According to the calculations the prototype, being tested in Iceland appeared to have an average heat-recovering efficiency of over 95% (the most upper curve). [4] This number of more than 95% efficiency calculated (the straight upper line) is some what flattering so one realises that some leakage in the heat exchanger exists.
The temperature meters on the reversible are accurate and simple to achieve high-energy efficiency. Temperature: T1 inside air/T3 fresh air incoming and T2 exhaust air/T4 outside air.

Two small reversible computerised fans could not cope with the extreme differences in air pressure (100-150 Pascal). During the test period we have easterly and westerly storm. The fans combine their capacity to keep the airflows in balance. Fan 1 (outer fan) runs fast reverse at storm leeward and also fan 2 cannot withstand the storm windward. The ventilation systems in large buildings also tend to lose their balance, as told me the director of a great ventilator factory. By closing the horizontal air supply and -exhaust ducts with heavy winds, in these circumstances there will be enough natural ventilation anyway.

CALCULATING ENERGY SAVING
There are 5080 degree hours in the heating season in the Netherlands. Between October and May the outside temperature measured is 4.8�C (before the global warming?), the inside temperature 20�C. The 'breathing window' ventilates on average (ranging from 25 to 50) 40 m3/hour with a heating regenerative efficiency (85 to 95)of 90% volume metrical heating capacity, that is 1212 joules/m3�K.
Saving 5080 x 40 x 1212 x [20 - 4.8] x 0.9 = 3.37 gigajoules / 'breathing window' per year.

HEATING COST REDUCTION PER HOUSE
Expressed in energy equivalents: one m3 natural gas is 32 megajoules in the heating efficiency of a 90% High Efficiency boiler, that is 3.370.000.000 / 32.000.000 x 0.9 = 117 m3 natural gas/'breathing window' during the heating season.
With 3 to 5 breathing windows in one house, its average multiplied by: 4 x 117 = 468 m3 natural gas or 13.5 gigajoules. At the end of 2004 the price of natural gas was � 0.416/m3. Thus the calculated saving is 41.6 x 468 = � 195/year per house.

The high-quality 8-Watt electricity is produced by a traditional power station (not connected to district heating), with 40% efficiency amounting to 8 : 0.40 = 20 thermal Watts.
The energy saving is 320 - 20 = 300 thermal Watts , therefore the net efficiency of the 'breathing window' is 300 / 320 x 0.95 = 89%, which is close to the 90% average efficiency assumed earlier. The electricity consumption of the CO2 meter and the intelligent control is to be neglected.