How to Size a Compressed Air Dryer Using Manufacturer Correction Factors
To size a compressed air dryer, establish the flow and operating conditions at its inlet, then apply the exact manufacturer’s correction procedure to the rated capacity. Compare the result with the capacity listed for your required pressure dew point, and check the candidate model’s operating limits.
The main trap in compressed air dryer sizing is treating the catalogue flow as the capacity available in every installation. A nominal rating applies at stated conditions. Your plant may run at a different inlet temperature, pressure, or ambient temperature, so a nominal flow match alone does not complete the selection.
This guide takes you from those inputs to a traceable worksheet, using one published manufacturer example.
Key takeaways
- Record flow units and reference conditions before comparing demand with a dryer rating.
- Use the correction table for the exact series and required pressure dew point.
- Name the quantity you are calculating: available capacity and required nominal capacity use opposite operations when the factors are capacity multipliers.
- Confirm delivered flow, operating limits, and any regeneration allowance before accepting a selection.
1. Define the airflow that passes through this dryer
Start with the dryer’s location in the system. Is it treating the whole plant, one production branch, or a single process? Record the flow that must pass through that location during the operating scenario you intend to cover.
For several compressors feeding a common dryer, identify which machines can deliver through it simultaneously. For separate branches or receiver arrangements, document the flow path rather than adding every plant load to every dryer. A simple marked-up system sketch can make that scope clear to the supplier.
Keep the flow basis attached to the number. CFM, SCFM, free air delivery, and m³/h (ANR) should not be treated as interchangeable labels without checking their definitions and reference conditions. If your demand measurement and catalogue rating use different bases, have the comparison resolved before applying correction factors. Our explanation of compressor flow, pressure and horsepower provides a terminology follow-up.
Motor horsepower alone is not enough to select a dryer. Atlas Copco’s dryer selection guide identifies flow, pressure, and temperature among the sizing inputs. Obtain the relevant compressor flow data or a documented system measurement instead of guessing airflow from motor power.
Also distinguish air entering the dryer from usable air required downstream. This becomes especially important where a dryer consumes air for regeneration. Keep both quantities visible on the worksheet; Section 5 explains the check.
2. Record operating conditions and the required pressure dew point
Collect the conditions at the dryer, not just the compressor’s nominal settings:
| Input | What to record |
|---|---|
| Airflow | Demand through this dryer, units, reference basis, and simultaneous operating scenario |
| Inlet pressure | Expected minimum during that scenario, with gauge or absolute basis identified |
| Inlet temperature | Expected maximum air temperature at the dryer inlet |
| Cooling environment | Relevant ambient temperature or cooling-water data required by the catalogue |
| Required pressure dew point (PDP) | Target temperature and the operating pressure to which it applies |
Use a credible demanding operating case, including seasonal variation where relevant. Kaeser’s sizing guide explains why operating conditions must be considered alongside nominal flow. A convenient reading taken during a quiet, cool shift may not represent the conditions the dryer must handle.
Keep the measurement locations explicit. A compressor discharge reading is not a substitute for a dryer inlet reading when the air passes through other equipment between them. Likewise, record the ambient conditions where the dryer operates rather than assuming the whole building has one temperature. State which readings are measured and which are proposed design conditions, so the supplier can assess the scenario.
Write down the required PDP before choosing a capacity column. If that requirement means reconsidering the drying technology, first review air dryer types and selection. The calculation below checks capacity against a defined requirement; it does not establish the application’s air-quality specification or guarantee process compliance.
3. Read the manufacturer’s correction table before calculating
Match the document to the equipment
Use the exact manufacturer’s series, regional document, and catalogue edition. Record the source URL and page so another person can reproduce the selection. Check the units, nominal rating conditions, and capacity column for the required PDP.
Read the table headings and notes together. Some tables combine variables, while others give separate factors. Applying an additional pressure factor to a table that already combines pressure and temperature can count the same correction twice.
Do not transfer factors from a different series or brand because the nominal capacities look similar. A maximum permitted inlet temperature is also not a promise of full rated capacity at that temperature. Operating limits and capacity ratings answer different questions.
Decide whether you need available capacity or required nominal capacity
When the manufacturer defines its factors as capacity multipliers, let F be the product of the applicable factors. The two calculations are:
Available capacity at the stated conditions = nominal rated capacity × F
Required nominal rated capacity = flow to be treated ÷ F
The first asks whether a known dryer has enough capacity under the stated conditions. The second asks what catalogue rating is needed to treat a known flow. These are two forms of the same relationship, not competing sizing rules.
Follow the manufacturer’s own formula and quantity names if its convention differs. A heading such as “corrected flow” does not, by itself, tell you which operation to use. In the SMC example below, the calculated quantity is the flow rating needed for model selection.
Before using the result, check that every input has an applicable table entry. If a reading falls between entries, use the manufacturer’s stated selection or interpolation instructions. Do not replace a missing factor with 1.00 or extrapolate beyond the published selection data without manufacturer guidance.
4. Compressed air dryer sizing: a published SMC example
The SMC IDFA catalogue, CAT.EUS30-26B-UK, gives a selection example for its IDFA60/70/80/90 series on printed page 4, PDF page 5. The following values belong to that example and are not Loyal product specifications.
| Published operating input | Value | Published correction factor |
|---|---|---|
| Airflow to be treated | 250 m³/h (ANR) | Not a correction factor |
| Inlet air temperature | 40°C | 0.71 |
| Ambient temperature | 30°C | 0.85 |
| Inlet air pressure | 0.6 MPa | 0.89 |
| Outlet air pressure dew point | 3°C | Select the corresponding capacity row |
First, multiply the three correction factors:
F = 0.71 × 0.85 × 0.89 = 0.537115
Then divide the airflow by their product:
Required rated capacity = 250 ÷ 0.537115 = 465.45 m³/h (ANR)
SMC reports the rounded result as approximately 465 m³/h (ANR). Its procedure then selects a model with a capacity exceeding that calculated requirement in the 3°C PDP row. The catalogue identifies IDFA80, whose listed capacity in that row is 552 m³/h (ANR).
The distinction matters: 250 m³/h (ANR) is the example’s flow to be treated; approximately 465 m³/h (ANR) is the rating needed for comparison with that catalogue row. The calculation does not mean the plant’s demand has increased to 465.
As an arithmetic cross-check using the same factors, 552 × 0.537115 is approximately 296.49 m³/h (ANR), above the example’s 250 m³/h (ANR) demand. This is a calculation from the published values, not a measured performance result.
Retain the catalogue’s performance caveat. SMC notes that actual outlet PDP varies with operating conditions and that freeze protection may cause the dew point to rise and become unstable, particularly for the 3°C and 7°C cases. Passing the capacity comparison does not remove that warning.
This is a worked manufacturer illustration, not a current purchase recommendation. Use the applicable current selection document for any actual equipment inquiry; do not reuse these factors for another dryer.
5. Check delivered flow and the model’s operating limits
For a heatless desiccant dryer that uses purge air, confirm what the flow rating represents. Section 8 of the Parker BV12–BV80 user guide describes outlet flow as inlet flow less purge flow. That guide is a legacy October 2012 revision; the distinction is useful here, but it does not establish a purge allowance for another model.
Ask whether the supplier’s stated capacity is inlet throughput or net delivered flow, and whether regeneration has already been allowed for. Use the model’s documented purge data and reference basis. Do not add a generic purge percentage or add an allowance a second time.
For any candidate, finish with these checks:
- Are the inlet pressure, inlet temperature, and cooling conditions within the model’s permitted range?
- Does the selected capacity row match the required PDP and stated flow basis?
- Are all factors applicable to this exact series and document edition?
- Is the usable delivered flow sufficient after any documented regeneration allowance?
- Are future demand and unresolved readings listed separately?
Keep a proposed future production load visible as a separate input. An unexplained blanket safety percentage can hide what was actually sized and can duplicate an allowance already included elsewhere.
If an operating limit is exceeded or the required table entry is missing, pause the numerical selection and request manufacturer guidance. A larger model number alone does not resolve an out-of-range condition.
6. Complete a worksheet for the supplier
Use this record to make the calculation reproducible. Attach the relevant datasheet and identify any values that still need measurement or confirmation.
| Worksheet field | Your recorded value or reference |
|---|---|
| Application and dryer location | Whole plant, branch, or point of use; system sketch reference |
| Flow through the dryer | Value, units, reference conditions and peak operating scenario |
| Flow basis | Inlet throughput or required delivered flow; regeneration allowance if applicable |
| Dryer inlet pressure | Expected minimum and gauge/absolute basis |
| Dryer inlet temperature | Expected maximum at the actual inlet |
| Cooling environment | Relevant ambient or cooling-water conditions |
| Target PDP | Required temperature and operating pressure basis |
| Exact selection document | Manufacturer, series, region, edition, URL and page |
| Nominal rating conditions | Flow basis, pressure, temperatures and PDP |
| Correction entries | Factor labels, table cells, any combined variables and formula convention |
| Calculated requirement | Unrounded result and units |
| Candidate model | Capacity in the applicable PDP row and operating-limit references |
| Outstanding items | Missing readings, delivered-flow confirmation and supplier questions |
This worksheet records the selection basis; it is not an equipment acceptance certificate. To discuss your compressed air dryer sizing requirements, send the operating data and applicable datasheet with your inquiry.
Do I multiply or divide correction factors?
Follow the manufacturer’s procedure. If its factors are capacity multipliers, multiply a known nominal capacity by their product to find available capacity. Divide the required flow by that product to find the nominal rating needed. Check which quantity the document calls “corrected capacity.”
Can I size a dryer from compressor horsepower?
Horsepower alone does not supply the required flow, inlet conditions, or PDP. Obtain the airflow data on a stated reference basis and apply the dryer’s own selection procedure.
Can I use another manufacturer’s correction table?
Use the table applicable to the exact dryer series. The SMC factors above are a worked example, not a universal table for other manufacturers or dryer designs.
Does dryer flow include purge air?
Check the rating definition. A heatless dryer may consume part of its inlet flow for regeneration, so inlet throughput and usable outlet flow can differ. Ask for the selected model’s documented delivered-flow basis before adding any allowance.