Frequently asked questions about our products and dehumidification

Did you know that the average relative humidity level in Sweden is 85% in January and 75% in July according to SMHI. The limit for general corrosion (rust) is at 60% relative humidity, this means that air must either be heated or dehumidified inside buildings. 

For more information on relative humidity.


Answer: See the movie on how to read an Mollier chart.

Answer: The energy efficiency of a dehumidifier is measured in the energy needed to extract a kilo of water from the air, in the climate in which it is to work. The capacity is stated in the number of kilos of water per hour, then you multiply it by the dehumidifier’s power consumption. In this way you will get the cost of dehumidifying! It is important to use the right temperature and moisture level when doing a comparison between technologies and products! Especially if you also want to save energy by lowering the temperature in the room. Favourable moisture levels in most buildings are below 60% RH. Then you avoid mould and corrosion. All older technology dehumidifiers require more energy at lower temperatures. Airwatergreen warm condensing technology is the only one completely independent of the climate the dehumidifier works in.

With the FLEX series, it only costs 2 KWh to extract 1 kilo of water from the air according to a test by the Swedish National Testing Authority (RISE), with the REX series about 1.5 KWh per kilo of water.

See diagram of Statens Provningsanstalt (SP) (RISE).

If you would like help with calculating moisture or life cycle calculations (LCC) for the next dehumidification purchase, please email us at

Answer: The important factor is called the Dew point level. When the surface of the pipe is colder than the air in the room, this will cause moisture in the air to start forming on the pipe with a risk of corrosion as a result. This is just like the condensation forming on a soft drink container on a hot summers day. We can calculate the Dew point and configure the dehumidifier to use sensors to ensure the correct humidity level to avoid corrosion.

Dew point chart

Answer: If requested we can carry out a humidity study using sensors. We place these humidity sensors in selected positions for a couple of weeks and can, based on data from these sensors, present an assessment of the moisture levels over time. Based on this data we can give advice on how to proceed depending on the type of humidity challenges using a calculation methodology that we have developed.

Answer: The Flex has drain pump options, though we also offer site specific options to both help you with the installation and, if necessary, install a drainage pump that will remove the water from the space if the installation is below ground or there is no drain available.

Answer: No, you can lower the temperature. Our technology is as efficient at low temperature as in warm. This has proven to be very successful in churches and buildings that are not always used. No unnecessary heating is needed and our FLEX and REX keep the humidity at the right level.

This means that you can save energy both from lower heating costs and from a more energy efficient dehumidifier.


Answer: Dehumidification of materials can be divided into three phases:

  1. Water is drawn by capillary forces from the inside of the material up towards the surface.
  2. Transport is carried out in a liquid phase capillary transport in the small pores and in the vapor phase (diffusion) in the larger pores.
  3. Transport from the surface is only in vapor phase. The speed is controlled by the difference in vapor content between the material and the surrounding air.

Step 1 is strongly dependent on what material is to be dehumidified. What is usually mainly affected is step 3, i.e. to ensure that the moisture leaves the material’s surface and goes into the air. If you can heat up the material in which the moisture is contained, the process is accelerated.

The easiest thing to do is usually to make sure that the air is kept dry at all times and preferably at a low relative humidity (RH).

This results in increased vapor pressure difference and a faster dehydration!

Same temperature in material and air.

See the graph to the right showing the differences in vapor pressure at different RHs when the air and materials maintain the same temperature.

In other words, if you reduce the RH level in the air to 40%, the drying process is accelerated. This will create an increased vapor pressure difference and a faster dehydration!

Warming up the air

The graph on the right-side show what happens if you only warm up the air. Then the vapor pressure difference can become negative at relatively low relative humidity levels.

If the air is too warm – the moisture in the air may start to condense on the wall instead.
This means Humidification instead of Dehumidification!



Answer: Warm condensation is a technique in which, in a first step, the moisture is trapped in an adsorbent (dessiccant) which is regenerated when the absorbent has reached saturation. The regeneration is done by warming up the absorbent. This means that condensed water and dry air is produced. No connections are needed except to drain condensed water, which makes the installation very easy and low cost. It also means that all the supplied energy stays in the room and is not vented out. With Airwatergreens technology the dehumidifier is independent of the surrounding temperature and work equally efficient in all climates down to minus degrees.

If you are interested to read more in detail how the warm condensation method works – this is described in this report Modeling a Novel Sorption Dehumidification Method – written by Per D.


Answer: Keeping the air warm can hardly be considered a dehumidification method since no moisture is removed from the air. However, warming-up the air will lower the relative humidity (RH) level as hot air can “hold” more humidity than cold air. No water is removed from the building’s air, which means that heating must be kept on forever, to avoid excessive relative humidity. A study done at Uppsala University shows that about 5 times more energy is needed to maintain the same relative humidity over the year as compared to using a dehumidifier.

Answer:Ventilation should not be regarded as dehumidification method as no water is removed from the air. Ventilation is entirely dependent on the outdoor climate and how the temperature is outside in relation to the temperature in the room. Maybe you bring more humidity to the building instead of removing it?

Ventilation is used quite often as it is considered to be a cheap and simple solution. But ventilation can create more problems than it solves. A typical situation we often see is when the ventilation enters warm humid air into buildings with a lower temperature during the summer – not a suitable method!

Answer: Water drops are created on a cold surface – this is well known. This is due to the fact that cold air cannot contain the same amount of moisture as warm air. This fact can be used in dehumidification because it actually takes the water out of the air. But at the same time, this phenomenon is also the reason why corrosion and mold occur in buildings and structures!

To use cold condensation as a dehumidification method, the air must be warmed-up again after the condensation. Otherwise, the relative humidity will stay at the same high level. This means that this method can only be used at certain temperatures to avoid ice build-up at the cold surface.

Answer: Sorption dehumidification is considered to be the modern dehumidification method that was created in Sweden in the 1950s to dehumidify under Swedish climatic conditions. Over the years, this method has been used in many installations. The method is to trap the moisture in the air in a slowly rotating dessiccant wheel and then use warm air in step two to remove the collected moisture.

The warm air then captures the moisture, which is then typically discharged through a hole in the wall. Installation can easily become costly depending on how one can vent the air and energy is lost through the hole in the wall.

Installation can easily become costly depending on how you can discharge the air and energy is lost through the hole in the wall.



  • Consumes 5x more energy
  • Not always desirable with heating the air (eg cold storage)
  • Efficient at high temperatures and humidity levels
  • Very low efficiency below 10°C

  • Energy consuming
  • Complex installation with regeneration air stream
  • Energy wasted to environment
  • Warm condensation or CVP Technology
  • Temperature independent
  • The humidity is removed from the air
  • The energy stays in the room
  • Does not create under pressure
  • Easy to install



Svar: With the Temp Guard function available as an option in the FLEX you can ensure that the temperature stays frost-free in smaller rooms using the built-in element in the FLEX as a heat source.

Read more about Temp Guard


Answer: To be absolutely sure of our case, we let the State Testing Facility (now RISE) test our dehumidifier and compare it with a traditional sorption dehumidifier. The results of that test show that our dehumidifiers consume half as much energy to dehumidify the same amount of water.

Answer: The water removed from the air is delivered from the outlet on the side of the dehumidifier. A hose can easily be connected to deliver the water to a drain or a tank. If no sewage is available, we have an optional container and pumps built for the purpose. A standalone model as well as a container that at the same time can act as a cart on wheels to easily move the FLEX around, if needed.


Answer: The FLEX is tilting to one side to create self-draining. The water flows out of the machine without having to use any pump. This reduces energy consumption and minimizes the number of moving parts.

Answer: If the green light changes from a steady light to flashing, the dehumidifier needs service. There are instructions in the manual under Chapter 6 – Service.

Or contact Airwatergreen support at

Answer: Yes, both the FLEX and the REX models are able to communicate via Modbus to BMS control, monitoring systems.

The Cloud model can be connected via WIFI. Dehumidifier status is available, as well as data from sensors that detect humidity (RH), temperature etc are available.

Answer: We recommend replacing granules once a year to maintain full dehumidifier capacity.

This is included as a delivery in our Service agreement.

Answer: Yes absolutely.
The granules you need for the replacement are delivered in a package.

How to do this is described in the manual (available for download from FLEX and REX downloading pages) or look at our Instruction video.