An open cooling tower is a device that uses water as a circulating coolant to absorb heat from a system and release it into the atmosphere to lower the water temperature. Its cooling mechanism utilizes the heat exchange between water and air to generate steam. The steam evaporates and carries away heat, achieving heat dissipation through evaporation, convection, and radiation. This process dissipates waste heat generated in industrial processes or refrigeration and air conditioning systems, thereby lowering the water temperature and ensuring the normal operation of the system.

The operating principle diagram of a counter-flow open cooling tower is as follows:

Counter flow Open Cooling Tower - B

Comparison of energy consumption costs between open and closed cooling towers

Project scenario: Taking a 300T cooling tower as an example, the selection is assumed to be two HBW-30A units, six 7.5kw fans, and four 2.2kw spray pumps for a closed system; and one HKW-43D unit and one 18.5kw fan for an open cooling tower.

Open cooling towers typically require the construction of a water tank. After construction, the open cooling tower needs to be dredged every six months. If scale forms on the cooling tower packing, water cannot flow through, and the packing needs to be replaced after a period of use. In a circulating cooling system, if scale forms on one-quarter of the packing, the cooling efficiency will decrease by 50%, and the entire system will frequently trigger alarms.

• Comparison of initial investment costs

Investment required for open cooling tower: 300t open cooling tower, one set of chemical dosing equipment; Investment required for closed cooling tower: 300t closed cooling tower.

• Equipment usage and maintenance costs

Open cooling tower: (cooling tower filler + water tank)

After a period of use, open cooling towers accumulate mud, moss, and other contaminants at the bottom of the tank, causing scale buildup on the cooling tower filler and preventing water flow, thus affecting production. Therefore, regular replacement of the cooling tower filler and cleaning of the tank are necessary, increasing costs accordingly. Open cooling tower filler needs to be replaced every 3 years. For this project (300t), the replacement cost is approximately 30,000 RMB per replacement. Regular addition of chemical descaling agents is also required, with an annual cost of 10,000 RMB.

2.1 Water consumption comparison

• The water consumption of an open cooling tower consists of: spray water drift + water tank evaporation + sludge removal and drainage. The drift rate of spray water used in an open cooling tower is 2%-3%, operating for 20 hours per day, 300 days per year.

The annual water consumption of an open cooling tower with an actual flow rate of 300 m³/h is: 600 m³/h × 2% × 20h/day × 300 days/year = 72,000 tons/year (maximum).

• The water consumption of a closed-circuit cooling tower is: the drift of water sprayed by the spray pump onto the cooling coils.

The drift rate of the spray water used in a closed-circuit cooling tower is 1‰-83‰ (the spray pump can be stopped for 60-80 days in winter); the annual water consumption of a closed-circuit cooling tower with an actual flow rate of 300 tons/hour is: 600 m³/h × 0.83% × 20 hours/day × 300 days/year = 29,880 tons (maximum).

2.2 Comparison of electricity consumption

Power consumption of a 300t counter-flow closed-circuit cooling tower: Total fan power 45kW, total spray pump power 8.8kW, operating 300 days a year, 20 hours a day.

Fan power consumption: 45kW × 11kW (adjustable start/stop) × 110kW (adjustable start/stop) = 54450 kWh (with temperature control device)

Spray pump power consumption: 8.8kW × 11kW (adjustable start/stop) × 110kW (adjustable start/stop) = 10648 kWh (with temperature control device)

The total electricity consumption is approximately 65,098 kWh.

The total power of the fan in the 300T open-type cooling tower is 18.5kw.

Power consumption of the fan: 18.5 × 20 × 300 = 111,000 kWh

The total electricity consumption is approximately 111,000 kWh.

Closed-circuit cooling towers use decalcified and magnesium-ionized water in a closed loop, preventing contact with the outside environment and thus eliminating scale buildup. The operation of the fans and spray pumps in closed-circuit cooling towers can be controlled by the inlet and outlet water temperatures, allowing for air-based cooling. Open-circuit cooling towers, on the other hand, have circulating water in direct contact with the cooled equipment, especially condensers, making them prone to clogging. Therefore, they require cleaning and sludge removal every three months. Furthermore, the addition of chemicals can pollute the water, causing environmental impact when discharged. Closed-circuit cooling towers do not require regular sludge removal and do not discharge polluted water, making them an energy-saving and environmentally friendly product.

In summary, a closed-circuit cooling tower with a capacity of 300 m³/h can save 50% more energy per year than an open-circuit cooling tower. Furthermore, due to its high degree of automation, automatic start-up and shutdown can reduce maintenance.

Through more than ten years of accumulation, Jiangsu Huatal has derived the following sets of data on fouling factor, fouling thickness, and energy consumption increase. Fouling factor unit: m².℃/kW; Fouling thickness unit: mm; Energy consumption increase unit: %, and the corresponding data are as follows:

If the system uses an open cooling tower and is supplemented with tap water, it will draw in dust and suspended matter from the air as well as calcium and magnesium ions from the water, causing scale to form on the heat exchange tube walls. This will prevent heat from being dissipated in summer and affect production.