ventilative cooling

Research indicates that low-energy dwellings are more sensitive to overheating than regular dwellings. In this research the ventilative cooling potential of low-energy dwellings is considered. A low-energy dwelling based on the Active House concept, “House of Tomorrow Today” (HoTT), has been investigated as representative for low-energy dwellings in general. A computational model of the house was created with the software TRNSYS (in combination with CONTAM) and this model has been calibrated with actual (intervention) measurements in the HoTT.

The increasing number of highly insulated and air tight buildings leads to the concern of indoor environment overheating and related comfort and health issues. This can already happen in a temperate climate as found in the Netherlands. This work studies the ventilative cooling process as a possibility to avoid overheated dwellings. A monitored dutch passive house was modelled in Trnsys and the impact of increasing air flow rates on indoor temperatures was simulated. The most overheated zone was chosen to be analysed.

This special issue on Breakthrough of natural and hybrid ventilative cooling technologies: models and simulations, together with the connected issue Breakthrough of natural and hybrid ventilative cooling technologies: strategies, applications and case studies (vol. 16, issue 1), focuses on methods, tools and technologies for reaching the above-mentioned goal through the use of ventilative cooling, i.e. cooling by controlled natural ventilation (CNV). This strategy is one of the most cost-effective alternatives to air-conditioning systems.

Ventilative cooling can be used as a passive cooling measure to reduce the cooling energy demand of buildings. It can be used during the day, directly removing excessive heat gains, or during the night (i.e. night flush), in which cold outdoor air flows through the building and cools down the indoor air volume and subsequently the thermal mass of the building. Night flushing reduces the indoor air temperatures at the beginning of the next day and the cooling demand over the day.

Low energy buildings are highly insulated and airtight and therefore subject to overheating risks, where Ventilative cooling (VC) might be a relevant solution. 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 (State-of-the-art-review, Kolokotroni et al., 2015).

The current development in building energy efficiency towards nearly-zero energy buildings (nZEB) represents a number of new challenges to design and construction. One of the major new challenges is the increased need for cooling arising in these highly insulated and airtight buildings. The cooling demand depends less on the outdoor temperature, and more on solar radiation and internal heat gains. This naturally gives better potential for the use of ventilative cooling technologies, because the cooling need is not only in summer, but actually all year round. 

Controlled Natural Ventilation (CNV) is one of the potential most effective passive cooling technique to reduce cooling needs of buildings in temperate-hot climate zones. However, a correct balance amid internal heat capacity, thermal insulation, and net opening area is important to achieve optimal results. The present paper shows results from an original simulation process carried out within the Course “ICT in building design” of the Master degree programme ICT4SS (ICT for smart societies) at the Politecnico di Torino.

Balanced ventilation units are well known to provide a sufficient amount of fresh air in residential buildings in a controlled way, without relying on ever-changing naturally driven forces. During colder periods, heat recovery ensures a reduction of the ventilation heating load. Outside the colder periods, recovery is reduced or shut off automatically, providing mechanical ventilative cooling. During warmer periods, the recovery is used again to provide a comfortably cool supply of fresh air.