Why a portfolio beats a list of separate projects
Most plants receive energy proposals one at a time: a new VSD compressor from one supplier, a leak survey from another, a heat-recovery scheme from a third. Each proposal shows an attractive payback on its own. Put together, the paybacks rarely hold, because the projects share the same kilowatt-hours.
A compressor bought before leaks are fixed may be too large for the plant that remains. A pressure-reduction saving shrinks once the leaks it would have reduced are already repaired. Heat recovery loses hours when better sequencing lets a compressor run less. On the other hand, a modest spend on flow meters or a pipe correction can unlock a larger, more dependable saving elsewhere.
A portfolio answers five questions together:
- What service must production keep: pressure, flow, air quality and standby?
- What losses are actually present, and how large are they?
- Which measures change the value of other measures?
- Which combination and order give the best lifecycle result within the budget?
- How will the combined result be measured and kept?
Lifecycle cost basics are covered in our page on compressed-air lifecycle cost and investment. Here we look at how projects interact and how to stage them.
Define the service before ranking spending
Write down what the compressed-air system must deliver, independent of any equipment being offered. Record the critical users and the minimum dynamic pressure at each, the flow profile across shifts and seasons, the air-quality class needed under ISO 8573-1, operating hours, how long production can tolerate an interruption and what standby is required when a compressor is down. Include known expansions.
Only options that meet this service are comparable. A cheaper-to-run arrangement that cannot hold pressure at peak demand is not a saving. Equally, a pressure kept high only out of habit may hide one of the best opportunities.
Separate essential repairs from discretionary efficiency. A failing isolation valve, poor compressor-room ventilation or an overdue pressure-vessel inspection needs doing whatever the energy case. Do not invent an energy saving to justify it; state the reliability or safety reason directly.
One baseline for every candidate
Every proposal must be measured against the same baseline, otherwise savings cannot be compared or combined. A good baseline covers:
- Electrical energy for compressors, dryers and auxiliaries, logged over representative production.
- Delivered flow and pressure at the station, and pressure at key users.
- Load and unload hours and control behaviour for each compressor.
- Production output, shifts and ambient temperature, so the baseline can be adjusted for change.
- Station specific power, in kW per m³/min of delivered air.
Where the measurement is weak, the first investment may simply be better data. A week of flow and power logging often costs far less than the error it removes from a large capital decision. See power and flow logging and the energy baseline adjustment worksheet.
Build the candidate register
| Candidate measure | What it changes | Depends on or affects |
|---|---|---|
| Leak repair programme | Removes demand | Reduces the value of pressure reduction on leaks; may change compressor size needed |
| Artificial demand and pressure reduction | Lowers demand and compression energy | Needs pipe and filter drops fixed first; overlaps with leak savings |
| Ending inappropriate uses | Removes demand | Reduces future compressor size |
| Piping and treatment pressure-drop correction | Allows lower generation pressure | Enables pressure reduction |
| Storage and control improvements | Reduces unload running and short cycling | Value depends on residual demand profile |
| Sequencer or VSD trim machine | Matches supply to demand | Should be sized to demand after reductions |
| Compressor replacement | Improves specific power | Size and type depend on all the above |
| Heat recovery | Uses compressor heat for process or water heating | Value depends on compressor running hours and a real heat user |
For each candidate record the scope, what it needs to work, its main risks, the measurement that will prove it and who owns it.
Model the interactions before adding savings
Savings from different measures cannot simply be added. Suppose the baseline station uses 1,000,000 kWh a year. Leak repair alone is estimated to save 150,000 kWh, and pressure reduction alone 80,000 kWh. Adding gives 230,000 kWh, but this overstates the combined effect: once leaks are fixed, the pressure reduction acts on a smaller flow. Applied in sequence, the leak repair leaves 850,000 kWh, and the same pressure reduction on that smaller base saves about 68,000 kWh, so the pair saves about 218,000 kWh, not 230,000 kWh. These are teaching figures, not results from any plant.
The same logic applies to controls and new compressors. A VSD’s saving is calculated on the residual demand profile after leak and pressure work, not on today’s profile. Heat recovery is valued on the running hours that remain once sequencing has improved.
Sequence the work around the remaining demand
- Measure: establish the baseline and the service requirement.
- Restore: carry out essential repairs and fix obvious defects.
- Reduce demand: leaks, inappropriate uses, unnecessary running time.
- Reduce pressure: correct pipe and treatment drops, then lower and regulate pressure.
- Match supply: storage, controls, sequencing and, where justified, VSD trim.
- Replace and recover: size any new compressor and heat recovery to the remaining duty.
- Verify and maintain at each stage before committing the next.
The order is not rigid. A compressor that has failed must be replaced now; in that case, a short-term rental can bridge the gap while demand work is done, so the permanent machine is sized correctly.
Count each benefit in its own category
- Energy: kWh saved, verified against the adjusted baseline.
- Maintenance: fewer compressor running hours, longer service intervals in calendar terms.
- Capacity: compressor capacity released for future expansion, valued as deferred capital, not as an energy saving.
- Reliability: reduced risk of a pressure collapse or unplanned stop.
- Heat: thermal energy delivered to a real, measured heat user.
Keep released capacity separate from cash savings. Air that is no longer leaking only saves money if the compressors actually use less energy as a result.
Compare incremental lifecycle cash flows
Compare each option against the do-minimum case using the same period, discount rate and electricity tariff assumptions set by your finance team. Include installed cost, energy, maintenance, spares, downtime during installation, any residual value and the cost of monitoring. Simple payback is a useful screen but ignores what happens after payback; net present value and lifecycle cost show the full picture.
Test the result against changes in assumptions. If eligible operating hours fall, or installation costs rise, does the choice still hold? If a moderate change in one uncertain input reverses the decision, invest in measuring that input before committing capital. Our lifecycle cost comparison calculator helps structure the comparison.
Choosing within a capital limit
| Situation | Sensible approach |
|---|---|
| Small budget this year | Fund measurement, leak repair and pressure-drop correction first; they shape every later decision |
| Budget for one large item | Choose the item whose value is least affected by later measures, or delay it until demand work is done |
| Uncertain production growth | Prefer modular or staged supply, and keep rental as a short-term option |
| Ageing compressor near failure | Plan replacement now but size it on the reduced demand, bridging with rental if needed |
Verifying and keeping the savings
Each stage should be verified before the next is approved. Use the same measurement boundary as the baseline, adjust for production and weather, and report each measure’s contribution alongside the combined measured result. Then protect it: a leak-repair routine, locked pressure settings, control parameters recorded and checked after service visits, and a review whenever production changes. Our measurement and verification page covers the method.
How Reddy Compressors helps
We carry out compressed-air audits following the ISO 11011 method: demand and pressure profiling, power and flow logging, leak surveys, pressure-drop and specific-power checks. We do not issue conformity certificates; we provide measured findings and a staged action plan. We can then deliver the work: leak repair, piping and treatment corrections, control set-up, service and AMC, and the supply of new or used compressors sized to the reduced demand.
As an independent multi-brand specialist, we sell, rent and service ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes, so our advice is not tied to one brand. Our rental fleet can bridge a failed compressor while the permanent solution is planned. Our office is at Tarnaka, Secunderabad; our service teams cover Telangana and Andhra Pradesh, and we supply equipment across India.
What to send us
- Compressor, dryer and receiver list with makes, models and nameplate photos.
- Monthly electricity consumption and any existing compressor energy data.
- Pressure settings and a line diagram of the air network.
- Proposals you already hold and the budget window.
- Planned production changes or expansions.
Frequently asked questions
Should the project with the shortest payback always come first?
Not always. A short-payback project may lower the value of others, or depend on a measure that should come first. Leak repair and pressure-drop correction often go first because they change the size of every later investment. Look at the sequence as a whole and choose the order that gives the best verified result over the life of the system.
Can savings from leak repair and lower pressure be added together?
No, not directly. Lower pressure reduces the flow through leaks, so once leaks are repaired the pressure saving acts on a smaller demand. Calculate measures in sequence, each on the demand left by the one before, and verify the combined result with measured flow and power against an adjusted baseline.
Does released compressor capacity count as an energy saving?
Only if the compressors actually use less energy. Freed capacity is valuable because it can delay buying another compressor when production grows, but that is deferred capital, not reduced electricity. Report it separately, and check that the compressor controls convert lower demand into lower kWh rather than more unloaded running.
Should heat recovery be part of the same portfolio?
Yes, but value it last. Recoverable heat depends on compressor running hours, which fall as demand and control measures take effect. It is only worth recovering if there is a real, matching heat user such as process water, boiler feed or washing. Size it on the hours expected after other measures, not today’s figures.
Can a portfolio be approved before every uncertainty is resolved?
Yes, if it is staged. Approve the early, low-regret measures such as measurement, leak repair and pressure-drop correction, and set decision points for later items once their inputs are measured. Where an uncertainty could reverse a large decision, spending on better measurement first is usually money well spent.
What proves that an energy portfolio has worked?
Measured compressor-station energy against an adjusted baseline, over a comparable production period, while the required pressure, flow and air quality were maintained. Specific power in kW per m³/min is a good tracking measure. Lower electricity bills alone are not proof, because output, shifts and weather also change.
Related pages
Field guide
Building an energy improvement plan you can fund
Compressed-air improvements range from free (fixing settings) to capital projects (new compressors or pipework). Ranking them by cost and saving lets a plant start with quick wins and fund later steps from the savings.
| Typical measure | Cost | Payback |
|---|---|---|
| Lower generation pressure, adjust controls | Very low | Immediate |
| Leak survey and repair | Low | Often months |
| Zero-loss drains, filter changes | Low | Months |
| Sequencer or master control | Medium | Depends on number of machines |
| Pipework upgrades | Medium | Depends on drop recovered |
| Heat recovery | Medium | Depends on heat use |
| New VSD or high-efficiency compressor | High | Depends on hours and current efficiency |
How to build the plan
- Measure demand, pressure profile and power for a typical week.
- List measures with estimated cost and saving.
- Do the free and low-cost measures first, then re-measure.
- Size any new equipment against the reduced demand, not the old one.
- Verify savings after each step.
What to send for a quotation
- Compressor make, model and rated power of each machine.
- Electricity tariff and annual running hours.
- Typical pressure at the compressor and at the furthest user.
- Any measurements you already have (power, flow, loaded hours).
Send it through find my part or the spare parts enquiry, or call +91 99590 60718 or +91 92468 88812.
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Combined savings of interacting energy measures
Combine the stand-alone savings of several compressed-air measures applied one after another, instead of adding them, and see how much the plain sum overstates the result.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Baseline station energy (kWh per year): 1000000
- Savings entered as: kWh per year
- Stand-alone saving of each measure, in order of application: 150000, 80000
Result
- Measure 1: alone: 1,50,000 kWh per year (15% of baseline)
- Measure 1: in sequence: 1,50,000 kWh per year, leaving 8,50,000 kWh
- Measure 2: alone: 80,000 kWh per year (8% of baseline)
- Measure 2: in sequence: 68,000 kWh per year, leaving 7,82,000 kWh
- Combined saving: 2,18,000 kWh per year (21.8% of baseline)
- Plain sum of stand-alone savings: 2,30,000 kWh per year
- Overstatement of the plain sum: 12,000 kWh per year (5.5% too high)
- Energy remaining after all measures: 7,82,000 kWh per year
- Value of the combined saving per year: Enter your electricity tariff (cost per kWh) above
Method. Each measure’s stand-alone saving is turned into a fraction of the baseline. Applied in sequence, each measure saves its fraction of the energy left by the measures before it: saving_i = residual_(i−1) × fraction_i, residual_i = residual_(i−1) − saving_i. Combined saving = baseline − final residual. The combined total does not depend on the order, but the saving credited to each measure does, so list the measures in the order they will be done (usually leaks and demand first, then pressure, then supply matching, then replacement and heat recovery). This is a multiplicative screening model; verify each stage by measurement against the adjusted baseline.
What to take from it. Report the sequenced figure, not the sum. Value VSD, replacement and heat-recovery projects on the demand left after leak and pressure work.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.
Project payback and net present value
Test whether an energy or reliability project pays back, with a discount rate for the cost of money.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Discount rate (%): 10
- Life (years): 8
Result
- Result: Enter your own prices above (investment and annual saving are needed; no amounts are assumed)
Method. Simple payback = investment ÷ (annual saving − upkeep). NPV = −investment + Σ (saving − upkeep) / (1 + r)ⁿ over the life. Discounted payback is the year in which the discounted savings repay the investment; IRR is the discount rate at which NPV = 0. Enter your own figures.
What to take from it. A positive NPV at your own discount rate is a stronger test than payback alone, because payback ignores what happens after it.