Efficient evaporative cooling technologies can play a large part in protecting the world’s water supply. An air-cooled condenser with optional adiabatic cooling can satisfy niche applications where water resources are limited but electric power is available.
Evaporative condensers have been used for decades in refrigeration and industrial process applications. When first introduced, these condensers often replaced once-through cooling systems and offered end users water and energy savings vs. the once-through systems they replaced. Today, evaporative condensers are used for medium-to-large systems due to the inherent energy savings offered and their smaller footprint compared to air-cooled condensers. The differences between evaporative and air-cooled condensers are shown in figure 1.
Water availability for plant and building operations is a primary strategic business concern for industrial processes. Based on 10- to 20-year climatic projections, the availability of water for evaporative applications will be scarce in many areas. Increased regulations on potable water use, water treatment and disposal costs may further limit the practicality of using evaporative-only cooled equipment.
The natural inclination is for facility owners to turn to an air-cooled alternative of equivalent capacity to save water. However, they may not have the real estate available for the quantity of air-cooled units needed to meet the same load. Most importantly, while the end user may reduce water consumption by using a completely dry solution, the energy consumed for the condenser and the entire system is significantly increased. As a result, the power-generating facility may consume significantly more water to produce the necessary power for the end user, resulting in higher energy and water consumption from a global point of view.
When considering water use, energy consumption and plan area issues from the energy producer through end user, a balanced choice is required to make the proper equipment selection. There are papers written on this subject, and often it is referred to as the water/energy nexus. In making these decisions, one has to strike a balance between selecting an air-cooled or water-cooled system, and the best choice may be a combination of the two.
Manufacturers of evaporatively cooled equipment have introduced various hybrid systems to help operators comply with water-use restrictions. Hybrid systems may incorporate features such as:
- An evaporative coil and dry coil in series.
- Separate dry coil circuits above the discharge airstream.
- Bare coils with extended fins.
The most recent hybrids include wetted adiabatic pads or misting nozzles on the air intakes that reduce the incoming dry-bulb temperature to the dry condenser.
Innovations in condensing equipment and technology are needed to reduce makeup water use and keep evaporative cooling — the most energy-efficient method of heat rejection — a viable choice. Evaporative condensers can play a large part in protecting the world’s water supply. However, if water resources are limited but electric power is available, there is another option — the air-cooled condenser with optional adiabatic cooling.
Integrated Adiabatic Cooling System on an Air-Cooled Condenser
Adiabatic cooling uses only a small portion of water to provide the heat rejection on the hottest days. With this design, water is introduced into the intake airstream either by wetted adiabatic pads or sprayed directly into the airstream. In either case, the entering dry-bulb temperature is reduced to a temperature closer to the wet-bulb temperature, producing lower condensing temperatures through minimal water consumption.
As the load and air temperature decrease, the water being sprayed at the inlet face of the coil or distributed over inlet air pads is shut off. (Note that the plan area will be much larger, and piping more complicated and expensive with an air-cooled condenser.)
Many options are available for conventional evaporative cooled, wet/dry hybrid and air-cooled condensers. These solutions also can provide other benefits with respect to maintenance, ice management and water regulations. Careful consideration must be given by the designer to evaluate present and future water availability and total impact to the system and environment when making a decision on which type of condenser to specify. The technology is available today for a better tomorrow.