natural ventilation

Outdoor air change qualifies the air that enters into the buildings. The outdoor air moves freely along the urban mesh favoured by the wind forces and stresses. Buildings, trees and other constructions alter the natural air flow pattern inside the cities, creating stagnated air masses in those wind-protected regions. Some outdoor spaces such as light shafts and confined light shafts inhibit the correct exchange of the stagnated air with fresh air coming from the outskirts and suburban areas. 

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.

Because of the need of energy conservation and Business Continuity Planning (BCP), natural ventilation system, which basically does not use non-renewable energy, is attracting academic/practical attention. However, it is difficult to predict the natural ventilation performance even after completion of the building, because it is easily affected by unstable conditions, such as outdoor temperature and wind. The designing and controlling method of natural ventilation system is not yet sufficiently established.

The British Standard Code of Practice, and other authoritative guides, recommend minimum rates of ventilation related to the size and use of rooms, and structural means for providing them. But the difficulty of measuring actual ventilation rates suggests that it is seldom done.

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.

Most natural ventilation (NV) systems used in non-residential buildings are single sided (SS). These systems are easy to integrate in the building layout, since, unlike in cross-ventilation (CV), these systems do not require access to two facades or a central stack. Current knowledge about SS NV flow penetration away from the façade can be found in building regulations and design rules of thumb.

Natural ventilation has the potential to provide cooling and fresh air and cut 40% of the total energy consumption of European office buildings. While in the milder seasons natural ventilation is an obvious low-energy choice, if poorly designed it can cause overheating in summer and poor air quality in winter. In order to promote the use and design of naturally ventilated (NV) buildings, it is therefore important to understand how current NV buildings perform in terms of thermal comfort and indoor air quality.

The Royal Wanganui Opera House (RWOH), in Whanganui, New Zealand, was constructed in 1899, and now seats 830 people. This building was designed with a natural ventilation system; however, this system is no longer in operation and the RWOH has received regular complaints from patrons regarding indoor thermal comfort. Various options for mechanical systems to improve indoor comfort during summer performances have been considered, but have been deemed too costly. The RWOH is listed with Heritage New Zealand as a Category 1 heritage building.

Combining heat recovery with natural ventilation is a relatively new topic of significant academic and commercial interest. The present study shows the performance of a recently developed Passive Ventilation system with Heat Recovery (PVHR) installed in a primary school building.