Brown (1992) describes the use of evaporative cooling in a university life sciences laboratory in Arizona.
The indirect precooler is comprised of a standard finned-tube heat exchanger connected with piping to a cooling tower. Water cooled in the tower is circulated through the coil to precool outdoor air. Accordingly, mechanical cooling is displaced by indirect atmospheric thermodynamic exchange. (All evaporative cooling components are commercially available and can be competitively bid.)
Basis of analysis
The baseline analysis is predicated on a conventional two-fan dual-duct HVAC system with steam humidifier (hereafter referred to as the conventional system). The actual system is identical to the conventional system except that a direct evaporative cooler is located downstream of the cooling coil in the cold deck, replacing the steam humidifier. In addition, the preheat coil is replaced with a preheat/precooling coil, which is connected via piping to cooling tower. A plate-and-frame heat exchanger in the piping loop provides a means to heat water during the winter.
Brown (1990) analyzes the effectiveness of indirect evaporative cooling and concludes that
Indirect evaporative precooling will only be effective where the difference between outdoor dry-bulb and wet-bulb remains high (13°F (7.2°C) or more) for the majority of the cooling hours. The concept is not applicable when the difference between dry-bulb and wet-bulb is small (12°F (6.7°C) or less) for the majority of the cooling hours. Thus, this energy conservation measure will be limited to dry climates.
