Quick answer: Choose a refrigerant dehumidifier for warm spaces at moderate targets such as 40–60 % RH at room temperature, and desiccant for cold spaces or dew points below roughly 5 °C. Refrigerant units cool air below its dew point on a cold coil and drain the condensed water; they are efficient at those warm, moderate conditions.
A desiccant dehumidifier adsorbs water vapour on a rotating desiccant wheel and drives it off with a heated reactivation air stream that is exhausted outside. It keeps working in cold spaces and can reach low dew points that a cold coil can’t, because the coil would frost. Some projects combine both.
Quick answer
- Refrigerant: warm spaces, moderate RH; most litres per kWh in warm, humid air.
- Desiccant: cold spaces, low dew points, dry supply air; needs reactivation heat and an exhaust.
- Decide from inlet temperature and target dew point.
How they differ
| Refrigerant | Rotary desiccant | |
|---|---|---|
| How water is removed | Condenses on a cold coil | Adsorbed on a desiccant wheel |
| What leaves | Liquid condensate (drain) | Warm, moist reactivation exhaust (duct outside) |
| Utilities | Electricity, drain | Electricity (or gas/steam) for reactivation, exhaust duct |
| Best at | Warm air, moderate humidity | Cold air, low dew point |
| Weakness | Capacity falls in cold air; coil frosts; limited low dew point | Uses more energy in warm, humid air |
| Effect on air temperature | Warms slightly (heat returned) | Warms noticeably (adsorption and reactivation heat) |
ASHRAE Technical Committee 8.12 covers desiccant dehumidification equipment (ASHRAE TC 8.12). ASHRAE has noted the practical limit of cold-coil systems: once water freezes on the coil, airflow and moisture removal fall (ASHRAE Journal Podcast, Episode 39).
Decide from temperature and dew point
| Space temperature | Target | Typical choice |
|---|---|---|
| Above about 15 °C | 40–60 % RH (dew point above about 5 °C) | Refrigerant |
| 5–15 °C | Moderate RH | Low-temperature refrigerant or desiccant; compare at the condition |
| Below about 5 °C (cold stores, unheated warehouses) | Any | Desiccant |
| Any | Dew point below about 5 °C (e.g. lithium battery rooms, pharma, dry rooms) | Desiccant |
| Warm, high load, very low dew point | Low dew point | Refrigerant pre-cooling + desiccant |
These are typical boundaries; confirm with performance data at your condition.
Energy needs a boundary
- Compare litres removed per kWh at your condition, not rated capacity alone.
- Refrigerant units are generally more efficient in warm, humid air; their performance falls in cool air.
- Desiccant energy is mostly reactivation heat. Our RY desiccant units remove about 0.6–1.0 L/kWh at 20 °C / 60 % RH; see desiccant power consumption.
- Include fans, reactivation heat source and any cooling needed for warm desiccant outlet air.
Inputs to compare models
- Space temperature range (coldest operating condition)
- Target RH or dew point
- Moisture load (kg/h)
- Airflow and distribution (room recirculation or dry supply air)
- Utilities: power, heat source, exhaust route, drain
- Operating hours and energy prices
Practical decision rule
- State the coldest operating temperature and the target dew point.
- If the coil would need to run below about 0 °C to reach the target, choose desiccant.
- Otherwise compare refrigerant and desiccant on litres per kWh at that condition, plus installation (drain vs exhaust duct).
See desiccant working principle, low dew point desiccant selection, R290 vs R410A refrigerant dehumidifiers, our industrial dehumidifiers and desiccant rotor dehumidifiers.
FAQ
Frequently asked questions
Which is better, refrigerant or desiccant?
Neither in general: refrigerant for warm spaces and moderate targets; desiccant for cold spaces and low dew points.
Do desiccant dehumidifiers use more electricity?
In warm, humid air, usually yes; in cold air or for low dew points, they may be the only option that works.
Can a refrigerant dehumidifier work in a cold room?
Capacity drops sharply and the coil frosts; low-temperature models with defrost help down to a point, below which desiccant is better.
Sources
- ASHRAE Handbook—HVAC Systems and Equipment, Desiccant dehumidification and pressure-drying equipment.
- ASHRAE TC 8.12, Desiccant dehumidification equipment and components.
