How Cooling Towers Work

You might notice that while your refrigerator keeps your food cool and fresh on the inside, there is a significant amount of heat coming off the grill-like device on the back of your refrigerator (called a condenser). The refrigerator is transferring the heat from the inside to the outside.

Cooling systems in buildings operate the same way. If you have central air conditioning in your home, you will have a condenser (the box-like machine with a big fan enclosed inside) on the outside of your house. The central air conditioning system removes heat from the inside of your house and transfers it to the outside via the condenser to keep your home cool in the summer.

For large multi-story buildings, using the type of central air condition system that works for your home isn't feasible. Instead of using air to remove heat, larger multi-story building cooling systems will use piped water to transfer heat. This type of system typically pairs a chiller with a cooling tower. Like the condenser used in your home’s central AC system, the chiller is a machine that removes heat from the building. A piped water loop runs through the building, picking up heat along the way, which is circulated though the chiller to be cooled—in a continuous loop called the chilled water loop. The heat removed by the chiller is rejected to the outside through a different piped water loop (called the condenser loop). This condenser water loop runs through a cooling tower, which uses evaporative cooling to cool this piped water—typically by 10 degrees Fahrenheit—which is circulated back to the chiller in a continuous loop.

Evaporative cooling is the same cooling process your body uses, i.e., as perspiration evaporates, it pulls heat away from your body. Just like the perspiration on your skin, the evaporated water carries heat and is lost to the atmosphere. This lost water must be added back into the system, or "made up."

Accumulating Solids

There is another reason additional water needs to be added back into the cooling system. As a result of evaporation, the solids in the water become more concentrated. If you have ever used a steam vaporizer when you are sick, you might notice the build-up of solids around the heating element, which is from the minerals and other solids that are suspended in the water from the tap. The amount of solids in the water will vary depending on the region or how the water utility treats the water.

If the build-up of these solids increases too much in a building cooling system, it can damage the cooling equipment such as a chiller. Therefore, some of this water must be "blow down" to the sewer to keep the solids from getting too concentrated in the water.

Using Chemicals

Chemicals can be used to treat the water so that the water can be used longer in the cooling system—even with the build-up of the solids—without damaging the equipment. Even with chemicals to treat the water, however, eventually the evaporation increases the solids in the water to the point that water needs to be "blown down" the sewer to avoid damaging the equipment.

Reducing Resources

Given the above dynamics of building cooling systems and cooling towers, we’re looking at three approaches to reduce water, energy and chemical use in the cooling systems of large buildings and data centers:

  • Technology Evaluation: Identify and track the performance of innovative water treatment technologies that dramatically reduce water and chemical use in cooling towers and analyze the possibilities of rolling them out to more sites.
  • Operational Improvements: Use best practices to engage facility managers and service providers to optimize traditional chemical treatment programs.
  • Maximize the opportunity for free air cooling: Identify sites where free air cooling – bringing cooler outside air in – can be used to reduce the need for mechanical cooling. Since conventional cooling methods can be energy and water intensive, reducing the load on those systems can drive significant savings in addition to water and chemical treatment savings.