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Water Damage Restoration: Understanding Building Heat Drying Processes and choosing the correct method for Drying Restoration

By:  Ron Rookledge, Technical Manager, Rainbow International,

The management of heat, relative humidity and air flow is crucial to the efficient delivery of any building drying process, as part of clean up after water damage or flood restoration.

Raising the air temperature within the confines of the flooded area enables the air within to hold or carry more water vapour, which through the chosen drying management process, can then be discharged out of the building either by gentle pressurised convectional air flow, or via a standard dehumidification process

Moisture Flush System

The Moisture Flush System is a very quick and efficient way of drying a building that has been extensively water damaged. It relies upon drawing in air from the outside, which is then heated to approx. 45°C by the aid of strategically deployed heat exchangers that are connected to an independent external  Mobile Hydronic Heating System.  The external air when heated and gently pressurised absorbs the subsequent humidity generated within, and through convection and controlled venting subsequently exhausts it out of the building. This moisture conveyor type process very quickly and efficiently removes all excess moisture from within the building, and this continual uninhibited exchange of air also reduces, and in most cases negates the need for extensive plaster and building flood damage repairs.

Supportive Drying System

The supportive drying system is designed to assist in making conventional drying equipment work more efficiently. A small lightweight gas fired boiler system which is placed outside of the property works in a very similar manner to the larger unit. It powers small heat exchangers that are strategically placed within the contained flooded area, and are deployed to provide background heat in support of standard dehumidification equipment during the water damage restoration process. It is also capable of carrying out Moisture Flush processes but is restricted to areas no greater than 150 cu.mtrs. maximum.

The psychometric requirements of drying with standard dehumidification equipment determine that the ambient temperature within the contained flooded area should be approx. 26°C – 28°C.  By raising the ambient temperature to this value, the subsequent moisture content of the free air is increased, and as a consequence the efficiency of the equipment to extract excess moisture is also increased, which in turn reduces the drying time considerably. The Supportive Drying process is usually applied to less extensive flood damage situations, or due to on site circumstances, the need for a more controlled and gentle approach to moisture extraction is required. i.e for more elderly structures or where there is a large amount of timber beams or panelling present within the property.

The Supportive Drying system can also be used to provide background heat for injection drying systems, as a higher ambient temperature within the operational area will also increase the efficiency of the air injection equipment.

Forced Drying as part of Water Damage Restoration

Forced drying requires energy. The higher the energy input by the drying system the greater its effect. Not all situations require or are suitable for large energy inputs. Relative humidity, heat and air movement are very important factors when drying materials. Intelligent application and management is required to ensure energy efficiency is maintained. Convention, conduction, radiant heat, desiccant and refrigerant driers and systems are all the most appropriate process given the correct conditions.

In conditions with high moisture loads >10 g/Kg refrigerant units are efficient if the temperature is the appropriate band 25-28oC. Desiccant units are more energy efficient at moisture levels <10g/Kg. Since the conditions change throughout the drying cycle ideally the drying system should also be changed to ensure efficiency is maintained. Desiccant units are ideal to use in reduced volume enclosures where dense material drying is being conducted. They will produce environment, at the material surface, circa 30oC and <30% RH. These are ideal condition for promoting moisture migration from dense materials.

Where material drying is being carried out the air volume of the drying system should be minimised. This can often be accomplished by tenting the affected area, volume reductions can be very significant, 95% reductions can be achieved. This can help to minimise the external environmental effects on the deployed system. It can also reduce the required equipment quantities and processed air volume. It concentrates the drying effort to where it is needed, against the material. Using this technique appropriately ensures efficiency is maintained and reduces drying cycles.

The skill of the drying operative is to create the most advantageous condition to remove the excess moisture. This will require balancing various factors to promote moisture migration from the material to the air within the drying environment and then removing this from the area. Volume reduction can make this task easier for both drying technician and reduce the impact on the policy holder.

Water damage restoration: Gathering the right information

The chosen method of drying is totally dependent on the circumstances that are relevant to the building at the time of flooding and the information gathered at the point of survey as listed below.

  1. Has the cause of the [flood damage] either receded, been diverted or switched off
  2. When did the flooding occur / how long has the property been wet / damp
  3. What Type of flood water contamination White / Grey / Black
  4. Is the property Commercial / Domestic
  5. What is the type of structure
  6. Wait is the age of the building
  7. What is the cubic capacity / volume of area to be addressed
  8. Is the property

a, secure

b, unsecure

  1. Is all of the building

a, wet

b, partially wet

  1. Is an electrical power source

a, available

b, not available

  1. Is the property

a, occupied

b, unoccupied

c, to remain occupied

  1. How many rooms are affected

a, number of rooms

b, type

  1. Is the property

a, furnished

b, unfurnished

  1. Are the contents to be

a, removed

b, partial removal

c, remain on site

  1. Does the property require

a, full redecoration

b, partial

c, minor

  1. Number of occupants

Adults ……


  1. Disposition of the occupants

a, infirmed

b, elderly

c, capable

  1. Number of Other factors to consider

a, Pets

b, Plants

c, valuables

Compiling an initial survey report that comments on all of the above aspects will enable the service provider to determine the most suitable and efficient type of drying programme to be employed for effective [flood restoration]

Given that items 1 – 7 are compulsory facts that need to be included within any report.

Items 8 – 18 will be contributory factors that when also considered will ultimately determine the best process to be deployed given the current circumstances and all of the relevant on site information.

Tel 01623 675100 for further information

Rainbow International’s Flood Restoration services

Rainbow International has been providing flood restoration and clean up after water damage for over 30 years.  Its wealth of technical expertise and knowledge is accessed by many of the UK’s major insurance companies on their domestic and commercial policyholder claims.

If your home or business is affected by floods, contact Rainbow for more details of their comprehensive flood damage restoration services, which include:

  • • Emergency 24 hour call out
  • • Flood water extraction and removal of flood water
  • • Drying of buildings
  • • On or off-site drying of property contents
  • • Drying and sanitising of carpets and furnishings
  • • Controlled waste disposal
  • Clean up after water damage
  • • Buildings & contents restoration

Rainbow International has more than 80 branches across the UK.  On average there is a fully operational branch just 23 miles from any postcode in the country.  Call our 24 hour helpline on 01623-422488, or visit our web site www.rainbowint.co.uk now to find out how Rainbow International could help you.

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