Air conditioning and natural ventilation: a hybrid solution from Northern Europe

Air conditioning and natural ventilation: a hybrid solution from Northern Europe

Client: A shopping mall
Location: Milan
Aim: Natural ventilation
Kind of project: Energy saving
Description: Designing a natural ventilation system to set up in parallel to air-conditioning in such a way that operating costs are reduced.

In Northern Europe this is common practice, while elsewhere few people are familiar with it. Running an air conditioning system together with a natural ventilation system is the new frontier for saving energy. Perfect for shopping malls and exhibition spaces.

Natural ventilation can be set up alongside an air conditioning system (either one that is already present, or designed ad hoc) and, by turning on during hours when the facility is closed and there is no public, make a significant contribution to the air conditioning action, providing immediate benefits in terms of energy savings.

This is a solution Bovema designed for a shopping mall in Milan. At the moment, this kind of project is an absolute novelty in Italy, although it is already standard for Northern European countries, and England and Holland in particular. In 2013 in Amsterdam, work was finalized for the rooftop of the Rijksmuseum, the most important museum facility in Holland and home to many of Rembrandt’s most famous works. The museum’s large transparent roof (see photo) was designed to make it possible to blend standard air conditioning with natural ventilation, with the double benefit of guaranteeing environmental comfort for visitors and protecting artistic masterpieces from humidity.

Amsterdam Rijksmuseum

In these countries, success has been built on solid bases: the advantages, particularly from the point of view of energy savings, are exceptional. Even though it does not actively produce energy, this hybrid system makes it possible to reduce air conditioning costs considerably. One need only consider that the preliminary study conducted by Bovema’s design offices showed a ROI (Return On Investment) achievable in just 3 years.

Performances of this level can be achieved because the system, turning on during the earliest hours of the day, can lower temperatures before the air conditioning turns on, bringing interior temperatures in line with external temperatures (roughly 21° Celsius in summer between 6 and 10 a.m.). In this manner it is possible not only to reduce (in this specific case by 4 hours per day, every day) the amount of time the air conditioning is turned on, but also to ensure that the moment it is turned on, the initial temperature is already much closer to the desired temperature, requiring active air conditioning only in order to maintain it on level during opening hours.

This is an extremely advanced kind of engineering, and still relatively unknown in many other areas. The reasons for this do not lie the in climatic differences between Northern and Southern Europe, but rather in an enduring misperception that views natural ventilation as a relatively unscientific process, one that is entrusted in the best case scenario to common sense and a designer’s willing efforts.

Bovema has a radically different style. The company’s natural ventilation systems have been conceived and designed to provide consistently measurable results and rely on precise engineering. Common sense is always useful, but it’s not enough on its own: a successful project needs the experience Bovema has matured across Europe through years of constant interaction with these themes, as well as the ability to decline the principles of technical physics (which, in the absence of specific didactics, constitute the only theoretical foundation) in increasingly different cases that this line of work presents. Simulation instruments do the rest, crosschecking sensitive data like the building’s geometry, internal and external thermal data and the relative variations both seasonal and within a given 24-hour arc. They also take into consideration additional information, for example the diverse uses the building will be required to provide (opening to the public or staff, the presence of materials that are sensitVentilazione naturale a lamelle standard Bovemaive to humidity).

In this specific case, the shopping mall was already equipped with an air conditioning system that was turned on every day from March through October from 6 a.m. to 10 p.m. In order to guarantee clientele an acceptable level of comfort within the various spaces in the building (overall area: 190,000 m3), the air conditioning system was designed for an average monthly consumption of roughly 281,000 kW/h, necessary to provide an overall thermal strength of roughly 259 kW.

The solution Bovema’s technicians proposed called for the installation of 54 aerators with standard blades, for a total air exit surface area of 68 m2. The entire natural ventilation system was structured so that it could guarantee the same overall thermal extraction power as the air conditioning unit for a 4-hour span running from 6 a.m. (the time stores opened for suppliers) to 10 a.m. (when stores opened to the general public).