Demand-based ventilation reduces the need for cooling and provides energy savings

A study by Ramboll Finland Oy highlights the VILPE Sense system’s capacity to diminish a building’s cooling needs during summer, leading to energy savings. The research juxtaposed the performance of the demand-controlled ventilation provided by the VILPE Sense system against both underpressure ventilation and a scenario involving an unventilated roof, examining both well-insulated and poorly insulated roofs. The findings clearly indicate that the VILPE Sense system outperforms pressure ventilation in reducing the cooling needs of a building. Thus, the study underscores that beyond its primary purpose, the VILPE Sense system offers the added advantage of lowering the energy consumption required for cooling, further enhancing its value proposition.

Flat roofs tend to absorb a significant amount of heat, especially in warm and sunny climates. The amount of heat gained by the roof varies greatly and depends on factors, such as, roof surface area, the U-value of the roof, the latitude of the building, roof type, roof exposure orientation and hour of the day. During the warmer months, the sun heats up buildings and there may arise a need for cooling, e.g. air conditioning. The purpose of this study was to determine the effectiveness of VILPE Sense in reducing the cooling needs of buildings and calculate the energy savings. The study was conducted by Ramboll Finland Oy and commissioned by VILPE Oy. It compared the demand-controlled ventilation of the VILPE Sense system, underpressure ventilation and an unventilated roof. In the simulation, U-values of 0.16 W/m²K and 0.22 W/m²K for the roof structures were used. The calculation period was one year. The U-value, also known as thermal transmittance, measures the rate of heat transfer through a structure divided by the difference in temperature across the structure. It is used to assess how well a building component, such as a roof, can insulate, with lower values indicating better insulation properties.

VILPE Sense and demand-based ventilation

Underpressure ventilation on a roof occurs as a combined effect of wind and underpressure vents. As the wind passes by the underpressure vent, it creates a vacuum, and the insulation layer is ventilated.

The VILPE Sense system, that was introduced to the market a couple of years ago, is a control system for demand-based ventilation using roof fans. The system includes sensors that monitor temperature and humidity both in the ventilated structure and outdoors. The system controls the roof fan to ventilate the roof when conditions for ventilation are favorable, for example, the roof fan operates at a higher power when the moisture load in the insulation layer becomes large. The difference between underpressure ventilation and demand-controlled ventilation using a roof fan is that the former depends on the weather and wind, while the VILPE Sense system’s roof fan can ventilate with significantly higher effect. VILPE Sense can be used for demand-controlled ventilation of both roofs and crawl spaces.


The findings indicate that the VILPE Sense system significantly mitigates cooling requirements, particularly for roofs with poorer insulation properties. The data reveals that underpressure ventilation can decrease cooling demands by 4% for roofs with inferior insulation and by 12% for those with superior insulation, in comparison to roofs without ventilation. In contrast, implementing the VILPE Sense system leads to a reduction of cooling needs by 12% on poorly insulated roofs and 21% on well-insulated roofs. Furthermore, enhancing the air volume of the VILPE Sense system to threefold amplifies the cooling need reduction to 31% for less well-insulated roofs. These results underscore the effectiveness of the VILPE Sense system in reducing cooling demands across varying insulation qualities, showcasing particularly pronounced benefits for roofs lacking adequate insulation.

Calculating energy savings for VILPE Sense

To estimate the potential energy savings with the VILPE Sense system, calculations were performed for a 20,000 m² bitumen roof with mineral wool insulation, considering both superior (0.16 W/m³) and inferior (0.22 W/m³) insulation characteristics. Additionally, for roofs with lower insulation quality, savings were further calculated when employing a VILPE Sense system equipped with a more potent roof fan (VILPE ECo 200 FLOW), aimed at enhancing air circulation and thereby increasing the effectiveness of ventilation. The kWh estimates are derived from the Ramboll study.

Table 2 shows that while VILPE Sense contributes to energy savings by lowering cooling expenses, the most significant benefits are observed in roofs with inferior insulation qualities and those equipped with a more powerful roof fan. The table shows that, in lieu of its primary purpose, cost reductions in cooling should be considered a supplementary advantage of the VILPE Sense system. It is important to highlight that the calculated energy savings were based on the cooler Nordic weather conditions. In warmer climates, it is expected that the energy savings could be considerably greater.

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