An energy audit is a structured review of how a building uses energy and where it could use less. It ranges from a quick walkthrough that finds obvious waste to a detailed study that estimates the cost and savings of specific upgrades. The value of an audit depends on choosing the right level of detail for your decision and acting on what it finds.
Why buildings get audited
- Rising energy costs, or bills that are high compared with similar buildings.
- Planning capital replacements and wanting to choose more efficient options.
- Applying for utility or government incentive programs, many of which require an audit.
- Meeting corporate or municipal emissions targets, or benchmarking and reporting requirements where they apply.
- Preparing for a green building certification or a sale.
Levels of energy audit
ASHRAE describes three commonly used levels of audit. Exact names and scopes vary between programs, so check what your incentive program or client actually expects.
| Level | What it involves | Typical use |
|---|---|---|
| Level 1: walkthrough | Review of utility bills and a site walkthrough to identify no-cost and low-cost measures and flag larger opportunities | A first look, or a building with obvious problems |
| Level 2: energy survey and analysis | Detailed inspection of systems, breakdown of energy use by end use, and cost and savings estimates for specific measures | Choosing and budgeting upgrades |
| Level 3: detailed analysis | In-depth study of major capital measures, often with monitoring and energy modelling | Large investments that need reliable savings estimates |
What an auditor looks at
Utility data
At least a year, and ideally two or three, of monthly electricity, gas and water bills. Comparing use with weather shows how much goes to heating and cooling. Comparing with similar buildings shows whether use is high overall.
Building envelope
Air leakage, insulation, windows and roofs. Heat loss through the envelope drives heating loads, especially in Canadian winters. See building envelope basics.
HVAC systems
Equipment efficiency and condition, ventilation rates, heat recovery, and above all how the controls operate. Schedules, setpoints and economizers often hold the largest low-cost savings. Our guide to building automation systems covers common control problems.
Lighting
Fixture types, lighting levels, controls such as occupancy sensors and daylight dimming, and operating hours.
Domestic hot water and plugs
Water heater efficiency, recirculation, fixture flow rates, and equipment left running such as computers, vending machines and block heaters.
Process loads
In industrial buildings, compressed air, process heat, refrigeration and motors can dominate. Compressed air leaks are a common example of hidden waste.
Types of measures
- No-cost and operational: tightening schedules, adjusting setpoints, clearing overrides, turning things off.
- Low-cost: fixing economizers, air sealing, occupancy sensors, pipe insulation, repairing leaks.
- Capital: equipment replacement, heat recovery, lighting retrofits, envelope upgrades, heat pumps.
Measures interact. Upgrading insulation, for example, reduces the size of the heating equipment you need. A good audit accounts for these interactions rather than adding up each measure separately.
After the audit
An audit report only saves energy once its recommendations are carried out. Many owners start with the operational measures, since they cost little and their results show up quickly on utility bills. Larger measures are then scheduled into the capital plan, ideally timed with equipment that is due for replacement anyway. Tracking energy use before and after each change shows which measures delivered and helps make the case for the next round.
A typical case
A two-storey office and warehouse building has gas and electricity bills that look high for its size, and the owner is about to replace two ageing rooftop units. An incentive program offers support for efficient equipment if an audit is done first.
Starting with the bills, the auditor plots monthly gas use against heating degree days and finds that gas use stays well above zero through the summer, which points to something heating year-round. Electricity use barely drops on weekends, which points to equipment running when the building is empty. The walkthrough confirms both: a warehouse unit heater with its thermostat set high and stuck, and the office rooftop units scheduled to run continuously after a controls replacement years ago.
Those are fixed for little cost. The survey and analysis level then looks at the rooftop unit replacement: comparing a like-for-like replacement with higher-efficiency units and with heat pump units, accounting for the reduced load once the schedules are corrected. The result is a smaller, better-matched replacement than the owner first expected, timed with the end of life of the existing units.
What the report should include
- A summary of energy use by fuel and, where it can be estimated, by end use.
- A list of measures, each with a description, estimated cost, estimated savings, payback and the assumptions behind the numbers.
- Notes on how measures interact, and the order in which to do them.
- Operational and maintenance recommendations that do not need capital.
- Anything the auditor could not assess, and why.
- What the incentive program requires, if the audit is being used for one.
Making an audit useful
- Be clear about your goal: cost savings, emissions, comfort or incentive eligibility.
- Give the auditor full utility data, drawings and equipment lists.
- Involve your operators. They know where the problems are.
- Ask for measures ranked by cost, savings and payback, with assumptions stated.
- Line up measures with planned equipment replacements to avoid paying twice.
- Assign an owner and a date to each measure you accept.
- Measure results afterwards, so you know the savings were real.
Check incentives before you start. Utility and government programs often have specific requirements for audit level, format and who performs the audit. Confirm them before commissioning an audit, so the report qualifies.
How ehZee can help
Our mechanical system inspections look at the condition and operation of HVAC and plant equipment, which is the heart of most energy savings. We can identify operational and control problems, help you plan equipment replacements with efficiency in mind, and coordinate with an energy auditor where a formal audit is required.
Common questions
How much can an energy audit save?
It depends entirely on the building and on whether the findings are acted on. Buildings with neglected controls often have the most to gain from low-cost measures.
Is an energy audit the same as an energy model?
No. An energy model is a computer simulation of a building's energy use. It is sometimes used within a detailed audit to estimate savings from complex measures.
How often should a building be audited?
There is no single rule. Many owners audit before a major capital plan, after a significant change in use, or when energy use rises without explanation.
What should we prepare before the auditor arrives?
At least a year of monthly utility bills for every fuel, drawings and equipment lists, operating hours and occupancy, recent maintenance reports, and a list of known problems and planned replacements. Access to the building automation system front end or trend data also helps.