The Capitol Complex utilizes a central plant to provide chilled water for cooling the buildings on the Complex. The chilled water is distributed through pipes in underground tunnels. At the buildings, the chilled water is circulated through coils to transfer the heat from an airstream to cool the buildings. On the Capitol Complex, cooling is required all year long for some of the interior building spaces and computer rooms throughout the campus.
- In the winter, when the outside air is cold enough, chilled water can be generated without utilizing a refrigeration cycle by exchanging the heat directly from the chilled water to the outdoor air to take advantage of “free cooling.”
- In a conventional chilled water distribution system, water is cooled using a chiller. The chiller uses a compressor to compress refrigerant to a higher pressure/higher temperature.
- The heat generated by compressing the refrigerant is transferred from the refrigerant to condenser water in the condenser. The condenser water is then circulated through a cooling tower to reject its heat to the atmosphere through evaporation.
- In the free cooling cycle, the chilled water is circulated through a heat exchanger where it rejects heat to a glycol solution.
- The glycol solution is then circulated through an outdoor coil, called a dry cooler, which cools the glycol solution by circulating cold outdoor air across the coil. The chilled water is then circulated to the buildings to provide cooling. At the buildings, the chilled water is circulated through coils to transfer the heat from an airstream to cool the building.