“Where should we put the sensors?”

Of all the questions we get asked, “Where should we put our kittens?” or “How many should we buy?” comes up the most often.

Answer: That depends what you want to know.

Look, I know that can sound evasive but my Christmas break proves my point. Some of you might already have read about the monitoring of 2 very different houses over the Christmas period and what we found. We saw some very interesting things in that experiment and we’ll pick up a few of those over the next few months.

At the 70’s house that we monitored I found something a bit odd. We were all sat around the laptop on Christmas Eve looking at what was happening and to see if anything surprised us. My parents have lived in that house for 24 years so we saw pretty much what we expected, however the main family bathroom intrigued us. It’s located at the top of the stairs, has a double glazed window and a fairly large towel rail style radiator. We have never been consciously cold in that room so why was it 17 degrees?

The sensor was on a fully tiled window sill right next to the window at about waist height, so we ran a little test and moved it to the top of a wooden bathroom cupboard at about head height and the temperature climbed by nearly 5 degrees! We all knew that it didn’t feel like 17 degrees in there but we never expected such a huge difference in temperature by moving the kitten less than 1m within the same room.

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We can occasionally be surprised about what we see when we put sensors in environments we thought we already understood, we see in real terms just how sensitive the kittens are and how temperature can change very quickly across space.

Which presents a useful tool for comparing performance. For example: my parents upgraded their windows to double glazing in a few separate rounds to spread the costs not long after they moved into the house. This window was one of the first ones to be installed in the house and are almost certainly getting on for 20 years old. Installing a larger number of sensors in some of the rooms to monitor exactly how well the double glazing is performing and even compare the windows installed at different times could identify if some or all of them could benefit from being replaced.

We also saw things that we expected like peaks in temperature when we had showers and when the heating turned on and off:

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We used humidity kittens across the house, some of you might be interested in seeing the graph for humidity across the same timescale. I managed to achieve 96.9% humidity with my post run shower. (In particular, you’ll notice the humidity continued to rise after my shower? This is a function of the way we measure humidity – as relative humidity – which we’ll cover in a later blog post).

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So, how can this help to inform you on where to place your kittens? Like we say, it does depend heavily on what you want to know, but here are some general guidelines:

  1. If you want your kittens to record the temperature that you feel in a room them make sure that you place it well away from any heat sources such as radiators, air con units or fans that blow warm air out of computers etc.
  2. If you want your kittens to record the temperature that you feel in a room then make sure that you place it well away from any sources of cold such as open door, windows, draughts or on cold materials such as tiles.
  3. It you want to record the temperature of in a specific place then be sure to locate the kitten exactly where it’s needed, they really are very sensitive i.e. next to a thermostat to check its functionality.
  4. Try to avoid putting kittens in direct sunlight as they will be effected by solar gain, unless of course this is what you are trying to measure.

Remember that if you want to see in more details what’s going on in a room then re-deploy your kittens or buy more, one of the main advantages of how small they are is that you can put them pretty much anywhere. Place them in a grid pattern around the room or if you are feeling really adventurous hang them off fishing line  at different heights to create a cross section of your space. This can be very interesting particularly in a mezzanine or tall staircase, you might be amazed to see whats going on.

If you want to know more about how Purrmetrix can help you to learn about your space then contact us by email at help@purrmetrix.com or call us on 01223 967301


Comparing Christmas in 2 very different homes

Happy New Year to you all, we hope you had a great Christmas break. Since we got back to work some of us here at Purr Towers have been looking at the results of a little experiment we set up over the break. At Christmas Hermione spent her time in an 18th century folly in North Yorkshire (DP) and I (Liz Stevens) spent it in my parents 70’s build house on the south coast (CC). We thought it might be interesting to take a look at how the 2 buildings behaved with all the family piling in and a roast dinner in the oven.



DP – The 18th century folly is a sprawling 2 story house with 6 bedrooms, single glazed, not insulated, 4 external doors, oil central heating, open fires and a large aga in the kitchen. 8 people stayed in the house over the Christmas period.






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CC – This is a 70’s build box shaped house with double glazing, cavity wall insulation, a very well insulated roof, 4 bedrooms, 2 external doors, a partly integrated garage and gas central heating. 4 people stayed here over night during the period and there were 9 people in the house during the day on Christmas day.





Cooking the Christmas dinner:

DP has an Aga which is constantly running at least at a low level where as CC has a conventional gas oven. The kitchen at DP is a large room with a dining table that seats 8 people, we can see that the cooking of the roast dinner doesn’t have much impact on the temperature in this room as the heat is dissipating and there is no clear time when the oven is working.

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CC has a conventional gas oven so you can clearly see when the oven is turned on (11am). The kitchen at CC doesn’t have any radiators which means it can get quite cold on a normal day but it was constantly warm with all of the cooking and people coming and going. You can also see the oven heating up the room on Christmas Eve while a ham is being roasted.

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Eating our Christmas dinner:

You might have already guessed that DP was rather colder than CC with one of the rooms hardly getting above 16 degrees over the period we monitored despite being heated by a radiator. It’s a very large room, which doesn’t get much daylight, with single glazed windows and a stone floor. This was actually the room where they had their Christmas dinner and the temperature peaked just below 17 degrees – ouch chilly.

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It makes a very interesting comparison to CC where our lunch time temperature was about 22 degrees and the temperature didn’t drop below 20 degrees for the whole period. You can see the difference when you have a well heated well insulated modern carpeted dining room.

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CC conclusions:

We looked to see what was going on with the temperature quite a bit over the Christmas period and there were a few things that surprised us about the findings. I found that I was only comfortable when the temperature was below 22 degrees, once the temperature climbed above this I felt like I was in a tropical jungle. Clearly other people didn’t always agree but it was interesting to know my threshold. We have always know that the downstairs bathroom (Kitten 29) was always rather cold but we didn’t really quite how bad it was and we had no idea that they temperature in the hall by the front door (Kitten 32) was so low. You can see from the Hotspotter view here that they spent rather a lot of the Christmas period below 18 degrees although it wasn’t surprising to see the kitchen (Kitten 13) above 25 degrees for 28% of the time.

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You can also see how the temperature changed from Saturday till Monday:



DP conclusions:

Well we already knew that it was going to be colder at DP over Christmas as it’s further north (so colder outside) and it’s an old building with a few poorly insulated slightly more modern extensions. I think we were all a little shocked at just how cold the dining room was but this room isn’t often used as there is a large dining room in the cosy kitchen not far from the Aga. It’s a big house and it’s going to take more heating than the average building even in warmer parts of the year. I think I for one might have been more comfortable with the temperatures at DP but it really does show us that comfort levels are very personal to everyone. The Hotspotter view below is very interesting and really shows you how cold the downstairs of DP was over Christmas, I’m sure there were lots of cosy Christmas jumpers being worn (I didn’t get to wear mine once at CC!). The dining room is Kitten 48 and the kitchen is Kitten 46 but I’m sure you could have guessed that.

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You can also see how the temperature changed from Saturday till Monday:


If you want to learn a little bit more about how you could use our system in your home, workshop, office or data centre please contact us via email on help@purrmetrix.com or call us 01223 967301

Finding your buildings’ data

Many organisations see the value in using data to optimise their property performance – reduced energy costs, deferred maintenance spends, improved space utilisation and staff productivity.

But the work needed to make this happen should not be underestimated. We are currently running a short email series on the basics of building analytics (sign up below) and one of the simplest but most daunting steps is often finding the relevant data and auditing it for quality.

Hence we have produced this short checklist of some of the commonest forms of data relevant to building analytics, and where you might find it.


Interested in reading the whole series, including how to use data, awkward questions for analytics platforms and building the business case?

Sign up for our short course on using data to improve the performance of your building. And the people in it.

The business case for building analytics – some case studies

Buildings offer a wealth of data about their performance. Getting information from building data isn’t easy – Pike Research estimate that 80% of FMs only use 20% of the data available in their BMS.

A lack of time and training is certainly one barrier. Another may be that it is difficult to build the business case for the work needed to collect and make sense of all this data. To help with this, we’re assembling a list of good examples of building data analysis for a range of goals. These examples come from vendors of a variety of solutions all over the industry.

Next time you want to have a conversation with your FD about investing in data tools, hopefully this will give you some benchmarks.

Carbon Credentials: optimising BMS controls for VUS Hotels. Forecast to save £20,000 pa in first phase.

A study from University of California of four enterprises and university campuses focussing on attained savings  

IES: a project for Glasgow City Council using BMS and metering data that highlighted annual savings of £85,000. A more detailed write up is also available here.

Demand Logic: Potential savings of £390,000 for Kings College

Concept Energy Data: Real time data reduces energy by 7% in four schools

Optimised Buildings: A <6 month ROI from energy savings identified in a Financial Services HQ.

Got a pet project that should be mentioned here? Get in touch! As long as it involves using building data (and ideally has some quantifiable results) we’ll add it to the list.




Baking with your own data – Import views

If you’re analysing the performance of your building and its HVAC systems you probably already have data from other sources – meter data, building management system data, occupancy data, for example.

We at PurrTowers have been working for a while on ways to allow you to use other data alongside your kitten data. So we’d like to introduce our Data Import view.


The Import view is available if you have an unlimited account (ie any tier above the free account). It allows bulk import of historical data, and attaches the data to a special external-data kitten. This kitten can be dragged and added to other views exactly as if it were one of our own sensor kittens and you can put this data alongside that collected by kittens.

How do I get my data in?

First create an import view as any other by clicking on the Import view in the Create Views selection:


This will create a new Import view:

Import view

Data formats

Data is added to the import by dragging a data file to this view. The data file is going to get analysed before it gets imported to your account, so it helps to get it into the right format. Each line needs to include a time and date, and a value, with a comma between the two:


This can be created using Microsoft Excel by saving a spreadsheet with two columns, one for the date time and one for the value, as a .CSV, comma separated value file. In order to get the date and time format right you’ll need to use a custom cell format which can be found in the cell format dialog box:

dd/mm/yyyy hh:mm

(For some Excel users you may find that this format doesn’t exist, but this link explains how to create the custom format you need)


OK, so you’ve got your data file sorted out, now drop it onto the Import view. This should put it to work, first uploading the file, and then checking the contents:

Analysing ….Found

Organising your Import Views

If everything went well then that Import view should tell you what it thinks of your data, and offer an import button that you need to press in order to get the data in. Once there just use the new Import kitten just as you would any other (yes, you can rename it just as you can rename the Import view).

We strongly recommend that you keep all your Import views in a dedicated project. This makes it easier to find each Import view when you want to add more data.

You can delete the Import view, it won’t delete the kitten or the data that you’ve already imported, you just won’t be able to add any more data to the kitten.

The small print – some important details

OK, as you might expect there’s a little small print:

You need one Import view for each thing that you want to import data for. Example: if you have three thermostats in a room you will need three Import views.

The Import view should happily eat several 100,000 points in one swallow. We have limited the import to 2MByte files at a time.

You can reuse an Import view as many times as you like, adding data from different times to the Import kitten to build up a complete history.

Sorry, but no, we haven’t worked out how to let you delete the data you’ve just imported. Please be careful to be sure that you are adding the data you actually want.

Yes, you can add data that might overlap the data that you’ve already imported. Our far-to-clever for its own good database will just average the data during those overlapping periods.

The Import view needs you to give it data points in time order. If you try to import data that is all backwards, or where some points are in backwards order then it will do its best but it will reject those points.

If the Import view cannot understand your data file it will warn you and let you try submitting different data:



And finally – how much will it cost? We will charge the same amount for an import view as for any other kitten, so depending on the number of end points you are measuring prices will start at £10 per end point, per annum.

This is a new view that will be in beta for the next month so we welcome feedback and bug reports. Enjoy!

Working out the numbers – how many sensors do you need?

Often, when we’re talking to customers they will ask us how many sensors they might need. This is a great question because it lets us talk a bit about the applications customers are using the sensors for.

Honestly, we don’t have all the answers on this because we’re still breaking new ground here. There are a lot of potential applications for Purrmetrix that haven’t been tested thoroughly. That said I thought it might be helpful to explain a few rules of thumb we tend to use in answering this question.

TL:DR – it depends upon what you want to achieve with your project. Contact us if you want to talk through the specifics of what you are measuring

How specific is your HVAC analytics project?

Many customers start working with us in exploration mode. They want to identify and pick apart all the problems in their estate. In that case we suggest a fairly high density to start with – a sensor every 10 sq m or one for every cluster of desks. So in a fairly average 60 person office we’d be thinking about 15 – 20 sensors.

In a case where you want to collect data around a known problem, it’s generally possible to be a bit more precise about the numbers, depending on the type of problem you’re looking at.

What sort of problem are you hoping to test?

If you are looking at problems with specific parts of your building services – for example in each fan coil unit – then you have a fairly obvious guide of one or two per FCU. Although kittens can be redeployed its always better in our experience to test all parts of the system simultaneously so allow enough numbers to do that.

On the other hand, you may be interested in how the building’s fabric is performing – how quickly certain parts of the building heat and cool compared with outside temperature. If you think you have generalised insulation problems then 3 or 4 sensors along each aspect can generate quite a lot of information on the rate of heat loss, although you should allow for more if the materials change significantly along each aspect.

Are you analysing or influencing?

If you are hoping to influence behaviour (whether to save energy or helpdesk time) then you need to be presenting data at the hyperlocal level for each person. The ideal extreme would be one for every desk or working area, but in practise we find that a sensor within the same 10 sq m is generally adequate. Remember they can always be moved to accommodate sceptics!

How are you displaying it?

Because monitors are limited in how many pixels they can display the webservice has limitations in the way it displays the image of your building/project, which will be sized to 600 px wide. This generally means it is tricky to display very large areas with a lot of kittens, or make very precise placement of kittens on a low scale (zoomed out) plan.

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At this scale it can be tricky to position this number of sensors correctly.

If you do have a project requiring a high density of sensors then make sure you zoom in and use the largest scale plan you have.

How the temperature gradients work

The colour gradient between kittens is not a reflection of the actual temperature in the gradient but of the confidence that it reflects the correct temperature. We don’t vary the size of kitten icon or the spread of the colour gradient so its spread is determined by the scale of the plan or image you upload the kittens above appear to be covering a floor area of around 6 sq m.

You can make the kittens disappear from the plan to better understand what is going on. Do this by clicking the arrow to the left of the view titla:

Temperature map of office

In general we don’t recommend uploading plans of any building of more than 60 meters.

In summary

  1. You don’t have to get it right first time, because you can redeploy your sensors
  2. Size your order to your use – general exploration and influencing behaviour will take more kittens
  3. Don’t try and display too many kittens in one heatmap view. Use other views (graphing) for that.
  4. Talk to us if you have a problem building and you’re not sure what the right level of diagnostics might be.

Four ways better data will improve your heating season

Are you getting the calls? Now its October, we’ve been noticing our heat maps warm up as our customer’s heating systems come on. For a facilities helpdesk, the summer’s steady diet of ‘too hot’ calls start to change – data from IFMA shows complaints of too hot and too cold run at the same rate in the autumn, so if your occupiers can’t make up their minds they’re not alone!

Getting your HVAC strategy right at this time of year can seem like an impossible task, but there are some ways to solve the conundrum and to set yourself up for winter.

Get a handle on temperature complaints

Your occupiers are confused. They have been accustomed to higher summer temperatures and while autumn weather fluctuates, their ability to adapt can’t keep up. So they are likely to feel different levels of comfort even where the temperature is acceptable. To add to the problems building systems may also struggle with temperature swings so some of their complaints will relate to genuine but temporary problems. What is needed is data of the real temperature for occupiers so that help desks can work out the right solution without calling out engineers every time. In this situation, data saves time and money, as well as the energy involved in constantly adjusting heating systems.

Setting up the right heating strategy

When to turn the heating on is a bone of contention in many work places. Some facilities managers run systems for short hours during the shoulder seasons to avoid see windows open and fans being used at the end of a warm autumn afternoon. Others simply aim for a lower temperature. The right answer will vary from building to building, depends on how much control you have, and how your building behaves. Temperature data help you spot the patterns of heat loss and decide which option will work best for your situation.

Call out the heating engineer

Underused over the summer, even well maintained heating systems can be temperamental when started up. A complete failure is easy to spot, but regional problems – broken TRVs in hot water systems, for example – can go unreported until you get into the cold months, leaving facilities managers with a series of small jobs which would be better dealt with in a batch. A comprehensive survey over the first weeks of the heating season to quantify all the problems will save time and complaints in the long run.

Finally, don’t forget the summer

Have you been fighting for budget to do something about HVAC problems all summer, only to have the exec team decide that since cooling is not now needed the decision can be deferred for a few more months? How do you keep making the case, when the ‘too hot’ complaints have died away? Collecting hard data on the extent of the problem defines the problem and creates the business case for intervention.

And in case all this data sounds intimidating or a potential time suck, take a look at our tools for collecting and working with it to tame your temperature problems. Or get in touch with your heating challenge.

Heatmap of the month – cross sections, not cross colleagues

This months heat map is a bit of rarity – an example of what happens when you get HVAC right.

To get this impressive cross section of a London office our customers hung kittens on strings at several points along the ceiling. Each string had a number of kittens, spaced a meter apart, to give a vertical grid of temperature sensors.

The office is a converted Victorian industrial building, with a first floor and mezzanine. It houses about 80 employees for a professional services company, and keeps them at the right temperature with a comfort cooling system that delivers cold air through ducts at floor level.

So what are we looking at here? This is three days from July where the external temperature varied from 9°c to 25°c. Even though this office has a huge volume of open space and floor to ceiling in excess of 8 meters, the temperature on the first floor and mezzanine is well controlled. The mezzanine is a degree or two warmer, but rarely gets outside the comfort band.

Just to be controversial we’ve included a Saturday – and a hot one! – when the comfort cooling isn’t operating, to show the huge heat gain that comes through the ceiling and particularly the skylight along the roof ridge. This poses a big challenge for the cooling system at the higher level.

Looking at the view across the desks on the mezzanine for the same period confirms how well the cooling does at keeping employees warm – providing they don’t get too tall.

Is your cooling doing its job? Or do you have a concerns about where your heating ends up? Let us know about your most perplexing HVAC challenge and we’ll help you diagnose what is going on.

Interning at Purr – Doing ‘all of the things’.

<We’ve had some great people come and do internships at Purrmetrix. Say hello to Fiona, our latest colleague, who’s agreed to answer a few some questions about her work experience here.>

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I’m Fiona, a sixth form student in Cambridge currently in the midst of applying to study engineering at university, and, for the last two weeks, a work experience intern at Purrmetrix.

What is all that fiddling with PCBs you’ve been doing?

All of the things!

Screen Shot 2016-09-06 at 11.38.07Over the last two weeks, I’ve got forty-eight gateways ready to go – this involves a small amount of soldering on each one, cleaning the components on the PCB, fitting the antenna, and installing the whole setup into the case. Once this part is complete, I’ve had help to find each individual gateway on the system so that I can get the correct passphrase for it printed out and stuck onto the case, along with the serial number. Finally, each gateway gets plugged in (only using one socket, since these ones have power over ethernet) so that I can check it’s transmitting to the system and install the latest version of our software onto it. Then the gateway is ready to go!

Screen Shot 2016-09-06 at 11.40.00But a gateway by itself isn’t much use…. So I’ve also been involved in building ninety-six kittens. My job covered the first few steps in the process of turning a sheet of circuit boards into a fully-functioning kittens: extracting them from the sheet, plugging them in via the programming widget, and installing the software that enables them to transmit their temperature data to the gateways. Once this update was done, I soldered a radio antenna onto each kitten to improve its range of transmission – and then passed them on to Winston for some more advanced testing and the final stage of assembly.


Was it all engineering?

Screen Shot 2016-09-06 at 11.52.27No! Throughout my time here, I’ve also been involved in other aspects of the company. This means going to meetings, and getting stuck into other types of task. I spent some time doing market research for Hermione – starting with some fairly abstract googling, and ending up with a (colour coded!) spreadsheet of the relevant information.

As well as that I’ve been creating a demonstration account. This needed a major Kitten Hunt around the office to find all of the kittens left in random places during test runs (this went fine until I found some on the ceiling, which were slightly out of my reach). I then took my pile of found kittens and used the system to identify them. Those that were involved in testing were returned to the person in charge of the relevant project, and I “adopted” the rest. I then put the “adopted” kittens into a new project and spent some time creating views for them that will later be used for demonstrations.

This was a great opportunity for me to really get to grips with the data outputs for the kittens, and the full range of analysis that the software can do.

What’s it like?

It’s a really friendly company – everyone here seems to be happy to explain things to me and to teach me how to do whatever I need to know for my latest task. Being set a variety of jobs is great, as it means I get to learn loads of new stuff and see how lots of different aspects of the company work. There’s also a set of company mugs with the kitten face logo on, which I found slightly too exciting…. All in all, I’ve had a great time learning lots of new stuff, building things, and finding out about Purrmetrix during my time here!

<Awww, thanks Fiona. You’ve got great kitten herding skills! Also insane ideas of what makes a good biscuit


Interested in an intern role in Purrmetrix? Get in touch with us – we are always interested in hearing from people who want careers in engineering or marketing. Baking skills not mandatory.>


Installing Kittens In Your Rack – Data Centre


If you have just taken delivery of your first set of kittens ready for deployment in your rack or you are thinking about ordering then I’m hoping to give you all the info you need to get them fitted. It’s not a difficult process and the installation guide will talk you through the basics but there are a few tips that I want to give you to help along the way.

One of our limited edition black kittens in a rack.Optimal kit installation:

  1. Our recommended kit for a rack would be a 8 temperature sensors, 1 temperature and humidity sensor and 1 gateway. This is to give you the best coverage and  the best visibility of your rack on the heat map.
  2. Fixing your kittens – We have found that it’s best to use the cable ties provided for the data centre environment. It’s warm and dry so it’s not the best conditions for sticky pads, they will work but we prefer the reliability of the cable ties. The doors on the front and back of the racks should be easy to slip the cable ties through.
  3. 4 of the kittens should be placed at the front of the rack equally spaced from top to bottom in order to get a full spread of temperatures to see whats going on in the whole rack.
  4. 4 of the kittens should be placed in the same way from top to bottom in the back of the rack.
  5. If you have purchased a humidity monitor then try fixing that in the top of the rack to see whats going on overall.
  6. The gateway is going to need power and an ethernet connection. You will be provided with a normal UK plug socket for the power, if you require power over ethernet then just let us know (extra cost).
  7. The gateway will need to be fitted within the rack for best signal, it can be sat on a shelf, on top of a server or better still attached to the top of the rack with cable ties.


  1. The kittens sense the temperature from their faces so make sure you face the kitten in the direction that you want the most sensitivity.
  2. Rename the kittens when you get them so you can easily know where they live. You can do this by clicking on the kitten and editing the name (you can also add notes to the notes field).
  3. If you aren’t sure which kitten you have in your hand at any one time just push the kittens nose, till the LED lights up (red for the normal temperature sensors and green for the humidity sensors) and it will flash up on your account.
  4. Don’t forget that you can move the kittens about as much as you like. If you have a problem area in a rack you could alway re group them all around a few machines for a few days or weeks to see whats going on. Just don’t forget to change the names of the kittens and change the heat map so you can see exactly whats going on.
  5. Try playing around with different view for your heat map like the rack views from the front or back, different analytics and even hot or cold alerts to get the best out of your purr account.

If you want some ideas about the kind of insights you can get from the information check out our previous blog: Using onboard monitoring? Here’s four things you’re missing.