Effect of high Ambient Temperature in Adiabatic cooling tower
The effect of high ambient temperature on an adiabatic cooling tower is significant and is the primary reason this technology is chosen. However, it introduces specific operational challenges.
Here’s a detailed breakdown of the effects, both on performance and system operation.
The Core Challenge: Reduced Heat Transfer
The fundamental principle of any heat exchanger is that heat flows from a hotter substance to a cooler one. The rate of heat transfer is directly proportional to the temperature difference (ΔT) between the hot process fluid and the cooling medium (the air).
- High Ambient Temperature = Warmer Cooling Air
- Warmer Cooling Air = Smaller ΔT
- Smaller ΔT = Less Efficient Heat Transfer
In simple terms, on a hot day, the air cannot absorb as much heat from the process fluid because their temperatures are closer together.
How an Adiabatic Cooling Tower Responds (The Solution)
This is where the “adiabatic” function becomes critical. The system is specifically designed to combat this effect.
1. Activation of the Adiabatic Pre-Cooling System:
- Trigger: When the ambient dry-bulb temperature rises above a predefined setpoint (e.g., 21°C / 70°F), the control system activates the water pump and distribution system.
- Action: Water is sprayed over the cooling pads, saturating them.
- Effect: As incoming hot air is drawn through these wet pads, evaporative cooling occurs. This adiabatic process lowers the temperature of the air before it hits the heat exchanger coil. It can cool the air to a temperature much closer to the ambient wet-bulb temperature.
- Result: Instead of the coil being hit with 95°F (35°C) air, it might receive 80°F (27°C) air. This restored ΔT allows the heat exchanger to reject heat efficiently, much like it would on a cooler day.
2. Increased Operational Cost:
- Water Consumption: The system now uses water, whereas it uses zero water in dry mode. High temperatures lead to higher evaporation rates, increasing water consumption.
- Energy Consumption: While the pre-cooling helps the heat transfer, the fans often must work harder (run at higher speeds) to move enough air to reject the required heat load. This increases electrical energy use.
3. Increased Stress on Components:
- Fan Motors: Are required to run at higher speeds for longer periods, potentially reducing their lifespan if not properly sized or cooled.
- Water System: The pump, nozzles, and pads are under constant operation, accelerating wear and the need for maintenance.
- Controls: The control system is cycling more frequently between dry and wet modes.