Study: The VILPE Sense humidity control system ensures sufficient ventilation of structures

According to a study by Ramboll Finland Oy, the VILPE Sense humidity control system significantly speeds up the drying of a wet insulation layer compared to underpressure ventilation. The study simulated a roof leak on a poorly ventilated low-pitched roof. The results showed that both underpressure ventilation and VILPE Sense demand-based ventilation dried the insulation layer, but demand-based ventilation was significantly faster (1.5 years vs. 3 years). In some cases, underpressure ventilation was too slow to prevent the formation of mold. According to the study’s author, D.Sc. Klaus Viljanen, especially on large roofs, demand-based ventilation is the safe choice to ensure sufficient ventilation.

In many countries, underpressure ventilation is commonly used to keep roof structures dry and healthy. Underpressure ventilation on the roof is created by the combined effect of the wind and underpressure vents. As the wind flows around the underpressure vent, it creates a vacuum, ventilating and drying the insulation layer. A couple of years ago, the VILPE Sense humidity control system was launched in the market as a control system for demand-based ventilation of structures.

The system includes sensors that monitor temperature and humidity both in the ventilated structure and in the outdoor air. The system controls a roof fan to ventilate the roof when conditions are favorable. For example, the roof fan runs at higher power when the system detects excessive moisture in the structure and when the outdoor air is sufficiently dry. Conversely, the system runs at lower power when the outdoor air is humid. Ventilation stops completely in very cold weather. The difference between underpressure ventilation and demand-based ventilation with a roof fan is that underpressure ventilation depends on weather and wind (air exchange rate of 20–40 changes per hour), whereas the VILPE Sense humidity control system can ventilate structures at a significantly higher power (140 changes per hour). These air exchange rates apply to a low-pitched roof construction with ventilation grooves.

VILPE Sense dried the wet insulation layer in 1.5 years

In a study by Ramboll Finland Oy, commissioned by VILPE Oy, the drying capabilities of the VILPE Sense humidity control system and underpressure ventilation was compared. A roof leak was simulated on a poorly ventilated roof by adding 30 kilograms of water per cubic meter of roof insulation (normal moisture level in insulation wool is less than 1 kg/m3). The roof was low-pitched and had ventilation grooves. The supporting structure was a 40 mm TT-slab, with bitumen membrane as the vapor barrier. The thermal insulation consisted of 370 mm of mineral wool and 30 mm of top wool, between which was ventilation grooves. The channels were 20 x 30 mm2 in size with a spacing of 200 mm.

The results showed that both underpressure ventilation and the VILPE Sense humidity control system dried the insulation layer. However, VILPE Sense and its demand-based ventilation dried the insulation layer significantly faster than underpressure ventilation. VILPE Sense completely dried the roof in 1.5 years, compared to 3 years with underpressure ventilation. According to the study, the slower drying capability of underpressure ventilation increases the risk of mold growth in the structures.

“VILPE Sense is the safe choice for ensuring sufficient roof ventilation”

The researcher and report author, project manager Klaus Viljanen (D.Sc.), states that VILPE Sense’s demand-based ventilation is a better option than underpressure ventilation if the roof is prone to leaks, large humidity or moisture loads from the environment, or suffers from poor ventilation. Viljanen notes that demand-based ventilation like VILPE Sense is the reliable choice, especially for flat roofs larger than 1000 m2, because ensuring sufficient ventilation on large roofs can be particularly challenging.

“On large roofs, the limits of underpressure ventilation can be encountered for several reasons. There’s often an attempt to save on underpressure vents, and they are not installed on the roof in sufficient numbers. Ultimately, the size of the ventilation grooves is quite small, and they can sometimes get compressed, resulting in insufficient ventilation. Overall, conditions for sufficient ventilation vary greatly and depend on many variables. VILPE Sense draws air from a wider area, solving many of these problems,” says Viljanen.

“Humidity problems involve significant costs, and a lot can be saved if the need to replace wet thermal insulations can be avoided with demand-based ventilation,” says Viljanen.

In his doctoral dissertation, Viljanen among other things studied the effects of climate change on the mold index. The mold index is based upon the Finnish mold growth model, and it has been developed by Tampere University of Technology (TTY) and VTT Technical Research Centre of Finland. It calculates the risk of mold growth on a scale of 0–6.

“Even a small increase in the relative humidity of the outdoor air has a surprisingly significant impact on the well-being of structures. According to the results, a 1–2 percentage point increase may raise the mold index of the roof structure’s ventilation gap to level four,” says Viljanen. Level four means clearly visible and observable mold growth.

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