What Happens During a Commercial Building Energy Audit?

What is the purpose of a commercial building energy audit?

The purpose of an audit is to establish:

• how the building uses electricity, gas or other fuels;
• what is driving consumption;
• whether energy use matches occupancy and operating hours;
• whether systems are working as intended;
• where energy may be wasted;
• which actions should be prioritised;
• where further investigation may be needed.

A good audit connects what the data shows with what is happening physically inside the building. This matters because energy waste is not always obvious.

What happens before the site visit?

The audit usually begins before the auditor arrives at the building.

The first stage is to understand the organisation, the building and the reason the audit has been commissioned. This may involve an initial discussion about:

• unexplained or rising energy use;
• high electricity or gas bills;
• out-of-hours consumption;
• heating or comfort complaints;
• controls that are difficult to understand;
• proposed capital projects;
• senior-management reporting;
• previous audits or recommendations;
• the need to prioritise limited budgets.

The auditor should also establish what information is available and which members of staff are best placed to explain how the building operates.

What information should the organisation provide?

Useful information may include:

• electricity and gas bills;
• half-hourly electricity data;
• meter readings and sub-meter data;
• Building Management System trend data;
• building operating hours;
• occupancy patterns;
• floor plans;
• equipment schedules;
• previous audit reports;
• maintenance records;
• contractor proposals;
• details of known problems or recent changes.

Not every organisation will have all of this information. The audit should still be able to proceed where records are incomplete, although gaps may need to be noted and further monitoring may be recommended.

Why is half-hourly data useful?

Half-hourly electricity data can reveal:

• when the building starts using more energy in the morning;
• whether plant starts before occupancy begins;
• whether consumption falls after closing;
• how much electricity is used overnight;
• whether weekends resemble weekdays;
• whether the building has a high baseload;
• whether unusual peaks occur;
• whether operating patterns have changed.

This allows the auditor to identify questions before arriving on site. However, data alone does not explain everything.

What should the organisation prepare?

Before the visit, it is helpful to:

• gather recent energy bills;
• request half-hourly data from the electricity supplier;
• identify the main meters;
• provide normal opening hours;
• note unusual operating periods;
• list known building problems;
• identify recent changes to occupancy or equipment;
• arrange access to plant rooms;
• identify someone who understands the controls;
• identify someone who understands day-to-day building use.

The organisation does not need to diagnose the problems in advance. Practical preparation simply helps the auditor spend more time examining the building.

Who should be involved?

The most useful person to accompany the auditor is usually someone who understands how the building operates in practice.

This may be a facilities, estates, building, operations, maintenance, sustainability, technical or site manager.

In some buildings, no single person has the complete picture. Facilities may understand the plant, finance may hold the bills, operations may know the opening hours and contractors may control the Building Management System.

What happens at the start of the site visit?

The auditor may ask:

• What are the normal operating hours?
• Which areas are occupied at different times?
• Are there evening or weekend activities?
• Are there comfort complaints?
• Have energy costs increased?
• Are any systems difficult to control?
• Have settings recently been changed?
• Are there planned projects?
• Are there known maintenance issues?
• Which systems must operate continuously?

This discussion provides context for the physical inspection and may reveal differences between the intended operating pattern and what happens in practice.

What does the auditor inspect?

The exact inspection depends on the building, but it will normally cover systems such as:

• boilers and heat pumps;
• chillers and pumps;
• air-handling units and ventilation systems;
• extract fans;
• local air-conditioning and electric heaters;
• hot-water systems;
• lighting;
• refrigeration or specialist equipment;
• meters;
• controls and BMS screens;
• sensors;
• occupied and unoccupied areas.

The auditor looks for evidence of how systems are controlled, when they operate and whether their behaviour matches the needs of the building.

Heating, cooling, ventilation and lighting

Heating systems

The auditor may check heating schedules, start and stop times, temperature set points, weather compensation, frost protection, zoning, pumps, local controls, portable heaters and simultaneous heating and cooling.

Even efficient plant can waste energy if it operates for too long, serves empty areas or is controlled poorly.

Cooling and ventilation

The audit may examine air-handling unit schedules, supply and extract fans, cooling set points, local systems, ventilation rates, heat recovery and occupancy controls.

Lighting

The auditor may review fitting types, operating hours, occupancy controls, daylight controls, external lighting, over-lit areas and opportunities for LED replacement.

Building Management System and controls

The auditor may review:

• time schedules;
• temperature set points;
• holiday settings;
• optimum start and stop;
• overrides;
• alarm history;
• sensor readings;
• trend data;
• weekend settings;
• control zones;
• competing systems.

A schedule may appear correct while the plant behaves differently. Sensors may be inaccurate, overrides may remain active or local systems may operate independently.

What does the auditor look for in occupied areas?

Occupied areas can reveal:

• rooms that are consistently too hot or too cold;
• windows opened while heating is operating;
• portable heaters;
• local air-conditioning units;
• lighting left on unnecessarily;
• equipment running continuously;
• blocked vents;
• thermostats in unsuitable locations;
• areas with different operating patterns.

Good energy management is usually about better control, not poorer conditions.

Does the audit disrupt normal operations?

A commercial building energy audit should normally cause little disruption. Most of the visit involves inspecting equipment, reviewing controls, looking at meters, walking through occupied and unoccupied areas and speaking with relevant staff.

Any areas with specialist access, security, conservation or safety requirements should be discussed in advance.

How long does a site visit take?

The length of the visit depends on:

• building size;
• number of systems;
• complexity of controls;
• number of plant rooms;
• access arrangements;
• number of meters;
• operating pattern;
• specialist equipment;
• the scope of the audit.

The site visit is only one part of the work. Time is also needed before and after the visit to review data, analyse findings, estimate savings and prepare recommendations.

Does the auditor switch equipment off?

The auditor will not normally switch off major systems without agreement from the responsible staff.

Essential, life-safety, security, environmental and process-critical systems must remain protected. However, the audit may identify opportunities for controlled testing, such as adjusting a schedule, checking whether equipment stops correctly or comparing consumption before and after a change.

How is out-of-hours energy use investigated?

The auditor may compare:

• occupied and unoccupied electricity demand;
• weekday and weekend profiles;
• expected and measured baseload;
• heating schedules;
• fan and pump operation;
• local systems;
• control overrides;
• gas use outside normal hours.

Common sources of unnecessary consumption include heating operating overnight, pumps running continuously, ventilation left on, cooling serving empty areas and weekday schedules copied into weekends.

What happens after the site visit?

The auditor brings together:

• energy data;
• site observations;
• photographs;
• equipment information;
• operating hours;
• control settings;
• discussions with staff;
• identified problems;
• potential opportunities.

The aim is to develop a clear diagnosis and decide which measures are appropriate, significant and realistic.

How are savings calculated?

Where sufficient information is available, the auditor may estimate:

• annual energy savings;
• annual financial savings;
• carbon reduction;
• implementation cost;
• simple payback;
• level of confidence;
• assumptions used.

Not every finding can be calculated precisely. Some measures may require a contractor quotation, detailed design, temporary monitoring, equipment testing or specialist investigation.

What kinds of recommendations might be made?

Recommendations may include:

• correcting schedules;
• reducing overnight operation;
• resetting overrides;
• changing temperature set points;
• repairing sensors;
• improving zoning;
• adjusting ventilation;
• maintaining plant;
• installing occupancy controls;
• improving staff procedures;
• upgrading lighting;
• improving insulation;
• reviewing plant replacement;
• investigating solar PV;
• introducing regular monitoring.

Recommendations should be specific to the building and linked to an identified problem.

Are quick wins identified?

What if more information is needed?

The auditor may recommend:

• temporary sub-metering;
• temperature or humidity logging;
• sensor testing;
• plant trend analysis;
• further BMS review;
• contractor quotations;
• specialist surveys;
• detailed design;
• monitoring after a control change.

Recognising where more evidence is needed is better than making a recommendation based on insufficient information.

What does the final report contain?

The final report should normally include:

• an executive summary;
• building and operational context;
• energy-consumption analysis;
• half-hourly data findings;
• plant and controls observations;
• identified sources of waste;
• practical recommendations;
• costs and savings where possible;
• payback estimates;
• prioritised actions;
• areas requiring further investigation.

What happens when the report is delivered?

The organisation should decide:

• which actions can begin immediately;
• who is responsible;
• which measures require quotations;
• what needs further investigation;
• what budget is available;
• how progress will be tracked;
• when energy data will be reviewed again.

A report is only valuable if the recommendations are followed through.

Does the process differ by sector?

The core method remains similar, but the focus changes according to the building and its operating requirements.

Questions to ask before commissioning an audit

• What information will be requested?
• Will half-hourly data be analysed?
• Is a site visit included?
• How long will the visit take?
• Which systems will be inspected?
• Will controls and schedules be reviewed?
• Will out-of-hours use be investigated?
• Will staff be interviewed?
• What will the report contain?
• Will recommendations be prioritised?
• Will costs and savings be estimated?
• How will uncertainty be shown?
• Is a follow-up discussion included?
• What might require additional work?

How much does the process cost?

Oxford Energy Services offers a fixed-fee Building Energy Audit for one commercial building at £1,500.

Energy audit, energy assessment or ESOS assessment?

These terms are sometimes used interchangeably, but they do not always mean the same thing.

A building energy audit is usually focused on understanding the performance of a specific building and identifying practical actions. An ESOS assessment forms part of a statutory compliance process for qualifying organisations and may cover a wider organisational energy picture.