Esky buildings and passively designed buildings represent two of the main schools of thought regarding the best way to design energy efficient buildings. 

To compare the energy efficiency of Esky buildings against passively designed buildings, let’s first understand these two types of buildings. 

The ‘Esky’ approach refers to a building style wherein the buildings are tightly sealed and well insulated to improve the efficiency of the air conditioning systems – similar to ice boxes sealed tightly and well insulated to keep the ice frozen. The windows are generally small, or of a type that does not open; therefore these buildings require the air conditioning systems to run whenever they are occupied. 

Situations where the ‘Esky’ approach is the most sensible building design include city centres and industrial areas where the combination of noise and air pollution makes natural ventilation impractical. 

The second approach is known as ‘passive design’, which describes the use of elements such as shading, adjusting the building’s orientation and maximising natural ventilation to make the building naturally comfortable. Passive design can still incorporate air conditioning systems for use during extreme weather but good design can minimise the frequency of air conditioning being required. 

Passive design is well suited to schools, homes, resorts, suburban offices and apartments. 
Openable windows required to maximise natural ventilation in passively designed buildings generally do not seal quite as tightly as the fixed windows used in ‘Esky’ style buildings. Therefore the air conditioning systems in passively designed buildings will generally run less efficiently than the air conditioning systems in ‘Esky’ style buildings. 

The big question then is whether a system that runs efficiently, but for many hours per day uses more or less total electricity than a system that runs less efficiently, but for only a few hours per day.

In an attempt to answer this question, Breezway commissioned a study to compare the annual electricity required for the cooling and heating of two identical buildings, one of which had fixed windows to maximise air conditioning efficiency, and the other had Altair louvre windows to allow some of the cooling requirements of the building to be met using natural ventilation at the expense of reduced efficiency when the air conditioning system was used.

The modelling showed that the benefits of ventilation through the open Altair louvre windows far outweighed the reduction in air conditioning efficiency; additionally, the building with Altair louvre windows used almost a quarter less electricity over the course of a year to cool and heat the building. 

The Breezway Technical Bulletin ‘The Impact of Air Infiltration and Natural Ventilation on Annual Air Conditioning Load’ contains more details on the modelling study.