Humidity is a naturally occurring phenomenon that occasionally reveals itself as condensation, mist or frost. This is generally the only time that most of us actually become aware of its existence!Conversely, airborne moisture is a perpetual destructive force that causes enormous irreversible damage to materials. It often impedes or immobilises many of our manufacturing processes.As humidity is predominantly invisible, the damaging effects caused by it are not always easy to recognise.It is therefore frequently overlooked as the principle contributing factor when searching for the solution to a particular problem.These pages provide a few examples of common problems caused by high levels of humidity.
Desiccant Dehumidifiers - Applications
Desiccant Dehumidifiers in PharmaceuticalsMost substances used in drugs today are hygroscopic and any absorption of moisture during the manufacturing process will affect the final weight, quality and durability.When hygroscopic ingredients are weighed and mixed, it is important that the products' weight is not influenced by absorption of moisture from the surrounding air. In powder form, moisture will affect the flow, caking, compaction and strength properties of the manufactured solid form. Yeast, moulds and bacteria require a certain amount of moisture to support growth. Controlling relative humidity is probably one of the most important factors in maintaining a sterile environment.A cool dry environment generally enables faster production, a better quality product and a longer shelf life. The majority of tableting processes require humidity control between 20 and 35%RH at 21 to 24°C.
Moisture LoadsIn most pharmaceutical air conditioning systems, the greatest moisture load is from the fresh air component that is typically between 5 and 20% of the total room supply air volume.Depending on the moisture loads in the room, it may be necessary to only “deep dry” the fresh air component using a pre-cooling coil (to 10°Cdp) and a desiccant dehumidifier (< 10°Cdp).Systems with a low fresh air volume or rooms with a excessive moisture loads from high infiltration rates (negative room pressure), frequent door use, high product moisture load, etc, will normally require desiccant drying of a mix of pre-cooled fresh air and some return air.Dehumidifier capacity is controlled by an RH sensor installed in the room or the return air duct. This simple design is often adequate to accurately maintain the required RH in the room.
Desiccant Dehumidifiers in ConfectioneryIn the confectionery industry the quality of the finished product is paramount. Close control of air humidity during the various manufacturing processes is now considered essential to maintaining these high standards.If powders, starches & sugars used in the various processes are not maintained and stored in a dry environment they will adsorb moisture from the surrounding air and form into lumps or cakes. This causes malfunction of the material handling machines.Moulding machines require the mould heads to be kept free of condensation during the cooling process. The introduction of dry air will ensure this and so avoid the possibility of the product failing to be released from the moulds to the coating lines.Storage of the finished product is critical to maintain the product in pristine condition. Storage in a high humidity environment will affect both the packaging and the contents. Chocolate and glazed products will lose their glaze finish and look dull and unappetising, whilst candies will become sticky and stick together and become difficult to remove from the wrapper.The controlled use of dry air can help increase production flow, reduce downtime and ensure that the product reaches the customer in the best possible condition.Chocolate Bloom ProblemsSugar bloom of chocolate is probably the most common problem encountered during the storage and manufacture of chocolate. It is a defect which manifests itself as a greyish-white film on the surface of the product. In most cases the eating quality of the product is not affected, but the appearance, which resembles bacterial mould, is not very appetising. Blooming may occur at any time - during manufacture, a few hours after, to several months later. Sugar bloom occurs less frequently than fat bloom and occurs when the surface of the chocolate is exposed to moisture or high humidity. The surface film of moisture dissolves some of the sugar particles in the chocolate which then crystallizes on drying. During the manufacturing process, this can easily happen if humid air is allowed to come into contact with the chilled chocolate as it leaves the cooling tunnel. If the surrounding air is maintained at a lower dewpoint this can be prevented.Properly stored chocolate can have a shelf life of one year or more and can even be frozen for longer storage. However, care must be taken when bringing back to room temperatures as condensation can easily form. Ideally chocolate should be stored at 18 to 20°C at less than 50%RH.
Desiccant Dehumidifiers in the Defence IndustryIn the early 70's, NATO organisations began to use desiccant dehumidifiers to protect valuable military equipment against corrosion and degradation caused by airborne moisture.For storage applications, dehumidification is far more effective and less expensive to operate than heating. Even at a constant temperature, relative humidity can fluctuate wildly and the correct conditions for storage are seldom being achieved.Our desiccant dehumidifiers use lower energy than heating and operate effectively and efficiently at all ambient temperatures - even below freezing.
Controlled Humidity EnvironmentsControlled humidity environments (CHE’s) have now become standard practice for most militaries worldwide.Inactive ships, tanks, aircraft, weapons and supplies are maintained in a state of readiness by dry air storage, thus providing an increased combat readiness.In CHE’s there is negligible material degradation. Electrical and sensitive electronic equipment is kept in good working order and ‘mean time between failure’ (MTBF) rates have been significantly increased.As equipment in CHE’s is constantly protected against the effects of moisture, inspection and maintenance routines can be adjusted accordingly, resulting in savings both on time and human resources.
Desiccant Dehumidifiers in MuseumsMoisture is a major enemy in the fight to preserve antiques and artefacts that form an important part of our heritage.Paintings, furniture, linens and other organic materials contain micro organisms which thrive and multiply in high humidity conditions - invariably causing irreversible damage.Valuable metallic objects and structures stored in museums are susceptible to oxidisation and corrosive degradation.To avoid expensive and complicated restoration costs, environmental conditions (which are naturally aggressive), will require adjustment and control. If the relative humidity is maintained within limits using a desiccant dehumidifier, no micro organism or bacteria activity will occur and metallic surfaces will be free from corrosion.Our heritage can easily be protected against degradation for future generations to appreciate.
EMCExpressed as a percentage, the Equilibrium Moisture Content is the percentage of the material’s weight that is made up by water. For example, if an object has an EMC of 10% at 40% RH, then there are 10 grams of water in every 100 grams of material once it has stabilised with the environment.EMC is therefore determined by the specific properties of a material and the relative humidity of the environment.ERHExpressed as a percentage, Equilibrium Relative Humidity is the relative humidity of the air at which a material is neither gaining or losing moisture for a given EMC.Using the above example, if the material is to be maintained at an EMC of 10%, then the RH of the air should be 40% (ERH).
Desiccant Dehumidifiers in Ice RinksMoisture from warmer outside air will inevitably find its way into the building through natural leakage and door traffic. This usually results in an increase in relative humidity and dewpoint of the cool ice rink air.When the humid air comes into contact with colder surfaces (eg: steel roof supports), the air can easily reach its dewpoint (saturation point) and condensation will occur. Dripping water will cause damage to the ice by pitting the surface or by forming "ice mushrooms", thereby lowering its overall quality.If humidity is allowed to rise, indoor fog can be a common problem, especially in Summer when the dewpoint of outside air (and hence moisture loads) are at a maximum.A desiccant dehumidifier system is designed to maintain a constant relative humidity or dewpoint within the ice rink.The re-circulated air (often combined with some fresh air), is prevented from reaching its dewpoint by controlled dehumidification. The dewpoint of the air is maintained below that of internal surface temperatures. Condensation and fog are eliminated!A lower humidity also helps to prevent formation of mould and mildew growth, reduces steel corrosion and improves general safety of electrical equipment
Desiccant Dehumidifiers in Floods & Water DamageA major set back in the restoration process is the time taken to dry out buildings prior to starting remedial building work. There are potentially hundreds of litres of water that remain hidden within the building’s structure.As a result, buildings remain unfit for use or occupation for many months during which time high internal humidity levels can cause secondary damage and increase the risk of dangerous mould growths.Whilst the drying rate of a material will vary according to its porosity and density, it is also determined by the ability of moisture to evaporate into the surrounding air. Drying rates are greatly improved by lowering relative humidity, adding heat and increasing air movement. Ideal drying conditions of 35 to 55 %RH can only be maintained if the dehumidifier capacity is greater than the rate at which moisture is being evaporated. If the internal relative humidity rises uncontrollably (e.g. condensation on external walls and windows), it is a clear indication that the dehumidifier capacity is too small.Dehumidification of flood damaged buildings The primary benefit of a refrigeration type dehumidifier is that it performs well when used in a warm humid environment. Moisture extraction rates will deteriorate rapidly as both temperature and humidity is reduced. It is generally accepted that refrigeration dehumidifiers should not be used below 10°C dewpoint. A desiccant dehumidifier operates on a totally different principle to a refrigeration type. The main benefit is that it performs exceptionally well when used in cooler climates, or when lower dew points are required. As there is no water produced during the drying process, these units work effectively at sub-zero temperatures.Air leaving a desiccant dehumidifier is warm, very dry and at high velocity, thereby providing the three essential ingredients necessary for fast and effective drying. The dry air can be easily ducted to where drying is needed most, whether it is under a floor, into a wall cavity or simply distributed to serve multiple areas.Whilst the purchase of a desiccant dehumidifier is probably not within the financial budgets of most home owners, some restoration companies now provide small desiccant units for hire. High capacity desiccant dehumidifiers should be used for drying larger buildings such as schools, warehouses, municipal buildings, etc ...
Desiccant Dehumidifiers in the Plastics IndustryInjection and blow moulding operations utilise thermoplastics which are heated to plasticity and shaped into forms using a mould. During this process, if moisture is present in the raw material it boils, releasing vapour that can cause both structural and cosmetic imperfections to the finished product.To ensure that the end product is defect free, raw materials must be free of moisture before being processed. Many of today’s plastic resins are hygroscopic (high affinity for absorbing moisture).To reduce forming time and increase production volumes, the majority of systems employ the use of chilled water to reduce the mould temperature. Generally, the cooler the mould, the faster the process cycle. However, operating at low mould temperatures will create problems with condensation, especially in summer. This can result in unacceptable water marks on the product as well as corrosion of expensive moulds and guide pins, necessitating repair or replacement. The problem can easily be overcome by simply increasing the mould surface temperature. However, as this will result in longer cycle times and reduced output, it is not the ideal solution.By incorporating a desiccant dehumidifier the air dewpoint can be controlled. Lower mould temperatures can then be achieved without the risk of condensation.Desiccant dehumidifiers are also used when storing expensive moulds. There is no need to waste time and effort greasing the moulds prior to storage. If the relative humidity is maintained below 45%, moulds can be stored safely without risk of rust formation (irrespective of store temperature).
Desiccant Dehumidifiers in Cold StoresHealth & SafetyIce, frost, snow, fog and condensation can all occur whenever warm humid air comes into contact with a colder surface or environment. When cold store doors are open, a turbulent exchange of air occurs across the door space.Moisture from outside air condenses on the cold store floor and other surfaces producing ice, frost and snow. This phenomenon creates a slippery surface; a serious hazard to staff and fork lift operators. Ice forming on ceilings will gradually increase in thickness and unless build-up is removed regularly, there is a serious risk of it collapsing, potentially causing injury to personnel.When humid air meets cold store air around doors and traffic routes, moisture vapour can condense to create low level fog that reduces visibility; another potential safety issue, especially with fork lift drivers.Refrigeration Plant EfficiencyAs cold store air is circulated through the evaporator coil, airborne moisture vapour condenses and then freezes to form frost. Moisture originates from the product and personnel, but by far the greatest source is from outside air infiltrating into the store through doors.Frost build up on the evaporator coils reduces the overall heat transfer coefficient and impedes air circulation. Both cause deterioration in the performance of the evaporator and refrigeration plant. A decrease in coil efficiency causes the compressor to work for longer periods and can reduce the refrigerant evaporating temperature. Both factors increase energy consumption.Regular defrosting of the evaporator is necessary because equipment performance deteriorates with increasing thickness of ice. This is an expensive operation which adds to the heat load of the cold store. Nevertheless, as equipment performance deteriorates with increasing ice thickness it is necessary to defrost periodically.A desiccant dehumidifier operates by extracting moisture in its vapour state, effectively removing moisture without producing condensation. In most cases, a dry air supply of minus 20°Cdp or lower is easily attainable. The dry air can be ducted into distribution boxes above the cold store doors. The resulting curtain of dry air provides an effective barrier against moisture infiltrating into the cold store.Alternatively, an airlock arrangement can be used. The dehumidifier continuously removes moisture in the airlock by recirculating the process air. The dry air outlet duct is positioned above the cold store door and directs the driest air down across the door face. The airlock and curtain effect together create a ‘buffer’ zone which considerably reduces moisture ingress into the cold store.
Dry Air Storage using Desiccant Dehumidifiers Although relative humidity is influenced by heating, it is a common misconception that moisture sensitive materials should be stored in a heated environment.Even at a constant temperature the relative humidity can fluctuate wildly, the correct storage humidity seldom being achieved.In winter, heating creates an atmosphere which is very often too dry. In summer when heating systems are switched off, a decrease in night time temperature will cause a significant rise in the relative humidity, frequently to a level where the products can be damaged.Excessive airborne moisture is one of the most destructive naturally occurring elements. Normally invisible, it affects both the quality and shelf life of food, raw materials and finished products.Sustained exposure to high moisture levels causes corrosion of metals, solidification of powders, degradation of chemicals, disintegration of cardboard and the promotion of mould growth. Building RegulationsTo comply with building regulations, heated buildings require minimum standards of insulation. As this does not apply to humidity controlled stores, not only can new stores be constructed quickly using cheaper, lighter materials but there will also be substantial energy savings, especially in larger volume buildings.As most materials are not sensitive to lower temperatures, the most effective and efficient solution to protecting products in storage is by using a desiccant dehumidifier to maintain the correct relative humidity at all prevailing temperatures.
Dehumidifiers to prevent corrosion of bridgesCorrosion of mild steel components and high tensile support wires can soon compromise structural integrity resulting in safety issues, costly traffic restrictions and ultimately bridge closure.According to a 1997 report, of the 581,000 bridges in USA, about 17% were rated as structurally deficient. The cost to rectify these deficiencies was estimated at $78 to $112 billion.While corrosion of the reinforcing steel was not the sole cause, it was a significant contributor and has therefore become a major concern.Steel protection using traditional paint coatings such as EVA and Polyamides is very costly and labour intensive and often fails to meet expectations. Corrosion of internal steel structures and associated support components can normally be eliminated by maintaining the air at 40 to 50%RH.
Dehumidifiers in Meat & Meat ProcessingAs meat products are processed within chilled premises, the subsequent high relative humidity creates ideal conditions for bacterial growth.Dripping condensation and wet surfaces are another potential source of food contamination.Under new EU legislation, stricter hygiene standards now include compulsory monitoring and recording of humidity levels in food warehouses, processing plants and cold stores.'Water Activity' is used as a measurement of moisture at the surface of food products. Multiplying the water activity by 100 gives the RH of the atmosphere in equilibrium with the food.Since yeast, moulds and bacteria require a certain amount of available moisture to support growth, maintaining a water activity of 0.7 (70% relative humidity) can provide effective control.Growth of the following harmful micro-organisms are generally inhibited below a water activity of 0.7:-Pseudomonas, escherichia, proteus, shigella, klebsiella, bacillus, clostridium perfringens, listeria, salmonella, vibrio parahaemolyticus, C. botulinum, serratia, lactobacillus, pediococcus, rhodotorula, pichia, candida, torulopsis, hansenula, micrococcus, staphylococcus aureus, debaryomyces, mycotoxigenic aspergilli, most saccharomyces (baillii), most moulds (mycotoxigenic penicillia) and most halophilic bacteria.Note: We will not knowingly provide equipment to any company who processes meat obtained from animals that have not been fully stunned prior to slaughter.
Lithium battery research and production facilitiesDST are the market leaders in the design and supply of climate control systems for ultra-low dew point applications. Air dewpoints as low as minus 120°Cdp can be achieved by utilising the Seibu Giken DLR Zeolite desiccant rotors.The processes used for manufacturing Lithium batteries are very similar to those used in the production of Nickel Cadmium cells and Nickel Metal Hydride cells with some key differences associated with the higher reactivity of the chemicals used in the Lithium cells. The anodes and cathodes in Lithium cells are of similar form and are made by similar processes. The electrolyte filling and sealing stage of cell manufacture must be carried out in a “dry room” since the electrolyte is highly reactive with moisture. Moisture will cause the electrolyte to decompose with the emission of toxic gases. Lithium Hexafluoride (LiPF6) for instance, one of the most commonly used electrolyte materials, when exposed to moisture results in an exothermic chemical reactivation and the formation of toxic hydrofluoric acid (HF), Lithium Hydroxide and Hydrogen Gas. Crucially moisture sealed inside the battery can continue to react after the battery is completed significantly reducing its lifespan. Recent research demonstrates that the ambient moisture present in the manufacturing room can degrade the “memory” characteristic of lithium and the newer advanced polymer-based batteries.General Design and Application ConsiderationsThe construction method and design philosophy of the climate control system and dry room are crucial to achieving and maintaining a stable low relative humidity. The dry room and climate control equipment should be designed to achieve:-•ISO Class 6/7 with air change rates ranging from 60 to 240 AC/H with a uniform air flow•As close to near vapour tight construction as practicable•Supply air of less than -60°Cdp (0.006 g/kg) with return air of less than -45.0°Cdp (equivalent to less than 0.5% RH at 25.0°Cdb) in order to achieve optimal conditions•Access to the space via ante room and airlock air showers•Optimised fresh air introduction to space for workers and pressurisation
Dry Storage in PVC BuildingsThese single skinned buildings are typically used for additional storage space.Being uninsulated, heating is not usually an option. However, because these structure are well sealed, correct storage conditions can be easily achieved using our desiccant dehumidifiers. Without dehumidification, these buildings are naturally susceptible to high humidity levels.Products in storage such as wood, paper & cardboard will rapidly degrade above 55%RH. Unless treated, steel products will usually corrode above 45%RH.Desiccant Dehumidifiers in Sports HallsSports halls often suffer from moisture condensing on the high density concrete floor or from dripping water off steel structural supports.This not only creates an unpleasant environment but a serious risk of injury to athletes.Above 70%RH, moulds and mildews will quickly form on the fabric internal surface - not only unsightly but another risk to health from airborne spores!
Dehumidifying Cargo Holds High humidity affects goods in global transit, shortening shelf life and reducing quality. Materials in cargo holds such as flour, wood and paper can be protected using our drying systems, ensuring that cargo arrives dry and undamaged.Dehumidification is far more effective than heating, as it actually removes moisture from the air. Our dehumidifiers require little energy and will operate efficiently at all ambient temperatures -even below freezing.Dehumidifiers in Ships & Oil PlatformsCombined with the aggressive nature of salt, humidity is a major cause of rust and corrosion to marine structures. It can dramatically reduce the lifetime of machinery and seriously affect the reliability of electrical and electronic equipment.While it may not always be practical or necessary to protect equipment in constant use, dehumidification should be considered during lay-up or refit.Machinery spaces, empty tanks and holds, accommodation, offices and other unused spaces can be protected from corrosion by using our drying systems.Using our dehumidifiers inside sealed steel structures is an excellent alternative to surface treatments. An air dryer system costs only a fraction of that used to regularly blast and paint such structures. As long as the relative humidity is controlled, corrosion can be eradicated - irrespective of temperature.
Dehumidifiers in Silos Most materials stored in silos are affected by high air humidity or moisture regain. Problems include irregular flow, agglomeration, increased microbial activity, chemical reaction with moisture and general degradation of the stored product.Temperature changes to the silo and moisture laden head space air cause the relative humidity to fluctuate. At lower temperatures the relative humidity of the head space air will increase, often to saturation point (100%RH) when the air begins to deposit moisture on internal surfaces of the silo. These problems can be eliminated by ensuring that air in the head space is maintained at a low relative humidity. A dry air circulation rate of 1 x silo volume per hour is normally sufficient.The simplest solution is to install the dehumidifier in the base of the silo skirt. Dehumidified fresh air is then ducted into the filling line or a separate pipe leading to the head space. This system creates a slight positive pressure which opposes the natural tendency of moisture to diffuse through the silo structure due to differences in vapour pressure. Excess air pressure is exhausted through the vent filter assembly on top of the silo. During filling, the dehumidifier's dry air supply duct must be isolated.A dehumidified air re-circulation system is normally only recommended when a very low humidity or dewpoint is required in the silo (e.g. storage of PLA, polylactic acid). Dust from some stored materials can be drawn into the air return line. This can potentially cause damage to the dehumidifier so additional air filtration modules may be necessary.Dehumidifying the air void above the product is often sufficient to maintain a low humidity condition throughout the silo. Any moisture contained in the air surrounding the material quickly migrates to the lower vapour pressure of the dry air in the head space (Dalton’s law). It is not usually necessary to inject dry air into the base of the silo.
Dehumidifiers in Power Stations & Wind TurbinesThe preservation and longevity of power generation plant and stored machinery components is a significant problem, particularly in prolonged cold shut down situations.Power station protection and component preservation using the desiccant dehumidifier method is not new and has been used since the mid 60’s in the power industry as a barrier to moisture related degradation.Places in a power station where desiccant air dryers are recommended during shut down include:-Re-heater – tubes are thinner than superheater tubes and more susceptible to corrosion. Inter-granular attacks on austenic stainless steel can be minimised using dry air.Generator - it is important to keep the windings dry to prevent corrosion and ensure a shorter restart time. Dry air can also supplement generator heaters.Condenser – must be kept dry after flushing to allow re-coating of water boxes and tube plates.Feed & Condensate Pipes – important to eliminate internal corrosion on pipes as oxides can contaminate feed water.Reactor Vessel – Where access is required, dry air is required to purge out CO2, eliminate corrosion and to dry the graphite prior to refilling with CO2.Boiler – surface temperatures of fireside boiler tubing drops below the air dewpoint and forms condensate. The condensate reacts with sulphurous parts of the ash and acid deposits and hydrolyses, forming a highly acidic solution. The end result is rapid, localized attack of the metal surface.
Desiccant Dehumidifiers - ApplicationsHumidity is a naturally occurring phenomenon that occasionally reveals itself as condensation, mist or frost. This is generally the only time that most of us actually become aware of its existence!Conversely, airborne moisture is a perpetual destructive force that causes enormous irreversible damage to materials. It often impedes or immobilises many of our manufacturing processes.As humidity is predominantly invisible, the damaging affects caused by it are not always easy to recognise.It is therefore frequently overlooked as the principle contributing factor when searching for the solution to a particular problem.