ventilative cooling

Recent studies have shown that ventilative cooling reduces overheating, improves summer comfort and decreases cooling loads. Therefore, it is considered as one of the most efficient way to improve summer comfort. Although, HVAC designers still lack of guidelines to improve the energy and comfort efficiency of their installations.  

The test lecture rooms of KU Leuven Ghent Technology Campus are one the demonstration cases of IEA EBC Annex 62: Ventilative Cooling. This nZEB school building is realised on top of an existing university building and contains 2 large lecture rooms for maximum 80 students with a floor area of 140m² each. An all air system with balanced mechanical ventilation is installed for ventilation, heating and cooling.

Ventilative cooling (VC) is an application (distribution in time and space) of air flow rates to reduce cooling loads in spaces using outside air driven by natural, mechanical or hybrid ventilation strategies. VC reduces overheating in both existing and new buildings - being both a sustainable and energy efficient solution to improve indoor thermal comfort. VC is promising low energy cooling technology that has potential to substantially reduce the use of mechanical cooling in airtight and highly insulated buildings.

Ventilative cooling (VC) is an application (distribution in time and space) of air flow rates to reduce cooling loads in spaces using outside air driven by natural, mechanical or hybrid ventilation strategies. Ventilative cooling reduces overheating in both existing and new buildings - being both a sustainable and energy efficient solution to improve indoor thermal comfort. In new buildings VC, may save cooling energy and thereby make it easier to fulfil future energy legislation for buildings.

The current type of construction preferred for new high energy efficient buildings in Germany, featuring highly insulated building components and an almost completely airtight building shell, raises several new challenges with regard to design, construction and use of these buildings. Cooling, in particular, is an issue that gains importance also in the residential sector, in connection with rising temperatures induced by the climate change.

Ventilative cooling through window airing presents a promising potential for low energy houses in order to avoid overheating risks and to reduce energy consumption of air conditioners. This case study aims at describing how ventilative cooling has been taken into account as from the design stage of a low-energy single-family active house located near Paris. Its performance on thermal comfort and air renewal, monitored from both sociological (feedback from a family) and scientific approach, is described and compares these two qualitative and quantitative approaches.

Overheating is an unwanted consequence of modern building designs and internal gains that will be aggravated by the effects of climate change on local climates within urban and suburban areas. To minimise the energy cost of limiting overheating several different approaches exist for passive cooling dissipation techniques. Free cooling by ventilation, or Ventilative Cooling, (VC), is a generally accepted effective, energy efficient, mitigation strategy to building overheating. There are many factors that influence the design and selection of suitable VC strategies.

The lack of indicators assessing ventilative cooling effectiveness in a way to compare it with active cooling technics, makes its acceptance more difficult. Practitioners, norms, standards and guidelines are used to design and evaluate cooling systems in terms of Cooling Power (CP) or Seasonal Energy Efficiency Ratio (SEER). What could be the CP of a passive technique based on a day to night offset of the cooling process? What could be the SEER of mechanical night ventilation for summer cooling?

We introduce a new method for defining ventilative cooling potential (VCP) for office buildings that depends not only on the climatic conditions but also on building thermal characteristics. The energy savings from ventilative cooling differs from building to building; therefore, VCP should be able to represent the actual energy savings—though not perfectly—in order to guide optimization of ventilative cooling parameters during the initial design stage.

CFD simulations were conducted to assess turbulent forced convection heat transfer and pressure drop through a ventilation channel using a stack of panels with different ridge configurations containing Phase Change Material (PCM). First, an experimental rig using an existing commercial panel provided by a PCM manufacturer validates the model simulated in Ansys FLUENT. After that, 3D simulations with different designs were tested until the optimum configuration in terms of heat transfer and pressure drop was achieved.