Computes the energy use of a building according to the hourly and/or monthly simplified models described in the European standard EN ISO 13790 and in Swiss standard, the energy needs contained in the French standard RT2005, RT2012, Bbio, in the Luxembourg Standard, and in the Italian DLGs 192. It computes transmission and ventilation heat loss as solar gains from windows, sunspaces, double-skin facade, window solar collector and transparent insulation walls. It can handle several zones and rooms at various setpoint temperatures and helps size peak heating power (EN 12831, SIA384.201) and the cooling needs (EN ISO 13790). Results are given in a full report, in a Sankey diagram, and a monthly heat balance diagram. It integrates Polysun-Inside for solar thermal simulation. This provides a histogram of possible results. Lesosai 7 integrates other calculations and methodologies, including Life Cycle Analysis; Meteonorm, worldwide monthly and hourly weather database; MaterialsDB.org database; USai: thermal transmission coefficient (EN ISO 6946), Dynamic characteristics (EN ISO 13786), condensation risk (EN ISO 13788, EN ISO 6946). Import gbXML from Sketchup and Autocad Revit. Useful for Minergie,-A,-P,-ECO and BBC labels. Multilingual: French, Italian, English, German Screen Shots


heating energy, cooling energy, energy simulation, load calculation, standards, life cycle analysis, gbxml


Certification no: 344 (OFEN), CSTB, Minergie-ECO

Expertise Required

Basic understanding of energy problems in buildings


First version distributed in 1984. Version 7.2 (2012), more than 2,000 users


Architects, building physics consultants, engineers, schools


For each building zone: rooms, floor area, volume, air change rate, areas, and U-values of all envelope components, orientation, areas, and types of glazing for windows and passive solar devices, occupation, etc. Input is object oriented and clearly organized in successive windows.

  • Wizard for renovation and pre-projects
  • From architectural drawings
  • Import gbXML format (Autocad Revit, SketchUp).

A wizard enables the user to quickly model a building. It is ideal for preprojects and renovation diagnostics.


Full report including transmission heat-loss coefficient for each component, ventilation heat loss, monthly, and annual heat balance, including losses, internal, and solar passive heat gains. The Sankey diagram illustrates the heat flows through main building parts, monthly heat balance. Exports to Excel.

Computer Platform

PC-compatible, Windows 2000 or higher

Programming Language

Delphi and Java


  • Complies with European standard EN ISO 13790.
  • User-friendly interface, official climate (Switzerland, Italy, Germany, France, Romania, and Luxembourg) and Meteonorm, characteristics of glazing materials (EN 673) and transparent insulation, solar collectors, direct connection with producer materials databases.
  • U-value calculation. Expandable users' database. German, French, English, and Italian versions.
  • The product has 23 years in the market performing thermal modeling of buildings.
  • Prints different official reports. Imports gbXML. Integrates Polysun-Inside.


  • Lesosai 7 can only be used in Windows
  • Lesosai 7 imports the gbXML but for the moment cannot export.
  • The screen resolution has to be at least 768 px



E4Tech Software SA


Av. Juste-Olivier 2
Lausanne CH 1006


+41 (21) 331 1579






Software price (1 license = 1 computer), Core version $950; Hourly Calculation module $530; RT2005 module $600; Life Cycle module $280; Polysun-Inside $440; for students free for 6 months; Special pricing for schools.