A simulation study was conducted to determine the economic justification of retrofitting an office building in Detroit from a double-duct fan system to a variable-airvolume system. The objectives of the study were to compare the energy consumption of these two systems and to project the cost reduction by retrofitting. The input variables for the simulation program were building structure model; actual weather data; solar radiation data; HVAC system configuration; interior load, such as people and lighting; control systems; and schedule of operation.

The results show that the simulation program’s predictions of the energy requirements are very close to actual energy consumption. The computed electrical energy requirement is 2.2% higher than actual consumption, and steam consumption is 9% lower than actual consumption. These small deviations can be attributed to differences between local weather data and those recorded by the weather bureau, due to some assumptions that were made regarding the building structures, and due to not including domestic hot water usage. The energy savings obtained from the retrofitting are 5.03 x 105 kWh for electricity (7.3% reduction) and a 7.677 x 106 Ib (79.4O/o) reduction in steam consumption.