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Keeping a sense of proportion

This web site doesn’t usually cover domestic energy saving but the topic is of indirect relevance when one is conducting staff energy awareness training. Learning about how to cut energy costs at home is one of the benefits to staff  of participating in such programmes.

At the time of writing UK energy prices are increasing dramatically and the media (as ever in such circumstances) are awash with energy-saving tips, many of which are trivial or patronising. As part of any awareness-raising programme it could be useful to steer people away from irrelevant time-wasting ideas and towards things that will actually make a difference. In this article I’ll put some numbers to some of the advice that’s currently doing the rounds. These are rough-and-ready estimates based on a lot of simplifying assumptions and the prices I will use are £0.08 p/kWh for gas and £0.30 p/wWh for electricity.

Tip no. 1: when cooking, avoid opening the oven door to inspect the contents

The argument presented here is that the hot air will escape and more energy will need to be put in to compensate. Let’s look at that: the capacity of the oven will be of the order of 60 litres. Let’s say all the air in the oven is replaced with room air. 60 litres of room-temperature air will have a mass of 0.07 kg. With a specific heat of near enough 1 kJ.kgK,  and supposing a temperature rise of (say) 180 degrees, that implies 0.07 x 1 x 180 = 12.6 kJ = 0.003 kWh, or one-tenth of a pence wasted. Verdict: bonkers.

To put that in perspective, it’s the equivalent of preheating the oven for 4 seconds longer than needed. But even preheating the oven prematurely isn’t a huge deal. Once up to temperature it will very likely dissipate something of the order of one kilowatt (costing 30p per hour) so ten minutes idle costs only about 5p.

Tip no. 2: don’t boil more water than you need

Suppose you boil 0.5 litre more water than you need. With a specific heat of 4.2 kJ/kgK and assuming cold supply at 10°C, the extra heat supplied is 0.5 x 4.2 x (100-10) = 189 kJ = 0.05 kWh or 1.6 pence worth. Verdict: trivial.

Tip no. 3: use a shower rather than a bath

Let’s look first at the cost of a bath using gas-fired hot water. I’ll assume 100 litre (kg) cold feed at 10°C and bathwater heated to 45°C. At a specific heat of 4.2 kJ/kgK that needs 100 x 4.2 x (45-10) = 14,700 kJ of net heat. Assuming 80% boiler efficiency that equates to 18,375 kJ gross , i.e. 5.1 kWh or say 40 pence.

Contrast that with 10 minutes in an 11kW electric shower: that’s 11  x 10/60 = 1.8 kWh, costing 55 pence, a bit more than the bath. Verdict: pointless

What about a shower fed from the gas heating? Suppose it’s a combi boiler with 16 kW water-heating capacity operating at 80% efficiency (ie 20 kW input) again for ten minutes. That would use 20 x 10/60 = 3.3 kWh of gas, costing 27 pence (13 pence less than the bath). Verdict: unexciting

Tip no. 4: turn off unwanted lights

Let’s take for our example an LED lamp rated at 10 watt. That will cost about 3 pence per hour to run but unlike ovens, kettles and baths, one tends to have a lot of them and use them continually so their cumulative effect in a  household could be relatively costly. Eight such lamps run on a daily basis for four hours more than needed would add 8 x 4 x 10 x 365 = 116.8 kWh per year, costing an extra £35 per year. Verdict: do it





Pipework insulation

MISSING insulation on hot pipework is not just a waste of energy and money. It can cause overheating of the space it occupies, may compromise delivery temperatures, and may even constitute a scalding hazard.

Allowable heat losses are stipulated in British Standard 5422, which lays down the requirements for compliance with building services compliance guides.

VESMA.COM provides a free on-line calculator which enables you to check whether a given thickness of a particular insulant is likely to be adequate.

STOP PRESS we are running a two-hour technical briefing on pipe, tank and duct insulation presented by Chris Ridge of the Thermal Insulation Contractors’ Association on 7 April, 2022. Details here.

Pre-audit desktop analysis

THE ANALYSIS TECHNIQUES that underpin energy monitoring and targeting have important applications in the search for energy-saving opportunities. A good energy audit doesn’t start with a checklist and a clipboard: it starts with some desktop analysis. Here’s how…

Regression analysis, in which we establish the historical relationship between consumption and its driving factor(s), can give us clues if we see anomalous patterns. Does consumption appear to be weather-related when it shouldn’t be, as in Figure 1? Does it fail to respond to production throughput (as in Figure 2) when logically it ought to vary? Do we seem to have unreasonable levels of fixed consumption?

Figure 1: electricity consumption on this campus was strongly weather related even though it had gas-fired main heating. The relationship should have been a horizontal line rather than sloping. Students were using portable electric heaters in their rooms
Figure 2: electricity consumption on this log-chipper did not fall with lower throughput as one might expect. The machine had high losses and was running continuously although logs were being fed through only occasionally

Regression analysis also enables ‘parametric’ benchmarking which is a simple but more effective variation on the theme (see separate article).

Cusum analysis meanwhile shows us whether past performance has been consistent, and if not, when it changed plus (when combined with regression analysis) in what manner. Did we add (or lose) some fixed demand? Or did sensitivity to a driving factor change? (Read more about cusum here).

Next, the concept of expected consumption enables the computation of ‘performance deficit’, meaning the absolute quantity of energy that we are using in excess of achievable minimum requirements. When translated into cost terms this gives us a clear view of where our most valuable opportunities lie (read more about performance deficit here).

And finally we could add visualisation of fine-grained consumption patterns. But that is costly. Everything else can be done with information collected at weekly intervals.

For training on energy analysis follow this link

Boiler sequencing

This bank of four boiler modules is operating at part load and infra-red imaging confirms that the left-hand module, which is shut down, is not losing heat to atmosphere thanks to an automatic flue damper which prevents cold air being drawn through it.

The other three modules are sharing a relatively light load by running at low output. This tends to incur less loss than operating one or two units at high fire, because the exhaust temperature is lower at reduced burner output.

Testimonials for energy monitoring and targeting training

Over the years I have trained hundreds of energy managers and consultants in the principles of energy monitoring and targeting. Here’s what some of them said…

  • Good combination of things I already knew and things that were new to me. Very engaging and I enjoyed the practical aspects and group involvement. – Jordan Harrison
  • Excellent course with Vilnis Vesma. Provided very useful and key techniques for M&T. Very engaging course as well, with regular exercises. One of the more fun and straightforward course I’ve been on! Thank you Vilnis. – GYE
  • The content is absolutely up-to-date and relevant to my role as energy expert and manager for the industry. All examples for were taken from practice, making this training even more interesting and trusted. It was not my first contact with deviation and CUSUM analyses. But this training brought me new and fresh perspectives. – JLS
  • Great course – RC
  • Great training, very interactive throughout – JW
  • A comprehensive course, packed full of useful nuggets of information – Tim Dennish
  • It’s so refreshing to find a lecturer that is firmly anchored to the ‘real’ world – David Parsons
  • Very useful course with lots of practical applications – Laura Storey
  • A simple approach to a complex subject! – David Roberts
  • Imperative knowledge for all energy managers – Levi Wong
  • The workshop was very worthwhile for someone like me whose business is energy saving products but not familiar with degree day concepts – Len Stevens
  • Excellent day giving basics of energy management – Bruce Claridge
  • A comprehensive workshop for people tasked with energy monitoring & targeting – David Enever
  • I never really understood degree days- and now I do! – Stuart Spencer
  • Vilnis delivers an enthusiastic seminar on energy metering suitable for professionals in the trade and company energy managers – Chris Steer
  • A much more useful way to spend £250 than simply paying your energy bill – Philip Wanless
  • Thought provoking – Ted Bradley
  • Very laid back and made to feel comfortable, being my first course
  • The most beneficial 1 day event I have attended
  • A very useful course with clear and concise information. Essential for any Energy Manager – Jon Farmer
  • Opened my eyes to the amount of added benefit that can be achieved with Degree Day data – Matthew Arnold
  • An excellent review of how to make the most of energy data – Gareth Ellis
  • Great course especially for engineers that use regression & cusum analysis, on a regular basis
  • I found the degree day training one of the most comprehensive and useful experiences of my career. Essential for anyone who needs to know about energy monitoring & targeting – Paige Hodsman
  • Vilnis is a polished presenter and makes a dry topic quite interesting + useful. Well done – Ed Farmer
  • Vilnis has many years of practical experience of energy monitoring & has a passion for sharing his knowledge; very refreshing – Catharine Bull
  • A well structured, thorough and valuable course ideal for businesses keen to save energy – Haydn Young
  • An excellent course for any energy manager wanting to make the most of analysing their consumption data in a meaningful way. Presented in plain English and exercises to help you apply your knowledge – Janette Ackroyd
  • I believe that the knowledge I have gained from the training day will be of great value to my clients and allow me to maintain a longer relationship with them – Laurence Fitch
  • Vilnis really knows his stuff. Excellent course. Highly recommended for anyone interested in monitoring + managing their energy consumption – Simon Hooper
  • A very useful and full day’s training on energy management & targeting. Knows his stuff – Nicholas Smyth
  • A fantastic course full of very useful techniques – Steve Ray
  • Fantastic, very powerful techniques to analyse consumption patterns – Denis Brennan
  • Good use of a day’s time and money – Adrian Evans
  • Within the first hour of the course I was itching to get back to work to put what I was being taught into practice – Adrian Stone
  • Excellent & very well designed – Jonathon Moffat
  • A focused, very practical and extremely useful day. Highly recommended – Nancy Higgins
  • Really targets the essentials – Neil Alcock
  • Gain more, use less. Fly Vilnis – S. Brown
  • Found potential savings the very day after attending the course – Stephen Middleton
  • Very well organised training with excellent presentations. Clear, precise & educational – Julia Clarke
  • The worked examples gave me ideas for analysis using data that was relevant to my organisation – Neil Fletcher
  • Enlightening energy analysis – Andrew Heygate-Browne
  • Excellent, well planned, well paced, inclusive and informative. Most helpful. Thank you – Alan Measures
  • Excellent course, well worth attending – John Taskas
  • All staff should attend this course – Mark Harrison
  • A course which I expected to be boring turned out to be quite interesting – Mick Morris
  • A very useful and extremely interesting course that was well presented – Robert Benson
  • Very interesting and thought provoking course – Avis Street
  • A very structured and well paced training event – Alan Asbury
  • Made concepts which had previously seemed very technical easy to understand – Charlotte Lythgoe
  • A teaching on the fundamentals of M&T that makes M&T simple – David Charles
  • A thorough understanding to the science of efficiencies! – Simon Mansfield
  • excellent, well balanced course and of practical use – George Zych
  • A comprehensive interactive course essential for all energy managers in every sector – Neil Bradley
  • Cusum isn’t the complex, scary thing I thought it was – Rebecca Taylor
  • Brilliant course- very relaxed delivery with practical examples making the material & subject easy to consume – Dave Belshaw
  • Has completely changed the way we analyse our projects going forward – David Dunbar
  • Lots of useful technical information presented at a good pace, and in a very accessible style
  • An excellent day, very sophisticated and detailed presentation for ‘aficionados’ of energy management – David Bradshaw
  • A very useful course, I wish I’d done it five years ago – Phill Windson
  • Excellent day- thanks Vilnis
  • If energy management is new to you then this is the course for you. It’ll get you on the right track straight away. All you could ever need to know- and more!
  • Excellent course that presented some very powerful energy saving techniques – Daniel Jones
  • This will completely revitalise our energy M & T – Donald French
  • armed with these skills you can tackle targeting with confidence – Gary Cooper
  • Excellent, knowledgeable presentation of simple but effective principles and techniques – Richard Ansell
  • Great course to understand the practicalities of energy M & T. – Tom Yearley
  • For once, a course I can actually put into practice at work – AD
  • A comprehensive course, well delivered
  • The course was very good, especially the section on setting targets and making them ‘aggressive but achievable’– AV
  • A necessary course for anyone handling energy data – looking forward to implementing as much of the content as possible across our properties.
  • Highly recommend this course for energy professionals or anyone wanting to know to monitor their energy. Excellent trainer, thorough course with practical exercises – Kate Ingham
  • A very useful and insightful course which has helped me greatly with my work in energy analysis – Grace Sadler
  • The course was delivered in a relaxed and friendly manner where questions and queries were encouraged which greatly assisted in the understanding of the subject. I would recommend the course to anyone interested in setting up an energy monitoring and targeting scheme – Tim Howard
  • A fantastic course to increase knowledge and confidence – Vicki Rees
  • A really helpful course which has enabled me to understand monitoring and targeting further – Alistair Mann
  • Very convenient location, informal, pleny of opportunities to discuss particular aspects and areas of interest, Fairly simple approach and not over-complicated, allowing everyone to keep pace. Some great take-away technical information. Time well spent. The energy monitoring and targeting training is a must for people new to energy management or those with prior knowledge. Some great and simple techniques to understand and inprove your energy performace, backed up with real world experiences – Peter Bowman
  • I now understand CUSUM! I felt it was very good at providing an overview and the theory.
  • Format, pricing and contetnt were all very good. Vilnis added a lot of depth to my understanding. If you are genuinely interested in energy management and making data-informed decisions, Vilnis Vesma will put you on the right track. – DC
  • I think the penny has finally dropped! – Gwen Kinloch
  • A very straightforward yet clever way of making sense of mountains of data. – Ben Foster
  • A great introduction to the fundamental techniques of monitoring and targeting. Highly recommended. – Darren Holman
  • Was very helpful for building confidence. – NKC

Book onto the next available course at

Frost protection: a point of weakness

Too often we see frost-protection thermostats set at too high a temperature, meaning that an unoccupied building will be heated for longer, and maintained at a higher temperature,  than is necessary for the purpose of preventing water services from freezing.

The diagram on the right shows how a common type of mechanical frost thermostat can be prevented from having too high a switching  temperature set. Or from being set dangerously low, for that matter. There is a protrusion on the dial and a series of bendable tabs is provided on a backplate which stop it at either end of the desired travel (in this case +2°C to +6°C). Your electrician will know how to do it.

Automatic control is one of the topics in our current season of energy technology briefings

Worst league table format ever?

The chart format on the left is a reconstruction of something I saw in an energy reporting system based on a generic platform who shall remain nameless (you know who you are). It is being used here to represent the relative total energy consumptions of a number of establishments. Although admittedly it is better than a pie chart, it is still one of the least user-friendly designs I have ever seen. The person who devised it should be ashamed of themselves.

Why have remote labels with a colour-coded key, when the labels could just be put alongside the bars they relate to as shown on the right-hand example? Especially as with so many entries the colours are hard to discriminate even for a user with perfect colour vision.

The right-hand version of the chart gives the identical information perfectly clearly with bars of the same colour, the additional advantage being that, if required, one specific item can be highlighted in a contrasting shade as shown. Oh, and it won’t matter if your computer monitor’s colour rendering is a bit off.

Zoom versus vroom

Participating in a remote meeting for one hour generates the same emissions as driving just 580 metres. That was my conclusion when someone asked me what were the relative environmental impacts of remote and in-person meetings. Here’s how I approached the question…

We’ll start by estimating the energy intensity of data communications. We know from an Ofcom study that in 2018 the average UK fixed broadband connection was using 240 GB per month, and if we assume £30 per month was the typical tariff, that works out at £0.125 per GB. Now let’s assume that this price covers the operator’s costs and that, pessimistically, 50% of that cost is for electricity which they were buying at (say) £0.15 per kWh. This implies an energy intensity of £0.125 x 50% / £0.15 = 0.42 kWh per GB.

But how much data is there in a remote meeting? Fortunately we can get a good direct estimate from the sizes of session recordings. My two-hour on-line events have typically resulted in recordings of around 500 MB, which must be the equivalent of all the data broadcast to each participant (as a sense check, that’s 250 megabytes per hour, or about 0.55 megabits per second bandwidth). To be conservative let’s add as much again for return traffic from each participant, giving a total of 500 MB (0.5 GB) per hour per participant.

At 0.42 kWh per GB that implies 0.5 x 0.42 = 0.21 kWh per participant-hour.

This only accounts for the communications element. To be fair we need to add the cost of central data processing and to do that I’m firstly going to guess that the server consumes 100 watts for the purposes of processing the meeting. Secondly I’ll assume that the meeting has four participants. That would imply 0.025 kWh per participant-hour, bringing the total to 0.235. The fact that it’s a small correction means the conclusions aren’t very sensitive to the number of participants. If we assume a grid carbon intensity of 0.3 kgCO2/kWh we arrive at emissions of 0.235 x 0.3 = 0.07 kgCO2 per participant-hour.

How does that final figure compare with car travel to the meeting? The average car in the UK emits about 0.12 kgCO2 per km, so attending an hour-long remote meeting equates, in emissions terms, to 0.07/0.12 = 0.58 km of car travel. Case closed.


This article first appeared in the Energy Management Register bulletin on 12 July, 2021. Subscriptions are free of charge: please follow this link. You can unsubscribe again from any issue.


M.E.P. event for energy assessors

Submitted by the Association of Midlands Energy Professionals 

The Association of Midlands Energy Professionals (MEP) invites you to join us for our FOURTH annual event for energy assessors and other energy professionals, under the title: “Gearing up for Change”.

With BREXIT behind us and the TRUSTMARK now up and running, MEES is having a significant impact on the type of work we do. WHOLE HOUSE RETROFIT, PAS2038, and THE FUTURE HOMES STANDARD are becoming even bigger drivers as the gathering momentum surrounding climate change is set to make 2021 a year of real involvement and opportunity for us in changing the behaviours of our customers.

We will be on the front line, giving advice and promoting change to UK consumers.

  • We will hear from a selection of keynote speakers who will be bringing us up to date on all the above and more. The speakers will include the leading lights from the Retrofit Academy, TrustMark, and the Accreditation Bodies.
  • There will be a selection of workshops to participate in. These workshops will give you tasters of the ‘state of art’ tools and techniques.
  • There will be a “BBC Question Time” style session where you can put questions to a panel of experts including the Accredited Bodies

This will be a full and informative day which will provide 5 hours CPD plus valuable networking with fellow assessors and other professionals.

  • Date: Wednesday 29 September 2021 (10.00 to 16.30)
  • Venue: SSDC HQ, Wolverhampton Rd, Codsall WV8 1PX.

The charge for the event is £50 for MEP members, and £60 for non-members. Subscribers to the Energy Management Register newsletter can join at MEP members’ rates using their customary discount code. There will be a £10 early bird discount for those booking before the end of August 2021.  Booking forms are available from

Case history – excessive cooling incident in a data centre


This story concerns a commercial data centre, and specifically its cooling system. The players are: (a) clients whose servers are housed in the centre; (b) a facilities operations team responsible for maintaining conditions in the server hall; and (c) a sustainability manager whose duty is to ensure that energy consumption is minimised. There is a service level agreement in place and the facilities team are contractually obliged to report regularly on the server-room temperature.

The sustainability manager regularly reviews consumption against weather-related targets, in order to detect excessive consumption. Specifically he uses the relationship between chiller electricity consumption and cooling degree days, as illustrated in Figure 1:

Figure 1: normal relationship between weekly kWh and weekly cooling degree days

The story

At the end of September 2020,  weekly consumption began to deviate from expected values. The first few weeks of abnormal performance are highlighted in Figure 2:

Figure 2: abnormally high weekly consumption is observed

Figure 3 is a control chart which shows that the deviation is not only statistically significant compared with anything previously observed, but it’s also persistent:

Figure 3: the control chart shows the difference between actual and expected consumption

At this point the sustainability manager challenged the operations team for an explanation. The problem turned out to be the location of the temperature sensor that was used for their routine service-level reports. It was not registering the actual air temperature at equipment level, but a higher value. To get around this problem the ops team had started overcooling the building to ensure that their temperature reports were within the specification.

The problem was ultimately rectified by relocating the sensor used for reporting, and reverting to the correct space temperature set point. Figure 4 shows how consumption then came back within its normal control limits:

Figure 4: once the situation was fully resolved, the difference between actual and expected consumption drops back