is related to external rain events.

Reporting and alerts

All of these tools can be wrapped up in our reporting function, which delivers reports via email on a regular cycle. Of course we also have live data, so if there are situations where a timely response is important then our alerting tools can be used to deliver a call to action. We’ll look at how to use these tools in more detail in a future blog, or you can visit our support section now.

News from account. Upgrade part 1.

Getting value from environmental data

Recently we’ve been upgrading the Purrmetrix web service to integrate new analytics and upgrade some of the features that make it easier to work with your data. 

This blog is about introducing a couple of new analytics – on ventilation rate and condensation risk – both of which make sense of a lot of data from environmental sensors to deliver a metric that can drive action.

(Later in the week we’ll also take the opportunity to remind you of some old friends in the analytics menu – one thing that we have learnt from chatting to users is that heat maps and graph views are doing a lot of heavy lifting in our account. We love graphs and heat maps, but if you’re investigating a problem building, or trying to benchmark performance, there are quicker and simpler ways to interpret Purrmetrix data using some of our other views.) 

For now though let’s talk about new analytics in account and what they mean for anyone in charge of a commercial, educational or residential estate.

Ventilation rate

COVID has taught us that ventilation indoors is crucial for our health; as a result CO2 monitoring in schools and workplaces is now becoming popular. But absolute CO2 numbers only tell you part of the picture – a high CO2 number may be a temporary result of too many people in a space. Or it may be a small number of people in a space which has very bad ventilation. The difference between the two is in how fast stale air is removed, and this is what our new ventilation rate analysis looks at.

By finding the data where the CO2 in a room is declining sharply we can make measurements of how quickly the air in a room is removed. This is an analysis that works particularly well for smaller, well populated rooms – living rooms in housing, meeting rooms or classrooms / lecture theatres, as well as break out zones, smaller offices or cafes. All we need are some people who will stay in the space long enough to breath out some CO2 and then leave.

The ventilation rate calculation takes a whole bunch of CO2 data and turns it into a single metric – an average for ‘air changes per hour’. This allows comparison across different sized rooms so that areas with poor ventilation really stand out. 

Currently our ventilation rate analyses are still in beta, but for any customer who wishes to try out the initial calculation we would be happy to upgrade your account to beta for free. Just get in touch.

Condensation risk

Condensation and its buddy mould growth are an expensive and persistent problem with real impact on health. It’s a tricky problem for landlords for a couple of reasons. Firstly, it’s often a hidden issue: the first time a landlord may be aware of them is a tenant complaint once the problem has escalated to mould and fabric damage. Fixing the issue can then be a lengthy struggle. Secondly, sometimes the causes of condensation are related to tenant behaviour and sometimes to fabric so it’s very easy to apply the wrong fix for the problem.

Identifying homes with hidden condensation problems before it escalates saves time and money on extensive repairs and helps avoid any health problems for tenants. Better yet is identifying ‘at risk’ homes; houses that may not show a significant problem but where a change in circumstances (such as significant changes to fabric, adding to occupancy or reducing heating) could tip the house over into a more serious issue. Because condensation can be a localised problem its often hard to identify from a single point of measurement, and to get a rounded picture of what is going on analysis needs to be done from several points within a home, including high risk areas like bathrooms, kitchens and bedrooms.

Measuring several points in a home can make things complicated but our new condensation risk metric helps to simplify the process and deliver a metric that highlights risk areas and allows them to be benchmarked to track which interventions are working. The risk metric identifies the conditions needed for condensation and mould growth to occur and calculates the portion of time each area is at risk. It then allocates an overall high / medium / low score to the home based on the conditions seen and calls out the area that is worst performing.

For high risk homes, further investigations using other Purrmetrix views can give a good understanding of whether the problem is being driven by behaviour or fabric.

Analytics for housing – what’s next?

These new analytics will be available to all Purrmetrix customers on beta accounts (contact us for access) for the next few weeks, following which we will launch them into the pro level accounts.

We’re always open to talking to customers about how to get value out of environmental data. Whether it’s diagnosis of housing defects, insights into occupant behaviour or forecasts of the impact of retrofit / heat pump installations, we believe data will give clearer insights and help drive better actions. If you have a data challenge, please do get in touch.

Managing Ventilation with CO2 Monitoring

In 2003, a healthcare worker infected with SARS went to a wedding in Hong Kong and checked into the Metropole Hotel. He fell ill the next day and went to hospital – but had already infected 16 other guests with rooms on the same floor, probably largely through their ventilation systems.

Move forward 17 years and managing ventilation is now a hot topic in reducing COVID risk. A person with COVID releases particles in droplets and aerosols whenever they speak, sneeze or cough. Droplets tend to fall to ground quickly, but finer sprays (aerosols) remain suspended in the air for long periods of time if the air is not removed from the room. Breathing in these aerosols puts other people in the room at high risk of developing a COVID infection, even once the infected person has left.

Fighting this means bringing in fresh air and removing stale air to quickly remove virus particles from the environment. It is an important piece of any plan to reduce COVID risks in a public building, along with keeping distance, hand hygiene and mask wearing, but it can be difficult to monitor how effective ventilation strategies are. CO2 monitoring can give reassurance that ventilation is working to help you get your building back to work safely.

How monitoring CO2 helps

CO2 levels provide a very useful signal for any facility manager trying to assess COVID risk and ventilation rates. Every person in a space breathes out CO2 at a constant rate, at a concentration around 40,000 parts per million (ppm) meaning it can give a good indication of aerosol load in the air, if someone in the room has COVID.

Over time this CO2 builds up in enclosed spaces, so that levels will exceed the natural background rate (around 400 ppm). An effective ventilation system will be able to expel stale air and bring in fresh at a rate that keeps the CO2 levels from building up to uncomfortable levels: and by diluting any infected air it will also reduce the risk of contagion to the people in the space.

Understanding CO2 levels across the whole building helps facilities managers identify what strategies are working, reduce high risk practises (such as holding meetings in unventilated spaces) and demonstrate to occupiers that the space is working for them in the fight against COVID.

What should CO2 levels be?

If you’re thinking about using CO2 to control COVID risks, it important to recognise that while absolute levels do matter, rate of change is important as well. A rapid build up of CO2 in a room is a clear sign of over occupation, and a slow reduction can be a sign of ineffective ventilation.

Background (atmospheric) CO2 levels vary slightly over time and location but are typically around 400 -420 ppm; in a mechanically ventilated buildings 800ppm – 1000ppm is a commonly used target for normal operation. Even before COVID, research shows levels above 1200 ppm have measurable impact on productivity and decision making (see CO2 and workplace productivity below).

The chances of catching COVID are affected by a range of factors as well as ventilation (including age, activity level and distance), and these effects are still being researched, so providing a single CO2 level as a target is misleading, but current consensus amongst authorities such as ASHRAE and the FEA suggests anything above 1000ppm should be avoided.

Prof Cath Noakes, expert in ventilation and infection transmission, goes a little further: “You should be looking for CO2 below 1000ppm, and ideally around 800ppm BUT there’s a bit more to it…to understand if the ventilation is adequate, you need to measure with the normal number of people in the space. If you measure with less people you will get a lower reading which could give a false impression that the ventilation is OK.”

What else can CO2 levels tell me?

As important as the absolute levels of CO2 is the rate of change. As Prof Noakes explains: “Transient effects also matter. The CO2 builds up and decays quickly when a room has a high airflow rate, but much more slowly in a poorly ventilated space. A single low reading doesn’t tell you the whole picture.”

Watching the rate of change gives a clear picture of which parts of the building are extracting waste air effectively. The graph below shows the decay of CO2 in a meeting room with good ventilation, vs ineffective ventilation.

CO2 decay in well ventilated (left) vs poorly ventilated (right) meeting rooms

Using decay curves like this it is possible to produce an estimation of air changes per hour and map these over the whole building to identify dead areas where ventilation is less effective. Sometimes there can also be ‘dead times’ – in one building monitored by Purrmetrix system last year meeting rooms that were effectively ventilated during operating hours were being used after working hours when ventilation systems were reduced. CO2 build up was rapid and dispersal very slow. The monitoring highlighted this risky behaviour which was discontinued.

CO2 and productivity

Improvements in ventilation have value beyond reducing COVID risk – many studies have demonstrated the link between high CO2 levels and reduced productivity in office workers. Most recently the Whole Life Performance study, from Oxford Brookes and LCMB, used Purrmetrix CO2 monitoring to demonstrate the relationship; finding subjects completed sample tasks 60% faster in environments with lower CO2 levels.

Decline in performance across a range of thinking tasks when exposed to high levels of CO2

In schools, high CO2 levels also a cause for concern, and have been associated with declines in cognitive function scores in at least one Harvard study.

How do I put CO2 monitoring in place?

With all this in mind there are several key things to think about when designing a CO2 monitoring project:

How accurate are my CO2 sensors – how do they calibrate?

Before getting stuck on accuracy, it’s important to understand when it’s important and when it isn’t. Sensor manufacturers list accuracy as ± ppm ± a percentage of the reading – it’s common to find variation of 50 ppm and 3%, meaning at the lower limit of 400 a sensor can measure between 358 and 442 ppm. By sampling rapidly (up to 20 times a second) and taking an average they improve the accuracy of the read and produce a result close to the actual target. Accuracy measured this way will improve at higher CO2 levels (measuring 1000ppm the same error could produce a result of 920 – 1080 ppm, before averaging) and it has little effect on rate of change measurements.
As important as accuracy for long term monitoring is how the devices are calibrated. Low cost devices can drift in performance over time, and manual recalibration is very labour intensive. The best solutions have sensors that can self calibrate and reset back to a base level of background CO2 on a regular cycle.

How easy is it to deploy and maintain the sensors.

Sensors need to be robust, easy to fit, and – if you are working with a large site – easy to identify. Once fitted, the best can be left with no further visits for calibration or battery replacement.

Where am I putting the CO2 sensors?

This is important as you want to get the most representative figure for a gas that will vary across the space. Measurements should be taken from every room where people regularly gather and ideally from the same number of points across an open plan office as points where the air is extracted. The best locations are fairly central, not too low (CO2 sinks so this will raise your result), not directly in front of a person or a vent. We favour underside of desks or meeting rooms, if power leads will extend to those locations.

How much data do I get? How do I make sense of it?

For professional ventilation management, transient effects matter, meaning it is important to be able to see data over long periods of time, and ideally understand quickly which area this data relates to. On a large site all this data must be quickly turned into actionable information, such as heatmaps, alerts and ventilation measurement.

As facilities managers plan for re-opening sites, ventilation provides an effective way to reduce COVID risk and CO2 monitoring is an important tool in managing ventilation strategies. With hundreds of CO2 sensors monitoring thousands of hours of CO2 data, the Purrmetrix solution is a proven and powerful system for measuring and analysing ventilation rates. If you are working on ventilation strategies in your estate and have questions, get in touch and we can help.