Checklist: Verifying Energy Efficiency Data in Supplier Proposals

When a supplier sends a technical proposal for a new compressor, the first thing many buyers check is the price. The second thing is often the warranty. The third is the energy efficiency data. That data determines the operating cost of the machine for the next fifteen to twenty years. A small difference in specific power consumption can result in thousands of dollars in extra electricity bills over the life of the unit.

However, the numbers in a proposal are only as good as the assumptions behind them. Vendors often use best-case scenarios to make their equipment look better. They may quote the efficiency at ideal ambient conditions while ignoring the high summer heat in your facility. They might list the motor efficiency but ignore the efficiency loss from the drive system. This checklist helps you audit those numbers before you sign the purchase order.

Check the Motor and Drive Specifications

The motor accounts for a large portion of the total energy input. If the proposal lists a motor efficiency class, verify that it matches the specific model number. Do not accept a generic “high efficiency” label. Ask for the specific nameplate data.

Look for the motor power rating in kilowatts or horsepower. Check the efficiency percentage at full load. For large industrial air compressors, the difference between a standard motor and a high-efficiency motor can be significant. If the proposal includes a variable speed drive, verify the drive efficiency class. A VSD adds its own losses. The total system efficiency is the combination of the compressor and the drive.

Ask for the voltage and frequency. A mismatch here can cause the compressor to run at a different speed than intended, changing the capacity and energy consumption figures.

Verify the Capacity and Flow Rates

The capacity in a proposal is usually stated in standard cubic meters per minute. Confirm that this is at the standard reference conditions. Different industries use different reference points. Some use standard cubic feet per minute. Others use actual cubic meters at plant conditions.

Check the pressure rating. A compressor rated for 7 bar is not the same as one rated for 10 bar. The energy required to compress air to a higher pressure is higher. Ask for the specific power consumption at the operating pressure. Specific power is measured in kilowatts per cubic meter of free air delivered. A lower number is better.

If the proposal gives a curve, look at the point where your plant actually operates. Most plants do not run at 100 percent capacity. They often run at 60 to 80 percent. Ask for the specific power at that partial load point. A compressor that is efficient at full load may be inefficient at partial load if it is not the right size.

Audit the Load Profile and Duty Cycle

The energy consumption of a compressor depends heavily on how the air is used. A plant that uses air continuously at a steady flow has different energy characteristics than a plant that uses air in short, heavy bursts.

Ask the supplier to model the load. If they provide a flat energy cost estimate, ask how they calculated it. A good proposal will show the energy consumption over a 24-hour period based on your actual demand. If the supplier only gives you a number per hour, they are probably assuming a constant load. That is a red flag.

Check the duty cycle. For on-off compressors, the duty cycle is the percentage of time the machine runs. A high duty cycle means the motor runs hot. It increases wear and can reduce efficiency over time. For VSD compressors, the duty cycle is less of a concern, but the control strategy matters. Ask how the controller manages the speed. Does it use a pressure switch? Does it use a proportional control? The method affects the energy data.

Consider Ambient Conditions and Altitude

Compressed air is a gas. Its density changes with temperature and altitude. A compressor in a hot, high-altitude location produces less dense air. It has to work harder to produce the same volume of free air.

Check the ambient temperature assumption in the proposal. Most standard ratings are at 20 degrees Celsius. If your plant is in a hot climate, or if the compressor room is not ventilated, the intake air temperature will be higher. Ask the supplier to derate the capacity and adjust the energy figures accordingly.

Altitude matters too. At high altitudes, the air is thinner. The compressor intake has more work to do to draw the air in. If the proposal does not mention altitude correction, ask if the numbers are for sea level. If your site is above sea level, the actual capacity and energy consumption will differ from the quoted figures.

Look for Test Standards and Third-Party Verification

Efficiency claims should be backed by a recognized test standard. Ask which standard was used to measure the data. Common standards include those from the International Association of Refrigeration and Air Conditioning and those from national energy efficiency agencies.

If the data is only from the manufacturer’s internal lab, be skeptical. Independent testing is more reliable. Ask if the specific model has been tested by a third-party laboratory. If they cannot provide a test report or a certificate, ask why.

Check the test conditions. Were the tests done at the same pressure and temperature as your operating conditions? If the tests were done at a different pressure, the energy data may not apply to your plant. A test report that does not match your operating profile is not very useful.

Red Flags in Supplier Proposals

While you audit the data, watch for these warning signs.

Red Flag	What It Means
Vague efficiency language	Phrases like “very efficient” or “top tier” without numbers.
Missing specific power	Only total power consumption is given, not power per unit of air.
No load profile data	The proposal assumes a constant load without checking your actual usage.
Idealized ambient conditions	The data assumes 20 degrees Celsius and sea level without adjustment.
Unexplained efficiency curves	The graph shows a dip at partial load but the text ignores it.
No test standard cited	The numbers are not tied to a recognized industry standard.

If you see these flags, ask for clarification. Do not assume the data is correct just because it looks professional. A supplier who hesitates to provide specific numbers may not have the data. Or they may be trying to sell you a machine that does not fit your needs.

How to Use the Checklist in a Negotiation

Use this checklist to ask targeted questions during the sales meeting. Do not just ask “is this efficient?” Ask “what is the specific power consumption at 50 percent load and 7 bar pressure, assuming 30 degrees Celsius ambient air?”

If the supplier cannot answer that specific question, they are not prepared to provide accurate energy data. They may be relying on general marketing claims. You can use this to push for a more detailed proposal. Ask them to run a simulation based on your actual load profile.

Keep a copy of this checklist. Send it to the supplier as part of your Request for Proposal. It shows that you are a serious buyer who understands the technology. It also sets the stage for a fair comparison between different vendors. If three suppliers all provide the same level of detail, you are in a good position to compare them. If only one provides the data, you have your answer.

The goal is not to be difficult. The goal is to buy the right machine. Energy efficiency data is the bridge between the sales pitch and the operating reality. Verify it. Audit it. Check the assumptions. Then make your decision based on facts, not promises.

Final Steps Before Signing

Before you sign the contract, do one last check. Compare the energy data in the proposal with the data in the operating manual. They should match. If they do not, ask for an explanation.

Also, check the spare parts list. Efficient compressors often have specific components that are expensive. Make sure the supplier includes them. If the energy savings are real, they will come back to you in the form of lower electricity bills. If the efficiency is exaggerated, the savings will disappear, and you will be left with a machine that does not perform as promised.

This checklist is a starting point. Use it to guide your questions. But remember, the best data comes from a supplier who understands your specific application. Ask for a site visit. Ask for a pilot test. Ask for a guarantee on the energy performance. If they are confident in their data, they will be happy to prove it.