Determining the cooling water demand of the cooling tower requires comprehensive consideration of multiple factors. The following is a detailed introduction:

1. Calculate based on the heat dissipation of the equipment

For heat exchange equipment in industrial production:

For example, reactors and condensers in chemical production, these equipment will release a large amount of heat to the surrounding environment during operation. First, the heat exchange power of the equipment must be obtained. Usually, the rated heat load (usually in kilowatts, kW) will be indicated in the manual or technical data of the equipment. This heat load is the heat dissipated by the equipment per hour. According to the principle of heat conservation, the heat that the cooling tower needs to take away is basically equivalent to the heat dissipated by the equipment (considering a certain heat loss coefficient, generally about 1.1 - 1.3). Then use the relationship between heat and water specific heat capacity to calculate the cooling water volume. The specific heat capacity of water is about 4.2kJ/(kg・℃). Assuming that the heat dissipation of the equipment is Q (kJ/h), and the temperature difference between the inlet and outlet water is Δt (℃), the calculation formula for the cooling water volume m (kg/h) is roughly: m = Q / (4.2×Δt). Then convert the mass flow rate to the volume flow rate (the mass of 1m³ water is about 1000kg), and you can get the cooling water volume required per hour (m³/h).

For building air conditioning systems:

Chiller: The chiller is the core equipment for generating cold in the air conditioning system. At the same time, it also generates heat during operation that needs to be dissipated through the cooling tower. Generally, the manufacturer of the chiller will provide the cooling capacity (also in kW) and the corresponding condenser heat load parameters. According to the same law of heat conservation, after considering a certain margin (such as 1.1-1.2 times), the cooling water demand is determined according to the above water specific heat capacity calculation formula. For example, for a chiller with a cooling capacity of 1000kW, its condenser heat load is 1200kW (assuming the margin coefficient is 1.2), and the inlet and outlet water temperature difference is set to 5℃, then the cooling water volume is calculated as: m = 1200×1000 / (4.2×5) ≈ 57143kg/h, which is converted into a volume flow of about 57.143m³/h.

Estimation of the cooling load of the entire building: If there are no detailed chiller parameters, the cooling water demand can also be estimated from the perspective of the overall cooling load of the building. First, calculate the cooling capacity required by the building through professional building load calculation methods (such as hourly cooling load coefficient method, etc.). Usually, the cooling load corresponding to each square meter of building area is 100-200W (different functional buildings have differences, such as office buildings are generally estimated at 100-150W/m², and shopping malls may be estimated at 150-200W/m²). Then, according to the energy efficiency ratio and other parameters of the air-conditioning system, the condenser heat load is reversed to determine the cooling water volume. However, this method is relatively rough and the error may be around 10%-20%.

2. Consider the system operating conditions

Ambient temperature influence: The higher the ambient temperature, the smaller the temperature difference between the cooling tower and the outside air, the smaller the driving force of heat exchange, and the worse the cooling effect. Therefore, in hot areas or during high temperatures in summer, in order to ensure the same cooling effect, it is often necessary to appropriately increase the cooling water volume to compensate for the adverse effects caused by the reduced temperature difference. For example, in areas with an average summer temperature of 30℃ in the north and 35℃ in the south, for equipment with the same heat load, the amount of cooling water used in the cooling tower in the south may be about 10% - 20% more than that in the north.

Impact of air humidity: When the air humidity is high, it is more difficult to evaporate water, and the cooling tower often relies on the absorption of heat by evaporation of water to achieve cooling. Therefore, in a high humidity environment, the cooling efficiency will be reduced, and the amount of cooling water needs to be increased accordingly. For example, in coastal humid areas and inland dry areas, under the same conditions, the cooling water demand for cooling towers in coastal areas may be higher. The specific increase depends on factors such as actual humidity differences, which may be around 5% - 15%.

System operation time and stability requirements: If the equipment needs to run continuously for a long time, or the stability requirements for the cooling effect are extremely high (such as some high-precision industrial production processes, the temperature fluctuation cannot exceed ±1℃), then in order to cope with various adverse conditions that may occur and ensure that the cooling system is always in good condition, the amount of cooling water will generally be appropriately increased based on the calculation, usually 10% - 15% as a margin.

3. Combined with factors such as future expansion

Expected expansion of enterprise production scale: For industrial enterprises, if there are plans to increase production lines and expand production scale in the next few years, the heat load of the corresponding heat exchange equipment will increase. When initially selecting a cooling tower, sufficient cooling water volume should be reserved. Generally, the selection of cooling towers can be determined according to the expected maximum heat load in the next 5-10 years, and 20%-50% (determined according to the specific expansion plan and industry characteristics) of cooling water volume margin should be reserved to avoid the need to replace cooling towers due to insufficient cooling capacity in the future, which will increase costs and affect production.

Changes in building functions or upgrades to air-conditioning systems: In terms of buildings, if there is a possibility of changing the use function in the future (such as converting office buildings into hotels) or upgrading the air-conditioning system (such as replacing higher-power chillers), the impact of these factors on the demand for cooling water should also be considered in advance, and appropriate margins should be reserved to ensure that the cooling tower can continue to meet demand.

In summary, determining the cooling water demand of the cooling tower requires accurate understanding of the equipment heat load, full consideration of the operating conditions and prediction of future changes, and comprehensive determination of the appropriate cooling water value through rigorous calculations and combined with practical experience.

Will the cooling water demand of the cooling tower change with changes in environmental conditions?

The cooling water demand of the cooling tower will change with changes in environmental conditions. The following is a specific analysis:

The impact of ambient temperature changes

In high temperature environments:

When the ambient temperature rises, the temperature difference between the cooling tower and the surrounding air decreases. The cooling principle of the cooling tower depends largely on the heat exchange between hot water and cold air. A smaller temperature difference means that the driving force of the heat exchange is weakened, and the cooling efficiency will decrease accordingly. For example, a cooling tower that can achieve the cooling target well at an ambient temperature of 25°C may not be able to reduce the water temperature to the expected set temperature with the same amount of cooling water when the ambient temperature rises to 35°C. In order to ensure the cooling effect and maintain the water temperature required for the normal operation of the equipment or air conditioning system, it is necessary to increase the amount of cooling water and allow more water to participate in the heat exchange process to make up for the cooling capacity lost due to the decrease in temperature difference, so the demand for cooling water will increase.

In low temperature environment:

On the contrary, in low temperature environment, such as winter or cold areas, the temperature difference between the cooling tower and the outside air increases, heat exchange becomes easier, and the cooling efficiency will increase. At this time, under the premise of meeting the cooling requirements, the amount of cooling water can be appropriately reduced, because less water can achieve the expected cooling water temperature through sufficient heat exchange with the cold air. However, it is also necessary to pay attention to not excessively reduce the amount of cooling water, so as not to have adverse effects on the stable operation of the entire cooling system and the equipment connected to it, such as causing the cooling water temperature to be too low, causing abnormal condensation of some heat exchange equipment, etc.

Influence of air humidity changes

In high humidity environment:

High air humidity means that the water vapor content in the air is close to saturation, and part of the cooling process of the cooling tower is achieved by evaporating water to absorb heat (evaporative cooling effect). In a high humidity environment, water evaporation becomes difficult, the evaporation amount decreases, the corresponding heat absorption effect will deteriorate, and the overall cooling efficiency will decrease. For example, in humid coastal areas, the cooling effect of the same cooling tower under the same working conditions will be greatly reduced compared to inland dry areas. In order to ensure that the established cooling water temperature is achieved, it is necessary to increase the amount of cooling water, and increase the circulation of water to take away more heat, so as to maintain normal cooling performance, so the demand for cooling water will increase at this time.

In low humidity environment:

When the air humidity is low, water evaporates relatively easily, the evaporative cooling effect can be better exerted, and the cooling efficiency of the cooling tower will be improved. In this case, the amount of cooling water can be appropriately reduced. Less water can achieve a better cooling effect with the help of good evaporative heat absorption conditions. However, the coordination of the entire cooling system and the impact on the operation of subsequent equipment should also be considered comprehensively to avoid other problems such as pipe blockage (due to the relatively high concentration of impurities in the water) caused by too little water.

The impact of wind speed and wind direction changes

In terms of wind speed:

Higher wind speed is conducive to accelerating the flow of air around the cooling tower, enhancing the heat exchange and mass transfer process between air and hot water (including water evaporation process), so that the cooling efficiency of the cooling tower is improved. In a windy environment, if the wind speed is continuously at a relatively high and stable state, the amount of cooling water can be appropriately reduced to a certain extent, because good air flow has helped to improve the cooling effect. On the contrary, if the wind speed is low, the air renewal and heat exchange slow down. In order to ensure the cooling effect, it may be necessary to increase the amount of cooling water to maintain the normal cooling water temperature demand of the equipment.

Wind direction:

The appropriate wind direction can make the air inlet of the cooling tower smoothly inhale fresh cold air, which is more conducive to heat exchange. However, if the wind direction changes, resulting in the cooling tower air inlet not being able to obtain enough cold air well, or causing the exhausted hot air to be re-inhaled into the air inlet (forming a reflux phenomenon), the cooling efficiency will be seriously affected, and then the amount of cooling water needs to be increased to make up for the lack of cooling capacity and ensure that the cooling effect meets the requirements.

Impact of atmospheric pressure changes

In high altitude areas, the atmospheric pressure is relatively low, and the boiling point of water will also decrease accordingly, which will affect the process of water evaporation in the cooling tower. Water evaporates more easily, and the evaporative cooling effect is enhanced to a certain extent, but at the same time, the overall situation is more complicated because the low atmospheric pressure may affect heat exchange-related factors such as air density. However, in general, in high-altitude areas, the amount of cooling water usually needs to be appropriately adjusted according to the actual situation. Generally speaking, the amount of cooling water may need to be appropriately reduced, but it should be comprehensively judged in combination with factors such as the specific cooling tower type and equipment operation requirements to ensure that the cooling system can function normally.

In summary, the cooling water demand of the cooling tower will indeed change with changes in environmental conditions. In actual applications, it is necessary to adjust the cooling water volume in a timely manner according to specific environmental changes, or fully consider the local environmental conditions when designing and selecting the cooling tower, and reserve a certain adjustment margin to ensure that the cooling system always operates stably and efficiently.