The necessary power requirement is found from the sum of the connected loads. If the exact connected loads are not available, you can work with empirical values obtained from identical or similar projects. The IEC recommendations and DIN VDE standards give no guidance on these factors and point out the individual aspects of each installation. Estimation the diversity factor as accurately as possible avoids unnecessary investment and unrealistic application to the electricity supplier. Depending on the purpose of the building, different diversity factors for the various groups of consumers shall use in calculation. The economic optimum choice of important system component, such as generator, power transformer and switchgear, will be greatly influenced by the ratio of the power required simultaneously to the total connected load. Below typical values for planning power requirement is useful. (Of course this information is a little oldie and you must check them in comparison to new buildings requirements) Type of building specific connected load Offices and administration Without air condition 80-120 w/m2 With air condition 120-150 w/m2 Per workplace 2.5-3 kva School and university School general 30-50 w/m2 Humanities departments 50-75 w/m2 Science department 120-200 w/m2 Hotels and dwellings Large buildings 40-80 w/m2 Per hotel room or dwelling unit 3.5-4 kva Hospitals Depending on size and facilities 60-120 w/m2 Up to 50 beds, per bed 3.5-4.5 kva Up to 105 beds, per bed 3-3.5 kva Up to 250 beds, per bed 2-3 kva Up to 300 beds, per bed 1.5-2 kva Department stores Without air condition 100-150 w/m2 With air condition 150-200 w/m2 Exhibitation halls For exhibitor power 25-50 w/m2 For hall lighting 40-80 w/m2 Industry Chemical 250-500 w/m2 Rolling mills, iron and steel 200-400 w/m2 metalworking 100-300 w/m2 textiles 50-150 w/m2