Technology Questions

Adsorption Technology

Q: What is an adsorption dehumidifier?

A: An adsorption dehumidifier uses a rotating wheel (rotor) with moisture adsorbing properties to remove water from an air stream passing through it. The wheel is afterwards dried (regenerated) by another, the heated flow of air. This means that moisture from one flow of air is transferred to another, warming the flow of air by taking advantage of the rotating wheel. This differentiates an adsorption solution from traditional cooling based (or mechanical) dehumidifiers. You’ll be able to find a more detailed description along with an animation and illustration of the technology at cotes technology at our webpage.

Q: What industries can Cotes adsorption dehumidifiers be used in?

A: Cotes dehumidification solutions are delivered into a wide range of applications within various industries. Humidity control can benefit the customer in many ways in regard of improved facility efficiency, higher hygienic standards, higher quality products, fewer breakdowns, improved comfort and extended lifetime of equipment. Though the list is not complete, you’ll be able to find an overview of different applications under solutions on our webpage.

Q: What is the difference between adsorption and cooling based dehumidification?

A: Cooling based (or mechanical) dehumidification relies on a temperature reduction in order to remove water. It takes advantage of the fact, that cooler air can hold less water. This means that the dehumidifier cools the air to the saturation point and further still, which causes the moisture to deposit on the surface as condensation. Naturally then, the relative humidity after the cooler will be high/saturated. Thus, heat is often added to ensure the right temperature and thus relative humidity.

Adsorption dehumidifiers remove moisture from the process airflow without reducing the temperature. The temperature increases a little bit due to the heat energy related to water depositing on a surface. Depending on the dryness of the rotor, the water will be likely to deposit on the rotor. By increasing the temperature on the regeneration, the rotor can be dried more and thus allow even drier air in the process outlet. Therefore, the adsorption dehumidifiers will be able to create humidity levels/dewpoints below 0°C without any issues with ice. This also means that adsorption solutions are less sensitive to low temperatures and dry air compared to cooling-based dehumidifiers. Whether one option is better than the other depends entirely on the air properties in each situation.

Q: I have tried to control humidity by means of a condensing dehumidifier but failed to succeed. Is there any chance that a desiccant dehumidifier can do the job?

A: Yes, there is. The operating conditions for condensing dehumidifiers are quite limited compared to desiccant dehumidifiers. The dryness achievable for condensing dehumidifiers relates to the temperature of the cooler. Since the desiccant dehumidifier does not rely on cooling, there is no theoretical limit to how dry the air can be made. This limitation means that condensing dehumidifiers loses their moisture removing capabilities in cold environments. A further description of this is given in the document ”adsorption vs condensing”.


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Product-specific questions

Finding the right dry-air solution

Q: What information is needed to specify an appropriate dehumidifier?

A: To specify a dehumidifier for a given application, it is necessary to know the required moisture removal capacity as well as the operating conditions of the unit. The capacity of the dehumidifiers will vary depending on operating conditions. Moisture load is determined by internal loads as well as infiltration, which also depends on operating conditions inside and outside. Air properties vary during the year, which doesn’t make it any easier.

For most applications, it is also necessary to pay attention to building properties, installations and equipment on-site to ensure that the solution will satisfy the customer.

To help you with collecting all the necessary information, Cotes has developed a requirement sheet which will remind you about what to be aware of.

Q: How do I find out, if a unit is suitable for a specific task? 

A: Once you’ve found design conditions and estimated the moisture loads in the working area of the dehumidifier, you’ll be able to select a unit with a size that matches the requirements. If you are in doubt on how to estimate moisture loads, please have a look at our guide. The easiest way to find a suitable unit is to use Cotes’ online calculation tools. Adjust relevant figures and try different machine sizes until there’s a match. If you are in doubt on how to use the online calculation tools, please have a look through our guide. 

After having found the right size of the unit, please consider any additional requirements. Perhaps there are special requirements to available external pressure, alternative heating source, controls, etc. Options will vary between different machine families and sizes. Please have a look in our brochures to gain technical details on our machines from our downloads page. 

Q: How do I know, if a specific product suits my application? 

A: In general, the technology of our dehumidifiers is the same across the entire product range and can be used within almost endless applications. Some units are configured a little differently to ensure certain advantages in different applications. A brief overview below 

  1. C-range: 4-holed machines with process and regeneration completely separated from one another. Pressure neutral operation for higher efficiency. These units are configured to cover a great range of dehumidification capacities and can be used within endless applications. 
  2. CR-range: 3-holed machines with one common air intake for both process and regeneration air. The layout allows for very compact, transportable units with fewer moving parts and easier installation. 
  3. CWO-range: 3-holed machines with one common air intake for both process and regeneration air. The layout allows for a positive pressure operation and de-salting capabilities. Units are specifically developed for wind turbine operations. 
  4. Flexible range: Units are relatively large with a high level of customization. Units can be configured in various ways to meet specific requirements and can be made as one-offs if need be. These units are widely used if operating conditions are extreme.

Q: What sensors can I buy through Cotes, and how can I decide on which one to use? 

A: If you have a configuration A dehumidifier, you might want to buy an external sensor to control for the desired humidity. 

The DR10 is our most simple hygrostat. The DR10 is a mechanical switch that will close or open depending on humidity. The hygrostat can be set in the range of 35-95%RH and will make sure to switch the unit ON/OFF around the setpoint. 

The DH24 sensor can provide an ON/OFF run signal for the dehumidifier depending on either %RH or DP. Further, the display is connected via RS485 to the controller unit itself. This allows the display and controller to be placed in separate locations. For further details on this controller, please have a look at the DH24 datasheet.

The DA20 sensor is the most frequently used electronic hygrostat. The display/controller is connected to the dehumidifier by a wire. The controller can provide an ON/OFF run signal depending on either %RH or DP. Capacity control (0-10V) is available only for %RH. For details about this sensor solution, please refer to the DA20 datasheet. 

The DCC controller is more capable than the DA20/DH24. The controller can handle up to 3 humidity sensors and measure both %RH and DP for these sensors. The DCC can be set up to control ON/OFF depending on either %RH or DP. Further, the controller can provide control signal (0-10V) depending on either %RH / DP or both. Note that the controller can be set up to control both a dehumidifier and a humidifier. Technical details can be found in the DCC datasheet. 

Q: How do I know which model line will suit my needs? 

A: Most applications can be resolved by means of a standard dehumidifier. The dehumidifiers can be either 3-holed or 4-holed. If you are in doubt of the difference between these two kinds, please refer to this topic. Generally, a 4-holed dehumidifier will offer better performance compared to a 3-holed unit. However, the 3-holed machines are more compacas well as easier to install. 

While the units are of different sizes, have different control options, and some have special features – they operate similarly and can be used for various tasks. For the most part, the standard family (C30, C35C65 and C105) will be an excellent place to start when considering a Cotes dehumidifier for stationary installations. For temporary installations / mobile units, the CR-B line will be an excellent place to start. 

You’ll be able to find a brief description of the product families here. 

Q: What is the difference between 3-holed and 4-holed dehumidifiers? 

A: 3- and 4-holed dehumidifiers have three and four holes, respectively. By having four holes, it is possible to have separate airflows for regeneration and process air. For 3-holed units, there’s only one inlet, shared by both the regeneration and the process air. This means that one fan can be used to drive both airflows. It also means that the dehumidifier will create a slight vacuum in the room where it is installed and thus increase infiltration a little bit. 

Main advantages of the 3-holed solution are that it is a cheaper unit and easier to move around and use in temporary installations (only one duct to leave the room). The main disadvantage of a 3-holed setup is that the slight vacuum will increase infiltration and result in a higher moisture load and thus decrease efficiency. 

The main advantage of a 4-holed setup is that the efficiency is kept higher as the “disturbance” in the room will be kept on a minimum. Main disadvantages of the 4-holed setup are that it requires two fans (bigger unit and higher cost) and two ducts to leave the room (regeneration in and out). 

In general: 3-holed setup is recommended for temporary installations and 4-holed setup is recommended for stationary installations. 

Q: How do I calculate the moisture load for my application? 

A: Even though different applications might seem to be very different, the moisture loads are calculated in a similar way within all industries. Depending on the industry, there might be other things to be aware of, but the calculations themselves is mostly the same. 

Cotes has prepared a document describing many kinds of moisture loads. Have a look in this document and decide what types of moisture loads exist in your application. In general, there’ll always be a moisture load from infiltration through windows, doors, ventilation with fresh air or similar. Often there’ll also be one or more internal moisture loads from persons, processes or something else going on inside the building. Please refer to the document mentioned above for more detailed descriptions on this topic. 


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Website-related questions

The Cotes partner area

Q: I can’t find the documentation that I’m looking for under “Technical documentation”. Where can I find what I’m looking for? 

A: The technical documents on the partner area is regularly updated to ensure that the newest revisions will be available. To avoid having an immense number of documents online, older revisions of the documents are overwritten. This also means that you might not be able to find the documentation for your unit online. 

If you need documentation that does not appear online, please send a request to tech-support@cotes.com. Don’t forget to include the serial no. of your unit if you need something specific for your machine. 

Q: When and how should I use the Cotes Calculators? 

A: Feel free to use the calculators in the partner area anytime. The calculators will provide help when dimensioning a suitable dehumidifier for your customer. Flowcharts can also be used to show the customer what conditions you have calculated with as well as what he/she can expect to get. 

In case you need support from Cotes when you are dimensioning a dehumidifier, we kindly ask you to attach the flow chart from the calculation tools when sending your request. The flow chart will provide us with important information on the issue and thus save some mailing forth and back and reduce processing time. 

In case you are in doubt on how to use the calculators, Cotes have prepared a guide for the tools. The guide might seem a bit confusing, thus if further assistance is required, we are more than happy to answer your questions or arrange an online training. Please refer to Tech-support@cotes.com  


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Product-specific Questions

C35, C65 and C105

Q: What are the differences between the different configurations? 

A: The C35, C65 and C105 comes in configurations A, B, C, D. The different configurations offer increasing options of controlling and communicating with the unit. Whereas A is the simplest machine – D is the most sophisticated one. You can find information regarding the different configurations in this document. 

Q: What is the difference between models ending on E, D, C and S? 

A: The units come in various editions named E, D and C according to the specialty of the unit. E is short for Energy whereas D stand for Drystands for Cold and finally S stands for Steam. E is configured to deliver a relatively high capacity at low energy consumption. D is configured to deliver drier air but at lower capacities. Thus, the D models often deliver a lower flowrate of air compared to E-models. C is optimized for cold applications and can operate down to minus 25°C. The C-models only comes in basic configurations but are well insulated and delivered with an external regeneration-heater and special controls to withstand freezing conditions. Some units can be configured with steam as heating source, which can be a more price-efficient solution in the longer run. 

For more information on the E- and D-models, please refer to our standard product brochures for C30C35 and C65. You will be able to find a separate brochure for the C-models.  

Q: How do I set up the PLC? 

A: Cotes have prepared some material on how to setup the PLC to suit your needs. Depending on the model and configuration you’ll have different options with the PLC. 

In this guide you’ll find an overview and descriptions of the individual programs available in the PLCs. It is also described how to adjust setpoints of the humidity controller. 

We have also prepared some videos where will be able to see some examples of how to set up the PLC. Examples includes water worksbasement and storage room. 

If you need to communicate with the PLC with external systems via Modbus, you might want to have a look in this modbus guide. 

Q: What controls do I need in order to run my dehumidifier? 

A: The desired level (and kind) of control depends on the whatever problem you are trying to solve. Configuration A is delivered without a humidity sensor which means you won’t be able to control for humidity unless you are connecting an external operation-signal from, for example a hygrostat. For configurations B, C and D, the dehumidifier is delivered with a humidity sensor capable of controlling the dehumidifier according to your setpoint. 

To decide the appropriate control option for your unit it might be a help to have a look at the overview and description of the different programs written in this document 

Q: What is an LK module? 

A: The LK module allows the moisture to be drained away in liquid form instead of as hot, humid air. The module encloses the regeneration circuit and cools it down by blowing room-air across the heat exchanges inside the module. By cooling the regeneration air, the moisture condensates on the surface of the heat exchanger and drains away at the bottom of the cabinet. The LK module includes a fan to ensure circulation of the room-air to cool the heat exchanger. 

With the LK module it is not necessary to drill holes for the ducts or extend them far to reach the ambient – instead a drain is required to lead the condensed water elsewhere. Thus, the solution is ideal in applications where it is a challenge to reach the surroundings with the regeneration air. However, note that the LK module will heat up the room with a heating power equivalent to the power consumption of the dehumidifier. 

Q: What is an HR module? 

A: The HR module allows some of the waste heat in the regeneration outlet to be used to preheat the incoming regeneration air. By using some of the waste heat on the outlet to preheat the inlet, the electrical heaters of the dehumidifier only pulls less power to heat to the desired temperature. This increases the overall efficiency of the dehumidifier. Increased energy efficiency lowers the operation cost of the system. You can estimate payback time for an HR module by using this spreadsheet. 

Q: What is a PRE-POST module? 

A: A PRE/POST module is a module that allows PRE-cooling and/or POST-cooling or -heating of the process airflow. If the process air inlet is warm and humid it might be a good idea to precool the air to remove water by condensation for the benefit of lower energy consumption. If the temperature level of the process outlet is critical for the customer, the POST-cooler or -heater provides an option of controlling the supply temperature. 

The coils are prepared to be used with various fluids including pure water and brines. Refrigeration circuits are not done by Cotes. When using a cooling fluid – the PRE/POST-module can supply a 0-10V control signal to an adjustable valve, controlling the water supply. Note that the valve itself is not included in Cotes’ scope of supply. 

Q: Where can I find capacities for CC (cold store) dehumidifiers at various conditions? 

A: The expected capacities of our CC-models are shown in graphs in this document. Be aware that the capacities for the dehumidifiers are dramatically decreased in cold stores because the water content in the air is very low at such low temperatures. This also means that the specific energy consumption is higher than average in cold storage facilities. 

Q: The regeneration air temperature is too high. How can it be reduced? 

A: The regeneration air can be reduced be reducing the setpoint temperature on the heaters. If you’re in a design stage, you might want to choose a bigger model with a lower regeneration temperature to satisfy the same capacity requirements. Another way to reduce the regeneration temperature is to increase the flow rateIf increasing the flowrate with the built-in fan, be aware that the backpressure will put a limit to the increase. If required, you have the option to add a booster fan to pull more regeneration air. 

Generally, the regeneration air temperature will become higher if the water content in the room becomes lower. Thus, reconsider the setpoint requirements – if the requirements are strict. 


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Problemes & Solutions

Humidity related issues

Q: I have condensed water dripping from my ceiling. Will I be able to avoid that by controlling humidity? 

A: Yes. Condensation is quite often a challenge in facilities where water is used for processes and cleaning cycles. Especially within food applications, there’re strict regulations to limit condensation but also high requirements for cleaning. Refrigerated facilities are even more likely to experience issues with condensation. By controlling the humidity/dewpoint of the air in the facility, you can avoid condensation to develop. You’ll even gain the side effects of shorten the drying time after cleaning and reduce the risk of wet and slippery floors as well as possibly protect the facility against degrading and mould formations. 

Q: I have mould growth at my water pipes, on my ceiling and at the walls. Can I avoid this by controlling humidity? 

A: Yes. Mould growth is a common issue within various industries including food production and wind farms. The issues with mould are likely the biggest in areas with cold surfaces and steady air. Therefore, mould is often seen in corners of the ceiling, at water pipes and similar. Issues with mould can be eliminated by keeping the relative humidity low enough to prevent the growth of the mould. By controlling the relative humidity, you might even experience side effects like avoiding degrading/corroding of your facilities as well as the improved environment. 

Q: I struggle with ice formations in my freezer. Is there a way to avoid such ice formations? 

A: Yes. A common issue in food production and storage. Challenges with ice in sub-zero applications are well known. By controlling the humidity /dewpoint to a level below the temperature of structural elements, you’ll be able to avoid ice formations falling from the ceiling, blocking door openings, causing slippery floors, etc. By controlling for a dewpoint lower than the temperature of the cooling refrigerant, you’ll even experience frost-free evaporators and thus eliminate the need for defrosting. By controlling the humidity, you are likely to experience side effects like improved final product quality, fewer safety hazards and increased overall efficiency of the freezer. 


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Wind Industry

Wind turbine issues, design & solutions

Q: What kind of humidity-induced problems can I face in a wind turbine? 

A: In general, we see three types of issues that clients want to have solved: Mold, corrosion or faster startup after grid loss. The latter is related to prevent arc flashing due to high humidity.  

Q: Is there any difference between onshore and offshore problems? 

A: Often, we hear that especially onshore WTG’s close to the coast (nearshore) are more exposed than dedicated offshore turbines because the offshore turbines are designed for that environment. Also, onshore turbines are more often exposed to rapid changes in temperature, that can lead to condensation inside the WTG’s. 

Q: What are the benefits of controlling humidity and salt in a wind turbine? 

A: The benefits are many. If you can keep salt out of the turbine and control the humidity, your assets are more likely to produce more for extended periods with less downtime and maintenance cost. If you have salt in your turbine and high humidity, it is a cocktail that is very corrosive.   

Q: Is mould a problem in a wind turbine?  

A: It can be a problem if technicians are exposed to mould for extended periods in time or if the technicians are already having respiratory issues, mould can exacerbate these health issues. Some technicians will flat out refuse to service assets until they have been cleaned, which is an unnecessary and costly consequence of mould in your wind turbine. 

Q: When is salt a problem, and why is it a problem? 

A: Salt is a well-known corrosive agent. The other disadvantage of salt is that it absorbs humidity from the air and thereby accelerates the corrosion inside a structure. 

Q: Why can’t I add more ventilation to the wind turbine? Will that not solve my issues with humidity?

A:  By adding more ventilation, you will have the same humidity inside the turbine as you have outside. It is known from various studies that the humidity needs to be below 60%RH, to stop mould from growing. Most of the electronics works the best at a low humidity. Further, corrosion is also slowed down at a lower humidity than 60%, therefore it is better for the asset to have the humidity removed than just added ventilation.  

Q: How dense is the structure of the turbine? 

A: It depends on the original design. Typically, if you have placed the converter or transformer in the tower, you need air to cool the equipment during operations. If it is possible to mount dampers that close the air inlets, when the high airstream is not required, then it might be possible to protect the whole structure with an overpressure system. Otherwise, we will recommend a targeted dehumidifier solution.  

Q: Can I get specific areas of the turbines protected against moisture and salt? 

A: Yes. With dehumidifiers in various sizes, we can make targeted desalting and dehumidification of specific areas in the structure. 

Q: Does dry-out time after grid-loss cause loss in production?

A: Yes, it does. Some OEM’s (Original Equipment Manufacturer) requires 24 hours dry-out period before the turbine can start producing again. The dry-out period cost energy, as the cooling water and heating elements inside the electrical cabinets requires power to get rid of the humidity. So instead of producing energy, the turbine is using energy. By adding a dehumidifier, we expect to be able to make the dry out time shorter, and we can make evidence-based startup when the humidity has reached a safe level. This is now being tested in the field.  

Q: What are the overall strategies to protect a wind turbine for unwanted humidity?

A: In general, you have two options, depending on the design of the tower and nacelle. Suppose you have a closed design, with limited air infiltration in your structure. In that case, we can create a slight overpressure in the whole structure that prevents air from entering whilst we remove the salt and humidity from the air inside the structure. In this solution, you have protected the entire structure against mould, corrosion, creating an office-like environment for the electronics inside.  

Suppose you have an open structure with a lot of air filtration. In that case, the best economical solution could be that we make targeted dehumidification of the area where you have the most valuable equipment.  It is possible to dehumidify several areas in the WTG’s using small dehumidifiers.

Q: Besides in the turbine itself, can other parts of a wind farm be protected with a dehumidifier? 

A: Besides WTG’s, we have made solutions for transition pieces (TPs) and substations. Furthermore, our solutions are used for transport and storage preservation by leading OEM’s globally as some turbine are exposed for extended periods before they become operational. 


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Food & Beverage Industry

Food & beverage issues, design and solutions

Q: We already have a cooling coil in our ventilation system, in what way does your solution differentiate? 

A: A Cotes dehumidifier works with adsorptioni.e. the efficiency is much less dependent on the air temperature. An adsorption dehumidifier is efficient all the way down to -20°C. If you install an adsorption dehumidifier you will experience an improved operation of your cooling system. 

Q: What about the risk of pollution of the air in the room? 

A: Each part of the rotor is heated up to ~120°C 5 to 8 times each hour, thus there is no risk that the processed air will be contaminated. We can install a HEPA filter on the outlet to ensure that nothing unwanted passes through and into the room. 

Q: Is adsorption dehumidifiers not expensive in energy costs? 

A: Cotes dehumidifiers are controlled by a PLC-controller that ensures that the unit runs as energy-efficient as possible. The regeneration circuit can be supplied with heat from different sources depending on what is freely available in your production such as electric current, steam, gas or waste heat if available. We can supply you with an estimation of energy costs based on your requirement and metrological weather data. 

Q: What about the cleaning agents that we use during cleaning, will it be harmful to the unit? 

A: The casing of the Cotes dehumidifier is as standard delivered in DIN 1.4301 (AISI 304) thus it can withstand the humid environment in any food production facilitiesThe internal parts are  

Q: Why do we only see problems with condensation in the summertime? 

A: In the summertime, the temperature outside is higher, thus the air will contain more humidity. When the hot air enters the room, the humidity will condensate on the cold surfaces. This doesn’t happen as often during wintertime as the air outside doesn’t contain as much humidity as during summertime. With a dehumidifier, you can create winter conditions in the summertime and thereby experience a constant climate in your production – all year round 

Q: Where can we install the dehumidifier? Can it be placed on the roof or does it have to be in the production room? 

A: Yes, both inside and outside. Normally we recommend installing the unit indoors, preferable in a technic room with other equipment. Depending on the model, we can supply wall or floor brackets, or if you need to install the dehumidifier outside, we have cases with insulation and an outdoor cover kit – whichever solution works best for you.


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