400-ton screw chillers specified for Virginia medical center
CEK Engineering, now Teng Engineering, an architect and the owner of the building conferred on a plan to modernize the cooling plant. Its two centrifugal chillers were nearly 30 years old and had nominal ratings of 800 and 400 tons. However, some tubes had deteriorated to the point that they had to be plugged. Others had corrosion or wear problems causing increased numbers of tube leaks. According to Ted Large, director of plant services at the facility, the combined nameplate rating of 1,200 tons had deteriorated to less than 1,000 tons. The refrigerant in use was R-11.
CEK designed a system consisting of two 400-ton centrifugal chillers and three 400-ton screw chillers with future ice capabilities. The third screw chiller offered the redundancy the hospital desired.
Because of limited space and difficult access to the existing basement mechanical room, another aspects of the project was to relocate the chiller plant to an adjacent plant services building. This building would be doubled in size to meet this need as well as to house the plant services staff offices and a standby electric generation facility.
Five Trane Model RTHC water-cooled 400-ton screw chillers were selected, with a full load efficiency of 0.58 kW/ton. Refrigerant used in these chillers is R-134a. With the new chiller plant, the cooling load for the entire facility can be carried by three of the chillers in all but the most oppressive weather. When temperature and/or humidity are high, a fourth unit is activated, but there is always one in reserve.