Supplier bid normalisation worksheet for compressor quotes

What the worksheet does

Compressor quotations rarely describe the same thing. One bidder offers a bare package at 7 bar, another includes a refrigerated dryer, filters and a receiver, a third quotes a variable-speed machine with a different flow unit and leaves electrical work to the buyer. Putting the three headline figures side by side tells you very little.

The worksheet keeps three questions separate:

• Is the offer technically eligible? Does it meet the required free air delivery (FAD), pressure, air quality and site conditions on supported evidence?
• What must be added to make it comparable? Dryers, filters, receivers, controls, electrical work, installation, commissioning and freight that one bidder includes and another excludes.
• What does the comparable arrangement cost over the chosen period? Purchase or hire, energy, maintenance, consumables and support.

The original quotation always stays visible beside every adjustment. The worksheet never rewrites a supplier’s promise or turns an estimate into a firm price. Each addition or credit carries a short note of where it came from and whether it is confirmed, estimated or awaiting clarification.

Inputs you need before reading any price

Freeze the requirement first. If the duty changes halfway through the evaluation, every bidder must be asked to respond to the revised duty, otherwise the comparison drifts.

Step-by-step method

1. File the original offers. Record each bid exactly as received, with its revision and date. Extract values into the worksheet and note the page or clause they came from.
2. Screen eligibility. Mark each mandatory requirement as met, not met or unclear. An offer that fails a mandatory requirement is not “scored lower”; it is ineligible until the bidder revises it.
3. Convert units. Bring all flows to one unit and one reference condition, and all pressures to bar(g) with psig alongside. Do not convert a flow quoted at 7 bar into a flow at 8 bar by arithmetic; ask for the data at the required pressure.
4. Build the scope ledger. For each bid, list required items as included, excluded (add a cost) or unclear (raise a clarification). “Included” must be confirmed in the offer, not assumed.
5. Deduct internal consumption. Subtract supported dryer purge, drain losses and any other air the package uses itself, to arrive at net usable flow.
6. Calculate comparable installed cost. Original price, minus confirmed discounts, plus required additions on a common delivery basis.
7. Add lifecycle cost. Energy from the operating profile and supported power data, plus maintenance, consumables and support over the chosen period.
8. Write the decision and the clarification list. State which bid is preferred, on what conditions, and which questions remain open.

Normalising flow, pressure and power

Flow conversions are the most common source of error. One cubic foot is 0.0283168 m³, so 750 cfm is about 21.24 m³/min. That arithmetic is only valid if both figures use the same reference conditions. A “normal” m³ at 0 °C and a “free air” m³ at site intake conditions are not the same quantity, and the difference is large enough to change a ranking.

Pressure needs the same discipline. Confirm whether a figure is the maximum working pressure, the rated pressure at which FAD was measured, or the setting at the package outlet after the dryer and filters. A package that reaches 8 bar at the compressor discharge may deliver noticeably less at the far end of the treatment train.

For power, compare total package input power at the duty point, including fan motors and dryer, not just the main motor nameplate. Two machines with the same 90 kW motor can draw quite different power for the same air. Specific power in kW per m³/min is a useful diagnostic, but only after both machines have passed the capacity check.

Worked example A: the lowest quote becomes the higher installed cost

This is an illustrative case with invented cost units, not real prices. Two technically eligible bids are offered for the same compressor-and-treatment scope.

Bid A starts 40 units cheaper but finishes 30 units dearer once the missing scope is added. The conclusion covers installed cost only; energy, maintenance and support still need comparing.

Worked example B: a unit conversion cannot fix a capacity shortfall

The requirement is at least 20.0 m³/min of net treated air at 8 bar(g) (about 116 psig). All three bids are assumed to use the same reference conditions.

Bid A has the larger gross figure but fails on net flow. Bid C cannot be credited with 22 m³/min at 8 bar because its data is at 7 bar; ask for the operating point you need. If A and B draw 124 and 126 kW, A looks marginally better on specific power only on gross offered flow (5.77 against 5.93 kW per m³/min). On net flow, the basis this page requires, B is better (6.23 against 6.29 kW per m³/min for A), and nothing cancels A’s capacity failure.

Worked example C: the load profile reverses the full-load picture

A fixed-speed and a variable-speed bid look similar at full load. The plant runs about 6,000 hours a year, of which only a third is near full demand and the rest is at 50–70% demand. When the energy is calculated hour band by hour band, using each bidder’s supported part-load power, the variable-speed machine can use less energy even though its full-load specific power is slightly higher. Reverse the profile, with long periods at full load, and the fixed-speed machine may win. Calculate kWh per year for each band, using each bidder’s part-load power, so the result follows your actual profile rather than a brochure claim. The live worksheet compares energy at one operating point, the required net flow, so run the band calculation separately.

Handling uncertainty and scoring

Do not convert every unknown into an arbitrary percentage penalty. If a bidder has not stated whether commissioning is included, the correct entry is “clarification”, not zero and not a guessed cost. Keep a short open-items list and send it to all bidders at the same time.

Weighted scoring can help where several eligible offers are close and non-price factors matter, such as service access in your region or spare-parts identification. Keep two rules:

• A low price can never offset a mandatory technical failure.
• Weights must be agreed before the bids are opened, not adjusted afterwards to favour an outcome.

Common mistakes the worksheet prevents

• Comparing a bare compressor with a complete treated-air package.
• Treating cfm and m³/min figures as equal without checking reference conditions.
• Ignoring dryer purge and drain losses when checking net flow.
• Comparing main-motor kW instead of total package input power.
• Leaving electrical, civil and piping work unassigned to anyone.
• Using full-load energy for a plant that mostly runs at part load.
• Forgetting interim supply: if the new machine arrives late, temporary air may be needed.

How Reddy Compressors helps

Reddy Compressors has worked with industrial compressed air from our office at Tarnaka, Secunderabad, since 2002. As an independent multi-brand specialist we sell new and used/refurbished machines, rent and service ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes, so we can review competing offers without being tied to one manufacturer. We are not an authorised distributor of any brand. We have tie-ups with all major and reputed brands.

We can help you freeze the duty, check offers for eligibility, list missing scope and convert flows and pressures to a common basis. Where the decision depends on real demand, an air audit gives a measured load profile to compare bids against, and our procurement and specification guidance explains how to write the duty. If the new machine will arrive after your old one fails, our own rental fleet of 50–2,000 cfm at 2–30 bar can bridge the gap. Our service teams cover the whole of Telangana and Andhra Pradesh, and we supply equipment across India.

What to send us

• The bids you have received, with dates and revision numbers.
• Your required flow, pressure at the point of use and air-quality class.
• Site ambient conditions, power supply details and plant-room layout.
• Your operating profile or recent load data, if available.
• Details of the existing compressors (make, model, serial, nameplate photo).

Frequently asked questions

Is the cheapest compressor quotation always the best offer?

No. The cheapest quotation often excludes items another bidder includes, such as the dryer, filters, receiver, controls, electrical work or commissioning. Once those are added on a common basis, the order can reverse. Even then, installed cost is only part of the picture: energy usually dominates the lifetime cost of an industrial compressor, so compare power at your real load profile before deciding.

Can two compressors with the same motor kW be treated as equivalent?

No. Motor nameplate power says little about the air delivered. Compare free air delivery at your required pressure and total package input power, including fans and dryers, measured to the same standard. Specific power in kW per m³/min is a useful check, but only once both machines meet the capacity and pressure requirement on supported data.

How do I convert cfm to m³/min when comparing compressor bids?

Multiply cfm by 0.0283168 to get m³/min; 750 cfm is about 21.24 m³/min. The conversion is valid only when both figures use the same reference conditions. Check whether each bidder quotes free air delivery to ISO 1217 or normal cubic metres, because the difference can change the ranking. When in doubt, ask the bidder to restate the figure.

What should I do when a required item is missing from a bid?

Record it as excluded and add a supported cost for supplying it, or mark it as a clarification if the offer is unclear. Do not assume it is included or treat it as zero. Send the same clarification questions to every bidder at the same time, and keep their written replies with the original offer so the decision can be traced later.

Is a variable-speed compressor always cheaper to run?

Not always. A variable-speed machine usually saves energy where demand varies widely and the plant spends long periods at part load. Where demand is steady near full load, a well-matched fixed-speed machine can use the same or less energy. Calculate annual kWh from your hour-by-hour profile using each bidder’s supported part-load data instead of relying on a general saving claim.

Can a low price make up for a technical failure in a weighted score?

It should not. Mandatory requirements such as minimum net flow, pressure at the point of use, air-quality class or hazardous-area suitability are pass-or-fail. An offer that fails one is ineligible until revised, whatever its price. Weighted scoring belongs only to eligible offers, and the weights should be agreed before any bid is opened.

Related pages

• Compressed-air procurement and bid evaluation
• Lifecycle cost comparison calculator
• Specific power comparison calculator
• FAD and reference condition conversion tool
• Reading compressor performance data sheets
• Compressed air knowledge and calculation centre