Category Archives: Audits and surveys

Impact of proposed changes to ESOS

Dateline 5 June 2023


Under the terms of the Energy Savings Opportunity Scheme (ESOS) Regulations 2014, the UK’s large private-sector undertakings have to assess their major energy uses every four years to identify cost-effective energy-saving opportunities. They are then supposed to notify compliance through the government-appointed scheme administrator, the Environment Agency (EA), before 5 December 2023. Compliance must be assessed and ‘signed off’ by a registered lead assessor.

We’re currently in the third compliance period, reporting on energy audits—which may have been carried out at any time since December 2019—related to the participants’ assets and corporate structures as they stood on 31 December 2022.

The issues

A number of participants have completed their assessments, and had them signed off, but the EA has failed to open a notification system[1] because it plans to change some of the requirements. Some of the proposed amendments to ESOS are potentially onerous, notably the extension—from 90% to 95%–of the proportion of energy use that a participant must audit. For many, that will mean suddenly having to add marginal minor energy uses where the cost of assessment is disproportionate to any possible gains. Vehicle fuel is the classic example.

The EA has been issuing guidance to participants (most recently on 24 May 2023) which assumes that the ESOS regulations will indeed change before 5 December. Although likely, it is not certain that they will change[2], which could potentially lead to participants undertaking needless extra work. This incidentally puts participants’ energy auditors and lead assessors in a difficult contractual and commercial position. Strictly speaking the EA has no legal basis for the guidance it is currently issuing because it cannot guarantee that the regulations will change nor, if they do change, that they will be applicable to participants certified as compliant before the new regulations take effect.

As a separate issue, part of the guidance issued by the EA is a template listing information that participants will need to supply during the notification process once it becomes available. A substantial part of the information relates to matters such as the savings achieved since previous ESOS cycles, and assorted (in some cases dubious) performance metrics. This amounts to market research or impact assessment and responses to these questions ought to be voluntary since they are not at present stipulated as requirements of ESOS and there appears to be no provision for them to become requirements in any new regulations[3]. If treated as mandatory, they will further add to compliance costs.

Suggested actions

The prudent approach is to assume that Parliament will approve new ESOS regulations before 5 December and EA will force the issue, making them in effect retroactive and incidentally making the market-research questions mandatory part of the notification process.  Whatever happens it is almost certain that new ESOS requirements will be in effect for the next compliance period, so the effort of setting up the necessary record-keeping and reporting now will not be entirely wasted.

However, to minimise the impact during the current ‘phase’ of ESOS I would suggest:

  1. Lobby against any revised regulations taking effect before 5 December 2023;
  2. If they do take effect, lobby for them not to apply to participants certified as having complied before the date that the new regulations become law;
  3. Lobby for the exclusion from the Notification System of questions related to market research or impact assessment.


[1] ESOS Regulation 8(1) obliges the Scheme Administrator to establish a Notification System but Regulation 8(2) allows it to make it available to participants only when they decide it is ‘reasonable’.

[2] The Secretary of State cannot at the moment even lay new ESOS regulations before Parliament; he lost the power when the European Communities Act 1972 was repealed. The Government is relying on the successful passage through Parliament of the Energy Bill (currently with the Public Bills Committee) to restore those powers and enable new regulations to be laid before Parliament and voted into law.

[3] The writer was unable to identify any specific provision in the relevant part (Part 10) of the Energy Bill

Link: Main article on ESOS

Energy audits and surveys: rule of three

ENERGY surveys and audits – deliberate studies to find energy-saving opportunities – can be done with three levels of depth and thoroughness, can look at three broad aspects of operations, and will generally adopt one of three approaches.

Depth and thoroughness

Let’s take depth and thoroughness first. Level 1 would be an opportunity scan. This typically has a wide scope, and is based on a walk-though inspection. It will use only readily-available data, and provide at most only rough estimates of savings with no implementation cost estimates. It will yield only low-risk recommendations (the “no-brainers”) but should identify items for deeper study.

Level 2 is likely to have a selective scope (based perhaps on the findings from a Level 1 exercise). It is best preceded by a desktop analysis of consumption patterns and relationships, which means first collecting additional data on consumption and the driving factors which influence it. It should yield reasonably accurate assessments of expected savings but probably at best only rough cost estimates. It can therefore provide some firm recommendations relating to ‘safe bets’ and otherwise identify possible candidates for investment.

Level 3 is the investment-grade audit. This may have a narrow scope – perhaps one individual project – and will demand a sketch design and feasibility study, with accurate assessments of expected savings, realistic quotations for implementation, sound risk evaluation and (I would recommend) a measurement and verification plan.

Aspects covered

Next we will look at the three broad aspects of operations that the audit could cover. These are ‘technical’, ‘human factors’, and ‘procedural’.

Technical aspects will encompass a spectrum from less to more intrusive (starting with quality of automatic control and set points through energy losses to component efficiencies). In manufacturing operations the range continues through process layouts, potential for process integration and substitution of alternative processes.

Human-factors aspects meanwhile will cover good housekeeping, compliance with operating instructions, maintenance practices, training needs and enhanced vigilance.

Thirdly, procedural aspects will include the scope for improved operating and maintenace instructions, better plant loading and scheduling, effective monitoring and exception handling, and ensuring design feedback.

Approaches to the audit

The final three dimensions relate to the audit style, which I characterise as checklist-based, product-led, or opportunity-led.

The checklist-based approach suits simple repetitive surveys and less-experienced auditors.

Product-led audits have a narrow focus and exploit the expertise of a trusted technology supplier. Because the chosen focus is often set by advertising or on a flavour-of-the-month basis, the risk is that the wrong focus will be chosen and more valuable opportunities will be missed. Or worse still, the agenda will be captured by snake-oil merchants.

Finally we have the ‘opportunity-led’ style of audit. This is perhaps the ideal, although not always attainable because it needs competent auditors with diverse experience and will include the prior analysis and preliminary survey mentioned earlier.

These ideas, together with other advice on energy auditing, are to be covered in a new optional add-on module for my “Energy efficiency A to Z” course which explais a wide range of technical energy-saving opportunities. Details of all my forthcoming training and conferences on energy saving can be found at

Tracking performance of light vehicles

Here is a monitoring challenge: suppose you want to do a weekly check on the performance of a small fleet of hotel minibuses. Although you can record the mileage at the end of each week, you will have a lot of error in your fuel measurement because you’ll only know how much fuel was purchased but not when. How can you adjust for the inconsistent fuel tank level at the end of the week?

One method would be to use the trip computer display which will show the estimated remaining miles (see picture). The vehicle in question has a 45-litre tank: at its typical achieved average mpg, it has a range of 613 miles of which it has used 39%, so we can add 45 x 0.39 = 18 litres to our calculated fuel consumption. Note that we will need to deduct an equal amount from next week’s consumption, and this “carry forward” is likely to reduce the error in the adjustment.

This procedure also helps if drivers do not consistently fill to the top. To the extent that they underfill on the last occasion in the week, the shortfall will increase the adjustment volume to compensate. The adjustment can only ever be approximate, however, so it’s better if they consistently brim the tank.

The other advice I would give is to track not miles per gallon (or any similar performance ratio) but to plot a regression line of fuel versus distance. This will pick up, and detect changes in, idling behaviour.

Monitoring electrically heated and cooled buildings

WHEN you use metered fuel  to heat a building (or indeed if you use the building’s electricity supply, but have no air-conditioning) it is straightforward to monitor heating performance critically because you can relate energy consumption to the weather expressed as degree days.

Things get difficult if you use electricity for both heating and cooling and everything shares a meter, as would be the case if you use reversible heat pumps (air-source or otherwise). Because the seasonal variations in demand for heating and cooling complement each other (one being high when the other is low), you may encounter cases where the sum of the two appears almost constant every week. Such was the case on this 800-m2 office building:

Figure 1: apparent low sensitivity to weather


Without going into detail, this relationship implied a heating capacity of little over 1 kW, which is obvious nonsense as there was no other source of heat. The picture had to be caused by overlapping and complementary seasonal demands for heating and cooling, which is illustrated conceptually in Figure 2:

Figure 2: total consumption is the sum of heating and cooling demands


The challenge was how to discover the gradients of the hidden heating and cooling lines. The answer in this case lay in the fact that we had sufficient information to estimate the building’s heat rate, which is the net heat flow from the building in watts per unit inside-outside temperature difference (W/K). The heat rate depends on the thermal conductivity of the building envelope and the rate at which outside air enters. There is a formula for the heat rate Q:

Q = Σ(UA) + NV/3

Where U and A are the U-values and superficial areas of each building element (roof, wall, window, etc), V is the volume of the building and N is the number of air changes per hour. Figure 3 shows the spreadsheet in which Q was calculated for the building in question (an on-line tool to do this job is available at

Figure 3: calculation of heat rate

In this case the building measurements were taken from drawings, the U-values were found on the building’s Energy Performance Certificate (EPC), and the figure of 0.5 air changes per hour is just a guess.

The resulting heat rate of 955.5 W/K equates to 955.5 x 24 / 1000  = 22.9 kWh per degree day. This is heat loss from the building but it uses a heat pump and will therefore require less input electricity by a factor of, in this case, 3.77 (that being the coefficient of performance cited on its EPC).  So the input energy required for heating this building is 22.9 / 3.77 = 6.1 kWh per degree day. This is the gradient of the unknown heating characteristic, the upper dotted line in Figure 2.

Need training in energy management? Have a look at

To work out the sensitivity to cooling demand we use a little trick. We take the actual consumption history and deduct an allowance for heating load which, in each week, will be 6.1 times the number of heating degree days (remember we just worked out the building needed 6.1 kWh per degree day for heating). This non-heating electricity demand can now be analysed against cooling degree days and this was the result in this case:

Figure 4: variation of non-heating electricity with cooling degree days


The gradient of this line is 3.5 kWh per (cooling) degree day. It is of similar order to the 6.1 kWh per degree day for heating, which is to be expected; the building’s heat loss and gain rates per degree difference are likely to be similar. As importantly, we now have an intercept on the vertical axis (a shade over 1,200 kWh per week) which represents the non-weather-related demand. Taking Figure 1 at face value we would have erroneously put the fixed consumption at around 1,500 kWh per week.

Also significant is the fact that Figure 4 was plotted against cooling degree days to a base of only 5°C. That was the only way to get a rational straight line and it means there is a finite amount of cooling going on at outside temperatures down to that value. I had been assured that cooling was only enabled “when the weather got hot”. But plotting demand against cooling degree days to, say, 15.5°C (a common default for summer-only use) gave the result shown in Figure 5:

Figure 5: non-heating electricity demand against cooling degree days to a base of 15.5C


This is not as good a correlation as Figure 4 and my conclusion in this case was that when the outside temperature is between 5 and 12°C, this building is likely to have some rooms heating and some cooling.

Chiller fan and motor replacement

By Lawrence Leask, Excalibur Energy

Recent changes to legislation means that operators of HVAC chillers and refrigeration equipment should review their equipment and the availability of replacement condenser fans.

In the past few months, we have had several enquiries to supply replacement AC axial fans for air cooled chillers from end users unable to obtain direct replacement fans, or where the cost has become prohibitive. Their predicament is not unusual and the situation is likely to get worse, with many fans no longer being manufactured, or only manufactured in short production runs.

Since 2017, all new condenser fan motors used on new chillers and condensers are required to meet the International Electrotechnical Commission (IEC) motor efficiency regulations and the Energy-related Products Directive 2015 (ErP). This has pushed manufacturers to look at the overall efficiency of fans and account for the entire fan, including the control electronics, motor, bell mouth and impeller and to define minimum efficiency requirements for the fans.

New Equipment manufacturers cannot use products that do not meet the regulations on new equipment but can continue to sell motors or fans that do not meet the regulations as spares to existing equipment.

Fan manufacturers and OEM’s have benefited from the spares market at the expense of the end user by selling replacement parts at ridiculously high margins. In addition to these high costs imposed on the end user, the end user should avoid trying to repair motors, as rewinds further reduce efficiency.

EC motor technology is around 30% more efficient than AC motors due to the secondary magnetic field coming from permanent magnets rather than copper windings

For many clients, we have removed all the existing AC fans and replaced them with the latest design IE4 Super Premium EC fans which have built in speed controls making them perfect for HVAC applications.

With speed control built into each motor, it allows all the fans on each circuit to operate together, modulating the speed to maintain accurate discharge pressure dependent on the cooling demand and ambient air temperature.

When you consider the CIBSE guidelines HVAC equipment life cycle is 15-25 years and that AC fans typically last 5-8 years it makes the retrofitting of EC fans a viable option to re-life an asset whilst improving efficiency and making use of the latest technology without the disruption and total cost of replacement.

Postscript: condenser cleaning
That’s the way to do it

Dirty condensers can also have a drastic effect on compressor efficiency. To clean an air-cooled condenser correctly the fans should be removed and the coils cleaned in the opposite direction to airflow. This is rarely done due to cost and disruption, but incorrect cleaning in the direction of airflow can bury debris deeper into the coil, further reducing airflow and efficiency.

The correct deep cleaning of condenser coils can economically be undertaken at the same time as fan replacement as access can be gained during fan removal.


Excalibur Energy is willing to provide fully costed proposals with an energy analysis showing how performance can be improved for refrigeration energy-saving projects in connection with ESOS assessments which includes air-cooled chillers and condensers, dry air coolers and evaporative condensers. Contact: 

Unit 115 Rivermead Business Park, Swindon SN5 7EX. 

Tel: 01793 934058 or email

Energy Savings Opportunity Scheme

ESOS is the UK government’s scheme for mandatory energy assessments which must be reviewed and signed off by lead assessors who are on one of the approved registers. We are now in the third compliance period, with an original submission deadline of 5 December 2023 postponed to 5 June 2024 to give the Government time to change the Regulations and make them more onerous.

I run a closed LinkedIn group for people actively engaged with ESOS; it provides a useful forum with high-quality discussion.

Background reading

Responsible undertaking contacts: ESOS lead assessors can notify the EA in bulk of the contacts in each Responsible Undertaking using this spreadsheet .