Dehumidification Blog

Updates and news about Puravents range of mobile dehumidification, fixed dehumidification, desiccant dryers, and controled humidity environments.

Cold Store Humidity Control the VRF 400

Cold Store Humidity Control for Meat Industry

Cold Store Humidity Control to prevent meat processing wastage

Cold Store Humidity Control to prevent wetness on meat

Cold Store Humidity Control – Background

In the meat business, carcasses are usually hung for a period of time before the meat is cut and further processed. The conditions inside the cold storage facilities in which the carcasses are aged is really important. Temperature is obviously important to enable the meat to develop its flavour over time and to prevent the meat perishing,  but so to is the humidity level in  the store.

Meat that has been stored in conditions which are too humid will become wet and sticky which not only makes it unpleasant to work with but also creates an unnessesary level of waste material, which is time-consuming to separate from the meat. If there is surface wetness on the meat for a prolonged period of time, such as during the maturing process in the cold store, then it can taint the meat and give it a musty flavour. A steady flow of warm fresh carcases into the store inevitably adds to the humidity level of the air in the cold store and left unchecked high humidity levels can be a real issue in cold stores for maturing and for curing meat.

Cold Store Humidity Control – Traditional Approach

One common solution is to use silica absorbent crystals. Whilst this is undoubtably a simple solution, it is also an expensive solution with an ongoing high cost burden to replacing the desiccant crystals, not to mention the regular hassle of actually changing the packets of desiccant silica crystals. A facility with a small cold store could easily be paying £60 – £150 per month for replacement absorbent crystals.

The other significant problem with the silica crystals approach is the lack of control. There is no control to prevent the silica packets from not removing enough humidity and conversely, nothing to prevent them removing too much humidity. And do silica crystals react to variable conditions caused by the access door being opened and closed and warm carcasses being put in, or cold ones being taken out of the cold store?  The short answer …no.

Cold Store Humidity Control  – Case Study

Cold Store Humidity Control to prevent meat processing wastage

Cold Store Humidity Control to prevent meat processing wastage

One company in the North West, Westgate Frozen Foods, has been using a small desiccant dehumidifier for their cold store humidity control for several years. Their cold

A desiccant dehumidifier is a controllable and realable method of keeping cold stores an optimum humidity

A desiccant dehumidifier is a controllable and reliable method of keeping cold stores an optimum humidity

store humidity control system sits unobtrusively outside the cold store, supplying dehumidified air into the store. It works on a closed loop so that the inlet air to the desiccant dehumidifier is drawn from inside the cold store. The beauty of the system is that the humidity level can be preset so that the dehumidifier works to achieve the preset value, so that the cold store is neither too humid or too dry.

As much of their beef can be hung for up to 4 weeks rather than a few days, the effect of the cold store being too dry is a marked reduction in carcass weight through product drying. Over the time that they have been using the current system Westgate Frozen Foods have carried out a certain amount of ‘test and adjust’ on the humidistat setting and now believe that presetting the desiccant dehumidifiers’ humidisat to 72% RH is ideal. At this humidity, and when stored at 0-1°C, the meat is cold, yet dry and not sticky to the touch, but does not cause the meat to dry out over the maturing process. Once matured the meat is easy to work and has only minimal  surface waste material.

Although Westgate found that 72% RH is right for them, it does not follow that this setting would suit other cold stores holding meat. The ideal humidity will depend on the size of the cuts of meat being hung, the residence time for the meat and the amount of staff ‘traffic’ moving into and out of the cold store. Although we can advise on a suitable a suitable size desiccant dehumidifier and initial setting for the unit, ultimately for each application the ideal setting will be discovered with small adjustments over time.

The humidity from the cold store that is removed from the air, is captured on a rotor made with a matrix of silica gel covered flutes which rotates inside the dehumidifier. As it turns it passes through a regeneration sector through which a separate heated air flow is passed, which dries the silica. The exhaust airflow from the desiccant dehumidifier is warm and humid.

At Westgate Frozen Foods the running cost of the desiccant dehumidifier is significantly less than the cost of replacement silica crystals which was the basis of their previous cold store humidity control method, and they reckon that the payback of the new system was measurable in months rather than years.  But the real benefit to Westgate Frozen Foods of the desiccant dehumidifier is the easy and accurate control of the cold store humidity and the sheer lack of hassle in keeping the carcasses in prime condition as they mature.

The cold store at Westgate is relatively small, and this together with the operating requirements called for a small desiccant drier. However cold store operations come in all shapes and sizes, and often much larger dryers are required.  We have the ability to supply units capable of handling up to 100000m3/hr, although so far we have not found an application big enough to warrant this size of dryer (here’s hoping!). More likely the dryers used for cold store humidity control, will be in the range 100 – 1000 m3hr.

Call us if you need humidity control for your cold store  –  01729 824108


Desiccant Dryers For Preventing Silo Clogging

keep the powder flowing - prevent silo clogging

Keep it flowing!

Silo Clogging  – The Desiccant Answer

The bulk materials that are stored in silos are often adversely affected by humid air, where issues can include silo clogging and agglomeration, and increased levels of corrosion to handling equipment. Within the closed environment of the silo humidity can fluctuate as the ambient temperature changes, such that a drop in ambient temperature means that the dew point of the air inside the silo is reached before that of the outside air. The resulting condensation will typically cause product caking inside the silo and associated handling equipment and corrosion. In short, silo clogging

The alternative to silo clogging

Evidence of the traditional approach to silo clogging

This problem is easily averted by using a desiccant dehumidifier unit to push very dry air into the silo head space, where a modest air change rate will have a profound benefit on the handling qualities of the stored product and prevent corrosion.

To reliably prevent silo clogging, we normally recommend the VFR (T) range of dehumidifiers for this application. Their higher than standard process fan pressure enables them to maintain a positive pressure in the silos head space and depending on the product being stored may even enable the supplied air to be ducted in at a level below the head space. Some times we can connect a unit to the filling line, which means that a new duct need not be fitted.

Just one of a massive range of industrial dehumidifiers

Industrial Dehumidifier – 800m3/h

Although the desiccant dehumidifier would typically run all the time on this type of application, silo filling is the exception to the rule. Typically the desiccant dehumidifier would be switched off and isolated from the silo air during filling operations, to prevent back flow of dust air through the dryer, and then once the filling is complete, the desiccant dehumidifier can be brought on-line again to re-establish the low humidity environment inside the silo.

Even if the dry air is supplied into the head space of the silo, this is enough to effect drying of the air amongst the material at the base of the silo because water vapour moves into dry air humidity areas to reach an humidity equilibrium because of Dalton’s Law.

With dry air throughout the silo interior, the granular or powder contents will be dramatically easier to handle using conventional conveyor equipment without the material ‘bridging’ or ‘rat holing’ in the silo hopper, or clogging in the pipe.  Silo clogging will become a thing of the past.

Want to know more about desiccant dehumidifiers? Try our guide or have a gander at the video

ATEX rated desiccant dryers

ATEX desiccant dryer 4 ATEX desiccant dryer 2
ATEX desiccant dryer 3 ATEX desiccant dryer 1
 All electrical components are individually ATEX certified and the finished desiccant dryer is then certified
ATEX desiccant dehumidifier components

ATEX rated desiccant dryers have components are generally larger, heavier, and far better insulated against gas and dust ingress than standard components.


Overview of ATEX rated desiccant dryers

It is fair to say that ATEX rated desiccant dryers are something of a rarity. The reason for this is twofold – they are costly bits of equipment and secondly they are typically putting air into a ducted system.

The first reason is more or less self explainatory. ATEX rated desiccant dryers are expensive because they are made from components which themselves are ATEX rated and both expensive and hard to source. Then the machine once complete needs to be certified, which adds both time and cost to the finished dryer. 

Because of their relativly high cost, users are always looking for alternative ways to solve their drying problems, and typically where there is a requirement for a desiccant dryer in a gas or dust ‘zone’, then where possible, the dryer is located outside the zone and the dried air ducted into the zone to where it is needed. This means that the desiccant dryer, being located outside the zone, does not need to be ATEX certified, thus saving the substantial difference in cost between the a standard desiccant dryer and and equivilant ATEX rated desiccant dryer ATEX desiccant dehumidifier components1


ATEX rated desiccant dryer may be rare, but these special machines do exist, although they are mostly built to

Standard VRF

This is what a standard Desiccant Dryer from the VRF range looks like

order because the requirements for them are so occasional. Having supplied ATEX dryers before, Puravent have jumped through the relevent hoops and can supply any of the VRF range of desiccant dryers as a custom-built special ATEX version. The exact specification and of course the pricing, depend on the duty, zone and temperature class that the dryer needs to be designed to.

But if you must have an ATEX certified desiccant dehumidifier and you can’t wriggle out of it by using extra ducting and putting the machine outside the ATEX zone, then give us a call.


Building Drying Top 10 Tips

Here comes the rain, and building drying top 10 tips

Here comes the rain, and our building drying top 10 tips

Here it is – Building Drying Top 10 Tips.

Your essential guide to drying rooms and buildings after a flood disaster.

The rain lashes down, drains block with fallen leaves and silt. The flood waters rise and search for new destinations. Houses, businesses, shops, offices, schools – the flood water does not discriminate between building types, only what ‘level’ they are at.  Although these days flooding can arise at any time of year it is still a particular problem in autumn. Buildings affected can be anything from a bit damp to massively damaged by flood water.  Here we provide our top tips for drying out buildings and rooms affected by flooding. These top tips are as useful for drying up after a burst pipe, or bath overflow as they are for a rainwater flood, and should help you get dry in quick time.

1.  If insured, discuss your claim and drying requirements with your insurer. They may hire a contractor to do the drying for you, in which case you can concentrate your attention on saving your contents and making sure that those you are responsible for are accommodated somewhere else. If it is a small drying job, perhaps one that is uninsured, or one that is not worth claiming for then the next 9 top tips are good to go, so long as you can establish that it is safe to do so by first consulting an electrician and perhaps a plumber.

2. Whats wet? No, it’s not a stupid question but the answer will affect how you dry the building and what equipment you use.

Say you have a traditional British type constructed building and the masonry walls and the suspended floor, complete with carpets is wet, then what you are looking at is potentially using a puddle pump (to pump out any remaining flood water from under your floor), a carpet dryer fan to blow air under the carpet, dehumidifier and a radiant heater.

puddle pump

Puddle pump – Good for pumping out flood water from under suspended floors

Big building dryer, otherwise known as an industrial mobile dehumidifier

Big building dryer, otherwise known as an industrial mobile dehumidifier

Mobile radiant heater ideal for warming walls

Mobile radiant heater ideal for warming walls

carpet dryer designed for blowing air under a carpet so that the air gets a chance to dry the floor underneath and underside of the carpet

Alternatively – If you have a modern solid floor with tiles, timber or laminate flooring, then the chances are that it has been laid with an insulation layer which is saturated and needs to be dried before it can again be an effective insulating layer. For this you will need a restorative drying unit  (to suck water out from the insulation layer under the floor), a dehumidifier and a radiant heater.

Restorative dryer, designed to dry out insulation layers under floors and in other difficult places.

Restorative dryer, designed to dry out insulation layers under floors and in other difficult places.

Big building dryer, otherwise known as an industrial mobile dehumidifier

Big building dryer, otherwise known as an industrial mobile dehumidifier

Mobile radiant heater ideal for warming walls

Mobile radiant heater ideal for warming walls

3. Use as big a dehumidifier as you can afford. Basically a little domestic plastic cased machine will not be up to it. You will need a big mobile dehumidifier – consider 30 ltr/day extraction rate as the bare minimum for drying a flood damaged small room. Bigger is better and quicker. More than one room to dry ? Then consider using extra dehumidifiers.


With only about 11 or 12 ltr/day removal rate @ 20 °C, it will take a long time, but is better than nothing


A bit bigger and a bit better

Big building dryer, otherwise known as an industrial mobile dehumidifier

Bigger yet, even better and quicker


4. When using a dehumidifier make sure to minimise air ingress into the building. Close all doors and windows and trickle vents (if you have them). The idea here is that by keeping the building air sealed, that the air in the building can be made as dry as possible with the dehumidifier, without giving it the extra burden of drying extra air from outside.

5. Ensure the dehumidifier is positioned so that it can treat the air without any obstructions. Placement in the middle of the room is best. If you have a large room and a number of dehumidifiers working simultaneously, spread them evenly in the room and away from walls.

6. Use portable radiant heaters for heating up surfaces, such as plaster work. Warm walls will evaporate water far quicker than cold walls. Either use conventional portable radiant heaters or use radiant masonry drying panels.  Don’t put them too close to the wall otherwise you will get a hot spot, but place them a distance away so that a greater area is gently warmed.

Set back from a wall it will provide heat to a large area of wall to speed drying

Set back from a wall it will provide heat to a large area of wall to speed drying

Masonry dryers are ideal for drying plaster and for drying out walls after flooding

Masonry dryers are ideal for drying plaster and for drying out walls after flooding


7.  Add extra heat. Radiant heaters when used will also (in time) warm up air in the building, but if it is still cold in the room or building put in electric space heaters to raise the air temperature. Don’t use direct fired oil or gas heaters for this purpose as they will deplete the oxygen in the building. If you need more heating power, beyond what the mains supply to the building can safely provide via electric heaters, then use indirect fired oil or gas heating, with the heater located outside and warm air ducted in, ideally on a recirculation system so that heat is not wasted to the outside.   Ideally the building air temperature needs to be raised to at least 20°C. The warmer the air is the more moisture it can hold, the more water will evaporate from surfaces, and the more efficiently the dehumidifier(s) will work.

indirect oil fired heater can deliver about 29kw of heat to a building

Arcotherm EC32 indirect oil-fired heater can deliver about 29kw of heat to a building. This model can not be fitted with a recirculation duct

Kroll HM200 indirect gas fired heating plant for large heating and drying jobs

Kroll HM200 indirect gas-fired heating plant for large heating and drying jobs. This model is fitted with a recirculation duct



FireFlo FF3 portable fan heater, ideal for putting extra heat into a room that is being dried


8.  Work out what happens with the condensate collected by the dehumidifier. If it collects in a tank, remember to frequently empty the tank. If you do not do this the dehumidifier will stop to prevent it spilling the condensate on to the floor.   If it has a continuous drainage arrangement make sure that it can flow by gravity to a suitable drain.  If the dehumidifier has a condensate drain that is great, because it means that you can get the condensate to a drain more or less anywhere within reach of the hose that you attach to the dehumidifier and means you can leave the machine to work for long periods. If necessary slightly elevate the dehumidifier on blocks of some sort so that the gravity drain will operate successfully.

9. Consider putting air circulator fans into the building. If there is not enough air movement from the various machines in the building, the dehumidifiers, heaters, carpet dryers etc., you may discover that some areas are holding air pockets which are being left by the general air circulation. In this situation use fans to move the air in these areas.

10.  Use a moisture meter to track drying progress. With active drying there is a danger that walls and floors appear to be dry when they are still damp under the surface. 2 pin or 4 pin moisture meters can be purchased for as little as £10 and they tell you what is happening in the wall rather than what is happening on the surface.  If you don’t get this right, you might think your building is dry and as soon as you remove the dehumidifiers and drop the heat to normal levels, damp will reappear.  Also use feel to determine how the building is drying. Drying of walls will start at the top of the wall and dry towards the base. As you run your hand over what appears to be a dry wall, top to bottom you will probably notice the temperature of the wall cool, part way down. This will be roughly where the wall has dried down to.

These Building Drying Top 10 Tips are designed to give a brief overview of the challenge drying a building or perhaps a room. The Guidance and standards for drying flood damaged buildings provides a really comprehensive guide to the subject and has much more information.

For more information or want to hear from one of our specialists, visit our website for further details.

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