The HVAC system is the largest user of energy and water in typical commercial buildings. In the past, energy costs overshadowed water costs. Recent droughts and the need to expand municipal water supplies to support growth have led to increased water costs nationwide. Combined with the focus on water conservation in green buildings, the payback associated with reducing building water usage is greater than ever. Most commercial buildings use water cooled chillers to provide air conditioning because they are much more energy efficient than air-cooled chillers. Achieving these efficiencies, however, requires large quantities of water to operate a cooling tower. Most buildings also use re-circulating hot and chilled water loops to distribute heating and cooling throughout the building. Although not designed to routinely use water, these systems can use large amounts of water if undetected leaks occur. As the major consumer of water, the building HVAC system is an obvious target for water conservation efforts and often provides significant saving.

Microbiological problems in cooling water systems cost businesses billions of dollars each year due to high energy costs, production losses, unscheduled maintenance, and replacement of corroded parts. Poor microbiological control can also lead to unsafe operating conditions, such as contamination by the bacterium that causes Legionnaires’ disease. While this article focuses on biocide contact time, there are many factors to consider when choosing the correct biocide, including:

In terms of raw energy efficiency and the ability to provide precise cooling under fluctuating load conditions, recirculating evaporative cooling water systems with chillers or heat pumps are the most efficient way to remove heat from a process or building air. However, adiabatic cooling systems can be a good fit with an overall lower cost for heat removal in some climates and applications.

Evaporative condensers are commonly used for heat rejection in low temperature ammonia refrigeration applications in cold storage and food processing plants. Although often confused with standard cooling towers, there are some key differences between evaporative condensers and the cooling tower systems used in HVAC applications. Understanding these differences and the challenges they present is important for water treatment program success.

Biofilm deposits are one of the most difficult challenges your cooling water systems face. They tend to start in areas not accessible to biocide treatments, and can quickly grow to form biofouling deposits that can cause corrosion damage, blockages, reduced heat transfer, and amplify the growth of Legionella bacteria. Once they become established, biofilms are incredibly tenacious and difficult to remove.