Since its installation, the system has been operated in two different modes: as an air conditioning system, which provides ventilation air and a portion of cooling/heating for the IW through recirculation air; and as a dedicated outdoor air system, which delivers ventilation air at a user selected temperature and humidity while cooling/heating is provided by other systems such as radiant panels and mullion pipes supplied with chilled or heated water. Supply air from the system is delivered to the IW through floor mounted air diffusers that are located at each workstation.
According to guidelines on high performance HVAC system design and operation, developed by the researchers in the IW, provision of ventilation air should be separated from space cooling/heating. Furthermore, space cooling/heating should be achieved by water based units whenever possible. Therefore, ideally the ventilation system should be operated to provide adequate amount of fresh, outside, air for the occupants at comfortable temperature and humidity conditions and at a humidity sufficiently low to allow for effective operation of the water based cooling units. The system is therefore a dedicated outdoor air supply, DOAS. Given the normal occupancy rate in the IW, 600 cfm (30 occupants at a 20 cfm/person ventilation rate) of ventilation air is required for reasonable indoor air quality. However, in order to take advantage of the cooling and heating capacity offered by Semco REV 2250, the machine was operated as an air conditioning system for most of the time. The supply air flow was set to 2000~3000 cfm. In addition, due to the operation of the active desiccant wheel, the system was able to deliver air dry enough to allow for effective operation of the radiant panels and fan coils in the summer. As a result, comfortable indoor conditions were maintained in the IW during both heating and cooling seasons and positive feedback was given by most of the occupants.