According to the 2002/91/EC, the Directive on the energy performance of buildings it is important to determine the expected energy consumption of the building in the step of the designing. There are imperfections in the actual available national and international regulations as for the methods to calculate the energy consumption of the air handling units. The actual calculation methods are fairly inexact approximations while they characterise the monthly energy consumption only with the average temperature or average enthalpy which takes into account the changing of the ambient air state only approximately. The most actual calculation procedures also not consider the systems that operate not continuously (only at night or in daytime). Based on the calculation procedure that uses the ambient temperature and enthalpy duration curves these problems can be solved. A new calculation method was worked out that takes into consideration the air handling energy consumption with the ambient temperature and enthalpy duration curves. To analyse the energy consumption of the air handling units fast and efficiently and to make energetic comparison of various constructed air handling units a computerised simulation PC program was made. The research work was supported by "Sustainable Energy Program" of BUTE Research University. (C) 2011 Elsevier B.V. All rights reserved.