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Dehumidifier Operating Instructions

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Building drying

Dehumidifiers reduce the relative humidity of the surrounding air by circulating the air through the machine and removing water (condensate) as the air passes over cold coils or through desiccant.

Dehumidifiers are rated on the amount of moisture they can extract from the air passing through at given temperature and relative humidity. A machine may be rated for 50 litre of moisture removal at 30 deg C and 80% relative humidity but at the lower temperature and relative humidity which is typical for UK use the moisture removal will be much reduced.

As the room dries and the relative humidity of the air in the room will reduce and the rate of moisture removal will also reduce. This is not a fault the equipment but is to be expected. This is explained in more detail in the psychrometry section of the main website.

The water is collected in a tank within the machine, discharged to adjacent container or is pumped away to a drain. The type of condensate disposal supplied will be agreed with you in advance or at time of installation.

Where you are using the dehumidifier to dry out a room the rate of drying will depend on a number of factors. A higher capacity dehumidifier will not necessarily speed up the process unless the rate of release of moisture from the fabric of the room is increased at the same time.

Drying rates in a particular room depend on :-

      • The relative humidity maintained in the room air whilst drying
      • Temperature of the room
      • Air circulation to prevent moist air remaining against the wet surfaces
If you want to accelerate drying then it may be necessary to increase temperature buy adding a heater or improving circulation with the use of a fan, but be aware that drying our too quickly can result in shrinkage and cracking, particularly in new construction applications.

Positioning of the dehumidifier will be important to achieve even drying in larger areas so the use of a large fan in addition to the dehumidifier in larger areas to ensure that lower relative humidity is achieved throughout the room.

Product Protection

Where dehumidifiers are used to maintain lower relative humidities to prevent deterioration of stored product there is a lower rating of machine required for a given building or room volume. The dehumidification needed is to control the humidity of fresh air introduced to the area by way of ventilation. An estimate of ventilation rates and the maximum humidity of the fresh air into the area will allow an estimate of the rating required.

The performance of the machine at the prevailing temperature and humidity must be used, rather than the nameplate rating. A good estimate of this can be obtained using the table in the psychrometry section of our main site.

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