1. 1 Riga Technical University, Faculty of Engineering Economics and Management , Institute of the Civil Engineering and Real Estate Economics , 6 Kalnciema Str. 210, Riga, LV-1048 , Latvia
2. 2 Riga Technical University, Faculty of Civil Engineering , Institute of Heat, Gas and Water Technologies 6a Kipsalas Str., Riga, LV-1048 , Latvia