A Hybrid Ventilation System in Carnegie Mellon’s Intelligent Workplace

An analytical and experimental study of hybrid ventilation is being carried out by Carnegie Mellon’s Center for Building Performance and Diagnostics in its Intelligent Workplace, the IW. Hybrid ventilation in this space will be carried out either operating a mechanical system, a SEMCO rev2250 desiccant wheel unit that distributes outside air conditioned, to a set temperature and humidity or alternatively opening windows when outdoor and indoor conditions are favorable, turning off the ventilation and the space cooling units. This hybrid ventilation approach will maintain a healthy, comfortable, and pleasant environment for the occupants of the IW and also will reduce the operating costs for the ventilation and cooling of the space. The key factor to the successful performance of a hybrid ventilation system is its operating procedures, the logical algorithms for opening and closing windows based on measurements of outdoor and indoor conditions: temperatures, humidity, wind velocity, rain, occupancy, etc. Algorithms have been proposed for operating the windows in the IW’s hybrid ventilation system. These algorithms have been programmed in a Trnsys model of IW with its windows and its mechanical ventilation and cooling units. This model has been exercised for an operating period including the spring, summer, and fall seasons in Pittsburgh to establish how much time the windows remain open and what savings in operating energy for the IW’s mechanical ventilation and cooling system are achieved. This modeling study evaluates the benefits of a hybrid ventilation system compared to a base case where mechanical ventilation is used. About 8% of the ventilation and cooling energy is saved. At this time a hybrid ventilation system, its hardware equipment and software controls, has been installed in the IW. Measurements are being made to establish that healthy, comfortable conditions are maintained in the IW and that model estimates of energy savings are confirmed. In future work, guides lines will be written to inform building professionals, architects and engineers, about hybrid ventilation and its benefits in the design of buildings across the United States.