There are two types of Fan Coil/Unit Ventilator systems, two-pipe and four-pipe. A two-pipe system includes only one line supplying either hot or cold water to produce heating or cooling, and one returning. The four-pipe system includes a distribution system that contains both hot water supply with return lines and a chilled water supply with return lines.
Air in most of Georgia Tech’s residence halls is conditioned with a four-pipe system, but not all (see chart below).
Two-pipe systems are less flexible than a four-pipe system, as the entire building is in either heating mode or cooling mode. When seasons change, the two-pipe system is switched from cold water to hot water or vice versa. The manual switchover takes a couple of days and is managed by the central campus facilities group. Occasionally, by the time this is accomplished the weather changes or there may be days of rapid change between hot and cold. During this transition time, residents may find indoor temperatures less than ideal.
Additionally, when the temperature outside is between 45 and 55 degrees (F), the two-pipe systems will not utilize chilled or hot water, but the fan will continue to pull in fresh air from the outside.
Controlling humidity in large, heavily populated buildings is challenging, especially in places with fluctuating weather like Georgia. Substances like mold and mildew can grow if a room is not properly ventilated, so residents should submit a maintenance request to report any problems with the air conditioning or heating systems.
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