To reduce the need for strip out when cavities and layered constructions have been affected by moisture damage, there are two methods used to remove the moisture from cavities in a non intrusive way. In the UK the restoration tech is more used to using the positive drying method (aka Injection drying) whereby in the rest of Europe, the negative pressure drying (aka suction drying) is preferred.
Modern building regulations mean that this construction is more and more common. This advanced drying technique avoids the need for costly strip out, which can be devastating to property owners or tenants.
Lets take a look at the different methods
Positive pressure drying (Injection Drying)
The flow of dry air is directed straight into wet cavities behind walls, floors, ceilings or almost every other spots where moisture is captured and inaccessible.
Dehumidifiers create dry air which is fed into a turbine. the turbine raises the temperature of the dry air and introduces pressurised warm dry air directly into wet cavities via a hose system. The hoses are plugged into the construction via holes that are drilled into the problematic areas. The warm, dry air is forced through the wet construction, where the arid air increases the vapour pressure in the damp material several times over, forcing the moisture out of the construction. The damp air is returned to the room via natural openings, or vent holes drilled in the construction, where it is taken into the dehumidifier and dried before it is forced back into the building construction.
Below the image has a desiccant dehumidifier pushing arid air into the turbine, the turbine is then creating the pressure and sending the pressurised arid warm air into the pipe system, and in turn into the construction.
The desiccant dehumidifier captures the moisture and expels from the affected area it via the vent pipe and the cycle continues.
Negatives
Produces heat that may not be suitable to the construction.
Pushes potentially harmful particles into the living space.
Other contaminants such as insulation fibers and silica dust also have the potential to be blown into the air and add additional cross-contamination risks.
Negative pressure drying (Suction drying)
Negative pressure drying – also known as vacuum pressure or suction drying – sucks the water out of insulation layers. The liquid water is separated and the moisture-laden air flow is passed through multiple filters – removing harmful contaminants such as mould, dust, and bacteria.
The main reason for using a suction-based drying technique is because it offers an unrivalled level of control over the air flow throughout the drying process.
Following a flood or a long-term pipe leak, there is a high possibility of mould and bacteria being present within the interstitial spaces of the construction, such as the insulation layers or within wall cavities.
Advantages
- reduced temperature load in building
- most systems have a built in HEPA filtration system, to ensure no contaminates re-enter the living space
- can be combined with a refrigerant dehumidifier (supplier dependent)
Push Pull solution
The push pull solution used in Europe is a combination of the above, but slightly different
The pull (negative pressure drying) is used with the push (positive pressure drying) . This gives a gentle push of arid warm air into the cavity and lets the pull side of the system remove the moisture and possible contaminants.
Of course, this approach will be more energy-intensive than using one of the systems separately. However, for contractors and insurers that want to turnaround more projects every month or year, this is an effective solution.
