Quick answer: Choose a desiccant dehumidifier when the air is cold (below about 15 °C) or when you need a low dew point that a refrigerant coil cannot reach without freezing. Size it from the process airflow and the moisture it must remove at your actual inlet condition, then check the reactivation air, the heat source and the exhaust route. For warm rooms with moderate humidity targets, a refrigerant dehumidifier usually uses less energy.
Quick answer
- Desiccant: cold rooms, sub-zero storage, low dew points, dry processes.
- Refrigerant: warm rooms (above about 15–18 °C) at RH targets around 45–70 %.
- Compare both at the same inlet condition and include all energy: rotor drive, fans and reactivation heat.
Compare models on our desiccant dehumidifier page.
How does a rotary desiccant dehumidifier work?
A slowly turning wheel (the rotor) coated with a desiccant such as silica gel sits between two airstreams:
- Process air passes through most of the wheel. The desiccant adsorbs water vapor, and dry air goes to the room or process.
- Reactivation air is heated and passes through a smaller sector of the wheel. It drives the absorbed water out and is exhausted outside as warm, humid air.
Because the desiccant attracts water at any temperature, the unit keeps working in cold air where a refrigerant coil would freeze. The dry air leaves warmer than it entered, because adsorption releases heat and some heat carries over from the reactivation side.
Desiccant or refrigerant?
| Condition | Better choice | Why |
|---|---|---|
| Room below about 15 °C, cold stores, unheated warehouses in winter | Desiccant | No coil icing; capacity holds up in cold air |
| Target dew point below about 5 °C, or RH below about 35 % | Desiccant | A refrigerant coil cannot go much below freezing |
| Dry-air processes: lithium battery rooms, pharmaceuticals, powders, candy | Desiccant | Very low dew points are required |
| Warm rooms at 45–70 % RH: greenhouses, warehouses, pools, workshops | Refrigerant | Lower energy per litre at warm, humid conditions |
| Mixed: warm, humid outdoor air plus a low dew-point target | Refrigerant pre-cooling + desiccant | Each technology handles the part it is best at |
Our refrigerant vs desiccant guide explains the comparison in more detail.
5 steps to choose a desiccant dehumidifier
- Set the target as a dew point. RH changes with temperature; a dew point does not. Write down the dew point the room, product or process needs and the tolerance.
- Define the process airflow and inlet condition. How much air must be dried, and at what temperature and humidity does it enter, in summer and winter? Include outdoor air, door openings and wet products.
- Check capacity at your inlet condition. Desiccant ratings are usually given at 20 °C/60 % RH. At colder or drier inlet air, removal in L/day falls, but the leaving dew point can still be low. Ask for the leaving-air condition at your design inlet.
- Plan reactivation. The reactivation air needs a heat source (electric heater as standard; steam, hot water or gas on larger systems) and an exhaust duct to outdoors. Allow for the energy and the duct route.
- Plan post-cooling if temperature matters. Process air leaves warmer. If the room or product has a temperature limit, add cooling after the dehumidifier.
Desiccant dehumidifier models compared
All ratings at 20 °C/60 % RH. Operating range −10 to +55 °C.
| Model | Removal | Pints/day | Process airflow | Reactivation airflow | Rated power | Supply | Weight |
|---|---|---|---|---|---|---|---|
| RY-100M | 12 L/day | 25 | 93 m³/h | 30 m³/h | 0.69 kW | 220 V, 1-phase | 12.5 kg |
| RY-200M | 15 L/day | 32 | 198 m³/h | 60 m³/h | 0.73 kW | 220 V, 1-phase | 14.5 kg |
| RY-300M | 48 L/day | 101 | 320 m³/h | 110 m³/h | 2 kW | 220 V, 1-phase | 35 kg |
| RY-600M | 72 L/day | 152 | 580 m³/h | 200 m³/h | 4.5 kW | 220 V, 1-phase | 58 kg |
| RY-750M | 108 L/day | 228 | 750 m³/h | 250 m³/h | 7 kW | 380 V, 3-phase | 90 kg |
| RY-1000M | 180 L/day | 380 | 1,000 m³/h | 400 m³/h | 11 kW | 380 V, 3-phase | 160 kg |
| RY-1500M | 240 L/day | 507 | 1,550 m³/h | 580 m³/h | 15 kW | 380 V, 3-phase | 180 kg |
| RY-3000M | 456 L/day | 964 | 3,000 m³/h | 1,100 m³/h | 30 kW | 380 V, 3-phase | 315 kg |
Rated power includes the electric reactivation heater. Desiccant and refrigerant ratings use different conditions (20 °C/60 % RH versus 30 °C/80 % RH), so compare L/day only within each technology.
How much energy does a desiccant dehumidifier use?
More per litre than a refrigerant unit in warm conditions, because most of the input heats the reactivation air. Dividing rated removal by rated power gives about 0.6–1.0 L/kWh across the RY range at 20 °C/60 % RH. In cold rooms, where a refrigerant unit loses most of its capacity, the desiccant unit is often the only practical option. To cut running cost:
- use waste heat, hot water or steam for reactivation on larger systems;
- control the unit on dew point, so it runs only when needed;
- seal the room and limit outdoor air, the largest moisture source in most cold stores.
Installation checklist
- Reactivation exhaust ducted to outdoors, sloped away from the unit, with a rain cap.
- Reactivation inlet away from the exhaust outlet, so wet air is not drawn back in.
- Filters on both airstreams, with access for cleaning.
- Duct pressure losses within the fan's capability at the design airflow.
- Room sealed: doors, cable entries and drains.
FAQ
Frequently asked questions
When should I use a desiccant dehumidifier instead of a refrigerant one?
When the space is cold (below about 15 °C), when you need a dew point below about 5 °C, or when ice on a refrigerant coil would stop it working.
Do desiccant dehumidifiers work in freezing temperatures?
Yes, within their rated range. Our RY models operate from −10 to +55 °C.
Do desiccant dehumidifiers produce heat?
Yes. Dry air leaves warmer than it enters, and the reactivation air is heated. Allow for this in temperature-controlled rooms.
Does a desiccant dehumidifier need a drain?
No. The water leaves as vapor in the reactivation exhaust, which must be ducted outdoors.
How long does a desiccant rotor last?
Many years with clean filters. Dust, oil mist and chemical vapors shorten its life, so filter the inlet air and replace filters on schedule.
Sources
- ASHRAE Handbook—HVAC Systems and Equipment, Desiccant dehumidification and pressure-drying equipment.
- ASHRAE Handbook—Fundamentals, Psychrometrics.
