Many buildings are air-conditioned by low-temperature water circulated through coils. Warm air from the building is blown over the coils to extract heat so as to maintain comfortable conditions for the occupants. The warmed water is then returned to a chiller to be cooled and recirculated through the chilled water loop. The heat from this water and from the chiller compressor is transferred in a heat exchanger to another water flow by the use of a refrigerant such as Freon.
The water that removes heat from the chiller heat exchanger is called the condensing water. This is not because the water condenses, but because it causes the high-pressure gaseous Freon in the heat exchanger to condense into a liquid. This liquid Freon goes to an evaporator that causes its temperature to decrease so that it can extract heat from the water in the chilled water system. The condensing water carries the heat outside the building by being pumped to a cooling tower. Here, the heat is removed by the evaporation of some of the condensing water.
Condensing Water Circulation
The condensing-water loop is a circulating water system that carries water from the chiller to a mechanism for cooling the water, such as a cooling tower. A pump forces the water flow through the condensing water loop. The suction side of the pump pulls cooled water from the sump of the cooling tower, pushes it through the chiller condenser, and then causes the warmed water to spray onto the media in the cooling tower. Air from outside the building is blown through the media, causing some of the water to evaporate, thus cooling the water flow that collects in the sump.
Condensing Water Supply
While the condensing water in a chiller causes the high-pressure refrigerant in the chiller to condense, the water itself is actually evaporated to make its contribution to the cooling of the building. This means that fresh water must be added to the cooling tower to maintain the water level in the sump. This is often done by using a simple float valve, like those used in many toilets, to add water to the sump automatically as needed.
Condensing Water Treatment
The water supplied to the cooling tower sump contains various minerals, and the air used to cool the water can introduce various organisms. Thus the water must be treated with a variety of chemicals to keep slime and scale from building up in the condenser and to prevent corrosion in the pipes, spray nozzles and heat exchanger. Good water quality is maintained using information from the chiller manufacturer and from water treatment professionals. Poor water quality can be evidenced by an increase in the difference between the liquid Freon temperature and the condenser water temperature leaving the heat exchanger.