Choosing a refrigerated dryer: purchase and rental
The refrigerated dryer offers the lowest energy and preventive-maintenance cost of all air dryer types. It suits general industry (dew point ≈ 3 °C), but it should be avoided if the process requires a dew point below 1 °C or if the environment is exposed to freezing, water jets or heavy dust.
Strengths and weaknesses of the refrigerated dryer
| Strengths | Avoid if: |
|---|---|
| Optimal energy efficiency | A dew point below 1 °C (33 °F) is needed, piping exposed to freezing |
| High reliability in a suitable environment (NEMA 1) | Possibility of water jets and heavy dust (NEMA 1) |
| Low maintenance cost | Sensitive to out-of-range ambient parameters (freezing and heat) |
| Ultra-simple operating principle, familiar to all refrigeration technicians | |
| No air flow loss, no regeneration |
Choosing an integrated or external refrigerated dryer?
Integrated dryer
The integrated dryer provides fairly significant space savings. This choice eliminates the cost of connecting to the compressed air network.
It is important to know that when the dryer breaks down, in order to carry out a safe repair, you must stop the compressor in addition to the dryer. No dryer redundancy is possible.
External dryer
The external dryer is more versatile and allows redundancy. The components are very accessible when repairing the refrigeration circuit.
Parts cost less and most local refrigeration technicians have the skills to carry out repairs and diagnostics, without the manufacturer’s assistance.
Installation planning
To plan for when installing a refrigerated air dryer:
| To do | Description |
|---|---|
| Electrical | Between 120 V and 575 V, depending on the dryer size |
| Provide clearance | Clearance to allow ventilation (depending on model and capacity). Plan for the possibility that the refrigerant compressor may be replaced when positioning the dryer. |
| Ambient temperature | Minimum 4 °C (39 °F) · Maximum 45 °C (113 °F) |
| Plumbing | Respect the dryer’s piping diameter and a velocity of 25 ft/s (7.62 m/s) or less |
| Condensate drain | Connect the drain outlet to the condensate treatment system (oil-water separator) |
| Pre-filter | A pre-filter is required for long-term reliability. Some manufacturers install it inside the dryer (e.g. Mikropor, Airtek). |
| Mandatory approvals in Québec | CSA and CRN/NEC |
| Optional | Provide a dryer bypass circuit |
Please refer to the specifications of your air dryer supplier. The scope above is for pre-project planning.
Unit used to determine a dryer’s capacity — SCFM
The unit is SCFM (CAGI). The dryer performance conditions are as follows:
| Conditions | Values |
|---|---|
| Compressed air inlet temperature (T° in the piping) | 100 °F |
| Compressed air inlet pressure | 100 psig |
| Maximum ambient temperature | 100 °F |
| Compressed air relative humidity (in the piping) | 100 % (saturated) |
CAGI SCFM is: volume of free air in ft³/min at 14.5 psia (1.0 bar), 68 °F (20 °C), 0 % RH.
How to choose the right capacity — sizing and selection
Method / formula
CFtotal = F1 × F2 × F3 × F4
- F1 = correction factor, inlet pressure
- F2 = correction factor, ambient temperature
- F3 = correction factor, compressed air temperature
- F4 = correction factor, final dew point
Dryer capacity = flow consumed by the plant ÷ CFtotal
Always round up to the larger dryer.
Correction factors for refrigerated dryers
Each factor adjusts the rated capacity in SCFM based on a deviation from the ISO test conditions.
F1 — Inlet pressure
| psig | 60 | 80 | 100 | 120 | 140 | 160 | 180 | 203 |
|---|---|---|---|---|---|---|---|---|
| bar | 4 | 5.5 | 7 | 8 | 10 | 11 | 12 | 14 |
| F1 | 0.78 | 0.90 | 1.00 | 1.10 | 1.15 | 1.20 | 1.25 | 1.30 |
F2 — Ambient temperature
| °F | ≤80 | 90 | 95 | 100 | 105 | 110 | 115 | 122 |
|---|---|---|---|---|---|---|---|---|
| °C | ≤27 | 32 | 35 | 38 | 40 | 43 | 45 | 50 |
| F2 | 1.11 | 1.09 | 1.05 | 1.00 | 0.95 | 0.85 | 0.75 | 0.65 |
F3 — Inlet air temperature
| °F | ≤90 | 100 | 110 | 122 | 130 | 140 | 150 | 158 |
|---|---|---|---|---|---|---|---|---|
| °C | ≤32 | 38 | 43 | 50 | 55 | 60 | 65 | 70 |
| F3 | 1.165 | 1.00 | 0.80 | 0.70 | 0.60 | 0.50 | 0.45 | 0.40 |
F4 — Pressure dew point (PDP)
| °F | 38 | 41 | 45 | 50 |
|---|---|---|---|---|
| °C | 3 | 5 | 7 | 10 |
| F4 | 1.00 | 1.08 | 1.20 | 1.36 |
Note: F4 > 1 means you can tolerate more humidity, so the dryer can handle more flow.
Calculation example
| Field conditions — in the plant / mechanical room | Values | Factor |
|---|---|---|
| Total plant consumption | 866 SCFM | — |
| F1. Compressed air inlet pressure | 120 psig | 1.10 |
| F2. Ambient temperature | 100 °F | 1.00 |
| F3. Compressed air inlet temperature (T° in the piping) | 122 °F | 0.70 |
| F4. Dew point tolerated by the process | 38 °F | 1.00 |
1. Calculate the correction factor
CFtotal = F1 × F2 × F3 × F4 = 1.10 × 1 × 0.70 × 1 = 0.77
2. Apply the correction factor to the flow to be treated
Dryer capacity = 866 SCFM ÷ 0.77 = 1,124.68 SCFM
Answer: the compressed air dryer must have a capacity of 1,124.68 SCFM or more.
Budget price of refrigerated dryers — 100 to 5,000 SCFM
Installation not included. Commissioning not included.
| Capacity (SCFM) | Cycling dryer | Non-cycling dryer | Filter (housing + element) | Commissioning |
|---|---|---|---|---|
| 100–200 | $3,000 – $6,000 | $2,500 – $4,500 | $520 – $870 | $575 – $800 |
| 300–500 | $5,000 – $9,000 | $4,000 – $7,000 | $880 – $1,420 | $575 – $800 |
| 750–1,000 | $8,000 – $15,000 | $6,500 – $12,000 | $1,480 – $2,260 | $1,400 – $2,000 |
| 1,500–2,000 | $14,000 – $25,000 | $11,000 – $20,000 | $2,400 – $3,780 | $1,400 – $2,000 |
| 3,000 | $22,000 – $40,000 | $18,000 – $32,000 | $4,450 – $5,400 | $1,400 – $2,000 |
| 5,000 | $35,000 – $65,000 | $30,000 – $55,000 | $6,900 – $8,500 | $2,800 – $3,500 |
Freight extra. Several manufacturers offer “drop-ship”.
Mistakes to avoid
- Installing an air dryer in an unheated space in winter (e.g. sawmill, warehouse, job site)
- Installing a refrigerated dryer outdoors, exposed to the weather (e.g. temporary outdoor rental)
- Calculating the correction factors with the wrong temperature parameters (see the CTD article)
- Connecting the dryer with a piping diameter smaller than the diameter at the dryer
- Buying a dryer with an unpopular or obsolete refrigerant type
- Installing a forced-air ventilation duct directly on the dryer