How To Size A Refrigerated Air Dryer?

Here are some FACTORS TO CONSIDER WHEN DETERMINING your DRYER SIZE:

Standard Rated Conditions Are:

• 100º F Dryer Inlet Air Temperature
• 100º F Ambient Temperature
• 100 PSIG Inlet Pressure
• 38º F Pressure Dew Point Temperature
• 40º F Minimum Ambient Air Temperature

Note: Any deviation from standard conditions requires air dryer size adjustments.

Use Correction Factor Tables to help determine dryer size.

• Pressure Dew Point needed (PDP)
• Volume of compressed air (SCFM)
• Maximum compressed air dryer inlet temperature (°F)
• Maximum ambient temperature (°F)
• Maximum compressed air pressure (PSIG)
• Maximum allowable dryer pressure drop (PSIG)

To size dryer capacity for conditions other than the Standard Rated Conditions, use the Correction Factors (Multipliers) from Table 1, 2 and 3.

Example: You’ve determined you need to treat 500 CFM (100 HP) of Compressed Air for your business. You are considering  a dryer which treats up to 500 CFM. But you need your dryer to run under the following conditions – different from the

Standard Rated Conditions (which may include higher temperatures due to hot days of summer):

• 120º F Inlet Air Temperature (Standard =100º F Inlet Air Temperature)

• 125 Psig Inlet Air Pressure (Standard =100º Psig Inlet Pressure)

• 110º F Ambient Air Temperature (Standard =100º F Ambient Temperature)

• 38º F Dew Point Temperature (Standard =38º F Dew Point Temperature)

The Model you’ve chosen can treat up to 500 CFM of compressed air under Standard Rated Conditions (listed above). When conditions change, like surrounding temperatures on hot summer days, these conditions affect how much compressed air your dryer can treat (it could be more or less CFM).If conditions vary from Standard Rated Conditions, then your air dryer may not meet performance standards.

Use the tables shown to determine the correct size of dryer you need under your specific conditions.

Look @ Table 1  (below)
Find Where Inlet (125 Psig) Pressure & Inlet Temperature (120º F) Intersect.
This number is Your Correction Factor (.74) Multiplier.

Multiply (500) X (.74) = 370 CFM Corrected.

Look @ Table 2   (below)
Determine the Maximum Ambient Temperature surrounding the Dryer.  For our example, we will use 110ºF (for hot summer day). The table tells you your Correction Factor is (.94). Use the corrected CFM number determined by Table 1 (370) and multiply it by the Table 2 correction factor for 110º F (.94).

Dryer Corrected CFM (370) X (.94) =348 CFM Corrected.

Look @ Table 3   (below)

What dew point do you need to prevent water from forming down stream in your piping? (38º F) The Dryer Correction Factor for 38ºF is 1.
Multiply that number times the Dyer Corrected CFM determined from Table 3.

(1) X 348 CFM = 348 CFM Corrected.

CONCLUSION FROM USING THE CORRECTION TABLES:

USING THE ABOVE TABLES, we can conclude that a 500 CFM Dryer working under these NON-Standard conditions is only able to treat 348 CFM and is too small for our needs.

THE DRYER NEEDED IS A 750 +CFM. DRYER CORRECTED CFM = 521 CFM.

CORRECTION FACTOR TABLES

Correction Factors (Multipliers) to Adjust Dryer Flow Capacity Other Than Standard Rated Conditions Are:

TABLE 1 – Correction Factors for Inlet Air Temperature 

COMPRESSED AIR INLET TEMPERATURE
INLET AIR Pressure (PSIG)	80ºF	90ºF	100ºF	110ºF	120ºF
50	1.35	1.05	0.84	0.69	0.56
80	1.50	1.17	0.95	0.79	0.66
100	1.55	1.23	1.00	0.82	0.70
125	1.63	1.31	1.07	0.91	0.74
150	1.70	1.37	1.13	0.95	0.80
175	1.75	1.42	1.18	0.99	0.84
200	1.80	1.47	1.22	1.03	0.89

TABLE 2 – Correction Factors for Ambient* Temperature (*Surrounding air temperature)

AMBIENT AIR TEMPERATURE	80ºF	90ºF	100ºF	110ºF
Multiplier	1.12	1.06	1.00	0.94

TABLE 3 – Correction Factors for Compressed Air Dew Point Temperature

COMPRESSED AIR DEW POINT TEMPERATURE	38ºF	40ºF	45ºF	50ºF
Multiplier	1.0	1.1	1.2	1.3